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vishnun0027

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eli5_dataset

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{ "a_id": [ "gslfd5v", "gslflbr", "gsn0sx5", "gslfnhx" ], "text": [ "With the amount of space available for placing solar panels (ignoring weight considerations), the power output of such panels could still take days to fully charge a vehicle, even with direct sunlight for most of the day. Typical solar panels put out around 15 watts per square foot under ideal circumstances, and at best, a typical car might only have about 20 square feet or so (a 5x4 foot rectangle or equivalent) to work with. As a reference, the Tesla Model 3 has a minimum battery capacity of 50,000 watt hours, which translates to ~3333 [sq. Ft * hours] to fully charge (~166 hours of optimal sunlight for a 20 sq ft panel)", "First, some do. Fisker has announced an SUV that has a solar panel on the roof that they claim will get you 1,000 miles of travel over the course of a year. The reasons that most don't come down to cost, complexity and marketing decisions. Having that solar panel on the roof adds costs to the car that might not ever be paid back over the lifespan of the vehicle. It also adds complexity to the charging mechanism which introduces more chances for failure. Finally, people like to buy cars with sunroofs and all glass tops.", "The answer is, it’s not worth it. I wish they would though! Get stranded in an EV, eventually the car is charged. Also, a small bonus on charging or range for the life of the car.", "Not really. The additional weight just wouldn't make sense given the benefit. Even for a fairly large car, it would be fairly difficult to get more than 2-3 sq meters of solar roof (unless it gets pretty crazy). Even with the most efficient panels (and drivers willing to park in the sun all day), this would be around 3-4kWH at best. A typical fully electric car has about 60-100KWH batteries. So it would make very little difference in terms of charging a car." ], "score": [ 29, 6, 3, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gslj3fm" ], "text": [ "There are many factors in how an engine sounds. Firing order and interval plays a big roll, bore and stroke differences, intake design and exhaust design. These all make a difference. An engine that fires cylinders 180 degrees apart will sound very different from one that fires 90 degrees apart." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "gsmzfjr", "gsmzjxt", "gsmzo22", "gsn4s5a", "gsn0dmt", "gsn0ajh", "gsn040n" ], "text": [ "There is a hot and cold water feed that comes into the faucet. The handle moves a valve that changes how much of the hot and cold gets mixed into the stream of water that comes out of the tap. If the handle is all the way to one side only hot water will come out, if it's all the way to the other side, only cold water will come out. Somewhere in between it will mix the two together.", "Hot water has a different source for you water which is the hot water heater. When you turn the knobs on the faucet you are adjusting the volume of cold versus hot water that you use. That in turn is why you can control the temperature.", "The faucets just mix hot and cold water together, the amount of each is based on how far each lever is turned. If hot is all the way on and cold is all the way on you’ll have warm water. If you slide the cold handle to off the temp will increase. Vice Versa", "it's like the ice cream machine that lets you get vanilla or chocolate ice cream but there's also the middle handle that lets you get both. Except that instead of only three handles the knobs let you go from all chocolate and no vanilla to all vanilla and no chocolate and everywhere between the two ends. Except replace chocolate with cold water and vanilla with hot water.", "Think of your mixer tap like a set of scales. If one tap is opened further than the other, the water will be tempered towards that end heat wise. Hot tap fully open and cold tap only half open = water roughly 75% as hot as your boiler could make it. Both taps fully open = water roughly 50% as hot as boiler can make it. These are examples only and are purely for the purpose of explaining the process (because cold water has a varied effect on hot water in various quatities)", "[This is a water heater]( URL_0 ), it takes in a large tank of water and heats it up with either gas flame or electrical heater coils. You'll have one somewhere in the basement. In your house, you have [hot pipes and cold pipes]( URL_2 ) bringing hot water (from the heater) and cold water (straight from the city supply) to your faucets and sinks. [Under your sink]( URL_3 ) you'll see hot water and cold water connected to the faucets. [The faucet]( URL_1 ) just combines the hot and the cold, more hot or more cold, depending on how you adjust the knobs. The knobs simply let more (hot or cold) water through when you twist them.", "The handles act as controls for a valve that mixes water that comes from two different places. Water comes into your house in a Main Line. That main line sends water to the cold water points all through out your home like sinks, showers, and garden hoses. It also sends water to a hot water heater which then heats the water to approximately 120°F. Once hot, the water heater has a secondary line out, feeding heated water to all of the hot water points in the sinks, showers/tubs, and typically a washing machine. At the sink faucet, when you turn the handle, you adjust how much hot water you're letting through and how much cold. They then mix into a single point and come out of the faucet at the resulting mixed temperature." ], "score": [ 22, 6, 4, 3, 3, 3, 3 ], "text_urls": [ [], [], [], [], [], [ "https://hbmcclure.com/wp-content/uploads/HBMcClure-Equip-WaterHeater-01-copy-682x1024.jpg", "http://sc04.alicdn.com/kf/HTB1uYCLKeySBuNjy1zdq6xPxFXai.jpg", "https://paulmaguirephoto.com/wp-content/uploads/2020/07/f35333.jpg", "https://previews.123rf.com/images/mettus/mettus1603/mettus160300194/54097291-two-flexible-water-pipes-for-cold-and-hot-water-connected-in-to-the-home-boiler-in-bathroom.jpg" ], [] ] }

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{ "a_id": [ "gsn7pj5", "gsn7myc", "gsn7n7l" ], "text": [ "They tried that, with every tugboat they could gather up. Didn't work. The Ever Given is a huge ship, twice the size of the largest aircraft carrier.", "It's very, very heavy and well stuck. More than a hundred feet at either end is sitting on the bottom, and the bow dug into the canal bank pretty hard. You'd have better luck trying to move a mountain with a tugboat. It's going to need to be dug out.", "I saw a photo with a large yellow Bob-the-builder-esque machine next to the side of the Evergreen, it looked like a mouse next to a huge whale. It's very large. Not a small boat." ], "score": [ 6, 6, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gsnosu6" ], "text": [ "Uninterruptible Power Supply devices exist exactly for that purpose. It's just an extra cost many users don't decide they want to spend extra on." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gsoze75", "gsp025i", "gsp129c", "gsp08j9", "gsp5a0n" ], "text": [ "They have a thing called rudder which is kinda like an underwater tail or fin. It normally keeps straight as the ship goes, but if you turn it to one side, then the water deflecting sideways from it will make the ship turn.", "Theres typically two methods of steering. One, a rudder increases drag to one side causing a ship to turn. This is kind of like an inverse steering wheel. In addition, propulsion can be set up so that uneven push/pull (example, two motors) can occur causing the ship to turn in the direction where there's less propulsion at a given moment. Then you could control it similar to how many tanks turn. Combining the two isn't against the rules too.", "To add on the the other comments- most ships rely on tug boats for harbor maneuvering. Their own steering / propulsion does not have fine enough control to navigate in close quarters.", "Most ships these days have some form of bow and/or stern thrusters, i.e. like a helicoptor tail rotor they can help pivot the ship's bow or stern around - they literally look like a smaller sideways propellor. But these are typically only used at slower speeds like when the ship is docking - when the ship is underway the ship's rudder can deflect the water flow + the water that is sped up by the main propellor(s). Turn the rudder to the right, water is deflected to the right which pushes the stern of the ship to the left and the bow turns to the right. It works like a giant paddle if you will. Some ships with multiple propellors can steer to some degree with broken rudders by varying the speed/direction of the multiple propellors, but generally this is only a last ditch (cough*Bismark*cough) thing. A few newer ships have what they call an azimuth thruster, or an azipod - these look like little propellor pods where the propeller is rotated direction - this removes the need for a rudder entirely and can make the ship much more maneuverable.", "Others have answered the basics, but since sailing is my jam I wanted to add to this, because sail boats (and the physics that makes then go) are really neat. Sail boats are powered by the wind, but they aren't just pushed by it, otherwise you would only ever be able to go in the direction the wind was blowing. Instead, the sail actually acts like a sideways airplane wing. When air flows over the two sides of the sail, it creates a vacuum between the low pressure outer edge, and the high pressure inner edge. Nature abhors a vacuum and the empty space will try to suck in particles around it to equalize the pressure. The pressure trying to equalize between the two sides of the sail generates force that makes the boat move known as the center of effort. But we aren't done yet! A vacuum from one side of the sail to the other would basically mean the boat can only move sideways, but we know boats move forward. Remember that every action has an equal an opposite reaction, when we take a step, we put our weight down on the ground, and the ground pushes back up on us. Well that happens with sail boats and water too! When the sail starts to move the boat, the water pushes back in an equal and opposite direction against everything underneath the boat... which, you guessed it, works like a wing underwater, creating that same lift but in the opposite direction. This is called the centre of lateral resistance, and we will come back to it in a moment. You now have 2 forces pushing against each other. The sail, trying to make the boat move one way, the equal opposite force of the water against the boat is trying to make it move the other. Both are perfectly balanced against each other. The easiest way to demonstrate how this becomes forward movement is to think about those funny internet videos where someone jumps on a ball and it shoots put from under them causing them to fall over. You can do this on a small scale for yourself without falling over by taking a pen/pencil, holding it on one side of its curve between your thumb and index finger, and squeeze. The pencil shoots out of your fingers! But what does this have to do with stearing the sailboat? Well built boats have the force of everything above and below the water in balance. They have the two fingers on the pencil at the same place... if you move one of those two forces away from that balanced center point, they will start to push the boat in that direction. Again, try this with a pencil. Put your pencil flat on a desk. Put your fingers on either side and push, if your fingers don't line up the pencil will turn. For a boat, you can do this in 2 ways. 1 adjust the centre of lateral resistance. This is the one most people think of, they turn the stearing wheel/tiller, that turns the rudder (a flat vertical plank underneath the boat), and as it turns, it has less area along the plain generating that lateral resistance force, thus generating less lateral resistance, and shifting where the forces are on the boat. The other option is to adjust the sails. If you move where the pressure in your sails are, you move the centre of effort backwards or forwards, and create that same imbalance that turns the boat!" ], "score": [ 12, 8, 4, 4, 3 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "gsriz3z" ], "text": [ "Because it's made up from glass fibres (hence the name) that are so thin they can bend easily without breaking. It's the same principle whereby a single piece of paper will fold and bend easily, but a telephone directory will not." ], "score": [ 16 ], "text_urls": [ [] ] }

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{ "a_id": [ "gsrmm8x", "gsrmspx", "gsrmop1" ], "text": [ "It's called pseudorandomness. What that function does is calls the clock time, does some math that makes the system chaotic such that every different second gives a completely different output number, and gives you that as your random number. A computer cannot make true randomness, as it is a deterministic machine and can only take inputs and give outputs. That clock trick is usually good enough, but for some applications, it's not, so other things are used, like weather patterns or even actual radioactive decay (a truly probabilistic event)", "So first you need to start with what random means. Random is a super strict physics sense means impossible to predict. That pretty much means just quantum collapses. We can’t really actually produce truly random things, we don’t know how. Now “psuedo random” is what most people refer to as random, which basically means stupidly/impossibly hard to predict. Random() and rand() and other functions use a few tricks to do this, like checking the third last used computer memory bit locations, and the exact millisecond you hit enter and using them together to make a third number and using that one. Its statistically random (and they do a lot of tests to show that it follows statistical premises that denote random functionality) and “random” for what we can tell, but technically speaking not true random. You could figure it out with an enormous (mind bogglingly enormous) amount of effort.", "Every component in a computer is meant to behave entirely predictably. If you hit it with the same input, it gives you the same output every time. Because of this, most computers can only give *pseudo*-random numbers. Pseudo-random numbers look random, but technically aren't. The simplest thing they can do is take the clock, since that number is constantly changing, and do some math to it. For most purposes, games and most physics simulations, this is fine. If you want a *truly* random number, you have to introduce some kind of noise that isn't controllable or predictable. There are some specialized services that you can subscribe to to get random bits, and they use more specialized equipment that samples random noise somehow. For example, one of these services uses a video feed of a big wall of lava lamps as a source of randomness." ], "score": [ 10, 6, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gsruwgv" ], "text": [ "Very carefully. Some tankers have a long tube which some guy at the back of the tanker can control(usually with wing like things that can twist). The planes have to fly very steadily with each other (not easy) and the guy has to control the tube into the fuel hole (extremely not easy) Other tankers put a flexible hose with a funnel like thing at the end. The tanker flies very steady, and the plane tries to put a tube into the funnel. The funnel keeps the thing at the back and level. Some funnels makes it easier, you can get it a bit wrong, but it is still really hard. Other funnels tip when you get it wrong, so they don't make it easier. Either way, only after everyone is sure that everything is plugged in do they start sending the fuel. To get it right, it's almost entirely cameras and eyeballs." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "gssu6bo", "gst6ffk" ], "text": [ "There is no such requirement. If you're doing a proper oil change (drain the old oil and replace the oil filter) then you can change brands and types. You should check your cars manual for recommendations. Generally they'll list a viscosity and a specification (such as SL, SN, MB 229.5, etc) As long as you use oil that meets those specifications you're fine. Now, if you're only topping off the oil (for various reasons) then I would try to stick with the same stuff -- at least within the same brand so you have some confidence the additive packages will be compatible. But if you're doing a full oil change then it really doesn't matter. Yes, there's always a little oil left inside an engine even when you let it drain for hours... But you're replacing 99% of the oil so it isn't an issue.", "It's a myth based from a distrust of synthetics and a mistaken belief that mixing even minute amounts of one with the other somehow causes problems. The distrust mainly comes from a false belief that it's not possible for it to be as good as \"real\" oil, even though it is made from real oil and is just modified to be better -- so much better that companies like Mobil put guarantees of 10-15k miles of protection right on the bottle for their Mobil 1 synthetic. If it weren't good to swap, oil bottles would warn people and car manuals would state it as a no-no, but they don't, and they're the degree-holding engineers so I trust their judgment." ], "score": [ 9, 5 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gsswxw2", "gssxu1m", "gssy23i", "gssx6f6", "gst26if" ], "text": [ "Modern trucks weigh a lot and would crush a Roman road. Asphalt weathers differently than rock, especially with a large weight load.", "In addition to what the other commenters said, survivorship bias. The roman roads we see today are the ones that survived as long as they did. The ones that didn't, well, aren't around to be commented on.", "Several factors: 1. Roman roads didn't just last millennia by themselves, they were maintained because they were useful. Roman roads that weren't maintained are long gone. 2. Stone is more tough (albeit harder to work with) than asphalt. 3. Damage to roads scales with the weight of the things using them to the fourth power. This scaling is so strong that when trying to estimate damage to modern roads and bridges one often ignores everything but trucks since the damage a car (not to even mention pedestrians) does to a road is negligble compared to the damage a truck does. Since the heaviest thing that would have used a roman road is a horse-drawn cart, they would have been subjected to far less wear than modern roads.", "Roman roads were built by laying down stone and done so by hundreds of slaves. Modern roads are built by a dozen or so people using asphalt. Asphalt is much smoother but doesn't last as long. We *could* build our roads the same way they did, but it would cost A LOT more and be horrible to drive on.", "Like others said you have survivor biais, the road we have might have survived but they are not in good shape, they had to support a lot less weight and traffic than modern road, their surface don't provide enough surface for the speed and safety of modern vehicles, etc. To all that, I'll add that it's amazing what you can do when you can just throw human suffering of slaves you took in wars of conquest." ], "score": [ 110, 81, 52, 11, 3 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "gsts91d", "gstsm1u", "gststbn" ], "text": [ "They're very well encased. Usually specific wiring is used as well in case of a crack. The only real part that gets dangerous is inside the mechanical parts where water usually isn't around. Plus it's trip the GFCI if anything serious happened.", "Mostly by following code and using waterproof casing, wire nuts, etc. Plus the voltage used for lighting isn't large enough to fry a pool full of people. Plus the wire will be insulated so even if it gets wet it won't short unless the insulation is broken.", "Most of the newer pools and spas use LED lighting which is low voltage/low current, and as stated already, pretty well sealed. But, if the seal were to break, there is protection in the form of a GFCI, Ground Fault Circuit Interrupter, which can kill the circuit before the electricity has a chance to do any harm. This is why you should never remove the ground prong from any plug if it utilizes a GFCI socket, or you have basically defeated the protection mechanism of the GFCI outlet." ], "score": [ 6, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gsuz69q", "gsuzbnm", "gsuzyyy", "gsv0snr" ], "text": [ "Early shells were detonated by a simple timer. Slight changes to the time meant explosions at different heights. Flak was a random shot in the dark, not very efficient. During WW2 the British developed a rugged vacuum tube that could be used to make tiny radio transmitter/receiver. When close to metal aircraft, the radio signal would be reflected back to the receiver, triggering the explosion. This was the first proximity fuze.", "Bursting AA shells were time-fused. You did the math to figure out how long it would take the shell to get to a certain altitude, and then set the fuse. Later in WW2 radar-fused shells were developed by the US that used a radar in the nose of the shell to detect nearby aircraft.", "The German flak could be adjusted with a shell timer. A flak spotter would call out if the flack was exploding too soon or too late. Once they had it dialed in, it could be withering. Especially to flights of bombers who are flying at similar elevations. Also, they were in formation, which made them easy targets. In the early runs of the eight Air Force bombing germany, on a single mission it was not uncommon to lose 30% of the bombers and crew.. Once they figured out the timer setting on the shell, this info was communicated to other flak batteries along the flight route of the bombing run.", "Early shells had timed fuses. Artillerymen were trained on how to estimate the height of aircraft and how to adjust the timer so that the shell would detonate at *around* that same height, depending on the type of shell and the firing angle. That's fairly simple math: shell goes at X feet per second, you need it to explode at Y feet, so you set the fuse to Z seconds. Of course, it's *not* that simple since the shells aren't going straight up, they're fired at an angle. So there's some trigonometry in there if you were to sit down and do it \"right\". They didn't have that kind of time so they just made estimates, fired a shell, paid attention to where it went off (and how close it was to the altitude of the planes they were shooting at) and adjusted the timer on the next shell accordingly. For the most part, though, the strategy was to fire an ass-ton of flak shells and hope that at least a few of them exploded at the right altitude and close enough to a plane for the shrapnel to be dangerous, and then hope that some of that dangerous shrapnel did its job. The other problem was that those timers weren't super reliable. WWI timing fuses were made from something that burned at a fairly predictable rate, like [a stereotypical string fuse]( URL_0 ). The problem is that those don't always burn at exactly the same rate, especially at different altitudes. By WWII most shells were using clockwork fuses, which greatly increased the accuracy. In 1942 British engineers figured out how to use reflected radio waves in the shell to create proximity fuses that would explode when the *shell* knew it was close enough to a plane. They still weren't perfect and sometimes exploded early or late, but they were leaps and bounds better than timed fuses. The British military actually restricted their use to the navy for a long time so that if a shell failed to explode it would disappear into the ocean where the Germans couldn't find it to figure out how exactly the British were suddenly way better at shooting down planes." ], "score": [ 62, 11, 10, 8 ], "text_urls": [ [], [], [], [ "https://www.youtube.com/watch?v=oq8jzn2sd-g" ] ] }

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{ "a_id": [ "gsw65wg" ], "text": [ "It's either programmed directly into the system with various timers or use a vehicle detection system or both. To detect if a vehicle is waiting, there is a wire coil near the location line where you're supposed to stop. If you ever see a darker line in a circular pattern around where a larger white stripe is for the stop area, then that's what the detection area is. This coil detects large metal objects above it and it'll trigger programming to change the lights. Late at night when there is very little traffic, this signal might trigger the light to change immediately whereas other parts of the day it might be ignored entirely. The specifics of the timings are proprietary and closely held by whichever company in charge of the specific logic of the timings." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "gswcfl5", "gsw6k39" ], "text": [ "REST is a style of API where you mostly get and set data and the API doesn't remember anything about you. Yes, that's vague. The word REST is vague. You say: Orders - create one. The API says: sure, that's order #42. You say: Order #42 - how's it going? The API says: it's cooking. You say: Order #42 - how's it going? The API says: It's been delivered. You say: Order #42 - delete it. The API says: okay. The biggest principle is that you're always talking about some object - in this case the order. The API is designed around objects. Before REST, many APIs were focused on actions - \"get order status - order number #42\" rather than \"order #42 - get its status\". The difference is trivial but it has big consequences for how we organise the API. The other big principle is that requests are self-contained. You don't say \"my order\" because the API would then have to remember which order you were talking about. Yes, the system knows which orders are yours, but if you designed an API based on \"get my order status\" and then you had more than one order, it would be easy to run into problems. You would have to say \"I'm talking about order #43\" and then separately say \"get my order status\"; only one program could use the API at the time or they might set the wrong \"my order\" variable.", "I want to tell something to do something via an api. REST defines 4 verbs/actions: get, post, put, delete. Think of them like this: get retrieves the information, post creates a new thing, put updates, and delete deletes. That's basically it. How you communicate with the api (eg. soap, json, xml, etc) doesn't really have anything to do with REST." ], "score": [ 8, 6 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gsxet6y", "gswtnx5" ], "text": [ "It comes from the factory sterile and sealed. It can become contaminated at any point after that.", "They don't. Freshly produced packings are clean enough anyway so all they have to do is not change that" ], "score": [ 3, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gsxeuqg" ], "text": [ "Some bits of biology/biomedical and neurology, I imagine. \"Bio and Brain\" sounds like the kind of thing a particular university might come up with to try and look innovative, it's not really a field in its own right (and you really won't get far in a neurology degree without a solid foundation of general biology knowledge anyway)." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "gszjypw" ], "text": [ "Wait, you don't understand digital logic? Then you don't stand a chance of understanding FPGAs. So let's start there: Digital logic circuits do (almost) everything based on \"logic states\", and there are only 2 possible states in a binary digital logic circuit. We call these \"on and off\", or \"true and false\", or \"1 and 0\". For example, imagine a light bulb wired to a battery through two switches in series, A and B. The light is turned on only if both A *and* B are turned on. So that's a binary digital logic AND gate. Make the same circuit, but put switches A and B in parallel. That's an OR gate. In integrated circuits, we use transistors in stead of switches. They operate a lot like tiny electronically-controlled switches. And we make other logic gates besides AND and OR. And more complex things made of logic gates. Putting lots and lots of them together with various gates' outputs feeding the inputs of others, and those feeding the inputs of others, allows the construction of very complex logical computations. That's how we build up very complex devices like microprocessors (CPUs). You can make binary digital logic gates do a lot of things if you are willing to use lots and lots of them. An FPGA contains a lot of logic gates built up into standard groups. They also contain the equivalent of fuses which can allow those units to be configured and connected to each other in a variety of ways. Using those \"fuses\" and configuring the FPGA correctly, you can build up a custom circuit virtually of your choosing. A lot of stuff gets wasted, but it's still a hell of a lot cheaper to make a small number of custom programmed FPGAs than it is to make truly custom-designed integrated circuits. It only becomes economical to make true custom ICs if you can sell a lot of them." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gt0bbo9" ], "text": [ "The type of plastic which zipties are made out of are very tough. And the way that they ratchet in provides a really strong grip which tightens as you pull harder" ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gt0kyue" ], "text": [ "The flame needs both oxygen and fuel to burn. The bottle only contains gas (fuel) and the pressurized gas moving outwards prevents air from moving in the bottle and mixing with it. So, the flame only burns outside where the gas mixes with surrounding air." ], "score": [ 22 ], "text_urls": [ [] ] }

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{ "a_id": [ "gt0rynl" ], "text": [ "CO2 emissions are determined by how much fuel you burn, and if an engine burns more fuel, it puts out more CO2. However, other harmful emissions (HC, CO, NOx) depend on how clean the burn is. In order to burn the fuel cleanly, the engine needs to mix air and fuel at exactly the right ratio. If there's too much fuel and too little air, you have unburnt (HC) or partially burnt (CO) fuel coming out of the tail pipe. If there's too much air and not enough fuel, some of the excess oxygen will react with the nitrogen in the air to create NOx. An engine that runs lean (with too much air and too little fuel) will consume less fuel, but it will produce a lot of NOx. Adding more fuel will increase the amount of CO2 but decrease the amount of NOx. So sometimes burning more fuel can result in a cleaner burn. Then there's the catalytic converter. Pushing the exhaust through a catalytic converter will make the engine work harder, reduce its output power by a bit and require a bit more fuel. But the advantage is that a catalytic converter can take the oxygen atoms from NOx molecules and give it to the CO molecules, so harmful NOx and CO gets turned into relatively harmless N and CO2. Again, you give up some power and fuel efficiency to reduce harmful pollutants." ], "score": [ 6 ], "text_urls": [ [] ] }

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{ "a_id": [ "gt0zwjn" ], "text": [ "The drag on the car isn't going to change a ton, the air on the highway is relatively stationary unless a car is actively traveling through it. The car loses energy to a variety of things from just base fuel consumption to rolling resistance to air resistance, increasing air resistance by 1% doesn't increase fuel consumption by 1%, but all those wind turbines do cost a lot of money to build and maintain. The bigger problem is that they produce squat for power. They capture wind in maybe a 2 meter x 0.5 meter area for 1 m^2. A wind turbine with 50 meter long blades (common these days) captures 7800 m^2 There's a reason we use big spinning discs for power generation rather than the vertical ones" ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "gt20wb9", "gt2yh16", "gt480hs" ], "text": [ "The fancy tripod is probably a total station. What it's doing is sending an infrared signal out at a reflector, and measuring the time it takes for the reflector to bounce the signal back to the device. That allows it to figure out how far away the reflector is from the device. It can also very precisely detect the angle between two different points. If you set the total station up near a point whose coordinates you know absolutely (such points are called survey monuments,) then you can work out the coordinates of any other point that you can see. The total station can work out its own coordinates based on its distance and angle from the monument, and then can work out the coordinates of other things based on that. Surveyors use it for all sorts of things - is the building straight. Are we building the forms in the right place. Did we pour enough soil into the foundation. Etc. etc.", "Could also be a transit depending on what construction your watching. As a plumber we use a transit a lot to to get our grade on pipe as small as a 32nd of an inch per foot of pipe.", "I saw a guy use what must of been a total station (from other comment) to straighten a building. They were putting up a 25 story building. When they got to about 5 floors they had the guy with the tripod at a pre-marked point on the other side of the street giving directions to a guy on the 4th floor that had cross shaped cables with turnbuckles. He would spot and then give directions so the steel girders could be plumbed to perfectly on plumb. Pretty cool operation. I think they did that about every 5 floors." ], "score": [ 249, 6, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gt26ton", "gt27yoi" ], "text": [ "Basically a score, you give it a score in the range of -1 to 1 for any action the ai takes and the higher the score the more “right” things the AI is doing", "Broadly speaking, the non-changeable parts of the program set a goal for the AI (which boils down to something like \"make this number go up [or down]\") in terms of some outcome or set of outcomes from the actions the AI takes. The AI is programmed to perform whatever task in slightly different ways, and gets a \"score\" as feedback from each trial. It uses that feedback to decide how to try the task next time, but again makes slight changes to see what happens. It keeps going either indefinitely or until it does the task \"well enough\", however you have defined that." ], "score": [ 11, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gt3xhbs", "gt3zlpq" ], "text": [ "Easier to see out of when driving. Helps me to better see my \"blind spots\" when making lane changes or backing around corners. If the windows weren't there, most suvs would have about a quarter or more of the side of the vehicle that the driver couldn't see through.", "The windows aren’t there for passengers. They’re for the driver. The driver needs to see adjacent vehicles when changing lanes." ], "score": [ 11, 6 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gt40cyf", "gt4p6p7", "gt40ql7", "gt41rag" ], "text": [ "Well, these are the two main reasons I would give: 1. The force of weight is directed downward, but the turning force that moves the wheel is to the side. You’re not fighting the weight of the car to rotate the wheels. However, the weight of the car does contribute to a frictional force between the wheel’s rolling surface and the road surface. It’s still hard to turn the wheels. This is greater when the car is stationary. Leading to number 2: 2. Power steering. The car mechanically helps you turn the wheels. When this system goes out, or on an older car that doesn’t have it, you really notice. There’s more to it, but this is ELI5 not ELIPHD and I think the majority of folks here haven’t met many 5 year olds lmfao.", "Modern cars have special parts that do the work for us. Many old vehicles do not have these parts, and it is pretty difficult to turn the steering wheel, especially when you're not moving.", "To begin, only half of the car's weight is on the steered wheels. Next, the pivot points are on machined parts called Ball Joints that create a well-lubricated joint on which to pivot. After that, the mechanical system you use to steer is gear-reduced, meaning you only need a little bit if torque to drive such a heavy load. Last, we generally have power steering. Traditionally a hydraulic system, more cars are going to electric assistance.", "Think of a really heavy cardboard box. Think of how hard it is to push that box forward. Now think of how easy it is to rotate that box. This is because the box's weight is spread out over the entire bottom of it, where it touches the floor. When you push the box, you're trying to overcome all of that weight at once. When you rotate the box, you only need to overcome a small portion of that weight. Also as that other dude said, power steering. The car has a system of fluids and mechanics that helps you turn the wheel faster with less effort." ], "score": [ 28, 5, 5, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gt59bpm", "gt59l2r", "gt597el", "gt5dr7c", "gt596jr", "gt5bx7g" ], "text": [ "It is because walking upright is actually a very impressive thing. To be able to walk upright on perfectly flat terrain is easy, but to be able to immediately adjust to a thousand permutations of incline, materials, stability, etc. is actually very hard. The human foot actually has more bones in it than any other part of the body - when combined with the number of other organs and systems we have dedicated to _balance_, the process of walking upright is an amazing interplay of systems effortlessly working together. We are getting closer with robotics, but it is still a very complex engineering process to get right.", "You have an advanced biological supercomputer in your head that’s monitoring millions of sensors and using that input to command thousands of motor control systems to perfectly balance you. Robots have just a handful of sensors and motors trying to do the same job, and the end result is predictably cautious and mechanical. They may get there some day, but it took a billion years for evolution to design the machine our robots are trying to replicate.", "The most important part of walking on 2 legs is balance. We make LOTS of tiny, fast, imperceptible movements of all of our arms, legs, fingers, toes, and the rest of our body to keep our balance as we move along. There's a lot of moving parts that need to synchronize and move in very small precise increments SMOOTHLY, and that's very hard to do for a robot. It takes a lot of processing power, but more importantly it takes a lot of mechanical complexity that we usually try to minimize because complexity equals higher cost. So we usually make a robot that moves in some simple, less mechanically intensive, manner.", "I'm assuming everyone has seen Boston Dynamics' bipedal robots, but if you haven't, definitely go check them out. They're really only a few years away from beating human mobility at all levels", "Can you define what you mean by “normal”? There are a lot of things that make up a typical gait and almost each one of those has posed different problems to roboticists at one time or another.", "When you're walking upright, you're kinda falling forward and catching yourself as you do, it's extremely difficult to programme for, our brains just do it automatically so we don't recognise how impressive it is." ], "score": [ 134, 43, 11, 7, 5, 3 ], "text_urls": [ [], [], [], [], [], [] ] }

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{ "a_id": [ "gt5kptw", "gt5r1dm", "gt5mlra" ], "text": [ "Modern ones have automatic defrost. From time to time, they introduce a small amount of hot, dry air. This removes the frost, and settles back to the bottom of the machine so the water can be condensed and put in the pan under the freezer. The objects in the freezer larger than frost aren't changed, as long as they are tightly sealed up.", "It's not old vs new, it's frost-free vs. manual defrosting. *In general* (in the US at least), combo fridge/freezers like you have in your kitchen are frost-free and stand alone freezers (chest or upright) have to be defrosted manually. The reason you'd want a manual defrost freezer is because it will hold food long-term w/o damage. In a frost-free freezer, the defrosting cycle gradually causes freezer burn in most foods. You wouldn't want to keep meat in your combo fridge/freezer for over a year, but that's totally OK in a standalone freezer.", "There’s tubing inside of the freezer behind a piece of plastic that zigzags back and forth so it looks like a squiggly line. Inside of that tubing is refrigerant and it makes the tubing very cold. Above the the tubing is a fan which moves the air across the tubing and through the rest of the freezer to make everything cold. Overtime, the tubing gets so cold that the moisture in the air will freeze to it. Eventually, it freezes so much that the ice can prevent the fan from working and moving the cold air around. Once that happens, the cold air just settles to the bottom of the freezer and the rest of the freezer gets warm and your ice cream melts. With an old freezer, this is when you’d have to defrost it. With new freezers, there’s a small separate tube under the cold tubes. The small separate tube is sometimes on a timer or hooked up to a temperature sensor. Once the timer reaches the set time frame (like every 24 hours) or the temperature sensor gets too cold, the small tube will heat up really hot. Because the small tube and the zigzagging tube are behind a piece of plastic and because hot air rises, the heat from the small tube is forced to travel up and around the zigzagging tube which melts all of the ice off of the zigzagging tube. The ice melts and falls down into a tray in the bottom of the freezer behind the plastic and another piece of tubing allows the water to drain underneath the fridge where it can evaporate into the air." ], "score": [ 5, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gt611n1", "gt621vt", "gt65qew", "gt6d3mg" ], "text": [ "They aren't - at least the underwater parts aren't. In almost every case, the platform is assembled on land, hauled out to sea on a barge, and then tipped off the side into the water. You now have a stable platform above the surface upon which to build your structures and transfer your equipment.", "Either built on stilts over 100ft over the water at high tide or with crazy floating platforms under the water that keep the rig hovering over the water line. Lots of structural engineering to make sure it handles waves or currents long term When it comes down to it though, it’s just one of those engineering marvels that can only exist if there’s butt tons of $$$ involved", "Oil rigs are basically ships designed for standing still. And they're also built like ships: on land in a drydock, and then they're towed out to sea and anchored down. Some are literally just held by cables like ship anchors, others in shallower water might have long legs like a bridge pylon, but in any case, it's all built on land and then towed out.", "There are at least two types of rigs. Floating and standing. Both are built on shore. Though they may be assembled at sea. Floating ones are big boats. No real challenge getting them in to place. Anchors and thrustors can keep them in place once they're there. Standing ones have legs that go to the sea bed. Typically they are retractable: the rig is floated out to position then lowers its legs until it is standing. You can also build the legs on shore, assemble them at sea then stick the platform bit on top later. Sea animals don't feature in the calculations a whole lot. Sharks aren't going to be interested. You will get diver crews that go down and inspect the legs/do other work. Again, sharks aren't going to be interested in them. There will be a lot of noise around the platform that will put off most large sea animals." ], "score": [ 11, 10, 7, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gt85jw5", "gt8b2vn", "gtenh1i" ], "text": [ "Currently it's mostly done by the PUREX process. The spent fuel is dissolved in nitric acid, and then a series of chemical processes are done to separate the plutonium (Pu) and uranium (U) from the fission products. URL_0", "So the waste from a plant isn’t out of useable energy like you see in coal. The daughter elements can still be radioactive and that produces useable energy. Further not all the fuel is consumed when a fuel rod is used. It can be repurified into a usable form again.", "Fuel in nuclear power plants is made of a fissile material and a fertile material. Fissile material makes the chain reaction work. Fertile material is turned into fissile material by the neutrons created by the chain reaction. So fresh fuel might be 3% U-235 (fissile) and 97% U-238 (fertile). After a long period of running it, the fuel will instead be 96% U-238, 2% fission products (very radioactive), 1% U-235 (fissile), and 1% Pu-239 (fissile, created by U-238 being exposed to neutrons). We've converted 2% of the original U-235 into fission produces (that is what happens when the atoms are split, releasing energy and neutrons), but in the process we've also turned 1% of the U-238 into Pu-239. Because they are different elements, you can use chemistry to separate out the fission products, the remaining uranium, and the newly-created plutonium. Then you can re-combine the uranium and the plutonium to create new fuel that has the same ratio of fissile and fertile materials as you originally created. The percentages I gave are just examples; real reactors use different levels of enrichment and end up with different percentages in the spent fuel. Some reactors (called breeders) can even create more fissile fuel than they consume." ], "score": [ 7, 3, 3 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/PUREX" ], [], [] ] }

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{ "a_id": [ "gta63ek", "gta5wzt", "gtab2qf", "gta82u1", "gta763p" ], "text": [ "In the early days of car manufacturing there was little or no thought paid to crash safety and aerodynamics. Not because they were ignorant, but because they simply didn't understand these things as well back then. The curved shape of early cars was part aesthetic and part strength. Early cars were built ontop of a sub-frame or chassis that held the drive train (engine, wheels, transmission) and the body was placed on top. Those kind of bodies got there structural strength from their shape. Today most cars are unibody, meaning that the frame and body of the car are one in the same. The strength of the body panels still comes from the shape but now those parts are spot welded at the factory to create the shapes needed to support the car. The body itself is the structure of the car rather than relying on heavy frame rails underneath the body. Unibody cars are much easier to manufacture, use less materials, and are quite a lot lighter than older cars as well which is why they are so common place today. Another factor is crash tests. Older cars may have seemed safer due to their heavier construction but they were in reality death traps compared to today's cars. Today's cars have crumble zones to absorb the energy from an impact which keeps you safe. The argument you hear from some people is that those crumble zones make the cars seem flimsy, because they get obliterated in an accident but the reality is older cars didn't absorb energy from a crash nearly as well so that energy was transferred to the passengers instead. So while an older car might be more dent resistant and the body panels survived crashes better, the injuries to the passengers were much worse and the death rates much higher. Aerodynamics factors in as well. Cars are now designed with aero in mind because lighter cars that pass through the air better are more fuel efficient. Since a handful of shapes are the most efficient cars end up looking kinda the same.", "One reason is aerodynamics. Another is simply styles and designs that are “in”- sleek look, black or white design, the appearance generally looks more expensive than it is.", "A lot of it is due to pedestrian safety regulations. These steer cars towards a rounded front end without sharp lines since its safest for any unfortunate pedestrian who is hit.", "Some study a while back found that the average car buyer treated it like an appliance, and were put off by styling that was \"different\" (ie interesting). So the big corporations churn out generic, bland boxes which get lapped up by the tasteless masses", "Back in the 30s and 50s the primary purpose of a cars design was to be functional and look good while things like aerodynamics were of secondary importance and safety were not considered. However today the cars have to meet strict safety requirements and be as aerodynamic as possible. And it is basically only one way to do this. You can not go far away from the current designs before you ruin the fuel economy or fail safety inspections. You can have no sharp edges as this may impale pedestrians and everything have to have a smooth aerodynamic shape. The body have to fit all the crumple zones, airbags and double bumpers in the modern cars while still stay small and smooth. The design requirements is simply not allowing for much esthetic decision making. It should also be noted that it is only the most notable car designs which have remained from the 30s and 50s. Sometimes what is now iconic cars were only made as a handful of prototypes while the cars that were mass produced is rarely remembered today. There are still some absolutely stunning unique car designs made today but they are usually out of reach of most people. So it is not as bad as you might get the impression of, even though it is a lot less variation in style in modern cars then it used to." ], "score": [ 11, 8, 4, 3, 3 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "gta7p1f", "gta7er0", "gta867o", "gta7l0z" ], "text": [ "These are flair stacks. If there is any kind of leakage in these places they need a safe place to vent the gas that is leaked. You can not just vent this gas into the atmosphere because it can be quite poisonous, explosive and a strong greenhouse gas. So the solution is to vent it through a fire where any bad gasses will burn into harmless ones.", "To redirect harmful vapor, fumes & sometimes that is the only thing saving us from a major explosion or further environmental damage.", "I only know the reason for gas rigs, when you pump gas directly from the soil, it usually comes up at a high and fluctuating pressure, kind of a whoopy cushion if we were to exagerate it. The industrial equipment used can break and explode upon reaching critical pressures, some very smart engineers came up with a solution to protect their equipment, the solution implies that a part of the gas is constantly released to stabilize pressure, natural gases being very harmful to the the environment it's better to burn it before releasing it. and thus the giant iconic flame on top of gas rigs.", "In industrial plants, flare stacks are primarily used for burning off flammable gas released by safety valves during unplanned over-pressuring of plant equipment. During plant or partial plant startups and shutdowns, they are also often used for the planned combustion of gases over relatively short periods." ], "score": [ 26, 20, 10, 7 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gtan7qf", "gtan8oj", "gtaot9r" ], "text": [ "Possibly more expensive models or different designs include something there. It’s easier to mass produce the same board for multiple products.", "Usually designers leave test-points for testing probes and un-populated component mount points on the board design just in case there are two likely options of a component being available when the board needs to be populated. The text says what it is for.", "They're just unused pads They could be there from an earlier revision, electrical engineers tend to sprinkle caps into designs because it prevents issues but if you're trying to be cost effective you'll pull off as many as you can, but its probably not worth scrapping all the PCBs you already have to order new ones They could be there because there are two parts that can fit on the main pads but need different supporting parts so leaving the pads open lets you put those little parts down later They could also be for different models that use the same board. Extra USB ports are all the rage, there is likely an upmodel to your motherboard that comes with support for 4 extra USB ports, some of those components could be used to connect those in (0 ohm resistors get used as jumpers) or to support their controller chip The more you can commonize a design the better, having a single PCB in stock and just having different programs on the machine to make the base model and the premium model makes creating a full spectrum of products a lot more straightforward." ], "score": [ 8, 6, 5 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gtazc40", "gtazf35", "gtazdxn", "gtb2463", "gtbgzdk" ], "text": [ "A passenger’s opinion of what constitutes an emergency is superseded by the driver’s opinion.", "> that a passenger could also pull in an emergency? That should *never* happen. In fact it is somewhat dangerous that it would even be an option. The parking brake is for parking, it should never be activated while driving. It is only used to lock a manual transmission vehicle in place, and as a backup for the parking pawl on an automatic transmission vehicle. There is no intention that it be used as some sort of \"emergency stop lever\" for a moving vehicle.", "That brake isn't really meant to be used as an emergency stop. You're actually likely to lose control and crash if you just yank that at speed. It's for holding a vehicle that's already stopped. As for why it's a foot pedal and not a lever in the middle, generally the foot pedal design is seen in vans and trucks where there's either a middle/bench seat, or no middle seat at all. Old American cars also had the pedals a lot because of the big bench seats.", "URL_0 Because dumb passengers pull them as a joke.", "The E-Brake is an emergency brake incase of the hydraulic brake sysrem failing and to secure the vehichal in the same spot while parking. The hydraulic system is powered by a dual piston conected to the brake pedal that forces fluid through steel lines thinner than a pencil to pistons on each wheel. One piston to the front brakes and one to the rear. This came as a safety improvement over a single piston controlling all brakes. Disc brakes are the norm now. The piston clamps on a rotating disk. Drum brakes use an expanding cylinder to press shoes outward inside a drum. Picture a bowl with straight sides. These were on the back aftwr disc brakes became a thing. They had a cable conected to the hand or foot operated lever to engage the brakes should hydro pressure be lost, parking on a hill or parking pawl has been damaged. Parking pawls are just a pin that sticks into a rotaty bit because park is actually another neutral gear. Newer E-Brakes are a drum/disk combo. Center of the disc sets out further and becomes drum as well. Still cable operated. Drum brakes are being phased out on anything smaller than big heavy trucks and even now the conversion has started. But those are controlled by air and use an S-Cam to push shoes out onto the drum. The E-Brake on that system is if there is little or no air the brakes set and wont let you move until the system comes up to pressure. US Army mechanic. Drove a 1963 Chevy C10 with a single cylinder master cylinder and drum brakes on each corner in HS. My 2001 Impala and 2004 Dodge Dakota both had the disc/drum combo on the back." ], "score": [ 36, 19, 6, 4, 3 ], "text_urls": [ [], [], [], [ "https://www.abc.net.au/news/2020-11-10/driver-of-car-that-killed-19yo-libby-ruge-denied-bail/12867680" ], [] ] }

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{ "a_id": [ "gtbcggk", "gtbbzza", "gtbahdv", "gtbebjz" ], "text": [ "I know of three reasons in my area of the US. -The builder or engineer didn't specify which way the door should open, and typically bathroom doors (in my area) always open inward so as not to block a hallway even if there is no hallway there. (This is the same for the toilet stalls normally) -Alot of bathrooms are built to be an emergency shelter and require the door to open inward so that many people can enter the shelter area quickly (an outward opening door is harder because you have to pull the door backwards against the flow of traffic to open it) - People who are disabled or have mobility issues can get into a bathroom faster when they urgently need to obey nature's call, and have 'more time / less urgency’ when leaving to deal with the difficult task of dealing with a door that has a closer mechanism on it. Some doors in my area are starting to have a hook handle that you can open the door with your arm instead of your hand. And I do take note when I observe the door opening outwards because it's more rare. Most builders and engineering has nothing to do with hygiene and everything to do with obeying the local building codes with out spending any extra money. AKA not my problem.", "You've gotten some good responses regarding the safety reasons for why the doors open inward. But you also asked about the cleanliness of the door handles. One solution is to keep your paper towel after drying your hands and use it to touch the handles. Then you can dispose of it outside. Or, if the bathroom doesn't have paper towels, get a tissue or even a bit of toilet paper. If all else fails, open the door, then keep your hands away from your eyes, nostrils and mouth until you can get to some hand sanitizer.", "It is a safety feature that has to do with the hinges. By making the door turn inward, the hinges are on the inside of the stall. Thus, no one could pop the hinges to access the person inside a locked stall.", "for that matter why the hell do stall doors have gaps in them? so you can make friends!?" ], "score": [ 24, 16, 9, 7 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gtbe39v", "gtbe6bb", "gtbftxo" ], "text": [ "The point of the \"bomb squad's\" involvement is to control when it explodes, to shield it if possible, evacuate people, to some extent nullify the damage.", "By doing it intentionally, they can make sure the area is cleared of people. They also sometimes put items over the bomb, to help contain the blast. And they don't necessarily have to use a large initial explosive, to trigger it. So, the cumulative effect may not seem much different than just the bomb they are trying to destroy.", "You’re correct in that it usually ends up being a larger amount of explosive if they determine that a bomb can’t be safely diffused. Usually they’re able to diffuse most devices so that they can be exploded later in the middle of nowhere, were it doesn’t matter if it’s a 1kg bomb or a 10000kg one. But when bomb squads do decide to explode a bomb in-place, they evacuate everyone and place a bunch of shields around the bomb so that the blast doesn’t damage anything or anyone. A decent part of their knowledge is how much/what kind of shielding they need, and how far to evacuate people. For example there was recently a WW2 bomb found in London. It was too large and unstable to safely transport, so they had to explode it in place. Similar bombs have been safely transported. They evacuated everyone, and did set it off with their own device. But when you’re setting off 1000kg’s, adding another two or so is a drop in the bucket. Especially after they’ve added barriers and evacuated everyone in 400m. URL_0" ], "score": [ 19, 4, 3 ], "text_urls": [ [], [], [ "https://www.google.com/amp/s/www.timesofisrael.com/unexploded-1000-kilogram-wwii-bomb-is-detonated-in-england/amp/" ] ] }

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{ "a_id": [ "gtcdm0c", "gtcyob3", "gtcdkq5", "gtcfyfe" ], "text": [ "Commercial jets almost exclusively use turbofan engines, which only push a relatively small amount of air through the center, \"burning\" part of the engine, and generate most of the thrust by spinning a large fan at the front, which pushes most air *around* the center. That air dampens the sound, and also increases efficiency. On a fighter jet, it's turbo*jet* engines all along. These generate all their thrust with the central exhaust, having no bypass flow via a large fan. That gives better top speed and a smaller engine, but increases fuel consumption and noise. So in part, they are louder *because* they must be small.", "Simply put, a jet liner engine with a large bypass, as u/AtomKanister just explained, produces a fairly small amount of hot exhaust. This hot exhaust is ejected from the engine at a fairly low velocity, because most of the energy from it is being used to produce mechanical rotation to spin the fan, that produces cold trust. And there's a relatively small amount of hot gasses to mix with the cold air around it that create turbulence and noise because of the hot and cold gasses mixing. But a fighter jet with a very small bypass (modern fighter jets actually always have a small bypass fan to increase trust, fuel efficiency and loiter times at low speed) in comparrison produces a lot of hot exhaust gasses, and they are ejected at a very high velocity, because the speed of the exhaust gasses being forced out of the rear of the engine is what gives the fighter jet it's trust, and allows it to go so much faster than an aircraft equipped with a high bypass engine. This comparatively greater amount of very hot, very high speed gasses being ejected out of the engine, physically crashing and turbulently mixing with the cold air around it, is what makes these fighter jets so incredibly loud. That, and the fact that they sometimes use afterburner. Which is pretty much litterally a continuous explosion happening in a chamber behind the engine, and propelling it forwards almost like a rocket.", "Airline engines are designed to be as quiet as possible whilst producing the power they need to. There is no requirement to keep the noise down on a fighter jet - they are designed to produce as much power as they can without worrying about the noise.", "In addition to the other replies: Motorcycles are substantially louder than passenger cars. That's because a motorcycle is basically the same type of engine, but with nothing to muffle the sound. It's similar in fighter planes: Most of their weight is the engine itself, everything else is as light as possible to allow good flight characteristics. Passenger planes spend tons of weight on making passengers more comfortable (including limiting noise), plus they have to conform to national regulations on noise pollution." ], "score": [ 13, 4, 3, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gtch1jw" ], "text": [ "There are two systems: - metric - standard (or imperial) Like all things metric, the **metric thread** system is simple and makes intuitive sense. It starts with “M” and has a number after — larger numbers are bigger screws. M1 is tiny. M5 is electronics enclosure sized. M10 is big. The number refers to the *root diameter* or how wide the shaft without the thread is. M1 is 1 mm in root diameter. The thread height and *pitch* (number of threads per length) is proportional to the root diameter. **Standard threads** come in 2 types: coarse and fine. These are variations of the *pitch*. A common size is 1/4-20. The first number is the root diameter in inches (1/4 inch), the second is the pitch (20 threads per inch of length). Now, standard being terrible, sizes under 1/4 or sometimes 1/8 are stated as a “number”. A number 8 screw is 5/32 of an inch in root diameter. So a #10-32 is a screw that has a 3/16th inch root diameter and 32 threads per inch. Don’t ask me where these numbers come from." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "gte3467", "gte39ht", "gte3adm" ], "text": [ "The difference is that road car tires have to work in wet conditions, and slicks are downright dangerous when there's water on the road. Because they can't channel water away from the contact patch, they offer very little grip on a wet road and hydroplane easily. That's also why racing cars don't use slicks on wet tracks.", "Road tires have to account for weather conditions. Racing slicks are designed witout grooves because they only race on dry flat asphalt. Not having grooves causes the tire to heat up faster and grip the asphalt better.", "Because race tracks are clean dry asphalt. The grooves in tires allow water to pass through a bit allowing the parts that stick out to make good contact with the road when it rains. Slick tires in the rain wind up hydroplaning almost instantly making them very dangerous. When cars are raced in the rain they swap out for grooved tires." ], "score": [ 25, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gtf6o9a", "gtgfx50", "gtf5y2e" ], "text": [ "Motorcycles have mufflers with less sound dampening baffles than a full sized car does. Some people also deliberately run shorter exhaust pipes and mufflers to make their exhaust louder.", "Motorcycles aren't inherently louder than cars. Motorcycles with a proper muffler system are quiet, and cars with modified mufflers are loud. I always give respect to people who are considerate riders. However, most of the time it's really about just being loud to impress their buddies. The [excuse that riders use]( URL_0 ) to justify making their mufflers so loud is that their hobby is so dangerous that they are in constant danger of being run over so they have to be as loud as possible. The reality is that [\"loud pipes\" DON'T \"save lives\"]( URL_2 ), because [science]( URL_1 ), but people still use this to justify having a bike that'll wake people up 1/2 a mile away. That's not hyperbole, btw. In communities with concentrations of motorcycles this is common and absolutely does happen. You can see similar behavior with cars except the cars don't have the same \"safety\" deflection they can lean on. They're modified to be as loud as possible for no other reason that some assholes like them loud.", "This is mostly for their safety but some exhaust are also for the obnoxiousness. The louder the exhaust, the easier it is to know if one is next to you while driving." ], "score": [ 10, 5, 4 ], "text_urls": [ [], [ "https://canadamotoguide.com/2016/07/29/the-truth-about-loud-pipes/", "https://www.revzilla.com/common-tread/stop-saying-loud-pipes-save-lives", "https://www.spauldinginjurylaw.com/blog/loud-pipes-saves-lives-myth" ], [] ] }

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{ "a_id": [ "gtgkzan", "gtgotrk" ], "text": [ "You are searching your favorite toy inside a big box that contains both a bunch of toys and smaller boxes. You can't find your toys in this first batch, so you open the first box, and this box contains smaller boxes and toys; your favorite toy isn't there, so you open the first box. This goes on until you find your favorite toy.", "You are sitting in a movie theater somewhere near the back. You want to know which row you're sitting in without having to count all the rows yourself. You can figure this out by asking which row number the row in front of you is sitting in, and add 1 to it. But those people may not know either. Extrapolate this to the people in the first row, whose answer is known for certain without any work. This is the base case. They tell the row behind them the first row's row number, obviously 1. That row takes the answer they're given and adds one to it. This goes on and on until they reach your row and now you know which row you're in. You've delegated the job to other subroutines which were a simpler version of the overall problem. This is basic use of recursion. Things get a bit more gnarly when you use it to solve Sudoku with techniques like [recursive backtracking]( URL_0 )" ], "score": [ 17, 17 ], "text_urls": [ [], [ "https://en.wikipedia.org/wiki/Backtracking" ] ] }

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{ "a_id": [ "gth779w" ], "text": [ "very carefully. the nurse spoon-fed them. eating while lying down is uncomfortable but asphyxiating is a lot worse. there are ports on the sides that allowed nurses to reach in and do necessary tasks like washing. patients used a bedpan to go to the bathroom and the nurses cleaned them afterward. it could be opened up completely when necessary but depending on how bad the patient was they would have difficulty breathing or be completely unable to while it was open. nowadays most people are intubated instead. there are very few iron lungs in use, like in the single digits." ], "score": [ 7 ], "text_urls": [ [] ] }

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{ "a_id": [ "gthoyv4" ], "text": [ "Where the smoke rises isn’t necessarily the location where charges went off. Without a closer view of what went wrong with the detonation/timing here it’s hard to say what happened or why the stack fell over sideways. It’s very possible that it did fall in the direction of the charges that went off. Incomplete demolition can fail to collapse the building and overload the remaining supports elsewhere, and this leads to unexpected failures in unexpected directions when those stressed components finally fail. That failure may be in a few seconds, or they may hold up for a long time. The smokestack in your video was presumably supposed to pancake straight down." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "gthtp4x", "gthtt4w", "gti4hz8", "gthttj6" ], "text": [ "Millions and millions of wheels driving over it. One truck on its own won't do much but compound that by hundreds or thousands of trucks a day, driving over the same stretch of road, over and over. Over time this extra wear on the road will deform the road, leading to cracks and potholes.", "Mechanical engineering major here. So, force is actually the driving variable in stress and strain, but a material can be stressed too much to actually return to its original state. A material that is stressed too much only retains a percentage of its strength even after the force being applied goes away. Too long in these states, and things start to crack or break. So, even if the trucks are only on the road for a second, if we drive tons of heavy trucks over a road, the road will break far quicker than if we drove sedans over the same road. Make sense?", "Pavement engineer here. I’m assuming you’re talking about asphalt pavements; concrete pavements also crack over time but for different reasons. As some said, the reason asphalt cracks over time is not because of the weight of one truck, it’s because of the weight of millions of trucks going over the same spot. Interestingly, when they were testing automated driving vehicles, they discovered the pavement damage happened much faster because the cars followed the *exact* same path as the one in front of it, allowing no normal distribution of weight. Pavement cracks/fails by a combination of several factors. One is truck loading (weight per axle, how far apart those axles are, how many axles on the truck for the weight, total weight of truck.) If you drive an overweight load, you have to get a special permit to do it, because nerds like me have to carefully study the route’s bridges and pavements and ensure that they can handle your load. Factors that damage pavement: Truck loading Weather cycle (extreme heat. Extreme cold. Fluctuations. Freeze/thaw cycles.) All of these make the soils under the pavement heave or compact, and any movement makes the pavement top layer of asphalt crack. Poor construction methods. Thickness of each layer. Thin asphalt cracks faster than thick asphalt... but the layers underneath the asphalt are just as, if not more, important... the aggregate thickness, geosynthetics, subgrade, natural rock, and moisture of all of those things effect how long a pavement will last. A pavement is built for what we think traffic loads will be in 20 years (depending on the state, but this is in general.) If an area sees a sudden population growth, those roads won’t last long. Patching/repair/seams. Any surface crack, even the man made ones, is an invitation to moisture into the pavement levels. Moisture creates issues. Lack of maintenance. Leave a slightly cracked road alone because of money, and in 5 years you have a very expensive road to fix. Slight cracking can be repaired with cheaper methods (overlay, mill and Inlay, micro surface, seal coat, etc) but the ones with deep cracking have to have the asphalt taken out, and sometimes the lower layers out too, to get a good repair. If you’re interested in concrete, I can wax on about that too.", "There's ground underneath the road. If there is a crack that gets filled with water, then every time a truck drives over that crack, it acts like a squeezed sponge, and pushes some of the water out, carrying away a bit of ground with it. That makes your crack even bigger, which lets more water in, which makes more ground run off when driven over, which makes the crack bigger... it's a positive feedback loop, any crack begets bigger cracks which leads to potholes." ], "score": [ 6, 6, 6, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gtm91kk", "gtng5vb" ], "text": [ "You have circuits because you want the electricity to do something specific. You could have just a simple wire connected to a voltage source and current will flow through it but it won't do anything. Current doesn't inherently do anything useful, you need a circuit to make it do what you want.", "One thing that hasn't been clarified so far is the difference between AC and DC current, so let me see if I can break it down in a way that clears up some of the mixed messages. First lets start with direct current. Electrons move from low voltage to high, following the path of least resistance. However one of the things that creates a voltage is electron density, so when you put a lot of electrons through a wire, they build up at the high voltage end, lowering the voltage until it is equal along the wire. A direct current generator or battery uses some means of forcing electrons through it, creating a voltage, but making it so they cannot flow back through. Then when you connect the two terminals with a wire, they flow along the wire back around and then the generator can force them through again. Alternating current flows both directions on the same wire, and as such does not need a return line as long as the endpoint is hooked up to a sufficiently large source of mobile electrons. The electrons are pushed down the wire for a short amount of time, then pulled back up it for a short amount of time. This does create brief buildups and shortages on the other end of the wire, lowering the effective voltage of the power. This is prevented either by running it back along a two wire, or running three wires with equally shifted phases. You could apply this to even more wires if you wanted, but its a lot less benefit for the cost." ], "score": [ 3, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gtpvdqa" ], "text": [ "Because you're stretching one side of the ribbon. This makes it so the ribbon wants to bend towards the short side. When the whole length is like that, the ribbon ends up curly." ], "score": [ 16 ], "text_urls": [ [] ] }

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{ "a_id": [ "gttgdi3", "gttho2d" ], "text": [ "Assuming you're in an automatic transmission, the engine and wheels aren't completely disconnected when you apply your brake - there's a mechanism that allows the engine to continue without stalling from the wheels not turning. That said, when you release the brake, the wheels will naturally attempt to roll forward at engine idle speeds. However, if you're facing uphill at all, it can stop the car from rolling forward. If you were to repeat this in the same car on level ground over and over again, it should pretty much always start moving forward when you release the brake.", "You braking stops the car in its place. You then put it into park. There is some play in your drivetrain from inside the transmission to the wheels, and where that parking pin stops the transmission from moving may not be directly lining up with what it catches on. So if you have gravity trying to force you downhill, taking your foot off the brake allows the drivetrain components to move a little until they take up the slack in the system and then use the resistance of the transmission to hold the car." ], "score": [ 13, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gtupcrv", "gtuquwo", "gtuq4ib", "gtwdld2", "gtuuikb" ], "text": [ "There are only a small amount of byproducts from nuclear reactors. These small amounts are still dangerously radioactive and fall in one of three categories: low, medium and high level waste, where low level is less than 5, medium level is between 5 and 100 and high level is beyond 100 years. These years indicate when a byproduct is no longer dangerously radioactive. Short and medium level waste can be stored in containers lined with protective material, which are stored in a warehouse somewhere. Some companies have an \"above ground\" mound of the stuff, where the entire mound is lined with a protective barrier. High level waste is not only highly radioactive, but also extremely hot. Therefore, these materials need to be stored in a cold, controlled environment, until it falls within the parameters of low or medium levels, after which it can join it's brethren in containers or in a mound. After the stuff has lost radioactivity, it can be disposed of or recycled for further use.", "Tough issue. First one has to understand half life. Half life is the amount of time half of a sample takes to decay. Say something has a half life of 1 day. After one day half of the material would decay, another day and half of tje half would decay, etc. Two points should stand out. The first is that isotopes with short half lives are more dangerous because they are decaying faster but become less harmful faster. Isotopes like U238 have a half life of 4 billion years. The stuff is radioactive forever but most people are surprised to find that the material is not dangerous because the decay rate is so slow. This means that most radioactive waste has to he handled differently early than it has to be handled later. Early on, the waste is high in materials that have a short half life. These are often stored on site under water(for cooling and containment) for a few years. After this time has passed and the material is considered low level waste it needs to be transferred to storage for a significant amount of time, maybe thousands of years. One of the best ideas in my opinion is ceramic encapsulation. The idea is that you pack the waste in a clay like material that does not allow water to penetrate and throw the stuff back in a nuclear mine.", "When spent fuel is taken out of the reactor, it's generating quite a bit of heat, so to keep it from melting it needs to be stored in a pool of water for a few years. But after that it's cooled down enough that, left to itself, there isn't much that will happen to it. I mean, it's a ceramic material. The medium-term solution is to store in large steel & concrete canisters; that's good enough for decades. And the volume isn't that big. If the USA got all its electricity from nuclear, at the density of this storage area, URL_0 one square mile would suffice for the next 40 years. The US has many square miles of desert. The long-term solution is some variation of 'dig a deep hole in the ground, put it in, fill the hole'. We know this will work because it worked in the distant past. Natural reactors ran, immersed in moving ground water *with no containment at all* for the fission products. And the result was ... nothing much. > Most of the non-volatile fission products and actinides have only moved centimeters in the veins during the last 2 billion years.[4] Studies have suggested this as a useful natural analogue for nuclear waste disposal.[9] URL_1", "Nuclear energy, contrary to popular belief, is remarkably clean, efficient, and safe. Accidents are rare, the only danger lies in disposing of waste. Typically this is done by storing the radioactive materials in deep indoor cooling pools for a while (5-10 years-ish) After this there isn’t much that can be done. Radioactive isotopes irradiate their surroundings ad Infinitum, and the only real option at the moment is to isolate them. One such option is to stick them at the bottom of an abandoned salt mine and fill it with concrete. It really doesn’t matter where you put it, the goal is to limit contact with dangerous materials. This means we need to take into account future generations; some isotopes have a half-life (the rate at which a radioisotope activity will reduce by half) of 150,000+ years, which means we would need to warn people about them, far into the future. Examples of some ideas are on this wiki page: URL_0 (They’re really cool ideas, like constructing a giant forest of black concrete spikes, and big stone obelisks in many languages warning of what lies there - here’s a really good video touching on the topic): [19:50-23:10] URL_1 The safest way is one in which nobody ever comes across the damn stuff ever again. We don’t know how foolish future generations will be, perhaps the big obelisks and black spikes, etc will attract even more visitors. I mean, the pyramids did a fat load of good.", "Just stick in a container and leave it here. I know it seem weird, but that very true. People freak out because some of those byproduct last thousands of years, but that doesn't make them that dangerous. Isotope either decay fast and strong, or slow and weak. You won't have an byproduct lasting millions of years while blasting high level radiation. So if you make a safe container, you can just leave it next to the nuclear reactor where it can be monitored. It won't last forever, but it's gonna be safe and since we can moniter it we can know when we gonna need to make another containement. Having it next to the reactor also limit the issues of transporting nuclear waste accross the country to an underground facilities, it's cheaper and make it possible to recover the waste if we ever want to reprocess it. We can also make underground permanent storage facilities, but it's debatable if that really the better option. What is true is that no matter what way we do it, nuclear waste is only a tiny amount. We reject in the environment way more dangerous waste chemical and nuclear on a day to day basis without a care in the world. The issues with nuclear waste is that it's concentrated, which make it way easier to deal with, but attract way more attention. Here some good video on the subject, and a video on reprocessing. [ URL_1 ]( URL_1 ) [ URL_0 ]( URL_0 )" ], "score": [ 10, 4, 3, 3, 3 ], "text_urls": [ [], [], [ "https://www.connyankee.com/html/about_cy.html", "https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor" ], [ "https://en.m.wikipedia.org/wiki/Long-time_nuclear_waste_warning_messages", "https://youtu.be/7MOKTU9tCbw" ], [ "https://www.youtube.com/watch?v=UA5sxV5b5b4", "https://www.youtube.com/watch?v=KnxksKmJa6U" ] ] }

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{ "a_id": [ "gtx2roh", "gtx5izl" ], "text": [ "Each individual house has an electric meter that measures how much electrical energy is going into just that one house. And then some guy from the electric company comes to each house once a month to read the meters and note how much energy each house is using. Or more often nowadays a “smart meter” can send that data to the electric company remotely.", "Consumers consume and the power distribution company logs that Producers produce and the power distribution company logs that There are going to be a couple fast response plants that are tasked with keeping the grid stable but if you've selected a green energy producer then they just produce what they can when they can. At the end of the month the power distribution company checks the numbers and says \"Your customers bought 1.2 MWh of power, you only generated 1.1 MWh, you need to pay another generating company for 0.1 MWh of power\" Its too clunky to attempt in real time especially since you can't really control how much power you get from your solar panels and wind turbines, so its settled either monthly or quarterly and the production companies have to buy/sell generation credits to make it line up, but since you generally pay a bit more to the green provider, they can buy from the guy running on oil and still make a bit of a profit." ], "score": [ 8, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gtzu06q" ], "text": [ "A properly designed sewer maintains enough velocity in the pipes to move stuff along. For the same reason that the water can wash the sand down your shower drain, it should happily get washed along the pipes too. At most sewage treatment plants, one of the first things after the big screens (to remove bulk trash) is a settling pond...and sand it really easy to remove because it's dense and so it sinks fast. It plummets to the bottom of the settling pond where big rotating rakes slowly push it into scoops or augers that pull it out (along with any other heavier-than-water material). Sand's so good at this that there are some water treatment processes (\"ballasted flocculation\") that basically glue lighter contaminants to sand to help them settle faster. That crap (pun partly intended) goes to landfill or into a big thing called a \"digester\" to allow bacteria to break down all the fun stuff into compost. The sand is just along for the ride." ], "score": [ 22 ], "text_urls": [ [] ] }

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{ "a_id": [ "gu0379a" ], "text": [ "The time spent on dialysis relies on the surface area of the filtering media. A tiny one may not have a useful amount of filtering capability." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "gu29qzz", "gu21xfj" ], "text": [ "Former aircraft mechanic whos had the pleasure of scraping birds off planes here. Bird strikes 99.9% of the time arent a big deal. You only hear about the ones that cause a lot of damage (and not even all of those) or cause an incident. Birds are generally small and fleshy, where planes are large and quite sturdy. An impact from a bird rarely causes any damage on an airliner other than a difficult to remove blood smear. Engines will also ingest a bird pretty well. Once they hit the fan blades they usually deflect to the outer part of the fan case where they then pass through the empty bypass section without any more damage other than the initial fan blade. We do have to examine the engine, because if part of the bird does end up in the core where combustion happens, the smaller blades can take damage that would require repairs. The reason we don't put a fence or something there is cost. Most birds dont do much damage. If we put a barrier there we change the airflow, add weight, increase drag, and most importantly introduce a new spot for ice to form. Ice would further reduce airflow, increase the chance of something being ingested, so they'd have to heat the fence or grate which would further increase cost and weight. Its just not a cost saving measure. Better to replace a few parts of an engine once or twice in its life than add another piece of expensive equipment. But for fun... [Heres what a condor or vulture did to one of my old company planes. (NSFW)]( URL_0 )", "A mere grill isn't going to help much at the speed a jet is going. Anything that could survive would be really heavy. Jet engines on planes don't encounter birds and other things often enough for the weight to be worth it. Jet engines on planes work better when they get unblocked air coming (or at least for the speed airliners go, for even faster ones they have a cone so the air doesn't blow out the engine). Helicopter jet engines on the other hand encounter birds and stuff often enough, and aren't going forward fast enough for the air coming in to be much use. [So they quite often have something guarding the intakes]( URL_0 ) It's a heck of a lot sturdier than a mere grill." ], "score": [ 40, 5 ], "text_urls": [ [ "https://imgur.com/gallery/m6J6Hhy" ], [ "https://www.picfair.com/pics/02559401-helicopter-rotor-blades-and-engine-air-intakes" ] ] }

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{ "a_id": [ "gu52jvs", "gu52kmm" ], "text": [ "The core of the XNOR gate is the XOR gate which implements the xor function. And you can extend this to three inputs by doing \"a xor b xor c\" because the order does not matter. What this essentially does is to output true whenever an odd number of inputs are true and false otherwise. The XNOR gate therefore outputs a 1 whenever an even number of inputs are 1.", "You can think of the 2 input combo as being true when the number of true inputs is even. With zero or two 1's, the result is 1 Expanding to 3 inputs follows the same thing, if there are zero or two 1's, the result is 1, if there are 1 or 3 1's, the result is 0" ], "score": [ 6, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gu6ja8y", "gu6q9x4" ], "text": [ "It is a manual effect. The simplest way I can describe it is the strap is pulling past a ball in a cone shaped cavity. If you pull slowly the strap just rolls the ball but if you pull it fast the ball gets pulled up and wedges against the strap which stops it. Edit - found it explained way better here: URL_0", "It’s mechanical, in most vehicles. a piece of the mechanism swings out and jams the seatbelt mechanism when it is spins too fast too quickly. Quite a smart idea." ], "score": [ 22, 5 ], "text_urls": [ [ "https://mechanics.stackexchange.com/questions/37669/how-do-seat-belts-function" ], [] ] }

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{ "a_id": [ "gu7mtxn", "gu7mz2d" ], "text": [ "They build a “detour” for the water while they’re working on the dam. Then, they drop in landfill in the main river at the entrance and exit of that detour, and drain the water remaining between the two landfills. Then they build the dam in the now dry section of river and remove the land fill and the detour when done. Sometimes they leave the detour.", "One of the first steps in the process is to re-route the water away from where the dam will be built. Then when the dam is ready the water is routed back to it's original path. It takes a lot of work to move a river but, depending on the surrounding geography, it can be a straightforward process of earth moving." ], "score": [ 30, 5 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gu9ac6y", "gu9h7rs", "gu99gl4", "gu9f609" ], "text": [ "It is an electromagnet with a rod in it. When you apply power to the electromagnet it will move the rod which usually does something useful. For example actuating an electrical switch or a valve. It is a quite useful thing on machines as it allows you to control fairly big controls using electrical control signals which means you can easily automate the machines.", "It is an switch controlled by electric current that most often turns a valve on and off. This can be for liquid or gas. You have a coil of wire that when an electric current is applied to it becomes a magnet (electromagnet) which then interacts with the steel plunger in the valve sucking it up into the 'on' or 'open' state allowing the liquid or gas through the valve. Depending on the situation, I prefer an electrically actuated ball valves for water applications because they are much more reliable than those 3/4\" sprinkler solenoids that seem to burn up in a few weeks to a few months of use. Bonus explanation of the applications between a relay, solenoid, and a contact switch with an automotive focus: [ URL_0 ]( URL_0 )", "It’s a coil of insulated wire that creates a magnetic field when a current is passed through it.", "In your setting a solenoid is going to function similar to a relay. A solenoid valve for example is going to take a signal from the PLC and use it to open a pressurized air valve and send it to a pneumatic cylinder. The electrical portion and pneumatic valve portion come as a single unit." ], "score": [ 27, 4, 3, 3 ], "text_urls": [ [], [ "https://info.waytekwire.com/blog/relays-vs-solenoids-vs-contactors-a-comparison" ], [], [] ] }

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{ "a_id": [ "gua8vky", "gua73yj", "guajhvv" ], "text": [ "A dynamometer is a torque meter and speedometer in one. It is attached to the wheel of a car while the car is suspended in the air. Then, the car starts to spin the wheel. The dynamometer measures the torque and the speed. Finally, power = torque * speed", "How is it measured today? They measure how much power the engine puts out in kW, then convert it into the archaic unit of \"horsepower\". How was it first measured? Apparently they lifted weights with a specific speed to a specific height. For each 33000 American Pounds lifted by 1 foot of height over the timespan of one minute, the car was declared to have 1 horsepower. I assume that is what their \"standard horse\" was capable of lifting, hence the strange numbers. Nowadays a horsepower is simply defined as 746 Nm/s or 746 W", "You don't measure horsepower. You measure torque, the turning force on the crank shaft. Then you put that into an equation with current rotations per minute the engine is running to get horsepower: horsepower = torque x rpm/5252 So all you need is something to measure torque and something to measure the rpm of the engine, and you get horsepower. This is why horsepower on a car is a curve, with it only achieving that highest horsepower for a small part of it. Now that would be shaft horsepower. To measure at the wheels you put the car on a dynamometer, which is like a treadmill for cars, then measure the torque the tires apply to the rollers while the car is at various rpms. This will always be lower than shaft horsepower due to power losses in the transmission and the rest of the drivetrain." ], "score": [ 51, 19, 13 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gua70ka", "gua7maq" ], "text": [ "A decent amount of the time they're made on the same molds and dies as the OEM parts. Some factory in China takes an order for 20,000 headlights from Ford, makes the tooling, makes the order, then files off the logos on the mold and runs off another 50,000 until the mold wears out. Most of the big OEMs aren't really interested in pursuing that sort of thing because it's just seen as the cost of doing business in China.", "They can be made from old molds if such are available. However the most common technique is to buy an OEM headlight and then make your own molds from that casting. These molds can be made to be almost as good as OEM or even better if they take some care in fixing all the casting errors during the transfers. The casting errors you notice might actually just be from them using cheaper materials for their molds so they wear out faster or just because they have not taken as much time to clean up the casting as the OEM parts have." ], "score": [ 50, 9 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "guc2xec", "guc1bp3", "guc2jkb" ], "text": [ "What you're referring to is called a \"delta wing\". There are pluses and minus, but the big reason you don't see much of it is that they are best for aircraft which travel supersonic. That is--really fucking fast-- faster than pretty much all aircraft except military fighters and (some) bombers. If you aren't traveling that fast, the traditional delta wing is actually generally worse than a traditional \"swept wing\" (the commercial airliner in your picture) as the delta wing causes a lot more drag in slower flight compared to a regualr swept wing. The delta wing makes a lot of trade offs in order to be as effective and as fast as possible at supersonic speeds, but if those speeds are not what you're doing most of your flight, then it sucks balls. Also note, that that a delta wing aircraft is not the same as a [\"flying wing\" aircraft, like the B-2]( URL_0 ). The flying wing style is completely different entire plane, not just the wing structure, its a entirely new way to construct an aircraft. These aircraft are incredibly lightweight and fuel efficient, but are extremely difficult to actually fly and as of yet, aren't really meant to fly at supersonic speeds. Your immediate next question is \"why don't we have more flying wings for stuff like commercial flights then?\" Well, remember how I said they're really hard to control? They are, it might not be as safe, and it might be very difficult to build an effective flying wing design with room for tons of passengers to be competitive with our swept wing designs. More advanced commercial designs have looked at things like [blended body aircraft designs]( URL_1 ), but these have issues in that while there are good savings to this configuration, its really only applicable to long-haul flights that can take advantage of the style better. For shorter routes, they're actually a bit heavy compared to a regualr plane", "Some are it’s called a delta wing configuration, most fighters have delta wings. Most wing types are dependent upon the aircraft intentions. More surface area means more control area for the aircraft to maneuver but more surface area the more drag , so most aircraft with delta wings are usually faster moving and highly maneuverable. Most commercial jets used a swept back wing configuration to increase efficiency since they are used to just shuttle people and cargo to keep cost down while flying and less material for manufacturing. Hope this helps", "In general, airplanes aren't hurting on lift. They generate as much as they need. What they *do* worry about is *efficiency*. How much lift do they generate *when compared to how much drag they generate*. It so happens that longer wings tend to be less efficient, to a point. So for higher efficiency, you want wings that aren't as long forward-backward (this length is known as the chord)." ], "score": [ 27, 23, 15 ], "text_urls": [ [ "https://imgur.com/HROfNh7", "https://imgur.com/g1yn4dw" ], [], [] ] }

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{ "a_id": [ "gudai5k" ], "text": [ "Kirchoffs Laws are two different formulas that describe how electrical current and voltage distribute in a network. Through analogies you can apply them to other forms of flow networks too. They are quite simple: The sum of currents going in and out of a node is always 0. That simply means electrons don't gather somewhere, what flows in must come out The sum of all voltages in a loop is always zero. This is easy to understand when you compare voltages to climbs in mountains. When you wander a circle and end up where you started all height differences you encountered must sum up to zero. Note that this applies only when you don't have electrical and magnetical fields messing with your network." ], "score": [ 10 ], "text_urls": [ [] ] }

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{ "a_id": [ "gudj20f", "gudm03c", "gudl5ci", "gudnjmg" ], "text": [ "The control is just a cheap mixer valve that changes the ratio between your hot water and cold water. Your hot water is whatever temperature the water heater is set at, and your cold water is whatever temperature the underground pipes are delivering at - you may notice the delivery temperature increases as summer approaches. The manufacturer doesn’t know what temperatures you’ll be feeding into the mixer, so they can’t make any attempts to optimize it.", "It's true that the valve can be cheap and etc., but a fancy, well-engineered valve is likely to also display this effect. There's an additional and important part of the explanation. The mix that one consumer wants to run verses another could be massively different. Here in Montana, the temperature of the cold water, which has been 6ft below the surface to avoid freezing, is about 45°F, and could be lower in places farther north or east in the early spring. In Florida or southern Texas, your cold water temperature could easily be 75°F or higher in the late summer, especially if the water main runs under asphalt. Hot water has an even wider range. You're supposed to have your tank-based water heater set to 135°F. However, a tankless water heater for showering/bathroom use could work just fine at 108°F (that's what mine is set to). On the other hand, we also have solar hot water, and it can exceed 180°F after a series of sunny days in the summer. So you need to be able to mix everything from 80/180 (lots of cold, very little hot) all the way to 40/108 (almost all hot) and everything in between. Meanwhile, the bodies of people in Alaska and Texas all run at about 98.6°F, so you can really tell the difference between 104°F vs 106°F vs 108°F shower water (my personal values for too cold/just right/too hot). The temperature of the water even changes quite noticeably between the shower head and the floor. So TL;DR - the range of input temperatures the valve has to accept is very wide, and the range of acceptible temperatures for humans is very narrow.", "It's an issue with temperature perception, not an engineering question. Your body doesn't have thermometer really, saying \"this is this hot and that is that hot.\" What it does is say \"this is tolerable\" and \"that is not.\" It does this because it is trying to protect your normal temperature. So where a thermometer would simply say \"88F. 89F. 90F,\" and so on as you slowly increase the temperature in the shower, your body says \"good, slightly less good, slightly less good, TOO HOT TOO HOT I'M LITERALLY DYING.\" By way of analogy: you don't have the ability to gauge weight when you pick something up. You only know \"liftable, difficult, and too heavy.\" The difference between difficult and too heavy can literally be a half kilogram but the way it feels is night and day.", "Well new showers have a mixer valve (USA atleast) that will not let you get the water hotter then say 110°F or any colder then 60°F so still a little hot/cold range but nothing like those showers from the 70s the one where when you start a shower then flush the toilet your boiled alive." ], "score": [ 150, 24, 20, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gugn61q", "gugl8de", "gugola1" ], "text": [ "Sound is air shaking. The shaking air causes a stretched thing to shake. The stretched thing has a magnet strapped to it, it goes up and down. Next to the magnet is a wire, the magnet moving causes electricity to move in the wire. The computer records the electricity moving. To play back. The computer sends the same electricity down a wire. The wire is coiled so it acts like a magnet if there's electricity in it. It pulls another magnet, causing it to move like the original magnet. The magnet is also strapped to a stretched thing. The stretched thing than shakes the air the same way causing the same sound. u/ddd615. Same thing, except it moves a needle, the needle scratches a groove. Later a different needle is put in the same groove causing it to shake the same way.", "I’m sure someone way smarter than me will chime in here, but I’ll give it a shot. First the sound card in the computer uses a Digital to Analog Converter to convert the digital signal of 1s and 0s to an analog wave. Then this gets sent to the speakers that use magnets to move the speaker coil, given the amplitude of the analog signal, which in turn moves the speaker cone. The different frequencies of the waveform vibrate the speaker cone which in turn vibrates your ear drum.", "A microphone is like a little speaker with a [diaphragm]( URL_0 ) that moves back and forth as the sound waves hit it. The motion moves a magnet, which causes current to pass down a wire, creating electric signals that can be measured. These signals look and act basically the same as a cross section of the sound waves that produced them, except they're now in a wire. An analog-to-digital converter (ADC) converts the electric signals into 1's and 0's by taking little 'snapshots' of the signal as it passes through the wire. How fast the ADC takes snapshots of the signal is called the sample rate, measured in samples per second, or Hz. Audio is usually recorded at 44,100 Hz, or 44,100 samples *per second*. It can then store the recorded audio as an ordered list of samples with a corresponding sample rate. If you divide the total number of samples by the sample rate, you get the length of the recording in seconds. In order to turn these numbers back into sound, you need a digital-to-analog converter (DAC). The DAC uses a method called *interpolation* to literally connect-the-dots between each sample. It strings together all the samples at the same rate that the sample rate gives, and fills in the gaps between samples to make the output continuous. Theres a bunch of different ways to do this. (In total jargon terms, a simple way is this: you can output the values as pulse-width-modulation and smooth using an analog low-pass filter) The output of the DAC is virtually the same as the input originally was from the microphone. This signal then has to go into an amplifier which just adds more power to it. With more power, you can move more stuff. This powered signal is then sent to the speaker wire. The current of the signal goes through a metal coil attached to the speaker cone which sits next to a magnet. The current through the coil causes it to repel or attract the magnet, forcing the cone to move back and forth, pushing the air at different speeds, very quickly. This creates sound waves that reach your ear." ], "score": [ 6, 4, 3 ], "text_urls": [ [], [], [ "https://lh3.googleusercontent.com/proxy/WBgbh_iD5ap8URnpupIHkqvlNMhjGs0xurRbRnjXnV-VIV0GyLz6BbBN898W4WQlP5dxrG1JjMlaF4u5v2r18vfXIxf65tlJPLc7KQKsjUsu_xys_aTbzQtGEu9Qg_45j-GUB2Z8IxJ-uIuV" ] ] }

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{ "a_id": [ "gugnsdd", "gugnh12" ], "text": [ "You are right that pumps, although they existed, were quite expensive to build and operate. But you do not need pumps as the water is already at a higher elevation. They would build plumbing sytsems from lakes and rivers in the mountains around the city. This water would be under pressure and with some speed as it entered the city so it would have enough energy to flow out the fountain. The plumbing systems were water and pressure tight because it was lined with lead, plumbum, hence the name. The first fountains were simple water spouts just intended to give the citizens an easy place to collect water. Even plumbing was expensive so they would usually have just a single fountain where everyone collected their water. But over time they installed more fountains and made these fountains even more extravogant.", "Essentially, the only thing you would need is pressure to make a fountain work, one thing that exerts plenty of pressure is gravity. So having a water source (Similar to the water towers you see on top of Hotels/apartments) above the location you want to deliver water to will supply enough pressure to cause water to have some inertia." ], "score": [ 13, 7 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "guibqyb", "guid5l4" ], "text": [ "When you melt certain alloys down the metals will separate due to differences in density. Pour the lighter metal off the top. Wash, rinse, repeat and you eventually separate. There are chemical methods as well that can be used to separate materials. Put the items into a solvent that is only a solvent for one of the elements. The metal it can dissolve is dissolved, the other settles in the bottom. Separate solid from liquid, then take the liquid with the dissolved metal and add another chemical so it can no longer hold the metal. Take the metal sediment out.", "It usually isn't possible to make pure metal out of recycled scrap, but that's OK because most metals are only rarely used in their pure form. In the steel industry, scrap steel comes in a variety of different types depending on where it came from (crushed cars, old pipes/structural steel, the stuff you get when you wave a magnet over municipal trash, etc.). When making a batch of steel from scrap, the people in the steel mill mix together different scrap types based on what impurities they expect there to be in each type. Once the scrap has been melted some impurities can be removed, either because they boil off at steelmaking temperatures (lead, tin) or through chemical reactions during the steelmaking process (sulfur, phosphorus, carbon). Finally there are some impurities which are pretty much impossible to remove, such as copper, so all you can do is dilute them with metal that you know has little or none of that impurity." ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gujztor", "gujzqa3", "gujzcbo", "gujzgsj" ], "text": [ "It cost about $10,000 to put a single kilogram of anything into orbit. Mainly because of the massive amounts of fuel needed (which causes pollution) The US produces more than 2,000,000 kilograms of nuclear waste every year. For $20 billion dollars, you could probably make a really kick ass waste storage place on earth, and it could probably hold several years worth of nuclear waste. Oh and if anything goes wrong with the rocket, either: 1. You contaminate a massive area. 2. You wrapped the nuclear stuff in so much protection it can survive a rocket mishap, meaning it's many many kilograms of stuff that aren't nuclear waste you have to pay $10k per kilo to put into orbit.", "Also, if there were ever an explosion from strapping rockets to large quantities of nuclear waste an accidental explosion would be beyond horrific.", "Because adding that much velocity to nuclear waste would take more energy than the reactors provided in which the waste was produced.", "It’s significantly more expensive to eject it into space than to bury it. Though the idea of a “space elevator” that would allow us to dispose of it in space is popular among futurists" ], "score": [ 11, 8, 7, 4 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gul98u1", "gul54nn" ], "text": [ "The internal circuitry runs on 3 V, the 5 V you may have seen would typically be referring to the input voltage from the USB port on the back (USB as a standard carries 5 V along its power lines), it either drops the voltage or its electronics can run on 3-5 V (which isn’t uncommon in the world of digital electronics).", "I'm not exactly sure how Xbox controllers do it but there can be a range of ways to solve this. First you could build a fixed ratio DC/DC converter to turn the 3V into 5V. It could also just simply be built in a way that it works in a range from 3V to 5V wich isn't hard when there aren't a lot of internal electronics" ], "score": [ 5, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gumnbuc" ], "text": [ "Potentially lots of different reasons. Could be the ground wasn't suitable for foundations that met up to date building regulations, and they had to replace the substrate with better quality soil / hardcore etc. They might also have had to dig down to install underground pipes or services, then refilled with soil that had been levelled and compacted to make suitable foundations in. It's also possible the ground was contaminated by pollution, and it was removed and treated before being replaced, and new foundations dug. There could even just have been a mistake or change of plans halfway through. Civil Engineering and groundworks construction are pretty complex topics, and the work is expensive, so there is probably a good reason for it, or they wouldn't do it." ], "score": [ 15 ], "text_urls": [ [] ] }

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{ "a_id": [ "gunp1ck" ], "text": [ "Leech fields (or drainage beds) carry water and microorganisms from a septic tank for percolation and evaporation. The exothermic process of decomposition of waste creates heat that keeps the immediate area around the drainage pipes relatively unfrozen, allowing water to percolate into surrounding soil. Also, any water that escapes the pipe and is subsequently frozen may be converted to water vapour through sublimation" ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "guos7aw", "guosjio", "guqtpae" ], "text": [ "Electrons can jump from atom to atom in conductive wires. If you imagine marbles filling a marble-sized pipe, pushing a marble into one end of the pipe will cause one to pop out the other side. The pressure (voltage) I push the marbles with determines the exit pressure. The rate at which I introduce marbles determines the mass flow (charge flow/current) of marbles per second.", "So you have a property of matter called \"charge\". You can have positive charge or negative charge. Negative charge carriers (electrons) can move easily through conductive materials, mostly metals. That movement of those electrons is known as electricity. One of the properties of a moving charge is that you can \"induce\" magnetic fields, and if you place that in proximity of a magnet, you can cause motion just through moving charges. That's an electric motor.", "Electricity is like a river, but instead of water it flows electrons. This flow of electrons can do work, just like a watermill with a waterwheel can grind wheat or saw wood. A larger number of electrons moving slowly can do just as much work as small number of electrons that move very fast. Just like water - if it's a lot it can do a lot of work. Current of water is similar to electric current in that regard. Small but fast current can be the same as large but slower current. What makes river flow faster? A steep riverbed or a large body of water pressing from the river basin can make river go very fast. In waterfalls water falls the fastest near the bottom, because it had a lot of height to get accelerated. So one way of saying that is that the water had a lot of potential to do work when it was high. Similar to that there is electrical potential for electrons to do a lot of work. The potential difference is what we call voltage. If there is a lot of pressure behind electrons they can reach large speed and therefore do a lot of work. When we say there's 9 volts in a battery it doesn't mean that the river of electrons is already flowing - it means that there's that much potential for them to flow." ], "score": [ 41, 7, 4 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gusvr6u" ], "text": [ "Solar panel efficiency is generally around 15-20%, while for comparison Nuclear power and Coal power is around 30%, and hydro power is around 90%. Individual solar cells can be much higher in efficiency, but cost factors and loses in the panel bring that down. But efficiency is only part of the equation. Solar panels require a great deal of space to generate a significant amount of power, while traditional power stations are much much smaller in terms of land area. Solar Panels have a minimal environmental impact though. Nuclear power meanwhile is the most energy dense, you get the most power out of a small amount of fuel. By orders of magnitude compared to other power generation types." ], "score": [ 6 ], "text_urls": [ [] ] }

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{ "a_id": [ "guvkl0g", "guvk0q8", "guvogfq", "guvjzhu", "guvjxca" ], "text": [ "Appliances that draw large amounts of current (like a microwave) can potentially exceed the rated current of a wall outlet if there are multiple other things plugged into the outlet. They might also draw more current than a (cheap) extension cord or power strip is rated for. Mostly, though, they just don't want you using an extension cord or power strip because it'll encourage you to plug more things into the outlet. If you have an extension cord that is rated 15A or higher, then you should be able to plug just about any 120VAC household appliance into it without an issue (just don't leave a long extension cord coiled up while you use it- they can overheat that way).", "A large current being carried over thin-guage wiring means a large resistance and therefore energy lost as heat due to resistance. A thin extension cord heating up when the appliance is in use is potentially a fire hazard.", "Because they know most people don't know how to check the amperage capacity of their extension cord and will use one that is too thin. You can often ignore this warning if you know how to select the right extension cord. But not my fault if you burn your house down.", "If they consume a lot of power, they generate a lot of heat in the wires they are connected to. The wires in your socket are thick enough to handle the heat. Extension cords less so becuase they are thinner etc and they could catch fire.", "Using an extension cord causes more heat in the chord overall. The longer the cord, more heat. Some extension cords cannot handle the amps it takes to allow voltage to flow to the device. Extension cords are trip hazards, and can be fire hazards depending on what setup your using. The instructions or rules may be a bit overkill sometimes, but it's due to the one in ten thousand chance that injury or death that has resulted in such manners." ], "score": [ 44, 39, 6, 5, 5 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "guzj8wi", "guzphuf" ], "text": [ "\"Lifetime\" pads don't last any longer than \"regular\" pads, the \"Lifetime warranty\" just means you get a free set once the first ones wear out. Lifetimes are more expensive up front but can pay off over time if you've got a lead foot. It's like a buffet. The business is counting on most folks not eating/using as much, and not getting their money's worth, to offset the cost of the people that do take advantage of the policy.", "Lifetime pads are just a gimmick that shops use to make you go back to them every time you need them changed. They \"give\" you a new set of pads but charge you for labor to install them, labor is where they make all their money anyways. Now you are paying more up front, and saying you will go back to them for the whole time you own the vehicle." ], "score": [ 11, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gv1l2z1", "gv17uze", "gv1b13j", "gv34vjo", "gv24r9w" ], "text": [ "The cables are not that tight. They're more like an extension cord lying across the yard. Lots of slack. In fact, if they have to do repairs, they snag the cable with hooks and haul it to the surface. There's plenty of slack.", "Plate tectonics aren't really an issue because they don't move *that* much. At most it is 10 centimeters a year, and usually much less than that. Leaving the cable with a bit of slack to slide across the ocean floor is more than enough to deal with plate tectonics. As for oceanic ridges, they aren't strung from one to another like suspended power lines. They are laid in the surface of the ocean floor; if the surface rises up as with a ridge then the cable follows it up, and then back down. Think a mountain road, not a taught string.", "It's the sharks you need to look out for. URL_0", "Others covered it well, but I'll add a point about them breaking. **They do.** There are a number of reasons why the cables might break. In Perth, Australia I used to play on a server in Singapore, and there was an undersea cable from Perth to Singapore, so ping times were pretty good. One day I logged on to find that ping times were about 7 times more than average. A captain had dropped an anchor on it. It took 3 months to fix. Before then, there was talk about the cable being old and not having the bandwidth it used to have. It would also loose data for a few hour-long periods every month. Some of its outer protective layers had allowed water to leak in or something. That's just one cable over a 4 year time period, and I'm sure there's more I don't know that happened. Often they lay a few cables at a time to provide redundancy against this kind of thing. These cables get damaged and broken all the time for a whole manner of different reasons. There are teams of specialists who's entire job is to keep these cables functioning, and they have to carefully plan for these issues and many more. It's very much a continued maintenance effort, and not a set-and-forget thing. Especially given the low initial cost of the cable, ongoing maintenance is a large part of the budget.", "Basically the cables are carefully laid in routes that avoid potential trouble areas like mid ocean ridges (ocean crust spreading), known fault zones, subduction zones (ocean crust colliding) and deep trenches. Also, the cables have lots of slack in them so they are not stretched tight like power lines. They are more like garden hoses- loops and meandering paths across the lawn instead of stretched tight." ], "score": [ 49, 35, 34, 7, 6 ], "text_urls": [ [], [], [ "https://slate.com/technology/2014/08/shark-attacks-threaten-google-s-undersea-internet-cables-video.html" ], [], [] ] }

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{ "a_id": [ "gv1lvqc" ], "text": [ "There are two separate concepts here. The ground in a circuit is what you define your voltage as a a reference to, voltages are just differences in potential so you can pick anything to be your 0 point, the ground is what you define as 0. Then the ground pin is a safety device, it’s connected to the case of the electronic device so that if there is a fault which would lead to the device being electrified the electricity flows through the ground pin rather than through the body of the next person to touch it. The ground in general is just considered to be an infinite source/sink of electrons, you can keep supplying it with them and it won’t become charged, usually this is achieved by using the literal ground because the Earth is massive so it doesn’t make a difference if you give it/take away some electrons." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gv1otzu", "gv1osyj" ], "text": [ "The filament IS a resister. Any load is a resistor. The resistors you're referring to just happen to be built specifically to resist electricity and not to create light or do work. You could test this yourself by taking incandescent bulbs of different wattages and checking the resistance across them. The resistance you find, the rated wattage and the voltage, should fit nicely into ohms law.", "I light globe, build for a certain power, has a certain resistance. For old filament globes, the lower wattage globes had longer and/or thinner filaments, that would allow less current through and so take less energy and produce less light. Modern LEDs (these days) have a string of LEDs and a controller chip that controls the current, and that chip is configured (with a few resistors) to a certain current level, which sets the light's power output. Creating a house fire with the wrong bulb would be hard - you'd have to jury fit a really high wattage globe into a domestic socket to overload circuit that badly. They did/do make 2400 watt globes, but they don't come with standard BC or ES fittings!" ], "score": [ 8, 7 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gv3kzcf", "gv3kvue" ], "text": [ "Because there's something called a differential. It takes two shafts spinning at different speeds and outputs based on the input speeds and the gearing of the differential. This transmits the torque of two inputs to the same output shaft.", "Somewhere inside you've got a component spinning the same speed, and some kind of transmission that's matching the wheel speed to the motor speed. That can be through gears, or through something speed-independant like electric current. For example, you can have a gas-powered generator running at one speed and a battery (which doesn't have a \"speed\"), both putting out electric current. You can add the current together (by hooking the wires together) and run that to one electric motor driving the wheels. There are many (many!) variants, but they all involve some kind of mechanical or electric (or very occasionally hydraulic) transmission that's matching all the speeds." ], "score": [ 3, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gv3kiir" ], "text": [ "Think of electric current like water flowing in pipes, and batteries like pumps. Pumps move a certain quantity of water through (that's current) and raise the pressure (voltage). Two pumps in parallel are obviously moving twice as much water (add current), but if they're both boosting the pressure by 100 psi then it's still 100 psi (same voltage). If there's in series it's obviously the same amount of moving water (same current) but it's going through two pressure increases (add voltage)." ], "score": [ 7 ], "text_urls": [ [] ] }

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{ "a_id": [ "gv57glq", "gv5fwqh" ], "text": [ "They were, when cars were invented. People preferred this feature called \"power steering\", and all auto manufacturers implemented it. Today, it's almost the only solution in production.", "Rack and pinion steering certainly has its place, but it isn’t that great for heavier vehicles are weak-armed operators." ], "score": [ 6, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gv5l8rk", "gv67e9j" ], "text": [ "Your cell phone is regularly contacting the local cell phone towers. It keeps sending out a radio signal saying, \"I'm right here!\" That way, if you're in New York City, and you get a call from a friend in Chicago, the phone company doesn't try to route the call to you through a cell-phone tower in Los Angeles. The company says, \"Oh, his phone says he's in New York, so send the call to a New York tower, and then forward the call on to his phone.\" But, if you're high up in an airplane, your phone might not be able to contact any cell towers. So, your phone will keep trying and trying and trying to contact one, just to say, \"I'm right here!\" But it will never get through. Those constant attempts at communication end up draining your phone's battery quickly. Airplane Mode tells your phone to stop trying to contact a cell tower, until you turn Airplane Mode off again.", "As I understand it, airplane mode also suppresses a phone's (or tablet's) WiFi and Bluetooth radio transmitters, not just the cellular radio ones. Other posts have discussed why it can be a good thing for the phone to shut off the cellular radio transmitter. You also asked how these transmitters can affect the plane. In recent years, mobile phones and other small electronic devices might not have much of an effect on the plane's ability to fly, maintain position in the air, navigate to its destination, or communicate with Air Traffic Control or other nearby planes. The prohibitions against passengers making use of small electronic devices originated 50-70 years ago when commercial air travel used very different ways of navigating. This post of mine in a thread two years ago explains how electronic devices could affect airliners back in those days and how it relates to modern practices: URL_0 The rest of the thread has some insight on other aspects of the question." ], "score": [ 26, 3 ], "text_urls": [ [], [ "https://old.reddit.com/r/explainlikeimfive/comments/9fyxro/eli5_why_do_electronic_devices_phones_laptops_etc/e60noql/" ] ] }

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{ "a_id": [ "gv63d5i" ], "text": [ "On an automatic transmission, cars give you various options to pick lower gears. You probably have a 4 or 5 speed transmission. The 3 and L aren't actually gears, they are just limiters of how far your transmission will go. If you put it into \"3\" mode, your transmission will only go from 1, to 2, to 3rd gear. Then stop there. This is good if you are doing a lot of mountain climbing. \"L\" is the same as \"1st\" and is rarely used. Don't even know why it's there. You would never need to use it under any circumstances I know, at least not in a van, maybe if you had a 4x4 or something." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gv6xx7m", "gv6xyv0" ], "text": [ "The cranes still need a wide stance in order to stay upright even with the counterweight. They usually have outriggers quite far out. The counterweight will move their center of mass close to the rear outriggers making them very rear heavy. However that means that they can lift a very heavy load before their center of mass gets all the way to the front outriggers both because the counterweight have already moved the center of mass to the rear and because the load is now a much smaller part of the overall weight and therefore needs a lot more leverage to move the center of mass.", "It is all about center of mass. The counterweights are designed to shift the center of mass back but it still ends up being between the supports. Then on maximum load the center of mass shifted forward but because of the counterweight it is still between the supports. ELI5: If you're standing you can lean pretty far back before toppling over, same for bending forward. The crane just starts slightly leaning back to offset the forward pull of its load. Interesting Fact: This is not perfect at all and things like heavy winds or bad weight assessment can topple cranes and they do topple all the time. From 2007-2017 they found on average 42 cranes topple a year." ], "score": [ 5, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gv7eyzr", "gv7fc38", "gv94d0k", "gv7ezol" ], "text": [ "Charles Lindbergh's Spirit of St Louis had no autopilot. In fact, it was designed with intentional instability, to aid in keeping the pilot awake. Earhart used a Sperry autopilot, which could maintain heading and pressure altitude.", "I can't comment on these people's planes in particular, but early versions of auto-pilot were mainly based on gyroscopes which are designed to keep themselves straight/level. They can't really navigate and follow a route, but they'll keep a plane level and more-or-less straight on their own. With a compass you can keep a straight heading more consistently.", "Lindbergh wrote that he would have fallen asleep (his flight was 33.5 hours), except there was a fly inside the plane which irritated him enough to keep him awake. He nodded off for a few seconds more than once, and nearly flew into the Atlantic. \"Use the bathroom\" would be a joke. He had an extra fuel tank fitted inside the cabin, and it had to be right in the middle to keep the plane balanced as it emptied. There wasn't even room for him to stand up, and it was so cramped he borrowed a mirror from a woman's handbag to help him see out of the side window. He did have two sandwiches and a bottle of milk, though.", "Pretty much how modern ones work: with feedback control. A specialized compass was invented in 1904 that allows to find the direction you're flying including the change of height. That information is compared to where you want to fly (spoiler: horizontally) and the difference is fed to the steering gear of the plane. That technology was known from steam engines wich use the same technique to keep the RPM stable (with a centrifugal valve that opens more the faster it spins) The only real difference is that today we do it in a microcontroller and not mechanically" ], "score": [ 30, 5, 5, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gva5ijt" ], "text": [ "Filtering the sound. The brain can recognize the slight change in different parts of a sound that naturally happens - the way it interacts with our ears, our skull, etc impacts the noise. Engineers mapped this frequency filter and programs can apply it to sounds. So it notices that the sound is equal in both ears, but has the frequency \"shape\" of a sound behind us instead of in front of us" ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gvagvmw", "gvaghur", "gvagqpw" ], "text": [ "A flywheel is a heavy round weight attached to the shaft of an engine. It maintains rotational inertia, meaning it takes energy to make it spin, but once it is spinning it wants to keep spinning. It is basically a top or a beyblade. For engines with a few pistons, the flywheel helps keep things spinning smoothly. Engines with more cylinders tend to run smoother and have lighter flywheels. Most cars add teeth to the outside edge of the flywheel, making it into a gear that can be turned by the electric starter motor when one turns the key.", "Flywheels store rotational kinetic energy. You can store energy in or by increasing its speed and free energy from it by transferring or converting that energy - make something move, convert to electricity, etc. How they're implemented depends on their purpose. On a car with a manual transmission, they're used to add rotational inertia to smooth the \"impact\" of releasing the clutch and putting a large load on the engine. In power grids, they can be used to store over produced power, allowing that power to be drawn from at a later time.", "A flywheel is just a wheel. Heavy wheels (relative to the application) take a lot of energy to get spinning, but once they do they really want to keep spinning. This means you can make an up front investment and then keep that mechanical energy stored in the rotation of that heavy object for some time. The applications vAry, but usually they're used to help balance out power fluctuations, the wheel can keep a system in motion when power cuts briefly or store up extra energy by accelerating when there is a surplus of power, or to temporarily power the whole system on their own after the initial power source cuts out." ], "score": [ 9, 4, 4 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gvbmxtz" ], "text": [ "First it’s important to understand how shower knobs work. They all basically work like this. When you first turn the handle, it opens a valve which starts letting water from the cold water pipe flor through the shower; then the more you turn the handle, the valve starts to open/pivot more and more, now starting to reveal the entrance of the hot water pipe. You get warm water in a shower by mixing hot and cold water, Then when you turn the knob all the way the valve flips all the way over to just allowing water from the hot water pipe to flow through. Older/worse quality shower handles might now move as smoothly as a nice new one, meaning you get less precision when turning the handle and a better chance the valve will have bigger jerkier movements that make it hard to control how much of each water (hot and cold) is flowing through the shower." ], "score": [ 11 ], "text_urls": [ [] ] }

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{ "a_id": [ "gvcw9vk", "gvcx5zs" ], "text": [ "The surveyor has something called a \"plat\" or \"cadastral map\" that shows exactly where all the property lines are. He uses that map to determine where the lines are on the actual ground, and mark them.", "The funky optical devices (usually yellow) on the tripods are called theodolites** - basically they measure distance and angles from where they are very accurately. And it can use GPS as a backup location assist. So there will be some known spot. Maybe a manhole cover for the sewer. The city knows exactly where that is in relation to... well whatever they use as an origin for measurement. City hall, who knows. The location of that manhole is know to within the inch. From there they use and move the theodolyte and the stick (for the other end of the distance being measured) to mark out where exactly the boundary of your property is according to the map of your street or development on file. Street and subdevelopment plans, accurately plotting every plot and street and utility line have been filed somewhere at city hall and are required before any work can get done. The reason the city keeps track is because they have to. Whups, we need to move this sewer. Can we move it a foot north? Nope, it'll run through /u/zeek1999's lot so now we have to get his permission. And for knowing where stuff is for safety (call before you dig etc.) ** so they know where they are right? Or you tell it where it is. The manhole cover lets say. The other surveyor goes over to some place and holds the stick - the theodolite shoots a pulse of light, it bounces off the stick - using the delay, it measures distance. Meanwhile you've calibrated the device to a particular origin bearing and very accurate angle measurement is built in. So if you know a distance and the angles from some reference bearing you can accurately measure anywhere in sight from your known reference point." ], "score": [ 7, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gvf3h3n", "gvf96xr" ], "text": [ "Have you ever jumped into the ocean and thought to yourself \"wow! that's hot!\"? I haven't, and I don't think most people have. This is because oceans are not, in fact, particularly hot. They tend to be roughly the temperature of the air above them, on the surface, and colder beneath. A lot of would-be heat is carried off by evaporation at the surface. So, with water that's actually *colder* than the surrounding air, you're not going to be able to power much of anything off of that water's heat. Rather, you can use the flow of heat from a hot object to that cold water to generate power. This is what powerplants already do.", "It's called Ocean Thermal Energy Conversion (OTEC), and it can be done ... in principle. But it takes a lot of hot surface water and cold water brought up from the deep, and it's not very efficient. URL_0" ], "score": [ 10, 5 ], "text_urls": [ [], [ "https://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion" ] ] }

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{ "a_id": [ "gvg0ame", "gvgq9eh", "gvgl5ys" ], "text": [ "Sometimes they’re reinforcing weak spots, where potholes exist or are starting or expected to form. Sometimes they’re doing exploration to check for such conditions. The ground beneath isn’t exactly solid, but is a bunch of piled and compressed solids that can be affected by the traffic on the road above, and movement or water below. Sometimes they’re doing other small maintenance, fixing smaller bits, adding or replacing sensors, and the like.", "If the holes are round, they may be \"core samples.\" These samples help to analyze the deterioration of the road way and to design the scope of remediation in terms of foundation and compaction.", "If they aren’t fixing potholes, then this is likely because a large project to replace underground utilities is planned and the contractor is digging small holes to verify the presence or absence of other utility pipes below ground and determine their depth. This practice is also called “pot holing.” When they are preparing to start the project they will mark off the area they will be in with white paint and then all the utilities who may have pipes/cables below will come out and mark on the street with spray paint where their lines are. Then the pot holing contractor will dig to make sure the mark is accurate, and determine how deep it is (the utilities will not provide depths so it has to be checked manually). Then they will know if it is safe to trench or bore the new pipe or conduit they are installing through that area." ], "score": [ 11, 5, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gvhtvwi", "gviw4bi" ], "text": [ "They start as a flat piece of metal and are then formed into a tube that is sharpened. At least that’s how this [how it’s made video]( URL_0 ) explains it.", "You can roll a much larger tube and weld it together. Then you draw that tube through internal and external dies to reduce the size. In the process the weld joint gets smoothed and drawn out and becomes indistinguishable from the rest. Look into CREW, HREW, Seamless and DOM tubing. There are lots of ways to start but they all end up with drawing through dies to stretch the tube and reduce its size to the desired dimensions." ], "score": [ 53, 16 ], "text_urls": [ [ "https://m.youtube.com/watch?v=i1tbJuE-UmQ" ], [] ] }

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{ "a_id": [ "gvi6b8b", "gvj1z9i", "gvig25j", "gvj4ytd", "gvia596", "gvicyk7", "gvisxgl" ], "text": [ "Not immediately, all objects in orbit are tracked by NORAD. Provided it's not military you can as a private citizen ask for it's orbit details. Debris in orbit can absolutely become a problem as you describe. Eventually with enough objects up there any collision could result in a perpetual chain reaction that leaves us locked in. The term for this (theoretical) state is \"Kessler Syndrome\" We currently track objects right down to paint flakes and bits of re-entry insulation, our slowly growing debris field is under close scrutiny. If it returns radar we track it, it's all moving at several kilometers a second, so no debris is irrelevant. Edit:. Since this ended on top I'll correct a few things based on other comments. Radar tracks down to about 10cm. Smaller stuff we use predictive models for. Extra research after my comment provided two numbers. We have about 6,000 satellites of which 60% are dead, we are aware of about 600,000 objects total including debris from anti-sat tests and exploded upper stages (mostly Deltas)", "The diameter of Earth is about 7900 miles, giving Earth a rough surface area of 196M miles. Adding 1000 miles to that doesn't seem like much, but it changes the area of the resulting orbital sphere to 307M miles, about 1.5 times as much, just as a frame of reference (the Earth's surface is huge, but LEO is even bigger). Divide that by 20,000 satellites, and you get 1 satellite for every 15,350 square miles. It would take a lot of launches to have even a 1 in a million chance of any of them colliding, even if they were just launching randomly.", "For anyone that wants to have fun. [stuffin.space]( URL_0 ) It's a real time 3D map of known stuff in orbit.", "I don't know exactly how big the satellites are for starlink but satellites can be as small as our phones these days.", "Not really. Remember, the area of space that geosynchronous satellites sit in is as vastly big as Earth itself. Slightly bigger, really. That leaves a lot of space for rockets to pass in between.", "Yes. Space \"traffic\" is just like any other form of traffic, the more packed it becomes the more you have to take care. However, the nice thing about satellites is that they are very predictable. So if you want to launch something, you can calculate weeks ahead if your path is clear at your desired time.", "Earth is big. Even with ten thousand satellites, there will still be gaps between satellites of a couple hundred kilometers. Further, groups of satellites are arranged so you might have a bunch of satellites in nearly the same orbit, just following one after another. This means there are gaps between those orbital planes without any satellites. There are already about 20,000 objects that are big enough to track." ], "score": [ 119, 46, 10, 5, 4, 3, 3 ], "text_urls": [ [], [], [ "https://stuffin.space" ], [], [], [], [] ] }

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{ "a_id": [ "gvl6emd", "gvl95x4" ], "text": [ "The amount of work done (i.e. the total energy used) is equal to the amount of force times the distance the force is applied over. A pulley may allow you to use one-third the force, but it’s also going to require you pull the rope three times as far.", "Mechanical advantage is a swap of power for distance. He easiest way to picture this is with a lever. A lever is just a bar, resting on a fulcrum. A fulcrum is only the thing the lever rests on. In something like a see saw, the fulcrum is in the middle. If you put 100 pounds on one side, it will take 100 pounds on the other side to lift the first side. So if you put two children on it, one on each side, they will balance and see saw fine. But... what if one of them weighs 90 pounds, and the other weighs 110? The lighter one sits slightly farther away from the center, and the heavier one sits slightly closer. Humans are real at balance, and levers seem natural to us. He two children will balance the distance, and poof, see saw. Mechanical advantage works like that too. Let’s just talk about levers for a second. If you have 100 pounds on one side, and the fulcrum the middle, it takes 100 pounds of force on the other side to pick it up. BUT what if you move the fulcrum closer to the 100 pounds? Now all of a sudden you can lift the weight with 50 pounds, but you have to move the lever down twice as far as the 100 pounds moves. 50% increase in force requires that force to be applied twice as far. Multiple puppies are like that as well. For each decrease in force desired to move it, an increase in the rope you are pulling through it is required. Mathematically it all stays even." ], "score": [ 20, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gvlpaph" ], "text": [ "The smaller wave, higher frequency ethernet signals are simply multiplexed on top of the bigger wave, low (comparatively) frequency waves of electricity flowing through your house. Anything that uses the big household 115/220V AC for power will probably not even notice the small high-frequency ethernet signals. Meanwhile, the powerline adapters have big filters that let them ignore the big power waves and just look for the high-frequency signals. The circuits to multiplex and de-multiplex signals like this are pretty fundamental electrical engineer stuff. Think of it like sending messages down a river using notes in a bottle. The river doesn't care about the teeny bottles, nor do the boats, the bridges etc. But if you know where to look to catch the bottles floating by... Signal multiplexing is used everywhere from analog radio and TV broadcasts to fiber optic cable (you can get multiple streams or channels down the same fiber if you use different coloured light)." ], "score": [ 10 ], "text_urls": [ [] ] }

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{ "a_id": [ "gvm581z", "gvm37e8", "gvlu1j0", "gvm0uqc", "gvlquyg" ], "text": [ "Imagine you are cooking something, you usually have a recipe that you need to follow, each steps builds on the previous one. For instance, if you wanna make fries you: 1. Find a potato (tool: fridge) 2. Wash the potato (tool: sink) 3. Peel the potato (tool: knife, peeler) 4. Slice the potato (tool: knife) 5. Fry (tool: stove, pan) 6. Serve (tool: plate, table) Each tool can be considered a different programming language, and each step can be considered a \"layer\" of your application. Each layer has an expected format for input and output (e.g. to peel the potato you receive a washed potato, and your output is a peeled potato). In practice, different languages pass input and output to each other using your computer memory (RAM) or storage space; they create files and pieces or information that follow certain \"structure\", such that the next layer can pick it up from there.", "Imagine you speak french and your friend speaks german. They both agree to talk in english so they both can understand each other. That's basically how standardized protocols work for applications", "Connection between two languages generally means connecting between two layers of a product. Eg we are communicating using an agreed upon format i.e. English text. Similarly the services use a format agreed by all layers. A product might have react, node, java and sql mode of communication between laters will be defined objects. React and node will use json format to communicate, node will use json request objects to communicate with java and vice versa and this goes on.", "Different software components can communicatie with eachother through - protocols, like TCP/IP - file formats, like xml or json - APIs: \"application programming interfaces\" that allow function calls between different components. All that's required is a common understanding of the syntax and semantics of data that is passed between components. For example, component A, written in python, sends a data packet to component B, written in C. The data packet contains a request, component B parses this request, interpretes the request, executes it and returns a response to A.", "The language is only there for the convenience of the programmer. Ultimately the computer runs off a binary code which is the same whichever language the programmer uses. So two programmers may well uses two different languages but before either of them can run they get compiled (converted) into binary and it is the binary that actually runs on the computer. As an analogy, if a group of people were making a wooden shed, some may cut the wood using a handsaw, some using a circular saw, some using a jigsaw but provided all the wood is cut to the right length then the shed will fit together perfectly." ], "score": [ 38, 30, 17, 11, 9 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "gvmrl9v", "gvnbcna" ], "text": [ "In an automatic transmission, as long as you're in Drive the transmission is in gear. There's a special fluid coupling (called a \"torque converter\") between the engine and transmission that lets the engine keep spinning when you stop the car with the brakes, but as soon as you release the brakes the torque coming through the torque converter is enough to start you rolling.", "It’s your torque converter. It’s filled with fluid and is between your engine and transmission. Some cars have a lower idle RPM like my wife’s Buick and won’t move when you let off the brakes. Others have a higher rpm and can get the vehicle significantly fast with the foot off the brakes." ], "score": [ 16, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gvmq639" ], "text": [ "it’s the way it surrounds itself with air and how heavy it is, it would take a lot of speed for a paper plate to not be pushed over midair" ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "gvn0vw7", "gvn32vc" ], "text": [ "There has been advancements beyond the traditional spring type lock washer. [Nord-Lock wedge lock washers are what you should be using in critical locations. ]( URL_0 ). I have a piece of equipment that I’m going to be changing out the spring washers to Nord-locks shortly. It’s amazing how you can see spring washer slowly back off over time. If I’m gonna take this apart, I want to never touch it again.", "They do force the bolt apart but that is a good thing. You get a nut of a bolt by rotating it not by pushing it apart. If you just pull them apart with enough force the threads will get striped or the bolt or nut snaps. You will not unscrew it that way. If you unscrew a bolt that is wery tight the required force will be initially quite high but will later drop significantlu. This will not just happen if you have somthing that have started to rust but even on new bolt you just tightern. It is hader because the friction it higher if the threads are pushed togheter. So a lock wacher will result in pressure even if there is vibration that reaulst the part in the middle compressing slighty or the bold slighty increasing in leghth. So vibration can reduce the pressure and friction and there is motion there so the nut can rotate. Another factor is thermal expansion. Metal will change in size when the temperature change and the amount depend on the metal and exacltly what alloy it is. If the bolt expande more then what is passes trough the friction will recuce and vibration move it. So a lock washer is a way to increase the pressure even if stuff change slighty in size so you have a constant high pressure and high firction." ], "score": [ 5, 5 ], "text_urls": [ [ "https://youtu.be/IKwWu2w1gGk" ], [] ] }

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{ "a_id": [ "gvn517v", "gvniycu", "gvn5kfl" ], "text": [ "The gist of it is that there's a couple ways to get rotation from an electric circuit. One involves a constant current (DC), but needs \"brushes\" to swipe along your spinning electromagnet, in order to keep your current flowing. In a brushless motor, you actually vary your current with 3 phase AC (alternating current), and that lets you rotate your motor without those brushes. This can give you longer tool-life, as those brushes get a lot of wear. (You'll see brushless motors called brushless DC, even though they run on AC. This is because you can run the entire assembly off of DC as it is turned into that 3 phase AC by a component of the motor)", "There are two parts to an electric motor: the stator and the rotor. The stator is the stationary part and the rotor is the part that rotates. Both the stator and the rotor have magnets, and the magnetic attraction or repulsion is what causes the rotor to turn. In most motors, the magnets are electromagnets, which are coils of wire that are hooked up to the power. The problem is, how do you connect up wires to the electromagnet on the rotor. It needs to turn, and if you just connect the wires directly they'll twist around the shaft until they break. You need a way to get the power to the coil but not have a direct connection. This is where brushes come in. Brushes are typically a small block of carbon that slide along, or \"brush\" along, a strip of copper attached to the rotor. The strip of copper is called the commutator. The commutator is connected to the coils on the rotor. With this arrangement you can supply electrical power to the rotor coil, and it is free to rotate without tangling the wires. The problem with brushes is that they introduce a small amount of friction. They will wear out over time and need to be replaced. Also, if the rotor has multiple coils (which almost all brushed motors do), the commutator will be divided into segments with each segment connecting to a separate coil. In between the segments there are gaps. When the brush bridges the gap, there is a spark. This can be dangerous around flammable gasses and is electrically noisy as well. However, there is no need for the magnets on the rotor to be electromagnets. We can create fairly powerful permanent magnets. By using permanent magnets on the rotor, we eliminate the need for brushes and commutators, and the whole rotor can be made smaller. The key to a brushless motor is that there needs to be a rotating magnetic field in the stator coils. This is done with a clever little electronic circuit that energizes the stator coils in sequence. As the magnetic field in the stator coils changes, the permanent magnets turn the rotor to maximize the magnetic attraction and minimize the magnetic repulsion.", "Electric motors have several electromagnets that need to be turned on and off at the right time to get it to spin. In a brushed motor this switching on and off is done mechanically by a set of brushes riding on a spinning 'commutator'. Picture a really tiny Wheel of Fortune with electrical contacts (brushes) instead of a flapper. Which magnet is turned on depends on which segment of the Wheel of Fortune is currently touching the brushes. In a brushless motor this switching is done electronically using transistors instead of mechanical contacts. This has a number of advantages: Since there are no brushes, they don't wear out, don't make noise, you can use higher currents and you also have more control over the timing of when you turn a certain electromagnet on or off. This is why brushless motors can be more powerful, quieter and they don't have problems with brushes wearing out." ], "score": [ 12, 9, 4 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gvnux7o", "gvnv6pw", "gvnwe84", "gvnushm" ], "text": [ "Rocket launches require a lot of infrastructure and equipment. Big facilities, lots of supplies, all this stuff has to be built and transported to the launch site. That would be pretty impractical to do on a mountaintop. Meanwhile, the savings in not having to go one extra mile out of the 62 it takes to get to space is not very significant. So, bottom line, it would cost more in time, expense, and effort to build launch sites on mountaintops and transport fuel and supplies to them than it would save in launch thrust.", "Because most of the energy spent getting a satellite into orbit is spent making fly fast enough sideways and not going straight up. The highest mountain is only 30,000 feet, roughly 6 miles; ISS is over 240 miles up. It has to go 18,000 MPH to maintain it's orbit. Satellites are also launched close to the sea so if there's a catastrophic failure the rocket will be more likely to crash into the sea instead of over land.", "There's almost no advantage to height. The real challenge is gaining speed, not height. URL_0", "It’d take a pretty significant effort to get the rocket to a launch pad at the top of a mountain. Also, they typically launch close to the ocean in case something goes wrong (better to fall into the sea than over land)." ], "score": [ 40, 17, 7, 6 ], "text_urls": [ [], [], [ "https://www.youtube.com/watch?v=RsbDRDFVObE&t=73" ], [] ] }

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{ "a_id": [ "gvr5eyz", "gvrp44f" ], "text": [ "As someone who works with the stuff: Soft Touch is a TPE generally used for extrusion blow-molded bottles, generally in a 90/10 bi-layer. What this means: imagine squeezing toothpaste from a tube. Now imagine the toothpaste is semi-molten 380F plastic. That’s extrusion in a nutshell. Imagine a hollow tube of toothpaste is being slowly squeezed towards the floor. It’s also got air running through it to make sure it stays hollow and doesn’t collapse on itself. The tube gets clamped in a mold in the shape of the bottle (go look at your shampoo for an idea, it’ll have either a line or a nub on the bottom where the plastic was clamped shut on one end) and cut from the rest of the plastic. It’s moved to an air nozzle and inflated like a balloon until it cools, then dropped from the mold. This then repeats. That’s blow-molding. Now imagine squeezing two tubes of toothpaste so one layer is completely surrounding the outside of the other. How fast each tube is squeezed controls how thick each layer is, and you only want a thin layer. Plastic bottles generally range from .018-.03 inches thick (.45-.75mm) and the “soft” layer is only, generally, 10% of that, so...very thin. That’s a bi-layer. The most I’ve ever seen is a tri-layer bottle. The “soft” part is a mix of rubber and low density plastic that leaves it slightly stretchy, even softer and with a little bit of give to it. That’s Soft Touch. The rest is either HDPE (picture milk jugs) or LDPE (squeeze tubes and plastic bags) High and Low Density Poly-Ethylene. So it’s really a thin layer of soft over a more rigid under-layer to give it stability. I know it’s also possible to do this in a spray application for things that are not bottles, but I don’t know how that one works.", "Great description for the tangible quality of the plastic-silicone like coating. 👍🏻 I knew exactly what you were talking about." ], "score": [ 62, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gvr9avy", "gvrafu9" ], "text": [ "A combination of several factors. Shorter distance between combustion chamber and exhaust pipe. Smaller muffler. Exposed (kinda) engine. 2 explosions per cycle is more distinct than 4 or 6 or 8. And, most importantly, Harley's V-Twin engine is specifically tuned to make that noise. A 2 cylinder Honda Goldwing isn't going to sound like that nor is a Kawasaki Ninja.", "If you pedal on a bike with gears you have a choice between a hard gear, where you pedal slowly but with each revolution requires a lot of strength, or a lighter gear where you pedal really fast but it is also super easy! The 2 cylinders vs. 4 cylinder work kind of the same way. If you have only two cylinders, you have less revolutions or engine \"pops\" when the gas gets ignited but the pops are loud. But with four cylinders there are many ignitions that are less powerful/loud. With 2 cylinders you can tell each pop apart until high revolutions where as with the 4 cylinder the pops can overlap and sound whiny. I once had the pleasure of driving a Ferrari Testarossa which is a 12 cylinder (only because I was asked to clean it... but still) and there was absolutely no way of distinguishing between individual combustions and the power was just so immediate! But back to motorbikes; 2 cylinder is more for cruising and 4 is if you are after performance" ], "score": [ 9, 5 ], "text_urls": [ [], [] ] }

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