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eli5_dataset

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{ "a_id": [ "gzic8lg", "gzicjnh", "gzia4sd" ], "text": [ "It's called induced demand - if there is a supply of potential drivers who currently don't drive but could, or who currently drive but on a different roadway, then adding new capacity could encourage them to take the new lane/road because of the perceived benefits. Note that this only holds true to the extent that there is a supply of drivers who would use that particular road. If you were to build a sixteen lane highway linking two villages out in the boonies there would not be a large enough supply of local drivers to make the traffic worse.", "If **all** the roads got bigger, it wouldn't. But that's not what happens. A bigger road allows more people to get into an area, causing traffic in destinations to get worse.", "Bigger better roads means more residents want/need to drive, and developing infrastructure that accompanies bigger better roads (more shops, more cinemas, more flats, and so on) attract more people from outside - who will come by car since there's bigger better roads. So if there's a traffic problem in a city and the local authority upgrades all the roads to fit more cars, the problem will return relatively quickly except now it's not a single-lane traffic jam, it's a 4-lane traffic nightmare. More roads == More cars != Less cars" ], "score": [ 10, 6, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gzkhw4v", "gzkcxbk" ], "text": [ "Quantity of launches and everyone now carrying an HD camera in their pocket As the rocket ascends it has a big plume of expanding gas behind it. Normally it's daylight or completely night time so you might see the trail going up but nothing comes of it But for dawn and dusk launches you can see this big plume. At ground level it's fairly dark because the sun is blocked, but 100km up can be in sunlight. When the rocket ascends past this point, the exhaust trail which is much denser than the local atmosphere gets lit up by the sun and since it's still dark where you are you can see the light bouncing off the exhaust This only happens at dawn and dusk launches and with spaceX currently averaging a launch every 9 days there are a lot of chances for it to happen", "All rockets can be used to capture these spectacular trails. What is done specifically is to capture a long exposure image of a rocket launch at night. There are not many space shuttle launches that took place at night and good cameras were expensive back in the day so there were not many experienced photographers who could dedicate a camera to try to capture such a photo. But there are a few such long exposure images of the space shuttle launching. You can often distinguish them from other rockets due to the huge cloud of white aluminum oxide from its boosters. But these types of photographs have become more common lately due to cheaper cameras and the increased frequency of launches, particularly night launches. And because most of this increase in launches are SpaceX launches these tends to be the ones we see. However there are long exposure photographs of almost any launcher." ], "score": [ 6, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gzlv5iv", "gzm3rtm" ], "text": [ "[Engines are not in perfect balance at every rpm. And can not be in perfect balance at every rpm (it would defy physics). So what engineers do is aim to balance the engine at the rpms the engine will run the most at throughout its entire life. Which are the rpms the vehicle would normally cruise at. ]( URL_0 ) My eli5 interpretation of that is, big engine is balanced to not rattle when going fast, thus causing an imbalance when idling to make it rattle", "Reciprocating engines, like the diesel engines in buses, are not perfectly balanced, so they vibrate as they run. The frequency of the vibrations is linked to the speed the engine is running at, in rpm. Structures all have certain frequencies where they will naturally vibrate, for example if you hit them, they will vibrate at a particular frequency (eg ringing a bell). If you forcibly vibrate a structure at a frequency where it naturally vibrates, it will vibrate very strongly, this is called resonance. If you forcibly vibrate a structure at some other frequency, it doesn't vibrate much. For things in buses like body panels, seat structures, grab-poles and the like, their intrinsic natural vibration frequencies are close to the vibrations produced by an engine at idle, so when the engine is at idle, it causes the bus to vibrate. When the engine is under load, it spins at a higher speed, so the vibrations from the engine do not correspond with the natural frequencies of those structures, and they do not vibrate as much." ], "score": [ 34, 4 ], "text_urls": [ [ "https://www.reddit.com/r/explainlikeimfive/comments/331nj1/eli5why_do_buses_vibrate_when_idle_but_not_when/" ], [] ] }

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{ "a_id": [ "gzny0tb", "gzo0brv", "gznztyx", "gzo6xr0", "gzo4yw4", "gznysfb" ], "text": [ "Some tunnels are drained before the drilling. You can also use explosives to blow a hole and then use rocks/bricks to make everything look nice You can also use pressure cannons to tunnel through things under water. Is there a specific tunnel that you're trying to figure out?", "The specific method depends on the individual tunnel and the construction methods available at the time, but the common trait is that they all involve someone/something digging a hole into either the seabed or into the bedrock beneath it and digging your path until you got your tunnel. Older subway tunnels like in New York City were usually dug out with machinery and people under the bedrock. More modern tunnels are either dug with a tunnel boring machine or with digging a trench into the floor of the body of water and submerging a prebuilt tunnel portion into it. With enough money, the right technology and the manpower you can practically build anything you set your imagination to.", "You dig a trench in the bottom of the harbor for the tunnel to go into. Then you make rectangular segments of tunnel out of concrete and steel on shore. Then you lower the concrete into the trench, bolt them together, and seal the seams. When you've done the whole thing, you pump out the water.", "The channel tunnel (the one that connects Kent in England with France for those who don’t know) was built with huge machines which cut massive holes into the ground under the English Channel. The machines started at the opposite ends and met in the middle, the machines were then dumped on the ocean floor and are still there today.", "There are 3 strategies. First, you go completely underground. If there's water above, it doesn't make much of a difference. Second, you create a submerged structure by building it above water and then submerging it sealed. Third, you build a coffer dam, which is basically a temporary dam for working on something underwater.", "They are pre-built above water then lowered and sunk with additional weight or buried to keep them under. Think of it like holding an empty bottle with the cap still on under water, it naturally tries to float but you can force it stay under. Then they connect the tubes to their permanent anchor and all of the sections are bolted or otherwise fastened together. Any water that enters during this process is pumped out once the tunnel is complete." ], "score": [ 16, 12, 11, 5, 4, 4 ], "text_urls": [ [], [], [], [], [], [] ] }

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{ "a_id": [ "gzpl2rw", "gzplfq9" ], "text": [ "The container is made out of two separate tubes that are put inside one another and then welded sealed at the top but before they're welded most of the air is sucked out so there's a vacuum between the two. Because of this there's very little air for the heat or cold in the inner container to transfer to the outer which keeps things hot or cold.", "Generally it's just a Dewar or vacuum flask. Basically one metal container inside another, that only touch at the opening. The space between them is a vacuum (so no air). And usually the surface facing the vacuum is coated with IR reflective material that has a low emissivity (doesn't make a lot of thermal radiation) That way the only conduction of heat is through the upper lip of the opening (which is small), there is no convection, and infrared radiation is very low and doesn't carry heat. Combined it makes for very good insulation" ], "score": [ 5, 5 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gzqwmyy", "gzqy5ux", "gzr5x02" ], "text": [ "I'm no engineer either but these might help; [Expectancy]( URL_1 ) [Demolition]( URL_0 ) A question like that might be best asked in r/AskEngineers Hope this helps!", "I mean yes and no. engineering is complicated and building sky scrapers is an incredibly technical and expensive endeavor. they use special components and reinforced parts to make it work. Now you are correct, things wear out, corrosion sets in, etc. However, they can maintain and repair it and keep it going over time. You can replace 1-2 beams at a time without the whole thing tumbling down. NOW if things go to shit too much they can do controlled demolitions. So by placing explosive charges in the right places, you can demolish a huge building an a crowded urban environment with minimal risk. You can find plenty of videos online. [ URL_0 ]( URL_1 ) Here is just one such for you. Now many times they will clear out a block or two nearby just in case. But its a rather safe act. Now it can go wrong sometimes but everything can. So your idea is partially correct. Huge buildings can suffer wear and tear but they are monitored and tended to. While theoretically possible that an entire building could be in disrepair and suddenly collapse it doesn't happen in actuality. It will be demolished long before it reaches that level of decay.", "TL;DR: The buildings should stand indefinitely. When a skyscraper is torn down it is normally because either maintenance of non structural components has become prohibitively expensive or the building is obsolete with regards to tenant expectations and the owner wants a new one that will make more money. Longer Version: The structures are designed to stand up indefinitely, albeit with design loads equivalent to wind/seismic events that occur with a ~475 to 1700 year return period depending on building code requirements. Even then there are “safety factors” in the design so if a building survives such an event it shouldn’t be a huge surprise. You’ll see things like “buildings are designed to last 50/100 years” - in some jurisdictions there is a convention for designating an expected service life, though this is more for insurance and financial planning purposes than a statement the building will be no good at 51/101 years old. Provided the building is maintained - mostly meaning keep water out - it should last a very long time barring things like fires. The interior components and the facade system will have a service life that is somewhat lower - seals around windows start to break down, the mechanical systems (heating/cooling) will first need major repairs towards the end of their service life and then become obsolete, etc etc and keeping them going starts to turn into a money pit. For context - the windows on a skyscraper can easily cost twice as much as all the steel and concrete combined, and the building systems (heating,cooling, plumbing, elec, technology) might cost twice as much again. When these all come up for replacement the owner may decide to replace the building with one that provides better returns on investment - by this time what was once “Class A” office space is going to have slowly turned into “Class B/C” as it falls behind tenant expectations (ceilings not high enough, too many columns, floors can’t support expected use, technology fails to perform) so commands lower rent." ], "score": [ 3, 3, 3 ], "text_urls": [ [ "https://www.google.com/amp/s/www.zdnet.com/google-amp/article/how-to-demolish-skyscrapers-in-crowded-cities/", "https://amp.reddit.com/r/AskEngineers/comments/1z02k9/what_is_the_life_expectancy_of_a_skyscraper/" ], [ "https://www.youtube.com/watch?v=yOE8H\\_1Dhz4", "https://www.youtube.com/watch?v=yOE8H_1Dhz4" ], [] ] }

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{ "a_id": [ "gzr58x0" ], "text": [ "There are two pipes supplying the faucet. One has heated water and the other has unheated water. These mix together to before they come out of the faucet. Turning the control changes how much of each goes into the mixture, which changes its temperature." ], "score": [ 16 ], "text_urls": [ [] ] }

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{ "a_id": [ "gzrjf20" ], "text": [ "Imagine you connect several pipes to supply water somewhere. The pipes have different diameters. The bigger diameter - the more water can fo through that single pipe in a period of time. I.e. speed of water (current) depends on pipe size. When connected in a series, the pipe with smallest diameter sets the limit for water flow speed (maximum current) for the whole pipe system. You can't make the water flow faster than it can flow through the smallest pipe The same principles are applicable for electric current. The wire is a pipe, the electric current (directed flow of charges, for example electrons) like a waterflow. The resistance is a value that depends on wire section area in inverse proportion. Also the voltage can be seen as a height difference between the pipe ends. If pipe is horisontal the difference is zero (no voltage), the water (and electrons) are not going anywhere. When pipe is not horisontal, the difference sets pushes water and electrons through the pipe (wire) and sets the speed (electric current strength, amperage). The sign of that difference (positive or negative polarity) sets the direction for current flow. EDIT: i HIGHLY recommend for everyone this YouTube channel, where lots of physics, math, electronics and other topics are animated and explained. URL_0" ], "score": [ 19 ], "text_urls": [ [ "https://youtube.com/user/EugeneKhutoryansky" ] ] }

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{ "a_id": [ "gzsemaa", "gzsg7q5" ], "text": [ "The best way to explain this is to compare it to a mountain bike with multiple gears. The first gear has a large sprocket and it's good for getting off from a stop or going uphill and through mud, sand and snow. You won't be able to go very fast but you have all the torque you need to power through the terrain. At the other end you have the final gear, it's extremely difficult to use this from a stop but once you're up to speed you can really get moving. The gear reduction in a cars transmission works on the same basic principal.", "If you've ever ridden a bicycle with gears you can get a really direct example of this. If you go uphill, it's REALLY difficult in a higher gear, in a lower gear you can peddle easily and get your mass moving but you'll have to peddle faster doing it. Same for a car, with the \"effort\" in modern engines being analogous to dumping in more fuel in an attempt to provide enough power until the point it bogs down or the torque converter just starts slipping. Conversely, you can only peddle so fast no matter how little effort it can take and engines can only run at so high an RPM. So if you're not trying to get up a hill, pull something heavy, whatever, that low gear will leave you spinning like mad but not getting anywhere fast, you've got to spin the tires more times to speed up and you can't spin the power source any faster so you change the ratio of power source spins to wheel spins, ie you shift into a higher gear. \"Overdrive\" refers to this ratio going beyond 1.0, meaning the transmission output is spinning more than 1 time, maybe 1.1 for example, for every rotation of the engine/pedals. Really fast cars need to have a high max RPM and hogh available gear ratios to avchieve those speeds while making enough power to fight things like air resistance, the rolling resistance of tires and the friction in the drivetrain. Cars also have a gearing in the axle, usually somewhere in the 3-4 ish range, which means that for every 3-4 rotations of the transmission output, the wheela will rotate once. This has the same relationship to speed/power as the transmission ratio. Numerically higher axle ratios (more driveshaft turns per wheel turn) provide a mechanical advantage for power, but require a higher RPM to achieve the same speed, all else equal. These higher numbers are seen in trucks, off road vehicles trying to fight the inertia of large tires, and drag vehicles where acceleration is prioritized over high top speed (up to a point of diminishing returns anyway). You'll also often see higher axle gearing in vehicles with the smallest available engine for that model since it allows the manufacturer to provide more mechanical advantage to the weak engine without having to build a different transmision with more advantageous gear ratios. Numerically lower ratios are seen in high cruising speed cars and in commuter vehicles that want to either maximize speed at a given RPM (optimizing for high cruise speed) OR that are trying to maximize fuel efficiency while cruising (lower rpm for a given speed means the cylinders firing fewer times means less fuel used). Gearing is always a trade off. You can only go so low before it's imptactically slow and demands way too high an RPM from the engine. You can only go so high before the engine can't produce enough power to keep the vehicle moving, it eventually needs more mechanical advantage from the gears to get the job done." ], "score": [ 11, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gzt0sog" ], "text": [ "It’s easier to understand the effect with rebar, because the effect is so pronounced and the materials are so different. Concrete is really good at keeping its shape and not breaking under compression, like if you were to push on either end of a block. If you were to pull on either end (tension), it wouldn’t be nearly as strong. The opposite is true for rebar. When you put them together, the weakness of the concrete in tension is balanced by the tensile strength of the rebar, and vice versa. The strengths of one offset the weaknesses of the other. You can go a step further by putting the rebar under tension before the concrete is set, so that when you release it, the slab is in compression. This makes it very strong, and is how most modern concrete structures are made." ], "score": [ 9 ], "text_urls": [ [] ] }

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{ "a_id": [ "gzt8zf5", "gzt8krm", "gzt94hi", "gzt90v1", "gzte7n4" ], "text": [ "Your opinions are shared with most of Paris and half of the rest of the world. It was designed in the early 80s when this type of architecture was quite new and modern, which did not last long. It is sort of minimalistic which is a great contrast to the surrounding buildings but its design is still more driven by aesthetics rather then functional design which was in contrast with brutalism which was the most popular minimalistic architectural movement of the time. It does provide a lot of light and open air to the lobby underneath it which is inspired by Roman villas. So you can say a lot of bad things about the pyramid. And some good things if you take the time at which it was designed into account. But at least it does make people talk about the Louvre and have become a very iconic landmark in Paris.", "I.M. Pei’s Pyramid immediately broke the architectural mold in France, a country defined so long by classicism and antiquity. The Louvre Pyramid brought a radical and tangible touch of modernity to the world’s most visited museum. It's primary purpose was to connect the museum's three wings via an underground lobby that had all natural light, hence a glass pyramid was used as the roof of the lobby.", "I mean, what often gets lost in all of this is that the Louvre Pyramid was actually built to solve a problem of crowd control; the greater Louvre museum complex couldn't really handle all of the people, and so there was a need to open a hole in the roof of the subterranean part of the complex through which people could enter and be distributed throughout the museum. As a result, there needed to be *some* sort of structure to put over what would otherwise be a hole in the ground. Whether or not it's a masterpiece or an atrocious scar on what is otherwise pristine French architecture is largely in the eye of the beholder, but it can't be denied that it has been influential.", "I think it's great there. The juxtaposition of something that is light, unfussy in ornamentation, primal of shape with the pyramid is in direct conversation with the French Renaissance of it's surroundings. The new and the old. Art isn't let's make everything the same, so why would you do it with the building housing them? That being said, it isn't carte blanche to just do shit and call it good because it's different. Pei does a great job here.", "To answer your question directly: tensioned cable glass facades, which look simple but were cutting-edge technology for the time. So for an architect of Pei’s stature (during the ascendency of the High-Tech movement launched by the British), it was about finding a language of form appropriate to the zeitgeist while matching the ambition of the original by pushing the limits of technical capabilities available. It was not about pursuing historicism or reviving lost building forms. So in short, a clean glass pyramid is an elemental form easily conceived and extremely challenging to materialize, manufacture, and construct irl. Yes, it was reviled as much as it was lauded. I found this link which looks very interesting: ( URL_0 )" ], "score": [ 23, 11, 10, 4, 3 ], "text_urls": [ [], [], [], [], [ "http://facadesconfidential.blogspot.com/2011/10/louvre-pyramids-revisited.html?m=1" ] ] }

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{ "a_id": [ "gzuwdk9", "gzui4ow", "gzv0y1g", "gzuptw3", "gzx2woe" ], "text": [ "I work for a road network managing organisation and in my department we have the unit in charge of the bridge monitoring. Here's what we do to ensure we don't end up on the front page of the news for a very bad reason. Most people think bridges fail abruptly and catastrophically. They don't. A failure like the Genova Bridge was probably in the making for several years, and if the monitoring was done correctly they could have taken measures to prevent it, or at worst to close the bridge before it happened. That's why we have an extensive monitoring set up in place. Every 6 year a very detailed inspection take place. All the components of the bridge are inspected visually but thoroughly : you check the supports, the cables, the curbs, the road or whatever the bridge carry, the water disposal system. Everything. If you see anything out of the ordinary we do more : radar analysis for example would allow us to check the concrete reinforcement steel. We can take sample of concrete or steel and such. We can also decide to use gage and sensors to really follow how things are evolving, like in real time and get a sense of how fast the bridge is getting damages. Every 3 years we have a checklist (taylor made for each bridge) that we check. That gives us a grade (from 3 to 1) for the general state of the bridge. 3 being in need of repair, 2 for needing monitoring and 1 for of no concern. Again this inspection is only visual but anything out of the ordinary could lead to a more thorough inspection or analysis. The grade is used by our DoT to get us funding for maintenance and repairs. Every year we have the \"normal inspection\", again visually. It's mostly used to check if the minor defects noticed in one of the big inspection, that didn't warrant more actions, does not evolve too quickly or too badly. We also have yearly and tri-yearly maintenance actions to take. Mostly to keep water out of the places it shouldn't go. Water is the biggest enemy of anything that has steel or concrete like bridge or rod. And God forbid if there is water and bellow zero temperature. That's the bane of civil engineering. Inspections are also used to check if the yearly maintenance has been carried as they should. For the bridge who have problems, most of the one under our purview are concrete ones so I'm gonna focus on those, we have several tools at our disposal.first we have the original plans and data sheet so we can estimate how damaged the bridge is. We also use them to know,for example, where are the main support steel in the concrete to check if they could be corroded (in case of cracks) or how many of them are they. Bridge are generally build for 80 to 100 years so if we don't have those data, we're basically shooting in the dark. Given the initial construction and design data we can easily recompute the load capacity and security factor of the bridge, and depending on the damage and results decide to reduce the authorised load. In my case most of the bridge are designed to accommodate normal traffic and exceptional loads up to 200 tons (normal trucks are 44t in my country). We can reduce that, and have done so in the past. We can decide to close the road or just lanes (luckily never had to do that). But often we just launch study to fix the damage components : rebuild a concrete beams, add strengthening cables, redo the support (which must be done every few decades for some type anyway), repaint, clear the drainage pipes, fix cracks in the concrete ... For a three if mine we are in the process of designing replacement because in The next 5 to 10 years we estimate that the load bearing capacity will have decreased too much and the safety margin won't be enough to allow everyday traffic on it (given the uncertainties of what everyday traffic in everyday weather actually is). As other commenters said, material science is good enough to allow us to estimate how and at what speed materials break so we know, given proposer maintenance and monitoring, that we have time to carry all of that. Sorry for the typos and such, I'm in my phone and not a native English speaker. I might have used the wrongs words for some things too. Edit : fixed some typos. There were really too much of them.", "Materials science has a good understanding of how materials fail from stress, so how the bridge or tunnel can fail is pretty well understood and they know what to look for. Obviously the main way a bridge or tunnel would fail after years of use is fatigue. Fatigue typically starts as microscopic cracks in the material that grow over time. So inspectors will look for cracks, and if they aren't too long, track their growth over multiple inspections, because many cracks do not pose an imminent threat. And appropriate repairs are undertaken for those that do become a problem.", "The owner of the infrastructure asset typically hires a consultant to perform routine and scheduled inspections to look for normal wear and tear, fatigue, cracks, corrosion, etc. This used to be an in-house inspection department but like most everything else nowadays, it’s done by outside consultants. Examples of owners would be: city/town/county/municipality for roads, bridges, sewers, etc.; transit authorities for train and subway tracks, bridges and tunnels; the big private railway companies for track and bridges; departments/ministries of transportation for highways, bridges, tunnels, etc. All of these owners use the inspection reports to develop a 5 or 10 year maintenance program and prioritize other repairs or replacements that are needed sooner.", "Well, the truth is both reassuring and frightening. Bridges, and really almost any architecture, are built with a huge added strength just to be sure. Of course nowadays we have computers to calculate exact forces and materials needed. But at least up to recent times I heard a rule of \"when not sure - multiply by 1.5\" among architects and that is a general approach. The scary part is that in a lot of countries, US included, there aren't nearly enough inspectors to keep an eye on ALL of the infrastructure we have. Bridges, dams, tunnels - a modern country had A LOT of them. So, they don't get inspected as often as they should.", "Civil engineer here. There is one major thing that I'm not seeing in alot of these explanations, that is how engineers design things to fail in expected ways. In most major pieces of infrastructure, the primary materials in use are steel and concrete. Thanks to alot of material science we understand these materials very well. Because of that, engineers can sequence failures to minimize loss of life, or allow time for the problem to be fixed ( keep in mind I'm talking about regular use cases here. Mega earthquakes and alien death rays are too expensive to design for, so when those hit you just have to put your head between your legs and pray.) So how do we sequence failures to make them safer? That depends on the materials in use, but I'll stick with steel and concrete because they are so common. Steel is strong, flexible, and ductile. Meaning it can bend and stretch without breaking. Concrete is really strong, but mainly in compression, it also fails really fast when it's max loads are reached. So for a steel reinforced Concrete beam we design the steel to start stretching and flexing before the concrete might give, this creates cracks in the concrete that we can see before the entire structure collapses. Depending on the mode or severity of the failure we might be able to repair the structure, or it might be condemned. Other than sequencing failure, factors of safety are designed into the structure ( so we design it for heavier loads than we think it should see under normal conditions). We also regularly inspect structures for cracks, or other signs of failure. Hope that helps." ], "score": [ 141, 109, 3, 3, 3 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "gzv1byg", "gzv1pz1", "gzv1h7v" ], "text": [ "What we see as the real world's colors is after a LOT of work by our brain. Different lighting conditions make colors look different, and the brain puts in effort to normalize them based on context clues. A camera can't capture the entire context, so the camera itself, or a computer has to do the work the brain usually does", "Because our brains naturally color balance the real world for us. What we perceive as a white sheet of paper actually looks quite different if it’s lit by high noon daylight, evening daylight, incandescent light, fluorescent light, or some other light source. Cameras capture real world colors and then attempt to alter the image the same way our brain does so that you don’t look sickly green or jaundice yellow depending on what light you were photographed under.", "If it was vas easy to perfectly copy real world colors everyone would do it. But it’s not simple to make really good filters and sensors that represent colors perfectly. And even if we had the perfect camera sensor, still it’s a machine, it measures colors objective as pure numbers, but our human eyes adjust to color balance and so the colors will still not always looks right without some kind of color balance in post processing If you are in a room lit by an orange light, you’ll still see the walls as white, but a camera will just see orange" ], "score": [ 9, 6, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gzv52gd", "gzvebnf", "gzvefve" ], "text": [ "Because the gas is supplied at a set pressure. There's a flow meter that reads the amount of gas that's gone through it. So given a set specific pressure and a reading of how much has gone through it's very easy to know just how much gas has been used.", "To measure compressed gas flow rate you need to know the velocity of the gas, the density at a reference temperature, current temperature and current pressure. In a residential application; density, pressure, and temperature are fairly constant, so all you need is a way to measure velocity. This is the sensing element in a flow meter, usually either a spinning turbine or a positive displacement type. There are other more complicated ways to design a flow meter that you can easily google but these are the basics. Source: am an industrial instrumentation tech", "From Wikipedia “Diaphragm/bellows meters A diaphragm type gas meter. These are the most common type of gas meter, seen in almost all residential and small commercial installations. Within the meter there are two or more chambers formed by movable diaphragms. With the gas flow directed by internal valves, the chambers alternately fill and expel gas, producing a nearly continuous flow through the meter. As the diaphragms expand and contract, levers connected to cranks convert the linear motion of the diaphragms into rotary motion of a crank shaft which serves as the primary flow element. This shaft can drive an odometer-like counter mechanism or it can produce electrical pulses for a flow computer. Diaphragm gas meters are positive displacement meters.” The positive displacement chambers combined with knowing the pressure provides a reliable reading for the low flow rates for home gas meters." ], "score": [ 38, 5, 5 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gzvshrd" ], "text": [ "You’re correct. Atoms vibrate more quickly as temperature increases, so it’s more difficult for electricity to pass through the metal. Alternatively, atoms will move less as temperature decreases so electricity can pass more easily. The thermometer puts a voltage across the metal part and a microchip measures the current that goes through it and converts it into a temperature." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "gzw7ony", "gzw8jmb", "gzwatrh", "gzwd0r7" ], "text": [ "I'm not 100% sure but I think that Opel Ampera 2012, Chevy Volt and BMW i3 used or use this configuration. Edit : But they also have batteries too so combustion engine basically only extends range. Trains use it because they are very heavy and clutch would be quickly destroyed. There are also diesel hydraulic trains.", "The reason train locomotives have been using diesel electric in this way is because they produce too much torque for any gearbox that could fit to handle. Diesel electric is able to produce a lot more torque then a traditional gearbox but there is a lot of power loss though the generators, wires and motors. In cars the torque is not that big of an issue for a gearbox. So the electric motor in a hybrid car is not primarily there to replace the gearbox but instead to provide additional performance through the use of batteries.", "It used in car in combination will batteries. The advantages of diesel-electric in the train are that you need to have high torque a low wheel speed. You need that in a train in a way that is not needed in a car. A car torque converter with automatic gearboxes or clutches with automatic works fine. A diesel engine, generator, and electrical engine will weigh more than just direct drive in cars Diesel eclectic is common in ships. There is space-saving if you have electric wires instead of long propeller shafts. You can put the engine in the middle of the ship for better weight distribution. It also makes it possible to have multiple engine-generator where all is not used at the same time. You can have multiple diesel generators for low-speed operation. For high-speed operations, you can add a gas turbine generator. Gas turbines are efficient if you use all the power from the and small for the power they provide. So warships and cruise ships have them when they like to go fast. Some cruise ships put them up in the smokestacks. So with multiple engines and lars space, they have advantages. The result is that is it not efficient for cars to just have diesel-electric drive. The idea can be used in cars if you combine them with batteries. You can then use the batteries to provide power when lost is needed like if you accelerate and store energy in them from regenerative braking. The batteries can also be charged from an outlet The internal combustion engine only needs to be powerful enough to provide enough power when you drive at a constant speed. You can operate and the most efficient power level. This is called a [Series\\_hybrid]( URL_1 ) and a [Chevrolet\\_Volt]( URL_0 ) or [Nissan E-power variants]( URL_2 ) is a common example. There is a drawback with this designer. You need more components in them compared to just using electricity or just an internal combustion drive. A pure electric will be more efficient if you just drive the distance of its batteries to reach. Just internal combustion engines cost less.", "Because it wouldn't offer any benefit in a car. Conventional hybrids are designed so that the electric motor can supplement the power from the internal combustion engine and reduce the fuel consumption of it. An ICE driving a generator and then using that power to drive an electric motor would just be adding extra inefficiencies into the process--the only advantage you might get is that you can have the engine running constantly at its most efficient speed rather than revving up and down." ], "score": [ 13, 7, 5, 4 ], "text_urls": [ [], [], [ "https://en.wikipedia.org/wiki/Chevrolet_Volt", "https://en.wikipedia.org/wiki/Hybrid_vehicle_drivetrain#Series_hybrid", "https://en.wikipedia.org/wiki/Nissan_Note#2017_model_year_update_%E2%80%93_e-Power" ], [] ] }

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{ "a_id": [ "gzzew0b", "gzzj1jm" ], "text": [ "You’re not completely wrong in your assumption. But there are many methods to build foundations in water. The image above shows one of those methods, which involves building a temporary cofferdam (the metal ring in the pic above) by driving long, thin, sheet piles through the water and into the soil below until it forms a closed ring. Then, they can pump the water out so the construction crews have room to build formwork for the actual structure in dry conditions. So, what you see above will be removed once the actual structure has been built.", "The cofferdam is the first step. Now if you look closely you will see several wire structures down there. Those are called cages. Those have been attached to long metal or concrete \"piles\" that have been driven down into the soil all the way to the bedrock. The cages are the beginning of the metal reinforcement for the columns that will be built on top of the piles. The entire structure is designed so that the entire weight of the bridge and cars and all the other stresses placed upon the structure are transferred to the bedrock, and not to the unstable soil above it. As they start to pour concrete there will be people there with huge vibrators stuck into the wet concrete. Those will ensure that no voids develope around the reinforcing metal preventing the load transfer. The vibration causes the wet concrete to settle evenly preventing aggregates from catching on the metal. They will continue the process all the way to the top of the column. It's actually fairly intricate work and impossible to automate." ], "score": [ 7, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gzziuf6", "gzzkotq", "gzzrqsd" ], "text": [ "There’s a switch that gets turned on when sunlight stops touching it, or when you turn on your windshield wipers there’s a switch that turns on the lights as well", "Photo sensitive electronics. Think like the tech that is used for solar power. It’s just an electronic switch that can tell how much light it is absorbing.", "There is a light sensor in your car, usually located on the dash right below your windshield." ], "score": [ 12, 7, 4 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h00bln6" ], "text": [ "Because zippers are a very precise machine. They work bc the “teeth” of one side fit exactly into the groove between the teeth of the other side. If that alignment gets shifted they can no longer interlock. Zippers made of metal last much longer, but the edges of the teeth can wear down and cause them to be misaligned. Additionally the bottom edge can come undone making it hard to re-align the teeth. Plastic zippers are much more easily damaged. Heat, sunlight, extreme cold, all affect the plastic causing it to warp. Again this means the teeth are no longer able to join properly." ], "score": [ 14 ], "text_urls": [ [] ] }

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{ "a_id": [ "h01f5ov", "h01de3j", "h01gv3k", "h01evde" ], "text": [ "[They did the math]( URL_0 ). A single bolt could power 56 homes for one day. But there's 139 million homes in the U.S. alone, so you would need about 2.5 million sky-to-ground strikes a day just to power every home. This does not include businesses that are taking tens of kilowatts or industries measuring their draw sometimes in several megawatts or more, just homes. Since there's 22 million strikes a year and we need over 900 million just to power *just* the homes, it's already looking pretty grim in terms of cost to benefit. This is assuming we manage to capture every strike (even more expensive) and that weather plays in our favor. Then you have to build a storage system capable of taking a sudden surge of millions of volts and thousands of amps. That's an extremely tough one. Any battery or capacitor would pretty much instantly vaporize.", "[A technology capable of harvesting lightning energy would need to be able to rapidly capture the high power involved in a lightning bolt. Several schemes have been proposed, but the ever-changing energy involved in each lightning bolt renders lightning power harvesting from ground-based rods impractical – too high, it will damage the storage, too low and it may not work.]( URL_0 )", "Because almost every way that we use and handle electricity is done in a steady, even manner, by moving electrons from one place to another over wires. Even a 'wireless' phone charger has a coil of wire in it that has to be very close to the coil of wire in the phone for any charging to take place. And that transfer of power can take many minutes to complete. Light bulbs and fan motors draw the power that they use constantly while they are being used, not in sudden bursts separated by large gaps. Lighting is kind of the opposite. Clouds being agitated by the wind build up a large electrical potential over several minutes, and then that energy is released in a fraction of a second in the lightning bolt between the cloud and the ground. And then it is gone. Lightning rods are just connections to easier paths for electricity to take between the ground and clouds. Any attempt to make the electricity passing between a lightning rod and the ground do work, by turning a motor or charging a battery, would make that path less 'easy', and thus more likely that the lightning will pass through the interior of the structure that the lightning rod is supposed to be protecting. Result: fried electronics, charred wiring and burned down buildings. We have no way of capturing lightning, no way to use it if we did, and no way to store a lightning bolt to use the power normally, later.", "Energy storage is difficult and expensive. That is one of the main drawbacks to solar energy. We could easily harvest insane amounts of energy from sunlight... When the sun is shining. How do you save that massive energy for later without extremely expensive batteries that require rare eath metals needing vast mining efforts to aquire?" ], "score": [ 36, 12, 6, 3 ], "text_urls": [ [ "https://www.windpowerengineering.com/how-much-power-in-a-bolt-of-lightning/" ], [ "https://en.wikipedia.org/wiki/Harvesting_lightning_energy?wprov=sfla1" ], [], [] ] }

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{ "a_id": [ "h02xbgd", "h03f65j", "h043mxg" ], "text": [ "Fighter jets have low bypass turbine engines. Passenger aircraft have high bypass turbine engines. High bypass engines used the turbines that turn big fans in the front. This are goes around the engine instead of through it. So it’s like a big room fan. You are hearing more of the rushing air vs the burning gasses inside the turbine. In a fighter jet, the majority of the air is consumed through the turbine and mixed with burning fuel. That burning of the fuel makes the noise you are hearing.", "The engines on jet fighters are designed to move a little bit of air very quickly, while the engines of passenger aircraft are designed to move a lot of air more slowly. Moving the air faster generates a lot more noise, hence why jet fighters are louder despite being less powerful.", "Flew out of Midland/Odessa and we're second in line. Pilot comes over the intercom and say \"Folks, you're in for a treat. There is a NAME OF PLANE in front of us about to take off\". Knew he was referring to an Air Force jet. It was one of the loudest things I've ever heard and the whole plane shook, loved that you could \"feel\" the power." ], "score": [ 25, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h04b40p" ], "text": [ "Aight, so the long and short of it is that, when you buy a battery electric vehicle (regardless of the type of battery chemistry), you have an initial \"debt\" of emissions in comparison to internal combustion engines (i.e. it'll have a higher amount of carbon emissions associated with it right off the factory floor) because mining isn't exactly great for the environment, but you work off that debt over years of usage because of the increased efficiency of the battery-electric powertrain and charging infrastructure, meaning the energy you are using has less GHG emissions associated with it. The actual metric is *excruciatingly* hard to pin down as the automotive supply chain is hilariously complicated (e.g. Japanese cars are made in the US, but American cars are made in *Mexico*, because economics) and trying to figure out the true scale of it can make your brain do a big sad, but very roughly speaking a battery electric vehicle will work off the initial emissions \"debt\" in anywhere from 3-8 years, depending mainly on whatever your electricity provider uses to make power, and how/when/where your battery pack's materials were sourced and manufactured (of note, this assumes you're putting on around 10-12k miles per year). ***However***, the jury is still out when it comes to getting rid of the cars at the end of their lifecycle, which is still a bit of an open question as we haven't had battery electric vehicles at large enough scales for a long enough time to know precisely how difficult it is to deal with the battery when the car is scrapped. However, it stands to reason that EVs will still be generally \"better\" assuming the battery/car manufacturers are in a position to recycle their own batteries and use the material to make more batteries. From a pure usage standpoint, though; BEVs will not kill ICEs entirely. Spark ignited engines are probably on their way out, but diesels and turbine engines will stick around because batteries will basically never have the energy density to make sense for heavy-duty ICE applications (the only way around this would require you to rewrite the laws of thermodynamics; good luck with that). Source: PhD in Mechanical Engineering, specializing in propulsion (primarily diesel)." ], "score": [ 8 ], "text_urls": [ [] ] }

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{ "a_id": [ "h05hhkx" ], "text": [ "It's somewhat about styling. Bigger and bigger tires (and rims specifically) have been becoming more en vogue, even now with say an 18\" rim standard there's still an upsell option to get 19s instead etc. Vans meanwhile aren't really built to appeal to mass markets looking like eye candy, they're more likely purchased as a fleet with the intent to haul stuff and make money with, not be a bragging point to the neighbors. And since bigger wheels means bigger costs to the business, sticking with more-affordable tires and rims helps shave off the MSRP. It might just be a $500 difference but a company buying 30 vans to run their parcel delivery service is gonna see that as $15,000 saved. There's also the tire capacity. Vans can be equipped with cargo tires meant for holding heavier loads, but these are offered in a rather limited range of sizes, for example the Toyo Celsius is mainly offered in a 16\" rim size, while their all-season touring stuff for regular cars is all over the place with sizes." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "h05mqaw", "h05owc9", "h06c7yk" ], "text": [ "The components are made of thermoplastics such as Polyether ether ketone (PEEK), with a melting point higher than 600°F, and Ultem (Polyetherimide), which is mechanically very strong and machineable. These are not the in the same family as the the polyethylene typically used in food packaging.", "The simple explanation is you use plastic that can handle the temperature they are exposed to. The plastic items you are used to in your home are made of plastics with relatively low melting temperatures. The ones used in car engines have higher melting temperatures. An example of plastic with a very hinge melting temperature is PTFE that is more well-known for one brand name Teflon. It meets at 326.85 °C (620.33 °F) You have it as a coating of frying pans and it does now melt when used. I am not saying that PTFE is used for the large plastic part in the engine, but it is an example of a plastic that can handle high temperatur. Car engines do not in general get that hot. The common cooling system is water that you pump to the radiator. IF you have a coolant system at 1-atmosphere overpressure water boils at 121 °C (250 °F). It gets a bit higher when you add antifreeze. So that is the max temperature of the engine where the coolant is. So most of the engine and centrally the engine room will not get warmer than that in normal operation. If the cooling system fails you will get high engine temperature warnings. This is temperatures where some plastic work fine as you can see in the engine. Some part like the exhaust pipes get but you do not use plastic to close to them", "In addition to different melting points, some parts of your engine just aren't particularly hot. The intake draws in air at ambient temperature, so plenty of that can be plastic. The cooling circuit operates around 100C, topping out about 130C, so plastics are just fine." ], "score": [ 15, 4, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h05q4pf" ], "text": [ "There is not any incentive for a manufacturer to do that. There is in fact an incentive to not do that, if they fail you are the only supplier of the spare parts. If you produce enough cars there is a significant advantage to use of the shelf components because you make enough for you to keep the cost down There are some advantages in using a custom part and that is you can make it so it fits perfectly with the engine you use. If you use the shelf component you will be limited in the physical shape of the part. The result is that very few parts are standard in cars. Fuses, lamps, and another part that the consumer replace themselves than to be standard. But anything that tends to be replaced at an automobile repair shop tends to be custom for the maufacturer." ], "score": [ 7 ], "text_urls": [ [] ] }

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{ "a_id": [ "h06ac75", "h06ba8f" ], "text": [ "Appliances do not use timers for every sequence. Especially modern appliances which have more sensors then older ones. For example when it fills the machine with water it is not just opening the tap for a set amount of time but instead opens the tap until the water level is at the desired level. How long this takes depend on the flow rate of the tap you connect it to. The wash time itself can be based on various sensors to detect how dirty the water is. The rinsing time can be similarly timed and based on how much soap is in the water. The last step is the drying which use sensors for various things. Both during the centrifuging stage it measures vibrations and either restarts to let the clothes move around a bit or even limits the speed if the vibrations are too high. It will also wait until all the water have drained down the pan before letting you know the clothes are done. If you have a washer drier then it also measures the humidity of the air and waits for this to get low enough. And all of these things depends on how much clothes you put in, the type of material, how dirty it is, how much soap you add, what kind of soap you use, the water in your tap, etc. So the machine does not actually know how long the wash is going to take beforehand but it can give you an estimate. Some appliances are able to learn from previous cycles and adjust their predictions based on this.", "A big part of how long a cycle takes, which is a bit random, is how well the machine is able to balance the load during the spin cycle. During the spin cycle, the machine tries to get to a certain speed for a certain time to fling the water out of the clothes. If the load is difficult to balance (for example a single towel), the machine's wobble sensor will kick in early and it will slow back down to toss the clothes some more in an attempt to balance them. This can happen several times. Eventually the machine either gives up, or spins the clothes for longer at a lower speed." ], "score": [ 6, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h06jybb", "h076df0", "h06hhuf", "h074dn5", "h073pxt", "h07p99j", "h07qtrs", "h078e5f", "h07dr42", "h073zi3", "h09pqtx", "h07qwyq", "h08stnc" ], "text": [ "Have you ever sat by a lake or river and dug a little hole in the ground? After a while, water will collect in the bottom, because the water flows through dirt and stone around the river too. When it rains, a lot of water flows down into the ground and that ground that carries water is called an aquifer. Depending on what kind of dirt and rocks are there and how the hills and mountains are sloped, it will collect in certain places. Very ancient people needed water to live, just like we do today. They usually chose to live near rivers, lakes, and streams. They also dug little holes in the ground nearby, and noticed the water in those holes was nice and filtered by the dirt and sand. If they dug a hole and covered it up, their water would taste good and stay clear of leaves, sticks, and algae. So they dug deeper and deeper holes, and found they could move further from lakes and rivers which would flood from time to time. Where to dig a well was trickier the further you got from water though. Sometimes they dug big holes for nothing, and that was disappointing, but they learned a lot from it. Parents taught their children what to look for, what kinds of rocks and plants made for good well ground. EDIT: WHOA!!! Glad so many people were amused by writing in my teacher-voice! A recurring question I’ve seen is “How can dirt filter water? Wouldn’t it be dirty?” So here’s a [link]( URL_0 ) to explain more about wells since it’s a pretty deep subject. In short, fine topsoil rich in organic matter doesn’t go very deep, clay settles out, and gravel and sand are excellent filters that continue to be used as part of modern water filtration systems.", "Knowing where isn't that easy. Throughout history people have dug for water and failed, start over somewhere else. That's why dowsers made money, that guy with a forked stick who claimed to be able to detect where water was. Either such a person was a complete charlatan, or he was just good at reading the land for water and the stick was his trick to wow the clientele.", "You do likely see how rain water will flow on top of the ground and collect in steams and rivers to flow down hill. However some of the water find its way through the grains of dirt instead of just on top of it. Water flows much slower through the dirt then on top of it but it will still flow in a similar way. The water will not be able to flow the same through different layers of dirt and bedrock so the grondwater will often collect in similar streams and rivers under ground. But they tend to be much wider and flow much slower. It can even form huge ground water lakes the size of countries. If you look at a terrain you can often see where the ground water flows. Both based on how the terrain is shaped how the vegitation look like and even the color of the dirt. You would then be able to dig a hole where you expect there to be water and hope to find water there. As for clean drinking water the dirt is usually a very good filter of particles and toxins so the ground water tends to be even cleaner then the surface water.", "dig deep enough literally anywhere in the world and you'll hit water there is water underground in most environments... even the desert... like vast underground lakes. However the best place to dig a well is somewhere where it rains occasionally so that the underground aquifer is replenished by rain water sinking into the ground. If you hit water in a desert and use the well a lot... the aquifer will eventually run dry..", "I have water well. In my father back yard. 7 meters deep. I believe they dug it when I was in elementary school. No science in there. You dug a hole deep enough, you found water. Of course the depth will be different in the desert or somewhere with a lot water sources (river, lake, swamp). And the quality of water are different too", "Primitive people learned much from observing nature! There are animals that dig for water. We ourselves are animals that have been passing down this type of knowledge.", "\"medieval people\" and people living 10.000 years ago were not the retard brutes you see in movies (at least not all of them, or not more than today). They were crafty and wise people who could work and cope in life, probably more than any of us, who don't know how to make anything work and have to google the plumber's phone when the toilet breaks.", "When it rains, water goes into the ground. When enough water builds up under the ground, you can get a little (or very big) lake that's inside of the soil. By digging deep enough into the ground, you can reach that underground lake and get water from the soil as it leaks from the soil into your well.", "I live about 450 feet from a river. Is it safe to assume as long as there is water in the river and my well is deeper than the river, it will never go dry?", "Rivers and Lakes are not like pipes in the water supply or the sewers. They are filled up by rain and snow melt. They leak into the surrounding areas so much that there is a constant amount of water underground if you drill near a river or lake. The further you are from natural water, the deeper you need to dig. Also, elevation matters because you have to dig through the height of the mountain.", "Medieval? We still dig wells to get water.", "My home has a well (and septic) and my water literally just started flowing again 10 minutes ago. I learned a LOT about residential wells over the past 72 hours. Once the drillers find an aquifer (about 620 ft down for us) they install a pump at the end of a very long string of steel and PVC pipe with a power cable running alongside it (about 500’ down for us). The power connects to the house (like any other power circuit), the pump starts running and is connected to a switch & pressure tank. The tank is pressured (with air) to between 30-50 PSI and this creates water pressure in the home to fill hot water heater, toilets, go to faucets, etc.. It was surprising how relatively straightforward (yet expensive) the process and equipment is.", "If you buy an undeveloped plot of land and need to drill a well, you typically apply for a permit from the county, a guy comes out with the survey map and tells you where you're allowed to dig. This will be setbacks from the property lines, roadways, wetlands, etc. There's no \"this is where water is\", you dig until you hit water. In hte USA you can pick a spot at random on a map of the country, and have about a 90% chance of drilling a successful well. this is why water dowsers are so successful...it's easy to find water, it's hard to find a spot where there is NO water. the comical part is how dowsers will walk around and say \"ok, drill HERE\" like underground water is in a pipe or something...they literally don't even understand how water tables and aquifers even work." ], "score": [ 20671, 475, 156, 52, 24, 12, 10, 9, 6, 6, 3, 3, 3 ], "text_urls": [ [ "https://www.usgs.gov/special-topic/water-science-school/science/groundwater-wells?qt-science_center_objects=0#qt-science_center_objects" ], [], [], [], [], [], [], [], [], [], [], [], [] ] }

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{ "a_id": [ "h06jok3", "h06n53t", "h06jdgv", "h06o42u" ], "text": [ "Because it's an AC supply. The electrons in the wire are just moving back and forth, so it doesn't matter to the device which way they start. However, for the sake of safety, we need to know where the power supply is. If we disconnect the red wire or the black wire, the effect is the same. Your device turns off. However, there will always be electricity present on the red wire. So if we decide to turn off your device by disconnecting the black wire, your poor electrician could touch the red wire and the ground, electrocuting themselves... This is not possible with the black wire though. This scenario may not apply to the device you're playing with though. Nevertheless, we've applied this rule to all wiring to remain perfectly safe. TL;DR It doesn't matter from a technical perspective. It's to maintain safety.", "TL;DR: for predictability. We make it a habit of wiring things the same at all times so that there's never any confusion as to where the power flows from or to. Plugs in the wall delivery AC or alternating current, which changes polarity from positive to negative several times a second. HOWEVER, the energy is supplied on ONE wire (live, colored red or brown), while the second (neutral, colored black or blue) simple provides a path to complete the circuit and return the current. There is actually NO power supplied on the neutral wire; it is inert while not connected to an appliance, so it is safer to touch than the live wire, which has main voltage on it at all times. BUT, knowing which wire is live is VERY VERY important, which is why it is ALWAYS required to use a specfic color for the live wire (usually red), and ALWAYS place it in the same receptacle on a plug/socket. The earth / ground wire is a safety mechanism, and does not affect the operation of your devices unless something is wrong. For most simple, basic devices the order of live/neutral doesn't matter. That's your lights or phone charger, for example. But in some cases, it *does* matter which direction the live and neutral are connected (and the device will have a non-reversible plug with an earth pin as well), in which case you can't expect a homeowner to pull out the wall wiring and make sure it's correct. This is basic safety and reliability.", "In electronics there are two types of power; AC and DC. Of these two, only DC power has polarity. This is because AC swings between positive and negative (hence its named Alternating Current) whereas DC power is 'rectified' to keep the waveform at a steady level. Wall outlets are AC power. A phone charger, for instance, then steps the voltage down and 'rectifies' the wace into DC power.", "There are not really positive or negative wires - there's live and neutral. For most appliances it doesn't really matter which is which, because it's the different in potential between the two that counts. You can get a shock from the live. In normal circumstances you shouldn't get a shock from the neutral - but it's better to be cautious - the wiring might be faulty and it's possible (if unlikely) that you can be killed by a shock from the mains." ], "score": [ 36, 5, 3, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "h09fubh" ], "text": [ "You have spinning magnets inside other magnets. The movement creates a moving electrical field that produces power. You have a regulator that controls how much voltage it makes and a rectifier that makes it DC power instead of AC power." ], "score": [ 6 ], "text_urls": [ [] ] }

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{ "a_id": [ "h0b1yd4", "h0b0w9b" ], "text": [ "It depends on the kind of light bulb. Old fashioned \"incandescent bulbs\" produce heat, a bit of light, by running tons of electricity through a super tiny wire (called a filament) made of tungsten in a vacuum. Tungsten has a very high melting point so it stays solid, and since there is no oxygen it doesn't burn. Eventually a tiny imperfection in the wire can serve as a weak point that melts, atoms boil off, or otherwise breaks, breaking the circuit and making the bulb \"go out\". Halogen bulbs work similarly but have a chemical reaction where as atoms of the filament boil off they can get replaced back onto the filament via some fancy chemistry, these bulbs still work similarly incandescent bulbs in that they produce tons of heat and bit of light. These bulbs get extremely hot though and usually carry warnings and/or come in cages for this reason. fluorescent bulbs work on a different principle. They have no metal filament and have exposed metal plates on either end of a long gas tube filled with a special gas. Due to quantum mechanics, electricity travels from the high voltage metal to the low voltage metal plate using the gas as a \"wire\" and this \"excites\" the gas. As the gas calms down from this excitement it releases mostly invisible light, and very little heat. Since the light is mostly invisible the inside of glass tube is coated with a fluorescent powder that absorbs the invisible light and released visible \"White\" light. The bulbs can \"go out\" by being damaged/losing their gas or having damaged electrical components, these lights need special devices called \"ballasts\" to work and these ballasts often become damaged leading to the lights to \"go out\". Since they produce little heat and last longer than incandescent bulbs these lights are often considered more environmentally conscious but it's worth noting both the bulbs and the ballasts often contain hazardous chemicals like Mercury and PFBs (cancer causing compounds) so they're not *great*. LED bulbs (called \"lamps\" in this case) also use quantum mechanics to generate light via low-voltage physics on special computer chip components called \"light emitting diodes\". Since these are low-voltage they produce essentially heat at all and last very long times since they don't have the wear and tear of high heat/voltage lamps. They also require fancier computerized parts to function and these parts can wear out causing the bulb \"to go out\". Generally though LEDs last extremely long times and produce very low heat making them the greenist option. fun fact - since office buildings were designed with Incandescent and Fluorescent bulbs in mind with regard to heat being produced, many office buildings are now being designed with larger, more robust heating systems to account for the lack of heat load being produced by the lighting systems.", "The thin tungsten wire ablates very slowly while glowing. Basically tungsten atoms get blasted off the wire and onto the inner glas surface. The thinner the wire gets the higher its resistance becomes. Higher resistance means higher temperature. So the process speeds up. At one point its getting so hot, that it melts the wire and boom." ], "score": [ 10, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h0eg9sb", "h0eg0dy" ], "text": [ "To avoid electrocution waterproof materials and thicker insulation is used. When you are welding the heat generates a gas bubble around where you are welding and you are welding in that bubble.", "When they’re not in tunnels (as another commenter pointed out, but missed the mark bc there are some who operate in water) You still could use electric-welding, so long as you know what you are doing. Water isn’t very conductive, though salt water definitely is. Still, whatever the electrical current is going to flow through needs to be an easy path to ground. A big metal object, such as a ship or pipe you are welding, is going to be that ground. So as long as you don’t activate the welding gun when you’re between the gun and the metal, or in that vicinity, the current is more likely to travel directly to (actually, from, but besides the point) the metal rather than through you and then there. Could be wrong about this- someone please correct me if there’s a special technique or equipment used or something. But some form of electric welding should still fundamentally work even under water. You just may or may not actually use inert gas while you weld, and you *DEFINITELY* should not try it at home." ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h0g6afn", "h0g7dot", "h0g6wzi" ], "text": [ "There's a meter on the intake valve by your home. Once a month, someone will drive by, take a reading, and then you get charged accordingly. You theoretically could install a bypass, but there's usually no valve before the meter, meaning you'd be working with active pipes full of high-pressure water.", "There's a [water meter]( URL_0 ) located on the pipe leading from the water main to the house. It measures waterflow through it. What stops a homeowner from adding a bypass is a) that would be fraud or theft (I'm not exactly sure which it would fall under) and you would wind up in legal trouble if you were caught b) Depending on where the meter is it may not be a trivial piece of plumbing to do.", "On the water line in to your house, there will be a water meter. It measures how much goes through it. This meter also has a small radio device that can communicate with the upstream office, typically through a relay in a utility box in the neighborhood. You *could* bypass it, but if your water usage suddenly drops, they will notice and come to inspect the meter." ], "score": [ 12, 7, 3 ], "text_urls": [ [], [ "https://www.waterone.org/home/showpublishedimage/3428/637520289381870000" ], [] ] }

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{ "a_id": [ "h0kiqfd", "h0kilca", "h0ldhna", "h0kiwhq" ], "text": [ "Air conditioning units have a compressor in them which is a rotary pump. This requires something to spin them. In a car, the compressor is driven by a belt running off the engine. The only way to do this is to have a shaft sticking out of the compressor with a pulley on the end and a seal on the shaft. It's basically impossible to make a shaft seal which doesn't leak a microscopic amount. If the seal was absolutely perfect then no lubricating oil could get into the joint and it would fail. In a fridge, there's an electric motor which is hermetically sealed inside the same chamber as the pump. This means even if gas/oil escapes to the motor, there's nowhere for it to go and you don't keep loosing gas. In addition, all the pipes in a fridge can be made from metal brazed/soldered together. This effectively makes a perfect seal. In a car, you've got to be able to replace damaged parts (it's not that big a deal throwing away a broken fridge - but it is a big deal throwing away a car because the aircon is broken). This means you've got various removable joints which are liable to leak. Finally the car has bits that vibrate, therfore you need to have some bits of the system that are flexible rubber hoses. These rubber hoses are slightly permeable, especially as they age/deteriorate. Edit: Some electric and hybrid cars now have hermetically sealed electric pumps which should be very reliable. However you can still get leakage from other joints and its very easy to get microscopic leaks from damage.", "Vehicles subject the pipes and fittings to hugs amounts of vibration, in comparison to what a refrigerator experiences. That vibration can let a tiny bit of the refrigerant gas out, as it's under high pressure. Vehicles are also exposed to huge swings in temperature, while they are turned off, which can also enable leaks when the system is powered up.", "I haven't had my car A/C recharged in literal decades. If it needs recharging, it means there is a leak in the system somewhere. Sometimes it's more economical to just top it off a bit each year than to painstakingly search for a teeny tiny refrigerant leak. That being said, some shady shops recommend a recharge when it isn't really needed just to make a little extra money. This sometimes skips over other possible causes of inadequate cooling, such as a bad temperature regulation system.", "Vehicles are a much more violent environment. Your refrigerator sits in a room and the two primary generators of vibration are you opening/closing the door and the compressor running. Neither subjects the system to much strain. Your car's A/C system is constantly subjected to a much higher and more severe level of vibration even when you are driving down fairly smooth roads. Every bump/pothole/crack you hit sends a shock through the system. Your vehicle also flexes and shifts as you take turns, accelerate, and brake. This means all the connections in your vehicles A/C are constantly being twisted, pulled, vibrated, severely heated, and possibly severely cooled. This creates tiny gaps and potentially cracks in o-rings and seals, allowing coolant to escape over time." ], "score": [ 83, 5, 5, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "h0lmwzt", "h0lm1zx", "h0lrxz8" ], "text": [ "Hours is probably the best indicator unless you want to use a much more complex system. Cars typically use mileage instead because traditionally it was quite easy to track with just a simple mechanical setup, and for the average car there's going to be a reasonably good correlation between miles and hours (though there are obviously exceptions). It was cheap and easy to measure and it was good enough, so that's what the car industry stuck with, at least on the driver-facing side. Internally modern cars will actually track a lot more. Manufacturers will sometimes deny warranty claims if they see that a car or truck has an excessive number of idle hours on it, even if the mileage is still inside the warranty limit. The oil life monitors on cars with flexible oil change intervals will actually take a lot of factors into account, like how hard the engine has had to work or how many cold starts have accumulated since the last oil change. But even though the engine computer is keeping track of those numbers, manufacturers only expose the mileage since that's what people are familiar with.", "Hours is a more accurate measurement. I think cars go by miles because most people are commuting and the starting, stopping, and shifting gears all the time puts more stress on the engine than just contralto running, like, say a generator, which doesn’t change gears. The mileage is also useful in tracking for other systems like the transmission, which doesn’t suffer wear when the vehicle is on, but in park. Also, cars are subjected to different environments, which have different effects on the engine and vehicle as a whole. Mileage vs engine hours is just a way to try to compensate for all of these factors.", "The reason is actually pretty simple - \"What measurement best estimates the wear?\". If we look at a forklift(tracked by hours) vs a car (tracked by KMs). The forklift is generally not covering great distances and a lot of the stress to the engine is coming from running the hydraulics (which means the tires dont need to be moving to be wearing the engine). The car on the other hand stresses the engine through running primarily the drive train, and so distance traveled is a better measure than the number of hours the engine was running. I have never actually never worked with maintenance schedules for long haul trucks, but I imagine they would have a combination of the two (5,000 KMs or 250 hrs, whichever hits first), since they idle enough to require taking that time into account on the wear." ], "score": [ 11, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h0nq1b1", "h0odrke", "h0nq9xi", "h0ohdol", "h0o0dfx", "h0o3lfe", "h0ocxa9", "h0o4cq7", "h0pz4ry" ], "text": [ "The problem with water isn't that it is there, but rather that it doesn't leave easily. In an unfinished house there is only the studs which will dry quickly because they are exposed to sunlight and lots of air while this might cause some warping everything is held togeather and doesn't really move. Now if you get water into a finished basement you now have water in the walls in the carpet or under the floor. Air cant get to these places so they stay wet for long periods of time and that causes problems. There are also materials that don't do well when wet regardless of how long they are wet for and those don't go in till after the house is water tight.", "There is a method to the madness when building a house and combatting weather. The foundation won't be harmed at all by short term wetness. The framing goes on quickly and the sheathing right behind it. The sheathing is either weather resistant zip board or its regular OSB with a house wrap installed that keeps most moisture from penetrating. The subfloor decking is a special material that is meant for short term water exposure, like Advantek plywood. Also, small holes can be drilled in the floor to eliminate ponding and allow the water to drain to the basement. The roof is again either zip board sheathing or its regular plywood that quickly gets coated with tar paper, which is fast, cheap and easy and keeps out 90% of the rain. At this point, windows and doors go in, and the house is generally considered \"dried in\" after all the openings are filled. Next step is installing The final siding and roofing, which can go on pretty much at the same time as the interior mechanical, electrical and plumbing systems get roughed in. Absolutely no drywall or insulation or carpet or basically anything that can't get even a little wet without adverse effects goes in until the house is fully dried in. So basically, it's all about moving fast and using purpose built materials in the early stages, and getting the right systems in place before you install anything that can't be exposed even short term.", "Wood does soak up water, but it also dries out over time. There’s usually not anything exposed to rain that will get damaged. Any wood that’s touched the ground is treated to resist rot, so I’m if there is a puddle of water on the foundation for months due to rain It won’t rot, and any other wood will shed water and dry out naturally. The wood frame goes up first, followed by the roof to protect the walls, flooring, paint, etc. that would get damage by rain if it was installed without a roof. If your house is wood framed, it will naturally absorb moisture from the air on humid days and dry out on dry days. That’s why you may see cracking paint at some point because the wood will swell stretching the walls and contract when it’s dry causing cracks over time. If you have old wood doors, you may notice on humid days its difficult to open or close the door because rot swells from moisture.", "3 words - order of operations Basically there is a point in building a house when it's all still pretty exposed that it's not a big deal if it rains. But then as it progresses there will be a point where it's paramount to get the roof up and generally waterproof the interior in case of rain so generally contractors will plan around this and put in a lot of manpower and resources into construction at that point. Once that's done then the house can survive rain like any other built house.", "It does but it remains exposed to the elements and will just dry up. Once it gets to the point where things can get damaged(usually the roofing and insulation is next, followed by drywall), it gets tarped up and flashing(the weird white paper you see on a house without brick or siding) is put on.", "Don't they bake the houses, too? I've seen in Seattle where houses that have gotten as far as having windows and doors installed will then bring in big propane heaters and bake the place for a couple days. Or at least that's what it looked like to a rando like me walking by.", "\"Fine\" depends on whether you ask from the one who built the house, or the poor souls living in it. Moisture management is essential in modern construction, and things getting wet typically leads into trouble down the road. But usually those issues take longer to develop than the builders warranty is, so builders won't care. In Finland increasing number of houses are prefabricated in a factory and then lifted to foundations. The level of fabrication varies from wall elenments, to sections of a house, to fully made houses made in a factory. And the key reason is that in a factory the construction work can be done in dry controlled environment. When the house arrives to the site it is typically constructed to waterproof state in one or two days. Building from scratch at the site is mostly done by frugal do it yourself types, or ones building from EPS molds that are filled with concrete. Which obviously is totally different process, but also there the moisture controlled part starts as soon as roof is done.", "Cut wood doesn't matter if it gets wet as long as it has a chance to dry. Engineered wood like plywood and OSB sheets, must be of a structural grade if used in housing. These structural grades use glues which are tolerant of getting wet (they will eventually degrade, but not over the course of a few weeks). Screws and fixings should also be of a grade where a bit of damp for a few weeks won't cause them to rust/degrade.", "The stuff that gets easily damaged by water doesn't get installed until the house is water tight with roof, windows and walls in place" ], "score": [ 1718, 110, 17, 13, 11, 7, 7, 6, 3 ], "text_urls": [ [], [], [], [], [], [], [], [], [] ] }

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{ "a_id": [ "h0qwo1z" ], "text": [ "Only if the water were somehow magnetized, which it wouldn't be. I'm not sure what's giving you the idea that this *would* work, so it's hard to explain where you've gone wrong." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "h0t5fm7" ], "text": [ "Its basically the same as a clamp on ammeter used in electronics. A clip on ring goes around the wire and through induction can sense when the amp draw increases in the line. By measuring changes to the magnetic field. You put the sensors on the lines coming out of your circuit box. Everytime something turns on it records the increase in draw Someone just figured out how to hook up a wireless control box for it so you can get updates on your phone. Anecdotally this same method was how they used to catch illegal grow rooms. They would start at the power pole then figure out which house and then watch that one. \" At 5 pm every day we sense a 20 amp draw for exactly 12 hrs. = Grow light." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "h0vj6ef" ], "text": [ "In most case a vehicle with notable idle vibration has worn out engine mounts and/or is idling at too low of an RPM. Most engines don't really smooth out their vibrations until they are running somewhere over 1,000 rpm but idle at somewhere between 600-800 rpm. There are rubber pieces that connect the engine to the body of the car, over time the rubber wears out so it stops absorbing those low speed vibrations and that's what you are noticing. Replace the mounts, and make sure your engine properly maintained and you won't feel the vibration." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "h0xlv03", "h0xko8l" ], "text": [ "Mastering a song is checking, and often correcting, how a song sounds so that it's not too quiet, not too loud, and works well with the media (CDs, FLACs, Vinyl, etc.) that it's on. For instance, a recording on Vinyl needs to be carefully equalized to let the bass come through, but if it's too loud, it can cause the player to skip! The mastering engineer also will make sure all the tracks on an album are at roughly the same loudness, and that the song order works well. Remastering is that same thing, but usually done to take advantage of technology that has come out since the album's first release. For instance, when CDs first came out, they had to remaster a lot of albums because CDs could reproduce high end tones at a higher volume than vinyl did.", "Songs are frequently recorded in individual tracks for each instrument and/or singer. When all those tracks are assembled, balanced for volume, etc., and combined into a single recording - that's the master. Re-mastering is going through the process again. Digitally remastering is taking those original analog recordings from before when digital recording was common, converting them to digital, and then mastering them." ], "score": [ 14, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h0zeqr7", "h0zbdtu" ], "text": [ "It’s also the size of piping in the sewers. Your gutters compared to the items clogging it are a lot closer in size than your poop and toilet paper is compared to the size of the sewer pipe in the streets. Your lateral (hookup from the house to the street) has the best chance of plugging because it’s only a few inches wide. But once beyond that, you can have from 12” to many feet in diameter before it hits your sewage treatment plant. It can clog but if your semi solids are the only thing going it, it would take a lot. But that is exactly why you are not supposed to flush wipes down the toilet. Since they don’t degrade in the water, they can clump together and clog stuff. Don’t flush anything but pee, poop, or toilet paper.", "They do. But it's designed as a system of pipes with built in redundancies, so when one pipe gets clogged the others can continue to function." ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h16eig5" ], "text": [ "Because interference tends to \"look like\" changes in amplitude. I.e., it's hard to tell the difference between the signal amplitude and the interference amplitude. On the other hand, interference rarely takes the form of changes in frequency (where the most likely form of FM interference is [multipath]( URL_0 ), where the signal interferes with itself)." ], "score": [ 7 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/Multipath_propagation" ] ] }

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{ "a_id": [ "h17rufh" ], "text": [ "When your tires roll over the road, its more like pushing over and over again in terms of physics. In a short distance, high acceleration event, the asphalt beats your tires by ripping bits of it off. In a long distance, low acceleration event, your tires wear out considerably slower. Sort of like washing dishes with short fast strokes versus long slow wipes. The former is much better at tearing things up." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "h192o2p", "h196moh" ], "text": [ "Well, they're actually not very durable, is the answer to that. They have to run in a totally sealed environment because even the slightest flake of dust could cause them to stop working. They can move so fast because they're built to be incredibly light, so it doesn't take much power to move them.", "They’re not that durable. Am easy way to more or less destroy a hard drive is to open it up outside of a clean room. Just a little bit of dust completely screws it up." ], "score": [ 10, 5 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h1cegov", "h1cf4z7", "h1cll1h" ], "text": [ "They aren't just \"planes\", they are **air**planes. Their engines take in air to combust their fuel, their wings push on air to keep them aloft, their control surfaces direct air to steer them. Know what there isn't in space? **Air.** Without air the airplanes won't be able to do all those things which are pretty critical to their function.", "Their engines and wings require an oxygenated atmosphere to function. At a certain altitude, the engines will not be able to function and the wings will not be able to provide lift (the altitude for each of these events is not the same however). Rockets carry both their fuel and oxidizer with them and require no outside material to function. This is the fundamental difference between jets and rockets, and why jets always have a forward-facing intake.", "Others have explained why planes can't make it to space, so I just want to add some wider context. NASA defines the edge of space (called the \"[Karman line]( URL_3 )\") at an altitude of 50 miles. The SR-71's altitude record in sustained flight is 85,069 feet (a bit over 16 miles), less than one-third of the way to the edge of space. > pull up on the stick and head into space [The absolute altitude record for air-breathing aircraft]( URL_2 ) was set by the maneuver you're describing—max out the throttle and accelerate vertically. The altitude record set was 123,520 feet (about 23 miles), still less than halfway to the edge of space. A few aircraft have managed to cross the Karman Line, namely the [North American X-15]( URL_0 ) and the [Scaled Composites SpaceShipOne]( URL_1 ). They were both purpose-built for the task, featuring rocket propulsion, gas thrusters for attitude control in the near-vacuum of the high atmosphere, and launched from a \"mothership\" instead of a runway. They have more in common with rocket boosters than they do with most other planes." ], "score": [ 49, 9, 4 ], "text_urls": [ [], [], [ "https://en.wikipedia.org/wiki/North_American_X-15", "https://en.wikipedia.org/wiki/SpaceShipOne", "https://en.wikipedia.org/wiki/Flight_altitude_record#Fixed-wing_aircraft", "https://en.wikipedia.org/wiki/Karman_line" ] ] }

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{ "a_id": [ "h1d14vs" ], "text": [ "Some microphones, mostly condenser microphones have a thin plate/diaphragm in them that reacts better when warm then it does cold, They are powered microphones, and require a power supply to heat up the plate and diaphragm so that it sounds nicer." ], "score": [ 7 ], "text_urls": [ [] ] }

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{ "a_id": [ "h1eheh6", "h1ehtik" ], "text": [ "You mean when the radiator fan kicks in?", "a couple things happen, if the car had higher load demand on it (like your ac is on and it just clutched up to cool the air) the vehicle will raise the cars rpms for a period of time to run smoother. I work on VWs are actually are lounder and higher RPM on first start up to run a system called secondary air which in ELI5 terms is a system that puts more air in the exhaust to warm the converter up in the name of better emissions. after about 30 seconds the RPMs drop and engine gets noise lowers" ], "score": [ 5, 5 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h1grw4y", "h1gsrdf", "h1gqsp1", "h1grntk", "h1hngfu" ], "text": [ "It's easy to lose track of what gear you're in, so when you come to a stop you just keep mashing the shifter down until it won't go any more. Then you know you're in first. It would also be dangerous to put neutral in the bottom-most position, because again, if you lose track of what gear you're in, you can end up in neutral when you really need to be in gear (such as a vehicle approaching from behind about to rear-end you). It's also important to note that neutral is a half-step. So shifting up form 1 to 2 is easy if you use the full travel of the shifter. You have to deliberately make a half-shift to get from 1 or 2 to neutral\\*. \\* Kawasaki transmissions have a Positive Neutral Finder, when you are stopped you can do a full upshift and it will lock you into neutral and not let you go into 2.", "It's a convention now, and bike riders expect it. Some companies did it originally because there were no synchos on first gear. You almost had to be stopped to engage it.", "Foot placement on the pegs while riding means it is easier to pull up to shift from 1 through to 6, neutral makes most sense near the lowest gear because that is where youd be traveling slowest, but if it was below 1 instead of between 1-2 you have the potential for accidentally going into neutral instead of 1 which is a bigger deal than accidentally going into neutral from 1-2. Additionally you are stopped while in neutral typically so pressing down is more ergonomic than reaching under the lever to push up.", "So that if you are shifting down, relying on engine braking, you don't suddenly find yourself in neutral. Neutral at the bottom are not unheard of, but are not common.", "I didn't see the reason as I understood it. Like a car, neutral is a rarely-used \"gear.\" It's for starting (bike stopped), and for long waits at a light (bike stopped) so you can relax your hand. Otherwise you just want to walk up and down the gears and use the clutch. For this reason, neutral can't be at the extremes. The next question is between which two gears should we hide the half-step to neutral? Of course it should be next to first gear - the one you use when you want to start up from a stop. So between 1 and 2 is the only logical place." ], "score": [ 86, 6, 6, 3, 3 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "h1haaz2", "h1hcbia", "h1hnu5a" ], "text": [ "Glass and aluminium are less likely to react with the beer, which could produce some off-flavors. They are also generally better at keeping stuff like oxygen out, even when not highly pressurized.", "light can cause some beers to go bad..why they originally came in brown or green bottles... clear glass beers are not \"alive\"", "1. It looks better and more fitting in a can or a glass bottle. 2. There are a lot of ultra cheap shitty beers that actually come in plastic bottles." ], "score": [ 20, 11, 5 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h1jaq01", "h1j95xz", "h1k0trt", "h1jdyx6", "h1jqwac", "h1kaks4" ], "text": [ "Two answers: 1) They don't always survive. Ships are lost every year to heavy seas. [And sometimes it turns out that a particular design or model of ship is particularly vulnerable.]( URL_1 ) 2) There are centuries of shipbuilding and sailing experience that inform ship design. Combined with modern design tools and materials, and ships can be designed to withstand huge loads from waves (like dynamic loads of up to 50+ atmospheres in severe conditions). [You can read more about how ship design in this paper.]( URL_0 ) Unfortunately, there aren't global standards for ships and, as I mentioned, ships do in fact break up all the time.", "They don't always survive. Plenty of ships are lost at sea, although much less so in recent times. Modern ships, while massive, are also very well designed. And while the fluid dynamics at sea can be wild, they're also decently well-understood, so ships can be designed to be strong enough not to collapse/snap in heavy seas. Of course, this isn't absolute, and ships can still sink from rough weather, poor nautical skills, bad luck, or any combination. But a modern vessel, properly crewed and maintained, and with a good captain who has good information (weather forecasts) will stand a very good chance of making it out of any given voyage safe and sound.", "There are other answers here explaining how they don't always survive, but none giving you the actual reason why boats CAN handle this treatment and survive. The answer to this is weight displacement and distribution and is basically the same reason the boat floats in the first place. Namely the boat displaces as much water equal to its weight. When the boat is getting tossed around, it is still displacing as much as it weighs, so it's not going to sink. Add to this that boat designers design the boat so its balanced to always return to an upright position. When a boat gets tossed upwards and strikes the sea on the way back down, the impact force is evenly spread across the area that impacts the water, and as its displacing its own weight, its no big deal. Imagine throwing a rubber duck into your bath and see how it \"bounces\" off the water. Basically the same effect. Likewise, when huge waves wash over the boat and spill all over the decks, the water isn't actually doing anything other than washing over it and off. The boat is sealed and unless the water gets inside and starts to lower the boats attitude in the water, its not gonna do much. Imagine trying to sink a rubber duck bath toy by pouring water over it. You will never do it. Cut a hole in the top and pour the water inside the duck though and eventually it will sink. And while thousands and thousands of gallons of sea water might weigh a huge amount to me and you, comparitively to the ship, it's nothing. So basically, enclosed boat is full of air and displaces the water it sits on. Without being able to overcome that, waves can't sink the boat. Waves don't break the boat apart because the energy of the water is quite spead out across the ship. Having said that, as others pointed out sometimes boats do go down due to severe waves and stormy seas. However this tends to be because the boat is either capsized (Rolled over and unable to right itself), or other mechanical defects that allows water to breach the boat and get inside it, thus making it heavier and heavier till it takes on too much water. In fact in most modern ships, this is 99% the cause of ships going down in rough weather, and it's now rare when mechanical reasons aren't counted. A mechanically intact and correctly run ship can take on some truly horrendous seas just fine. [Here's a famous example]( URL_0 ) of a ship being broken up by heavy (Actually not considered all that bad by most maritimers) seas. The cause? Poor maintenance and an even poorer inspection programme for the ship.", "The Edmund Fitzgerald springs to mind. It broke in half when the bow of the ship was on a different wave than the stern. Snap... Gone.", "These ships survive because of their design and different systems on the ship that can work together to keep the ship stabilized. The most common system onboard to stabilize the ships are their ballast tanks. These tanks generally hold seawater to create weight. Because of this weight, the ship has a lower point of gravity thus giving it more stability. Imagine a Formula 1 car. It is designed for high speed. One of the reasons it can go that fast is because it is build as low to the ground as possible. Because the F1 car is lower to the ground, it has a lot more stability to handle these high speeds. The stability comes from a lower point of gravity. The placement and dimensions of these tanks are calculated before the ship is build. They come in many different shapes and sizes but generally have a squarish or rectangular shape. The seawater is pumped into, or out of, the tank via pumps. These pumps are either operated by crew onboard (most common) with the use of Alarm and control systems, or by manual control on a switchboard. Depending on the design of the piping system that is installed they generally come with one or two valves on smaller ships but can have more depending on the use case of the ship and the tank. The amount of seawater in the tank is managed by trained crew on board with the piping system. There is more to it than just filling the tanks. You have to take into account your current cargo on the ship as well as different types of liquids in different tanks located throughout the ship. For example: The more weight on the left side of the ship facing forward means you will have a bias towards the portside of the ship. The more weight on the right side facing forwards means you will have a bias towards the starboard side of the ship. Other than the ballast system there will be electrical systems that will help stabilizing the ship. These systems can help with planning the route of the ship so they don’t catch bad weather or heavy winds. They can also take over steering to stabilize the ship. The captain will be in charge of this and will judge whether or not it’s safe to go through storms and what route to take. All of the systems are driven by an onboard power plant which will generate power for the ship. If these power plants fail then the aforementioned systems don’t work. The captain also has to go to manual steering when there’s no power. You can imagine on a large ship that the rudders will be driven by large electrical motors. In the case these don’t have power, you won’t be able to rotate the rudder. With all of these systems having failed, the chance of capsizing or splitting will increase tremendously. Of course there is backup power after the power plant fails. This is only for a certain amount of time. The minimum amount of time you’ll have is based on regulation for different components on your ship. I am a project engineer for a company that is specialized in Alarm and Control systems on different sized ships. For us the general minimum norm is 30 minutes after the power plant fails. This can differ for electrical motors on a rudder or pumps on a ship. If you have any other questions about a ship or about it’s control and logic. Please reply or send me a DM!", "I saw a video of a container ship, filmed along the row of bulkhead doors below deck. In the row of maybe, 20 doors, it flexed far enough that you could see the end of the row, then only the next door along. Both ways." ], "score": [ 249, 57, 50, 19, 9, 3 ], "text_urls": [ [ "http://shipstructure.org/pdf/2007symp09.pdf", "https://en.wikipedia.org/wiki/Liberty_ship" ], [], [ "https://www.youtube.com/watch?v=DMNhO8dKJjQ" ], [], [], [] ] }

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{ "a_id": [ "h1l6vvm", "h1l1s2h", "h1l2a15", "h1l47yt", "h1l1viy" ], "text": [ "They don't. Its value is vastly overrated. If you take 10 glock 19s load then with the same ammo. You aren't going to be able to reliably tell the difference. Shows like CSI have vastly over stated the accuracy of the test, while prosecutors and police just go along with it.", "Short and off the top my head answer: Microscopic differences between rifling, primer strike, and twist pattern. Long and well researched answer: URL_0", "Because machines are not perfect; there is a little bit of play between every part of every machine. If this tolerance was not present the machine would seize up at the slightest change in temperature. Tolerances get looser every time the machine gets used and wears down.", "Because no machine is 100% perfect. There are always small defects or imperfections in the manufacturing process. They may be microscopic, but they're measurable, and because they're random, they're different in part of ever gun. In addition, all guns wear over time as they're used, and the wear pattern is different in every individual gun as well. This isn't just true for guns, it's true for literally everything.", "Guns are precision devices, but small imperfections are unavoidable. The pressures are very high, and those pressures deform the shell casings." ], "score": [ 29, 13, 10, 7, 3 ], "text_urls": [ [], [ "https://www.scientificamerican.com/article/how-can-a-bullet-be-trace/" ], [], [], [] ] }

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{ "a_id": [ "h1npsuk", "h1nq0hg", "h1o1bzq" ], "text": [ "A quartz clock works because quartz wiggles a little bit when you apply a voltage, and it creates a little voltage when you wiggle it. If you make a little bit of quartz in the right shape and apply a known voltage, it wiggles back and forth in a very predictable and regular manner, and with Some Electronics you can turn that into an electric pulse every second to drive a little stepper motor.", "It depends on the mechanism. If it is a quartz clock the battery triggers a bit of quartz material to resonate at a very specific frequency. Since this frequency is known, time can be measured accurately. quartz watches lose or gain 15 seconds in a month. Mechanically driven watches lose or gain a few seconds per day.", "The trick behind keeping time is finding something that is very consistent and predictable that you can count. In the case of a traditional mechanical clock, this might be the swinging of a pendulum, in a mechanical watch, the rotation of a balance wheel. In a quartz clock, the vibration of a quartz crystal. In an atomic clock, the transition between energy levels of an electron. Each of these things is very predictable, perhaps surprisingly so - a well tuned pendulum or sprung balance wheel can have a consistency measured in beats per day, which means that by counting the beats, your clock can keep accuracy at the seconds per day level. After that, we just need to find a way of converting that counting into a display were can read. In a quartz watch that means using the count to move a stepper motor once per second to tick the hands forwards, or in a mechanical watch, having the balance wheel swinging at 4hz let a spring unwind enough to move the second hand 1/8th of a second forward (4hz to an 8th of a second is because the mechanism used ticks once when the balance swings one way, and a second time when it swings back). The ability to be so accurate then comes from the precision of the mechanism - cheap parts and sloppy tolerances and your watch will keep poor time, but the more accurately they can be made, the more accurate the timekeeping." ], "score": [ 11, 10, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h1ntvpt" ], "text": [ "How do you eat an elephant? - one bite at a time. You break the project down into lots and lots of smaller parts (or work streams). Each one has someone to oversee and make sure it's on track, these folks all regularly report in to someone overseeing the whole project, so they can see if bits are starting to drift off and can redeploy resources to get it back on track." ], "score": [ 8 ], "text_urls": [ [] ] }

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{ "a_id": [ "h1o81b3", "h1ohuo0" ], "text": [ "Have you ever seen one of those pens where you click the end and the nib pops up? It's basically the same thing, a little clip holds it down and then when you press it again it releases.", "Usually there's a little V-shaped notch in the switch/casing and a pin that sits in that notch on the other part. The V has one long side and one short side. When you click the button, pin travels down the V, and when you let go it rises up on the other side (e.g. now on the short side). When you press it again, the same happens, the pin goes down the V and comes up on the \"long\" side. Same way that retractable pens work." ], "score": [ 19, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h1p2a2s", "h1p67w7", "h1p5k8e" ], "text": [ "The discharge rate of a battery is limited by it's internal resistance. The internal resistance of a small battery is rather high, because they are not meant to discharge rapidly. This means that even when you short the battery, it will discharge at a reasonable rate, and not do a whole lot. The internal resistance of car batteries is very low, since they're expected to deliver hundreds (or sometimes thousands) of amps to start an engine. When you short one of them, you discharge current very quickly, which turns to heat. As for your second question, capacitors act very similarly to batteries (with a very small capacity, but a VERY low internal resistance). Mechanically and chemically, they are different, but from an outside perspective, they can be treated the same.", "High voltage batteries in electric vehicles aside, the main concern with a car battery is shorting it out with something metal while working on it, like a metal ring around your finger. The extremely high currents traveling through such a ring make it heat up and burn you. Smaller batteries aren't able to provide as much current, so the risk isn't quite as big. Though even some smaller batteries can pass enough current to be dangerous, especially lithium cells. But you won't get electrocuted from a normal 12v car battery, because your body has too much resistance for 12v to push dangerous levels of current through it. Can totally get electrocuted by a 600v battery from an electric car though.", "For most electricity, it takes a large voltage to get any current going through our relatively resistive skin. At 12V, our skin is going to restrict the current to almost nothing; regardless of how much current can be supplied by the battery. The danger with large batteries is the fact that they can supply 100’s of amps of current if given the chance. So if you have wet hands or cuts, IE. something to reduce that resistance, then you can accidentally have amps running through you. Small batteries are less dangerous simply because they don’t have the ability to put that much current through them. But generally, neither are particularly dangerous; it takes a fair amount of voltage to really get through our skin. Which is why you don’t touch random electronics or capacitors. They can be at much higher voltages that will get through our skin. Capacitors act like low-capacity extremely quick discharging batteries; great at holding high voltage and dispensing it instantly, but at the downside that they only hold a tiny charge." ], "score": [ 18, 6, 4 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h1qcnov" ], "text": [ "Hi, ex-civil engineer here. Good question! The main reason that we use rebar or other inserts during the casting process is to help the concrete during tension. Compression is almost like a ‘squashing’ force on an object, concrete has incredible compression strength but it lacks in tensile (‘pulling’) and shear (‘ripping’) strength. The reinforcement helps with the last two. Another purpose of rebar is to allow the concrete to move ever so slightly without shattering to help deal with all of the forces acting on it. I hope this helps! :)" ], "score": [ 22 ], "text_urls": [ [] ] }

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{ "a_id": [ "h1qhv15", "h1qi113", "h1qiai0", "h1qsbpi", "h1qiyni", "h1qn3lm" ], "text": [ "It's just a convention that's generally used for \"tighty righty, lefty loosey\"--you can easily make a screw that goes the opposite direction just by making the \"spiral\" around the screw shaft go the other direction. The likely reason that direction was chosen is that most people are right-handed and tend to be stronger when turning things to the right than to the left.", "That is exactly it, they do have screws that tighten in the other direction, mainly for applications where the device is spinning at a high speed that could cause the screw or nut to come loose. Think of a circular saw, they have bolts that tighten in the opposite direction so when the blade spins the screw doesn’t come loose.", "It’s just the way the threads are cut into the shaft, yes. You can easily make a left-handed thread by cutting the threads like that. There are time when left-handed threads are used, the one that pops in my head is the locking nut on my pedestal fan’s blade. It’s a left handed thread because the blade is spun clockwise by the motor and having the nut threaded opposite keeps the blade from coming loose. Why right handed? The vast majority of humans are right handed and you have more strength rotating your hand outwards than you do inwards.", "FYI before they converted to fluorescent, the NYC subway system used light bulbs with left handed threads to prevent people from stealing them, since they wouldn't screw into any standard socket.", "They do make bolts with both right-hand and left-hand threads. The 'usual' threading is right-hand which tightens when you turn clockwise. Exactly the opposite for left-hand thread.", "Yup, we settled on a convention so things were compatible. That one is it. There are things that have reverse screws. Bikes, for example. The two pedals are often screwed on in opposite directions. This is because each side is effectively rotating the opposite way (clockwise or anticlockwise). If both had the same thread, one would tighten and the other loosen as you pedalled. As they are, both pedals try to tighten." ], "score": [ 28, 17, 6, 4, 3, 3 ], "text_urls": [ [], [], [], [], [], [] ] }

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{ "a_id": [ "h1wqvsj", "h1xyxs0", "h1wtcz6", "h1x35wi" ], "text": [ "> Does doing this way increase the torque produced by the engine? No, it reduces the resistance from the wheels. The clutch is two plates pressed together to transfer the torque, and by releasing slowly you are engaging them with less pressure for a time. This lets the plates slip, transferring some torque without it being enough to stall the engine.", "The clutch works like the brakes, just in reverse. If you slam on the brakes, the wheels lock up. If you drop the clutch, the engine \"locks up\". If you press the brakes gradually, you bring the car speed down at a rate that the tires can handle. If you release the clutch gradually, you bring the car speed up to a rate that the engine can handle. To be more clear, the engine has a minimum working speed. If you connect it directly to the wheels at a dead stop, the engine doesn't have enough torque to turn the wheels before the engine speed drops below that minimum working speed.", "> I know when you stall your car is because the resistance torque is greater than the torque generated by the engine. Not really, that just causes the engine to slow down which is fine until a point. The engine needs to operate at a minimum speed. & #x200B; In the circumstances you are talking about letting the clutch out slowly allows the clutch to slip. This allows power to be transferred while still keeping the engine operating at the min speed. After a few seconds the cars speed has accelerated such that it is travelling fast enough to allow the pedal fully up...no slipping. At that speed the minimum engine speed and the vehicle speed are about the same? Does that make sense? If you tried to start in second gear you would have to slip it a whole lot more and for longer.", "The purpose of the clutch is to disengage the driven from the driving. When in a low gear, the engine output (driving) approaches maxed out while the driven (transmisssion selection + wheels) is still going pretty slow. When you depress the clutch, you disengage this coupling, allowing the transmission to go from low (e.g. 1 turn of driving = 3 turns of driven) to a higher gear (e.g. 1 turn of driving = 6 turns of driven). So by releasing the clutch slowly, you allow the speed of the engine output (driving) to gradually match the speed of the driven (higher transmission selection + wheels). The slippage involved is just the mechanism by which the two sides equalize rotation rates. The faster that happens, the more impactful the transition. Sometimes it's too much torque for the engine to match and it stalls. Think about releasing the clutch quickly in first gear, the wheels bark, the car jerks, but the driven isn't too far away from the driving, and the engine can recover. Try this in fourth gear, and the drag on the engine is just too great, it can't match the rotational speed of both sides of the transmission (required when both sides are engaged at higher gear ratio) instantly (due to mass of car) and the engine stalls (Thank God)." ], "score": [ 11, 8, 5, 5 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "h1y9tnu" ], "text": [ "Do you mean how it gets generated, or how it gets used? Let's try both. Generated: do you know how car engines work? A bunch of pistons push and pull, and this gets turned in to a spinning motion? Well electrical generators can do this in reverse. A spinning motion creates a push and pull. If you move a magnet past a wire, it makes the electrons in the wire move. If you spin a magnet around near a wire, it can make them push and pull. So, if you have something spinning in circles, say a wind turbine or a water wheel or a steam turbine (you get the steam by using coil or nuclear fuel to heat up water), you can spin magnets around and create this push and pull, the alternating current. But how is this used? Well, plenty of older devices don't really care which direction the electricity flows in. A filament light bulb heats up because electrons flow through it. But it doesn't care about the direction. So, if the direction changes 100/120 times a second (i.e. it cycles 50/60 times a second), it still works. Modern devices do tend to care. But we can still use this. There are electrical components called diodes that are like one-way streets for electricity. LEDs are Light-Emitting Diodes, so they only work when electricity flows in one direction. Plug an LED into an AC circuit, and it'll only be on half the time. But, the flickering is so quick that we don't notice. If you really want it to work, you can plug one in in each direction. Then they'll alternate. One will be on during the push phase, and the other during the pull. We can even use ~~transformers~~ rectifiers to convert from AC to DC. These can work like the two diodes thing with LEDs, but they can then recombine the two phases, and smooth things out so it's not as bumpy. That's what the big block on a laptop cable is doing, or the small block on a phone charger." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "h206qpc", "h202l3b", "h2076qz" ], "text": [ "I think this was actually unintentionally invented by the british, when they forced german goods to be labelled as \"Made in Germany\". Soon, that label intended to keep people from buying stuff, was rather perceived as a sign of quality and reliability. In my understand, this was the foundation of the germans image of having very good engineers / engineering / quality. For further reading: [ URL_1 ]( URL_0 )", "Rudolf Diesel made the first diesel motor. Germany is home to most car brands (non US), most being luxury. Daimler (Mercedes) and BMW are also one of biggest manufacturers of trucks in China and around. They have many brands worldwide. Someone will probably have a waaay more detailed version, but mine is a TL;DR version :)", "I think it's more a case of outstanding marketing. The Germans have always been good at that. Not that they don't have excellent engineers, engineering and design skills, I just don't believe that they're really that much better than any other industrialized nation. Japan, Korea, France, Italy, even the USA and China all have great accomplishments in modern day engineering feats." ], "score": [ 7, 5, 4 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/Made_in_Germany", "https://en.wikipedia.org/wiki/Made\\_in\\_Germany" ], [], [] ] }

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{ "a_id": [ "h21ya9g" ], "text": [ "This is one of those things that make a lot more sense if you can see it rather than have it explained. Try this video: URL_0" ], "score": [ 5 ], "text_urls": [ [ "https://youtu.be/6BCgl2uumlI" ] ] }

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{ "a_id": [ "h238mnh" ], "text": [ "The thing used up is electric energy (which by itself says nothing), a useful picture might be that of a spring (or more concrete, think of one of these wind up-toys - those contain springs). The basic idea is that you wind up/expand the spring and \"store energy in it\" which you can then use to make the toy walk (or lift something with a mere spring). There's no matter being used up. This is the essence of how electricity works, just that you don't have a mechanical spring, but separated charges. In practice, it's a little more complicated (e.g. batteries use something called a \"galvanic cell\" to create the power which involves some electro-chemistry), but that's the basic idea." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "h23xzo2", "h24111s", "h23yjsn", "h23ynvp" ], "text": [ "Space is empty. Really, space is really almost completely empty. There are things out there, damage has occurred, and maneuvers are made to avoid the big things that are being tracked. But mostly, space stations depend on space just being empty.", "You know those really tense scenes in sci-fi movies where the heroes have to bravely maneuver their ship through the asteroid field? Yeaaaaaaaaah. Sorry, but nope: Real-life asteroid fields have *thousands and thousands of miles* between each asteroid. They're only an asteroid field because they only have thousands of miles between objects, as opposed to the rest of space that has *millions* or even *billions of miles* between objects. You cannot imagine just how empty space is.", "Because space is pretty empty. Sure, there are a lot of things flying around in space, but there's also a **lot** of space. The chance that any given satellite is hit by a piece of debris isn't super high. And larger pieces of debris (that could cause significant damage, like destroying a satellite) are tracked by NASA/other aerospace agencies.", "Space is *really* empty. The accumulation of high speed debris in Earth orbit is certainly a concern as the number of lost screws and rocket boosters and satellites continues to grow, but you’re unlikely to hit anything significant while wandering interplanetary space. We do occasionally see small impacts from micrometeorites on the shields and solar panels of space probes - and a piece of the ISS did get clocked by something a few weeks ago if I remember correctly. A larger piece of random space gravel big enough to punch a significant hole in something important is always a possibility, but it hasn’t happened to any of our missions yet." ], "score": [ 26, 5, 3, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "h24swym", "h24rez2", "h24what" ], "text": [ "Because they can go that fast, so if you go over 70 you know how fast you are going. Imagine a thermometer for your refrigerator. Temp in a fridge should be right around 36 degrees. What if your thermometer stopped at 36? Well, if it gets warmer than 36 you would never know if it was just at 37, or 39, or 70 degrees. Two of those are fine, one is definitely reason to panic.", "The reason is twofold 1. Cars are most efficient below their top speeds, so the top road speed will be below what a car can do for more efficiency 2. If there is a road that can utilize the maximum speed of a car, you'd want to know your speeds if you are traveling that quickly", "You don't build a car to go only the maximum speed because that's extremely inefficient. A car that can only go 70 as an example will need to rev really high, burning lots of fuel to reach its top speed. Instead they gear the car so that in top gear it can maintain 70 at a relatively low rpm because that is the most fuel efficient way to drive. By extension that means when the car is rev'd to its highest rpm in that highest gear its capable of going far over the speed limit." ], "score": [ 13, 6, 6 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h279ikt", "h27aff7" ], "text": [ "Diesel engines operate by causing the fuel to ignite by the rapid heating that occurs when the air and fuel is compressed. In a gasoline engine, the mixture is ignited by the spark plugs. To get the fuel/air mix to combust without a spark requires *much* higher pressure than in an equivalent gasoline engine. The result is also a much more powerful explosion, making for more noise, but also more energy released for a given displacement size, which is why diesels tend to have higher horsepower and torque, and somewhat better efficiency than gasoline engines.", "1 bar is atmospheric pressure. Remove the air from a steel oil drum - 1 bar is plenty enough to crush it. In petrol cars the explosion in the cylinder reaches about 20 bar under low load, and about 70 bar full load. In diesel engines the pressure explosion would be around 80 bar at light load, and potentially almost 200 bar at full load. This higher pressure makes the characteristic loud chugging sound. Also the fuel injectors which work at a crazy 2000 bar (!) make a characteristic clicking sound each time they inject fuel. This makes the characteristic click. Also tractor engines are generally diesel. Incidentally lots of small, compact European diesels aren't particularly loud nowadays since they are very effectively isolated and shielded." ], "score": [ 16, 9 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h27i6m4", "h27r8ty", "h27hk6h" ], "text": [ "You support the cart in multiple directions so it is impossible for it to leave the track The common way today is that the wheels roll on a pipe. You can have a wheel on the top bottom and outside of the track on each side. With wheels on both sides of the cart, you have wheels in all directions and as a result, the cart can move away from the track unless some part breaks. Take a look [on this image]( URL_0 ) and the design quite obvious.", "Roller coasters don't just have wheels on top of the track, like a regular train does. They also have wheels on the sides, and bottom of the track, which come together and hug the track, so the roller coaster can move, but the train stays on the track. Some older, wooden roller coasters just have wheels on top of the track. But these coasters go pretty slowly, and don't go upside down or through corkscrews, or anything like that. They mostly just go up and down.", "The engineers calculate the g-force so as to give you a thrill but not enough to throw you out, meanwhile there are casters/wheels on the bottom of the cart as well as the top so you aren't sitting on the rail as much as you are sliding the rail through the two wheels" ], "score": [ 44, 12, 8 ], "text_urls": [ [ "https://image.shutterstock.com/image-photo/roller-coaster-260nw-65166040.jpg" ], [], [] ] }

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{ "a_id": [ "h27vtng", "h284kgx" ], "text": [ "> Sticks, strings, Add *levels* and *sights* Example of level: URL_0", "None of the other commenters have answered the actual root of your question so I'll give it a shot. The methods for measuring distance and elevation changes on land are refered to as [surveying]( URL_0 ). Before things like GPS, radar mapping satellites, etc. (I'm assuming that's what you mean by \"technology\"), surveying was, very broadly speaking, done with a combination of ropes/chains of a known length and various measuring devices to determine the angle of the rope. If you know that your rope is, for instance, 100 meters long and you tie the ends so that both are 1 meter above the ground directly below them, you just need to measure the slope of the rope relative to gravity and you can do some pretty simple geometry to determine the change in elevation *and* the distance when drawn on a map between the ends of the rope. Add in a compass and you've got all you need to make a very accurate map with elevation lines. Nowadays it's possible to skip the ropes/chains in many cases and just use some sort of electronic range finder, but the same basic principles are still used for planing stuff like construction projects to this day; that's what's going on when you see people looking through those little binocular things on a tripod around a construction site." ], "score": [ 5, 4 ], "text_urls": [ [ "https://imgur.com/a/oSknNtr" ], [ "https://en.m.wikipedia.org/wiki/Surveying" ] ] }

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{ "a_id": [ "h2au7bb" ], "text": [ "There are liquid crystal molecules in between the glass and the entire glass is electrified. This “orders” the crystals and they all line up in such a way to allow light to pass through and the glass appears clear. When the switch is turned off and the electricity goes away, the crystals just randomize and therefore the light is partially blocked and you can’t see through the glass anymore." ], "score": [ 10 ], "text_urls": [ [] ] }

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{ "a_id": [ "h2dsc77" ], "text": [ "In short, it's because the lift generated over the wings by the aircraft speeding down the runway exceeds the airplanes weight allowing it to take off. It's why the thrust on take off is higher than what's required in flight, the pilot has to move the heavy weight of the aircraft fast enough down the runway to generate the lift required to take off, which is dependent on the size/weight of the aircraft and length of the runway. Smaller aircraft that weigh less can take off from many more airports than larger aircrafta can, which require longer runways and more powerful engines to generate the lift required to take off." ], "score": [ 8 ], "text_urls": [ [] ] }

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{ "a_id": [ "h2f8egf", "h2f5h05" ], "text": [ "The steel support beams go perpendicular to the floor joists and major supports. Say that you were standing in front of a house with the floor beams running front to back. The front and back foundation walls would holding most of the weight. This means that you can safely take out some blocks on the left and right sides without the building collapsing. Once you have the opening in the foundation you can just slide in the steel beam from the sides and jack up until it carries the load. You can repeat as many times as you need for the specific structure. Small wood houses only need a few beams where brick and larger would need many beams. Our area was flooded by Hurricane Sandy and they are still working to raise most of the houses, so have been seeing houses jacked up on beams for the past 9 years.", "Just like how the walls and ceiling of your house has support beams that hold up the roof, it has the same support structure for the floor. When you need to replace the foundation, the worker will find the major “load” points (the places in the support structure where the weight of the load, the house, is being supported at) and use very strong steel to instead act as the support as opposed to the previous foundation (concrete slab or otherwise). The structure is inherently designed to hold up and stay together as long as the load points are properly supported and there isn’t significant damage to the support system (from, let’s say, termites eating your wooden floor support)" ], "score": [ 6, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h2f8j9i" ], "text": [ "Horizontal axis wind turbines do indeed turn into the wind. On some older smaller systems this was done by the help of a rudder so the wind would push the wind turbine in the right direction. However modern turbines use motors to turn them into the wind at all times. This would obviously not be needed with vertical axis wind turbines. And this style is being researched as a possible better alternative. However a big problem with vertical axis wind turbines is that the blades are only catching the wind perfectly once per revolution and is even going against the wind at times. While the blades on a horizontal axis wind turbine always have the perfect angle into the wind." ], "score": [ 29 ], "text_urls": [ [] ] }

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{ "a_id": [ "h2fntd2", "h2fnv1l", "h2fol24" ], "text": [ "Your guess is correct. The water is pressurized coming in to your house which forces the cold water through the pipes. The hot water gets staged in a heater which also allows for some pressure to build up.", "Essentially, yes. There is usually a water tower that provides pressure for the entire town's water system; the water up in the tower is pushing down on all the water in the pipes. When you open the tap, there's a place for that water to go, so it rushes out. The water is replaced by the water a little further up in the pipes, all the way back to the water tower.", "Yup, water from \"behind\" pushes the water in the pipes. This is called \"pressure\" in physics. Every city has a water treatment plant, to filter the water and make it ok for drinking and use. They also have pumps that force this water into pipes, creating pressure and basically \"pushing\" the water to go flow out to whatever faucets are open. The problem is that we consume a lot more water in the evening than at night, for example, so really big pumps would be required for the evening, but not so big pumps would be required for at night. So what they do is they use a \"medium\" pump, and pump the water up into a [water tower]( URL_1 ), just a big water tank up high, so that gravity itself can pull this water down into the pipes and create pressure. So actually the water in your faucet flows because your faucet is lower than the water tower, and it's like spilling a drink really, water flows down (due to gravity). They pump the water up to refill that tower throughout the day and night, and the city consumes it as necessary, more in the evening, less at night. The Romans [knew about this]( URL_2 ) 2000 years ago, btw, and built all these [aqueducts]( URL_0 ) to transport water from high lakes to their cities." ], "score": [ 8, 5, 3 ], "text_urls": [ [], [], [ "https://kidsdiscover.com/wp-content/uploads/2013/11/Roman-Aqueducts.jpg", "https://lh3.googleusercontent.com/proxy/ZTNbeilEyPkVnT_z70PkP98YRA2zcj6dwJuViqB01GhPe-UK-aMYz7_KxV1w3tFtXPbrzURJpH7YtTvN8LJY9da3BBDOijPTndOJmL3m4gFNDkmAu_ZU-H9xEQYDhvF03zfs-Y_H1w", "https://images-cdn.9gag.com/photo/adLOmoj_700b.jpg" ] ] }

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{ "a_id": [ "h2gdh4m" ], "text": [ "In the case of Rome there was a massive renovation project in the 30s. A lot of other European cities were renovated in the late 40s and early 50s. In some cases renovated is the wrong word to use and rebuilt is more appropriate. But these are kind of the exception and even though they were forced through major changes there have been a lot of upgrades to these cities outside of these events as well. The way it usually is done is step by step. Electrical lines and phone lines can be stretched up in the air tied to the facades of buildings or poles in the street. So it is fairly quick and easy to put up something fast. Sewage, water, gas and more permanent cables tend to be installed in the ground street by street. You close down half the street, dig a big trench, put down your utility pipes and then close up. It can be hard to notice if a street have some work like this done in it that takes a few days but most streets will be dug up at regular intervals. Using this technique it may take twenty years to install a new sewage system but once it is there it will last a long time. A lot of inner city areas and main highways do have culverts installed as well. These are tunnels under the streets where utilities can be installed without the need to dig up the street above it. This allows for much faster upgrades of the infrastructure whenever needed." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "h2hzzq3", "h2i08d4", "h2i2l3y", "h2i3zvm" ], "text": [ "> They must need a supply to explode The thing that makes explosives explosives is that the oxygen is already in them. Instead of interacting with atmospheric oxygen, they just need to rearrange the atoms already present into simpler molecules, and a lot of energy is released.", "Explosive compounds don't need separate sources of oxygen. The explosive chemical has enough oxygen in it to serve both as fuel and oxygen.", "Just like a bullet which is sealed from atmosphere by itself and by being chambered, there's something that provides oxygen within it. Pretty much anywhere we need combustion but can't have (or don't have) atmosphere to complete the fire triangle, there is something that provides some O2 to the mix, like oxidizers in rockets or part of the magic mix in a naval mine. The trick is just to make sure it doesn't just take off and do stuff without any control/input.", "Only loosely related since it's not part of the explosive but you can also read up on Otto II fuel, which is used as torpedo propellant, and also needs no oxidant." ], "score": [ 11, 10, 4, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "h2ia60u", "h2ib6rq" ], "text": [ "Let a refrigerant absorb some heat from inside the refrigerator. Move it outside of the refrigerator. Compress it so it gets hotter than the outside of the refrigerator. Let it shed heat to the now-colder environment. Pump it back into the refrigerator and let it expand so it cools down a lot. Now it’s colder than the inside of the refrigerator so it can absorb some of its heat. Repeat. It uses the relationship between temperature and pressure to pump heat out of the refrigerator and into the environment. Overall it is generating heat, but it’s not letting any of that heat stay inside the refrigerator.", "It doesn’t make cold. It moves heat out of the box. And the motor that moves that heat also gets warm doing that work. The box gets cold, but everything else gets even warmer. If you left the fridge door open in a well sealed room, that room would get hotter and hotter, not colder." ], "score": [ 10, 7 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h2ifn3k", "h2igdtl", "h2ifnqk", "h2igdi8", "h2in08d" ], "text": [ "It's easier to pump water up to a tower and then use gravity to distribute it than it is to pump water directly to where it will be used. Each household could have its own pump and bring the water up to each apartment, but by having a single system and using gravity to keep water always pressurized, things are a lot less complicated and easier to fix, not to mention cheaper.", "So I'm a controls engineer, and while I've never designed or programmed a water system, I've done some deep dives into their instrumentation and control schemes and therefore have a fair understanding of how they work. Water towers are a way to pressurize a water system without constant use of mechanical means. The water generals comes from a well or reservoir, and if the municipality has a treatment plan then what is in the tower will be treated (chlorinated or filtered, other chemicals possibly to raise pH, etc.). Towers are filled from pumps on the ground that take the water from whatever source and fill the tower. This saves money, because the pump only has to run until the tower is full. In a large city (I have some knowledge of the water system in the las Vegas valley), they use pumps to keep the mains pressurized because there is always demand. At lower demand times, the system can use less pumps but they always need pumps. Smaller towns don't, so a tower allows them to keep the mains pressurized without a pump running. The tower also acts as a buffer so that the pumps don't even have to be sized to keep up with instantaneous demand, the pump can be a smaller unit that fills the tank as it gets low. I assume placement isn't random, but that it is the best location for proximity to the water source and elevation to allow for the pressure needed to push water where it's needed.", "So basically water towers are there for storage, mainly in older towns. During the busy times of the day 5-7 am and 6-9 pm, when people are showering, cooking, etc. Some cities water pumps can’t keep up with the load. Water towers were invented to help combat that. Basically during the rest of the time, they slowly get filled up, so when the time comes when there is an increase in water demand, the water will get taken out of the tower and distributed to houses. They’re built high up so that gravity can help maintain the water pressure.", "Water towers are used to provide water to buildings that are higher than the water source. When the water source is higher than the building, gravity will carry the water there. However, if the building is taller than the water source, then a pump is required to get water to all outlets in the building. Water towers are built to be higher than the surrounding buildings so pumps aren’t needed to get water from the tower to the surrounding buildings, just one large pump is needed to fill the tower itself. Many rural towns have water towers but some city buildings also have water towers set up on the roof since they are often taller than their water sources. This means that so long as there is enough water in the tower, everyone connected to it will have access to some water, even during blackouts or mains water failures.", "A public water supply must maintain 3 basic standards- quality, demand, and pressure. Quality is handled at the water plant, then water is pumped out to the distribution system. Water towers equalize demand and, more importantly, pressure. If your town uses 2 million gallons a day, the plant's pumps can make a constant 1400 gallons a minute 24/7 and keep the towers full. Spikes in demand from morning and evening showers are accounted for with adequate tower volume. Pumps and chemical dispensers last longer under constant load. Pressure, however, is primary. Water distribution lines crack, and joints fail. Adequate pressure( > 35 psi) means that clean water leaks out and icky ground water doesn't leak in. Keep in mind that water lines often go under roads, cars leak oil, ag chemicals wash off into streets, roadkill happens, etc. Gross, right? Well the height of the water column in the tower is what determines pressure in the lines. Shape and volume of a water tank don't actually influence pressure like we imagine they might. It's a straightforward .43 psi per foot of water height. If power goes out at the plant, the supply in the tank keeps pressure high enough to keep your water safe until we can fix it. As for being in odd places, the towers go where a spot is available. Same reason county roads are bendy- they're often built on parcel borders where land is cheaper and easier to get." ], "score": [ 10, 7, 6, 6, 3 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "h2ip3mk" ], "text": [ "The water doesn't reach 100 C all at once; the water near the heating element will turn into gas sooner. The noise is the water near the heating element turning into steam, rising and either turning fluid again when the temperature at the top is still low, or escaping the kettle as steam. The gas bubbles collapsing again makes more noise than the steam escaping - so after a while you just hear the bubbling." ], "score": [ 7 ], "text_urls": [ [] ] }

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{ "a_id": [ "h2lt1d1", "h2lfmrx", "h2lx21f" ], "text": [ "> CPUs and GPUs must have a chance to experience these single event upsets Yes, CPUs, GPUs and all electronics can experience SEUs. It is more common in the memory component (as the memory is often the bulk of the space in these chips). > Why would FPGAs be more susceptible to SEUs than CPUs? They aren't by design. It's just that SEUs are very common in space so using CPUs and GPUs is error prone. They are just not designed to handle lots of SEUs. So you need redundancy. At the same time, its not financially worth it to make a custom chip with all this redundancy, so people opt for FPGAs. You can fill the FPGA up with multiple copies of the same logic and have them 'vote' so an error in 1 is nullified. > If I'm writing a Python script and I set a boolean to False, what's the probability it gets set to True instead? The chances of these happening on earth are both really really small. But not zero as you said with the case of the Super Mario 64 speedrunner. A nintendo 64 wouldn't have any protection against that. But in modern systems if an SEU happens on say the system's main memory, error correcting codes would catch and fix it. So that would further reduce the chances that a user would even know an SEU happened.", "For a python script that chance is impossibly small, as a Boolean is not a single bit. Modern programming languages don't typically express things is such primitive representations anymore. Moreover, computers have techniques for handling these errors. They are a non issue for the vast majority of computational need.", "SEUs (or \"soft errors\") are a non-zero hazard in modern computing. There are a lot of variables, but in general the issue becomes more of a risk on smaller-geometry (higher density) circuits. If your computer has ECC memory, it can deal with single upsets. Your microprocessor and GPU generally can't. (Well, they could, but it would make everything more expensive so they don't.) They typically don't even use ECC on their cache memory arrays. The biggest hazards come from cosmic rays and alpha radiation from materials used in packaging of the integrated circuits. The atmosphere helps quite a bit with cosmic radiation, but not much else practical can. Unless you like using a lot of lead or rock around your computer. Fortunately, your error rate at sea-level with low-alpha packaging materials is fairly low. Using your computer on an airplane flight makes your chances go way up, ~10-30x the last time I did the calculations. Even going to high terrestrial altitudes makes a significant difference. FPGAs are not intrinsically more susceptible. In fact, space applications often use them in older technologies to help mitigate the risk. You can also instantiate voting systems for computations, but that increases costs. Run a standard PC long enough, and it will eventually have an SEU. It can cause a hang, a crash, or data corruption. (Or nothing at all, but those don't really count.) I can't cite a number, since there are a lot of variables. But for a typical PC, I'd say that it won't go a full year (24/7) without a good chance of an event. Source: *I'm a former semiconductor reliability engineer who did a fair bit of SER work.*" ], "score": [ 7, 5, 4 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h2lhbt5", "h2lhewb", "h2m6wk1", "h2lh6mn", "h2lzyx3" ], "text": [ "If you can get through a corner going faster, you'll be faster all the way along the straight, even if the cars accelerate at the same rate. Also, the car behind can accelerate faster by slip-streaming the car in front. And Formula 1 has DRS (Drag Reduction System) to give an artificial advantage to the car behind. At one or two points on the track, if you're within 1 second of the car in front, you can open up your rear wing on a section of the staight which allows you to go faster.", "F1 cars are all at max throttle on the straight, but there's more factors than that to consider. Fuel weight for one, the less fuel in your tank the lighter your car and the faster you can go. Tire type and wear. The harder the compound the more durable it is, but the less grip it provides. The more worn out the tire the harder it is to accelerate, brake, and turn. Tire temperate also makes a big difference. Downforce. The more downforce a car has, the more drag it produces and the slower it's top speed. Engines. The different engines have different power outputs and can be operating in different modes depending on the need to save fuel. The engines are also hybrids so depending on where you are in the lap the battery store will have a different amount of charge you can deploy to the MGU-K for an extra 160 HP. There's also the DRS. If you are within 1 second of the guy in front you can open the DRS flap which is worth an extra 10-15km/h of top speed.", "1. **Driver skill** does influence speed on the straight. Not by pressing the gas pedal harder like in the movies, but in the \"exit\" of the previous corner. Shockingly small variations in car placement allow you to press the accelerator sooner (or later) when you're on the way out of a corner, and these small differences result in reaching high speeds sooner. The differences between drivers are small, but at top speed 0.1s might be 10 meters of space, which can be enough to lock in a pass. But most of the driver skill that leads to an overtake on the straight occurred in the previous corner (or several corners), and is often not shown on tv. 1. **Tire grip varies**, and grippier tires allow more aggressive acceleration on corner exit. At different points in the race, cars run more or less grippy tire \"compounds\", and newer tires grip better than older ones. Deciding what tires to run when is called tire strategy, and for a given pair of cars can result in one having the advantage near the start of the race, and the other having the advantage at the end. Driver skill influences how quickly they wear out their tires as well. 1. Not all F1 cars are equal, **some have slightly stronger engines** (many non-F1 racing series do have ~equal engines, but in F1 they vary in power). 2. Not all F1 cars are equal, **some drag more against the wind**, either in an attempt to use the air to be faster during turns or just because they're less well designed and have more drag. 3. The car in front pushes the air and leaves a \"wake\" behind it. A close following car experiences less wind drag in this wake, and goes a little faster than it otherwise would as a result. They call this a \"tow\" because it feels like **the front car is pulling you along**. 4. Modern F1 rules give each car a special rear-wing flap called **DRS (Drag Reduction System)**. In order to make overtaking easier and make racing more exciting, the rules allow the trailing car to open that flap and reduce drag in at certain places on the track when they're close enough to the car in front that the extra speed might help them complete the overtake. 5. Modern F1 engines don't have constant power output. They have batteries and energy recovery systems that let them **boost the engine power in short bursts**. If the trailing driver has somehow conserved their battery power while pressuring the leading driver to spend theirs, they'll have a temporary but significant advantage in top speed if they juice up their electric systems for the overtake. Various bits on the car can also overheat as well, which can also lead to temporary variation in performance as drivers are forced to drive conservatively to let temperatures recover. Managing all these temperature and power resources while driving as fast as possible is a big differentiator in driver skill. 6. Also they do actually [press on the gas pedal a little extra]( URL_0 and legend has it this does help if you believe hard enough.", "Many ways. More engine power, the pull that the following car gets from not having to cut into the air, and also there is a strategic flap on the rear wing that will flip down only certain times so there is much less drag on the rear wing. It’s called DRS", "It's drafting basically. The car in front breaks the air and reduces drag on the car behind it. That's why you see a car shoot up like its going to rear end the car in front and swerve out at the last second. They pretty quickly lose the advantage once they are back in air again. Same reason all the NASCAR guys are riding each others bumper and a group of them can pass the car in front. They can't do this in corners since the car needs air over the wings to create downforce on the wings." ], "score": [ 51, 16, 8, 6, 3 ], "text_urls": [ [], [], [ "https://images-wixmp-ed30a86b8c4ca887773594c2.wixmp.com/f/6a56e759-c201-4084-9a4f-f1af42bdcfa3/db1n4yk-85aae30c-dfe8-498c-ac21-5925353c2ddf.gif?token=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJzdWIiOiJ1cm46YXBwOjdlMGQxODg5ODIyNjQzNzNhNWYwZDQxNWVhMGQyNmUwIiwiaXNzIjoidXJuOmFwcDo3ZTBkMTg4OTgyMjY0MzczYTVmMGQ0MTVlYTBkMjZlMCIsIm9iaiI6W1t7InBhdGgiOiJcL2ZcLzZhNTZlNzU5LWMyMDEtNDA4NC05YTRmLWYxYWY0MmJkY2ZhM1wvZGIxbjR5ay04NWFhZTMwYy1kZmU4LTQ5OGMtYWMyMS01OTI1MzUzYzJkZGYuZ2lmIn1dXSwiYXVkIjpbInVybjpzZXJ2aWNlOmZpbGUuZG" ], [], [] ] }

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{ "a_id": [ "h2nkjrt", "h2nxwv5", "h2onnvc", "h2nmjwk", "h2olw2z", "h2otbp1", "h2nsior" ], "text": [ "When new pavement is put down, the paving machine smooths it out with a roller. Freshly paved roads have a very smooth surface with no bumps or irregularities. That’s why there’s less road noise. The noise is caused by your wheels hitting things on the road surface. Over time, the asphalt surface will start to wear out in places, or settle in places, and you’ll start hearing more road noise.", "The asphalt actually remains liquid and gradually flows downward as it ages, exposing the rock aggregate and shifting the surface profile from what starts as flat to more pebbly. The gaps between the pebbles cause extra noise because tires expand into and out of them as they roll on over. Fun fact: roads near exposed sand like beaches or deserts tend to remain quiet because the sand getting blown on fills in those gaps as they form. Fun fact #2: asphalt is near 100% recyclable. Just lift it up and heat it enough and the liquid will flow freely again and the whole mix can then be reapplied.", "**Asphalt is Porous** Asphalt (Hot mix asphalt or HMA) is porous since it's basically a bunch of aggregate glued together. This allows water and air to pass into the HMA layer. In regards to road noise, this means the air is being compressed by the tire into the pavement structure rather that outward into the air. This results in less noise. Over time, the HMA will compress and become less porous (rutting as an example). *Additionally dirt and debris will also clog up the voids, causing less air to pass, which leads to more road noise. **Asphalt dampens the load** Pavement structures typically have a spring reaction and a dampen reaction (spring and dashpot reactions). When the asphalt is initially paved, it can be squished to reduce the impact, and almost return to it's normal thickness. This will provide a smoother ride, and reduced noise. Over time, the asphalt layer compresses, you will have less of a dampening factor, and that will increase road noise. **New types of asphalt** There are new types of asphalt being placed as well that are designed specifically to be more porous to allow air/water to travel through them than the other types of asphalt typically layed down. You will really notice it on rainy days because cars won't spray water from their tires. Instead, it passes through the HMA layer, just as air does. *These different types of asphalt will affect road noise, essentially because of the difference in gradation of the aggregates and the mixes.", "When it's first paved it is nice and flat. But due to a mic of cars using it and the weather damaging it the asphalt become more bumpy and gets more cracks.", "Independent of the other responses here of \"new road smoother\", it is also possible your newly paved roads make use of porous asphalt which is a newer (~1980) special kind of asphalt. One of its advantages is absorbing some of the tire noise.", "If you think driving on new asphalt is fun, try skating on it. I have dreams of skating on freshly paved asphalt... sooo good!", "Newly paved roads make the surface, called a roadway, smooth and easier than roll over. Run your finger nails over corduroy the run your fingernails across a bed sheet. You’ll notice a difference in the sound. If you cover the corduroy with a few layers of smooth material, the no’s will become quieter with each layer. The roadway is actually made of smaller pieces of rock than the base or the sub-base which creating the smoother top coat. The base is better at holding its shape and supporting weight because it is made or larger materials . The sun base is better still at holding its shape and made of even larger material that has irregular edges which lock in place by pressing against one another. Over time, the top coat will become stressed and possibly worn but most importantly the weight of the vehicles will push the top coat into the rougher material of the base. So, when repaving, the top coat (roadway) is removed and replaced with a smooth(ish) and level coat." ], "score": [ 359, 181, 9, 7, 4, 3, 3 ], "text_urls": [ [], [], [], [], [], [], [] ] }

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{ "a_id": [ "h2p5jer", "h2p5r35", "h2p51sz", "h2p5e53" ], "text": [ "What you describe could happen from laceration or friction, or both, and that can happen without the suit breaking I would assume is due to friction and the road \"twist\" the suit around your leg and can cause the damage to the skin anyway. I don't know if I'm transmiting the thought very well, English is not my first language", "Your clothing garments are loose against your skin, so they have a little more play upon impact. The impact makes the clothes shift and rub against the skin and with your skin not being “loose fitting”, it comes off. Your removed skin is somewhere inside your pant leg. Depending on the material of your clothes, the fabric can certainly rip depending on how much you slide on gravel or whatever surface. Just keep in mind, your skin isnt woven fabric. It’s just tissue. Hope I helped explain. I’m a rider too (2000 zx9r). I wish you a speedy recovery and better luck on the road. Most times we as riders can avoid the assholes, but just be safe 24/7. Please be safe. Cheers !!", "Sounds like a friction burn. If you were to take an object say a tennis ball and rub it back and forth on your pants while pressing hard your leg would wear out before your pants in most cases. Now scale that up to concrete, momentum, and gravity you got a nasty burn.", "Skin is all mush. Presumably (with a fair amount of certainty) denim is harder to tear than mushy flesh full of liquid. Clothing is generally designed to withstand stress with hems and sewing patterns. *Some* parts of our skin (like the creases in our knuckles) are fortified, but not against something as intense as road rash." ], "score": [ 6, 6, 4, 4 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "h2pnxch", "h2qi4wq" ], "text": [ "The gear knobs on your bike manipulate something called a derailleur that will help select the gear you want to be in. There are two because one controls the front gear and one controls the back. The front gear is called the drive gear. It's what your pedalling inputs on. And the BIGGER it is, the taller the gear (taller means harder, or the more a single pedal rotation moves the chain). The back gear is the output gear (or driven gear). The SMALLER that gear is the taller/harder it is. So small front and big back means low gear, lots of pedalling but easy. Big front small back means hard but fast. A little pedalling will move the back wheel more. So. Depending on the shifter type you have you will be able to push or pull each lever to select gears in each axle/wheel. Start in a low gear and experiment to see what happens.", "I'm glad you asked! I have been a mechanic for a decade and so few people bother trying to understand what's going on even though it could save them so much effort (and repair bills). Bicycle gears work on the principle that different sized gears will turn each other at different rates. So, imagine you have a large gear and a small gear touching each other. For every one turn of the large gear, that smaller gear might turn several times. This is the principle of bicycle gears - you mix and match different sized gears to achieve different rates of rotation. You select one gear where the pedals are and select one where the rear wheel is. So, for every turn of your pedal gear, you'll get a variable rate of rotation on the rear wheel. Every \"speed\" of the bike can be expressed as a ratio between these two gears. (Obviously, if you stick two gears next to each other, they'll turn each other in opposite directions. The chain fixes this problem so that the pedals turn in the same direction as the rear wheel, and also allows the rear wheel to be spaced sufficiently far back from the pedals.) Now, how it works. Your rear wheel has a set of gears on it, with the chain attached to any given one of them. The chain is moved between these gears via the derailer - a mechanism that moves laterally and \"derails\" the chain by pushing it up onto the next bigger gear or pulling it down to a smaller gear. The derailer has a spring that always\\* pulls to the smaller gears. However, there is a cable that pulls against that spring, and the more you pull, the more the derailer will slide towards the bigger gears. Your shifter therefore pulls on the cable, which slides the derailer in one direction, or lets out cable slack, which allows the derailer spring to slide in the other direction. & #x200B; Notes: \\-For the record, I kind of hate spelling it \"derailleur.\" There's no need for a French spelling of a part that was invented by an Italian, and it obfuscates the figurative purpose of the part, which is to \"derail\" the chain. \\-The springs on both your front and rear derailers always pull towards the smaller gears\\*. However, because of the way gears work, the effect is different: a smaller gear in the front will produce a lower gear ratio, whereas the smaller gears on the rear produce higher gear ratios. \\-I always just tell people to associate \"high\" gear with \"high\" speed and harder pedaling. Maybe that connotation only works in my head though so YMMV. \\*except for some rare obsolete systems" ], "score": [ 5, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h2qv9l5", "h2qjnji", "h2qhx78" ], "text": [ "In order for “fusion power” to exist, we need to produce more energy from the reaction than the energy cost of sustaining it. The current record is around 70% (0.7) which is still less than break even. We’ll need to get to around 5-10x break even to generate electricity on a practical scale. The ITER reactor currently being built is the most funded fusion project. It aims to reach 10x break even for 5-10 mins at a time. ITER won’t produce electricity because it doesn’t have a turbine - the heat generated will just be discarded. But if it succeeds, we’ll be able to build another reactor (DEMO) which will be even more effective. The roadmap includes a third reactor, PROTO, which will serve as an actual power plant, with turbines and other equipment to produce electricity. There’s still a *lot* that needs to be done before we see commercial fusion power plants. - Reach 10x break-even on energy out/energy in - Sustain the reaction for long enough at a time to be practical. The expectation is for reactors to run continuously instead of mere seconds at a time. - Effectively breed tritium in sufficient quantities, as this is required to fuel the reactors. The fusion reactors themselves are being designed to breed their own tritium. - Develop new materials that can survive facing the inside of the reactor chamber for long enough to be practical - Develop methods to perform remote maintenance/material replacement on the highly irradiated reactor chamber These barriers are pretty significant, but it’s all at least theoretically possible. Hopefully it’ll also be economically feasible to run them commercially. Fusion does have to compete with other low carbon methods of generation e.g. solar+wind+energy storage.", "Fusion isn’t just real “in the sun”. We can do fusion reactions already here on earth with technology. The tricky bit is that it takes more energy to make the fusion occur (safely) than we can harvest from the reaction. So.. making it a power positive generator is being worked on, making fusion happen is possible to do in your garage (with a few thousand bucks of parts and some knowledge of electronics and vacuum systems)", "It is more than feasible in theory, we seem to be getting close to getting it in practice. People are confident enough about that in France millions and millions of dollars have been invested into constructing the first experimental fusion reactor. It’s actually already mostly built and being tested, with the goal of achieving fusion by the mid to late 2020s. URL_0 Edit: By achieving Fusion I meant in a stable, efficient, manner where we are able to harvest energy from it. Fusion tests have been done before (and there’s obviously Hydrogen bombs, nuclear fusion bombs)" ], "score": [ 19, 16, 14 ], "text_urls": [ [], [], [ "https://www.energylivenews.com/2020/07/29/assembly-of-worlds-largest-nuclear-fusion-reactor-begins-in-france/" ] ] }

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{ "a_id": [ "h2rqjjt", "h2rqpel", "h2rql72", "h2rswgv" ], "text": [ "Same reason why you can't ban guns even though it would be safer. People want to buy fast cars, companies want to sell fast cars. If the state tries to prevent that you upset both groups. And there are legitimate places where you can speed with your car, just like you can legitimately go hunting with your rifle. They argue some bad apples shouldn't be the reason to punish all that abide the rules.", "The way engines work, they are most efficient in terms of fuel use at some speed called “cruising speed”. This speed is always lower than the maximum. You can always make the car go faster than its cruising speed, but it will result in reduced fuel efficiency. So if you designed cars to only ever go at a maximum speed of 130 km/h, then the cars going at that speed on a freeway would be very inefficient and burn up too much fuel.", "Some manufacturers put limiters in their car, but just as easily as they can limit; there's always going to be an aftermarket way to bypass. The other issue is they don't want to have to make \"one off\" models to fit a certain country / speed limits. In Australia as an example, there's limits everywhere, but there's also roads without speed limits in the country. So it becomes harder to dictate specific limits, and that's without factoring countries like Germany. Germany is a good example of speeding doesn't necessarily mean there is going to be a collision / accident, and shows the important factor is in driver education. Hell we were all 20 at some time, we all thought we were invulnerable. Unfortunate thing is for a lot of people, who gives a single fuck til it affects you and your family . My sister and her partner passed in a car accident, leaving their daughter without parents. Not for a single second do I think that speed was the issue, but the mentality of our younger generations. IMO the answer is always going to lie in awareness and education. Edit: mobile formatting, sorry < 3", "From an engineering perspective, you really can't make it so that the engine won't turn the wheels that fast without sacrificing something. On a traditional combustion engine, your engine will spin anywhere from 1000 to 6000 RPM (more than that, but you get into redlining at that point), and you'll use gears to change the ratio of engine turns to wheel turns. You need those high RPMs so that you can reduce the number of gears you have. Whenever you change gears, you want to get the wheels up to a certain speed using the lower gear, apply the clutch and temporarily detach the gears, and then let your RPM drop so that on the higher gear, the lower RPM results in the same speed. This means you need a decent range of RPM, otherwise you need more gears to get those steps. The higher RPMs though generally consume more fuel. This means that when you're coasting at a constant speed, you want to do so in the highest possible gear that can hold that speed without stalling out. If you're going 100km/h on the highway at only 2000 RPM, then the engine could go to triple the RPM's and you get 300 km/h. In practice, the drag on the car starts to become too much and you can't reach that speed, but that's the only thing that is really stopping the car from getting that high." ], "score": [ 13, 6, 5, 4 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "h2u2t3j", "h2ucxee" ], "text": [ "In F1 it's subtle things that make all the difference All 4 manufacturers (Ferrari, Mercedes, Renault, Honda/Red Bull powertrains) each have their own unique V6 hybrid engines. The engines have the same basic specs, displacement, size, components, but they vary greatly in design. On the Hybrid engines the exhausts are routed into the turbo charger and that's what makes the biggest difference. There's a noticeable difference between the Turbo whine of the different manufacturers. The turbos vary in size and RPM The engines also have different noises when they are harvesting electricity (the MGU-K/MGU-H is harvesting) and when they are trying to save fuel by disabling cylinders and changing the timings. Each manufacturer does this differently.", "The teams have a degree of choice where they place the on board microphone. This accounts for most of the sound difference between the engine manufacturers that we hear on broadcasts, which I'm pretty sure most people won't mention. For example, Renault's very pronounced turbo sound last season was because they placed their mic near their turbo. This thread shows some good videos demonstrating this: URL_0" ], "score": [ 15, 3 ], "text_urls": [ [], [ "https://www.reddit.com/r/F1Technical/comments/d8ti0a/why_does_only_the_renault_car_sound_like_an/f1cwlky" ] ] }

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{ "a_id": [ "h2xlj9f" ], "text": [ "Explosions in open air create pressure waves that expand uniformly in all three directions. Fireworks are nothing more and nothing less than explosions in the air, with combustible pieces that burn pretty colors. Their containers however, can impose some restrictions on which directions pressure is able to expand. When you fill them with materials that are carried by the pressure wave, and then restrict expansion directions, you can influence the observed shape from the ground. In general though firework combustion patterns are spherical in shape while each individual element is following a parabolic trajectory downward under the influence of gravity. You get this sagging round shape that gets more pronounced the longer the pieces are in the air. The other way you control the shape of fireworks is by packing things in the firework in creative ways. So when they explode and send things out uniformly in 3 directions, you've aligned them such that they disperse in a neat pattern. Then you use differential fusing, and the relative weights of each element to control how far from the center of burst it is when the pyrotechnic powder starts to burn and give off colored flame. You'll notice with large fireworks, there will be a large central \"boom\" and then a couple seconds later stuff starts to light up around it. The \"boom\" is the dispersion charge, and then the heat works its way to the powdered metals that finally burn in open air to create to cool colors and crackling sounds. [This]( URL_0 ) is a good ELI5 example. edit: added link" ], "score": [ 60 ], "text_urls": [ [ "https://www.youtube.com/watch?v=dScMYwJTPgA" ] ] }

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{ "a_id": [ "h2z0rk5", "h2z1erh" ], "text": [ "The rods that connect the wheels to the gearbox (drive shafts) are articulated at both ends. This allows for the steering to turn and the suspension to move up and down freely. It's difficult to describe without showing you but I'll look for something and update this comment. URL_0 URL_1", "Constant velocity joints. Using balls and tracks cut into an inner and outer race/cage, no matter what angle the inner spins, the balls align with the outer to form a gear of sorts of the same diameter/tooth. Pictures or videos would better demonstrate the concept. Look up \"cv joint\"." ], "score": [ 24, 7 ], "text_urls": [ [ "https://youtu.be/j1pOGY5vGWY", "https://youtu.be/M_8IlwZUfIM" ], [] ] }

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{ "a_id": [ "h2zgqsf", "h2zn646", "h2zfgae", "h2zo94z", "h2zlbn7", "h2zgm8i", "h2zqte2", "h303kcv", "h2zsggf", "h2zw3vk", "h30a3l7", "h30tldu", "h31yhmw", "h30seam", "h2znxac", "h31xfg1", "h30z0me", "h3238qo", "h30v5ad", "h32f2sr" ], "text": [ "Because death-by-Jenga-collapse is basically manslaughter. You can't just pile in and shift hundreds of tons of collapsed rubble without it moving underneath you, potentially killing anyone who's surviving in a small pocket underneath. People can and do live for days in such scenarios, and it's better to recover them safely than find out that you caused a collapse which killed someone who would have been relatively uninjured. Also, what you want in those circumstances is SILENCE. Every now and again you must ALL stop work, to listen for cries of survivors so you know where to focus your efforts, even if all you can do is reassure them or get water to them, it'll extend their life by days, sometimes weeks.", "Adding on to many other helpful comments: most people don't realize that excavators and other heavy machinery essentially do their job by pushing large amounts of material around. So, even if you identify someone trapped in the rubble in a place where further structural collapses aren't a problem, you have to dig them out by hand. Using machinery will just shove more debris onto them, crushing them to death. Incidentally this is often the mistake people make when workers are trapped by mounds of dirt in collapsed trenches, or other dig sites. Trying to dig them out with an excavator is more likely to get them killed than not. You have to use a shovel.", "I'm no engineer but I believe two reasons: 1) They have to do a search and rescue. Just going in hog wild and removing debris could lead to further collapse, which plays into 2) They have to do it in a certain way to prevent further collapse and risking the lives of first responders.", "Also, after all the search and rescue operations are complete, and the investigations by a number of agencies and even insurance companies, (like all the other commenters have said) you still have to actually remove the debris. The big side dump trucks only hold 14 cubic yards per trip. So you need to be able to hire enough trucks, and have a place to dump everything. All of this takes money and coordination that often can’t occur until the insurance pays out. For example, the 9/11 debris wasn’t fully cleared until May 2002, and took 108,000 truckloads-1.8 million tons. Where I live, tipping fees are $169 per ton at the landfill… so just clearing the debris was a multi-billion dollar operation.", "It could be holding up \"triangles of life\" which survivors could be in. Taking the pressure away could collapse it Then there's rescuer risk, and the fact there's usually live wires and fire risks in the rubble as well.", "You mean after the immediate search and rescue / making sure it won't further collapse operations are over? Same reason they don't immediately remove a dead body from a potential murder scene and bury it. Gotta figure out what happened - insurance companies, lawyers etc. send their experts to investigate the rubble. To figure out why the building collapsed, if there is someone to blame, to figure out who has to take responsibility. If they would just remove it and clean up immediately they would basically destroy potential evidence.", "You know that giant arch in St. Louis? Imagine if you took a giant 10 foot chunk out of the top most section center of that arch. What would happen to the rest of that gigantic structure? It'd fall in on itself. Collapsed buildings are far more complex bits and mess that are all resting against each other and there are possibly people under them. So if they take a random thing out, that could cause even the slightest of collapses underneath possibly killing a person pinned in a pocket. Additionally adjusting the weight anywhere can do the same thing so the bits don't even have to be intertwined, just resting on top. Engineers are trained essentially to treat the pile like a Jenga game, they find the bits that have the least influence on the debri and try to remove them, they also have equipment that scans far into the mess to try to find bodies and people first so they know if an area is safe to disturb slightly.", "After the Oklahoma City bombing, it took 17 days to recover the bodies of all but three of the victims. The rest of the building was deemed too unstable and was slated for demolition. The demolition was delayed for a few weeks to give defense lawyers an opportunity to examine the wreckage. It was only after demolition that the big trucks came in to remove the debris and recover the remaining three bodies. So we may have a similar situation in Florida, where the rest of the building will be demolished before removing the debris.", "Turn off and secure utilities (Water, Gas, Electric) Search and rescue people. Recover property that might not be damaged or hold sentimental value. Investigate the cause of the collapse. This is usually the most important one why it's not removed. Insurance may be invalidated if it's removed strait away as no cause of the incident has been established and all evidence would have been removed. Once a cause has been established, the Insurance company will then pay to have everything removed and rebuilt.", "Because you have to make sure that you're not going to cause the rubble to settle by removing the debris in the wrong way. You may have people who are still alive in there, because the rubble fell in a way that they have a pocket of space where they're safe. If you start taking out debris randomly, you might accidentally remove a piece that is actually supporting that void and keeping their pocket of space open, causing other material to crush them.", "Put your hand on a big rock and then put another rock on top of it. The top rock may be heavy, but your hand is still okay. If you put more rocks on top of that, your hand has the ability to withstand a tremendous amount of weight. If you want your hand back, you want to carefully remove the rocks on top of your hand. If you try to pull your hand out from under the rocks, you're going to do more damage. Rubble isn't able to be removed carefully, without risk, and without disruption of what's below it. There may be survivors in small pockets or be trapped by pressure of rocks on top of them. Removing the rubble is like pulling your hand out...it can cause more damage. The best chance for victims is to find where they are and mindfully remove the rocks on top of them, without injuring or killing them in the process.", "you ever play jenga? imagine jenga but if you mess up, you end up crushing dozens of people trapped beneath the blocks still.", "I think they might have meant like ‘why dont they immediately remove rubble from [the top of the collapse to slowly find the people who are highest first going back down to ground level]", "Amongst all the other reasons mentioned, in this particular case, there is a possibility of a sinkhole being the cause. Throwing a bunch of heavy machinery onto the site could cause the ground to collapse.", "Let’s assume an accidental collapse. There are sometimes ownership & liability concerns. Are there environmental concerns? Was the gas turned off. Are there gasses that need to disappate? Contracts have to be signed. Equipment & crews assembled.", "I understand the reasoning of my engineers here, but I can’t wrap my head around why it’s not possible to lift and horizontally translate a piece of debri that is obviously just supported by debri below it. Like removing a block from the *top* of the jenga tower?", "The rubble sometimes (often) falls in a way that traps people sometimes alive sometimes injured sometimes deceased. The most important thing is recovering those people. It’s not an engineered building moving one wall could lead to further damage. So first and second and third is recovering as many people as possible as gingerly as possible. The equipment comes in when everyone possible is accounted for.", "To add to some other comments, I believe there is also a medical aspect. I heard Sanjay Gupta talk about it today but basically when your muscles are compressed they build up myoglobin for shock, and if that myoglobin is released to the rest of the body, it can kill someone who might otherwise just have broken bones. So when someone is found, paramedics/surgeons need to asses them and see if it's even safe to take them out. At least, that's how I understood it. I very well could be wrong and I'm sure some other people could add to this/correct me.", "In addition to the logistics of clearing the rubble which have been excellently explained here, you have to consider the medical care of people potentially trapped beneath heavy objects. Crush injuries readily lead to a state of rhabdomyolysis whereby the muscles damaged by a crushing trauma begin to break apart, releasing very toxic byproducts into the bloodstream. If that dying muscle is compressed by a heavy object, bloodflow to and from that muscle is greatly reduced, therefore containing all those toxins in a confined space and inhibiting their systemic circulation. The moment you lift the heavy object from the area, you give that toxic blood the opportunity to flood into systemic circulation, leading to systemic shock, organ and brain damage, a very painful death, etc. If you don't have a medical team right there capable of assessing the degree of crush injury, administering necessary care prior to, during, and after removal of the crushing object, and extricating the individual in a manner to prevent further injury, simply removing rubble can lead to further fatalities.", "In the hours after the Christchurch Earthquake a man was talking via cellphone with his wife who was trapped in a collapsed multi-storey building. From what I remember she was in good condition, just trapped, not really hurt. She didn't make it, and the general consensus is that she was crushed by incorrect recovery techniques - ie: diggers being used to clear rubble. It was heartbreaking - we were watching this man live on TV, frantic with worry, pleading for help for his wife and also pleading that they be careful, but also just so grateful, as the death toll was rising, that she was alive and uninjured. A great story. Until the next day when the reporter went to his house to hear how she was, expecting her to be home or at least in hospital with a broken leg or cuts, only to be told live on air that she had passed. I know he instantly accused the rescuers of killing her, and I have a vague recollection that an official report came out a few years ago stating this was the most likely cause of her death, but my husband doesn't remember hearing anything more about it. Those who helped that night were amazing individuals, many who were drawing on training they never thought they'd have to use, others trained only in crowd control and following instructions, or in the use of machines in different situations, and many people who couldn't walk past without doing what they could to help. If this poor woman died as a result of people just getting in and clearing rubble without knowing what they were doing, it's it's tragedy, but one we don't appoint blame on, instead one we learn from. My heart goes out to those trapped in the rubble in Florida and those waiting for them to be found, but also to those searching for them. I don't envy them the sights they will see." ], "score": [ 10538, 3557, 857, 441, 171, 81, 69, 36, 22, 13, 9, 4, 3, 3, 3, 3, 3, 3, 3, 3 ], "text_urls": [ [], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [], [] ] }

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{ "a_id": [ "h30ctab", "h30d55z", "h30gwjq", "h30e8h2" ], "text": [ "Supply can be high so long as demand is even higher. Pretty much every company of any respectable size has an IT department these days (and not the 'turn it off and back on again' IT department). It doesn't really matter what you do anymore - you have complex computer systems running your business. These systems need to be maintained, upgraded, integrated, installed, etc. and their complex nature means that you need talented and knowledgeable people do to the work.", "Not everyone who enters the field gets a high salary though. The people who get the high salaries are the ones with years of experience or have a specialization that is in demand.", "I felt a need to mention here as a person in the biz. Not all CS students or programmers are equal. Anyone can program, but not many people do it well enough to earn those high salaries. Same as any other field. A lot of people do not command a high salary.", "Even with the supply, demand is still waaay too large, especially given how diverse the field is." ], "score": [ 29, 11, 8, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "h30cjpg" ], "text": [ "A lot of times, they all have the same rim. When the dual wheel is combined, the two rims are configred to be facing each other." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "h30jfuc", "h310gqh" ], "text": [ "Sometimes they don't, but in general it's because the opening to their burrows/dens is lower or goes deeper than the \"living space\". Centuries of evolution has provided them with the instinct to dig dhow for a bit, then level off and start going back up for a living spacer. The amount of normal rain (heavy storms and floods will be too much water) that gets into their burrows only goes to the point where their burrow starts to go up again", "Not all holes you dig fill up with water when it rains. I see rabbits making homes in dirt that can absorb water (not clay or something that would hold it in). If you pick the right dirt it seems like its just a matter of digging deep and long enough so overhead is stable and doesn't get you wet, and your home is not under the hole (so you don't get wet)." ], "score": [ 11, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h34zt36", "h34xhgi", "h34vbeq", "h364vqx", "h352i7d" ], "text": [ "Multiple people all working on different blocks CPUs aren't laid out by one dude just going as fast as he can, they're modular designs. A CPU will have a cache, cores, memory controllers. The cores will have instruction units, adders, multipliers, and other blocks. There will be design teams for each blocks, and as each block is upgraded its design just gets pasted into the bigger structure where it fits. A team might optimize a multiplier that has 10000 transistors (~2500 gates), and that adder will be copied into the 8 cores of the CPU so they impacted 80,000 transistors without having to go through and count them all GPUs are even more of a copy paste job. While a CPU might have 8 large cores that match, a GPU will have thousands of small cores that are grouped into medium sized blocks and those blocks are connected in large groups so adding a few transistors to the design for the small core can add tens of thousands to the overall chip For CPUs these days, the biggest driver of transistor count is CPU cache. [You can see it on the labeled die images]( URL_0 ) how big of an area the L3 cache takes up, and that's from Ivy Bridge with just 8 MB of cache. It was 27% of the 1.4 Billion transistors on the chip. Something like a 10th gen intel chip with 20 MB of cache will have an even larger percentage of the die dedicated to it.", "Design is done at a higher level than traces and gates, there are memory modules and logic modules composed of many many transistors themselves, and these can be moved around on the chip layout as a single structure. We're also not counting the transistors one second at a time; the clock in a modern processor operates at multiple Gigahertz. It can effectively count to a billion in less than a second.", "Our current silicon design are generally speaking an evolution of the designs that started in the 70s. When Intel or AMD release a new line of processors, it's not 100% new design from scratch... Think of it like a car, if Ford had to start from scratch, designing the combustion engine, the drive train, the steering etc they'd never managed to release 50 new cars a year, but they don't. The reuse existing designs with minor improvements. In addition, people aren't designing these chips with pen and paper, there is very advanced software tools for developing silicon chips and modelling their behaviour, their thermal profile etc.", "You've gotten multiple correct responses, but not all in one place. There's not a single answer, there are several: Cut and paste. Multiple teams of people. Using software tools to do much of the work. Reuse of previous designs.", "Because they're not designed transistor by transistor. In much the same way that software is written using programming languages, not 1s and 0s, logic circuits can be designed using a [hardware description language]( URL_0 ) to describe the logic at a high level, which can then be \"compiled\" into an actual circuit diagram using software. Also, a CPU or graphics card is made up of many different sub-units, which are themselves made up of different components. For example, in an SRAM memory circuit, you'll have a particular circuit to store 1 bit, which is then repeated millions of times to be able to store megabytes of data. That's a lot of transistors, but most of it is just copies of the same circuit (there's also addressing logic to allow data to be read/written, of course)." ], "score": [ 18, 9, 5, 3, 3 ], "text_urls": [ [ "https://images.anandtech.com/reviews/cpu/intel/IvyBridge/review/Ivy-Bridge_Die_Label.jpg" ], [], [], [], [ "https://en.wikipedia.org/wiki/Hardware_description_language" ] ] }

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{ "a_id": [ "h35tixu", "h35sro4" ], "text": [ "Septic tank attaches to the outgoing pipes of your home. They are generally a large concrete box that houses the waste from your toilets. There is a pipe that leads out to a tube with holes in it surrounded by limestone allowing the water to escape. This is called a leach field. While inside the tank bacteria and yeasts break down the waste. The broken-down waste is constantly taken out by the water that runs out into the leach field. Occasionally septic tanks require being pumped out, but generally, as long as the bacteria and yeasts that break down the waste remain healthy this is not very often. You can buy yeast that you flush down the toilet occasionally, flushing large (abnormally large) amounts of chemicals down the drain can hurt the life in your skeptic, but regular use is fine. Don't flush anything that will not break down naturally like wet wipes, and paper towels are not a good idea. Now you should have warning signs before you need to have it pumped like the smell of waste in your yard or water leaching above the surface of the ground where the caps of the tank are.", "It's a giant holding tank for anything that goes down your drain. It's not that hard to take care of it. Where most people run into problems is putting things down the drain that would NEVER GO DOWN ANY DRAIN. Such as tampons, paper towels, grease, etc... These items should never go down any drain, septic or sewer. Another issue sizes of people don't get their teams drained every so often. Thanks are typically thousands of gallons, so while you can go a while between drained, you still need to drain it every few years" ], "score": [ 14, 9 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h35wopv", "h35wq66", "h35x1qx" ], "text": [ "Eventually the heat transfer into the evaporator from the hot surroundings would just raise the refrigerant's temperature and it would stop cooling you. The condenser is where it rejects that heat to the outside.", "The cold refrigerant absorbs heat and approaches equilibrium, the same temperature as the environment. At that point it can't absorb more heat. It needs to be compressed and cooled again to be able to absorb more heat. The easy analogy is the old ice-box type of freezer which just used a block of ice to keep the compartment cold. It worked great until the ice melted and had to be replenished. The modern refrigeration cycle makes this replenishment automatic.", "Its the act of evaporating that takes away the heat, and since you have a limited amount of refrigerant, once its all evaporated the now gaseous refrigerant just warms up and doesn't remove any more heat from the system You need both the compressor and the evaporator for the system to work. The compressor pressurizes the gas (or converts it back to liquid depending) which concentrates its energy and raises its temperature, now it can radiate away heat to the surrounding environment. Now you can expand it again which drops its temperature and lets it capture heat from the cold side. You need to compress it and dump the heat again before you can evaporate it again We haven't invented infinite heatsinks yet despite what thermo classes would like so you need to keep removing the heat from your refrigerant for it to be able to absorb more again" ], "score": [ 14, 8, 7 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h36keun", "h36ilpg", "h36k0h4", "h373eb8", "h36jlul" ], "text": [ "You can't destroy heat, only move it somewhere else. The only way for A/C to make something cool is to also make something else hot. A/C takes hot outside air and makes it even hotter in order to get rid of the inside heat.", "Air from the outside doesn’t usually come inside, the air in your room is circulated and the outside air is just to transfer heat into", "An air conditioner transfers heat from one place to another, it doesn't \"generate cold\" because that's impossible. So, what you want it to do is to extract heat from the air inside the room and transfer that somewhere else. The best way to do this is to pull air in from outside, transfer the heat into that, and then pump it back outside again, so your room is cooler and the outside air becomes some tiny fraction warmer. If you used air inside the room for both purposes then no cooling would happen--if anything, the room would heat up slightly because the AC generates some heat as part of its operation.", "Most AC units do not exchange any air between the inside and outside. What they have is a piece that gets very cold, a piece that gets very hot, and a closed loop of pipe filled with a fluid connecting the two. On one side the fluid sops up heat like a heat sponge, then it gets pumped to the other side where the heat it picked up gets \"wrung out\" to the outside air. You are literally pumping heat energy out of your house. The reason you have hoses is because when your AC unit is portable, the whole thing is inside your house. That includes the hot side. With no hoses, that would make it pretty pointless. You could make it suck air from inside the room, wring out the heat into that air, and pump it outside using only one hose--and indeed, single-hose portable air conditioners exist--but this creates a problem. Now you are pumping air out of your house. This creates a lower pressure inside your house. Your house is pretty decently sealed, but it's far from airtight. So when the pressure inside the house goes down, air starts to leak back into the house from, guess where? Outside! All the air you're working so hard to pump out is just being replaced by warm air all over again. And some of the air it worked so hard to make cold for you is being sucked up and pumped outside anyway, what a waste! This significantly reduces the effectiveness of the air conditioner unit. With two hoses, your AC can instead suck in air from outside, wring out the heat into that, and blow it back out. By doing this you're more or less bringing a piece of outside to meet the hot side of your air conditioner in a (mostly) closed loop. You're not pumping air from you house outside anymore, so no low pressure zone created, meaning no hot air will be sucked into your house. And you're not blowing your precious cold air outside.", "It's using the outside air to cool its internal parts as opposed to a single-hose unit which would cool its parts with the air inside your room." ], "score": [ 7, 4, 4, 4, 3 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "h39h6e1", "h39h2vg", "h39hcql" ], "text": [ "There should be. Basically, in a properly-built storm bunker, there will be ventilation pipes that go straight up to the surface, then curve over in a “u-shape” and point back at the earth so that they don’t allow water in. This lets air circulate without flooding the bunker. But if a bunker has been built improperly, it is still going to take a long time to suffocate, if it happens at all. It is remarkably hard to seal a room completely. *You should not test this.* But draughts have a way of getting in. In the time it takes for a tornado to fly overhead, most bunkers will have a good supply of oxygen even if it’s just a hole grandpa dug into the ground in the 60s. You don’t want to stay there for days, but people won’t suffocate within an hour.", "Yes. Most shelters have an air intake of some sort. If you want a good example look up home bomb shelter plans from the 50's or 60's. These will have extra ventilation filters or a particle trap to deal with nuclear fallout.", "If it's your WW2 type bunker then you don't really need a ventilation system if you're going to be down there a day or two. If it's a cold war style nuclear bunker then yes, you need a proper air ventilation system. They will often be passed through various filters to purify the air. It would also be possible to buy oxygen or simply air storage tanks. You can also have plants in your bunker I believe. Ultimately it just comes down to time and the number of people, well, also how sealed off it is. I use to worry as a kid that we'd suffocate in the house unless the windows were open. But because of tiny gaps and drafts, enough oxygen gets into the air anyways." ], "score": [ 6, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "h39m8p6", "h39qljc" ], "text": [ "When the GC Dam was completed and Lake Powell came into being, the depth of the lake kept the water at the lower depths colder, so as the dam releases water into the Colorado River, its at a constant 45 degrees F. Before the dam, the water flowing in the river would be much shallower and would be heated by the sun, driving the temperature up to 80 degrees.", "Note to the reader here: \"Closing\" means \"completion\" here. It's not that they shut down the dam, it's that they finished the dam." ], "score": [ 8, 6 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h39yn77", "h3a0reh" ], "text": [ "The flying object itself becomes the “ground” or at least the “neutral” of their circuits. It may not be the same as the *actual ground* but that’s OK because nobody is going to be touching *both the ground and the aircraft* while it’s in flight, so no current can flow through them and cause harm. The problem with an ungrounded stereo or computer in your house is you are likely to touch the ground and the electronics at the same time, so electricity could travel *through* you from the electronics to the ground. Electricity requires a circuit to flow and a person touching something with high voltage *but nothing else* doesn’t form a complete circuit so they won’t get zapped. So as long as the outer body, and the seats, and any touch-able parts of the electronics in an airplane are at the same voltage, nobody’s going to be hurt, even if that voltage isn’t exactly the same as the ground.", "Electronics and electrical systems in airplanes are grounded via the aircraft’s exterior body. Practically all commercial airplanes are manufactured with a conductive body, such as aluminum. When an electrical phenomenon occurs that results in excess electricity being produced, the extra electricity travels outside the aircraft to its body where it’s safely dissipated. Most airplanes are also designed with static dischargers or “static wicks” that release this excess electricity into the atmosphere." ], "score": [ 15, 7 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h3bpewq", "h3d48rr", "h3bosau", "h3cygom", "h3bx5bo", "h3da0yb", "h3d3gpw", "h3cqlsp", "h3cu1wq", "h3c2a64", "h3d2o6l", "h3d3l1s", "h3cy0i2" ], "text": [ "Heat pumps are seen as environmentally friendly *compared to other methods of heating,* since they don’t convert energy directly into heat like gas furnaces or electric space heaters do. They instead use relatively low power to move existing heat into an area it normally wouldn’t go. Air conditioners, on the other hand, are seen as environmentally unfriendly compared to other (admittedly less effective) methods of staying cool like cold drinks, turning on a fan, or just sweating it out.", "TL;DR: It's about the history of air conditioning, US environmentalism, and \"heat pumps\". This is a question about culture that is related to architecture in the United States. Before air conditioning in homes was common, the US had many residents in the northeast and midwest, and in much of that area winter requires some form of heating for life safety, while A/C is a comfort item, or a \"nice to have\". Pre-A/C traditional architecture in the American South, and in the sparsely populated non-coastal southwest, often had features to support air flow and shade for easier cooling and limited need for heating. The 1940s-1960s were (a) the period when air conditioning for homes started to become popular (b) the period when the south/west started to see rapidly expanding population and (c) the period when aggressive construction of hydropower was making electricity incredibly cheap across the west. So many many homes were built in hot-weather parts of the US with virtually no insulation or architectural cooling powers -- just an assumption that unlimited cheap electricity could be pumped in for A/C. So in the 1960s-70s, when the American environmental movement was taking off, the northeast and midwest had most energy coming from either natural gas, propane, or fuel oil (for heating) or coal/nuclear for electricity. So all energy use was seen as environmentally unfriendly, and electricity was expensive, so focusing on things like insulating your home were both the environmental and economical thing to do. Environmentalists from these areas looked at the south/west's blaring air conditioners slurping up electricity and ignoring insulation, and decided that was bad for the environment because of assumptions about energy source. (Side note: there's a second, entirely distinct environmental criticism of A/C! Enviromentalists in the west *also* saw problems with A/C, because A/C enabled development and population growth that destroyed sensitive desert and mountain ecosystems that had previously been mostly out of reach, strained local surface and aquifer water, and justified damming mountain rivers.) Fast forward to now. Heat pumps for heating are still relatively niche, due to the expense of retrofit geothermal and the novelty of cold weather air-source heat pumps. The kind of person whose house has a heat pump for heating is usually the kind of person who already has maxed out the efficiency of their home with insulation, all-LED lighting, etc; might have rooftop solar and/or a plug-in electric car; and raves about their induction range. (Induction ranges are awesome, ps.) So heat-pumps-for-heating tend to be installed on otherwise very efficient homes, and to replace either fossil fuel heating or much less effective electric resistance heating. Meanwhile heat-pumps-for-cooling (air conditioning units) are at worst still linked to inefficient mid-century construction, and at best are neutral in connotation.", "Heating a home is seen as a requirement, whereas cooling a home is not necessarily the same level of requirement. The other reason is that when you have a heat pump set into a heating mode, the \"waste heat\" ends up in the house, so you are fully efficient. When you have it in reverse (like an A/C), the waste heat is exhausted outside.", "Hi hvac guy here! It isn't that it is more or less impactful on the environment as all a heat pump really is is an ac reversed (there's a little more to it than that of course but basic premise.) The issue isn't ac versus heat. The issue is what is being used to heat/cool the space, the refrigerant. One molecule of r22 refrigerant has the ability to destroy 10,000 ozone molecules so we are transitioning to different refrigerants like r401a r404a r134a etc etc over the old ozone destroying refrigerant r22 r12 etc", "> If heat pumps are seen as a green way of heating a home, They are \"green\" *only* in that natural gas or heating oil are not burned for heat. Still, efficiency drops with heat pumps in relation to how much electrical energy is used when temps drop below 40*F. Which they then alternate into defrost mode, which is not comfortable inside the dwelling. And/or use a heating coil to keep the outside coil from freezing up. More electrical energy used!", "In rich countries heating is seen as a necessity and cooling a luxury. (Just put the fam on, drink some water) In other parts of the world cooling is more needed (but harder to afford). Heating is seen as a luxury (just put a blanket on) So it’s a cultural perception.", "Air conditioners generate heat. It's a fundamental outcome of the laws of thermodynamics that if you want to make one system colder, you must take all of the heat from that system and move it to another, however, you cannot do this with perfect efficiency - it's physically impossible. So you add *more* heat to the exhaust system than you took from the system being cooled. This is fundamentally different from any kind of heating system, where you're just straight up adding the amount of heat needed. This puts air conditioning into a fun little category where the more we use it, the more heat we dump into the Earth's ecosystem. It's not simply moving heat from one system to another, it's directly adding more heat.", "The most important part of the answer lies in the word \"seen\". It's a perception. Therefore, there isn't a single objective answer, but you can get broad-strokes generalizations. The generalization is: heating a home is seen as essential; cooling a home is not seen as essential. So any expenditure of energy on cooling is seen as being environmentally unfriendly from the start, while heating systems are compared by efficiency. After that you get into details of specific cases. For example, geothermal heat pumps can both heat *and* cool a house and are reasonably considered \"environmentally friendly\" in both cases. Some air conditioning is much more efficient than others. Etc.", "First principle, heat transfer is all about the delta T. The larger the delta (difference), the easier it is for heat transfer to occur. AC units have to take heat from the area you want cool, \"upgrade\" it through compression to a higher temperature (much higher than ambient) so that heat can migrate into the atmosphere. This work is energy intensive and therefore, not exactly \"green\" because off all of the work compressing the refrigerant. So why is a heat pump \"greener\"? Because the heat sink is already below ambient, and therefore you don't have to do nearly the same amount of work to have a useful temperature delta between the source and the sink. Some caveats, if your sink is too small then eventually you will exhaust its ability to supply or absorb heat, in which case your heat pump will do nothing (no delta T, no heat exchange).", "The process itself is equally energy efficient in principle. What it comes down to mainly is a question of: is this a necessary or reasonable use of energy? Heating your house to, say, 65-70 Fahrenheit (19-21 centigrade) would not be considered excessive by most people. But blasting your A/C to bring the temperature down to 65 F on an 85-F day (\\~30 C) is arguably a waste of energy, if you could also cool down by wearing less clothes, having a cool drink or running a fan. Some use of A/C in hot weather may be justified, but blasting it so hard that you need to put on a sweater is probably not. In addition, A/C systems aren't always installed very well and so may actually be less efficient in practice than a heat pump. An A/C installed and manufactured to the same standards should be equally efficient as a heat pump, but in practice many people will e.g. buy cheap window units and install them with poor insulation (because that's all that fits their house & budget), so in many cases they do end up being very energy-hungry for the cooling power they deliver.", "To add to what others have said most air conditioners use refrigerants that are not environmentally friendly, they are not supposed to be released, but they do get released int the atmosphere for various reasons.", "Heat pumps only really make sense in very well insulated houses, while air conditioning systems are retrofitted to pretty much every house. As an example, a refrigerator, i.e. a small room from which the heat is extracted, would not really be of much use without insulation.", "If your alternative is just no a/c and a gas-powered furnace, you could argue that converting to a “dual-fuel” heat pump system is more environmentally friendly, depending on the climate where you live, since using an electric heat pump throughout the winter May be more environmentally friendly than burning gas. But if you live someplace really cold, the heat pump won’t work once it gets below like 35 degrees and then you’re just running off the gas furnace all the time anyway. But if you live in a milder climate (coastal pacific nw for example) you could get a lot of use out of a heat pump and rarely need the furnace to kick in." ], "score": [ 1690, 134, 49, 36, 12, 11, 10, 8, 6, 5, 4, 3, 3 ], "text_urls": [ [], [], [], [], [], [], [], [], [], [], [], [], [] ] }

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{ "a_id": [ "h3cg0il", "h3ciat4" ], "text": [ "Are there cracks where there shouldn’t be any? Where cracks are expected are they bigger than they should be? Are any cracks showing signs of widening? Is there visible corrosion? Is concrete spalling? (Popping off the reinforcement). Is water getting in? Are beams/columns/walls/floors heavily deflected when they shouldn’t be? Has anyone made any modifications to the structure - eg has someone cut a hole in a structural wall to install a door, or commonly in houses has someone cut pieces out of wood floor beams to install cables and pipes? Are there any other signs of damage? Is the current building use consistent with the loads it was designed for?", "It all has to do with math basically. There has been a lot of experiments and real world experience that tells us a concrete post of a given size can support a certain amount of weight. Add the right kind of steel reinforcement and it can support more weight than plain concrete. Likewise, we know how much weight a steel I-beam of a certain size can support, how far apart the posts supporting it can be. As part of this, it has also been proven that a crack of a certain size will subtract so much load capacity. Corrosion subtracts strength from steel, and if the steel inside a piece of concrete rusts enough, it will cause the concrete to break apart. (This is called oxide jacking) So inspection of any building, bridge or other structure starts with an engineer who uses established lists of how big the beams and posts need to be, what size reinforcing steel needs to be used and so on. During construction, inspection consists of making sure the construction workers are actually putting in the right kind and amount of concrete, the right size and amount of steel reinforcement and so on. A common job for new engineer interns is going out to a job site before concrete is poured and physically count the number and size of steel reinforcement that is in place. Because of the experiments and real world experience, we also know roughly how fast a building will go bad. Concrete doesn't last forever, steel can rust, the ground can shift. So even after something is built, there are rules for how often the thing needs to be inspected. We know we will find problems, what we're looking for is whether those problems are severe enough to require repair or if they can wait. So a qualified inspector looks for cracks in the concrete posts, looks for certain kinds of damage that can happen to concrete, especially when it is exposed to water. If the reinforcing steel is rusting, it will cause bowl shaped pieces of concrete to flake off. If there is too much water against the foundation you will see discoloured patches on the concrete wall. (called efflorescence) This causes a chemical reaction to occur that can drastically weaken the concrete because it leaches out minerals. After physically looking and discovering how much damage is done, it is possible to calculate how much physical strength is left in the structure. Repeated inspections over time gives you a good idea of how fast the structure is going bad. The amount of damage and the speed with which the damage is occurring is what the engineer bases their formal report on. Some engineering failures, such as the recent one in Florida, are often the result of property owners not performing the required repairs or modifications soon enough, or failing to have regular inspections in the first place." ], "score": [ 14, 7 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h3e6kth", "h3e0o2a", "h3e0u2b" ], "text": [ "With DC power, you push the electrons down the wire in one direction, like water down a hose. With AC power, you keep switching direction back and forth - so it's suck-blow-suck-blow-suck-blow. For a whole lot of cases, it doesn't matter which direction the electrons are moving, just so long as they move - like moving a saw back and forth instead of going in one direction; it cuts just fine either way. One reason to use AC is there are a bunch of side-effects with DC that make it difficult to carry over power lines. You get big magnetic fields building up that end up causing transmission losses - if you keep switching direction, this effect is minimized.", "AC alternates direction, DC doesn't. They are different in an almost unlimited number of ways. Chemistry, which is used in batteries, only makes DC. The downside of DC is that you can't change the voltage easily. AC, on the other hand, lets you freely change the voltage using a transformer, constrained by the power. This ia a very braod topic, and many fine explanations are out there already. Perhaps a more specific question could get a more satisfying answer.", "Power is voltage times current. Current is the measure of “flow” of charge. In DC (Direct Current) charge flows in one direction. In AC (Alternating Current) the charge continuously changes direction. If you were to view AC current vs time, it actually makes a sine graph. It speeds up in one direction, then begins to slow down, until it is going backwards, and goes through this cycle multiple times per second." ], "score": [ 13, 5, 4 ], "text_urls": [ [], [], [] ] }

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