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6ncff7 | How do trains make turns if their wheels spin at the same speed on both sides? | Engineering | explainlikeimfive | {
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"Train wheels are actually conical. So, when a train turns, it slides to the larger part of the cone on the outside wheel and the smaller part on the inside wheel. That way the wheels still turn at the same rate, but their radii are different.",
"As others have stated, some trains have a conical shape to the wheels that lets them rotate at different speeds. Others don't, and the wheels slide/slip creating a deafening screeching sound. It's especially loud when the train is travelling uphill and needs to exert a lot of force on the wheels. Source: am locomotive engineer",
"Why do the wheels have to be conical? Isn't the train just following a track? Would that not turn it? E: whoever downvoted me can fuck off. I'm trying to learn shit by asking questions",
"Here's a [gif]( URL_0 ) showing how. Basically the wheels are conical and the contact point with the rails change during a turn.",
"A lot of light rail systems (BART, VTA, etc) don't have the conical wheels and whenever they make a turn or take a slightly curved parh the outer wheels start slipping and make a very annoying loud sound.",
"In addition to the conical wheel explanation, any curve they go around is very slight and some slippage/difference in travel distance is very negligible. It's not like making a full lock turn in a car.",
"Somewhat related: how do old school steam locomotives with like 4+ fixed axles go around corners?",
"URL_0 As has been said its basically a cone so as it starts to go around a corner the radius of one wheel becomes larger than the other thus it begins to turn... strangely not all that unsimilar to how a motorcycle turns",
"Great question. The wheels are actually conical, not cylindrical. The wheel diameter is larger as you get closer to the flange (flat part on the inside of the wheel). A good illustration is shown below. [Rail and wheel. ]( URL_0 ) When the train takes a curve, the flange of the wheel on the outside is pushed toward the rail, while the flange of the wheel on the inside is pulled away from the rail. This allows the wheels to spin at the same speed and travel different lengths of rail.",
"Also worth pointing out that on a set of rails coming to a bend, one rail is slightly elevated more than the other to encourage a turn. This is called the \"cant\" of the rail.",
"Radius of the curve to wide to make much a difference. Tracks on curves do get greater wear that straight line track.. Tight curves have oil boxes- rail greasers, as the radius is tighter.. but it dont account for much, but suppose to limit squeal (noise).. not sure it helps on wear .. Im not even sure they use it any more due to the environment laws.. I work for a railroad but Im just a paper shuffler. Ill ask tho..",
"Hey, I pass a rail yard every morning on my way to work and have a different question that maybe one of you can answer. How in the hell do locomotives turn around?",
"I don't understand the question. Every wheeled vehicle from Conestoga wagons to the Model-T Ford made turns on wheels that moved on a fixed axle, didn't they? What's the issue? It's on tracks; where else is it gonna go?",
"In Ukraine, street trains seem to lack conical shape, so they make loud rattling in series with ~0.5 sec interval. There are marks on the rails because this been going on for over 40 years. The interval is probably explained with wheels shaft tensions and micro-twists. [Edit - spelling]",
"I inspect and repair freight trains. The body of a train car sits on a center pin in what is called the bowl (for it's bowl shape) this allows the trucks some wiggle room for when the track curves. The body is still in the bowl but the trucks can turn with the track allowing the wheels to stay on the rail."
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6nf8lh | Why does my ABS get activated if I am braking on a bumpy road with my motorcycle even though the tyres are not locking? | Engineering | explainlikeimfive | {
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"Because as you go over the bumps there are fractions of seconds where your tire doesn't have the full traction from the road. If the road isn't moving the tire as it goes across it your brakes can actually do their job efficiently. So the sensors that detect that you're brakes are locking think that you actually are locked up."
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6nfddx | How do missiles from fighter jets that are fired have such good accuracy? How can they change their direction in mid air by themselves and hit a moving target? | [Here is an example of what I mean]( URL_0 ) How does the missile turn so well and have exact coordinates? | Engineering | explainlikeimfive | {
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"There are a couple of ways missiles can be guided: - Through infrared tracking. The missile has a heat sensor on it that finds the massive amounts of heat put out by a jet engine and points the missile at it. - Through laser designation. The missile or a ground, sea, or aeroplane based laser points at the enemy craft and the missile has a camera that picks up on the very specific wavelength of the laser as it scatters off the enemy hull. When you see a fighter get a 'missile lock' on an enemy, this is usually what's its doing. - Radar tracking. Bounces the radar off the enemy to find it. These are augmented with onboard computer systems and software that help the missile figure out what's an enemy craft and what's the ground, reflections off clouds, friendly craft, etc. As for actually turning, missiles are lightweight and traveling at high speeds. Small adjuments to the fins create a high torque that can point the missile where it's aiming, generally much faster than a plane can maneuver with its much higher inertia (also a plane has to not kill its pilot with high G-force when maneuvering). Some missiles may use gimbaled thrusters, where the nozzle of the thruster can rotate to orientate the missile. Similarly, because a missile is mostly fuel and a small amount of payload/electronics and is rocket opposed to jet powered it can produce very high accelerations hence getting to very fast speeds quickly. Where the missile is pointing is determined through gyroscopes, accelerometers, and onboard cameras. These are all electronic and can give feedback many times a second to the fins allowing it to quickly change course. The big factor is the speed at which electronic systems operate, able to process information and make corrections much faster than any human controller ever could."
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6ngs1c | Why have jet engines seemingly gotten wider and wider over the years? | Engineering | explainlikeimfive | {
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"A modern jet engine is what is known as a turbofan. There is a gas generator core (what you would think as a \"jet engine\" - suck air, compress, burn fuel in it, use it to spin a turbine and use the remaining exhaust as reactive propulsion) that drives a large fan on the front, and most of the thrust is produced by the fan. The larger the fan, the higher the thrust at the same RPM (rotation speed). The slower the fan spins, the quieter it is. So a larger fan that spins slower would produce the same power as a smaller one that spins faster. Efficiency of the engine also depends on the size of the fan compared to the size of the core (known as bypass ratio), since the fan is more efficient as a propulsion at airliner cruise speed that the jet exhaust.",
"The jet engine compresses the air, inject fuels, compresses mixture, ignites it and exhausts the gas at an accelerated speed through an exit nozzle. A wider jet engine can have a larger air intake and larger forces can be exerted by the engine to accelerate the plane at a faster rate. It's owing largely to improved materials and manufacturing as these can survive much higher forces and temperatures."
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6nh1vy | Why do most cars need a transmission | I know that most cars need a transmission in them, manual or automatic, to make sure that enough torque is applied to the wheels from the engine, but I don't really understand why some cars can start in higher gears or or cars can be direct drive (electric/steam), what are gear ratios and how do they affect the "gear" of the car? | Engineering | explainlikeimfive | {
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"Power, in engine terms, has two factors Torque - how hard you're pushing RPM - how fast you're spinning Gears in transmissions like you take a high speed low torque input and make a high torque low speed output, perfect for getting a car moving. You can also take a medium torque, medium speed input and make a high speed low torque output, perfect for cruising at highway speeds If you don't have a transmission then the speed of the engine is always the same proportion of the speed of the wheels. This will result in you either having great acceleration but minimal top speed or terrible acceleration and good top speed. If you put in a fixed gear ratio and choose that your idle RPM (~1000 RPM) should result in ~5MPH so you can travel slowly, then your red line RPM(~6500 RPM) will only get you 32.5 MPH. If you decide you want to be able to hit 80 MPH without quite redlining(~5000 RPM) then your idle RPM will push you at 16 MPH, if you try to go any slower than that you'll stall the engine. An engine generates more power as the RPMs go up so in our example above the first car will have slow acceleration up to about 15 MPH and then it'll really pick up until it tops out around 33 MPH. The second car will struggle to get off the line and likely require a push to get going, then give you very poor acceleration up to about 50 MPH Electric motors don't need multigear transmissions because they have full torque at 0 RPM and a much flatter power curve than a combustion engine, and no minimum RPM like your car."
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6nhdca | How do erasers work? | Engineering | explainlikeimfive | {
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"They most common kind is made of an abrasive substance that removes the layers where you have written. That's why you can rub a hole through the paper if you erase too much."
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6nihv8 | How do we make so many unique key and keyhole shapes? | Engineering | explainlikeimfive | {
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"The secret is that we don't. Some high quality key systems might have a few thousand different combinations but a lot of cheap ones only have a handful of different keys. It is just enough that walking around with a giant key chain and trying every key when you find a lock is impractical. However if you have the time and a bunch of keys or locks in the same series then take the time to try different keys in different locks or just compare the keys. It usually does not take long to find a matching set of keys and locks."
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6nm3yh | How do new houses hook up to existing sewage and water lines without disrupting service or spewing liquids? | Engineering | explainlikeimfive | {
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"Residential sewer is pretty much all gravity main (a pipe that relies on gravity to take wastewater to a larger gravity system that might join several neighborhoods and in most cases ends up at a pump station). You can trench to the main and tie in by drilling a hole and fitting a saddle while still in operation. Water service is largely the same process but done under pressure. The process is called hot tapping a main. A special drill rig is used that fits through a saddle and valve. The residual pressure from the pipe pushes out any debris generated by the drilling process and (ideally) the line would be flushed at the end of line blowoff after drilling to ensure that this is true. Demo here: URL_0",
"Engineer working in the drinking water industry here. The answer to water and sewer are separate. Water: \"Tapping\" machines insert a new valve (typically 3/4\"-1\" diameter for residential) into an existing water main while it's live, and the valve is installed in such a way that it is closed when the installation machine is removed, so water doesn't go everywhere. The new valve threads right into the existing water main, which is typically made of iron, though there are other materials (plastic, concrete) used throughout the country. These machines also exist for larger buildings, which sometimes require 4-8\" connections for domestic water and sprinkler systems, but this process is much more expensive when you get to these sizes. In both cases, since the valves are installed closed, the contractor can then run the water pipe into the building and connect to the plumbing, then only when everything is hooked up open the new valve. Sewer: Sewer mains are generally gravity flow, and are not full. As a result, you can often cut a hole in the top 3/4 of the pipe, install a new pipe to form a T or Y, and then seal up the hole without too much mess.",
"Sewer and water guy here. Finally a question I can answer! Sewer mains are gravity operated, so you can cut a hole into the top of the pipe and no liquid will escape. Sewer mains are made of various materials, from plastic to clay to concrete, but all are tapped the same way. We usually dig down to expose the main, and cut a hole in it using a cordless drill and a 4\" diameter hole saw. Then a rubber boot is placed on the main, and fastened using metal bands that wrap around and tighten with a screwdriver bit. We coat the pipe and the rubber boot with a type of cement to prevent roots penetrating into the pipe and causing blockages. The boot has a mouth on it that accepts a new 4\" plastic line that runs to the new house. It's inserted into the boot, and tightened using the same style metal band clamps. Water mains are a different process. It really depends on the material the main is made from. For cast iron of ductile iron mains, we have a \"tapping machine\" that drills a hole and inserts a new tap while the main is still under pressure. The device is made of brass. We place a rubber ring on the pipe, and sit the machine on it. A chain wraps around the pipe and connects to both sides of the device. We tighten two nuts to put tension on the chain. They have to be pretty tight so the rubber ring compresses enough against the wall of the pipe to prevent water from blowing out under pressure. The device is a long tube with a flap halfway down inside, that can be opened or closed with a lever on the outside. The cap that fits on the end of the tube has a metal shaft on it that accepts a special drill bit. The bit drills a hole, then cuts threads in the hole so it will accept the new tap. The cap/shaft/drill bit assembly is slid into the shaft and tightened into place. The shaft can be slid in and out without removing the cap. A large drill is attached to the end of the shaft, and the tapping process begins. The drill is geared very low. It doesn't spin fast, but has a lot of power. The tapping device has an arm that flips up and turns slowly with the drill shaft. The arm applies downward force so the bit cuts faster. Once the new hole is drilled and tapped, the drill is removed and a ratchet wrench is placed on the shaft to back the bit out by hand. The tapping device arm is still holding the shaft, because without it, once the bit is backed out of the threads, the water pressure will force the shaft out with an extreme amount of force that could possibly impale or otherwise seriously injure the man holding it. Once the bit is screwed out, the tapping device's arm is removed and the shaft is pulled out as far as it can go. This is where the flap inside the tube comes in handy. With the shaft retracted, you pull the lever to close the flap, and release the pressure from the end of the tube. The water pressure holds the flap closed, allowing us to remove the cap/shaft assembly. We remove the drill bit from the end of the shaft, and replace it with the new shutoff. The shutoff is a brass fitting that has one end threaded so it screws into the pipe wall, and is made to accept a piece of pipe in the other end. The water can be shutoff by turning a small flat piece on the side with a wrench. A metal cap is screwed onto the shutoff, and it attached to the tapping machine shaft. The shaft/cap assembly is placed back in the tube, and the flap is opened allowing the water to pressurize it again. Once the pressure is equalized, the flap is opened all the way. The shaft is pushed down until the threads of the shutoff touch the hole we drilled and tapped earlier. The shaft is turned with the ratchet wrench until the shutoff is tightened in the hole securely. With the shutoff in the hole, the tapping device can be removed from the pipe. We take a wrench and tighten the shutoff some more if it's too loose or leaking. We attach a pipe to it and connect the other end to the customer's new water meter, completing the new water service. If the main is plastic, the process is slightly different. Plastic pipe is too thin and weak to screw a tap directly into it. A saddle must be used. A saddle is a metal fitting that has a rubber ring on the surface that mates with the pipe. It has metal clamps that go around the pipe and bolt to the saddle. Once these are tightened in place, a shutoff is threaded into the saddle. The shutoff is turned to the \"open\" position and a tapping machine similar to the kind used on larger pipes is threaded onto the shutoff. The tapping machine has a shaft with a drill bit on the end inside it. A drill is attached to the end of the shaft, and a hole is drilled into the plastic pipe, inside the saddle. Once a hole is drilled, the shaft is retracted, and the shutoff is turned to the closed position. The tapping machine is removed from the shutoff, and a pipe is attached and ran to the new meter. These methods of tapping a pipe \"hot\" allow new services to be added without shutting down the main at all. Edit: thanks for the gold! I posted this before bed last night. I'm vacationing in Indiana and we're in the middle of nowhere. I have no internet at the rental cabin, so I'm on mobile. I also have no cell phone service inside the cabin and very little outside. People probably think I'm batshit crazy, walking around in the front yard holding my phone up in the air. I'll answer as best as I can. Lots of people asked about metal shavings getting in the main when tapping. I can't say for sure that none get in there, but most stay inside the tube. There's no water in the tube until the drill bit punctures the main. When the water floods the tube, the shavings get sprayed away from the hole. In order for the water in the tube to get back into the main, the pressure inside the tube would have to be greater than inside the main. That doesn't happen, so I would think it all stays in the tube. If a stray metal shard did find its way into the main, it would probably just settle to the bottom. If it made it into your service line, it would get caught by the plastic mesh screen inside the water meter. If it made it past that, it would get caught in the strainer of your faucet. For it to make it into your cup of tea, there would have to be some kind of Final Destination type shit going on. Edit2: [Here]( URL_0 ) is the small tapping machine. You can see a saddle in the picture around the plastic pipe. [And here]( URL_1 ) is a video of a larger tapping machine that is vaguely similar to the one I use. The one I use has been at our company since the 1970s and I can't seem to find an identical one online, but you'll get the idea.",
"/u/toddlikesbikes has service lines covered, but I figured I might as well mention how water and sewer main construction is done. When water mains are rebuilt, there's really no choice but to shut down the main since they are pressurized unless you are hot tapping as has already been mentioned (you can do it with big mains too). That doesn't mean that everybody serviced by the main will go without water for the duration of construction though. For a planned, lengthy shutdown of a main, the construction crew will run temporary water lines to each house. These smaller lines (usually just 2-4\" PVC) are hooked up to a fire hydrant outside the work area, and ran above ground through the yards of the homes. Then, a hose is hooked up to the house somewhere, usually the garden hose spigot on the exterior of the home, and the main water supply valve is closed. This allows the homes to continue receiving water service as usual. Sewer mains cannot be \"shut off\" because they are gravity fed. When a run of sewer main is to be replaced, the crew will go to a manhole upstream of the work and drop a hose into the manhole. Then, they will hook it up to a big trash pump, and run more hose to another manhole downstream of the work. Then, they turn the pump on and dam the outlet of the upstream manhole with sandbags and wait for the main to drain. Since there will usually be sewer services within the project area, flow won't be completely eliminated, but the amount of sewage coming out of just a few houses is negligible. This isn't what you asked exactly but I thought you might find it interesting as well.",
"Intermittent valves that can shut off particular stretches of pipe for service. There may be a temporary disruption in service (particularly with a water line), but it is pretty infrequent that someone is running new water lines from the main in an established neighborhood. Additionally, when a new line is installed for a house, a separate valve is installed at the same time that can isolate their water line from their neighbors' in case they need to do a repair, or can't pay their bills because they spent all their money on coke and their wife left them with his kid and my water got shut off.",
"On the sewer side it's worth mentioning that when the mainline is installed they will often also install pre-connected taps that are plugged off but ready for future service connections.",
"Give the question about the sewer a bit more thought - \"what would happen if a sewer line were pressurized?\" The first time someone flushes a toilet, they get a big, wet, nasty surprise. Now, such accidents have happened on submarines, where the waste system has to be pressurized in order to dump the waste into the sea. The sailor who ignores the warning signs put in place when the system is pressurized gets to spend the next 8 hours cleaning the head.",
"Hot tapping. URL_2 It is even more interesting with a natural gas pipeline. With smaller pipes they weld a flange on a mains pipe, install an open valve on the flange, insert drill through the open valve, punch the hole, remove the drill (punch rod) and close the valve. With large diameter gas pipelines they weld a piece of pipe with flange (to create a T junction) and then use torch to cut the hole in the mains line. Then they install a valve and close it. On the city mains this might be interesting sight, with 6 meter flames during welding/cutting live gas pipe. Or at least used to be, like 50 years ago. See URL_1 Nowadays, there are fancy systems, like this one URL_0",
"Usually if it's in a area that's already developed they can do a hot tap while the line is still on and have minimal water spraying. With sewers similar concept the drill into the side and but a saddle on it most sewer aren't even full when in service so there is little mess.",
"Where I come from we have a dense population but a significant proportion of people still are not connected to the main drain. They have cess pits to take toilet waste which are pumped out by government services as and when necessary. Septic tanks or other bio-systems are not allowed on the island as a significant proportion of the land is used for potable water capture. To answer OP's question in regard to my locality, when a main drain is run under a road as the government lays more services, individuals bordering the new pipe may choose to pay to connect to the sewer via a private contractor as any pipe on their land is their responsibility. The team installing the main drain under the road will leave connection points adjacent to any property along its route and cap this pipe off ready for future connection. If the householder wishes to keep using their cess pit for the time being they can do and connect to the main at a later date. The last connection point I connected a house to was 10 feet below road level. I ran new 4\" below ground waste pipe from their house to the boundary with the road. At that point my trench was already 3 feet below ground. I got the main drain pipe plan from the government office and dug down 10 feet and found the capped off main connection tee where the plan said it would be. I installed something called an interceptor (a water trap like a toilet U-bend) and a vent near this connection and also an inspection chamber for the interceptor. Uncapped the tee on the main drain and connected my 4 inch pipe to it. The main drain is only a 1/4 full with fluid (think of a swimming pool flume ride but with turds in it instead of people) and the connection is near the top of the pipe so you can open it up without getting covered in poop. That's how we connect to sewers where I live anyway. Rain water is gravity piped into soakaways - pits dug in the ground, filled with irregular rubble historically but today [plastic crates]( URL_0 ) are used to create area for water to drain.",
"They actually have competitions at the state water/wastewater operators convention where they do wet taps on pressurized sections of pipe. They're judged on time, quality of work and safety. They can do a tap and hook up a meter in just a few minutes.",
"There's also a thing called a wet tap. A sleeve with gaskets is placed over the main while the tap is made. This allows the tie in to be made without closing a valve and shutting down service to the line.",
"Plumber here. All the answers are great and shit but not many rural people use that shit. You get a black plastic pipeholder, wrap it around the pipe. These pipeholders have one side which you can attach a pipe to. And they are very easy to put valves on. So, we get the valve ready, get an iron rod blazing and push it through the water system's pipe, when the water comes out, you quickly connect the valve to the pipeholder. You get a bit wet but not a problem $ saved.",
"Waste lines arnt under pressure so it's not a big deal. Doing a hot tap on live water lines are pretty cool actually... at least mechanical piping is im not sure how cool residential water Hook ups are. Go on YouTube and watch a couple videos. Also look up \"hot tap natural gas line.\" It's badass.. Union pipefitter",
"Sewage - insert bung. Risk is more of gas than liquids. Water - speacially designed tap in that creates overlapping seal before hole is drilled into main.",
"Valves. Same way you can isolate your apartment or house from mains to service them. Also, it is possible to \"hot tap\" into piping if there isn't a valve. Basically, you weld a stub in, hook up a device to the stub in and the device will drill the pipe and install a valve, all without leaking.",
"In a big subdevelopment, the infrastructure for water/sewer is already there, they attach the new house then open the right valves and all is working. In rural homes, they often build brand new water well/pump, and a septic system on the property, no outside connections. Major city infrastructure can be isolated prior to construction, then once connections are made, they open all the taps without contaminating any of the surrounding buildings.",
"Sewer, for the most part, is an open system. Not under pressure. There are some lines under pressure, but most are only gravity fed. Main pipe runs down the bottom of a manhole, new house connection goes half way up/near the top. No-where near the sewer running down the lower pipe. Water, there are screw 'taps' you can 'break into' existing lines. For major works, they just turn the water off to that particular line.",
"There are two main types services that need to be hooked up. Water and Sanitary sewer. Somebody in the comments above talked Water services and about tapping into the pressure main with a special machine, that's how that's done. As for the sanitary sewer, most answers I have seen don't address connecting a new sewer into an existing active sewer main. This is usually done by finding there nearest 'upstream' manhole, sending a person down that hole (with all sorts of safety equipment for sewer gases which will kill you before you can get out of that hole) and that person will plug up the sewer pipe that is flowing downstream. They then stick a trash pump down the hole and bypass pump to the 'downstream' manhole. They will then excavate for the tie in, cut the sewer main, add in the Y connection and attach the pipe from your house there. Once it's all connected and back filled, some goes down the hole again and unplugs the upstream manhole."
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6nm74j | How do home coffee makers move water from tank to pot without a pump? | My first thought was it was some sort of gravity fed system, or a siphon but the pot is higher than the lowest point of the tank on my maker, now I think it uses the heat somehow but I don't know how that would work. | Engineering | explainlikeimfive | {
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"There is a one-way valve at the bottom that only allows water to travel out towards the top. The water moves through the valve and is heated. As it heats up, it expands, and some of it turns to steam, creating pressure. Because of the one-way valve, the pressure pushes the water up the tube where it will eventually spill over the coffee grounds. Between the slight cooling and rising out of the way, the pressure is equalized on both sides of the valve, allowing more water to pass through from the reservoir to the heating element. Again, the water is heated, expanding, and pushing against the one-way valve, closing it and expanding upwards. [Here is a wonderful video explaining it]( URL_0 ).",
"The power of boiling! (and little valves!) The flat plate that the carafe sits on is a heating element with two jobs. One is to keep the coffee that's been made hot. The more important is to heat the water from the tank so it can actually make the coffee. Water flows through a little tube to the heating elements. The heating elements are very hot (source: ouch!) and cause the water to boil. When that happens, the water turns to steam and expands. There's a little valve to keep the water from pushing back on the water in the tank. Instead, the only way for it to go is up to the basket of coffee grounds, where it turns ground-up toasted plant matter into liquid awesome. So, no, there's no pump, just physics."
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6nmt8r | Passenger jet thrust reversers. If the air coming in is equal to the air being pushed out, wouldn't they both cancel eachother out? | Engineering | explainlikeimfive | {
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"text": [
"No, because the thrust isn't just the mass; its also the speed that mass is moving at. After going through the turbine, the air has been accelerated significantly and so provides more thrust."
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6nnfgr | Why is it that when I pump my tank full of gas the nozzle will shut off right when it's full but when I prepay it crawls through the last .50 cents or so worth of gas at an agonizingly slow pace? | Engineering | explainlikeimfive | {
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"text": [
"Because the pump has to slow down if it wants to stop on a precise, to-the-cent amount, which is what happens when you pre-pay. When you just fill up your tank, the pump isn't trying to land on a specific cent amount, so it can just stop whenever the air backpressure from inside the tank indicates that it's almost full.",
"Gasoline and diesel pump nozzles are designed to ensure that the air displaced from the fuel tank flows back through the nozzle itself. When this airflow abates, a valve on the nozzle closes and fuel flow is cut off; this prevents a tank from overflowing. When a predetermined maximum amount of fuel is to be dispensed, the pump needs to slow down to ensure that no more than the predetermined amount of fuel is actually dispensed. To be put this in mechanical terms, the nozzle has a valve that closes when it senses that the tank is full. When the valve closes, the hose pressure rises and the pump shuts off. When the tank is not full, the pump must slow down in order to drop the hose pressure, which causes the valve to close once the pressure drops below a calibrated point."
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6npmqj | how are lead aprons or suits flexible? | Engineering | explainlikeimfive | {
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"text": [
"the lead inside isn't a solid plate of lead. it's lead pellets. and it bends just like a sandbag can be moved and twisted"
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6npqoo | Why aren't we supposed to top off our gas at the gas station? | Engineering | explainlikeimfive | {
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"text": [
"There are a few reasons, but the most like you're five answer is so that you don't spill. There's a little tube inside the big nozzle that can tell when gas reaches the end of the tube. That last bit of tube accounts to a few ounces (or milliliters) and really won't add much to your tank or the mileage you expect. When you stick the nozzle into the gas hole (I'm sure that's what it's called) it only goes on a little (just the tip), and isn't actually in your tank (unless you're on a motorcycle, filling a can, or maybe a small motor), so you've already filled the tank and all that's left is the gas filling tube (or gas colon, if you will). However, if the gas flows freely for just a few moments while you realize the blunder you just made, it can amount to lots... Including running down the side of the vehicle, leaving a flammable puddle, and possibly getting on your clothes or person. It's full of waste, environmental icky, and potential fire. All of that \"maybe\" far outweighs the drops of extra gas."
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6nu5xp | Could you detonate a grenade by shooting at it? If yes, would the type of gun and bullet matter? | Engineering | explainlikeimfive | {
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"Military grade grenades would not detonate in this fashion. As an example, here's a MKII US grenade (used in WW2) ; URL_0 Grenades activate when the primer lights the fuse, which then descends down the grenade and into the metal powder, which then ignites and causes the chemical reaction which makes the grenade explode. Because it uses metal powder, it has a very high ignition point (it has to get really hot) before it will explode. A bullet, no matter where it strikes on the grenade, would not cause the chemical reaction to take place; No boom.",
"Mythbusters did a segment on this if I remember correctly it all mattered if the round penetrates the detonator inside the grenade if it didn't penetrate the grenade went off if it did then the grenade didn't explode but even with a shotgun that did penetrate it deflected the grenade away from its target",
"skeet shooting is done using shotguns. you don't shoot bullets. you shoot lead pellet shot. this is shot URL_1 this is a bullet URL_0 a grenade works by having a fuse ignite a gunpowder charge inside a hard sealed metal shell. the gunpowder ignites , and equally presses on the sealed shell until it fractures and explodes, sending shell fragments everywhere. if you break the shell, the gunpowder just spills out. and without a shell to contain it, it'll just go poof, and not explode."
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6nv0kw | why aren't all yellow lights the same duration? | Would it not prevent a lot of trouble to have all yellows be either three or six seconds? | Engineering | explainlikeimfive | {
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"There are a few things that affect yellow light timing: 1. Travel speed. The yellow light has to be long enough for someone seeing it to come to a complete stop at the line, or someone driving through to clear the intersection on the yellow. 2. Intersection width. The yellow light has to be the correct length for the distance being covered for those clearing the intersection -- related to point 1. 3. Red Light Cameras. Some jurisdictions install red light cameras, and they have been accused of tuning the amber lights such that they get enough profit off the cameras to be profitable, but not enough to spur public outcry. A man in Oregon recently has undergone a bit of legal trouble because he did a study of optimal amber light timings and found that Oregon lights were not at optimal timings. He was fined for not being an engineer and speaking publicly about engineering topics. URL_1 URL_0",
"A general rule of thumb is that the yellow light lasts one second for every 10mph the speed limit is set at. A road with a 30mph speed limit would have a three second yellow light, while a road with a 55mph speed limit would have around a six second yellow light. The yellow light is warning drivers to slow down because the light is about to turn red. An intersection with fast moving traffic needs more time to slow down, so it makes sense that a yellow light on this intersection would last longer, whereas a traffic light in a residential area doesn't need a six second yellow light."
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"https://www.techdirt.com/articles/20170601/09011437496/licensing-body-agrees-to-temporarily-allow-man-to-criticize-government-without-license.shtml",
"https://www.techdirt.com/articles/20170425/14273237238/guy-fined-500-criticizing-government-without-permit-sues-oregon-licensing-board.shtml"
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6nv31j | How do hotel rooms on the sea or on islands operate, sewage and electricity wise? | You know these pictures of the five star hotel bungalows in the middle of the sea? Like Bora-Bora or the Maldives? I cannot help but ask myself how they get supplied with electricity and potable water, and how and where they discard waste from the room (you know, flushed waste). Thanks! | Engineering | explainlikeimfive | {
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"text": [
"Many countries, including some part of the maldives, I hate to say it, still pump their raw sewerage straight into the oceans. Many carribean islands still do this. As far as water is concerned hotels will usually have sophisticated water irrigation setups for collecting rainfall and then to supplement this when needed will use water from desalination plants ( although this is very expensive )"
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6nvat8 | Why do Harley Davidson engines painted black stay cooler than a stock non painted engine, how does this not cause the engine to overheat? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"where is the support that a black engine stays cooler? Google turns up nothing but maybe Im searching wrong. The coating is powder coating, not paint, small difference, but we can be fairly certain that powdercoating to a high gloss finish is not improving the engines cooling. Not that its devastating, just... not helping. But if you have evidence to the contrary, Id love to read it.",
"White reflects light the best, emits heat the worst. Black reflects light the worst, emits heat the best. That's why on the Space Shuttle, there's a black side and a white side. The black side is the part that is subject to re-entry heating, and needed to emit heat to cool down. The white part was pointed towards the sun when in orbit so as to reduce the absorption of light and infra-red to make sure there wasn't so much heating that the vehicle became too hot to live in. Silver is in the same boat as white. It reflects light well, and emits poorly. Edit: I just want to make it very clear that that I am just explaining how colour effects cooling. I'm skeptical as to whether it makes a difference in the specific case OP mentioned. Heck, maybe a thin layer of black paint is actually a slightly better insulator leading to less transfer of heat to air, canceling out any effect, if not worse.",
"It emits heat better by radiation, but i can't see how it would work to actually cool the engine. See all the louvres on the cylinders are there to increase surface area to aid cooling by convection, i.e air passing over the hot engine. A paint layer will act as insulation against convective cooling which is undoubtedly the largest factor at speed. Radiative cooling will have an effect, but i doubt it is very significant unless you are stationary anyway. Do you have any litterature backing up your claim?"
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6nxq44 | Why do some lamps click 4 times? | Engineering | explainlikeimfive | {
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"The ones that click twice in each position are made for a \"3-way bulb\". That's a bulb with two filaments, low and high. They are made to do low, high, low+high, off. But if you put a regular single filament bulb in that socket, you get off, on, on, off. (It's only on when the \"high\" filament is supposed to be.)",
"Usually you can take a look at the fixture and it will tell you the wattages that it is rated for, say a 50W/100W/150W bulb. You can go to a local hardware store and pick up a 3-way Bulb for them and the CFL and LED 3-way bulbs are getting decently cheap nowadays. The four clicks offer 3 levels of brightness, as others have stated here. Source: I work in a hardware store. Finally a little relevant.",
"They're designed for a special bulb that offers 3 levels of brightness plus Off. If you don't have the special bulb you get this weird behavior. URL_0",
"The other top level explanations are correct, but I wanted to share this animation that I've found helpful when explaining it to others... [Pic]( URL_0 ) Note that there are two different parts involved: * The bulb has two different filaments, with four different possibilities: No filaments lit, filament A lit, filament B lit, filaments A & B both lit. * The wiring in the switch is such that different positions of the switch produce the four different lighting conditions of the bulb.",
"ELI5: What is OP referring to? I don't recognize this as a Swede.",
"Because your lamp is a tri light which has three brightness settings. Low, normal, bright and off. You need to use the correct bulb to use this feature.",
"Do they make 3-way LED bulbs or are these lamps now just artifacts of the incandescent era?",
"That means it's a 3-switch lamp. (Three different levels of light, and the off position, totalling in four clicks.) However, because of what you described you don't have the correct lightbulbs in the lamp. They make special multi-filament bulbs for those types of lamps."
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6nyb3g | How is it that aircraft engines can handle large amounts of water and sand during ingestion tests but are incapacitated by small birds? | Engineering | explainlikeimfive | {
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"For the same reason that your lawnmower can flawlessly cut large amounts of grass without any issues but if you were to say, run over a stump it might break a blade. Yes, a bird is a lot less dense than a stump. But aircraft turbines rotate much, much, much faster.",
"Apparently, commercial aircraft engines are supposed to be able to shut-down after ingesting a bird weighing up to 1.8 kg (4 lb). The engine does not have to survive the ingestion, just be safely shut down. (Wikipedia)",
"Think about the things you are comparing. Water and sand can easily pass through the engine fan blades because when dispersed in the air the particles spread out and are less solid. As [this video shows]( URL_0 ), while the mass may be greater, water and sand is a flexible mass that has no muscle or vertebrate to cause significant damage,"
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6nyfcy | The Mcmillan Tac-50 has a firing range of 1970 yards, yet the longest confirmed kill is 3871 yards with the Mcmillan tac-50. How is it possible to shoot about 2x the maximum firing range of a sniper rifle and hit someone in a vital organ? | Engineering | explainlikeimfive | {
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"text": [
"URL_1 > Effective firing range 1,800 m (1,970 yd) URL_0 > The effective range (maximum effective range) of a weapon is the furthest distance an effective shot can be taken with reasonable certainty that it will hit. It is determined by a number of factors: type of cartridge fired, inherent precision of the weapon, and volume of fire delivered. Basically, in order to pull off that shot, that marksman had to be both extremely skilled and lucky. You **can** hit a target beyond the effective range, but it is pass the point of reasonable certainty.",
"So there's two simple answers to this question: \"Effective range\" is a metric that is used to explain the standard, conceivable distance that adequately trained, basic personnel can use the weapon system from. Anything beyond that is considered a distance that a specially trained \"operator\" can shoot from. And honestly, you really don't need to hit a vital organ when you're slinging a .50 caliber bullet at someone. Even if you're a mile away, that round will shred you to pieces. You do not need to be accurate within an inch to kill someone when you're firing that round. So a kill is attained merely by hitting a target the size of a military aged male.",
"The problem you're facing is that the firing range which you are referring to is what is called an \"effective range\". It is within the effective range that the weapon can be considered effective, being suitably accurate at that range in order to reliably hit targets at that range. However, skilled users can potentially use a weapon at ranges beyond the established effective range (albeit at great difficulty). They would do this by accounting very precisely for factors like wind. Edit: others here have beat me to the punch with good explanations, but I might as well leave mine here."
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6nz3wb | Why, when building robotic hands, can't we build an exact copy of the human hand only using mechanical parts? | Engineering | explainlikeimfive | {
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"I'm a grad student working on some related this research in replicating biological systems as machines. There have actually been some pretty good attempts at mechanical human hands, but trying to make a soft fleshy part out of rigid components is never going to be exact. We can use tiny motors to control the wrists and fingers, but then you end up with awkward heaviness wherever the motors are sitting. You can put tactile sensors to detect finger touches, or encoders to keep track of joint positions, but with current tech you cant get enough accuracy to identify the shape or texture of an object you're holding, how hard your grip is, is the object warm, is it slipping from your grasp, etc. Is the hand waterproof? Does it sweat to cool itself? If we are really going for an \"exact copy\" we are a long way off. My research is is in what we call \"soft robotics.\" In general, we try to replicate some of the functions of living tissue in such a way that the final product is soft, flexible, stretchable, damage resistant, and so on. We try to develop parts so that all the functionality you need is just built into the material itself. I mean, think of all the things just your skin does. Instead of motors we develop artificial muscles out of different materials so they can be made into bundles of controllable filament. Instead of copper wires we use conductive fabric or liquid metal in tiny tubes. Instead of ratchets and mechanical stops, we use stiffening and softening fibers to hold the grip in place. Eventually we hope to weave all these together in a sort of \"smart fabric\" that will resemble a living system at least a little bit. Take a look at these guys at Yale who I will be working with this fall. They are *specifically* working on the technology to make soft hands like that. The Yale [GrabLab]( URL_0 ) Edit: some detail added",
"The purpose of a robot is to *do a job*, not to copy humans. Human hands are pretty good general purpose devices, but if you want to perform a specific task, especially one that might put too much wear and tear on flesh and bone, other approaches are better."
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6nz8ip | How do road workers place the cones on highways prior to construction? | Engineering | explainlikeimfive | {
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"text": [
"They start on the shoulder with a vehicle that has bright flashing lights, or sometimes a lightboard with a direction arrow, and slowly place cones outward towards traffic, squeezing traffic to one side or the other while they set up the work zone. If this is at night, they use spotlights for extra visibility and safety. Citation: Just watched a work crew do it (I work alongside construction crews, occasionally on road work.)"
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6o0349 | why does a scissor not work for left handed people but does for right handed? | Engineering | explainlikeimfive | {
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"text": [
"scissors are actually made for right handed people typically, it's the way the right hand applies pressure on the handle aligns the blades. When you try and use your left hand, the blades separate and nothing cuts.",
"My question is: do lefties use their right hand for scissors or just learn to use it with the left? It requires a weird hand tension/flex.",
"I am a lefty and I find that the blades are on the wrong side (the top blade is on the right side, blocking my view) and make it slightly harder to see where I'm cutting. Also non \"ambidextrous\" scissors have the handle shaped in a way that doesn't fit your left hand very well."
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6o1qs1 | Do you burn different amounts of gas in a car going depending on the speed, even if the speed remains constant? | Scenario: Two cars of the exact same make, model, year, and specs are driving on a completely straight and flat road. Both are using cruise control but one is going 70 mph and the other is going 25 mph. Not counting for acceleration, during the time those cars are maintaining a consistent speed, are they burning the same or different amounts of gas? Sorry for the title typo, the word "going" is unnecessary. | Engineering | explainlikeimfive | {
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"very different. ultimately they are counteracting drag, of which there is much less at 25mph. now if you asked, how much fuel has each burned to travel 10 miles at this pace, recognizing that the slower car burns much less per minute, but takes 2-3x as long to get there. the answer to that is more complicated, but this is where efficiency comes in. the peak efficiency of a car is probably around 65mph, it varies by car, depending on how its engineered."
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6o2lew | How does a small amount of Spandex woven into a non-stretchable fabric like cotton give the entire garment stretch ability? | Wouldn't the cotton restrict any stretch from occurring? | Engineering | explainlikeimfive | {
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"text": [
"It's not really that the spandex is allowing the cotton to become more stretchy, it's that the spandex (until it is stretched) is retaining the tight/original shape of the garment. Instead of thinking of a garment-with-spandex vs an equally tight garment-without spandex, think instead of a garment-with-spanex against a looser garment-without-spandex. The looser garment is roughly as loose as the maximum stretch of the 'garment-with-spandex.' The addition of the spandex keeps the garment/weave tight.",
"You can easily stretch most knit cotton clothing. The problem is that it has limited elasticity, so it will mostly stay stretched. The elastic spandex mixed in causes the fabric to return to its original shape. Woven cotton fabrics, for example denim, have much more limited capacity to stretch."
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6o3l07 | lava lamps | Engineering | explainlikeimfive | {
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"text": [
"They can be all kinds of shapes, I think the only limiting factor would be the height in ratio to the heat. It has to get hot to rise and cool back off to fall again to complete the cycle. That might work differently in a container if it were too short or tall because it would either never cool and stay up top or cool too fast and never make it to the top. You can see some different shapes and sizes here: URL_0"
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6o98dt | Why are commercial airplanes all sub-Mach 1? | Engineering | explainlikeimfive | {
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"The faster you go, the harder it is to push through the air - and the relationship is not linear. So, going a little bit faster needs a LOT more power which means more fuel, bigger engines, more noise, etc. etc. Put your hand out of the car window at 30mph - easy. Now try 60mph - wow, the air is a lot more forceful! Now try 120mph (OK, don't really) you can't hold your hand up, the air is like a brick wall. At 600+mph you can imagine it's not easy! If you look at Concorde, it's a tiny cramped thing that burns massive amounts of fuel, which makes it expensive to run and you can't fit many passengers on it. Additionally, stuff happens the faster you go - stuff heats up, shockwaves happen, the whole airplane has to be made to withstand the extra forces & strains, lifespans of components get shorter, stronger stuff is heavier and bigger, etc. etc. *Please don't put your hand out the window and then sue me because you hit something*",
"Going faster than the speed of sound is not very fuel efficient, and supersonic airliners bring issues like sonic booms over towns. This is why one of only commercial supersonic airliner we've tried (Concorde) was restricted to flights that were mostly transatlantic. In today's world, for environmental and economic reasons, fuel efficiency trumps a shorter trip.",
"They *weren't*. Concorde famously went faster than Mach 1, as did the Tupolev Tu-144. Not many were built and they have all been retired from service now. The reason why the idea hasn't caught on is economy. When you start traveling supersonic, air behaves in a very different way leading to shockwaves and much higher drag. The aircraft must be shaped very differently to be able to sustain those speeds with reasonable efficiency... Because of the higher drag and turbojet engine efficiency issues leading to more fuel consumption, and the fact that the body had to be narrower for aerodynamic reasons, a Concorde uses about the same amount of fuel for a jeourney as a 747, but carries three times less passengers. In addition to that, a Concorde is only at it's most efficient when traveling supersonic, and because of the noise issues associated with supersonic travel, it was often not allowed to go supersonic over land, which limits it to very few routes where it could be made commercially viable. British Airways certainly did manage to extract money out of the Concorde for luxury passengers for a time. There is yet still hope for supersonic and even hypersonic travel. Reaction Engines in the UK is developing fascinating engines that use hydrogen as both fuel and a coolant to cool down the incoming air which allows them to travel at Mach 5, very high, with a very light engine. The concept of the pre-cooler was actually devised for getting from the ground to space with a single stage with air-breathing rocket engines. Doing that requires incredible efficiency only possible by using the high pressures possible thanks to cooling the air. Using the same technique for a plane means you get to travel fast pretty efficiently apparently... One of the problems, however, is that Mach 5 is so fast that it's too hard to make windows that won't melt but are also light enough... so the plan has to have no windows!",
"Profit. Concorde was a hugely expensive vanity project heavily subsidised by the British and French governments. Modern airliners such as the Dreamliner are much more profitable.",
"There are two main reasons. The first, and probably the biggest reason, is that it's really loud. This was the reason that the Concorde failed financally: It wasn't allowed to fly over land because sonic booms are so disruptive (and they can be destructive). If it had been able to fly over land, the fleet would have been larger and the finances more sustainable. Reducing sonic booms is actually one of the main thing that research institutes (i.e. NASA) are investigating. The second big reason is the engineering complexity and the increased costs associated with it. Generally, engines and wings on aircraft are optimized for a specific altitude and speed, so if you want an aircraft to cruise at supersonic speeds, it will have pretty poor performance at subsonic speeds (landing, takeoff). So that automatically means that you have more costs due to fuel. Additionally, flying at supersonic speeds is a lot harder on the aircraft itself, so you need to use more expensive materials and spend more time and money on maintenance."
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6o9afy | What do the Watts and Volts mean in a 12v 5w water pump and a 12v 20w solar panel respectively? | I'm very confused. From what I think I understand: a 12v 5w pump requires 5w at 12v to function? If so, what would occur if I connect the mentioned solar panel to it? Does it require a resistor or something? | Engineering | explainlikeimfive | {
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"dkfk2k3"
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"It means if you connect the pump to as 12V source, the pump will draw 5W of power. The solar panel rating means that the panel is capable of delivering 20W of power at 12V. So if you connect the solar panel to the pump, it'll run. Certainly you will want to make sure this stuff is wired to code and has all the appropriate breakers."
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3
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6o9z75 | Can someone please explain me the working of a dehumidifier? | And how is it similar/dissimilar to an air conditioning unit? | Engineering | explainlikeimfive | {
"a_id": [
"dkfppcy"
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"text": [
"Yes..Similiar. there are a few types...But the one that is similiar to an AC unit works by cooling the air. this reduces the airs capacity to hold moisture. The moisture condenses out.. the (drier) air is then heated back up to its original temperature...But now contains less moisture (Humidity)... It's just like when you see a cold can of soda \"sweating\".. the warm (and Humid) air gets close to the outside of the can.,,,it is cooled down rapidly and the moisture condenses out of the air and onto the side of the can There is also a desiccant type of dehumidifier. this works by pushing the air through a object which absorbs moisture (Like those little \"do not eat\" packets that are in a lot of packaging"
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6ocn7w | How these modern tiny loudspeaker / amplifiers sound so good? | When I was a teenager you needed huge loudspeakers and a 40W amplifier to get decent bass plus a tweeter for the top end. What magic is at work here? | Engineering | explainlikeimfive | {
"a_id": [
"dkgdi40"
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"text": [
"I know part of this, much stronger permanent magnets. Back then we didn't have neodymium magnets, utilising those in speakers allows for much more powerful motion of the speaker cone so you can get much louder and better sound from a smaller speaker with less power supplied to the coil. I'm 37 and I'm also really impressed at the quality and bass you can get from these tiny speakers you can plug into your phone or whatever. I wish we had them in the 90s."
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6oho6f | Why can't my car alert me when my battery is low/about to die, but other battery-operated objects can? | Engineering | explainlikeimfive | {
"a_id": [
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"Your car doesn't actually run off it's battery The battery is used to start your car, but once it's running you could disconnect it and nothing would know When your car is running electricity is provided by the alternator, this charges the whole circuit and makes it impossible to know the battery voltage. When your battery dies it is usually because you left something on with the car turned off and that drained the battery over a few hours. There is no way to warn you about that beyond the binging from leaving headlights on when you get out Tldr - your car battery serves such a different purpose from a normal device battery that this would never help",
"Honestly, it *is* possible to detect if a battery is running low in many cases. Many cars have either a voltage meter or a battery warning light. Here are some more detailed thoughts that go beyond what your dashboard could do by itself. 1. [What are the warning signs before your car battery dies? ]( URL_1 ) 1. [Six Signs of a Failing Car Battery ]( URL_0 ) 1. [Five Signs Your Car Battery Is Dead (or About to Die) | AxleAddict ]( URL_2 )",
"It can. My car will do this. So the question really is why don't manufacturers add this feature to their cars ? The answer is cost and priorities. Features like integration with your cell phone and increasingly online (music streaming, real time traffic info, use of searches to find nearby points of interest - shops, hotels, restaurants, car parks, gas stations etc) are more attractive to buyers, so manufacturers will add those features before a battery warning. The other aspect is that the battery failing isn't an every day occurrence - you may experience it once in the ownership of a car (unless it has an issue or the batteries you buy are bad). Compare that to the warning that you're low of fuel (weekly?) or that the washer bottle is empty (every few months?)."
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"https://www.pepboys.com/car_care_corner/car_care_basics/maintenance/signs_of_a_failing_battery/",
"http://www.driveprime.com/blog-what-are-the-warning-signs-before-your-car-battery-dies/",
"https://axleaddict.com/auto-repair/Whats-Wrong-With-My-Car-Five-Signs-Youre-Battery-Is-Dead"
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6onvrw | How would you be able to stand up straight in one of those spinning donut shaped spaceships that simulate gravity? | I understand the concept, I understand why water doesn't fall on you when you swing it over your head. What I dont get is why the force you experience in one of those modules would be pointed straight down, towards the "floor". In my head the force you would experience is pointed 45 degrees down against the rotation. | Engineering | explainlikeimfive | {
"a_id": [
"dkir6jq"
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"text": [
"This would indeed be a problem with small-radius rings spinning quickly, as the amount of 'gravity' you felt at your head would be dramatically different from that felt at your feet. For this reason, it is better to use a large, slowly rotating ring instead; the proposed radius of the NASA Nautilus-X SEV centrifugal habitation ring was around 30 metres."
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3
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6oskqu | How does the Koenigsegg Regera accelerate to these crazy speeds with only 1 gear? | Engineering | explainlikeimfive | {
"a_id": [
"dkjvjl8"
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"text": [
"Hybrids are funny At low speeds( < 30 mph) the wheels are only driven by the wheel mounted electric motors and the engine just spins a hydraulic clutch not doing much At higher speeds the hydraulic coupling locks the engine and the crank shaft electric motor to the wheels. The reason we have gears is because internal combustion engines provide low torque and power at low RPMs but significantly more at higher RPMs. Electric motors don't. Electric motors produce full torque at 0 RPM and can provide full power across their range. Tying the two together gives a very flat power band, with the electric motor covering for the ICE when its at its weakest When at low RPMs the ICE doesn't generate much torque or power but the electric motor does resulting in tons of torque and its full 215 HP. At medium speeds the electric motor is generating medium torque but still full power, the ICE is generating medium torque and medium power. At high speeds the load will be mostly on the ICE because it generates so much more power than the electric motor once its up to its target speed."
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13
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6ovfhx | Why do farmers keep their grain in silos? | Engineering | explainlikeimfive | {
"a_id": [
"dkkjgn8",
"dkko7fr"
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"text": [
"Actually it's silage kept in most of the tall silos. Grain is kept in grain bins which are shorter than silos. They are metal and usually raised off the ground (but not always) which keeps out mice and rats.",
"Silos are basically storage vats that stand free from the ground. That means they're free from moisture that collects on the ground and out of reach from vermin while being able to use gravity to empty themselves when needed."
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|
6owxxp | Why do spatulas usually have slits in them? | Engineering | explainlikeimfive | {
"a_id": [
"dkktozh"
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"text": [
"If you are cooking something oily or with a lot of liquid the slits let it drip back into the pan."
],
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8
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6oxz0c | How do cellphone/radio towers work? Does the whole metal frame act as an antenna? | Or is it just the top part? Is there anything else cool going on with them that wouldnt be apparent to someone like me who doesn't know much about them? | Engineering | explainlikeimfive | {
"a_id": [
"dkl3o87",
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"text": [
"Just the top part. One cool thing is that there are several antenna elements stacked vertically inside each panel. That gives extra gain in the vertical plane. The generic term is sector antenna because each covers a 120 degree sector horizontally. That's why they are almost always mounted in a triangle. Newer ones contain the power amplifier as well.",
"For AM radio, the structure IS the antenna. An antenna works by applying an alternating current to some sort of conductor. In an alternating current, the electrons are not all traveling one direction like water in a pipe, rather they move back and forth like waves on a beach. The number of times per second that the electrons move back and forth is called the frequency, and is often measured in Megahertz (MHz). When electrons move through a conductor, they create a magnetic field. If you have ever hooked up a battery to a coil of wire and created an electromagnet, you have seen this phenomenon. When an alternating current is applied to a conductor, the magnetic field is alternating in strength and polarity (north or south magnet) with the motion of the electrons. There is also a related electric field due to the distribution of electrons along the conductor. The changing electric and magnetic fields make electromagnetic waves, more commonly known as radio waves. Radio waves travel at the speed of light, which is about 300,000,000 meters per second. This speed is not dependant on the frequency. If you imagine an electron starting at the bottom of the antenna, which then travels up along the antenna until it is pulled back down to is starting position by the alternating current. This cycle repeats (like a child in a swing) and causes a radio wave to be radiated by the antenna. The radio wave travels a certain distance in the amount of time it takes for the electron to return to its starting point. This distance is called the wavelength, and is usually measured in meters. The length of an antenna element is typically either 1/4 or 1/2 of the wavelength depending on the type of antenna (although there are other designs that use of lengths such as 5/8). Most vertical antennas (like those for broadcast radio) are 1/4 wavelength tall. To determine the approximate size of an antenna, divide 300 by the frequency in MHz to get the wavelength in meters. Divide the wavelength by 4 to get the length of the antenna. For cell phone (around 900 MHz) the wavelength is about 33cm and the length of an antenna would be about 83mm (3.25\"). For FM broadcast radio (around 100MHz) the wavelength is about 3m and the length of an antenna would be about 750mm (29.5\"). For AM broadcast radio (around 1.7 MHz) the wavelength is about 176 meters and the length of an antenna would be about 44 meters (145 feet). Smaller antennas can be put on top of tall towers, but for larger antennas, they just use the tower as the antenna."
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6oy9e1 | How does a police officer's radar gun precisely gauge the speed of vehicles moving left to right/right to left/toward him/away from him/etc even when his own vehicle is moving? | Engineering | explainlikeimfive | {
"a_id": [
"dkl4slg",
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"text": [
"Typical radar guns do not offer this feature. They are designed to be used from a stationary vehicle, and only measure the speed toward or away from the operator. Thus, police usually use from a location parked on the side of the road, and pointing along the length of the road.",
"Moving radar systems are real, and common. Ignore other posters who say radar is only stationary. Mobile radar works just the same as stationary radar, with a bit of math added in. Stationary radar sends out a wide beam of radio waves at a specific frequency. A moving object will modify that frequency when it bounces the signal back. The radar gun can calculate based on the change in frequency the speed of the object. Since the beam is wide, though, a lot of it goes around the object and will hit stationary objects. The radar sees that signal returned, but it knows that those objects aren't moving, and it ignores it. Mobile radar does the same thing; sending out a wide beam. The returned signal this time comes back as the total difference between the moving police car and the other vehicle. So far, all you know is that the two cars are approaching each other at a total of 130mph. The radar then takes all that extra signal that is going out, around, and past the other car, and hitting stationary objects to calculate the speed of the police car (say, 60mph). It then subtracts the police car speed from the approaching speed, (130-60) and you're left with the approaching vehicle's speed! As far as left right movement goes, the radar can only determine how fast the car is getting closer to it. If the vehicle is also travelling at a bit of an angle to the radar, the calculated speed will actually be a bit lower than the full speed of that car, actually making the radar think you are going slower than you really are."
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6oya1l | Special spark plugs | At the most basic, a spark plug provides a gap across which a spark arcs to ignite the fuel air mixture in a gasoline engine. I get that. What I don't understand is why some engines will only run well on one particular brand of spark plugs. I've read where a car would not run after a spark plug change and the owner was advised to use the equivalent XYZ brand and it runs great. What makes a particular car so finicky? | Engineering | explainlikeimfive | {
"a_id": [
"dkl7m6q"
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"text": [
"There's quite a bit that goes into spark plugs and how the systems work. You want a quality spark and engines are designed around certain specifications. On top of gap, There a also plugs that run hotter or colder ( has to do with the lengths of the plug). The above post about greed is a bit conspiracy. Automotive engineering is about materials properties. The trick that most people screw up is that they don't buy OEM spec plugs which natch the OEM requirement. As long as you match that the car will run fine (I use plugs that cost 1/3 what OEM recommended brand cost)."
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6oz55n | Why do planes always go around the world instead of going past the poles to get to the other side quicker? For example: Alaska to Europe over the North Pole. Does it mess up internal navigation systems too much? | Engineering | explainlikeimfive | {
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"There are many routes that take you over the Arctic. Sometimes longer routes are used to take advantage of east/west prevailing winds. In the past, polar routes were less frequent, because of Extended Operations (ETOPS) rating. ETOPS was how far away from any airport, measured in time, an airplane was allowed to go. Early ETOPS ratings were low, 60, 90, 120 minutes, which left much of the earth, including arctic regions, inaccessible. Once ETOPS ratings reached 180 minutes and beyond, most of the earth except for the Antarctic is open to flight routes.",
"Polar routes are common. If you were to fly LA to London you're going through the article circle, and not thru the East Coast of the United States.",
"They do Planes follow what are called Great Circle routes, these are routes which are the shortest routes between two points on the surface of the sphere. They tend not to pass over the north pole because there aren't a ton of tourist destinations in the middle of Siberia so they tend to stay a bit south of it You can see the [flight path for KLM 682]( URL_0 ) between Vancouver and Amsterdam looks pretty curvy and goes pretty far north, if you were to plot it on a globe it'd be nice and straight",
"It's called the Great Circle route. The Great Circle Route is the shortest distance between two points on a globe. URL_0",
"Some countries also own their own air space, so if you were to fly straight over them you could be shot down. This happened in Russia before and almost started WW3 debating whether it was actually legal"
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6p0rnm | How was Washington DC turned from a Swamp into a city that can be built upon? | This baffles me, that Washington DC was once a Swamp. I would assume the ground is saggy due to the moisture in the soil and all. But how was it that the government was able to turn a Swamp into land that tall heavy skyscrapers can be built on? Washington DC even has large underground tunnels. How is that stable on swamp land? | Engineering | explainlikeimfive | {
"a_id": [
"dklpixt",
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"text": [
"Washington DC was never a swamp. Part of what is now the National Mall was marsh land that was filled in, but that's a far stretch from a swamp. Also, there are no skyscrapers in DC.",
"It is not literally a swamp unfortunately. And the downtown area was built on more solid land. But you can build anything in a swamp provided you fill it with enough dirt and drain the water out. The city is located in a low lying area and it does get super humid so summers are definitely swampy though."
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6p0tzt | Why do modern airplanes not use reverse thrust on all engines? | I remember vividly when I was flying at a young age (think 727, A300 etc.) that after touchdown all engines went to reverse thrust. It was awesome for me as a child to see the jet engine "morph" like that. I have learned that most of the "braking" comes from the wheels. So my questions ist, why did they use it more in the 80s/90s. Why less nowadays? If it is inefficient, why do modern planes use it at all? | Engineering | explainlikeimfive | {
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"The only modern aircraft I can think of that doesn't have reverse thrust on all engines visible from the cabin is the A380. From what I understand the decision to expel reverse thrust from engine number 1 and 4 (the two outboard engines) was due to their position. The A380s wings are so large that the points at which the outboard engines are mounted can actually end up extending past the runways width. Usually this area is filled with grass. Now for this to make sense you need to understand what reverse thrust actually does. The thrust coming out of the engine when reverse thrust is engaged is not entirely redirected forwards it is also directed up and down and basically all directions but backwards. Its job is to destroyed the airflow over the leading edge of the wing (to diminish the wings ability to create lift) the redirected thrust will also cause the aircraft to decelerate, obviously... though its not that effective in actually stopping the aircraft. The effectiveness decreases with the speed of the aircraft. You can see what the thrust coming from the engines are doing when reverse thrust is engaged in [this]( URL_1 ) video. There is a lot of thrust being directed down towards the runway. On an A380 seen [here]( URL_0 ) the outboard engines will be most likely running over the grass or very close. If they had reverse thrust capabilities it would cause a lot of debris to be sent flying possibly hitting the aircraft or being blown onto the runway which would then cause problems for other aircraft. Also keep in mind that reverse thrust is only engaged at the pilots discretion. If the aircraft needs to take the last exit at the end of the runway the pilot may decide to use a lighter auto brake setting for the main gear and not engage reverse thrust so the aircraft can just use its inertia to get to the end of the runway faster. Its also common for 0 reverse thrust to be used. The engine still creates a small amount of thrust when it is running at idle. To maximise breaking efficiency on landing when reverse thrust isn't needed it is engaged but power kept at idle. The small amount of thrust created at idle power will still be redirected. Kind of off topic but good to know anyway. Hope that answers your question."
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6p143f | How do washers work and when should I use them? | I am specifically thinking of use with screws and bolts - but other uses are welcome too. | Engineering | explainlikeimfive | {
"a_id": [
"dklrlvq",
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"text": [
"Flat washers spread the load so the screw head doesn't dig in. Spring washers reduce the chance that the screw will loosen. These articles will help a bit. 1. [Why do we use washers with screws? - Quora ]( URL_2 ) 1. [When to use washer or not?? - Mechanical engineering other topics - Eng-Tips ]( URL_0 ) 1. [Washer (hardware) - Wikipedia ]( URL_3 ) 1. [The Straight Dope]( URL_1 )",
"Generally they'd used to spread the load around the material you're screwing into, and/or to prevent the screw from digging into whatever you're screwing it in to. For example, I like to make skateboards out of household objects or other things and the things I try are often abbot fragile, so I use washers so the trucks don't pull the screws through the board when I do anything on it."
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"https://www.quora.com/Why-do-we-use-washers-with-screws",
"https://en.wikipedia.org/wiki/Washer_(hardware)"
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6p3zym | Why does the UK still use two pipes instead of one? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Many UK homes have a cold water storage tank that feeds into the hot water heater...due to various issues in their construction, location, etc the resulting heated water is not considered safe for drinking. The cost of retrofitting the plumbing to meet modern standards is prohibitive so many just tolerate the twin taps. An increasing number of people are doing away with their old system and installing point of use hot water heaters on their cold supply line along with a mixer valve to give them the single faucet at a lower expense than replumbing their entire house."
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6p4ryj | Why do sidewalks sometimes have sections of metal grippy things? | I often see this on sidewalks with crossings, there will be a metal plate integrated with the sidewalk cement structure such as this: URL_0 | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"These are to alert blind people that the walkway ends here -- you're about to step into a more dangerous zone (such as the street)."
],
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6pasxp | Brian May famously uses his own, handbuilt "Red Special" Guitar, in a video, i saw him describe it having 3 Pickups and each pickup being in and out of phase, what effect does this have (other than sounding like Brian May!) | For example, why would he need 3 pickups? what does being "in phase" mean? etc. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"A pickup is a coil of wire wrapped around a magnet. The coil has two ends, let's call them + and - for ease. When a string vibrates in the magnetic field produced by the magnet it slightly alters the magnetic field and this alteration is sensed by the coil. The output from the coil is alternating current/voltage. If two pickups are \"in phase\" they are wired with their like ends attached to one leg of the circuit and the other ends attached to another leg of the circuit. This results in the signal two pickups adding on top of each other because they are both picking up the same vibration. If it is wired out of phase (+ end of one with - end of the other) the result is that some of the negative output from one pickup negates some of the positive output from the other. The end result is a slightly quieter overall signal with some frequencies dropped out altogether. It's not perfect destructive resonance because pickups are positioned at different points along the string and, therefore, are not producing equal and opposite signals. In terms of number of pickups, you only need two to produce an out of phase tone, but having three to play with gives you multiple sets of two that you can select to suit your taste."
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6pbjbr | What are the benefits of salt grinders? | I totally get the benefit of pepper grinder. Pepper locks some aromatic oils, and when left ground for long, the oils evaporate. Salt, on the other hand, has no oils in it, just solid minerals. So what is the different between "freshly ground" and not freshly ground? I crushed some salt and left it aside for 2 weeks, couldn’t find any difference between it and "freshly crushed" salt. | Engineering | explainlikeimfive | {
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"Aesthetics. It allows the salt and pepper grinder to match more closely since they now have similar mechanisms in them. Also, to some extent, you can choose grind size as others have mentioned, but that relies on the grinder actually having a grind selector. But it's more reliable to simply buy salt with the desired flake size and crystal structure, IMO. Size of crystals isn't really important, though; it's shape that is important. table salt has a dense cube shaped crystal, and kosher salt has a light flake like structure- kosher salt is more preferable to use in cooking because the flakey structure is better able to stick to moist surfaces when sprinkled, such as when seasoning meat) It's also important to know which a recipe is calling for- a teaspoon of table salt will contain more grams of salt than a teaspoon of kosher salt (which, incidentally, is one reason why you really should measure everything by weight, not volume, when baking)",
"The main thing that separates different salts is the size of the salt grain. Some salts might taste different or have different colors because of trace minerals, but that's a different topic. Typical table salt is pretty small and cubic. That's fine for when you want to dissolve salt into something, but it's not good for making something taste uniformly salty with a small amount of salt. Sea salt and kosher salt tend to be larger flakes with a larger surface area. When you put those salts on top of something they tend to taste saltier with less salt. Ground salt isn't as large as most kosher or sea salt, but it is irregularly shaped and as a result tends to make things taste saltier with less salt when the salt is sprinkled on top of something. So when suing on top of food, table salt requires more salt to taste equally salty and is a little harder to spread uniformly. There's not really any difference if you're dissolving it into the food, though."
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6pbune | Why aren't airports given trucks full of gravel/sand/peanut butter/any other viscous fluid to fill the runway with and stop an airplane in case of emergency? | Engineering | explainlikeimfive | {
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"Some airports do have overrun prevention systems (aka Engineered Materials Arresting Systems) that are composed of a soft, almost styrofoam-like concrete pad at the end of the runway. When a plane overruns onto the pad the landing gear digs in, slowing the aircraft. Pouring anything onto the runway would pose a huge FOD hazard, which is why it isn't done. Generally speaking it's better a plane run off into the grass than ingest a whole bunch of gravel into the engines. The Concorde disaster also demonstrated that hard objects kicked up off the runway by landing gear can seriously damage aircraft.",
"Stopping the aircraft moving isn't generally a problem, they could just run straight into the ground if that was the goal. What is trying to be accomplished is stopping the aircraft in a less than sudden manner which the passengers and crew can survive. Filling your runway with various gunk doesn't help accomplish that."
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6pdjvd | Why did steam locomotives in the United States get drastically bigger, heavier, and more powerful compared to their European counter parts? | Towards the end of the steam era, US steam locomotives got much larger boilers, fireboxes, wheels sizes, and more wheels, while engines in Europe (namely Britain) did not under go this change as drastically over time. Why was this the case? | Engineering | explainlikeimfive | {
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"The US had a lot of wide open spaces and long, straight track. That made *huge* trains practical and economical. If you want to run a 2 mile long train full of coal or iron ore you're gonna need some seriously big locomotives. In Europe on the other hand huge trains simply weren't economical because of the shorter distances involved, and there were many old bridges and tunnels that couldn't support larger and heavier locomotives.",
"Germany is only 399 miles wide. England is 271 miles wide. France is 572 miles wide. The United States is 2680 miles wide. We had a lot more room, which means larger and longer trains.",
"A long drawn out process. Railroads tended to go for longer distances in the US which means they needed to be able to carry more coal. After a point this requires building a bigger Engine in order to not volume of goods that they can carry. These bigger sizes then allowed you to carry more goods on shorter runs, which in turn put pressure on the long haul trains to up their size again to meet that higher goods volume. By the time Diesel and Electric Engines were being made these larger trains and the trend to make the bigger and longer was well established. In fact it is not uncommon for some major trains to now use 4 or even 6 engines (3 pulling, 3 pushing) to haul enormously long trains shipping goods in some regions."
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6pf2s1 | Why can we not achieve efficient and relativity low energy flight the same as birds through the design of a similar winged style flying machine? | Engineering | explainlikeimfive | {
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"Short answer is we do! We make gliders in a similar way to large marine birds but: When you say birds wings are efficient they are for a bird is doing but aircraft wings are more efficient for what an aircraft is doing and per kg. Look at an example of probably the best long distance most efficient birds going the Wandering Albatross and it's huge 3.5m wing span and weighing in at 12kg. It can travel 10'000 miles in a single trip and without flapping it's wings much if at all, truly amazing efficient bird! It does this at low altitude using dynamic soaring and averages a speed of..... 35mph. Ok so that's great and really efficient but do you really want to spend 5 or 6 days to get from New York to London? You can sail it in that time! Now look at an aircraft say A350. It can fly 300+ people totalling about 120ton 10000km in about 11 hours. Cross the Atlantic in 8 hours. An aircraft flies fast and high to gain efficiency if it tried to dynamic soar it wouldn't get very far or very quickly. We do make aircraft like that. Gliders. Very light with large broad wings to gain as much lift as possible. We don't make airliners like that as they wouldn't gain from it. Edit spelling",
"The [square-cube law]( URL_0 ) strikes again, the answer to pretty much any question about why we can't do something that tiny animals can. Specifically, if you simply scale up the body plan of a bird, it stops working, because at twice the size, its wings will create four times as much lift - but it will weigh *eight times* as much, so its weight-to-lift ratio is actually only half as much. And the same goes for the strength of the bones. The only we we can make big flying engines at all is by using far stronger materials and far more powerful sources of energy than nature does.",
"The short answer is weight. Humans are immensely dense relative to birds, so it is not feasible to attach huge wings to us that can then move quick enough to generate and maintain lift."
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6pfb2g | What is a Kalman filter? How do they combine sets of data such as gyroscopic and magnetometer data? | Engineering | explainlikeimfive | {
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"A Kalman Filter is a mathematical technique for finding a kind of optimal weighted average for combining data from multiple sources. It is based on Bayesian statistics, which it helps to be versed in. ~~---------------------------------------------------------~~ To explain like you're five: Imagine you have two friends, Alice and Bob, and the three of you are trying to figure out how far it is from your house to Alice's. You think you're pretty good at measuring distance, and can probably get it right to within 10 meters or so on your own, but you know you can do better if your friends help. Alice is more accurate than you, getting distances right to within 5 meters or so, and Bob is the worst of you three, only getting distances right to within 20 meters or so. You each run from your house to Alice's house. At the end, you say the houses are 100 meters apart, Alice says they're 90 meters apart, and Bob says they're 80 meters apart. How far apart are the houses? You decide that you want to average the average of the three numbers is 90 meters, but you're probably more accurate than Bob so maybe your estimate should count more. Alice's should count the most, of course, but how exactly should you be weighted? You ask your kindly old Hungarian math professor neighbor, Rudolf Kalman, and he gives you some precise numbers for the weighting and sends you on your way. You estimate the distance to be 92 meters, and run back to your house. When you ran back, you got new data as to how far the houses are apart. This time it really felt like they were 95 meters apart to you, Alice thought they were only 85, and Bob thought they were 110 meters apart. Puzzled, you go back to Dr. Kalman. He chuckles and explains that all measurements have noise and that's why you have to take into account how trustworthy each each measurement source is. He also points out that if you want a new, better estimate of the distance, you can update your old estimate with the new data. In order to do this, you need to know how accurate the old estimate was. Fortunately, Dr. Kalman shows you that it is very easy to find out based on how accurate each of you are and those special weighting numbers he gave you earlier. Then, he gives you a new set of weighting numbers so you can combine your old estimate with your new measurements, and out pops your new, more accurate value of 93 meters. As you get more and more data you can keep updating your estimate to get closer and closer to the truth. ~~---------------------------------------------------------~~ The next section is more technical, so I apologize in advance if it stops being \"explain like I'm five\" and starts being \"explain like I'm a student struggling to implement one of these\". Now, in this example the measurements (running) directly observed the state (the distance between houses), and the state was unchanging. In reality, you will have some model of how the state changes over time (e.g. I was 10 meters along the axis and moving at 1 meter per second, so when I update 1 second later I will be 11 meters along the axis) and you will have to have some model for how your sensor measurements turn into your state. In the majority of cases (speaking from personal experience, YMMV), it is easier to calculate the measurements from the state than the state from the measurements. For instance, in the case of GPS, the math is simpler for me to find the timing differences between clocks from my position than to find my position from the clocks. So I will calculate what my measurements would be if my current estimate of my position is accurate, then update my estimate based on the error between my actual measurements and my the measurements calculated from my position estimate. This error is usually called \"innovation\"."
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6pftjr | How is helium used by an MRI Machine? | Based on a post below saying that MRIs use helium, I’m now wondering how. Can anyone explain? | Engineering | explainlikeimfive | {
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"It is a coolant. The magnets in and MRI are incredibly powerful, they use superconductors to make such a powerful magnetic field. With regular copper wire, if you coil the wore and run electricity through it, it forms a magnetic field, and around 1% of the energy is lost to heat. MRIs are so powerful that the small loss to heat would melt the wires. So, they cool the wires with liquid helium, the coils become superconductors, which lose no energy to resistance at all. Liquid helium is very cold, it is -269C or -452F. It takes a lot of helium, compared to a balloon, because a liquid is much more condensed than a gas. Liquid helium is strange stuff. If you pack a hose with sand, a regular fluid like water will flow very slowly through it. Liquid helium has no friction, the sand won't slow it down a bit. If you started it flowing through a tube full of sand, bent the tube into a ring shape, and left it alone, it would keep spinning forever.",
"Fun fact, once the magnets are powered up they stay powered up nearly indefinitely until things leach them down by converting their magnetic field into electricity or heat. IF you can keep them cool.",
"Further to the above, not all MRI scanners use liquid helium. Superconducting systems using liquid helium as a coolant are the most common, as they have the best combination of performance at reasonable cost. There will need to be some sort of cooler used to condense any helium which boils off, but even without the cooler, the magnets are well insulated (they use a vacuum insulation), so it would take weeks for the magnets to warm up and lose superconductivity. Early MRI used permanent magnets - huge C shaped blocks of steel which were then magnetised - just like the horseshoe magnets you might have used at school, but 10 feet tall and weighing 40 tons. These are still used in niche applications - such as \"upright\" scanners. In an \"upright\" scanner, the magnet is on its side, and surrounds a reclining chair. You sit in the chair or stand up, allowing a scan of your back to show what happens when there is weight on your back. Permanent magnets are much cheaper than superconduncting magnets - but much, much weaker, so the picture quality isn't as good. The massive weight of permanent magnet systems also makes installation difficult, as they require super strong floors, massive cranes, etc. The latest technology is zero-helium superconducting magnets. Instead of putting the superconducting magnet inside a bath containing 1500 litres of liquid helium, the magnet is fused to a block of copper or aluminium, and that is then soldered to a cryo-chiller, which reduces the temperature to liquid helium temperatures without the need for liquid helium. In comparison, these are very expensive compared to liquid helium systems. They also run into big trouble if there is a power outage, because without the chiller running, the magnet will warm up and the magnet wires will stop super conducting, and discharge. It may take many days and cost many $k to recool the magnet and recharge it if that happens."
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6pjg1w | If we can make sets of gears go faster or slower by adding different types of gears to them, why wouldn't it be possible to make a set of gears where the last one could spin as fast or faster than the speed of light? | Engineering | explainlikeimfive | {
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"Assuming that you could overcome the engineering problems with the gear not breaking, heat not melting everything etc, I believe what would limit you here is the fact that the relativistic mass of the gears would increase as they approached the speed of light. This requires increasing energy to be added to the system to turn it. Special relativity says the energy and momentum (relativistic mass) of the object approaching the speed of light will increase without bound. So, you simply couldn't produce enough energy to turn the gears fast enough to make this happen.",
"Because speed does not 'add up' exactly like we think it does. Let's say you are on a train going 100 miles an hour. You have a model train on a table on that train. It's an expensive model that can itself go 100 miles per hour. You and I, from simple grade school math, would figure that the model train on the real train would have an actual speed of 200 miles per hour. Right? Well, it doesn't! The actual combined speed ends up being 199.9999999-ish miles per hour. The WHY of this is more complicated, but it's one of the things Einstein and the folks of his time figured out, and every test we've ever run proves his calculations right. The same not-quite-adding-up effect will happen to those gears.",
"You would run into issues with friction and heat long before you got fast enough. The gears would simply break apart long long before you got anywhere close to the speed of light.",
"Gearing doesn't \"add\" speed; a large drive gear pushing a smaller gear results in the smaller gear making more revolutions per minute, but the overall distance the edges of the gears moves doesn't change. In order to make a gear spin at the speed of light (ie, to have a fixed point at the edge of the gear move 299,792,458 meters in one second), we'd need the drive gear ahead of it to move at the same speed, which is well outside our current abilities in terms of power (we can't generate enough kinetic energy to get something going that speed) and structure (nothing we currently build could withstand the forces involved)."
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6pk9cf | Why do American cargo trucks have the engine sticking out in front of the driver whereas European trucks have the engine below the driver? | Engineering | explainlikeimfive | {
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"US laws have maximum trailer restrictions, EU has total length restrictions so it makes sense to have as short of a prime mover as possible so you can have a longer trailer.",
"European trucks tend to have to get into smaller spaces inside older cities built before cars were invented. The engine below trucks otherwise known as *cab-over* are shorter and allow the drivers to maneuver better in tight spaces.",
"The regulations for the maximum length includes the truck in the EU, so to have a longer trailer you need make the truck shorter."
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6plju8 | Why do you need to change the oil in a car | Engineering | explainlikeimfive | {
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"Motor oil is made of chains of hydrocarbons. The longer the chains, the more viscous the oil. Engines are designed to use a certain range of viscosity to lubricate the moving metal parts of an engine. Over time, these hydrocarbon chains will start to breakdown into shorter chains. At some point, this causes viscosity to drop below the design tolerances of the engine. This means the oil can no longer provide sufficient lubrication for engine, which can lead to increased wear and eventually catastrophic failure of the engine components. Also, as the motor runs, small amounts of metal will come off from the engine through wear between tight tolerance metal on metal seal areas. This builds up in the oil and can act like a polishing agent that grinds into all the other metal surfaces that the oil encounters, which again leads to increased wear and a chance of catastrophic failure.",
"Motor oil breaks down, or leaks as time passes and the heat from the engine changes the chemistry of the oil so it's less effective at lubricating the metal moving parts such as pistons and bearings. Most older cars needed to be changed every 3000 miles or so, but newer cars can go longer. I drive a 2002 VW Jetta and according to the manual each oil change is good for 5000 miles. Some cars like BMW and Mercedes-Benz can even go over 10,000 miles between oil changes. It all depends on how the car is built."
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6po25a | Picking the strings of a guitar while the other finger is resting on a fret doesn't produce a sound, except for certain frets like the 12th. Why? | Engineering | explainlikeimfive | {
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"I believe why you're describing are harmonics. The 12 fret is special because it divides the string in half, that's producing sound when played. How it works beyond that is beyond me. You can also find natural harmonics on the 2nd, 5th, 7th, and 15th frets. In addition, you can create more harmonics by pressing down on a fret and touching it in increments after."
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6po600 | At what point do architects and engineers have to factor for the curvature of the earth ? | Does the curvature of the earth affect only the largest scale mega construction, like sports arenas and major bridges? Would someone have needed to account for this while building an average sized office building or large house? | Engineering | explainlikeimfive | {
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"Earth curves downward 8 inches per mile. This is much less than the natural variation of terrain over that distance, which builders have to level. So for any structure no longer than a couple of miles, they can simply measure plumb (vertical) and level (horizontal) around the center of the project, and level the site all the way outward without thinking about Earth's curvature.",
"Lighthouses consider the earth's curvature. They need to know how far the light must be cast to determine how tall they need to be.",
"Keep in mind that gravity is going to flex whatever physical structure you put in place. Nuclear reactors have a crank shaft (for want of a more accessible term), that is this huge, long, metal, pole that is spun by the reactor to create electrical power. It isn't very long in the grand scheme of things (50, 60, 70 yard something like that), but it is still so long that when you do a maintenance shutdown you have to keep a backup motor running to slowly turn it so that it doesn't start to sag. We don't think of steel, or cement, or whatever flexing, but it does to a degree far greater than the curvature of the earth."
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6pp6hn | How does a Qubit collapse into its correct state? | I'm doing a project on Quantum Computing and I've hit a bit of a wall when it comes to Qubits being in the "right" state as it were. As an example if a Quantum computer were asked to find the two prime factors of a number (like in decryption/encryption), how would the Quantum computer read the selection of Qubits to give the correct solution? The only way I can think of this happening is to have a selection of logic gates that somehow collapse the Qubit into the correct state when observed; however, I'm not too sure how this actually would work with Qubits. Any overview/condensed answers would be as much appreciated as those which go into a more atomic/chemical depth about how it would all physically function. Cheers! | Engineering | explainlikeimfive | {
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"By the end of the computation, before the answer is read out, you no longer have to maintain the coherence of the quantum computer. So the trick of quantum computers is to keep them coherent during the course of the computation. It then becomes a question of when to check the results. You can set aside one of the qubits of the computer as a flag for completion of the computation. The qubit starts with the value 0 and the computer doesn't interact with it unless the computation terminates, at which point it sets the bit to 1.",
"What's your background? What's this project for? In general, this is something that gets very complicated very quickly, and in general ELI5 isn't a good place to ask this question.",
"That is a very, very, very, very complicated answer. Literally no one on Reddit could answer it (that answer would take pages and pages). Quantum computers can't do the majority of calculations, they can only answer very specific questions (you'll never play a video game on a quantum computer). And worse, the answers have to interpreted. You'll need a PHD to even understand whatever answer it would spit out. A couple of dudes got a Nobel Prize, for just having one keep time. URL_0"
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6pqysp | How does resistive charging work? | My friend has an electric longboard that says that braking helps to charge the battery. How does that work? | Engineering | explainlikeimfive | {
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"This would be an example of regenerative braking. An electric motor works by running electricity through coils that produce magnetic fields. These magnetic fields in turn force a rotor to rotate, providing mechanical power. However, this process also works in reverse. If you manually spin the rotor, those magnetic fields oppose the motion and you induce a current in the coils (producing electricity). An electric generator and an electric motor are the same device (at least as the level we're talking about) - it's just one is performing the mechanical/electrical conversion one way while the other is performing it the other way. As a result, you can set up your motor to draw energy from a battery to create motion or you can switch a bit of wiring and use the mechanical motion to charge the battery. When you're charging the battery, the power you're putting into the battery makes the rotor harder to turn (causing a braking effect)."
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6pr1ey | If airplanes can only carry a fixed amount of weight which is why luggage has strict weight restrictions, why are there no restrictions for the weight of passengers? | Engineering | explainlikeimfive | {
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"Jet airliners usually fly far from their maximum weight. Luggage weight restrictions are for easier handling of each piece, and to prevent abuse (no you can't check a 400 kg crate of bricks). Very small propeller planes do have more serious weight restrictions, and on these the operators do in fact make you declare your weight. If you are too heavy the very smallest planes may not be able to accommodate you.",
"Probably because some would find that to be offensive. You could easily get sued for discrimination if you tell someone they can't do anything because of their weight.",
"First ever comment on Reddit so please don't shoot! Commercial aircraft do actually need to have an accurate weight figure for all flights, so it's not enough to say \"Captain, you are under your maximum take off weight\". You need to give the captain an accurate figure. How is this achieved without weighing people? Average weights! There's an average weight for an adult male; adult female; older child; younger child and infant. Don't have the exact weights to hand right now. Though fun fact it increases by 5kg for adults in the winter season to take into account heavier clothes! Experiments have found that the weights calculated using this method are accurate to within an acceptable margin of error.",
"I've heard that luggage was restricted to keep a uniform weight for the baggage handlers to reduce the amount of muscle injury.",
"The reason for a limit on a single pieces is mainly for the safety of baggage handlers so that they don't throw out their back picking up a bag that looks 30 lbs but is actually 130. So heavy bags require special handling. The reason for an overall limit is to prevent abuse and make sure there's room for everyone to bring a bag. If you read the fine print, they sometimes say if you check more than 2, they won't guarantee they'll all be on the same flight. They'll also charge you a fortune to encourage you to ship them another way. For passenger weight it's mostly for PR reasons. Though there is a sort-of weight limit based on the size of the seats. Most airlines have a policy that if you can't fit in the seat with the armrests down, you have to buy a second seat."
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6pr9i5 | If NASA built a giant, empty storage tank in space, is there a means to pressurize it (with breathable air) without bringing air from Earth. | Engineering | explainlikeimfive | {
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"Sure. Space is full of stuff that could be made into breathable air. The simplest way to do it would be to find some ice (probably in the form of a comet) and use electricity (generated with solar or nuclear power) to crack the water into hydrogen and oxygen. The oxygen can be fed into your storage tank for breathing air, and the hydrogen can either be discarded or kept as rocket fuel. There are also other ways to get oxygen out of certain minerals found in space. However at this point bringing the air with you from Earth is cheaper than finding the materials in space to make air.",
"you could bring oxygen and nitrogen in non-gaseous forms and then separate them into your bubble. the best way is to harvest ice (a plentiful material in certain areas) and heat then electrolyze it with solar power, netting you oxygen for breathing and oxydizing rocket fuel, and hydrogen you could use for maneuvering thrusters, back up power, and various other uses. The second best way is bringing enough green plant matter to sustain a viable balance of CO2 and O2 - you will need a 'seed' atmosphere though. I believe they've done tests with dogs and/or monkeys."
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6psca1 | Is there a hard limit to skyscrapers? Or, what would prevent a building from surpassing a certain altitude? | Engineering | explainlikeimfive | {
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"Randal Monroe did an article on this. To simplify his answer, the limit to skyscraper height is wind, elevators and cost. URL_0",
"Two answer the second question: Money One of the practical limits stems from the fact that in order for additional floors to be reasonable, people have to get up and down from those floors, otherwise nobody will buy that floor space, and constructing a building just to have a tall building doesn't make much financial sense. The increasing space requirement for elevators and utilities can make building higher floors very expensive, as some of the floor space on lower floors gets consumed by elevators. Building a tall structure has huge structural concerns. Wind can be pretty nasty on tall buildings, so some solutions [like tuned mass dampers]( URL_0 ) can be used, but once again, structural elements eat of construction cost and floor space."
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6psvxf | How are train engines strong enough to pull that much weight? | Engineering | explainlikeimfive | {
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"It's not too complicated -- they have an *enormous* generator inside that powers *huge* electric motors that drive the wheels. In [this photo of just the diesel portion]( URL_0 ) check out the lockers in the background for scale.",
"Huge, powerful engines and low friction. A locomotive engine is about the size of a delivery van, and some trains have a dozen of them. On top of that, steel wheels on steel track have very low rolling friction. Car tires have to be stickier to prevent side to side motion, the crown of the track makes that less of a factor. Once a train gets going, it doesn't take much power to keep it going.",
"Nearly all locomotives today are Diesel-electric, meaning a very large Diesel engine turns a very large generator and produces electricity to power electric motors known as \"traction motors\". There is no mechanical linkage between the diesel engine and the wheels. A really long train will feature multiple locomotives in order to provide the force needed to move the train. Older Diesel locomotives did have a mechanical linkage to the wheels and used gear reduction to transmit power from the engine to the rail. This method has it's limitations and consumes much more fuel than Diesel-electric."
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6pt1rb | How does a gas stove prevent the flame from going in? | Isn't gas highly flammable? What stops it from shooting back and causing a chain reaction within the line itself? | Engineering | explainlikeimfive | {
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"Combustion requires three ingredients: fuel, oxidizer, and heat. Only when all three are present can a flame occur. This happens at a stovetop burner where gas from a pressurized pipeline mixes with oxygen from the air in the room, with a spark to ignite it. Inside the pipeline, however, there's only gas. You can heat it all you want but it won't burn if there's no oxygen to react with.",
"You need three things to make fire: fuel, heat, and oxygen. The gas line is pressurized and full of just fuel. With no oxygen (or at least not the correct amount of oxygen), the heat at the end can't ignite the gas inside. That's also why there's a gap between the exit and the flame; the gas has to disperse and mix with oxygen before it can ignite.",
"Flame needs oxygen and fuel to work. The fuel is the gas, the oxygen is in the air. Inside the cylinder there is no oxygen, only fuel. In the air there is no fuel, only oxygen. This means flame can only burn where fuel meets air: the top of a lighter (butane meets air); the surface of a log (the wood being the fuel); and indeed the top of your gas stove. The exception is when fuel and oxygen are premixed inside the container, then a lot of fire is produced very quickly inside the container this is how most bombs work. Your gas cylinder is especially designed NOT to explode, so has no oxygen inside it.",
"Combustion requires Oxygen, Fuel, And heat. Inside the gas line there is too little oxygen for combustion to occur.",
"Because a flame needs oxygen to burn. The flame wont go into the line because there's no oxygen (or very little) inside just natural gas."
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6ptxk7 | How does a mechanical watch know exactly(ish) how long a second is when the input speed slowly changes | Engineering | explainlikeimfive | {
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"text": [
"You know how the period of a pendulum is constant based on its weight and length but ignores the amplitude of the swing? if not, trust me - it does. Inside a mechanical watch, you've got a [balance wheel]( URL_0 ) which is a spring-loaded wheel with weights on the edges that oscillates back and forth. The oscillations of the wheel follow pretty much the same behavior. Your main-spring drives the balance wheel, creating a (relatively) constant speed of motion. This then drives the rest of the mechanism forward at a (relatively) constant speed so you can keep track of time. [Here's a visual overview of how it all works]( URL_1 ).",
"You are correct that the force a mechanical watch's main spring supplies varies depending on how unwound it is. No mechanical watch is ever truly independent of this effect, however there are ways of minimizing it. One way is to use much more spring than is really needed. Sure the difference between a maximally wound spring and a full unwound one is huge, but the difference between the middle 25%? not so much. So prevent the user from completely winding, prevent the watch from fully unwinding. Another one was have the main spring wind up a smaller spring and use that to power the clock. That smaller spring acts as a buffer, and the smaller size means the difference isn't as much for fully wound and unwound. Also it tends to average out imperfections.",
"What \"input speed\" are you referring to? A mechanical watch does not take any input to determine speed or timing."
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6pu3wd | Can we use ocean water for toilets, car washes, etc. and leave freshwater for drinking cause there is much more ocean water available to us? | Engineering | explainlikeimfive | {
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"Two problems, firstly you would need an awful lot of extra infrastructure to have two water pipes to every home, and the salt water would have quite a damaging effect on pipework, as the salt would crystallise out over time, would build up inside pipes,and dry and damage rubber seals.",
"For toilets maybe, but sea water has a bunch of bacteria, diseases and corrosive shit in it and it wouldnt be good to use",
"> leave freshwater for drinking cause there is much more ocean water available to us? The problem is that ocean water isn't really available to us. Our water distribution infrastructure is based on it raining up high and flowing to where it is needed lower down. Ocean is about as low as you can get, so the water there really doesn't do us a whole lot of good, fresh, salt, or otherwise.",
"Another problem is that even if you use it only in toilets, this may cause health problem. Imagine a child or a pet dying because they drank salt water from the toilet."
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6pw7te | The Hubble Space Telescope, how does it capture images? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It's got eight 0.64 megapixel digital camera sensors built into the telescope. Unlike a digital camera where filters are mounted in front of the sensor, Hubble's filters are optional depending on what sort of light is radiated. To give you an idea of what they look like, this is Kepler's (a different space telescope) [digital imaging sensors]( URL_0 ).",
"The Hubble Space Telescope has 6 cameras on it. These cameras have CCD sensors that are effectively equivalent to a digital camera but they're much more sensitive."
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|
6pwnca | - Why are some fuel caps on the left hand side of the car yet some are on the right? | Engineering | explainlikeimfive | {
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"text": [
"Saturn once explained it this way: Putting the gas cap on the passenger side was a safety issue. If you were to run out of gas and had to use a gas can to put some in then you would be out of the way of traffic. A cap on the drivers side exposes you to possible high speed traffic on a highway. Don't know if it was made up propaganda from a car manufacturer after the design or not.",
"It depends on how the car is built. Different manufacturers make different decisions in regards to where their gas tanks will be mounted and where there is space to run the fill tube. These differences change where the fuel cap will be.",
"Why not? Gas pumps can be approached from both sides, so if you're coming from the same direction it's actually better to have 1/2 and 1/2 to equally use each side of the pump. And worst case you can turn around to use the gas pump on the other side. Because there is no reason not to have them on different sides, the reasons to move them could be really small or depend on other non-obvious parts of the car design. Steering wheel's on the left so there's no space? Put it on the right. Engine is on the right, because the steering wheel is on the left, and now there is no space because of the engine? Put the gas tank on the left. Need to run a gas tube and want it to be short for cost/safety reasons? Put the tank as close to the engine as possible."
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6q0a31 | How do theme parks have fewer accidents than carnivals? | Engineering | explainlikeimfive | {
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"text": [
"Carnivals set up and take down their equipment to relocate every couple of weeks. Thus the chances of assembly error are much higher. Theme parks are usually extremely well funded, as one can cost $100 million to $2 billion to build. So yes, they do indeed hire safety engineers and a full-time staff of mechanics.",
"The easier the carnival is to take down, the cheaper it is. If they are easy to take down, they don't have to pay as many people. Therefore, they are less sturdy. They are not properly tested like theme parks.",
"Walt Disney wanted to build the world's cleanest and safest carnival. That's why. His inspiration included Coney Island. Carnivals are especially bad. They have no professional reputation. Their rides are based off what doesn't injure their customers. They use equipment until it's wrecked."
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6q2iub | If we were able to achieve such phenomenal speeds with the Concorde, why has commercial air travel not replicated this (without the fatal flaws)? | Engineering | explainlikeimfive | {
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"Breaking the sound barrier and flying faster then the speed of sound adds a lot of drag on the airplane. This means you need bigger engines and more fuel to travel supersonic. This means the ticket prices for the Concorde were much higher then for big subsonic aircrafts. In the 70s when the design of the Concorde started this made sense. The extra cost was well worth it for busy celebrities, wealthy and business people. However what brought down the Concorde was computers and the Internet. You no longer need to have breakfast in New York and Lunch in Paris because you already talked to the people in Paris in a video conference. And when given the choice of spending three hours in economy class or six hours in first class most people will just bring their laptops on first class to get some entertainment and work done. There is a small market for supersonic travel. The fastest passenger aircrafts today is private jets and there is some plans to make supersonic private jet aircrafts. If you can afford to buy and operate your own jet then you are likely not so much interested in the operating cost and supersonic travel might be an option you are willing to pay for.",
"Because it was very expensive. It was starting to not make financial sense, it was merely a fun thing to do for the rich and wealthy. It didn't make any sense to have it as a regular airliner anymore. And then, the accident.",
"Because some of the integral, crucial problems still exist today. Technologically advanced as we may be, we're not capable of suppressing a sonic boom, nor suppressing the force of drag. The concorde had a very high maintenance cost, and a high fuel consumption. Take a look at the concorde's engines - without going into too much detail, they're turbojet engines, rather than the large, round and highly efficient turbofan engines you find on typical airliners. Afterburners also consume massive amounts of fuel, adding to the cost. If you take on top of this the fact that, with the internet, it is no longer necessary for one to cross the ocean at quite such a high speed, you've got a death sentence for the concorde. Even at the end of its lifetime, the concorde saw falling passenger counts, and it likely wouldn't be too much better now.",
"Other people have given you good explanations already but I wanted to add a YouTube video that directly answers your questions in a nice manner: URL_0 The basic answer is money and the existence of red-eye flights. It doesn't matter as much that it takes 10 hours to get across an ocean if you can sleep the whole way through."
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6q5hfc | Are Volvos actually safer than other cars?If so why? | Engineering | explainlikeimfive | {
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"text": [
"Yes they are. If internet is not lying then one of Volvo's co-founder's wife died in car accident, and safety was the highest priority from the start. They invented three point seatbelt (and gave it away for free to other car manufacturers, which was very generous move) and side airbags.",
"I own a Volvo actually, partially because of the reputation for safety. However, it's not that they're necessarily *that* much safer than any other major car brand, but that they do make it a priority in ways that others might not. Basically, they've found a market niche for cars that prioritize safety over cost and then sell to that market. It's kinda like Subaru marketing to folks with outdoorsy hobbies by making cars that can carry a lot of gear over rougher roads or through snow. They're not doing anything that other car manufacturers can't or don't do, but they make it a part of their identity where others don't."
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6q7dh7 | why do trains usually have engines on the front and back rather than just the front or back? | Engineering | explainlikeimfive | {
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"text": [
"So the engine can push the train no matter what direction it's going. Instead of turning the whole train around, they can just use the other engine",
"A great many trains do not. But when they do, there are two main reasons. For commuter trains, it's because they go back and forth all day. For large cargo trains, it's because of the enormous stress put on the connections if all of the driving force is a pull from one end.",
"Trains are designed to be as efficient as possible, which is why they have steel wheels on a steel track, to reduce the rolling resistance, and as a result, they actually don't have a great deal of power available to them. Most big freight trains have a power to weight ratio of less than **one** horsepower per ton. Compare that to a high end superbike which will have well in excess of five-hundred horsepower per ton. This is why they're slow to accelerate, and they really can't deal with hills particularly well. It also follows that if the conditions aren't ideal, some extra power would not be unwelcome. The result is often adding another locomotive at one end or the other."
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6q9djy | Why do some houses/buildings have balconies without a door leading out onto the balcony? | I see so many houses with very pretty balconies and then I realize that the only way to get onto the balcony is by climbing out one of the windows. I am sure it saves a little bit of money by not adding a door, but there most be some other reason | Engineering | explainlikeimfive | {
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"text": [
"These balconies are meant only as decorations, to make the building look prettier from the street."
],
"score": [
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6q9ypz | What would happen if a nuclear missile where to be shot by bullets? What about by another missile? | Engineering | explainlikeimfive | {
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"text": [
"A normal bullet probably would do nothing. Artillery fire or missile fire would likely disable the nuke. Nukes are very sensitive instruments, they are not conventional explosives, they are very difficult to set off accidentally. The main issue is that nukes often move so fast that it is very difficult to target them in such a way.",
"Most likely nothing. Nuclear missiles aren't like some older conventional artillery shells where there's an \"impact fuse\" that will detonate or ignite when receiving a significant impact. And they're typically quite large. Same pretty much goes for conventional missiles, although their payload COULD explode under certain circumstances depending on their purpose and design. Depending on the nature of the bullet and the area it hits you might do any of the following. - Not much, really. Just leave a bullet hole or mark on the missile. - Punch through or glance off and create a minor instability that the rocket could likely compensate for if guided, or might create serious issues if in the propulsion system areas. - Loosen or penetrate a part that becomes a problem during the stresses of launch, such as if an exhaust system funnel was hit. - Punch through to the fuel, possibly igniting it and causing the missile to prematurely launch and explode without setting off the nuke. This is highly unlikely though. - Hit vital electronics and interrupt an important circuit, completely disabling the nuke, its guidance systems, or its ability to properly detonate."
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6qazw4 | why aren't traffic lights made with one light that changes color instead of three. Wouldn't they be easier to manufacture and install? | Engineering | explainlikeimfive | {
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"text": [
"Several reasons. Technology has only recently evolved to where this would actually work. Prior to LEDs, all bulbs were white with colored filters in front of them and having the filters change mechanically would be a huge failure point. Our eyesight notices movement much quicker than color changes and the change in location of the light acts like motion. And what about all of our color blind friends? The position of the light helps them to know which one is on.",
"I can't say for sure, but one reason having three in a consistent order is helpful is for people with color blindness. They can tell what it is from the relative position.",
"In the old days of gas lights it was easier to have one light with different colors. This was how the British rail signaling in the 19th century were designed. However even then there was also a flag connected to the mechanism in case the color were hard to see. When electric lighting were invented it was much easier to switch on and off power then to move leavers to change the color filter. And since the light bulbs and fittings took up space they used different lights one on top of the other. This also meant that even if the colors were hard to see you could see the position of the light that was on. It is only recently with modern LED lights that we have been able to put three different colored lights inside the same fitting. You can even get three lights of different colors and a control circuit to give you millions of colors inside a 5x5mm chip. However the lights are standardized, especially considering that it should work for people who are color blind and in all situations."
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6qckja | How come a lot of recycling bins say 'no plastic bags' on them, but are lined with plastic bags? | Are those lining bags sorted out and not recycled? So if I put plastic bags in there they wouldn't get recycled? Why wouldn't we use different liners on recycling bins then? I'm just thoroughly confused by this one. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Yes, the lining bags are sorted out and either reused, discarded, or recycled separately -- all of which are a pain for the company that is actually trying to collect metal, glass, or heavier plastics."
],
"score": [
7
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6qd72l | How is a cruise ship's electricity powered? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"In modern cruise ships, electricity is provided by diesel generators. Since cruise ships already have to carry fuel for propulsion, it's simpler and cheaper to just use generators to provide electricity rather than use solar panels or batteries. Plus solar panels and batteries don't have the capability to power the amenities of a cruise ship for several days at a time.",
"The large diesel engines not only run the propellers, they also run large generators much like the ones that would power a small town."
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6qds4i | how do 3D printers work in space, wouldn't the filament just float around? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The printers head almost touches the bed and the hot filament extruded by the printer sticks to the printers bed, it's not simply laying over it. The final piece usually needs to be pried from the bed. It's also common practice to spread glue on the bed to increase adhesion. ELI5: It's kinda like putting toothpaste in your brush, you scrape the paste on the brush and it sticks."
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6qe0t6 | For electric trains, why does the friction from the part on top of the train that contacts the power cables not cause the cables to wear out and need frequent replacement? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The friction does wear metal but contacts on the train's antennas are made of a softer metal and this is the one that wears out. The pads as easily replaceable.",
"The [pantograph]( URL_1 ) contacts are made of graphite, which is very soft and doesn't significantly wear out the [caternaries]( URL_0 )."
],
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"https://en.wikipedia.org/wiki/Pantograph_(transport\\)#Weaknesses"
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|
6qfmo9 | Why is merging 2 audio inputs into 1 output hard to do / potentially bad for the devices? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The naive way of merging two audio inputs is to just wire the connectors together. However if you do that then there will be points when one input will try to drive the line high but the other will try to drive the line low. So current will pass between the inputs and not to the output. This means that a lot more current can pass though the amplification circuits then it is designed for and may overheat.",
"When an electrical circuit is 'shorted' out, usually some non-zero voltage is being connected to ground (i.e. zero volts). If that same voltage were to go to ground through, say, a light bulb, there isn't a problem because the *resistance* of the light bulb limits the amount of *current* that can flow. But if two wires without some kind of resistance between them are connected, there is nothing to limit the current that can flow between them until something somewhere breaks: a fuse is blown, a breaker flips, a transformer up on a pole somewhere blows. If you connect two audio sources together, this process happens in miniature. If the audio is analog, at any given time it might be that a high part of one wave is dumping current into the low part of the other wave; if it is digital, it might be that the voltage that represents a \"1\" is dumping current into the voltage that represents a \"0\". Current always flows from higher voltages to lower voltages, and if there is no resistance between them *something* will heat up and possibly overload... like a fuse protecting the amplifier stage, if there is one, or the output transistors in the audio source that is supplying the most current. Many circuits have safety features in place to prevent destruction of the circuit if the overload is short enough or small enough. Good audio hardware often has a user-replaceable fuse on the back. A lot of electronics will just heat up until the smoke comes out. There are cheap circuits that make it safe to do what you are describing; nowadays for non-audiophile consumer electronics these circuits might be molded into a cable that connects things the way you want while protecting everything well enough to keep the smoke in. Back in the day we'd make or buy little boxes that had a circuit in them that safely connected two RCA inputs to one RCA output (which would then be connected to the input jacks on a home stereo systems) or two 1/4\" mono jacks to a stereo TRS (tip/ring/sleeve) jack, for hooking two instruments (two guitars, guitar and bass) to an amplifier that only had one input."
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6qh9au | Why aren't coal and oil interchangeable? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Coal can be converted into liquid fuel through a few different processes that are broadly called \"coal liquidation\". There are some plants that exist today that convert coal into things like jet fuel and the Nazi's used similar processes during WWII when they were cut off from oil supplies in Russia and the Middle East. The problem with is that the process is expensive and dirty."
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6qnnbr | Why are airplane windows not aligned with the seats? | Engineering | explainlikeimfive | {
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"text": [
"One airliner can choose to have 20 rows with a lot of leg room, or 25 with minimum leg room. Or they push all of the coach seats further back so that first/business class has 10 rows instead of 8. Bottom line: seats are movable. Airlines place them so that they maximise the profit of each flight.",
"Because the windows are a part of the fuselage structure and can't be moved. The seats are installed by the airline and they can choose where to place them.",
"Yer not alone in askin', and kind strangers have explained: 1. [ELI5: Why are airplane windows never aligned with the seats? ]( URL_4 ) 1. [ELI5: Why airplane windows aren't aligned with seats. ]( URL_1 ) 1. [ELI5: Why do passenger aircraft's seats and windows not line up? ]( URL_0 ) 1. [ELI5: Why don't airplane windows line up with the seats? ]( URL_2 ) 1. [ELI5: Why don't the windows on an airplane ever line up with the seats? ]( URL_3 )",
"Because airliners have the option to add more seats onto a plane than the manufacturer has suggested, sacrificing leg room for profits. When they slide the seats back to add more, the become misaligned with the windows."
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} | [
"url"
] | [
"url"
] |
|
6qspl8 | Uh, how do you dam the water while you're building a dam? | Chicken and egg in my mind :) | Engineering | explainlikeimfive | {
"a_id": [
"dkzp5o5",
"dl05x09"
],
"text": [
"You divert it around the construction site and then close the channel when you are done or build the lake and then divert a river afterwards to fill it.",
"So, you realize that all the water that piles up behind the dam after it's finished isn't there before it's built, yes? There's just the original river. No lake or anything. Some or all of that river can be diverted for a time, either just around the construction site in the existing river bed, or along an alternate path entirely. But we're just talking about the normal volume of the river. There's no lake until the dam is completed."
],
"score": [
20,
7
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
6qtvlp | My washing machine has 4 sections: Perm Press, Heavy Duty, Knit and Delicate, and Pre-wash. What's the difference? | My mother said something about using perm press for everything, except towels and sheets go on heavy duty. Thirty years later, it occurs to me I know nothing about my washing machine. ELI5? | Engineering | explainlikeimfive | {
"a_id": [
"dl03vbz",
"dkzzyjz"
],
"text": [
"Pre-wash: clothes are washed a little bit before they enter the main program (use this in case they are full of stains). You need detergent in two of the boxes. Knit and delicate: it doesn't spin as fast, and water is not too warm. I don't know the others. But my gut tells me: listen to your mother.",
"Just noticed my dryer has 4 modes: perm press, timed dry, knit/delicate and air dry. Are they any different? I don't think I've ever used anything except perm press. (Again thanks to my mother.)"
],
"score": [
6,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
6r025t | if you leave an appliance, lamp, charger, etc, plugged into the wall when not in use, does this eat electricity and run up your electric bill? | Engineering | explainlikeimfive | {
"a_id": [
"dl1ba3p"
],
"text": [
"Depends on the device, for a cell phone charger, yes. The older ones use to use quite a bit of power when no phone was connected. Newer ones turn off 99% of their stuff when there is no phone, but they still consume something. As for the other things, well it depends, but stuff like a cheap toaster, no, it contains a physical switch, and has exactly two states, on and off, when off the power is physically disconnected and it uses zero power. Many appliances with physical switches are similar (microwaves, washers, dryers, etc), they might have an on switch with a spring powered timer, and when off physically disconnect power. The modern ones have fancy screens, touch buttons, clocks, wifi, whatever, that stuff stays on when it's off."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6r0ofy | What is the difference between machine learning and deep learning? | Engineering | explainlikeimfive | {
"a_id": [
"dl1gbeg",
"dl1g879"
],
"text": [
"Deep learning is a kind of machine learning. Machine learning is the more general term, while deep learning is generally used to describe programs designed to emulate thought. In a neural network each image or item in the network isn't stored as a single item, but as a series of associations. Instead of an apple being stored as an apple, it would be stored as an association of something like fruit, red, round etc... This is why deep learning hardware is described as a neural network. This is obviously oversimplified but think of a program designed to look at traffic lights. A simple machine learning program could take a look at a traffic light and see green on top, yellow in the middle, and red on the bottom. It would have an idea of what a stoplight was and how to behave around it. This simple program would probably be at a complete loss if show a stoplight mounted sideways instead of vertically. A neural network doesn't rely on a fixed idea of a stoplight, but instead as an association of a device, at an intersection, with three lights that are colored red, yellow and green. Even though this new stop light didn't match any existing lights the program had seen it would likely be able to deduce that this new light was a stoplight. (And yes, I'm from the northeast where our stoplights are vertical.)",
"Machine learning is basically any system that can improve its performance at a task by example. Neural networks (including deep learning) is one way to do that. There are others, such as decision trees, support vector machines..."
],
"score": [
6,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6r12lh | Why is it that we still can't provide clean water to Flint, Michigan? | Engineering | explainlikeimfive | {
"a_id": [
"dl1kb3l"
],
"text": [
"[The water has been safe since at least July 1 of 2016.]( URL_0 ) They're still replacing all of the pipes in the city but since they knew that the pipes would stop posing a risk by early to mid 2016, the work is being done at the same pace as any other large public works project. The project itself will take until 2020. The reason for that is they need to completely dig up every street in the city and replace the water mains which is a monumental amount of work even under the best circumstances. When you read stories about how the water isn't safe they are basing that on the State of Michigan currently recommending that people in the city don't drink their water without first having it tested. The reason for this is that while the city's water supply is safe, individual houses may not be - though that's more related to the age and quality of the lead pipes in the house than it is the water crisis. If you have 100 year old lead pipes in your house they're going to be leaching lead, and there are a lot of residences in Flint with pipes that old."
],
"score": [
6
],
"text_urls": [
[
"http://www.cnn.com/2017/01/24/health/flint-water-crisis/index.html"
]
]
} | [
"url"
] | [
"url"
] |
|
6r239f | How do they make the machines in factories? Is there a factory for factory machines? | Engineering | explainlikeimfive | {
"a_id": [
"dl1r3ji",
"dl1tf59"
],
"text": [
"Yes, machines are made in factories that use metalworking machines, often called [*machine tools.*]( URL_0 ) Sample tools they use (which you can google) include: - Metal lathe - Plasma cutter - Press brake - Punch press - Five-axis (or six-axis) milling machine Check out the YouTube videos from How It's Made to see many examples.",
"Yes, there are factories that makes machines for other factories. I actually work for a company that makes factory machines. We don't make all of the machines we use. However our machines put together circuit boards. And the circuit boards on our machines were made by our machines. If we wanted to make a new machine, we'd tell our current machines to make different kinds of circuit boards. Before we built our machines, we used circuit boards built by other people's machines, and they probably made their machine's by using other people's machines. And so on, until at some point, someone was making those circuit boards by hand. Likewise with everything else in our machines."
],
"score": [
10,
6
],
"text_urls": [
[
"https://en.wikipedia.org/wiki/Machine_tool"
],
[]
]
} | [
"url"
] | [
"url"
] |
|
6r5zr2 | Why do stadium/arena lights take a long time to turn on, yet other lights are basically instant? | Engineering | explainlikeimfive | {
"a_id": [
"dl2mjhv"
],
"text": [
"Short version: It takes a little while for the stuff inside to melt and vapourise. The yellow ones like they used to use for streetlights are low pressure sulphur. the white kind are mercury vapour in either a low or high pressure gas, depending on application. Either way, an electrical arc goes between an electrode and cathode that by itself is not all that bright, but is very hot. The heat from that vapourises the mercury, which takes a minute or so, and when the arc is going through the mercury loaded gas it starts to make a very bright white light. Fun fact: back in the pre-electrical days, the same kind of principle was used by using a gas flame on a block of lime, which made a much brighter and whiter light than just gas flames. It took a bit more work and care for this type of light though, so it was just the lead actors that got the limelights. Stadium lamps are (I think) typically low pressure mercury vapour lamps, or metal halide lamps (which is just mercury vapour with some additional metal halides mixed in) ( URL_1 ) which take a longer time than high pressure mercury that get used in stage and studio and projector lamps. ( URL_0 ) For traditional incandescent lamps, all you need to do is heat up the metal in the filament, and it's the direct glow of the metal that makes light. It just takes a fraction of a second for the metal to heat up. Neon is just the energy flowing between an anode and cathode through neon gas, which glows, sort of like mercury vapour, but there's nothing that needs to melt, so it can happen pretty quickly. Fluorescent lamps are similar to Neon, but the energy by itself doesn't make light - it just excites the phosphors on the inside of the tube, which glow. Older ones do take a second or so to get to the point where the phosphors are glowing fully, but it's pretty quick. As far as I can tell, LEDs work by magic, so I can't tell you how those work."
],
"score": [
23
],
"text_urls": [
[
"https://en.wikipedia.org/wiki/Hydrargyrum_medium-arc_iodide_lamp",
"https://en.wikipedia.org/wiki/Metal-halide_lamp"
]
]
} | [
"url"
] | [
"url"
] |
|
6r6sa6 | Why do so many passenger planes use the Deakin method (dragging the nose and then lifting off suddenly) instead of allowing the plane to naturally lift off and having a slower initial climb? | Airport runways are more than long enough to account for the latter and it should be a lot less strain on the planes and is arguably a lot smoother. I understand that this allows the passenger plane to get to *Vy* faster, but is that the only reason? It seems more risky to passengers and if getting to *Vy* faster is the only reason, it seems like a dumb business decision that puts more stress on the plane and quite frankly, the passengers than what is needed. | Engineering | explainlikeimfive | {
"a_id": [
"dl2r2n7"
],
"text": [
"Noise abatement, mostly. Long, slow climbs over populated areas tend to piss off the whiny bitches who moved in next to the airport and then complain about the jet noise. Just look at what the planes do at John Wayne (SNA). Line up and wait, lock the brakes, stomp on the gas and wait for clearance, then release the brakes and go hurling down the runway. At speed, yank back on the yoke and climb at 20-25 degrees nose up. All so you don't piss off the princesses in Newport Beach. It's also a matter of getting the planes up into the thinner air at the flight levels so they don't burn quite so much gas pushing through the lower, thicker air."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6r7s31 | When locksmiths started producing keys on a large scale for public consumption how did they make them different enough to only open one lock but not change them so much that they would eventually run out of key designs? | Engineering | explainlikeimfive | {
"a_id": [
"dl2ytjw",
"dl30vs0"
],
"text": [
"Locks don't *need* to be totally unique. If you have a few hundred different combinations, that's good enough to stop anyone from accidentally getting into the wrong door with their key. Anyone who wants to make all possible keys would be better served by picking a lock or just breaking down the door.",
"OK, so your basic lock has inside of it a series of spring-loaded pins in a line going back from the key-hole. Each pin can be pushed up to varying heights by the teeth of a key. If you look at a key, the 'divots' on the key are where the pins rest, and you can see that some are higher and others are lower. So let's consider a basic five-pin lock, where each pin has up to five positions. We can think of this like a number puzzle; let's say a lock opens with the pins in the following order: 4,2,4,3,1 Just looking at that, and knowing that each pin has five possible heights, we can estimate there are several **thousand** possible combinations. (1,1,1,1,1 to 5,5,5,5,5) So the odds of one key working in a different lock would be less than 1/10th of 1%."
],
"score": [
11,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6r9pzp | How solar panels work | Need a simple explanation for my grade 5 science students. Most of the videos I've watched are too complicated for me to understand fully, so I need a simplified explanation that 10 year olds would be able to grasp. Thanks in advance! | Engineering | explainlikeimfive | {
"a_id": [
"dl3g2eh"
],
"text": [
"2 layers of silicon crystals are laid on top of each other. One layer likes having extra electrons, the other layer likes giving up electrons. The sun's energy bounces electrons all over but in general they move towards the top layer causing a negative charge to build up and since it took those from the bottom, the bottom is positively charged. At that point its like a weak battery and just needs some metal leads to go to a motor our light or DC to AC inverter."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6rbk2b | How do Maglev trains compare to regular trains? And, why is one preferred over another? | Engineering | explainlikeimfive | {
"a_id": [
"dl3sw3l"
],
"text": [
"Maglev (magnetic levitation) is needed if you want to go much faster than conventional trains. Conventional rails expand when heated and they move when driven over. That limits the safe speed. Maglev is much more expensive."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6rdb8u | How do they make all car keys for the same vehicle different? | Engineering | explainlikeimfive | {
"a_id": [
"dl458bt",
"dl44wcx"
],
"text": [
"they arent, in fact there arent that many combinations for a typical key. there are a series of tumblers, and each tumbler has a few possible inputs, but the possible combinations is probably less than 100,000. Enough that you wouldnt want to try a random key on cars in a parking lot. but not so much that they are all unique either. With that said, the electronic chip is the real blocker, there are trillions of combinations there.",
"They don't Sometimes keys for a certain car type will open a cars of the same make and model. There are plenty of stories of people accidentally getting into the wrong car because their key (either physically or electronically) opened the wrong car. They do make different keys (they're not all the same) but they don't make a unique key for every car."
],
"score": [
8,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6rdbjb | What does it mean for an engine to "break in" and why is it important? | Engineering | explainlikeimfive | {
"a_id": [
"dl45erx"
],
"text": [
"Engines are manufactured to tight tolerances, but nothing is perfect. Cylinder pistons never perfectly match their cylinder walls. Bearings never perfectly match their races. Operating at lower loads and varying speeds enables these parts to \"work out their imperfections\" without sustaining damage. The bearing that's a little bigger on the left than the right wears the race unevenly until it's got the matching imperfections. After this break-in period, all the systems should perform to their specifications across their entire operating envelop."
],
"score": [
52
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
6rdtmn | What dangers could artificially reflecting sunlight as a preventative measure to global warming have? | I read an article a few years ago about releasing chemicals to reflect sunlight and reduce the global temperature that discussed the risks involved but I was wondering what would the likely results be and if this is still being considered. [Article]( URL_0 ) | Engineering | explainlikeimfive | {
"a_id": [
"dl4aphx"
],
"text": [
"You ever hear about the old woman who swallowed a fly? It is kind of like that. Reflecting sunlight at a large scale will result in large scale climate change. Some of it might be good, like lowering the average global temperatures. Less sunlight means less evaporation which means less rain. In saving the coast, you could very well turn your food producing plains into desert. That's just one example of the sort of unintended consequence you might get by effecting such a large change."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6rhjim | Why are most surfaces in and around swimming pools slippery and hard as a rock? | The other day my brother's friend tried to do a backflip at a pool, slipped, and ended up with stitches in his head. We started wondering why NO ONE we asked has seen or even heard of a pool with soft or cushioned edges. This could possibly do away with "No running or diving" rules and would be much safer with little drawbacks (that I can think of). Might this be a revolutionary idea??? | Engineering | explainlikeimfive | {
"a_id": [
"dl5302j"
],
"text": [
"To avoid the loss of water into the surrounding soil every surface in contact with a body of water needs to be completely waterproof (impermeable). For in the ground pools all the cost effective ways of doing this use hard materials that are too solid for water to seep through. While softer materials for pools do exist (see: those above ground pools made of rubber) it would generally be impractical for an in the ground pool to use a flexible material as the motion would make it much more prone to cracking over time. Also if an edge was too soft it could risk people slipping into the pool. If this happened and someone drowned as a result it could easily be argued that it was the pool maker's fault. No one wants to get sued (or drown somebody I guess) so nobody takes the risk."
],
"score": [
13
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
6rjv02 | What are those balls on either rear sides of a boat? | Edit: Found out they are called float ball scuppers! | Engineering | explainlikeimfive | {
"a_id": [
"dl5j0l8",
"dl5j3vv"
],
"text": [
"Bumpers, poly balls, whatever you want to call them. They allow you to tie up to other boats or a dock without scratching your boat. Basically shock absorbers.",
"Are you talking about these? URL_0 They're called fenders. Their job is to stop the boat and dock from damaging each other when the boat is berthed."
],
"score": [
4,
3
],
"text_urls": [
[],
[
"https://upload.wikimedia.org/wikipedia/commons/thumb/f/f1/Fender_protecting_the_side_of_a_sailing_vessel.jpg/220px-Fender_protecting_the_side_of_a_sailing_vessel.jpg"
]
]
} | [
"url"
] | [
"url"
] |
6rkj0l | My speedometer goes up to 160mph but the max speed of my car is 115mph. Why does the speedometer go so high? | Engineering | explainlikeimfive | {
"a_id": [
"dl5o3lo",
"dl5r5yu"
],
"text": [
"Most are designed so that the 55-65 MPH position is \"attractive\". Then it's just linear extrapolation to fill out the dial. It's all styling, so that the dashboard looks good. The mechanism is then engineered to look that way and be inexpensive to manufacture.",
"And often the dashboard is not only used for a specific car. Think of the same model with different motors. Some can only go to 115 but a bigger engine may can go to 150 mph. And that's not only for the same model. Even different models from the same brand can have the same dashboard. While most of those dashboards go up to more than the official car speed... But for example.. if have a really long downhill road you may can get over this limit. My old car's official max speed was 190kmh (~118 mph).. but on a good day on the Autobahn I got it to 230 kmh (~142 mph) (according to the speedometer)"
],
"score": [
3,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
6rkrk5 | most electricity application today is DC but a lot of electricity is transferred using AC then transformed to DC. Why dont we transfer it over electrical wires just using DC? | Engineering | explainlikeimfive | {
"a_id": [
"dl5q4ia",
"dl5qnwv",
"dl5wiar"
],
"text": [
"This is what Thomas Edison's idea of the electrical grid first looked like. He had DC generators putting out DC power every few miles. However, it turns out that you lose a lot of power transmitting DC over long distances. AC is much more efficient and allows you to build your power plants much farther apart.",
"The problem with DC is that it is difficult to make DC transformers without moving parts whereas an AC transformer is just two coils of wire next to each other. When you transmit power you want to transform it to high voltage, then step it down as it gets into cities, then step it down again before it gets to your house. If they were all DC transformers it would be a lot more expensive.",
"DC transmission has not gone away and is actually becoming more common, thanks to more recent developments in high power solid state technologies. It has some advantages over AC * Joining two AC grids requires that they operate at the exact same frequencies, absolutely in sync. This can be difficult for various reasons, but DC interconnection avoids those issues. * If you try and run an AC cable under the sea, you run in to problems caused by the capacitance of the sea itself, and power losses that make it impractical over long distances. DC avoids this e.g. the UK and Ireland are connected by the [East/West Interconnector] ( URL_0 ) that uses DC. It also means Ireland and the UK don't have to be synchronised as above. More examples: [HVDC] ( URL_1 )."
],
"score": [
8,
8,
5
],
"text_urls": [
[],
[],
[
"https://en.wikipedia.org/wiki/East%E2%80%93West_Interconnector",
"https://en.wikipedia.org/wiki/High-voltage_direct_current"
]
]
} | [
"url"
] | [
"url"
] |
|
6rlxlq | How much fossil fuel usage do electric cars save (compared with gas engines) as the electricity they use is often generated from fossil fuels anyway? | Engineering | explainlikeimfive | {
"a_id": [
"dl5zzrs"
],
"text": [
"They don't really save that much in fossil fuels if they are powered by them originally, but you can't power a gasoline car with hydroelectric, or solar, or wind, or nuclear power. But another major benefit is that even if you ultimately use fossil fuels to power an electric car, those fuels can be burned in a power plant away from the center of the city and pollution scrubbed much better than a car that needs to carry around its exhaust system."
],
"score": [
5
],
"text_urls": [
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]
} | [
"url"
] | [
"url"
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