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{ "a_id": [ "golp31m", "golptm3", "gollhzg", "golrsgw", "gom8n8z", "gomejkk", "gomp01l", "gomybb2" ], "text": [ "Two main reasons: Power tools use smaller motors that spin very fast but that don't have much torque, so they need gearing to reduce the speed and increase the torque. The noise is produced by the fast-running motor itself and a lot also comes from the gearbox. The strongest and lightest gears have straight cut teeth, but they're also quite loud. The gears used in electric cars are helical cut and much quieter, if they have gears at all. It would be quite difficult to have a power tool without a gearbox because slow-spinning electric motors with a lot of torque would be physically larger and a lot heavier.", "Teslas and other EVs have a single reduction gear that allows the motor to spin many times faster than the wheels, to enhance wheel-torque and also efficiency so they can get a lot of power from lower amps. The reduction gear in a Tesla is a sophisticated double herringbone gear, which is specifically designed to handle high power while running very quietly. Also, there are anti-vibration mounts for the gear housing, along with noise insulation. A cordless drill is under a tremendous pressure to provide adequate performance at the lowest possible price, so the reduction gear is made very cheaply of a strong design. AvE has some very good tool teardown videos on youtube. You \"could\" make a cordless drill run much quieter for maybe an extra $20 per drill, but...millions of customers worldwide dont seem to be asking for that.", "Power tools have almost no shielding between the motor and you. Most of the sound created by the motor is exposed quite directly to the environment. Electric cars on the other hand have an entire auto frame, various metals, rubber, upholstery, etc to distribute and absorb the sound as well as environmental noise (such as tires rotating on the ground) to mask the comparatively little noise that does leak past all that.", "I think it might have to do with the type of motor. Electric cars apparently almost always use DC brushless ( URL_0 ) And a lot of power tools use a noisier type of motor: URL_1 Related, my washer has a direct drive digital inverter brushless motor, and it's eerily quiet.", "There are several incorrect answers in this thread including the highest rated comment. There are two reasons for the difference in noise. The design of the motor and the design of the gear box. Amount of shielding has relatively little effect on the noise in this case. Submarines have mega-Watt class motors and they are so silent that even sophisticated listening equipment have difficulty hearing them. So the sound of an electric motor does not directly depend on the power. Power tools use a type of motor called a brushed universal motor that tends to be noisy. That is a safety feature for the power tool. The gear set is inexpensive and durable, but it is noisy and again that is not a problem for the power tool. Electric vehicles use a brushless permanent magnet motor that is specially designed to be as quiet as possible. The gear set is made with super smooth, helical gears that are also designed to be quiet. I can't tell you how submarine motors are made as quiet as they are.", "Short answer: Different types of motors, bearings and gears. Power tools are made to be cheap, so they use noisy and inefficient parts. Expensive or very large power tools, and electric cars need to use more reliable and efficient parts and tend to run very quietly. Motors: Basic power tools use brushed motors. These motors are cheap and simple, but they throw of sparks, make noise, and need to have parts regularly replaced. Electric cars use brushless motors, which are much quieter and more efficient, and generally don't need much maintenance at all. Bearings: When you have spinning shafts under load, you need to support those shafts without too much friction. Bearings are used for this. Power tools generally use ball bearings, which have a limited lifespan and make quite a bit of noise when spinning fast. Cars use heavy duty roller bearings, which are quieter, but still need to be replaced regularly (one of the few maintenance items on an electric car). Gears: Small power tools use motors that spin very fast but don't have much torque. Generally this needs to be turned into a slower rotation with more torque to be useful. A gearbox is included in almost every power tool. The gears inside a power tool gearbox are called \"straight cut\" gears, which are cheap and easy to make, but create a huge racket. This is responsible for most of the noise of a power tool, the loud coarse grinding/whining noise. A straight cut gearbox for a car would make an unbelievable racket. Car transmissions and gearboxes use helical cut gears, which are more expensive but much quieter. Even with the helical cut gears, the gearbox whine is still one of the loudest noises made by an electric car.", "Everyone is also missing physical resistance, most power tools are interacting with their environment (drilling, cutting, sanding etc) a hell of a lot more than a tesla rolling along over tarmac", "There are a lot of answers that are close, but miss important points: - Most of the noise comes from the motor cooling fan, and the gear-box: - Power tools typically use compact, air-cooled motors that spin at extremely high speeds. They spin at high speeds in order to get the maximum amount of power they can out of a given size. This means a lot of heat is generated in the motor. This heat requires a powerful fan to get rid of the heat. - The cheapest and mos effective way to get a powerful fan into the tool is to attach a fan-blade directly to the tool's motor. Since the power tool's motor spins extremely fast, the fan also has to spin extremely fast whenever the tool is on (regardless if the motor is hot yet). That extremely fast spinning fan makes A LOT of noise. - Most power tools use \"straight cut\" gears. These gears are cheap to manufacture and are durable. The downside is that they are extremely loud. Some tools use \"helical\" cut gears, and they are noticeably quieter. - Many corded tools also use what is called a \"brushed\" motor. There are carbon brushes riding over copper bars. This makes a very distinctive clicking sound at low speeds, to an extremely loud \"scream\" at higher speeds. Electric cars on the other hand typically have larger, slower spinning, brush-less (so no brush clicking) motors that are liquid cooled (so no loud fans). Additionally, automotive transmissions and gears are almost always made using helical gears with a very \"steep\" helix-angle. These are more expensive & trickier to manufacture, but are much smoother and much quieter." ], "score": [ 7049, 619, 182, 72, 22, 14, 13, 10 ], "text_urls": [ [], [], [], [ "https://www.tesla.com/blog/induction-versus-dc-brushless-motors", "https://home.howstuffworks.com/question338.htm" ], [], [], [], [] ] }

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{ "a_id": [ "goo3zsn" ], "text": [ "The number of cylinders is just one characteristic of an engine. Other things that can change the sound include engine size, cylinder configuration, rpm, stroke (2 or 4 stroke), fuel type, muffler size and condition, age, the presence of a turbo, and much much more." ], "score": [ 7 ], "text_urls": [ [] ] }

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{ "a_id": [ "goo4p0z" ], "text": [ "When you first rev the car up at a standstill with the clutch open there’s no load on the engine, so it spins up easily. When you start to engage the clutch the energy in the engine is transferred to the wheels. This load on the engine tries to slow it down. To get the car going you need to give it more gas and let the clutch slip a bit as it engages. A stall occurs when you aren’t giving it enough gas to overcome to load of getting the car moving, and the wheels and transmission actually bring the engine to a halt." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "goo2uht", "goo3wg6", "gooxq6p", "goosva4" ], "text": [ "Google “caissons” and “”Brooklyn bridge construction”. But remember to get some sleep, it’s fascinating.", "Basically you build a sealed frame in the water, pump out the water, start digging and later pour some (a lot) of concrete in there.", "one I don't see mentioned is just sinking the supports. silly as it sounds, they do sometimes just make giant masses of concrete, sink them into the water, let them settle for a few years, then build on top of them.", "In addition to caissons there are actually types of concrete that are designed to set hard underwater. So build a formwork and pour it in - the concrete will push the water out. And in some situations you build the bridge at low tide and hope everything is dry before the water covers it again." ], "score": [ 19, 17, 6, 4 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gooj1qk", "gopptbl", "goool36" ], "text": [ "Firmware is the operative system of any appliance or machine. For example, the firmware of a tv, is the program that show the menus, react to the remote controller or decode the streaming signal to show the content.", "the simplest way to see it is to compare it to us humans. our software woudl be the skills you learn over the course of your life, nice Quality of life additions but not mandatory the firmware would be the most essential skills like Breathing, Heart Bea brainwave pattern and the other absolute basic things you need to just be there(think of it as \" knowing how to be \"you\") same applies to all electronic device, firmware will be a set of instructions that tell the actual hardware how to operate at a basic level(Bios) while the software is a layer above that adds features to it(Operating system) and provides instructions of how to leverage to the nonessential hardware(Drivers).", "Firmware is a type of software that runs directly on the physical hardware. Usually in computers you have things work in layers. The program running on your computer doesn't talk directly to the hardware, it talks to your operating system, your operating system uses drivers to talk to the hardware and on the hardware the firmware talks back. There may be many more layers in between thanks to virtualization and abstractions. But somewhere deep down there has to be an actual physical hardware underneath it all and that hardware needs to have some rudimentary software to do stuff. Originally firmware was often read-only or close to and build into a device, but nowadays it is usually writeable and updateable and the barrier between it an other types of software have become more and more murky. Not just what you normally would think of as computer have firmware, but all sorts of electronic devices and components have them too. You desktop or Laptop computer will have a BIOS (or UEFI), that runs on your computer and shows up when you turn it on before Windows or whatever your OS is loads. Your home computer may also have firmware in various other components in it like the GPU or the various peripherals. This includes smart ones like your printer or your router which are basically specialized computers to dumber and simpler ones like your mouse or keyboard. All sorts of smart and not so smart appliance will have some firmware on them and the smarter ones will have an OS running on top of that. The line between the two can blur on occasion." ], "score": [ 3, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gopkprr", "goozduq", "goozi3r", "gop11zi", "goozmyk", "gop7x6f", "gop9nwx", "gopgv2a", "gopm1ry", "gopaefv" ], "text": [ "Electricity comes in two flavors: spicy (AC) and bland (DC). There's also two other things that are important: how fast do you want it coming in (voltage) and how much do you need (amps). When you plug into a wall outlet you're getting Spicy AC power at 120 volts in America or 230 volts in Europe and a standard house circuit can supply 20 amps (at least in America, not sure about other places). In either case that's the electrical equivalent of having your garden hose on full blast, it's coming out pretty good but it's still relatively safe and usable for the average person. For big dumb things like a hairdryer or a blender that just want to go fast or get hot this is great. Just take that full blast spicy power and go brrrrrr. Similarly you could hook that full blast hose up to your lawn sprinkler and it'll work fine. If you want to run something a little more sophisticated though like a laptop or a Playstation you need that bland DC power. AC power is all wiggly, DC plods along in a nice straight line and if you want to do math with electricity it needs to move straight. You also probably don't want it coming in so full blast. Your sprinkler may be able to handle the hose on full, but if you stuck it in your mouth you'd probably have a problem pretty quickly. So you gotta turn the spicy AC into bland DC, that's what the power brick does. You also need to turn the hose down, it also does that and brings the voltage down from 120 or 230 to usually something like 5-12 depending on what you're running. Instead of your hose on full it's your faucet on at a trickle. I also mentioned amps earlier, basically how much power do you need. Keeping with the hose analogy how big a hose do you need? Your house circuit can supply up to 20 but you've got to filter that through the transformer in the power brick.. If you're just charging your cell phone you don't need much at all so the dinky little block that fits in your hand is fine. If you want to run an Xbox though you'll need more. All that math requires a lot of power, so you gotta have that much larger brick to get the same bland 5 volts, but you need 2 or 3 amps worth and you need more space to accommodate the hardware for the additional capacity.", "A laptop needs to convert the AC power from the plug to DC to use it. That power brick is what does that. A hairdryer uses AC so it doesn’t need to convert, the only reason it has a block on the plug at all is for its gfci protection to avoid shocking the user if it touches water. Things like kettles and hairdryers don’t care about the power source very much, at their core is just some coiled wire that electricity is passed through, the resistance creates heat. Laptops need to charge the DC battery and use a lower voltage also.", "Kettles and hairdryers etc all run directly off AC voltage. Laptops and phones (all electronics) need DC voltages. That brick is a converter that generates DC voltage from AC mains. Bigger electronic appliances like desktop computers, TVs etc have a built in AC/DC converter so they don't have a separate brick.", "“Nearly all electronic devices use DC power internally. Many of the components that make computers possible, especially transistors, require electrons to move in a single direction. This is because logic gates work by turning the flow of electricity on and off very quickly - much faster than AC power oscillates. Some components, like memory cells, also need continuous power to maintain their state. If the electric power inside a computer was constantly turning on and off, which is what’s happening in an AC world, then the computer would not be able to maintain its state, pretty much making it useless.” -quora guy 2007", "Kettles, hairdryers, etc. use power mainly for heating or to run a motor. These things can take the full mains voltage and does not need any form of power convertion. However things that use transistors and other semiconductor devices to run logics circuits need a very low voltage. Similarly with batteries as each battery only have a small voltage across it. This means that these devices needs to transform the main voltages of about 120V to 240V into eventually something like 3.3V or lower, however usually with an intermediary voltage of maybe 12V or 20V. This is what the big power brick does, it transforms the higher mains voltage into this intermediary voltage that can then more easily be converted to the correct voltages. The size of the power brick is roughly proportional to how much power it can transform. So something which draws just a tiny bit of power like a control chip in a device or for example an LED light might have a tiny power transformer built into it but a larger device like a laptop or a TV need a larger external device.", "Things like hair dryers don't care too much about what electricity is given to them. So long as it's close enough, they'll work just fine. But things like laptops are more sensitive. They need the electricity to be *just right* in order to function properly. The power brick takes the electricity from the wall and makes sure the laptop can use it safely.", "Eli5? A hairdryer and kettle both do one big thing, take a lot of energy and turn it into heat. A laptop does a lot of tiny little things and therefore can't take big power, it needs a whole lot of little power. Shrinking the power down generates some heat and since it doesn't have to be part of the laptop, which makes it more portable. Looking at the other responses I see there is a focus on the fact that most power bricks (or wall warts if you want an older term) convert to DC. I disassembled a hairdryer, and it had some diodes inside to convert the AC to DC to run the motor. Those power bricks are also lowering the voltage to a consistent level. If you look at the label on most power bricks they have a range that includes 240 and 120v. In the past those power bricks would have to match the voltage available in your particular country, but most work internationally. It's easier to get a nice and steady 19v DC than it is to get a nice and steady AC voltage from a transformer. Be careful if you take that hairdryer or waffle iron traveling.", "First lets think about electricity as if it were water moving in a pipe.There are two types of electricity.Alternating current, where water basically sloshes back and forth from the pipe.And direct current thats like a stream coming from a hose. Well Kettles, and other applieances that make heat, only need the water to move.Friction of the movement makes heat, thus kettle work, it doesn't reall matter if the movement is in the same direction, or bakc and forth.And it tend to be sturdy so teh \"pressure of the water\", and its speed is not going to cause much issue.Maybe it will heat a bit faster or slower, thats not the end of the world. Hairdriers are the same thing as far as heating goes.However the motor responsible for moving the air is a clever thing. As it CAN acts both as a bike pump where the pump handle is pushed by the back and forth sloshing water, or it can act as a waterwheel turning the propeller thats in URL_0 it also doesn't care much about the pecularities of electricity, as long as it gets it. & #x200B; Computers and other electronics on the other hand are extremely delicate - and only work with water flowing in one direction like out of a hose. With part in the processor as thin as the human hair. Now in pipes that thin, its not exactly hard to break stuff by putting too much pressure, or putting too much water through it. So the \"powerbrick\" sits there to act as a pressure regulator, that doesn't allow water in with too mcuh pressure, thus preventing damage - and to make sure that waters movement will be a nice even stream, not the sloshing back and forth type affair.", "Laptops usually do not have their power Supply unit built in as that would add to the weight of it and would make them run hotter as PSU's require ventilation. that's what the power brick does, it fills the role of the Power Supply unit(PSU) converting the Ac current of the outlets in current that is usable by the system., if laptops had their PSU's built in a power brick would not be required, but laptops as whole would be quite a bit bulkier and heavier.", "To expand on some of the other answers; Simple devices like kettles, hair dryers, etc. are fairly dumb, they use an AC motor to move things or blow air and they use a simple piece of resistive (usually Nichrome) wire to make heat. These things need a lot of power and don't really care too much what they get so high AC voltage is a very efficient and cheap way of powering them. The sensitive digital and analogue circuits inside laptops, TV's, etc. need a very stable steady DC voltage to work and avoid damaging the circuitry - modern chips have *billions* of tiny transistors inside them and often need a very low voltage - 1.8v or less is common - and straying even 5% over that can damage the part, literally the parts are so microscopically small that a higher voltage will be able to jump or punch through the part, killing it. This is why static electricity kills things - the chips etc. just can't stand a 5kV shock even for a microsecond. Your laptop brick takes the mains AC down to some intermediate voltage, usually 16-19v DC, that the laptop will then have a load more power supply circuits inside to further reduce to power all the various parts and charge the battery. The adapters are also handy because they are a fairly universal and simple part so you only need to change the adapter/plug to work in each country around the world. The laptop running from this low DC voltage then does not need to go through anywhere near as many safety checks & tests (which get expensive quickly if you have to do them for each country) as it's classed as a much safer \"low voltage\" device. This way manufacturers can just safety certify a few power bricks and re-use the same part over and over across the range. Keeping the large high-voltage stuff out of the laptop etc. also greatly reduces the size of the thing as you need large components and large gaps to stop high voltages jumping around where they shouldn't." ], "score": [ 9608, 8207, 393, 205, 46, 34, 16, 8, 3, 3 ], "text_urls": [ [], [], [], [], [], [], [], [ "it.So" ], [], [] ] }

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{ "a_id": [ "goppro5", "gopptdc", "gopq44m" ], "text": [ "The key word here isn’t “perpetual motion,” it’s “machine” You want the machine to actually *do* something productive, doing some sort of work or expending some sort of energy. Energy can’t come from nowhere, so the machine must lose energy in the process. If useless perpetual motion is what you want, that’s certainly possible. Spin a ball in deep space and it will keep spinning until the end of time.", "With a perfectly loss-less machine, you can have perpetual motion. But any attempts to harvest energy from the machine will reduce the motion. And a perfectly loss-less machine does not exist. There are *always* losses in one form or another.", "If the machine is producing energy, then that energy has to come from somewhere. If the energy is coming from somewhere, then it will eventually run out. A perpetual motion machine requires a machine that produces energy *without that energy coming from anywhere*, which is nonsense." ], "score": [ 12, 4, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "goqvpyd", "goquzl9" ], "text": [ "Its really very simple - the hot water pipes in your walls don't stay hot forever. Eventually, the water cools down inside the pipes to room temperature. When you start the shower or faucet, it has to clear out all of that cool water and replace it with new, hot water from the water heater. How long this takes varies based on how far you are from the hot water heater and how much pipe there is to flush. Once the hot water is there, then the pipes are filled up with hot water again, so you can go between cold/hot very quickly.", "It all has to do with the distance from the water heater. Once the hot water is in the pipe and the pipe is warmed, it takes less to switch between it." ], "score": [ 12, 5 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gorso5r" ], "text": [ "We figured out how electricity works (something with charge is flowing around) before we figured out what was actually going on at an atomic level (electrons are the things that are flowing). We labelled one charge \"positive\" and one charge \"negative\" and all agreed that we'd model current like it flowed from positive to negative. As long as we all agree, all the analysis works fine and we can design circuits that work. That's \"conventional current\". \\*Later\\*, we figured out that it's electrons that are the things that are physically moving and they carry negative charge, so the flow of of electrons, and hence the actual physical movement of charged things, is actually from negative to positive. That's \"electron flow\". But by the time we learned that, we'd already designed a bazillion components and circuits and analysis techniques and textbooks and schematics and formulas and...(you get the idea) based on conventional current and it's a hell of a lot easier to stick with that for circuit design and just remember in the back of our head that, physically, it's electrons going the other direction." ], "score": [ 12 ], "text_urls": [ [] ] }

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{ "a_id": [ "gos8jaf" ], "text": [ "Most modern touch screens use a capacitive method-a tiny electric charge is carried in the touch screen. Putting your finger on it completes a circuit that causes a slight change in the charge at that point. There are sensors at each corner that detect how far away this change is, and you can combine those 4 distances to get an exact point for where you’re touching it. Problem is you need something that conducts charge at the correct point. Plastic doesn’t conduct that charge, and water distributes the charge so the phone won’t correctly determine where it is" ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gotqk4i" ], "text": [ "They are kind of cheating a bit. The current does not actually go through the ground all the way from the load to the supply. Earth return systems are AC. This means that the current changes direction at regular cycles. So instead of sending the charge back in every cycle they can store up the charge until the next cycle and then send it back through the load path. The earth is used as a place to store the charge between the cycles. So the current does not go far from the ground rod at all. And it will quickly spread out into many small currents which have less loss in it." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "gp36iq2", "gp36vh2", "gp36s3v" ], "text": [ "They absorb or reflect radio waves away from the source. Stealth planes are never invisible to radar, just less detectable.", "Radar is light, and it bounces like light does. Radar detection works by shining radar at the sky and waiting for it to bounce off stuff. If it bounces off and comes back to your detector you can detect the presence of *something* in a particular location, and you can be reasonably confident that something is something you should take a closer look at. Light bounces in very predictable ways, which is how radar works. Most things will bounce the radar off in a predictable direction and can therefore be detected. Stealth planes are designed to reflect radar light at weird angles, so instead of going back to the detector, they fly off somewhere else. Since the plane is never getting detected, no one knows its there. [Here's]( URL_0 ) a mouldy video that contains practical demonstrations and more detail.", "The main thing that makes them stealthy is their shape. They're designed so that when radar hits them, it reflects at odd angles so that they appear a lot smaller than they actually are. You can still see them with your eyes though, so they're definitely not able to reach helicarrier levels of stealth." ], "score": [ 13, 6, 5 ], "text_urls": [ [], [ "https://www.youtube.com/watch?v=z5cR6EA2jGY" ], [] ] }

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{ "a_id": [ "gp5qje4", "gp5pgti", "gp5rudr", "gp5xs0d", "gp68gji", "gp5z8t2", "gp62hz0", "gp5zsbg", "gp67xlm", "gp5uz27", "gp5pmj6", "gp6w9fo", "gp7tx01", "gp5ps44", "gp60ilc", "gp7o5r6", "gp61ssv", "gp622zm" ], "text": [ "Bicycles are power and endurance limited by the cyclist so minimizing friction and drag are paramount. Racing cars on a track with curves is typically grip limited (ie tires lose grip before engine max power). So wider tires that improve grip reduce the time it takes to go around the track.", "Fast cars need a lot of traction, which means they need a lot of surface area on their tires. Otherwise, they spin out really easily thanks to the high speeds and power. Bicycles don't really have that problem because you aren't going fast enough for it to matter. Thinner tires weigh less and weight is a big selling point for bicycles.", "A really fast car with wide tyres would most probably be even faster with narrow tires, it would just suck at turning and accelerating, which is important things for most fast cars.", "The tire choice depends on what you want to do with it. If you have low acceleration and don't take many corners (and are able to lean into corners) you don't need very wide tires, so you go for the lightest. If all you do is accelerate, brake, turn into a corner, accelerate again, take a high speed corner etc you want all the grip you can get so you go for wide tires. This is combined in drag racing, the rear wheels are the ones that transfer the power of the engine to the road surface and 'push' you off. The front wheels are not used for acceleration ~~and braking~~ so they are very thin.", "Funny that you ask this because the bike industry is going through some major rethinking about tire width and speed. It used to be just accepted that narrower tires were faster and people accepted this because the vibrations made them feel faster. Now people are diving into it with data and the data are showing that the standard 700x23 skinny tires are not faster. The transmission of vibration and bouncing rather than rolling smoothly is actually working against speed. We're starting to seeing tire widths go up in the pro circuit and they'd probably go up faster if cycling didn't have such a devotion to tradition and institutional inertia. URL_0", "The fastest cars, land-speed record cars not formula one cars, also have very thin tires. The premise of this question is wrong.", "That's actually not true for bike tires. On a perfect surface skinny tires are faster but on normal road conditions a slightly wider tire is faster. That's why pro's have gone from 19mm tires up to 25mm tires recently.", "Fastest cars don't have wide tyres. Th best racecars have wide tyres - however they are not even remotely closeto being able to set landspeed records.", "This is actually changing as road bikes move towards wider tires. There are a number of factors to balance including: 1. Air resistance. 2. Rolling friction and contact patch size. 3. The feel of the bike and riding comfort. Many of those issues don't matter to the same extent with cars. For instance aerodynamics... When the car itself is 6 feet wide it matters a lot less just how thick the tires are. Similarly riding comfort is less important when the human isn't being asked to provide the power. This more naturally biases those cars towards wider lower pressure tires, but these days road bikes moving in the same direction.", "Fast cars regarding top speed need little turning or accelerating ability as they reach their speed at a steady rate and in a straight line. Fast cars on a track need wide sticky tires for the largest contact patch available in a corner and because they accelerate at a insane pace.", "Thin tyres reduce fraction - as the power of the cyclist is limited, you choose the as lightweight as possible option Cars have enough power - and wide tyres give them better tracktion", "Because cars cannot lean when they turn. The fastest cars do have really narrow tires URL_0", "As an avid cyclist and a physics teacher, these comments worry me. There’s a lot of confidently incorrect comments going on around here.", "Thin tyres equals less resistance on the road resulting in less effort required to peddle. Thick tyres on a fast car does create more resistance but the advantage of having more surface area on the road allows for more grip and so the ability to put more power down before having wheel spin.", "Bicycles are limited to the power of the rider, so to make them faster you reduce resistance by using narrower, high pressure tyres and making it more aerodynamic. Fast cars have plenty of power, and are limited in how fast they can (safely) drive by how much grip they have - put 1000hp in a car on tiny tyres and it can drive fast, but will wheelspin when accelerating and skid when braking or cornering. Fat tyres give more contact area with the ground which improves grip.", "Note that jet powered cars on the salt flats use skinny tires. They have no need for traction.", "Cyclists are actually moving away from the thinnest tires as the weight and aerodynamic benefits do not outweigh the benefit of added traction with wider wheels. So basically, your initial statement isn't correct.", "Think about the front tires on a drag race car, they are very thin just like bicycle tires specifically to reduce rolling resistance. The reason cars need wide drive tires is because the extreme amount of power needs traction however just like a wide tire robs speed on a bicycle it robs speed in a car, the difference is the car has to have them for traction and the bicycle doesn’t. TLDR the cars engine makes waaaay more power than a human and cars are waaay faster so it needs bigger drive tires" ], "score": [ 14214, 3108, 274, 159, 33, 28, 26, 25, 16, 12, 7, 5, 4, 4, 4, 3, 3, 3 ], "text_urls": [ [], [], [], [], [ "https://www.renehersecycles.com/12-myths-in-cycling-1-wider-tires-are-slower/" ], [], [], [], [], [], [], [ "https://www.racecar-engineering.com/articles/the-tech-behind-the-bloodhound-ssc/" ], [], [], [], [], [], [] ] }

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{ "a_id": [ "gp64y4i", "gp630yr" ], "text": [ "Once the windows are in everything is fairly enclosed. Then electrical, plumbing & heating are installed. This takes weeks. Plenty of time for drying out. Space heaters & fans used if needed. Drywall installed near the end of the process", "Yes after building the house is wet and needs to be dried by cranking the heating up for a few days to weeks. At least thats the procedure for brick houses" ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gp74qy3", "gp74y9p" ], "text": [ "Music is sound, and sound is vibrations. A record has a very fine spiral that goes from the outside to the inside. In this spiral, there's tiny, tiny bumps that make the fine needle that's carefully resting in the spiral jump and thereby vibrate, making sound. If you have a sound at 400 hertz, meaning 400 vibrations per second, there will be 400 bumps on a record that makes this sound. To get the sound in the first place, a \"microphone\" that's actually just a plate with a needle behind it is exposed to the music, vibrates with it and etches that into a stencil out of which vinyl records can be made later on.", "Sound is a bunch of vibrations. To capture this one a plastic disc, you need to carve little canyons into the plastic that correspond to tiny movements based on the sound being produced. When you drag a very sensitive needle across it, it replays that sound." ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gp7rz3q", "gp8alzo", "gp8m8e0", "gp87jxc" ], "text": [ "In 4 wheel drive mode, all 4 wheels are driving the vehicle and turning at the same rate approx. In all wheel drive mode the computer picks which wheels get power based on direction of the vehicle, road conditions, turning, etc. All wheels have the potential to have power, but don't have power all the time.", "4 wheel drive is either on or off and is manually engaged to lock the 2 wheels not normally powered so that they also get power. All wheel drive is computer controlled and automatically sends power only as needed to other wheels because of slippage detected in ones that typically provide power.", "I don’t have an answer better than others have commented, but just wanted to say that your quip about the spare tire spinning cracked me up. Thanks for the laugh.", "These days, the SAE standar (SAE J1952) does not differentiate (anymore) between 4WD and AWD. Definitions are now part-time AWD, full-time AWD and on-demand AWD. & #x200B; Historically, 4WD was used for cars that have a transfer case and allow you to select low and high gears (a system with two gears for the secondary axle). However, these days, most systems are automatically controlling power/torque over the different axles, which makes all \"traditional\" definitions of 4WD and AWD very blurry. Probably the reason for SAE to try to define a clear terminology. Going a bit deeper in the SAE definitions (didn't double check the standard, so there might be some slight inaccuracies ...) \\- full-time AWD: by default all four wheels deliver torque/power all the time, the power to each wheel can -pending the system- be passive or active regulated. But in essence all wheels are always connected to a powersource (engine / electric motor) \\- on-demand AWD: the secondary drive / wheels are only producing torque when needed (typically controlled by the vehicle based on your throttle / vehicle behaviour / steering wheel / ...). For most smaller cars the front wheels would always be connected and rear wheels would only be \"connected\" when needed. This tries to reduce losses when AWD is not needed. \\- part-time AWD: you can push a button / lever to get your vehicle in AWD.Traditional 4WD would fall under this." ], "score": [ 26, 6, 4, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gp9m1jk", "gp9i3e0", "gp9lzo6", "gp9wy2m", "gp9llvt" ], "text": [ "At the core of all \"jets\" is the actual gas turbine. It consists of the compressor stages, the combustion chamber, and be the turbines that capture energy from the exhaust gas. All the variants strap different bits on the front or rear A high bypass turbofan on a jet airliner straps a fairly large fan on the front and spins that slowly (relative to the compressor) to accelerate a huge volume of air just a little bit and directs most of it around the compressor and turbines A low bypass turbofan like on a jet uses a smaller fan to accelerate some air more and puts a nozzle on the back to get more thrust from the hot exhaust gas A turboprop is a lot like a high bypass turbofan but instead of driving a pretty big fan they drive a really big propeller and direct almost all the air around the main turbine, but the compressor stages can pull in more than enough air for what it needs. The gas turbine portion of a turboprop is much smaller than in a commercial jet liner or fighter jet, and the propeller take a huge amount of air and accelerates it just a tiny bit to push the plane along making it quite fuel efficient", "Nope, the propeller is there just to move more air, providing more thrust but without also trying to push the plane too fast. They use normal jet engines but then use gears connected to the center of the turbine to spin the prop but at a much lower RPM than the jet engine. Basically they're using a jet engine to spin a propeller instead of a piston based engine. Helicopters work in a similar way. They have a jet engine, but the jet itself isn't being used to provide push. It's just being used to spin the main prop.", "You can kind of think of a turboprop as the same as a turbofan, except the ducted fan is replaced by a non-ducted propeller. The ducted fan itself doesn't contribute to compressing air prior to combustion, as the air the fan encounters is bypassed to produce thrust. Just like the fan which is driven by the turbine, the turboprop propeller is also driven by the turbine. The main differences between the turboprop and the turbofan have to do with the advantages and disadvantages of using a ducted fan vs. a propeller. The propeller has a higher aspect ratio, so it can be more efficient, this also means it has to operate at a lower flight speed/RPM which may require a gearbox. The ducted fan can be operated at a higher speed due to being smaller/slowing air down first due to the duct. Ducted fans are also quieter then propellers. Basically the suck on both the turboprop and the turbofan is done by the core stage, which is independent of the fan/prop. Between the bang and the blow, there is also a turbine, which is what drives the compressor (for the squeeze), and also the fan/prop. Neither the fan/prop actually do any suck/squeeze that contributes to the core stage (the ducted fan may compress the air, but its not the same air that is later combusted).", "A turbojet creates thrust by compressing air, adding heat from fuel, using some of the energy to turn turbine to drive the compressor, and then blowing the high-pressure air out the back through a nozzle. A turboprop works the same way, but instead of squirting high-pressure air out to create thrust it uses a bigger turbine to drive both the compressor and a propeller. It's pretty similar to how a turbofan works but if you didn't get any thrust at all from the jet part.", "Turbo props suck in air the exact same way a turbo jet engine does. There's a little fast spinning fan in front. The difference is, rather than using the hot gas coming out the back to push the plane forward, they instead put a gear on the spinny bit in the jet engine and use that to spin a propeller much slower. As only a tiny bit is spinning very fast, it can be very efficient. For comparison, a turbo fan engine put a big fan on the spinny bit, and uses that to push the plane forward." ], "score": [ 8, 7, 5, 3, 3 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "gpbk6zc", "gpbklue", "gpbkly5" ], "text": [ "Rockets are typically launched over the ocean for this reason. The \"boosters\" which is more or less what you're referring to can be reused/refurbished potentially, after being recovered from the ocean", "They just crash. Rockets are usually launched over ocean or deserts^[1] to reduce the risk of debris doing damage when falling down. China is a notable exception and there have been instance of rocket parts crashing near or in villages. One exception is the falcon 9 core which tries to come back and land. (F9 fairing also do) *************** [1] the ESA launch from kourou in south America, going east over the Atlantic. The USA does the same from Florida and has a launch site in Vandenberg, CA. which launches going south over the pacific. Russia launches from Plesetsk or Baikonur (Kazakhstan), going north-east over Siberia & the arctic ocean.", "There absolutely is! Launch sites are selected with this in mind, generally resulting in a location with a wide expanse of water or deserted land along the entire launch path." ], "score": [ 11, 5, 4 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gpdh0ik", "gpd971c" ], "text": [ "Think of it like a chain. First link in the chain is the idea, move water from point a to point b, next link is you decide to put it in buckets, next link is the size of the bucket and you go off what a human can carry and so on. You aren't getting enough water. What do you do? You go back to first principles. Moving water from point a to point b. Then examine each part of the chain to see if the assumptions built into it still work. Maybe the amount of buckets you would need is too great, you need to start inventing pipes, buckets are a dead end.", "The idiom used is typically \"starting from first principles\". At least unless you give some kind of context. There is no \"thing\" called First Principles, generally. The idiom means to start from the basics. An example: Much software borrow pieces of code from previous versions. If the developer says their new application was developed from first principles, what they mean is that they developed all new code and did not reuse old code." ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gpdmxxf", "gpdor6w", "gpe344r", "gpdgxhf", "gpf7h3c", "gpemtnm" ], "text": [ "I'd love to know how you're managing to go through wiper blades in 6 months? The wiper blades on my car haven't been replaced since I bought it 3 years ago and they're still working fine.", "If you're constantly dragging your tires across the road (burnouts, skids, doughnuts), they aren't going to last anywhere near 70,000 miles. If you had rollers instead of wipers on your windshield, they'd last a lot longer, though wouldn't really get your windshield clean. Also, when you get a tiny pit in your tire, they still work fine. Not so much with wiper blades.", "They're both made of rubber, but do different jobs. Perfectly cleaning a windshield is a lot harder than rolling on the ground. Is it harder to walk down a sidewalk with a suitcase, or paint an entire sidewalk green?", "Rubber comes in many flavors, natural and man made. You can also mix the two together to make a lot of unique blends. You normally add surfer and and an anti oxidation as well as other chemicals and minerals. Thus you can make a durable rubber that lasts thousands of miles as a tire, an Expensive tire. If it did not last long, guess what, I buy someone else's, so there is an incentive to create long lasting tires. Wiper blades are cheap. $7-$30. So they are made from a cheaper to produce blend. Cheaper would also mean lass anti oxidants, less pigments against UV, you know, the sun. And last but not least, heat. A tire can handle heat dissipation better, more mass, filled with air. The little wiper bakes in the sun.", "I'm not a scientist or an engineer but maybe it has to do with the fact that one is rolling on the ground but the wipers are rubbing with friction against the glass? plus glass is harder anyways.", "Not an expert but i'd guess it has to do with the shape. Wipers are a bit like razor blades, long and thin, and they need to be pretty \"even\" (the \"blade\" needs to touch the surface of the glass equally to not make stripes). Dragging the wiper across the window will inevitably lead to part of the \"blade\" getting a tiny bit more resistance and thus wear out sligthly faster which means the blade will be uneven and it will cause stripes. Tires will also wear unevenly, but it's not as much as a problem in tires, because they'll still perform normally even when a part of them is worn. As long as they have grip, they'll still perform their function. But a wiper that only wipes part of the glass is pretty much useless. So I'd say, the function and the shape are important metrics here. Also, like /u/captainsalmonpants mentioned, wipers are skidding across the window, while tires are rolling. Skidding creates a lot more friction and therefore wear. Just like if you'd slide a knife across a surface over and over it would get blunt really quickly while if you actually cut things with it, it doesn't really get blunt that quickly. Unfortunately we haven't found a better way to wipe windows, because the act of wiping in that way does naturally wear out the blades quickly, just because that specific motion is pretty taxing to the material." ], "score": [ 42, 27, 6, 4, 3, 3 ], "text_urls": [ [], [], [], [], [], [] ] }

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{ "a_id": [ "gpjib8e", "gpi5jua" ], "text": [ "Most V8 engines are what they call a \"cross plane\" design. This causes periodic interference between exhaust pulses that give the distinctive \"V8 burble\". The other kind of V8 is a \"flat plane\" design, most often heard in Ferraris (though Ford has used their own version in the Shelby GT350). That has a smoother sound without burble. The sound can be changed by varying the length of the exhaust manifold runners to add or remove interference, but the default sound is what you are used to hearing.", "I don't know if I agree that a I4 sounds \"faster\" than a V8, but they are distinct. One thing to remember is that in a V8, typically no two cylinders get to the top/bottom of the travel at the same time.... Or another way to put it is that all the cylinders are timed to fire separately from one another. This is different from say a V6, where 3 cylinders go up and down at the same time, so in terms of \"pulse\" you are really feeling the combined push of three cylinders at a time, where a V8 you can feel the pulse of each individual cylinder. For that reason you get that rough v8 burble noise." ], "score": [ 3, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gpi5vx2", "gpi5x0h", "gpidg0d" ], "text": [ "Jet engines are so incredibly strong that if there was a grille it would simply chop up the bird. Either way, anything biological in front of that engine is going into it or getting stuck on it and preventing air flow, so there’s no use wasting time and money to design and implement a component that is essentially useless.", "They're 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.", "They're not worth it. A grille would block airflow into the engine which would directly reduce thrust and require the engine to use more fuel. It's also going to be heavy and either reduce the plane's payload or require it to burn more fuel. It's also useless for most of the flight. Bird strikes happen at several hundred mph/kph. That's going to tear the bird to pieces and likely damage the grille as well sending bits of metal into the engine which is *exceptionally worse* than bird bits." ], "score": [ 7, 4, 3 ], "text_urls": [ [], [ "https://www.picfair.com/pics/02559401-helicopter-rotor-blades-and-engine-air-intakes" ], [] ] }

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{ "a_id": [ "gppfxtz", "gpppeab" ], "text": [ "I would say the business model is a huge factor. If you want a custom SoC, ARM is a cheap way to do it. ARM sells an IP core (think the design), so you can configure and add stuff, and then send that off to a chip factory to make an SoC. ARM runs Linux well, it's got good performance, and unlike x86, you can get the chip customized.", "a lot of it is licensing x86 is too closed. only intel/amd can design new chips, so you're stuck with whatever they make. because intel/amd have been in an arms race of performance they neglected efficiency so x86 is bad for phones. there have been x86 phones but their battery life was terrible openRISC is too open. anyone can make their own purpose-built chips, but you have to share whatever design you come up with. that alone makes them a non-option for companies that feel compelled to hoard their \"trade secrets\" ARM is a goldilocks zone for these companies. they give just about any company lots of freedom to design their own chips and little requirement to share anything. there are low-power ARM systems that barely use any electricity at all, and there's apple's M1 that competes with high-end x86 CPUs of course there are other architectures between x86 and openRISC but they may have other shortcomings. for example, POWER licenses were expensive as fuck and given out sparingly before IBM open-sourced it another advantage of ARM is that ARM Holdings made decent reference designs available for use. companies can design their own chips, but they can also just take stock ARM cores and throw them in their SoCs as-is" ], "score": [ 8, 6 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gpps7cy", "gpptr2k" ], "text": [ "A clutch is the intermediate between the engine's output and the transmission's input. It's essentially a hjgh-friction surface that mates to both components, and transmits rotational force. When you shift gears, the engine needs to be momentarily disconnected from the transmission by pushing the clutch because their speeds will become desynchronized as the transmission shifts into a new gear. When the clutch is released, the friction surfaces \"grab\" onto the transmission input and the two resynchronize back to normal driving speed. Without a clutch, shifting would have to happen with the engine spinning at exactly the right RPM for the desired gear before shifting- this is known as [floating gears]( URL_0 ).", "The problem is a combustion engine can't start turning from stop - that's why it needs a starter motor... but we need to be able to connect it to the wheels of a car that is stopped without grinding the metal of the gears together and allowing us to do so gradually for that acceleration. If the weight of the car were introduced to the engine instantly it would just force the engine to slow down so much it would stop - this is stalling the engine. So how do we get the car moving when what we have is an engine that can't be stopped? Gears alone can't solve that specific problem. The answer is to introduce another part - the clutch. It tolerates slipping - it can move at a different speed from the engine and partially transfer the power. So we can use the clutch to introduce engine power gradually while allowing the engine to spin faster than the gears during that starting-from-a-stop phase. The clutch is a big round disc with material on it like what your brakes are made of. It connects to the transmission/gearbox facing the engine with that brakepad material facing the engine. The engine has a big round disc of its own facing the clutch which is what the engine is turning, and the clutch is push into this engine disc by a strong spring-like mechanism. Like brakes they lock up when the pressure is at maximum and they're as good as bolted together most of the time, spinning together. However the clutch pedal, when pressed, pulls the clutch disc away from the engine. The pressure on the clutch pedal is that spring. As you release the clutch pedal the clutch disc is pressed back into the engine. When the clutch is partially down there's partial pressure onto the engine, like when you're applying the brakes gently to stop - rubbing together causing a force to be applied. To prevent grinding gears when moving the gear lever around, press the clutch pedal all the way down so the clutch disc is fully separated from the engine. Now with minimal weight on the gears you can move between them without issue. Release the clutch slowly so the friction between the clutch and engine will make the engine slow down a little bit - add gas here to help compensate - and the gears will start slowly turning, hence turning the wheels. Now... in theory you don't need to press the clutch pedal to change gears while moving. If the engine speed is exactly correct for the current car speed, then the gear lever will go into gear without fuss even if you don't touch the clutch pedal. In practice there is very little room for error here and a mistake will cause metal to grind. Disconnect the engine from the gearbox while changing gears to make the procedure safe, and then reconnect the engine and gears with the clutch. Let it take the speed difference - that's what it's designed to do. Seriously, never do this." ], "score": [ 9, 3 ], "text_urls": [ [ "https://en.m.wikipedia.org/wiki/Float_shifting" ], [] ] }

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{ "a_id": [ "gppy1v9", "gppx6ja", "gpq00a1", "gppxnz1", "gpq2znf", "gpq23va" ], "text": [ "Getting into space isn't about getting high up. It's about going really really fast horizontally so the arc of your trajectory causes you to continually miss the ground as the earth curves away from you. The only reason why rockets go up at all is because they want to get out of the atmosphere (or at least to the very thin parts of it) so drag doesn't slow them down. So flying up into the atmosphere doesn't really help achieve this objective all this much, other than slightly reducing the initial drag force. Planes need air to provide lift. The higher go, the less they can lift, so the smaller the payload they can lift. So an aircraft very quickly becomes ineffective at lifting any sizable rocket up into the air. In theory air-launch can be more efficient than vertical launch for some smaller rocket sizes, so they have been attempted. But the margins are actually quite small. And the maneuver from horizontal to vertical often requires added aerodynamic surfaces to perform, which means the added drag and weight of these features offset the theoretical efficiency gains made. They just aren't worth the added engineering complexity. As it turns out, the best vehicle for lifting a small rocket up high above the ground is a bigger rocket. This is basically what a two-stage rocket is.", "Don't have to but, fuel has weight and it takes a lot to reach that height. A large Craft carrying fuel to reach orbit needs to be as light as possible. Apollo fuel load was about one million pounds per stage. Going off memory here, could be wrong. Going straight up reduces forces on the Body of the rocket to mainly length-wise.", "The term for this is air launch to orbit. Its only slightly more efficient (space is surprisingly close to the ground), and leads to a large increase in mechanical complexity. It does make a little bit of sense for very small payloads that don't really need to make it to orbit. Like rockets on a fundamental level are pretty simple things, and we still mess them up every now and then.", "You need wings and control surfaces to fly like a plane, and they become redundant (excess weight) when you leave the atmosphere. Orbital rockets start going straight up, but soon roll over to take an orbital path", "Getting to orbit is the easy part of a launch, it's staying in orbit that's hard. To do that you need to go really really fast to the side. For low earth orbit you need to be going at **7.8 km per SECOND**. For comparison, the SR-71 is the fastest jet plane ever made, it took insane amounts of engineering to get the plane's outsides to survive the kind of forces that its speed through the atmosphere was putting it through. That speed was about **1** km/s It was spending so much energy fighting against the atmosphere slowing it down, which was also heating up the aircraft and putting stress on the hull. So rather than fighting the atmosphere, they boost past it and start going sideways after they're out of the vast majority of it. Furthermore, the SR-71 was operating at the edge of how high jet planes can possibly work at. About 25 km up. The minimum line for space is 100km up. Low Earth Orbit is usually 200km up. TL:DR even the best jets only work at a tiny fraction of what space ships need to work at.", "In a sense, that's what we do. First we go straight up to get out of the thick atmosphere to reduce drag and fuel consumption. then as we get higher, we actually move towards the horizontal to build up speed and gain orbital velocity. If you took off from an air strip and flew up like a plane, you'd just be fighting the thick atmosphere and taking a lot longer to get to an altitude that lest you get your speed up enough to get into orbit. Virgin Galactic tried to bridge that gap by making the orbital module launch at very high altitude from an aircraft designed to get it there, so kind of a hybrid concept. Another idea was to put a launch platform under a bunch of ultra-high altitude balloons and launch from there. Whatever the case, the most expensive fuel consuming part of the flight is from ground level to very high altitude where you don't have to fight the atmosphere to get your speed up. ELI5: Air is thick, so you want to get above it as fast as possible. You can worry about getting orbital speed when you're really high up." ], "score": [ 18, 8, 4, 3, 3, 3 ], "text_urls": [ [], [], [], [], [], [] ] }

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{ "a_id": [ "gps1l9a", "gpsqflw", "gps4586", "gpt8h6v", "gprz2nr", "gpsz6rm", "gptgc83", "gptln28", "gprz75l", "gptmdef", "gpte4cp", "gpt7ro1", "gptu1ni" ], "text": [ "Pilot here- it's 99% theatrics to make it more dramatic in TV and movies. The 1% of the time when it's real would occur in only a couple situations. In a fly-by-wire aircraft, the pilot's inputs are fed into a computer that in turn actuates the control surfaces. A malfunction in the computer that causes a sudden, extreme control input, such as what happened in [Flight 302]( URL_0 ) would be a situation likely to have the pilots fighting the controls to override the input (though there are established procedures that go beyond just fighting the control input) In a manual flight control aircraft, where movements of the flight controls move pulleys and wires attached to the control surfaces, a failure such as a jammed pulley or sudden disconnection could leave a control surface-and the plane- in a dangerous configuration in which the pilots might be attempting extreme control inputs to stabilize the aircraft. But overall, dramatically fighting the controls as in movies is a mostly futile endeavor. There are procedures and redundancies in place in most aircraft that make it unnecessary.", "As others have said, that's largely theatrics in movies and TV. There are essentially three systems in use: * Fly-by-wire is what you will predominantly see in modern airliners and military aircraft. Here, your stick isn't actually physically linked to any control surface - instead, your inputs send signals to a computer which then positions flight control surfaces to do what you are asking the computer to do. The computers are, in relaxed stability aircraft (like fighter jets), actually continuously sending signals to the flight controls to keep the jet flying stable. In some aircraft, if you turn off the flight control computers entirely, your jet is no longer able to maintain controlled flight. In this case, the fighting control stick does absolutely nothing. In fact, you won't even feel the actual feedback from flight control surfaces on aircraft because the stick isn't directly linked to them. * Hydromechanical. This is used in older fighter jets and in airliners/aircraft with big control surfaces. Basically, when flying at faster speeds (which creates larger pressure/air loads on control surfaces), human power isn't enough so the control stick is *mechanically* linked to hydraulic systems that move the control surfaces for you. These hydraulic circuits operate in the thousands of psi. For instance, if you pull the stick back, you are mechanically telling the servos and actuators to move the stabilator (or elevators) to pitch the aircraft up. In this case, if you did have something go wrong, fighting the stick doesn't do much either. Most likely, if something went wrong, it's because your hydraulic line or mechanical linkage broke, or you lost a control surface. In which case, fighting the controls won't do you anything. * Direct linkage. This is what you commonly see in older aircraft/lighter aircraft/general aviation like in your Cessna. Here your control surfaces are directly linked to your control stick/rudder via wires and pulleys. You will directly feel the loads on the control surfaces. Here is where you could, like in the movies, perhaps try to fight for control via physically fighting the stick more. A jammed linkage or connection might require more force to fight through. But even then, you risk breaking something even worse (sudden snapping of control surfaces can overwhelm mechanical limits) OR getting into a PIO (pilot induced oscillation). MORE likely to happen is if you have a failure in a control surface (e.g. an aileron fails), you have to put in some input like rudder or opposite aileron to keep the plane flying straight and level. In that case, you are \"fighting the controls\" by keeping some force on the stick to maintain the flight attitude you want. But you aren't \"fighting the stick\" like in the movies - instead, you're precisely and finely putting your control inputs in (or trimming the aircraft) to offset what was lost.", "They don't, that's just in the movies. In fact fighting the controls can make things worse. A perfect example is [American Airlines Flight 587]( URL_0 ), the aircraft flew into the turbulence behind another aircraft, and the First Officer, who was the pilot flying, panicked and fought the rudder so hard that he ripped the tail off causing the aircraft to crash killing everyone.", "Helicopter pilot, answer is you don't unless the hydraulic system has failed. This is less likely the larger the helicopter as they have multiple independent hydraulic systems so one failing has no effect at all. Smaller helicopters like Jetrangers or Astars are harder to control with a hydraulic failure but not even that bad, we train to land with the hydraulics off by flying real aircraft with the hydraulics turned off, it isn't considered dangerous to do so. For a large helicopter if you somehow had all hydraulics fail at the same time depending on the type it is a major emergency and possibly unrecoverable.", "The controls are often (especially in older aircraft designs) physically linked to the control surfaces by steel cables. If the force of air is pushing on the ailerons/elevator/rudder it's also moving the stick around.", "One thing I haven't seen directly mentioned is World War II era fighters/bombers were all cables and pulley rigging for the control surfaces. If those planes dive at the ground during dogfights or attack runs and get going really fast, the forces to move the controls becomes extreme. Thus, you could get into a dive you couldn't physically pull out of. So, this can be quite realistic for some movies but for modern aircraft the biggest issue where a pilot is straining against the controls is something like runaway trim/autopilot. For most everything else you're not fighting with the controls.", "Another pilot here. All the controls in my plane are directly connected to the yoke and pedals (manual). When airflow is low, especially during slow flight such as during landings, controls require exaggerated expression. They don't have much lift being generated to cause a change. Alternatively, very strong winds in lighter aircraft can definitely cause you to fight. They can quickly push you and change your pitch, yaw, and roll (these are the axis of motion). In this case you have to counter the effects of the wind. Most of this is experienced extensively by all pilots in training. But it can take real physical effort (without much return from the controls). Usually however, you fly with \"two fingers\". A light touch will do it 9 times out of 10 if you're trimmed in (tuned controls to stable). Remember, flight is across long distances and you generally navigate on 10° increments (eg 010° - 360°) or smaller so planes must fly on small movements and corrections not grant turns like you see on movies. The only times I've ever done movement like that when not training and with passengers was during some landings where the wind goes dead on me or once with an engine out on takeoff with about 400 feet below me to return to runway.", "Probably the same reason in NASCAR movies the cars have 73 gears and that final majestic last gear that only the hero uses to win the race when all the other drivers were afraid to do so. In other words: pure bullshit purely for the sake of cinamatics.", "They don't. That's a thing in movies. When things go wrong it's usually caused by damage and/or pilot error.", "we don't. you've been watching too many movies. most of the time the pressure from your pinky is enough to make all flight adjustments. if there's moderate to heavy turbulence, I'll hold on with my hand If it's heavy or more, I'll stay home.", "Do they? Or is that just what you've seen in movies?", "There is one plane crash (can't remember which one ) where the two pilote were inputting opposite order on the stick, basically fighting each other Edit: it's [AirAsia Flight 8501]( URL_0 ) Don't know if the two sticks are linked", "Answer: Former helicopter mechanic and crew chief here. Helicopters have a mechanical linkage from pilot input to control output. These linkages are hydraulic assisted. In emergency situations, you may lose or have to disable the hydraulic servos. As you can imagine, the feedback from the rotor blades can make it quite difficult to smoothly operate. As an example, when you drive your car, stick your hand out the window and feel the air flowing. Your muscles are the servos controlling your hand. Now imagine you didn't have control of your finger but still control hand overall. It's a rough, but you can still keep your hand more or less in place, even if the finer details aren't the same." ], "score": [ 9533, 465, 132, 66, 64, 29, 17, 11, 9, 8, 7, 5, 3 ], "text_urls": [ [ "https://en.m.wikipedia.org/wiki/Ethiopian_Airlines_Flight_302" ], [], [ "https://en.wikipedia.org/wiki/American_Airlines_Flight_587" ], [], [], [], [], [], [], [], [], [ "https://en.wikipedia.org/wiki/Indonesia_AirAsia_Flight_8501" ], [] ] }

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{ "a_id": [ "gpsrelj" ], "text": [ "Notes are not major or minor. It's only the relationship between notes that is major or minor. C and E is a major third interval, C and Eb is a minor third. On a well-tempered scale, the ratio of frequencies in a major third interval is 2^(4/12), about 1.26. In a minor interval it is 2^(3/12), about 1.19." ], "score": [ 18 ], "text_urls": [ [] ] }

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{ "a_id": [ "gpxmrtw", "gpxw9en", "gpxjonv" ], "text": [ "Internal combustion engines have a lot of moving parts. There's the spinning crankshaft, the pistons going up and down, the valve cams that open and close the intake and exhaust valves for each cylinder, the timing chain or gears that keep those in sync with the crankshaft, the water pump, alternator, oil pump, fuel pump, and probably more stuff I'm not thinking of at the moment. Because of all those moving parts, the engine has limits for how fast it can spin. If it spins too fast, the physical limits of the metal all those parts are made of is passed, and something will break. But at the same time, internal combustion engines also don't work very well at low RPM's. Too low and they'll completely stall. Because of that and the aforementioned limits, they can only work between about 1000 RPM and 4000 RPM for average cars. So, in order to be able to go 15 MPH sometimes and 80 MPH other times, there needs to be a gearbox to allow the engine to maintain that operating RPM range despite how fast the car is going. **Electric:** Electric motors don't need to maintain a certain RPM in order to deliver power. They can exert full power from a dead stop and also exert the same power at full speed at 100+ MPH. So there's no need to have a gearbox at all. An electric car's motor can be rotating at 10 RPM while crawling down a driveway without issue.", "Combustion engines have to run at a particular set of speeds (RPM) such that they can sustain their momentum. The pistons roll round from the previous explosion and get into place for the next, and if they fail to get there in time, the next piston won't be ready for the next explosion and you'll get a stall. Alternatively, they can only move so fast and do so many explosions in a certain time (heat, strain on the components, lubrication, etc.) Thus a combustion engine has a range of RPM that it can run at before it either stalls or becomes dangerous. This RPM range does not generally match the speeds that you want the tyres to go round at, thus you have to gear it right so that the best RPM (efficiency, power, etc.) matches with a good road speed. The problem is that the range of RPMs isn't enough to just link it to the wheels directly. You'd be very limited in road speeds and extremely inefficient. And there's no one fixed gearing that would be suitable - you'd either have trouble pulling away from a standing start, or the engine would be SCREAMING along trying to get you to a reasonable speed. So you use gearing to select different gears depending on what you're currently doing. An automatic will select from those gears for you, in a manual you have to know to pull off in first, corner in second, and get up to 5th/6th gradually on a motorway, and to know when to change between gears so that the engine doesn't hit unnecessary strain and is able to change smoothly between gearings without the RPM going too low or too high. In an electric car, it's just an magnetic electric motor. As you apply voltage to it, it turns. You connect it direct to the wheels. There's almost no lubrication, there's no mismatch in speeds to compensate for, it's just directly driving the wheels. The more voltage you give it, the faster it goes, and it can turn slowly or very, very fast without hindrance. It literally fits all the speeds you want to do, directly, without having to match speeds between engine and wheel.", "Electric motors can deliver full torque at any speed, while engines have a torque to rpm curve where they produce maximum torque at certain speeds. A gear box will allow the driver to allocate the optimal torque to different speeds." ], "score": [ 288, 19, 5 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gpxu7qs" ], "text": [ "So, sound is just air moving back and forth quickly. The faster that back and forth is, the higher the pitch, whereas if you make those back and forth movements bigger, you get a louder sound. With vacuums, the motor inside is moving a lot of air in order to collect the dust and hair and things you want to clean up. A natural byproduct of this is lots of noise. One way that engineers can reduce the sound something makes is by insulating the motor. This prevents some of the sound from reaching your ears with the same intensity as a non-insulated motor. You can also make the parts of the motor so they move the air more smoothly, reducing vibrations and therefore noise. Somewhat related, but a good vacuum cleaner should be kinda loud. It’s an indication that lots of air is being moved through the machine, meaning more dust picked up. My mother has a Kirby from the 80s, that thing sounds like a jet engine but it cleans the carpet to within an inch of its life." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "gq03yc5" ], "text": [ "If you own a car and I take your car to make some uber trips and earn some money, you'll be angry, even if I return it in good condition and replace the gas I used. Why? Because it's your car. I didn't try to sell it, and I returned it, and I agree that it's your car; but it's still not OK. The point is that you could have chosen to rent me the car, or not, and I stole that choice from you. You got your car back, but not your choice. Especially if you would not have rented a stranger the car. Now just replace \"car\" with \"data\". If you would never have rented your medical records to help a drug marketing firm, they are stealing your choice. If you would have rented those records, they avoided paying you. It's wrong either way." ], "score": [ 10 ], "text_urls": [ [] ] }

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{ "a_id": [ "gq10xkr", "gq0x6kw" ], "text": [ "Long one for ya Well hmm. The entire premise of a space suit is protection but there is a lot of little things that go into protection of a suit as well. Not only that but it also depends on the suit! I will assume that we are talking about the big white Extravehicular Activity suit (EVA suit) First problem: protection from vacuum! Solution: make it air tight. Problems it has: How do you get rid of CO2 or bad air? Solutions: vent bad air and add more or create a system that makes new air! Problems: now we need bulk on back and it's heavy Solution : No weight in space!!! Second problem: moooommmm. It's hooottttt. Now immm cooollllld. Solution: Insulation! Problems it has: I am now a 4\" round ball of fluff and can't move new solution: liquid temperature regulation! New problems it has: its big and bulky New new solution: WE STILL IN SPACE!!! Third problem: that sun is awful bright. Solution: sunglasses! Problems: I look cool but now I can't see when it's dark out and I can't remove them because helmet New solution: add a giant \"pair of sunglasses\" to the outside. NOW YOU LOOK LIKE BUZZ LIGHTYEAR Forth problem: that sun gives me cancer faster now Solution: lots of lead!!! Problems: we can't move when we are encased in metal New solution: make lead into a kind of fabric. New problems: I am now fluffy again and can't move my joints. Solution: Metal joints work better than fabric! Problem: air escapes again! New solution: air tight fabric OVER the mettal joints. There are so many other things that they have to add to fix these problems. Example. How do you itch your nose? Add a sponge on a stick in the helmet!!!", "The space suit is trying to do a lot of things: 1. Keep air in. 2. Maintain shape with a vacuum on the exterior 3. Allow for movement 4. Keep heat out (space is hot when you’re in sunlight, and a very effective insulator when you’re not) 5. Protection from micro-meteors This is a pretty rough set of requirements, and a few more I’m sure, so needs a lot of layers and a lot going on to work properly." ], "score": [ 30, 7 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gq3m7st" ], "text": [ "There are two possibilities, depending on if you're seeing it with your own eyes or through a video camera. If you see this effect with your eyes, like when a car is turning out in front of you at an intersection, what's happening is that the Sun or some other light source is reflecting off the hubcap and as the car turns the angle changes. The reflected light on the hubcap appears to travel backward and makes it look like the tire is rotating backward. If you see this effect in a video, it's because the wheel is spinning faster than the camera is recording frames. Consider drawing a dot in white sharpie at the 12 o'clock position on a tire and taking a picture. Now let the wheel rotate clockwise until the dot is *almost but not quite* back to noon—now it's at the 11 o'clock position—and take another picture. If you compare the pictures it looks like the tire moved backwards a tiny bit, but actually it moved forwards a lot. There's no way to distinguish them. If this happens for a long time (a second or two) in a video it makes it look like the wheels are going backward consistently. See the wiki articles on [Nyquist rate]( URL_1 ) and [Nyquist frequency]( URL_0 ) for more information." ], "score": [ 4 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/Nyquist_frequency", "https://en.wikipedia.org/wiki/Nyquist_rate" ] ] }

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{ "a_id": [ "gq3ueqh", "gq3zaq8" ], "text": [ "You aren't really hearing electricity. Youre hearing the wires or whatever be literally moved around by the electric current and thats what you hear", "In an AC motor, transformer, or anything with an iron core, it is called magnetostriction. It is caused by the constantly reversing AC magnetic field trying to elongate the iron molecule first in one direction, then the other." ], "score": [ 10, 5 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gq51b5m", "gq53ntm" ], "text": [ "bistable refers to the fact that the circuit has two stable states. Anytime the circuit is between two of those two states, such a state is unstable and will collapse into one of the two stable states. For instance take what is called a flip flop, it’s a transistor circuit that outputs either a 1 or a 0, high voltage or low voltage, and usually remembers its state until an external trigger changes it. During that change say from high to low, there is a period when it is in the middle, but this is not a stable state and moves into one of the stable states.", "It's exactly what it sounds like: \"bi\" = two, and stable is...stable. It has two configurations where it's stable. An ordinary light switch is a bistable system: if it's on it stays on, and if it's off it stays off. Why it's so important is the fact that you can store information in it: a light switch \"knows\" that someone has turned it on before, even if that person has already left. Make a billion tiny light switches, automate the switching on and off, and you got yourself a USB stick (in veeeery oversimplified terms)." ], "score": [ 8, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gq90b6z" ], "text": [ "The two reasons you need a gearbox are: to change the speed of the rotation, or to change the output torque compared to input torque. To change the speed and torque you choose a gear ratio that when multiplied by your input, gives you the desired output. Sometimes this is best done by just having two gears, but sometimes it's much more economical (especially on very large reductions) to have multiple sets of gears that change the speed/torque in steps instead of through just one set of gears. To further increase the economy, you don't want to overbuild your gears. So each time you step up in torque, you need to make sure the gears, shafts, and housings that are supporting that step can withstand the new torque level, but not by insanely large factors. (This is a large reason why gears are different sizes and widths throughout a gearbox)" ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "gq8ywea" ], "text": [ "The upper theoretical limit is about 1 petabit per second, which implies a pulse rate of 15 petaHz or a pulse length of 1 femtosecond. REALLY fast. It means the length of the pulse is incredibly small, about 0.000008 inches. In practice you don’t go that fast, but it’s still really fast. Real cables going tens of Gb per second are perfectly normal." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "gqatwnf", "gqautpv", "gqb1dp4" ], "text": [ "There are cables under the oceans that can communicate using light. The speed of light is able to circle 7.5 times around earth in 1 second and that's how it is able to communicate in seconds. An simplified overview would be Your computer WiFi- > LAN to your Internet provider - > underwater cable to the Internet provider for the website - > LAN to the Website's building - > Website's WiFi Edit: Typos", "There are many thousands of wires that go hundreds or even thousands of kilometers around the world these have to connect to something. This is called a switch and works the same way to how different devices in your home work. The switch knows what's connected to each port and it can ask each decide at the other end of each cable what it knows. These switches communicate directly with each other using MAC addresses and can only be used to communicate directly, whereas an ip can be used to identify anybody on the Internet When you ask for a website let's say URL_1 that's fine but who is URL_1 how do I find them. You have to ask a domain name server like he one at the ip 1.1.1.1 so your computer sends a message to your network who has URL_1 tell me (in this case me will be 192.168.1.2 on your network likely nobody knows so you ask the domain name server the same question and it tells you it's at 172.217.25.132. Fantastic we know where we are going but how do we get there well that's not your problem. You send a message to 172.217.25.132 saying I'd like to connect that's gets sent to your router and your router says does anyone have 172.217.25.132. but this time we get a different type of response from a5:93:67:fa:6d:91 saying I can get it there so your router remembers this and sends the message there. This process repeats along every node until it reaches 172.217.25.132. Then 172.217.25.132 sends a message to 192.168.1.2(you) saying yes. Then you say ok I'm connecting. Then you request URL_0 and the server sends a message full of text to you.( You can. Look at this text by clicking inspect element.) This text is read by your web browser is displayed on the screen. Around these paragraphs sould be < p > and < /p > for paragraph your browser knows these are paragraphs I'm no professional so this may not be 100% accurate and it brushes over a LOT but it is the general prodcess of how it works", "The internet, and all technology really, operates on layers of abstraction. What this means is that when you do a complex thing, that complex thing is generally expressed at a high level in a simple way, and each component of that expression is itself explained at a slightly lower level in as simple a way as possible, and so on, down the hierarchy, until you get to the point of individual transistors and cables. This sounds a bit abstract, which is sort of the point - when you operate in a higher level, you don't really need to know about the lower levels *except* in abstract. Otherwise, it would be far too complicated to get any work done. When you write a recipe for cake, you don't need to explain metallurgy for creating measuring cups, or how to grow wheat, for example, since you can assume those things are handled at a lower level of abstraction. When you go to a website, a series of things happen, but where those things occur on their hierarchy vary; [there is the OSI model of networking]( URL_5 ) which has its hierarchy, but the actual way your keyboard, mouse, monitor, modem, etc, function are all their own hierarchies. The very short answer is, you resolve the IP address of the server, connect to it, and request the resource. This sequence of requests is encapsulated into packets of information, basically like pieces of mail with a 'from' and 'to' field. The 'from' and 'to' fields correspond to your IP address and the server's IP address, respectively, sort of like a street address. These packets are further encapsulated into, for example, ethernet frames, which handle the case where your PC is plugged into the internet with an ethernet cable. These ethernet frames also have a 'from' and 'to' address, which is a MAC address, which basically represents your physical ethernet jack/network card. The important thing to note is that your web browser doesn't really need to know anything about ethernet - because it operates at a higher level of abstraction. Wifi is similar too - different forms of encapsulation and different abstraction, but the browser doesn't really care because it operates at a higher level. Once the packets reach your router, they are de-encapsulated from their ethernet frame, or wifi, as the case may be. They then need to get onto the internet 'proper'. This can occur via further encapsulation via the DOCSIS protocol over coaxial copper cable, if you have Comcast, though there are separate schemes for DSL, satellite, fiber, etc. Eventually your packets reach your ISP, who then use a protocol called BGP to know where to send that packet. BGP is kind of like the \"IP address of IP addresses\", in that the IP address of a given website is 'advertised' within a block of IP addresses according to an AS number. So if the website (like [ URL_1 ]( URL_0 )) has an IP of [37.24.9.82]( URL_2 ), perhaps the whole range from [37.24.9.0]( URL_3 )\\-37.24.9.254 is advertised through one AS number (basically identifying a router who has knowledge of where those IPs live). Physically, getting from your local ISP's AS (which knows where *you* are) to that AS (which knows where *they* are) will nearly always involve encapsulation within a fiber-based communication protocol. It's a common misconception that the internet uses satellite for long-distance communication; in reality, satellite is only ever really used for \"last mile\" delivery of internet to individual subscribers, not the sort of 'backbone' connectivity between regions. Instead [we have many fiber cables ran on the ocean floor]( URL_4 ) to connect countries and regions within countries. So, tl;dr, in your case, your browser speaks IP packets, which your PC encapsulates for ethernet or wifi delivery, your router then de-encapsulates to get the original IP packets, uses a separate encapsulation to deliver those to your ISP, and your ISP repeats this process to get your packets to another ISP and eventually the particular business which hosts the server for the website you're trying to access. You may think about it in terms of how the postal system *could* work. Imagine you want to send a piece of mail to Google. You write your letter. Now what? Put it in an envelope, put on your return address, and use a phone book (DNS) to figure out what google's street (IP) address is, and put put that as the 'to' address. **This is sort of like an IP packet. This is what you 'first' send out, and ultimately what google's server will receive in the end - but in between, it will be put in different containers/encapsulations depending on how it needs to be send next.** Now let's say you put it in your mailbox, which you might think like a router. The mail truck comes by and picks up your envelope. Here the mail truck is something like the secondary encapsulation used by your cable/comcast modem. Note that, writing your letter or putting it in an envelope, you don't care about how a truck works or what road laws are. That's another layer of abstraction; it's not your problem to worry about. The truck brings the letter to your local post office, like your ISP, who then remove the envelope from the truck and decide where to send it to. They find out what post office is nearest to Google's street address - which post office handle's Google's mail, their AS number in BGP terminology - and then use some other method of encapsulation (an airplane, a train, a boat, etc) to send it to that post office. *This is almost always fiber cable on the internet.* Maybe it has to pass through several other post offices on the way there, but each one does basically the same thing - receive mail, figure out where to send it next and how to send it. Eventually a truck drives to google, drops off the mail, and then it is opened and the letter is read." ], "score": [ 7, 6, 5 ], "text_urls": [ [], [ "http://www.google.com", "www.google.com" ], [ "https://google.com", "google.com", "https://37.24.9.82", "https://37.24.9.0", "https://www.submarinecablemap.com/", "https://s7280.pcdn.co/wp-content/uploads/2018/06/osi-model-7-layers-1024x734.jpg" ] ] }

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{ "a_id": [ "gqd84it", "gqcwq1h", "gqcxwvk" ], "text": [ "You already have two good answers, but I'll contribute with a third one too, that's hopefully at an even simpler level... Many turns of wire around the core makes more inductance. More inductance essentially means more \"electrical momentum\". It takes longer to get a current running in the coil, so the motor will run slower, but that current also produces more magnetic field strength since every turn contributes more. Another way of getting more torque at lower speed is to make a large diameter motor, in which case it's as simple as leverage. Longer lever with the same force means more torque, just like using a longer handle on a wrench. It'll also be slower then. Finally, increasing the current through a motor increases both torque and speed. Current is increased by increasing the voltage. It can be increased for more power until the motor overheats, the magnetic core is saturated, magnets get demagnetized by the field strength etc.", "It depends on the type of motors, some can be run at varying speeds by adjusting the input voltage (DC motor) others have to have the input frequency varied because they run at a multiple of that. Power pretty much comes down to the strength of the magnetic field in the motor. Lots of little windings running at high voltage and low current, or a few large windings running at high current and lower voltage will both produce a lot of power because it comes down to current through the wire times the number of turns. We usually go for small wires with lots of turns because they generate less heat and weigh less letting you have a cheaper denser motor. Speed control varies by design. Brushed DC motors increase in speed as you turn up the voltage, there are little \"brushes\" that provide power to the inside coils, if you make them push against the outside magnets harder then it'll spin faster. AC motors and brushless DC motors (confusingly very similar in construction) have multiple electromagnets on the outside that are fed a changing voltage [and that forces the rotor to spin in frequency with that changing voltage]( URL_0 ). Brushless DC motors use permanent magnets on their rotors, Induction AC motors induce a current into coils of wires to make electromagnets on the rotor. If you want to make a motor that spins faster then you can put duplicates of the \"poles\" in the motor, in the example GIF if it had 6 sets of coils (3 pairs) being fed the same signals then it would spin 2x as fast, if it had 12 (3 sets of 4) then it would spin 4x as fast. You could also adjust the frequency being fed to the coils to get speed control during operation (like in a Tesla)", "When you run electrical current through a conductive wire, it generates a magnetic field around itself due to the relationship between electricity and magnetism. This magnetic field can exert force on things. If you take that wire, and bend it into a loop, your magnetic field lines up such that there's no net force, yet there is a net torque about a point in the center of the loop. Put a whole bunch of those loops together and stick a shaft with magnetics on it in the center of that loop and that torque value is determined by: τ=NIABsinθ N is the number of windings or loops of wire. I is the current. A is the area inside the loop of wire. B is the magnetic field. and theta is the angle between the current loop and the magnetic field. So in this equation you can see that motor torque depends on winding count, current level, magnetic field strength, and the angle of the magnetic field. There are lots of different flavors of electric motor. Some run on DC and use permanent magnets and a commutator. Some run on AC and have an iron core with no magnetics, and they induce a field. Some the windings are stationary and the shaft inside rotates. Some have stationary shafts and the windings rotate about it. One phase, three phase, multi-pole, etc. Lots of different options depending on what the motor is for and how it's being used. The motor torque is dependent on the number of windings, and current. The speed however is a little tricky. Looking at a DC motor, it has magnets on the rotor. When you put a magnet inside a loop of conductive wire, and then you start spinning it, that alternating magnetic field induces an electrical current in the wires. This is how generators operate. In a motor, you want to use electricity to spin the shaft...but spinning the shaft produces a charge that's trying to move in the opposite direction. It's called the back EMF, or back electromotive force. At a certain speed, that back EMF is pushing charge backwards hard enough that your supply current through the motor windings decreases and your torque decreases to the point where it can't speed the motor up anymore. That's the max speed of the motor." ], "score": [ 3, 3, 3 ], "text_urls": [ [], [ "https://upload.wikimedia.org/wikipedia/commons/f/f1/3phase-rmf-noadd-60f-airopt.gif" ], [] ] }

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{ "a_id": [ "gqeg0xy", "gqefz1z", "gqeg7ii" ], "text": [ "The 9mm Luger round came about in Germany, so it uses a metric measurement. In terms of size, it is about .354 inches, so it is towards the smaller end of the common pistol calibres. The number is a measurement of the diameter of the bullet (the projectile itself, not the casing). Calibre itself doesn't really indicate \"power\", for example .45 ACP has a lesser powder charge than .357 Magnum (even though by calibre alone .45 > .357). Stopping power is really a combination of the calibre and the powder charge, you really must know both in order to assess how great of a \"punch\" a particular cartridge will pack. 22 cartridges are rimfire and are very small, both in terms of calibre and powder charge. They are also very cheap and thus very popular for messing around at the range. 12 and 20 are shot shell gauges. They fire shot rather than bullets. The terminology for describing shotgun ammunition is quite dated, as the \"gauge\" measurement is derived from the weight of a lead sphere that would fit in the shotgun's barrel (e.g. a 1/12 lb. lead ball would fit in the barrel of a 12ga shotgun, a 1/20 lb. ball would fit a 20ga and so on). The larger the gauge, the smaller the bore diameter (since it's actually the denominator in a fraction).", "The basics is the inside diameter of the barrel: 0.22 inch = 22 caliber, 9mm = 9millimeter, while gauge is how many lead balls can be made out of a pound of lead for that diameter (more gauge is a smaller barrel).", "There are two measurement systems being used which complicates things. The 9mm for instance was first introduced by George Luger in Germany where they used metric. The bullet being 9mm in diameter is where it gets it’s name. The .45 was made by John Browning in the US where they used english. The .45 refers the the caliber which is 0.45 inches. The .40 and .22 calibers are similarly named. The 9mm for reference would be .35 caliber. The 12 and 20 are probably gauges for shotgun shells. Shotguns are measured in gauge which is related to the diameter of the barrel inversely. So 12 gauge is larger than 20 gauge which is larger than 28 gauge and so on." ], "score": [ 7, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gqifv24" ], "text": [ "Why? Because if it overheats it's a fire hazard. You have safety fuses to prevent short circuits and protect your house. They work by providing a single point of failure designed to fail safely, ie without causing a fire. Wire resistance depends on the material, the cross-sectional area and the length. If high current goes through a thinner wire, it will overheat, almost like incandescent lamps. But because it's copper coated with plastic instead of tungsten in an inert atmosphere, it will be damaged." ], "score": [ 5 ], "text_urls": [ [] ] }

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{ "a_id": [ "gqj17j4", "gqj10hd", "gqjexpp" ], "text": [ "The pilot steers. Either by using the rudder, nose wheeel (or tailwheel), or both. Small planes usually have the nose wheel (or tailwheel) connected to the rudder input (pedals). Larger planes can have a separate control wheel for the nose wheel.", "What do you mean? Every plane I've ever travelled on has been rocking left, right, up and down the whole way. It's never been a smooth, straight line for me.", "Pilot here, we use Rudder, nose wheel steering, and skill and that’s and that’s about it" ], "score": [ 12, 4, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gqjsiem", "gqjrqtc", "gqjunpt" ], "text": [ "The theory is that if there is nothing between two metal grains, no air, no oxidation layer, nothing, then it is no different then having one object and they will over time become fused together as atoms migrate from one structure to the other. It is more common in space where there is no air to begin with and no oxygen to create oxidation layers. However due to the amount of precision mechanical objects on Earth it is a much bigger issue here. In fact you may have experienced mechanical failure due to cold wielding on things already. It is very hard to take advantage of this effect though. Firstly it is very hard to create the conditions where this happen and even then it only happens by chance and is therefore very hard to control. It is also a very weak form of wielding as it only takes place at certain points and not all over the surface. So it is more of an annoyance and source of mechanical issues then anything useful.", "Pieces of metal on earth almost always have something in between them, either air or rust or a thin layer of dust or grease or whatever. This layer prevents the metal from really \"touching\" perfectly. If there's absolutely nothing in between two flat pieces of metal, the metal atoms just kinda stick together and bond the pieces of metal together. Yeah, you could do it on earth, but it's probably much harder than normal welding.", "What's the difference between two things and one thing? There's something in between. On earth there's usually air inbetween. In vacuum there is nothing inbetween. So the two things become one thing. Unfortunately for anyone wanting to do anything useful with this, there's often tiny contaminants on the surfaces of the metals. So the join is very weak. Too weak to do anything useful, but just strong enough to cause problems. Most of the time space programs will coat the metal stuff with oil to prevent it." ], "score": [ 5, 4, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gqlvqew", "gqm12j1" ], "text": [ "It's a trade-off - as you raise your gear ratio, the torque you need goes up, and the extra fuel you need to do that offsets the effect of the lower RPM. At some point, the lines cross, and you've reached your optimum gear ratio. Not surprisingly, the manufacturer knows this - that's why they've chosen the gear ratios they have (balanced as well with the need for ease of manufacture, ease of use, etc.).", "This is what CVTs try to do, they don't have fixed gear ratios but can instead shift smoothly between ratios in a given range so the engine stays at the optimum RPM. 9 speed automatic transmissions are also fairly common these days But more gears only helps to an extent. The fuel consumption of your engine is tied to the RPM, but it is also tied to the loading. If your engine is heavily loaded (say you're doing highway speed) but the gearing means it only needs to spin at 3000 RPM then it will still draw more fuel than spinning at 3000 RPM at city speeds. In order to stay at 3000 RPM at highway speeds it needs to generate more power than at city speeds so it lets in more air, mixes more fuel with it, and pushes harder. The most efficient speed for an engine is around peak torque (2000-3500 RPM depending on the engine), you want to use your gearing to keep the engine RPMs around this point so more of the fuel is being turned into mechanical work and less is being lost as heat and inefficiencies in the engine. At a certain point more gears don't really help because you're limited by the efficiency of the engine and the transmission and not by inefficient gear ratios." ], "score": [ 11, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gqmq47z" ], "text": [ "When fuel is burned in an engine, like those on a jet, one of the main products flowing out of the exhaust is very hot water vapor. If the temperature and humidity of the air the plane is flying though are right then that water vapor from the exhaust will cool down and form a bunch of tiny droplets which, just like a cloud, appear white in the sky. Those clouds, called contrails, eventually get blown apart by the wind which is why they usually get larger and more diffuse the further they are from the plane that made them." ], "score": [ 18 ], "text_urls": [ [] ] }

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{ "a_id": [ "gqn52tr", "gqn5hdu" ], "text": [ "a significant amount of the power plants were not equipped to handle the cold. parts froze over and they weren't able to function properly causing them to shut down. On top of that, Texas isn't connected to the federal power grid and was unable to import any significant amount of power from other parts of the US.", "Do you remember how a lot of people in Texas posted photos of water pipes that had exploded during the freeze? But people up north, where it freezes yearly, never have that issue? Water pipes up north are dug deep into the ground to prevent them from freezing and the people are used to it so, when it freezes, they leave their water on a slow drip to keep it moving. Basically what happened with the electricity is the same thing that happened with the water. Texas doesn't have freezes so it didn't design a system built to work during a freeze. The national grid requires the components that would have prevented the grid from going down but it's expensive and Texas didn't want to do it because what are the odd it would be needed? So they made their own. Then this happened. There is just no infrastructure in Texas for freezes because the infrastructure is expensive and, until recently, unnecessary. It saved money but sacrificed lives. Fun, related, fact: the lack of freezes is also why Texas has so few basements. Up north they have to dig 6+ feet down for pipes to prevent freezing. At that point, go a few more feet and make a basement. You only have to dig about a foot down in most of Texas to get under the freezeline." ], "score": [ 7, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gqpm7xu", "gqponw0" ], "text": [ "If you have gas in a closed container and try to compress it (squeeze the container), the gas will also get hotter because the molecules of gas get closer together and rub one another more vigorously, generating heat. So you used energy to generate heat. If, on the other hand, you expand the container, the gas will actually get colder. So you just used energy to \"generate cold\". Such a machine is in the refrigerator expanding the gas, \"generating cold\", absorbing the heat from inside of the fridge, and taking it outside to cool to room temperature. Basically you transport heat energy from inside to the outside by cooling the gas in one place, letting the gas warm up a little bit and absorb the heat of the inside, and let it out somewhere else. And repeat.", "Fridges don’t make things cold, they move heat around. They cool the main box by taking heat from the inside and putting it on the outside, specifically the back of the fridge. Fridges can get hot on the back. HOW they move heat is the hard part. Essentially they use a trick that you might not have heard of or understand fully. It takes energy to heat something, but it takes a very large amount of energy to break the threshold and turn a material from liquid to gas, from gas to liquid, etc. This is why you cool down very fast when you sweat. The evaporation process requires very large amounts of heat, and that heat leaves your body with the evaporating liquid. Fridges abuse this “trick”, and have a substance inside that is a liquid or a gas at just the right temperatures they want. They move it around the fridge and change the temperature and pressure so that it’s a liquid sometimes, and a gas at other times in the cycle. Hooking a system like this up correctly allows the substance to take heat from one part of the cycle and give it to the other part of the cycle. One half is hooked to the cold box, one to the outside of the fridge. The exact process is somewhat complicated, so I encourage research on the topic. Technology connections has great YouTube videos on appliances such as this explaining them in more detail. You would also further understand the topic with physics courses. A refrigerator is the opposite of an engine, and is a little like a steam engine in reverse." ], "score": [ 13, 5 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gqpryx7", "gqpqzcf" ], "text": [ "It isn't at all difficult to burn stuff. The volcano is not a very convenient form of heat. There is no free ride here. Stuff doesn't \"disappear\" in the heat of the volcano. It burns and releases whatever toxic or greenhouse gas it would when it burns regularly. Most of it won't sink into the ground forever hidden - most things float on molten rock. If burning is the solution, simply pile all the garbage into the nearest stadium, douse it with fuel and light it up. Probably more convenient and cheaper than a conveyor belt with pretty much the same after effects.", "There are actually tons of articles on why this is a bad idea. [Here is one.]( URL_0 )" ], "score": [ 9, 3 ], "text_urls": [ [], [ "https://www.forbes.com/sites/robinandrews/2017/09/28/this-is-why-we-cant-throw-all-our-trash-into-volcanoes/amp/" ] ] }

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{ "a_id": [ "gqq0met", "gqq0u3p", "gqq173a", "gqq2e9y", "gqq38sl", "gqqq92t", "gqq90vm", "gqq2jh3" ], "text": [ "The energy that you generate from letting the water run back downhill will always be less than the energy that you had to spend to pump it uphill in the first place. This is an inevitable conclusion of the second law of thermodynamics. The way that my 8th grade science teach explained it to me: * **1st Law of Thermodynamics**: You can't create energy. * **2nd Law of Thermodynamics**: You can't even break even. So, you can't generate extra energy by pumping the water uphill. But, pumping water uphill is, in fact, an amazing way to **store** energy for use later. One of the biggest problems with renewable energy like solar or wind is that sometimes the sun doesn't shine and sometimes the wind doesn't blow. But, if you use the excess energy to store water in a higher location, you can recover most (but not all) of that energy later by letting it run back downhill.", "We can and we do - it is just terrible energy inefficient and isn't worth the trouble most of the time. The electrical grid is very on demand and doesn't have much storage, so we are constantly increasing and decreasing power generation so need = production. When the solar panels are kicking out tons of energy, we just scale back the variable sources (like fossil fuels or nuclear) so need = production, and scale those others up when solar is under performing. This is far more efficient than trying to store excess solar. Now, that said, we do sometimes do what you are suggesting - pump water up hill and then have it run turbines later - but if memory serves there is something like an 80% loss of energy in that process.", "We can. But there are a few issues that prevent us from doing this everywhere immediately. 1) There are frictional losses when you pump water through a pipe. This means the amount of energy you get back is less than what you put in. But that’s true if all energy storage systems. 2) You need a large supply of fresh water that isn’t readily available everywhere. Salt water can be used but you have to spend more on your machinery to prevent the salt water from degrading it. 3) Most importantly, geography. You need a large steep hill to pump the water up to. And then you have to move a huge amount of earth to create the reservoir. If the hill isn’t steep enough, your pipes will have to be really long to transfer water from high elevation to low elevation and those friction losses from (1) really skyrocket. Not all places have hills like this close to where we need them. You should watch this video by the Real Engineering YouTube channel which covers these points. URL_0", "This is done, but it doesn’t create more energy. It is an efficient way to store energy, though.", "Ludington, MI has a system like the one you suggest. Although it can't break the laws of thermodynamics (as explained in other replies), it is a fantastic potential energy battery for the surplus energy created by the many wind turbines in the area. There is also a magnificent disc golf course in the area between the turbines and the reservoir. [ URL_0 ]( URL_0 )", "We do. Renewable energies like wind and solar are unreliable - they don't work when the wind doesn't blow or the sun doesn't shine. So if you generate a surplus of energy, you can use it to pump water up hill. When these unreliable sources aren't generating, you can let it run down hill. You have a very large battery. Hydroelectric in the traditional sense takes advantage of nature replenishing the water, so you don't have to produce your own energy to move the water up hill yourself, you can just rely on the water cycle. I mean, the water behind the Hoover Dam or Niagara comes from somewhere...", "We can and do. Taum Sauk hydroelectric power ststion is an example of this. Theyd use electricity to pump water up into a big ass reservoir at night when rates were cheaper, then when they were more expensive during the day they'd generate electricity. It was quite the marvel back in its day. In 2005 it failed though, and cream pied the shit out of Johnson's Shut Ins state park. Luckily no one was cream pied to death. You can go there, its not far outside of Saint Louis, and id suggest you do. There is also a really neat park called Elephant Rocks somewhat near by, and a few interesting cases too.", "The short answer is, we can. This is slowly becoming a fixture in water utilities, but for a long time it did not make economic sense. Now as budgets get tighter, and water utilities can no longer pay for capital costs with water revenue alone, they are looking for alternatives to increase revenue. Below is one example. [Water System generates electric power]( URL_1 ) There are other places that use pumped power hydro electric plants using untreated water from a river, lake, or reservoir. The use of these typically needs to be in tandem with larger plants because of the volume of water that would need to be needed to generate enough electricity. This is an old article, but gives a good idea of what is going on. [Gravity Powers Pumped-Hydro Energy Storage]( URL_0 ) There are lots of other reasons these are not more popular as well (energy loby, cost, geographic restrictions, etc) but we don't need to go down that rabbit whole yet. We will leave that for the comments." ], "score": [ 85, 15, 10, 8, 3, 3, 3, 3 ], "text_urls": [ [], [], [ "https://youtu.be/JSgd-QhLHRI" ], [], [ "https://en.m.wikipedia.org/wiki/Ludington_Pumped_Storage_Power_Plant" ], [], [], [ "https://www.greentechmedia.com/articles/read/gravity-power", "https://www.good.is/money/portland-pipeline-water-turbine-power" ] ] }

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{ "a_id": [ "gqs5p46" ], "text": [ "A quick google search seems to indicate that top loading machines use a more bubbly detergent. Meaning you could run top machines with less bubbly front detergent, but not the other way." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gqt91bq" ], "text": [ "Inertia. Things that aren’t moving don’t want to move and things that are moving don’t want to change their motion. And the heavier stuff is the more it wants to resist change. Steadicams are basically a system to add inertia to a camera (with mass and resistance) while still making it relatively easy to carry for the operator (the harness and gimbals). You can try out the “add inertia” part of the system by attaching a small bolt that fits a camera’s tripod attachment to the handle end of a small sledgehammer and attaching this contraption to your camera (hammer head down, holding the handle, with the screw connecting the handle to the camera) and trying a few tracking shots. It works!" ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "gqt40qn", "gqt3vvh", "gqt49ey", "gqt4e48", "gqtbmci", "gqt8epp" ], "text": [ "Basements don’t often exist in areas where the water table sits high-up; places with a low elevation relative to sea level and / or high annual precipitation. This is because they can and do flood due to a higher water table. In these areas, precipitation doesn’t have to go down as far into the ground before it hits an area of high water saturation, therefore the water content of the soil is much higher, which can cause structures underground to shift as the soil is much softer and water-laden. Dig a hole at the beach, and see how far down you have to go before you notice the dirt becoming more wet and eventually revealing standing water. Now do that at a higher elevation. You have to dig further down to reach the same level of water saturation. The former is Florida, the latter is the Appalachian Mountain region. What happens in the beach scenario when you dig? Eventually the water starts carrying the sand back down into the hole, because it is unstable. You have to manually remove the water to make progress in digging, and even then it’s only a matter of time before the surrounding water-saturated soil starts pouring in. I’m high, so hopefully that made sense.", "Sometimes they do flood. Generally speaking though, they are waterproofed on the side that touches dirt, and they've got drainage tiles and sand on the outside and underneath, and all that water gets pumped away from the house before it really has a chance to flood.", "A basement foundation is just a cement bowl that whose lip is 12-18 inches above the ground that your house rests on. Barring damage it's going to take a lot of rain to flood. Of course as homes age and settle and undergo thermal expansion/contraction, cracking can occur which is why a completely 1dry basement in older construction in New England, for example, is a rarity.", "Mainly because not everywhere is Florida and water is able to drain away whenever it rains. In most places water flows through dirt. So any water that soaks up in the dirt will flow down and away without soaking the ground completely. Humidity can be a problem in basements. This is why they have to be quite watertight, have good drainage around them and have good ventilation. There are some places that do occasionally have issues with ground water, for example if building near rivers and the river overflows. But you would not build a basement where this is a yearly issue.", "Actually one benefit of basements in colder climates is they leave a nice warm air space below the structure. If you have ever gone camping you know you need to protect yourself from the ground more than the air as the ground will rob you of heat faster than the air. It's something similar with a basement.", "In addition to everything said above, some basements are prone to flooding and a pump must be used 24/7 to prevent the water from pooling." ], "score": [ 30, 13, 11, 10, 4, 3 ], "text_urls": [ [], [], [], [], [], [] ] }

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{ "a_id": [ "gqusmtb", "gquedq6" ], "text": [ "Way back farmers used horses to do their work. The farmers knew exactly how many horses they needed to do different tasks. When the steam engine was being marketed to farmers they needed to know what size engine they would need to replace the work the horses were doing. So the engine's power was expressed in horsepower. So if a farmer used 3 horses to run his hay bailer, then he knew he needed a 3 horsepower steam engine to get the job done, or he could use a 6 horsepower engine and cut his time in half.", "Horsepower is a measure of power, which itself is a measure of the work performed by something over the time that it acts. 1 horsepower is defined as the power required to lift a 550 lb weight by 1 ft in 1 second. 2 horsepower could do any of: lift a 1100 lb weight 1 ft in 1 sec lift a 550 lb weight 2 ft in 1 sec lift a 550 lb weight 1 ft in 1/2 sec The metric counterpart is the watt , which is the power required to lift a 1 Newton weight 1 meter in 1 second, or one Joule per second. 1 hp ~= 745.7 W. What does this mean for you? A higher horsepower will let you move a larger mass more quickly. Too much horsepower can cause damage to parts or be wasteful for some applications. In an ideal scenario, a car with higher horsepower will be faster and able to tow/carry more. However, too much power to the wheels can cause adverse effects like causing the tires to break traction far too easily. Higher power engines also consume more fuel, although in some cases they may be more efficient by still providing sufficient power at or near idle." ], "score": [ 4, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gqv5r4q", "gqv7gpe" ], "text": [ "Computers wouldn't be able to interact with the outside world, and computer audio/video formats (mp3, DVD, BluRay, etc.) and controllers wouldn't work. The world is entirely analog but computers operate on digital logic. They have to convert analog to digital in order to do their thing (and convert it back to analog to output to us analog entities).", "When you convert an analog signal to digital, you turn it into bunch of numbers, and numbers are very easy to copy and transmit without losing any quality. Copying an analog signal is a bit like making photocopy of something, and when you make a photocopy of a photocopy, you lose a bit of detail each time and you add noise and artifacts. Let's say you write down the number '3843' on a piece of paper, you give that piece of paper to someone else and ask that person to write down the number onto his own piece of paper. And then that person gives it to someone else and so on. As long as everyone involved has somewhat decent handwriting, you could do this with a chain of 100 people and the 100th person would still be writing down '3843'. Now do the same with a Chinese character instead of a number, and ask someone who doesn't read Chinese to copy yours. If you do this with 100 people, what comes out at the end is probably not going to look anything like the character that you originally started with. That's what happens with analog signals, whereas the number-copying exercise is how digital signals work. People know what the numbers should look like, so even if your '3' isn't written perfectly, the next person would still be able to recognize that it's supposed to be a '3' and write down his '3' perfectly." ], "score": [ 5, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gqzil1l", "gqzjj3t" ], "text": [ "They install a smaller crane to bring pieces of the big crane down. The small crane then gets disassembled and usually fits in the elevator. If it doesn’t, a smaller crane of that is used. Look up Derrick crane for more info", "There are three methods for removing tower cranes. 1. If the building isn't too tall, they have massive cranes specifically built to reach from the ground that disassble the crane and bring it down. Because it can be taken apart into sections, they don't need too much loading strength, just height. 2. They build smaller \"Derrick Cranes\" on the roof of the building to disassemble and lower the big tower crane. In some cases, they'll have to build a smaller Derrick to disassemble the first bigger derrick. 3. Some cranes have hydraulic collar systems that can add and remove sections to themselves, however these cranes are built alongside tall buildings rather than built through / ontop the roof." ], "score": [ 18, 17 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gqzswj4", "gqzszl5" ], "text": [ "A data lake is a pile of raw data. You haven't processed it or put it all into one format yet. A medical record system for a hospital might have a data lake that contains structured database entries, raw images from medical scans, JSON data pulled from some external source, and a selfie from Alice at the front desk. A data *mart* is a structured data set, created for the purposes of a specific user or group of users, that usually contains some processed subset of the total available data. For example, our hypothetical hospital needs to bill patients for services rendered. The billing department needs to be able to find out how much someone owes, and potentially to be able to itemize a bill on request, but doesn't need (and shouldn't have) access to actual medical data like test results or x-ray images. So you set up a separate database or other queryable data store containing only billing data, structured in a way that makes \"how much does X owe and for what\" queries fast, and expose *that* to the billing department. If you're doing sophisticated enough architecture to be using these terms at all, you probably build this separately from the data lake. Once a day or so, you go through the data lake, process the information in it to find the stuff you care about, pull it out (\"extract\"), reformat it for the purposes of the data mart (\"transform\") and store that data to the mart (\"load\"). The combination of these three operations is called 'ETL' (and is implemented as an 'ETL pipeline' - the analogy here is of a pipe carrying water from a central tank) and can be a giant pain in the ass depending on how unstructured/unreliable/hacky the input data is. Finally, a data warehouse is a larger thing that incorporates the initial intake of data, its storage in a data lake, ETL pipelines that carry it, data marts that make it available, etc.", "The differences can be understood by looking at the second word. A data \"lake\" is like a lake of water: big, unstructured, formless. It's where you find a massive pile of data that's not set into any structure. A \"warehouse\" has shelves and a record-keeping system so you know what's where and how it's meant to look. A data \"mart\" is a sub-set of the warehouse, and implies a structured way to retrieve data from the warehouse." ], "score": [ 8, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gr143ni" ], "text": [ "In a manual transmission, you have an input shaft from the engine, and an output shaft to the wheels. The input and output shafts have pairs of gears at different ratios. The gear on the input shaft is fixed to the shaft and spins with it. The gears on the output shaft are on bearings and spin freely about the shaft. There are collars on the output shaft. These are fixed to the output shaft following grooves. This means they can slide up and down the shaft, but they also spin with the shaft. They have a form of gear tooth on the side of the collar - not along its perimeter, like a typical gear you would imagine. A gear is selected by meshing the collar on the output shaft with the free spinning gear about the output shaft. That means rotational energy is transferred from the engine, to the input shaft, to the input shaft gear, to the output shaft gear, through the collar, into the output shaft, and down to the tires. The shifter is a lever connected by mechanical linkage to selector forks. How you move the lever will move the forks, one at a time, in or out. The forks push or pull the collars. In a 6-speed transmission, there are 6 gear ratio pairs along two shafts, and there are 3 collars between them. So one collar services two gears - you can pop the collar out of one gear, and keep sliding it down to the next gear. Moving the shifter over to the next column requires popping a collar out into a neutral position and selecting a different column. There's also a collar for reverse, which uses 3 gears instead of 2, in order to reverse the direction of the output shaft. Gears are cut helically, which aren't as strong or as efficient as straight cut gears, but they are quieter. Reverse is very limited in speed, often a small gear ratio, so high torque, and they are often cut straight, which is why reverse whines in most cars. There are also synchronizers, which are friction devices to help the gears and the collars match rotational speed so they mesh without grinding or damage. Race cars tend to have straight cut gears without synchros for simplicity and durability. There is also a clutch. This is a friction device that is controlled by a spring and a foot pedal to engage/disengage the engine. This is necessary because engines are shit. They have a minimum speed, or they stall, they produce shit torque except at an ideal RPM, and gears are merely approximations that approach the torque curve of the engine at one point. CVT transmissions are great because they can follow the torque curve of an engine perfectly. They even tested them out for F1 racing, running the engines at ideal speed the whole time - they found the transmissions would wear out, or the engines would wear out, or they would run out of fuel. Pick one before the end of the race. Electric motors are best because they can generate 100% torque at 0 RPM and don't need a transmission. A transmission is a torque multiplier because combustion engines are so bad at producing it. Automatic transmissions have many of the same parts, but how the collars are actuated are by hydraulics. The shift point was originally controlled by valves and hydraulic pressure, but today they're computer controlled. Instead of a clutch, they use a torque converter. This is a drum of oil and a turbine. The drum and oil is spun by the engine, the oil spins the turbine inside the drum. The input shaft of the transmission is attached to the turbine. This transfers torque. If you understand how a water or steam or wind turbine works, it's the same thing. The disconnect allows for slip, so the engine doesn't stall. Modern torque converters have clutches as well to mechanically lock the engine and drivetrain together for greater efficiency." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "gr0kwqi", "gr0jws7", "gr0l61f", "gr0udmb" ], "text": [ "Nails are just friction fit When you drive a nail in it just pushes the material in front of it to the sides and scoots through. This material on the sides pushes back and puts pressure on the nail generating quite a bit of friction keeping it from just popping back out But generally you want to use a nail where the load will be from the side rather than straight up/down because the friction can be overcome to let you pull the nail straight out but pushing from the side requires breaking the nail before the parts move Screws are better for straight up/down loads because their threads catch on the material and keep you from pulling them straight out", "While you're hammering a nail you're not removing the space that was there, you're just pushing it to the sides . That means that the wood is pushing back with so much force that by power of friction alone the nail can be held in place.", "The point of a nail pushes the wood fibers to the sides. And, the nail holds by friction. As the structure ages, the wood dries and shrinks. This grips the nail even tighter. This is why it can be so hard to pull nails out of old boards.", "One of the big differences between nail and screws is that nails are made from a softer steel, so they are more likely to bend instead of break, screws may snap in half. Also nails cost less. When building a back yard patio, it is usually better to make the frame with nails. However, the handrails and flooring planks can expand and shrink due to humidity and dryness cycles, along with hot and cold cycles. This means nails would \"pop out\" slightly over time and that means planks and handrails should be connected with screws." ], "score": [ 88, 11, 5, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gr2ucvc" ], "text": [ "At the very top is an unpowered line called a static line, that periodically runs to the ground. It is there to take a lightning strike instead of powered lines. Next are transmission lines, the lines that go from the power plant. Below those are distribution lines, for taking power to your house. Then come communication lines like phone, cable, and internet, which are lower powered. For a picture of this (more detailed than ELI5) see here: URL_0" ], "score": [ 8 ], "text_urls": [ [ "http://www.annsgarden.com/poles/poles.htm" ] ] }

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{ "a_id": [ "gr58y54", "gr58lp6" ], "text": [ "It’s probably a spherical magnet that is free floating inside the plastic. If it comes up against an opposing polarity, the sphere rotates to align correctly.", "I could be very wrong but it's possible there's a way for the magnet to spin around inside." ], "score": [ 6, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gr66dmj", "gr68j19", "gr667j7", "gr6bvie", "gr66caq", "gr6cnqp", "gr66f72" ], "text": [ "Almost all electrical generators work by using spinning a turbine. When you spin magnets and coils of wire, it generates a flow of electricity in the wires. You can burn coal or natural gas to boil water to spin turbines with steam, you can flow water down a dam to spin turbines, or you can use wind to spin the turbines.", "Do you mean \"store\"? They *generate* electricity through electromagnetism, powered by the kinetic energy of the spinning turbine. *Storing* energy on large scales is a huge project. You may have seen the Tesla battery station compounds going up. Other methods of storage are gravity storage, where they pump water uphill using excess energy keep it there, and use it to spin turbines flowing downhill when they need the power again. Probably a million other ways, too.", "Electricity is generated by magnets spinning around wires. Then this electricity is transferred through these wires to where it is needed.", "Imagine a bicycle. You turn the pedals to make the wheels turn which makes you move forward. While moving, we say you have kinetic energy (the energy of motion). At the very simplest level, this is similar to what’s happening with the wind turbines. We’re taking essentially huge kites and using the wind to turn something. Theoretically, we could hook this up to a gigantic bicycle and make it move. But we don’t want the wind turbines to give us kinetic energy in the end because kinetic energy is really hard (in fact, impossible in our conditions) to store for any amount of time. If you stop pedaling, your bike will eventually roll to a stop. One type of energy we know how to store pretty well is electrical energy. Here it’s important to understand is that electricity and magnetism are fundamentally linked. Magnetic fields are created by the flow of electrons (aka electricity). But it also works in reverse. Using magnets, we can cause electrons to flow. So you can think of wind turbines as moving huge magnets which makes electrons move. But where do we want them to go? Electrons will always flow if given the opportunity, so we can sort of store them up by moving them somewhere and then cutting off their ability to go back. Magnets interrupt typical electron behavior and allow us to put more electrons in a place than would ever naturally (which causes them to want to leave when the magnets are removed). By simply blocking off the exit path, now you have stored a bunch of electrical energy to be released whenever those connections are opened again (like putting a battery in a remote). Note that you don’t need to have the electricity flow into a battery, you could just as easily direct it to something that needs it like someone’s house to power their lightbulbs. But by putting it into some sort of battery first, though, we can continue to power stuff even when the wind is stopped (assuming we generate more than we need when the wind is blowing). This is pretty basic and probably not 100% accurate, but I think it gives you a decent understanding. Workable at least.", "The wind turbines are all connected to an electrical substation, which converts the electricity to the correct voltage for transport. That electricity then goes down a transmission line, which will connect to another substation once it gets to the city. The substation in the city will step the voltage down to distribution levels, and then that voltage is distributed to homes and businesses.", "Most of these comments are answering how you GENERATE the electricity, but I think what you meant by \"collect\" was how do they STORE the energy. If I understood that correctly, here's the answer: They don't. At least not in a quantity that could make a difference. Sure they have battery banks in large wind/solar farms, but at best that can stabilize production in the short term, like a few minutes at most. This is exactly the greatest challenge for electricity production in general and renewables in specific - the electricity produced anywhere in the world has to be consumed almost instantly somewhere else (the closer to where it is produced, the better). This means, for example, that solar* farms are absolutely useless at night, no matter how much they produce during the day. Same goes for turbines in non-windy periods. P.s. How they do this balance between production and consumption is another story filled with statistics and estimates, but they do it. Source: I'm doing a masters in renewable energy storage systems.", "The wind turbine converts the energy into electricity. There is no \"collecting\" or storing electricity. You have to feed the electricity into a motor/light/... in realtime." ], "score": [ 125, 26, 17, 7, 6, 6, 4 ], "text_urls": [ [], [], [], [], [], [], [] ] }

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{ "a_id": [ "gr6oppr", "gr6onb7" ], "text": [ "There are several ways to measure how robust a material is. You've touched on one of them: hardness. This is the measure that diamond excels at. It measures how well a material resists being scratched, or how well it can scratch another material. When you try to scratch one material with another the harder material will have almost no damage, while the softer one will see all of the damage. The harder the hard material is the closer to zero damage it takes. This same thing happens when cutting, where the cutting or grinding, where you want the cutting or grinding tool to take as little wear as possible, so hardness is the thing you care about. There's also strength. That's the measure of how much force it takes to break something. That's the measure by which an object will fail at its weakest point. Generally the tools you mentioned aren't breaking due to forces, so strength isn't the quantity that needs to be as high as possible. Note that strength may be measured in terms of the strength of a material as an intrinsic property (e.g. \"steel is stronger than brass\") or as an extrinsic property of an item (e.g. this rope has a strength of 100 lb). Another quantity is toughness. A tough object is the opposite of brittle--copper is tougher than ceramic. Tough materials can withstand impacts well. More formally, toughness is a measure of how much energy it takes to break a substance. Then there's stiffness, which measures how much a material bends when you apply a force to it. Very often materials that are hard are not very strong, tough, or stiff. With a cutting tool you want the bulk of the tool to be strong, tough, and stiff, but the surface you need to be very hard. To achieve this the tool is often set up with two materials, such as a steel tool with a titanium carbide coating, or steel with a diamond coating. This gets the best of both worlds.", "The diamonds fall out and break pretty quickly because technically they’re just glued on (resinoid bond) or embedded in the tool. There are lots of other types of bonds that we use for abrasives, one of the most prevalent being the vitrified bond which heats an abrasive and bonds the grains together. You see this in AlO3 often (corundum) which is a 9 on the MOhs scale of hardness as opposed to a 10 for diamond. I’m not sure what answer you’re looking for, but due to the hardness, diamonds are in fact quite brittle and therefore fall apart during use. Vitrified bonds take advantage of the grain falling apart to reveal new cutting edges, but I’ve never seen a vitrified diamond cutter." ], "score": [ 9, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gr70l9w" ], "text": [ "They’re generally stiff when new, so when you wear them materials like leather, rubber, other types of fabric get stretched out and soften so they aren’t as stiff and are softer or more comfortable to wear" ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gr8wr6c", "gr8w3tc" ], "text": [ "Physical space If you get water on an outlet it only needs to bridge about an inch to connect hot to neutral and create a short Electrical poles have insulators that keep the wires spaced several inches off the pole and are designed so you really can't get a path of water across the surface. On high voltage poles the insulators can be a couple feet long. In the event that something does bridge the gap like a tree branch it will generate an arc and will probably be burned away by it. If it doesn't quickly burn away then the breakers trip and shut off power to those lines. We don't actually insulate power lines on poles, it'd be really thick and add a lot of weight. It's more useful just to have physical spacing on the poles", "The electrical posts and wires are insulated - covered in plastic or rubber wrapping so that the water doesn't actually touch the wiring that the electricity is traveling over. Electrical outlets, though, only have some basic protection (the face plate). Otherwise, it's just a direct connection to a charged wire - that way when you plug something in, the plug makes contact with the wire and the electricity can freely flow between them. That *also* means though that if you dump water on there... it can cause electricity to spread to *other* areas (like the walls) where it's not supposed to go, and cause sparks and fire." ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "grb9008", "grbb1bc", "grbciym", "grb9dq7", "grbbrpr", "grbmf6r", "grb97a2", "grbc0ry", "grbg7yv", "grb9ido" ], "text": [ "Normally, it makes it so traffic doesn’t have to stop, only yield. It is much smoother than changing lights. Also, roundabouts reduce traffic fatalities, but often increase accidents .", "They are also MUCH safer because if there ever is a crash it is never directly from behind or from the side. If there’s ever a collision it’s usually the corners of the car being struck which greatly reduces fatalities.", "Uninterrupted traffic flow, and cheaper than traffic lights. It turns the problem of a multidirection intersection into a much simpler merge with all the traffic going the same way. But the US isn't great with them yet. People seem confused about how to use them, so they will pull out unexpectedly or come to a complete stop instead of flowing through. Roundabouts only work well if you can trust the other drivers to do the right thing. The US also tends to put crosswalks over the roundabout the same as you would with traffic lights, but that is generally a stupid idea because it just adds more confusion and the point of the roundabout is for traffic to flow without stopping.", "Pretty straight forward actually (little roundabout joke there): traffic lights are very inefficient at moving cars through an intersection. Keeping cars moving as much as possible, and as few as possible stopping, means many many more vehicles can navigate an intersection in a shorter amount of time. There’s also a case to be made for conserving fuel. Cars that don’t come to a full stop, and thus conserve momentum and don’t have to get back up to speed from a standing start, use less gas. While the savings to any one car may be small, the cumulative effect becomes huge over time.", "In addition to what everyone else has said, I'll add the fact that you only have to look in one direction before joining the roundabout regardless of whether you're going left, right, straight on, or doing a U turn. It's almost never a 90-degree corner, so the sight line to check for oncoming traffic is usually out the front window giving you a much better view. (Edit to add that you do still have to check your mirrors before turning just like at any intersection. Cyclists shouldn't be passing cars approaching a junction, but they do so it's important to check your mirrors and indicate before turning.)", "I think everyone made quite good points here- I’ll add one as seems to be the trend here; Roundabouts also have an effect of increasing engagement of driving. One common issue with stoplights is blind trust in them. Green is go, red is stop. We all get told to double check the junction at a green light, but let’s be honest, do we really? With roundabouts you’re forced to see, think, understand and take an action leading to (an apparently) safer traffic situation", "Most simple explanation --- NON UK drivers: No left turns needed to \"make a left\". for UK drivers, no right turns needed to \"make a right\".", "Another reason I haven’t seen mentioned yet is the reduced number of [conflict points]( URL_0 ), meaning roundabouts improve safety by reducing the places where a collision could occur", "It's basically free, keep traffic flowing, and reduces fatalities in comparison to a set of traffic lights. While they do sometimes increase the number of accidents, these accidents are much lower intensity because the cars are traveling in broadly the same direction. The only real downside is they can do often lack high capacity intersection options but while better traffic lights aren't awesome at these either. It's kind of baffling how little the US use roundabouts, they are probably one of the most impressive feats of traffic manament systems. They improve just about every aspect of an intersection for basically nothing.", "It allows for a much more consistent flow of traffic, instead of stopping and starting individual directions every couple of minutes. Also it's safer, since it's very difficult to get t-boned at 50 mph by a red light runner in a roundabout, even though it's easier to get bumped and dinged up by someone merging into you." ], "score": [ 72, 72, 64, 28, 26, 14, 11, 8, 7, 5 ], "text_urls": [ [], [], [], [], [], [], [], [ "https://www.dot.state.mn.us/stateaid/trafficsafety/safety/intersection-treatments.pdf" ], [], [] ] }

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{ "a_id": [ "grd4ldf", "gre1bkh", "grd5n1r", "grd5603", "grd0h2t", "grd88gu", "grebmda", "grdyo08", "grd18nr", "grfg3zm", "grdwkpp" ], "text": [ "Modern reactors are very safe, because the physics that's going on inside them is pretty well understood. Sure, things can go wrong, but things can go wrong with other sorts of power plants. When something goes wrong, you shut the reactor off and wait. The TEPCO plant at Fukushima was quite old, and all the cooling and backup power generation was underground, precisely to protect it from earthquakes. Alas, it turned out bad when there was a tsunami. Should the tsunami risk have been considered? Of course. This plant was not safely designed, and it wouldn't be approved today. Modern GenIV nuclear plants have to be passively safe, even with no power input, they don't malfunction. Alas, anti-nuclear activists are greatly slowing deployment of nuclear plants in hopes that hydrogen fusion will be the power source of the future. There isn't ever going to be enough \"green energy\" to run the entire Earth at a desirable standard of living. Nuclear is a key component in addressing climate change.", "ELI5: Imagine being an engineer designing a car. You know that the gas pedal can break in two ways. It can break so the car slows down or the car speeds up. You're job is to make sure that if it fails the car slows down. This is called \"fail-safe.\" Nuclear reactors fail safe by requiring specific conditions to keep doing Nuclear Stuff TM. If you lose control of the reactor, the reaction stops so it is failing safely. Sure it's a mess, but you can clean up a safe mess.", "Nuclear Energy has a pretty extreme saftey oriented design many of the plants running are only second generation. Redundancy, proactive safety protocols go a long way. I feel it is important to know some designs for nuclear are actually passively safe (fail safe). Currently, no commercial plants use these models but it is likely to be more heavily used, particularly in gen 4 reactors", "Earthquakes shake the earth. The amount of acceleration and thus force experienced by equipment is calculable and thus the equipment can be designed to withstand it. To avoid an accident on the nuclear side of a power plant, you need to make sure the primary containment and primary coolant loop doesn't break during an earthquake, so it needs to be sturdy and isolated well enough from shocks. Turns out this isn't that hard to do, given that you spend enough money on the foundation and suspension methods of the equipment. Earthquakes are actually not much of a problem for nuclear power plants and never have been. Maybe you're thinking of secondary effects a la Fukushima, where it was the tidal wave created by the earthquake that caused problems by flooding the power plant. Different matter. The earthquake itself didn't pose a risk to the power plant as it had been built to withstand it. The second part would be recognizing just how overrated nuclear disasters are. The worst nuclear power accident, at the Chernobyl power plant, has caused less harm to health and environment than a Chernobyl-sized coal power plant causes during normal operation (without even considering climate change, just air pollution). That's not to say the nuclear accident isn't a problem to be avoided, just it needs to be put into correct, objective perspective, without the emotional hype around it.", "> How would someone avoid a nuclear disaster in case of an earthquake? Generally, they would build the nuclear power plant somewhere that *isn't* prone to experiencing earthquakes. We know where a lot of the plates and faultlines are so we can reasonably predict *where* earthquakes are more likely to agree. Nuclear energy isn't 100% safe, either. Like the leaks of contaminated material in Fukushima after a major tsunami and storms there. But, it doesn't produce a lot of pollutants like burning coal and oil does, and they do have a *ton* of safety procedures in place to shut down a reactor and keep it from going supercritical and melting down/exploding a la Chernobyl (folks learned a lot from that). The biggest hazard from nuclear power plants is the spent fuel rods that are still heavily contaminated, but there have been proposals to make more efficient reactors that can use even that fuel or burn up *more* of the fuel to reduce how much waste is produced.", "Nuclear reactors and earthquakes. I guess we should explain fukushima. Fukushima is 2nd gen and is not 1 point safe. it means it requires interaction after shutdown to stay safe. Now the issues that failed were pure negligence, the seawall was half the height it was supposed to be in the original design and the buildings which had the backup diesel generators were below sea level, if those 2 things were done right fukushima would not have happened. Like chernobyl, no containment building, cheap control rods that don't have boron segments, and bad training. Modern nuclear reactors are clean, one point safe and easy to use, and breeder reactors even reprocess their own fuel so the nuclear waste is actually used as fuel by them. But. many countries which are earthquake prone have developed construction techniques which compensate and make buildings more resistant, including shock absorbing fundations, stronger but flexible building materials, better load balancing and spreading. Building for earthquakes has advanced a lot, but if you want to ask a question, be more direct. the worst nuclear accidents were mostly caused by negligence and bad design. Hell, if you saw windscale in the UK, you would shit your pants, imagen a open nuclear reactor that you pushed the fuel through and was air cooled... worked as well as you can imagen.", "Talking from a US perspective: Per US regulations for selecting a nuclear power plant site, you have to evaluate all natural hazards at that site, then design your plant to be protected at levels that exceed those standards. As part of chapter 2 of a plant's safety analysis report, they need to perform studies on seismic events which could occur in the area. As part of chapter 3 they need to specify the safety systems and structures which must be protected from those events and how they will protect them. All equipment in a nuclear plant that is vital to safe shutdown is classified as Seismic Category I, and must be designed to exceed the safe shutdown earthquake. All equipment which is not required, but is located in the same area as safety equipment must be designed as Seismic Category I/M (one over M) or II or equivalent, which means that the equipment is allowed to stop functioning, but it must not break in such a way that it can damage safety equipment. All seismic classified systems (I, I/M, II) must survive at least 10 OBE (operating basis earthquake - a lower level of earthquake that the plant is expected to continue operating). So by identifying the worst case seismic events, reinforcing the seismic category 1 systems and testing those reinforcements on shaker tables or through complex computer modelling software, and ensuring seismic I/M or II equipment cannot break category I systems, the plant is ensured to have minimum required safe shutdown functions during an earthquake.", "I don't think I have enough time to thank everyone individually, but you were all so helpful, thank you!", "In case of an earthquake nuclear reactors are supposed to shut down automatically. Modern safety measures are way better than they were at the times of Chernobyl. Also over the decades the number of deaths caused by nuclear power is much much lower than the number of deaths caused (directly and indirectly) by fossil fuel generators. And even in terms of radioactive waste - coal-powered plants produce way more of it than nuclear, by burning up huge amounts of coal containing trace radioactive elements and sending them into the atmosphere.", "Although alot of good points have been made about \"new reactors are safe, they can't cause a disaster\" is to be taken with a pinch of salt. Most of the disasters we know (fukushima/chernobyl for example) were due to human error, negligence and overall bad management. Yes we learn from these things, however one of the things alot of people don't account for is the human factor in these cases. Yes, newer reactors have alot more safety regulations etc. to even consider being built, however even back in the time of the above mentioned disasters it was pretty much the same. Built to be 'safe', however humans are the common denominator in nuclear disasters for the simple fact that we are flawed. Chernobyl for example, RBMK reactors were designed to pretty much be completely and physically unable to meltdown or cause any nuclear disasters, however once factoring in the human element of the Soviet Union cheaping out on crucial materials, suddenly a 'safe' reactor becomes a ticking time bomb. And as pointed out by other commenters, Fukushima was similar in regards to the human element. I'm not necessarily saying Nuclear isn't a good idea, because statistically speaking, even considering the impact from disasters that have occurred the damage is lower than conventional coal/fossil fuel plants in terms of illness/fatality, and dramatically lower in the case of pollution - The main thing with nuclear energy, is although its incredibly rare that things go wrong, when they do, they can go VERY bad and cause a large amount of damage, which when looking at a broader scope, isn't as bad as conventional energy, however it's alot more dangerous to be around when it does go wrong. Simple fact is although all of these comments mentioning passive fail safes etc. make a great point at the greatly increasing security and safety measures of new reactors, there will always be issues of the human factor, which almost always ends up being a product of greed completely screwing over everyone else. Although in more developed countries this is becoming a more miniscule issue with every rollout of new reactors, the fact is the risk is still there. When I was in school, at a much younger age, I did a report on this very debate, and back then I believed Nuclear energy was 100% the way forward and that the benefits massively outweighed the cost of the human factor. But almost 6 years later and being in the actual world, and realising how it is, I'm not really 100% sure the trust I can trust the 'human element' anymore.", "The idea is not that it is safe so to speak. It is hot and radioactive and all that jazz. The key is that it can be designed to fail safe. They design it so that everything ends up held in a relatively strict alignment with positive engagement keeping it there. When you lose that the positive action holding everything together fails and so does the reaction." ], "score": [ 4508, 2894, 288, 211, 58, 45, 18, 16, 10, 4, 3 ], "text_urls": [ [], [], [], [], [], [], [], [], [], [], [] ] }

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{ "a_id": [ "grdaynn" ], "text": [ "There is no net difference in the amount of water vapor from before your fuel cell. That's because the process we use to get hydrogen is often the electrolysis of water, so you're breaking water apart, then using the hydrogen and putting it back together. This results in no net water vapor in the air. (In addition, more water vapor in the air will just raise humidity, and then condense out of the air as rain) That's not to say hydrogen cells are perfect, there's lots of energy needed and some pollution that comes from the electrolysis part of the reaction, but as far as direct impact on the air, it should be negligible." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "grdiut5", "grdiy0o", "grdjgl0", "grdto16", "grdrqj5" ], "text": [ "It takes more gasoline upfront to accelerate, especially from a stopped position, than it does to maintain speed on a highway, especially since you've got some sort of momentum help carry your car. Also, idling at a stop = burning gas without covering any territory. So you're reducing your average miles per gallon towards *zero* very frequently when driving in a city because of all the stopping and going and idling. On a highway, you're just... going. Smooth sailing, so you're covering more territory per gallon burned.", "City driving has a whole lot of accelerating, which uses more gas than cruising, and it has a lot more stoping and standing. Think about it - all the time the care is just sitting there... Idling... *NOT* getting you to your destination, even when breaking, you're *wasting fuel* just keeping the engine from stalling rather than using that fuel to actually get you to where you're going. It takes a lot less fuel to keep your car running at a steady state once you're at speed than it takes to get you up to speed in the first place, and at least when you're on the highway, you're using your fuel to actually GO.", "Becuase going in a straight line in a fixed speed will always be more efficient then starting, stoping, changing direction every minute or two and wasting energy stopped with the engine on. Most highway driving is just cruising at a fixed speed with momentum, so as long as you´re driving in a reasonable speed (60-100KPH) and are in the correct gear to keep the RPM´s in an efficient range. fuel consumption will be low. While in a city, you´re going to accelerating, breaking all the time, turning to change direction, so the engine is forced to change ts momentum and RPM all the time, change gears all the time. its inefficient. Also why it was a mistake to make small diesel city cars. Diesel is best when doing long runs aka highway cruising, using it in the city for short hops is inefficient and negates all benefits of higher combustion efficiency. TL;DR : engines are most efficient when running at optimal fixed RPM, if you´re forced to change speed, accelerate and brake all the time, they are much less efficient.", "Short answer: It doesn't. What uses more gas in the city is the constant start/stop. In order to go forward, a car needs to overcome a few things: wind resistance, the energy lost to friction (both within the car and rubber-to-road), and, importantly, the inertia of the car itself standing still. This last one takes a lot of gas, because (citation needed) cars are heavy. When you are driving on the highway (presuming no traffic), you use a lot of gas to accelerate (get up to speed) one time. Then, instead of the inertia of the car standing still, you have the momentum of a car moving forward. If you've heard the rule \"an object in motion stays in motion,\" this is now your car -- it *wants* to keep moving forward. You only have to use a small(er) amount of gas to counteract the wind resistance and rolling resistance. In a city, you are constantly using gas to get up to speed, then stopping at lights, crosswalks, traffic, etc. Then you need to re-accelerate. By breaking, you've essentially *wasted* all of the energy you took to get up to speed in the first place. This is converted to heat (your brakes get hot) and released into the atmosphere. That said, wind resistance gets exponentially greater as your speed increase. It is actually more fuel efficient to drive slowly -- if you got on the highway, drove at a constant 30 miles an hour (and didn't get killed), you'd arrive at your destination half as quickly, but with a little more gas left in the tank, then if you drove 60.", "For 1 gears, your car is more efficient at a certain RPM, second, on the highway you're barely changing speeds. Remeber newtons first law, objects at rest or at a constant speed it will remain that way, basically on the highway you really only need to compensate for drag that is slowing you down. On a city you're constantly stopping and going again, and that takes way more energy, because objects are lazy and they want to stay the way they are" ], "score": [ 137, 19, 13, 5, 4 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "grfa53i" ], "text": [ "Was never a tanker, but my guess would be that driving a car is a common skill these days that's pretty much universal across the planet. Driving in a potential 360 degree horizontal plane using two levers is not so much. While the concept of steering and manipulating the direction the tracks travel with the levers makes sense and is simple, most people in nations who have tanks in their military are already familiar with driving vehicles by the time their military service begins. It's easier to work with what you know I guess." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "grfj6e2", "grfy18y", "grfvf0t" ], "text": [ "The importance of having synchronized amd agreed upon times is so much more important than having the same lengths. Plus, many civilizations are going to end up using similar or the same units for time based on what there is available. Whats the easiest unit of time to notice? The time between sunrises, phases of the moon, etc. How many different simple units of measurememt could arise though? Oh, this long stick looks good, mayne the kings foot, the queens hand, this rock, etc Even if historically months/years/weeks have been different lengths, the base unit of all systems has been pretty much agreed on (a day).", "There used to be. [China had their own system up until the 17th century]( URL_1 ) and [France tried their hand at making a decimalized time during the revolution era]( URL_0 ). The former was replaced by a system introduced by Jesuit missionaries and the latter never caught on.", "There are different systems for time. Most of them are not useful for global usage. To help illustrate, first look at temperature. There are four common systems for temperature C, F, K, R. They all measure temperature in their own version of degrees. The other time systems use hours, minutes, and seconds as well. Other calendars also use days, weeks, and months. However, each system defines each term differently. One such time system: each day begins at sunset, and there are twelve evenly spaced hours until sunrise. Which is called Crepuscular Noon or mid-day. Then there are twelve evenly spaced hours until sunset, and the next day starts. In this system, there are still 60 minutes in an hour, and 60 seconds in a minute. But the length of each varies every day of the year, and also on the latitude you live at. It isn't useful for global time. Another time system, Metric Time, has 10 hours each day, 10 minutes in an hour, 10 seconds in a minute, 10 thirds in a second, 10 quarters in a third. A metric quarter is just shorter than a normal time second. A metric second is a little bit less than a normal time minute and a half roughly. It also banned the usage of time zones, so people do things at different times globally. (People have a hard time giving up concepts like: eat lunch at noon, instead of having a local time for lunch). There are also at least 6 calendars in common usage. Each in their own month and year." ], "score": [ 7, 6, 3 ], "text_urls": [ [], [ "https://en.wikipedia.org/wiki/Decimal_time", "https://en.wikipedia.org/wiki/Traditional_Chinese_timekeeping" ], [] ] }

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{ "a_id": [ "grfspnc", "grg0kqf", "grftr3r" ], "text": [ "If you put natural uranium and graphite together just right it can become a chain reacting system because a fraction of uranium is excellent nuclear fuel, called U-235. If you put natural thorium in any configuration it will never make a chain reacting system because natural thorium contains no fissile material like U-235. If you have a nuclear reactor you can use the neutrons produced by it to bombard thorium and generate fissile U-233, which is great nuclear fuel. But you need a reactor to do that. If you need a reactor before you can turn thorium into nuclear fuel, you necessarily have to make uranium reactors first. After we had a bunch of uranium reactors, there was never a compelling enough case to switch over to thorium breeder reactors.", "No thorium reactor is design ready yet. None have a design certification with the nuclear regulatory commission and none are even ready to go to them for certification. There are still some things being worked out on the drawing board.", "Thorium reactors are not rare, they don't exist. India is building one, but none have actually been turned on. It's not a proven product. It's still just a theory for now. But there's no reason normal reactors can't be just as safe. So the value isn't really there. Still some value if it works, but not a major value." ], "score": [ 5, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "grnm4z2", "grnn4aw", "grnlu36" ], "text": [ "Potato peelers need to be sharpened like any other blade. It just doesn't come up often because they don't take a lot of wear, since you use them to cut through relatively soft stuff only.", "They just cut through water based potatoes, not hard things, and you don't hit them against a surface (cutting board).", "I've wondered this! My favourite kitchen tool. My theory is the design aspect that guards your fingers from the blade has the secondary benefit of guarding the blade from general wear and tear. There might be more to it, though: the angle that it is used at is always acute, by design, which is coincidentally the way you apply a blade to a stone to sharpen it..." ], "score": [ 16, 6, 5 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "grntjx9", "groamnb", "grnxbj6" ], "text": [ "The flush sensor on a toilet faces toward the front of the stall, and the sensor spreads out in a V. It expects to sense 3-4 feet away. It works when it senses a bounce back (which could be anywhere bouncing around the walls as you move). The flush sensor on a sink is facing down into a curved reflective surface which is constantly bouncing back the signal. It works when it _doesn't_ sense a bounce back, so you have to block the entire sensor.", "Engineer here, but I do not work in the industry that makes these. But my buddy owns a plumbing company and I asked him this one day over dinner. He said mainly its plumbers that don't want to take the time or read the directions how to adjust them properly. They usually just install and go, or leave it to the apprentices.", "The sensor is sending out a signal and track the time until it comes back. With that, it can tell if the signal bounced off of you, or the bathroom door (This is essentially how radars and sonar work). So the toilet uses this signal to know when the user sits down (start sending out the signal) and gets up (flushes the toilet). However, if your bending over a bit far for whatever reason, that signals can bounce on your back and bounce away from the receptor on the toilet, hitting the wall behind you. The toilet is then like “oh shit (pun), this is taking a while, so the dude might have just left and we didn’t catch it.” So then it flushes, even when you’re sitting right there." ], "score": [ 14, 5, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gropuvi", "gropos1", "gropsk8" ], "text": [ "Really the same way they account for distance. Just because something is straight ahead doesn't mean that's how a bullet moves. Bullets aren't immune to gravity, so the scope is meant to be set with your range and it will be angled in such a way that pointing your gun slightly above the target is translated to a direct shot. For shorter range things like a hand gun it barely matters, but rifles especially sniper type things it matters a lot, you'll see in TV and movies them mention range and adjust the scope The fact it's above the barrel to start is just one of those factors is includes", "After you attach a scope to a particular gun, you have to calibrate it by firing at a target and making adjustments. This is called 'sighting in.'", "A user of the scope will perform a practice called sighting the scope where they go out and make sure the scope is pointed correctly for the distance they plan to shoot. Keep in mind bullets don’t travel in straight lines." ], "score": [ 5, 3, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "grozhq9", "groyr6r", "grp1nlq", "grp76rw", "grpfrds" ], "text": [ "Treads are only there to give water somewhere to go if there's rain. Without tread cars aquaplane when the surface is wet, sliding very easily, but they have more grip in the dry. F1 cars do have treaded tyres for use in wet conditions.", "They want as much contact between the road and the tires as possible to deal with the crazy torque and braking of those cars so they make them with out treads.", "As an additional answer, in tyres with tread patterns the rubber can move about as it comes under sideways pressure when cornering etc. That generates more heat and wear so F1 tyres with tread for use in wet conditions degrade very quickly on a dry track. As the track dries after rain you will often see the drivers deliberately drive onto wet areas of tarmac off the main line to keep the tyres cooler if they can't be swapped just yet.", "Wets do, slicks don't. Slick tyres aquaplane in the wet. Treads channel the water away. Racing tyres are not meant for regular use, but your regular tyres are.", "Tires with no tread have much more grip in dry conditions. They're also typically a much softer compound of rubber than street cars so they heat up to 100C to stick to the track even better. Combined with the downforce of the aerodynamics it provides maximum performance at the top level of motorsport." ], "score": [ 40, 19, 9, 3, 3 ], "text_urls": [ [], [], [], [], [] ] }

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{ "a_id": [ "grp0gf9", "grp0i7v" ], "text": [ "Most of the time what you see is just the pilot flame - unless there is a full blown roaring candle jet going on (which usually indicates there is an upset or maintenance related issue somewhere in the plant). Light by-products (hydrogen, methane, ethane, propane) from the refining processes are generally recovered and used back in the plant (for furnace firing, boilers for generating steam, etc.) - they don’t like paying for their fuel as much as you don’t, not gonna just burn it up to light up the sky. However in some cases like equipment failure or planned maintenance events there is a temporary imbalance of this light fuel gases from production vs nett consumption within the plant, and needs to be released safely into the atmosphere (ie. H2O, CO2) instead of a flammable gas cloud which can then ignite elsewhere. The pilot flame is there to ensure the gases are ignited at the last point of exit of the plant (the flare stack, which is also built way up high so it’s safe for personnel and surrounding at the ground level).", "Oil refinery engineer here. They are called flares and they burn any excess gas, most of which come from vessels that are relieving any excess pressure. Gases burned may be hydrogen, light hydrocarbons, or in rare cases, hydrogen sulfide. Burning them is better than releasing them directly to atmosphere." ], "score": [ 11, 9 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "grscbsa" ], "text": [ "I'm going to ignore the horsepower and torque for the moment. You hit the nail on the head - it's mostly the amount of air that engine can hold that makes the difference. More air/fuel mixture, more chemicals to blow up, more power to move the car. The number of cylinders help smooth out using the power to turn the wheels. Ever try pedaling a bicycle with onky one foot? There's a power stroke, and then the bike slows down as you wind the pedal around before you can push it down again. So a one-cylinder car would be a lot like that. Boom. Explosion. Then wait until the piston is the right spot again. Then boom. Two cylinders will smooth that out a bit (on opposite sides. Four is even better, eight, twelve, whatever. There is that added benefits that with smaller cylinders, it's easier to design something to hold them, as opposed to two huge cylinders that will only fit under the hood in a few ways. Finally, there's one difference with engines (versus pedalling a bike). There's a power stroke *every other* rotation. (Don't worry about details - it basically allows it to separate pushing the exhaust out from taking in more air/fuel mixture). I'm also skipping rotory engines and forced induction (like turbochargers). Hope this helps." ], "score": [ 7 ], "text_urls": [ [] ] }

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{ "a_id": [ "grstuo4", "grt1f9z", "grt6x88", "grsz29u", "grte54g", "grsu0qb", "grsnuev", "grtkgxb", "grt2l8b", "grsxoaq", "grtk66v", "grusdp1", "grucgmm" ], "text": [ "It's a commonly held myth that the airflow on a sedan removes rainwater, but doesn't on a hatchback. In reality it has more to do with the lack of a boot (trunk). This means dirt is thrown up from behind the car onto the back screen. Also, tradition plays a part. Some sedans have rear wipers, some are optional etc.", "It's not that flat windows need them and angled windows don't, because trucks don't need rear wipers. Instead, what's happening is that the wake that the car creates pulls moisture directly onto the rear window. Sedans and trucks don't need a rear wiper since their wake is further back from the window, but hatchbacks, SUV's, and vans need one since their rear window is at the rear of the car.", "All cars create a vortex behind themselves as air comes over and from underneath the car to re-converge at the back of the car. The one from underneath pulls a lot of road grime with it. On a sedan, the distance from the rear glass to the edge of the trunk lid separates the glass from the swirl of grime and its only exposed to the relatively clean upper flow and doesn't get very dirty. On a hatch, its directly exposed to the dirty underflow vortex and it deposits a lot more grime on the window. Combine that with the fact that rear glass on hatchbacks is generally pretty vertical and therefore doesn't get washed by rain as easily, and many cars these days have overhanging spoilers for aero, and you have a window that can get grimy enough in one trip that you can't see out of it, which is a safety hazard. So, some clearing mechanism is necessary.", "What kind of country doesn't have rear wipers on all cars?", "All this talk of rear windshield wipers makes me miss my 4Runner and the rear window I could roll down.", "Also has to do with regulations, for instance most USDM cars won't have rear wipers on sedans but JDM cars such as the Mitsubishi Evo 8 or 9 do URL_0", "theoretically, because the rear screen on a hatchback is almost vertical. It gets super dirty, real quick. The more diagonal placement on a sedan gets dirty too, but nowhere nearly as fast. (yeah. that was a personal anecdote, of course. But that is pretty much my experience with it.)", "This was the first question that arose in my mind when I transitioned from my first car (sedan Chevy Malibu) to 2nd (hatchback Chevy Equinox)", "The vertical shape of an SUV or hatchback profile creates essentially a vacuum (or more accurately an area of turbulent air) behind the vehicle that allows dirt, etc. to be tossed up and cling to the window. This also happens to the back of a sedan, you will see the trunk and rear bumper gather dirt as well. The window is far enough out of the way and has different airflow so less dirt on those vehicles thus less need for a wiper.", "Lots of answers but no one mentioned this: In a hatchback, there is a place beneath the rear window where the window wiper blade can naturally attach to the car. That place (beneath the rear window in the middle), is part of the hatchback rear door into which the window is also fastened, so the window and the wiper are part of the same construction and their relative position is always maintained, even when the rear door is opened. In a sedan, there does not exist such a place. In a sedan, immediately beneath the rear window there is usually the boot (trunk) lid, which opens up and is not part of the same rigid construction in the car body where the window itself is fastened.", "Another question for you: Do you know why Yugo's have a defroster on the rear window? To keep your hands warm while you push.", "So many people here do not realize that a hatchback is defined by where the trunk door hinges (at the roof) and not by the flat rear end. Here is a hatchback: URL_0", "Rear wipers are essentially meant for vehicles with an upright rear window that collects dust, dirt, snow, etc., because of aerodynamics – the flow of air over the right angle where the roof and rear window meet creates a low pressure area that pulls that nasty stuff in and deposits it onto the surface" ], "score": [ 6839, 581, 245, 52, 42, 38, 29, 10, 5, 5, 3, 3, 3 ], "text_urls": [ [], [], [], [], [], [ "https://images.app.goo.gl/XKRW3oBSNV4Vk7ADA" ], [], [], [], [], [], [ "https://img.drivemag.net/jato_car_photos/SKODA%2FOCTAVIA%2Fhatchback%2F5%2F2004%2Fexterior-photos%2Fo%2Fskoda-octavia-hatchback-5-doors-2004-model-exterior-photos-1.jpg" ], [] ] }

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{ "a_id": [ "grugswc", "grucekx" ], "text": [ "The lighter portions of the highways you're driving may be made of concrete rather than asphalt. Concrete is more rigid, and it has different auditory characteristics than the more plastic-like sections of asphalt., and concrete highway surfaces are also often ridged for better traction. Dropping a stone on poured concrete will have more of a \"ping\" sound as opposed to the \"thud\" sound of dropping the same stone on asphalt.", "Asphalt refers to the petroleum product that binds the aggregate together that makes the road, and it's black. The road is light because so much driving over it has worn the surface material down, exposing the stone aggregate underneath the binder. So lighter roads are more worn and more prone to noise. And worn by more than just traffic, but also weather. A black road is freshly paved and recently rolled smooth, so there's less variation to make all that noise." ], "score": [ 16, 9 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "grvz95m", "grvkl7w", "grvzq7g" ], "text": [ "The issue you’re having is that whoever setup that sight did it wrong. [This is what the full sight should look like.]( URL_1 ) A plane goes very fast, if you shoot at where it is, you miss. You have to shoot where it’s going to be. The whole sight is trying to make sure you shoot at the right place. The thing at the center is where (if everything goes right) the plane will get hit. You are supposed to aim so that the plane is on the ring, and headed to the center in order to get hit. [This is what it's supposed to end up looking like.]( URL_0 ) You have to guess how fast the plane is going and bring the ring closer or further. If it’s going faster, move it close, that way the ring appears bigger and your aiming is further ahead of the plane. Now it’s tilting because of how high the plane is coming from. The ring is parallel with the ground. If the plane was flying from eye level, you only need to lead left/right. So the ring becomes a line. If the plane were coming from higher, you would need to aim more up/down. So the ring becomes more circular. The ring is attached to a weight to ensure this. Bullet drop is not being compensated for, the plane is too close for it to matter much. Larger AA guns have to compensate for this, which means in addition to dialing in how fast the plane is going they also have to figure out how far the plane it, because depending on how far the plane is, it could mean aiming up or down. This sight doesn't have a \"how far the plane is\" setting.", "Because the bullets fall as they travel. When you shoot them nearly horizontal they are moving very fast horizontally so their trajectory deviates slower by dropping because of gravity. The higher up you aim, the lower their horizontal velocity and the higher the effect of gravity is on where they fly.", "The theory behind how that sight works is that you put the front of the plane on the ring such that the plane pointing towards the dot in the middle. Then you shoot and the plane flies into your bullets. There were actually three different sized circles you could put into the sight, the gunner would have to guess how fast the plane was moving and then put the appropriate sized circle into the sight. The reason the circle gets flat close to the horizon is because if a plane is low to the horizon then it's going to seem to move less and therefor less lead needs to be given to hit it. If you're curious here are some articles about how the sight worked. URL_0 URL_1" ], "score": [ 12, 9, 3 ], "text_urls": [ [ "https://www.lonesentry.com/articles/ttt09/pics/ring-sight.jpg", "https://www.lonesentry.com/articles/ttt09/pics/aa-sight-30-38.jpg" ], [], [ "https://www.lonesentry.com/articles/ttt09/german-aa-sight-30-38.html", "https://www.lonesentry.com/articles/ttt09/german-ring-sight.html" ] ] }

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{ "a_id": [ "grwgx1o" ], "text": [ "Birds gather building materials such as sticks and twigs, and binds them together using their saliva. Their saliva is pretty gelatinous and when solidified creates a pretty strong structure, especially when reinforced with sticks that act like rebars. By the way, nest of certain birds are actually a chines delicacy (swallow nests). You can clean the sticks and feathers out and be left with solidified bird saliva. People eat it by soaking it in water first and making soup or congee. Supposedly it has high nutritional content... But probably just some carbohydrates and protein." ], "score": [ 8 ], "text_urls": [ [] ] }

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{ "a_id": [ "gry6h3c" ], "text": [ "Naturally aspirated means that the engine breaths on its own. The movement of the pistons inside the cylinders pulls air in, which combines with the fuel, and combusts. A turbo charged engine has a turbo charger. The turbo charger is spun by the exhaust air from the engine. The spinning turbo chargers then forces more air into the engine. A turbo charger can force more air into a smaller engine than a naturally aspirated smaller engine can get on its own, so that allows for more power output. The downside to a turbo charger is it doesn't provide much power at the immediate low end RPM range because it isn't spinning as fast with less exhaust. They can also drop off power at very high RPM. A super charged engine has a super charger. The super charger is powered mechanically by the spinning crank shaft. It also forces air into the engine to allow for more power output. A super charger gives more low end power than a turbo because it does not need airflow to be powered. The downside of a super charger is it can put more stress on an engine and is less fuel efficient as a turbo charger because it is powered mechanically." ], "score": [ 6 ], "text_urls": [ [] ] }

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{ "a_id": [ "gry5ye3" ], "text": [ "Starting an engine is a slightly chaotic event. The starter motor gets the engine turning and keeps it turning while combustion is established. The control system has to work out where in the four stroke cycle the engine is and where top dead centre is, to establish the correct firing order and timing. With a cold engine, some of the injected fuel will condense on the cylinder walls, and then evaporate again as things warm up. All these things mean that there is a bit more fuel flying about than is needed to run the engine at idle, as combustion is established. This results in the engine speed flare that you have noticed. Edit: typos" ], "score": [ 14 ], "text_urls": [ [] ] }

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{ "a_id": [ "gryoppr", "grynkjw" ], "text": [ "It's calibrated. Let's say you've built a retinal scanner that, given a picture of an eye, compares it to all of the eyes it knows and gives a similarity score between 0% and 100% where 100% means it's exactly the same picture and 0% means they have nothing in common. The same person on a different day might get a score of 96% or 98%. But where to set the threshold? If you set it too low, like 90%, then you have a chance of a false positive - someone being matched even if they're a different person. If you set it too high, like 99%, then you have a chance of a false negative - the system doesn't recognize you even though it knows your retina. So you calibrate it with thousands of actual eyes, and pick the threshold that gives you the desired false positive and false negative rate. No security system is completely infallible, and retina scanners are almost always used along with some other form of authentication like a key card or password.", "By being really picky. If the retina looks similar enough then it is vanishingly unlikely that it could belong to another person than the first. The patterns of blood vessels in the retina are formed randomly and there is basically no chance someone else is going to have a similar enough pattern to be confused with another person." ], "score": [ 4, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "grzg51v", "grzg5me", "grzgqqk", "grzik3k" ], "text": [ "They exist. You can find aluminum bottles for beer at sporting events. They get used in stadiums because you can't use glass in stadiums. If you google aluminum bottles of beer you'll find pictures under the images tab. I imagine the reason they don't get used for soft drinks is because of cost.", "Because plastic is cheaper and big corporations are not worried about the environment. They’d rather pay lip service and donate to charities than actually reduce their profit margins in the interest of the greater good.", "Aluminum bottles are relatively expensive to make compared to plastic, and the easy availability of plastic and cans limits the demand so companies aren't motivated to buy all the equipment. That said, I hope they catch on because plastic is just so awful for the environment.", "Nobody has pointed out that even with aluminum cans, there's a plastic liner. But yes, aluminum does cost more to manufacture and even costs money to recycle." ], "score": [ 9, 6, 6, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "grzhas8" ], "text": [ "When an engine is \"cold\" (90°F is cold to an engine), it requires a richer air-fuel mixture to start. The choke blocks off some of the intake air, so that there's more gas per unit of air being sucked in to the engine. The choke should not be necessary after the engine has been running for a few seconds up to a minute or so. Continued choking will make the engine run very rich and be low on power. As an alternative, some engines have a primer bulb that squirts a big blob of gas into the intake, again to enrich the air-fuel mixture, but without restricting the intake air. Computerized fuel injection systems do the cold start enrichment for you by injecting extra fuel." ], "score": [ 13 ], "text_urls": [ [] ] }

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{ "a_id": [ "grzjkmm", "grzjh55", "grzjh72" ], "text": [ "Those taps have what's called an aerator in the them. It mixes air into the water stream so that the water comes out in a bubbly stream that doesn't splash about as much. [You can read more here]( URL_0 ).", "Bubbly water comes from a diffuser that is screwed on the end of the tap. If you take it off you’d get high pressure insanity.", "Usually the nozzles on the us Taps have an area behind the flow where air can come in and mix with the water. The flow of water creates a vacuum that sucks the air in. It's just a different faucet nozzle, and if you replaced yours with a US type faucet nozzle, it would work the same." ], "score": [ 12, 9, 5 ], "text_urls": [ [ "https://en.wikipedia.org/wiki/Faucet_aerator" ], [], [] ] }

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{ "a_id": [ "gs2oh9l", "gs2rew5" ], "text": [ "Lead acid car batteries can emit hydrogen gas (hydrogen sulfide typically) under certain conditions which is flammable. Since we are taught to attach the negative last, it usually creates a spark. Attaching the negative to a point of the car away from the battery puts distance between the spark and a potential (albeit rare) ignition. So safety is the reason. Note that even many “sealed” batteries can off-gas.", "Your starter is shorted to the car frame for the safety reasons given by other users, and to prevent electric shock. However, if you're trying to start your car, if the leads are connected to the battery the electricity must first flow through your battery and then to your starter. If you connect the ~~positive~~ negative to the car frame, the current can flow directly through the starter, which is faster and more efficient." ], "score": [ 23, 4 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gs2u13l" ], "text": [ "Your engine has a cooling system. It circulates coolant (water or antifreeze) around the engine to prevent overheating. The radiator is the part that takes hot coolant from the engine, and cools it down so it can be sent back to move more heat. When the coolant leaks out the system starts to run low, which means it can't cool down the engine so the engine overheats." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gs6d0i7", "gs6bnly", "gs6mz1f", "gs6brsm" ], "text": [ "While everyone's answer of \"gears\" is close, I don't think that's the answer you are looking for. The motor in the car does not stay synchronized, as you describe it, with speed because of the torque converter. The back of the motor has an output shaft. That output shaft is carrying all the \"twisting\" power the engine outputs. In a vehicle wtih an automatic transmission, it goes into a torque converter. It's a donut shaped part has a fluid in it, and 2 \"fans\" facing each other. [Here]( URL_0 ) is a diagram. The \"fans\" spin the fluid, so the fan on the input side spins the fan on the output side (which is the side that goes to the transmission to power the wheels). The reason the car doesn't spring forward is because of this fluid coupling in the torque converter. It's also why when you stop, the transmission can stay in gear. The torque converter has a \"stall\" speed. This is the fastest the engine can turn, in RPM, before the torque converter can no longer just absorb the engine and MUST turn the output shaft or risk damage. For example, my Yukon stall speed is around 1600RPM. That means if that if I press the brakes and the gas, at around 1600RPM the torque converter is done, and I better take my foot off the brakes because something is going to break. Torque converters do have a \"lockup\" that makes them 1:1, where clutches essentially make the output shaft match the input shaft speed. It's generally part of the higher gears (my Yukon, for example, locks out in 5th and 6th). Automatic transmissions are amazing pieces of engineering, what a GREAT question!", "Most cars in the US have automatic transmissions, and most of those are coupled to the engine by a torque converter. The torque converter is essentially two turbines. The turbine on the engine spins a fluid inside the torque converter, and that fluid spins the turbine coupled to the transmission. Due to that coupling, the input speed will not always match the output speed. On top of that, gears in the transmission and differential multiply the torque of the engine, so that even a thousand revolutions a minute might translate to only a few miles an hour", "In an automatic car, you have a torque converter. This is a drum of oil bolted to the back of your engine. The engine spins, the drum spins, this imparts spin on the oil inside the drum. Sticking out of the drum is a shaft. This shaft is connected to a turbine. As the oil spins, it imparts force upon the turbine, also causing it to spin. The shaft attached to the turbine is connected to the input shaft of your transmission. So there's a physical disconnect between the crankshaft of the engine and the drivetrain, and the energy is transferred across that gap through the oil. Why? Because piston engines suck. No really. They're not very energy efficient at all, they produce miserable torque, they have slow speeds, their torque and horsepower output varies over their range of engine speed, and worst of all, they suck so bad at producing torque, they have a minimum engine speed before they stall. Once an engine is running, it has to keep itself running, and it can't do that below stall speed. So if your engine and drivetrain were mechanically connected all the time, then how can your engine produce torque when you're at a stop? The drivetrain isn't rotating, meaning the engine wouldn't be able to rotate, meaning it's not producing torque to get the car moving from a standstill. You need the ability to impart torque without stalling, you need slip. And that's what the torque converter does. You have to sacrifice efficiency in order to accelerate the drivetrain, and thus the car, in order to prevent the engine from stalling. Modern torque converters also have clutches. These are friction devices that clamp together, mechanically interlocking the engine and drivetrain. This is how manual transmissions work - you operate the clutch with your left foot, gradually introducing torque without stalling the engine, until the drivetrain is moving at sufficient speed that the engine won't stall. Once you're up to a sufficient speed, you don't need slip. Even with a manual transmission, you can shift gears without the clutch pedal. The only time you need to introduce slip again is when braking to a stop. Automatics will disengage their clutch, presuming they have one, when you accelerate hard enough in order to allow slip - a sacrifice made to reduce vibration, people don't like that. Cheaper or less sophisticated automatics will always suffer slip. A manual transmission, if you try to accelerate too hard, or in the wrong gear, would just cause the car to vibrate like crazy. The problem with this approach is that slip causes a delay - the engine revs high and the car isn't synchronized with it yet, which causes the car to lurch. Screwing around with an automatic car like it's a sports car can make it unpredictable. This is exactly how teenagers wrap their mom's soccer van around light poles, like idiots - that lurch is actually very hard to control, even in a straight line. Electric vehicles, by comparison, are some 98% energy efficient, and regenerative braking certainly captures the pure loss of energy that you suffer with a piston engine. The sacrifice is that batteries have absolutely nothing near the energy density of gasoline. Also about electric motors, they produce 100% of their torque at 0 RPM, which means they don't have to idle. Transmissions are torque multipliers because piston engines produce so very little of it at low engine speeds, electric motors don't need them. They can spin to higher speeds, and produce almost no vibration, and almost no noise.", "Sounds like you have an automatic gearbox, possibly even a CVT? If you had a manual car then it would work just the same as a motorbike does." ], "score": [ 19, 6, 4, 3 ], "text_urls": [ [ "https://resize.hswstatic.com/w_285/gif/torque-cutaway.jpg" ], [], [], [] ] }

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{ "a_id": [ "gs7h2m3", "gs83tvz", "gs7mvez" ], "text": [ "Cost, standardising the shape makes it cheap, if a product decides to use a non standard shape the set up cost will be huge. Ideally a nobble around the perimeter of the lid like a tyre track would help but it isn't going to happen . If you struggle try inserting the handle of a spoon or blunt table knife under the rim and lever a little bit, there will be a little pop when you let air inside the jar and it will then open easily.", "There's some German jars that are oval shaped to give better leverage. I just tap the edge of the lid on the floor, works every time.", "Lots of lids are ridged, hammered, or patterned to give more grip. Most mason jar lids, mayo or pickle lids, prescription or drink bottles... honestly I think they're more common than smooth ones. It just costs more to make, so the really cheap ones are smooth. You also see smooth lids on things that are trying to look elegant or sleek, like \"fancy\" candles, but that's just a matter of aesthetic over functionality." ], "score": [ 19, 5, 5 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gs9r5d1" ], "text": [ "The third prong is for safety, so you don't get electrocuted if the device breaks. If the device is designed so touching it won't electrocute you even if the circuit shorts out, it doesn't need the third prong." ], "score": [ 11 ], "text_urls": [ [] ] }

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{ "a_id": [ "gsaqd60", "gsaqgwu", "gsb5use", "gsbd3wd" ], "text": [ "the imperial hp is not the time it takes for a horse to lift a 550 pound weight of 1 inch, but more the power needed to lift a 550 pound weight of one inch in one second, which is roughly 750W", "Imagine it’s the 1800s and you’re developing newfangled steam and electric motors. You have to market this device to industry using some sort of reference that they’re familiar with. So what were they using for these sorts of applications? Horses. 1 horsepower is roughly equivalent to the amount of work a horse can do at a lazy pace all day long. It’s not a sprint or major effort, it’s what you’d actually get from a bored horse dragging a plow around. The working horses have mostly retired by now, but the unit of work measurement has survived.", "Your understanding is not exactly accurate; horsepower is defined as a rate of work equal to 550 foot-pounds every second. It's not an amount of time it takes to do a job; it's a rate of work (which is literally what power is defined as being). The entire idea is that engines replaced horses as the primary powerplant for all sorts of power applications, so it became useful to compare the amount of work an engine could do to that of what a horse could do. Thus, a horsepower is defined as the amount of power a horse can sustain over a relatively long time period, which ends up being around 550 foot-pounds per second (or 746ish Joules per second).", "In thermodynamics, work is energy transferred in a system to its surroundings. Energy is a quantity - somewhat abstract, that must be transferred in order to perform work. Energy can be heat or momentium, for example. Power is how fast energy is transferred over time. The basic unit is the watt. We often use watts to express the work of electrical systems. Horsepower is another unit of power that is directly convertible to watts. This means you can compare a car's engine to the car's stereo system, as to which is performing more work. 1 hp = 745.699872 W So: P(w) = 745.699872 * P(hp) I own a Nissan 350Z which makes 306 hp. Therefore, my engine produces: P(w) = 745.699872 * 306 hp 228184.160832 W = 306 hp --- There's a technical nuance you need to understand, and that is time. Power is energy over time. So if you're going to compare an engine's horsepower to an actual horse, how much time do you take into account? If you look at a horse's actual peak power output, a horse really can produce about 15 horsepower in a moment. But if you average out the work of a horse over an entire day, including the fact the horse has to rest, eat, etc, then a horse over the course of a day averages to about 1 horsepower. Does this sound a bit misleading? And how does this relate to horses and cars? James Watt derived this unit, it was for marketing purposes. James Watt made improvements to the steam engine and wanted people to buy them. If he said that his expensive engine had the same short-term output as a horse, people wouldn't buy it, as they already had horses. Instead, he compared it to the amount of work a horse could do in a day, giving it the output of ten horses instead of just one. Suddenly his invention became much more tempting. Although Watt bent the truth to make his engine more appealing, he was not technically lying, because the advantage of the engine is that so long as it's fuel and water is sustained, so is it's energy output, all day long." ], "score": [ 58, 20, 14, 5 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gsbsq6k", "gsc83oi" ], "text": [ "They have a microphone that picks up sound, amplifies it depending on the criteria set by the audiologist and then relays that to the wearers ear via a small speaker. The criteria for amplification is defined based on the results of a hearing test, so that only frequency bands that the user has difficulty hearing are amplified.", "The little machine listens to the sounds around you that would normally not be able to hear, because your ears don’t work very well. Then, the machine yells those sounds into your ear so you can hear them better" ], "score": [ 5, 3 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gscivy4", "gscl6pc", "gsciiz1" ], "text": [ "Different ways of controlling cars existed in the early days, but the industry settled on what we have now. A wheel can turn without hitting anything (unlike rudder-like bars that some early cars had). Pedals exist because there's a lot to control in a car, and your hands are already occupied with steering (and working the gearshift). We have the setup we have because it worked better than the other setups that people tried.", "The control layout we know now comes from the 1916 Cadillac Type 53. It was first car to have steering wheel and gas, brake & clutch pedals in that order. Austin Motor Company copied the layout from Cadillac and released a very popular cars in Europe, and then everybody else copied as well.", "A gasoline powered car, the standard before these fancy electrics, moves by burning gasoline fumes. The amount of fumes you push into the engine, the more power is run through the pistons, and the faster it goes. A gas pedal is used to regulate how much gasoline goes into the engine. Pushing the pedal in adds more gas. The steering wheel is used because it naturally mimicks the turning if the tires. Turning to the right turns the wheels right, which turns the car right. Because most cars only move in two dimensions, and the forward movement is determined by the gasoline, a control device that only moves left or right was all that was necessary." ], "score": [ 14, 8, 3 ], "text_urls": [ [], [], [] ] }

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{ "a_id": [ "gsea8dm", "gse7vej", "gse8q40", "gseauaq" ], "text": [ "The thing you can't really see in photos is the fact that the whole front end of the ship is wedged into the shoreline, like a dart. It doesn't look it -- it looks like it's still completely floating in water -- but the water near the shoreline is deceptively shallow. This ship is, at least in part, resting on land. The vessel has essentially beached itself, like a whale. The Ever Given is a *huge* ship. One of the largest of its kind. And it's fully loaded, too. For all serves and purposes, it's a skyskraper floating on its side. When this thing gets going (and it can move at a pretty surprising clip) all of that mass doesn't just stop when it hits something. When the ship hit the shoreline, it didn't just bump into it. It likely *kept going*. It cut into the shore and wedged itself in, again, like a dart. It likely also bottomed out below, forcing the bow out of the water and up, reducing its buoyancy. It's wedged in there pretty good. Boats are really great at cutting through water. But they're really awful at being sleds on land. The ship was able to force its way onto land with its incredible momentum, but you can't exactly do the reverse now that it's stuck. Theoretically, it would take at least an equally massive ship steaming in the opposite direction at the same speed to yank it free. Realistically this can't occur because A) there are few ships out there this big, B) there's no room in the canal to do anything like this and C) the only way you could transfer this force would be either by ramming (which would destroy both ships and need even more cleanup) or by towing (which would snap any chain that wouldn't just rip through both of our ships like giant cheese wire).", "What solution seems so easy? You gonna tie it to a truck? This things got tens of thousands of tons sitting on the mud. It would take very roughly that amount of force to move it. It's difficult to find anything that can pull it off of the ground with tens of thousands of tons of force.", "Yea I think the very front is pretty dug in, big ass ships like that have a long skinny pointed part on the front I assume that is very well dug into the earth.", "It's lodged in there like a two-way door wedge. Have you ever hammered a post into the ground? Do you remember how it's more secure the more force you use to drive it into the soil? When trying to get that stuck stick out, it's easiest to wiggle it free at the tip furthest from the ground. Problem is: Both ends of this very large stick were incomprehensibly forcefully driven into the banks. There's no wiggling it out, so they dig. Then again, it's a very, very large vessel, so it takes a long time. It's a quarter mile of ship, mind you." ], "score": [ 14, 6, 3, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gsfa75d", "gsfaq31" ], "text": [ "Even at 100% coal energy generation electrical cars are still more efficient than combustion. The efficiency of turning heat into usefull energy is highly dependant on temperature (and especially the temperature difference between combustion and exhaust), thats why a gas car in absolutely perfect conditions gets at most 25% efficiency while a modern coal powerplant reaches 45% (and even 60% for Gas+Coal hybrids) If you substract transport of electricity and the efficiency of battery and electrical drive you end up at roughly 35% Every bit of renewable power is then free enviromental benefit on top. I sadly don't know much about the enviromental impact of the batteries, but they have a lifetime of years of saved energy so I doubt that will tilt the equation in favor of internal combustion cars Oh and EVs lose less efficiency for driving in non-optimal RPM. Combustion loses so much that dieselelectrical drives are used in ships and other large machines to keep their RPM constant and still change speed", "There are a few benefits (and some drawbacks) to EVs in terms of environmental impact. I'll quickly mention two benefits that under as key. 1. Efficiency Internal combustion engines are not very efficient. Big powerplants are. So are power distribution networks in most developed countries. In short it will often be more efficient to have one big energy generator than thousands of small ones. 2. Street level pollution I don't think this one gets talked about enough. When we burn fuel in cars the pollution from that is emitted where we live/work/play. This is most noticeable in cities. If we generate centrally (even by dirty means\" that is concentrated in one place. That place is unlikely to be (for instance) outside a school. This also makes it easier to mitigate" ], "score": [ 10, 5 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "gshltq8", "gshqvxa", "gskhuak", "gshm0ns" ], "text": [ "Connected to the reel that holds the excess belt is a small cam that is spring loaded. When the reel spins fast enough the cam is subjected to enough centrifugal force to move outward against the spring and when it does so it hits a stopper that prevents it from turning any more. There are also electrical locks that keep it from turning when your brakes are on and the vehicle is moving.", "I'd like to add though it is not in the realm of your question exactly, I recently learned that because of the locking function it will leave a stretch mark in the belt during a crash and investigators use this mark to determine if the driver or passenger was wearing their seat belt. The marks can also correspond to a mark on the person's body like a bruise. This can help determine who was the driver, like if they switched places with the passenger to avoid charges or some such reason.", "There's two things at play here. First of the inertia aspect - just pull the seatbelt out very fast and it will lock. This requires no power and is entirely mechanical. These so your from routing forward when the cast suddenly slows down Second is the seatbelt pretensioners. These are set off by explosives and are intended to pull you back into your seat and build you there. These are wired into your cats safety systems and they determine when to fire them.", "The main mechanism is a centrifugal clutch. This use a number of weights in the spindle of the seatbelt. They are held towards the center of the spindle by some springs but not very hard. So if you pull the seatbelt hard and spin up the spindle fast then they will overcome the springs and be flung outwards. When this happens they end up locking the spindle in place so it can not move. There is some other mechanisms used in modern cars in addition to this simple system. When the car thinks you are crashing it deploys the airbags but also a small explosives in the seatbelts pulling them tighter and locking them in place." ], "score": [ 11, 9, 3, 3 ], "text_urls": [ [], [], [], [] ] }

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{ "a_id": [ "gsi0vko" ], "text": [ "There are two pipes going to the shower handle - one for cold (from the city water supply) and the other hot (from your water heater). There is a valve behind the shower handle that allows water to move from one (hot or cold) , both (hot and cold) or no pipes (off) depending on how the handle is turned, through the valve and to the shower head." ], "score": [ 3 ], "text_urls": [ [] ] }

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{ "a_id": [ "gsijebg" ], "text": [ "More costly and less efficient than what? Glass factories use a lot of recycled glass when making new glass. One reason is that you need a lot less energy to make new glass from melting old glass than from raw materials like sand and lime stone. How much recycled glass is used depends on what kind of glass products you are making. For green wine bottles where colour and impurities don’t matter that much you can go as high as 80% recycled glass. For clear sheet glass it’s more like 15-25% because using more could affect the color and other properties of the end product." ], "score": [ 4 ], "text_urls": [ [] ] }

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{ "a_id": [ "gsjv5f5" ], "text": [ "Burning fuel requires a mix of fuel and oxygen. When the exhaust leaves an engine, there’s still some oxygen left that wasn’t used in the burning of that fuel. Afterburners inject fuel directly into the hot exhaust and burn the additional fuel using that leftover oxygen." ], "score": [ 4 ], "text_urls": [ [] ] }

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