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bw0959 | Why are the front of commuter trains flat? | I’ve lived in or near 3 different cities (DC, Philly, and Trenton) and all of their local metro trains have had flat fronts. Wouldn’t it make more sense for them to be shaped more like cars or Amtrak trains when it comes to aerodynamics? I don’t understand how the flat front design could be efficient. | Engineering | explainlikeimfive | {
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"There are 2 main kinds of air resistance or drag at low speeds: form drag and skin drag. Form drag refers to drag resulting from a objects geometry on the front/leading or end/trailing edges while skin drag is caused by friction with the air along the objects length as air moves over its surfaces. It turns out that for aspect ratios greater than 100:1 (an object 100 times longer than it is wide) that the skin drag will always be more significant that the form drag, so no matter what the front or end of the train looks like, the shape along the sides matters more. Thus if you are going to sink time and effort into reducing one, skin drag is the best bang for your buck and the flat front really isn't that bad. This doesn't mean a pointed end isn't helpful though, especially as the average speed of the train increases.",
"You're right: it's not an efficient design for high speeds. And while it seems like your local subway or commuter rail might be going fast, there are practical speed limitations that normally prevent these trains from getting up to, or staying at a high speed where aerodynamics would really matter. The main one being, the stations are close enough together that the train barely has time to get up to speed before its starting to brake for the next. A secondary factor: local trains are frequently electrically powered. Regional trains like Amtrack are not. So the impetuous to be fuel efficient and thus aerodynamic only is a factor for gas-powered trains.",
"After you factor in all the weight of the entire train, and the long snake like shape, and the lower speed, i don't think there is much savings at all. The cost savings of having similar shaped cars (and manifacturing/maintenance savings) probably outweighs the energy savings of having a different shape.",
"There is the practical standpoint of maximizing interior face. A box has more room than an oval. Commuter lines also need to worry about hitting people or running over them. If a person is on the track and the train hits them, a flat surface will do less harm than a point and is less likely for someone to get sucked under. Cars in recent times have modified bumper standards that prevent [too pointed of a front end]( URL_0 ). Now they need to be like [cow catchers]( URL_1 ). The flat face, like a school bus, can allow the driver to see anything in front."
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bw89oj | why does the water pressure drop a little bit once the water heats up? | When I have a shower, I leave the hot water on to heat up and I can hear the drop in pressure when it's done. I also notice this when using the kitchen sink and the water seems to become less oxygenated(?) Always wondered why, if the water heats up in the pipe shouldn't it expand and the water pressure rise? | Engineering | explainlikeimfive | {
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"Do you mean water flow? Usually rubber in taps expands when it heats so the flow decreases."
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bw8wsg | Planes use flaps to land and to take off. So why do they retract them while they are on the ground, ie why not just leave them deployed? | Engineering | explainlikeimfive | {
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"People keep mentioning the possibility of damage to extended flaps (which I'm sure is a secondary reason), but the main reason is to keep the plane on the ground. Flaps are designed to create significantly more lift at low speeds at the expense of increasing drag. They deploy them on takeoff and landing so the plane can transition to and from flight at lower ground speeds, which reduces stress on the airframe and landing gear and is just easier for the pilot to manage. If you leave flaps deployed on the ground you risk gusts of wind lifting one or both wings while the aircraft is parked. That's bad. Since they also increase drag (especially in landing configuration) in windy/gusty situations they also increase the forces on the brakes and chocks while parked. The risk of the aircraft moving uncontrollably, tipping, flipping, etc is all significantly increased with the flaps down on the ground. So they retract them when they don't need them.",
"All the reasons everyone has given, but also: taxiing with your flaps down at the very least used to be a signal for hijacking. It possibly still is. I know if you for any reason are going to be taxiing with your flaps down you must notify the tower. Source: URL_0"
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bwfkff | How do they trap the air inside bubble wrap without leaving a hole for the air to escape through? | Engineering | explainlikeimfive | {
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"The bubbles aren't blown up like a balloon; rather two sheets of plastic are \"stamped\" together in a honeycomb pattern, leaving empty (air-filled) bubbles."
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bwkzdw | Why do automatic car windows have to exert so much force that it can break bones or cause serious injuries, at the least? | I mean I can understand that the glass mechanism is heavy and to move it, you would need a lot of force. But it's possible to design a gearing ratio to provide the exact force needed to push the heavy window up, without it being dangerous. So why are car windows designed with the potential to cut fingers off? | Engineering | explainlikeimfive | {
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"How many times have you seen that happen?"
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bwldpa | How are we able to build oil rigs and other infrastructure under the ocean? | Engineering | explainlikeimfive | {
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"There are a number of different types of 'oil rigs' in the ocean. In relatively shallow water (less than 200 feet, or so) we can use 'jack up rigs'. These are triangular shaped floating vessels with long legs on the three corners. When the rig is where we want it to be, we jack the legs down to the bottom of the ocean and lift the vessel above the water 25 to 50 feet. We then drill wells from that platform. When we are finished we jack the legs back up, lowering the vessel back to the water where it can be floated to a new location. Drill ships are ships that have drilling rigs on them. They can work in very deep water. The ship is floated to the location where the wells are to be drilled then anchors are taken out from it in all directions and dropped. The anchor cables are attached to machines that pull or slack the cables as necessary to keep the ship in one place, even in high winds or heavy seas (big waves). This is called dynamically positioning. Some wells are drilled from platforms that are giant structures that are floated out to the spot where the wells are to be drilled and then stood up and anchored to the sea floor. These can be as tall or taller than the largest buildings on earth. There are other methods that are a hybrid of these or similar in some ways. All of them are very expensive and require lots of engineering.",
"There isn't a lot of actual building that happens underwater. We're certainly capable of it, but it's expensive and time-consuming. Depending on what \"other infrastructure\" you're talking about, most of it is built above-ground and sunk, or we build a dam of some sort to keep the water out while we build, then let it back in when we're done. Some \"oil rigs\", in fact, aren't even \"underwater\". For example, as can be quite amazingly seen in the Mark Wahlberg movie of the same name, the infamous Deepwater Horizon exploration rig is actually a giant boat. So mostly, we don't if we can get away with it. When we can't we try to keep it down to just assembling large pieces to keep the costs down. When we do build underwater, it's mostly limited to welding or concrete. Welding actually works better in the absence of oxygen, so most welding techniques already use some form of protective gas to protect the weld. At that point, it's more about the logistics of finding welders who can dive (or divers who can weld) and getting the resources down to them. Concrete doesn't \"dry\" like most would expect, it's actually cured via a chemical reaction. That chemical reaction is exothermic (gives off heat) so curing concrete underwater where that heat is easily carried off actually creates a stronger structure--although it does slow the cure time down some. Some links you might like: * URL_1 * URL_0"
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bwrhvi | How do guns work? | Like for example a revolver, how does it shoot a bullet so far and so strongly? | Engineering | explainlikeimfive | {
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"When you pull the trigger on a double-action revolver, a couple of things happen. 1. The part holding the bullets rotates into place to align with the barrel. 2. The hammer pulls back. 3. Once a certain point is reached the mechanism pulling back on the hammer drops out and the hammer springs back and strikes the back of the bullet. The hammer strikes a small part on the bullet called the primer, it's a tiny cap filled with basically the same stuff as pop snaps, rocks that if you rub them together they cause a spark, but they are in a tiny sealed chamber, so the spark is really strong. This lights the gunpowner in the bullet casing. Gun powder, when lit usually burns really slowly, but when packed closely together it burns really quickly, having nowhere to go, the energy is released forward, it expands the casing just enough to release the lead bullet a bit and push it down the barrel. Then Physics takes over! When the gas exists the barrel behind the bullet it also kicks the gun back in the opposite direction, this gives the bullet a ton of momentum, speed. Tiny bullet, going at really high speed, translates to a lot of power.",
"The exact way gun work changed over time and depend on the design, but the overall principle stay the same. You have a propellant that you ignite, which cause an explosion. An explosion is a rapid expansion of gas and if you contain this explosion this leave only one way for the gas to expand, which is down the barrel. But there is a bullet is the way so the gas have to expel the bullet out of the barrel to exit. It's a bit like when you blow a straw with a bit of paper in it, the pressure push the paper ball outside of the straw. But instead of you blowing it's an explosion that force gas to expand, instead of a straw it's a metal barrel and instead of a paper ball it's a bullet. & #x200B; The main part here is the containment of the explosion. If you just make the propellant explode on the ground, it would be huge of an explosion (depending on the size of it). But since the barrel is often somewhere between 15 and 4mm in diameter, all the force of the explosion is concentrated in a really small area behind the bullet."
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bx3i5m | Why do charging cables not spark when held close to the intended device? | close as in almost touching but not inserted. | Engineering | explainlikeimfive | {
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"Something not mentioned yet is that most high power chargers only supply 500mA until a device that supports more power is detected, it then ramps up the amperage to 2 or 3 amps (3000mA).",
"The charging cable doesn't have enough voltage to jump the air gap to create an arc. This makes low voltage electronics pretty safe to use. USB for instance is 5 volts, while outlet power is 120 volts (or 220v depending where you are)",
"The voltage on a USB charger is only 4.2 volts and a max of 2.1 amps. This is extremely low lower and unless released quickly with a capacitor will not really spark. Small electronics, by design, operate on a tiny bit of power, most of it going to the screen. The batteries can get very hot and burn even but to get a spark your need quite a bit more voltage.",
"They do, you just can't see it because the voltage isn't high enough to overcome the resistance of air at an appreciable distance, if you make the gap smaller, it will arc across air. Tiny tiny voltages of like 5.2 or 4.2 volts, aren't enough potential to cause a visible spark. & #x200B; Noted that a circuit must be completed for this to happen, so just touching any part of the device will not do, rather only parts of the device that will complete the circuit."
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bxetd9 | What are the technological/physical limitations regarding smartphone camera advancements? Will we ever see them match traditional ones? | Engineering | explainlikeimfive | {
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"Small lens size limits light entry, so no, will probably never match the quality of a traditional SLR"
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bxk2v4 | What makes boilers so dangerous to be around? | Quote from /u/ABomb117 from [this TIL thread]( URL_0 ) > You know those reddit threads that are called “Reddit, what do you NOT fuck with?” > > Boilers. You do not fuck with boilers. There is a reason why you have to be a certified boiler operator. --- * What makes them so dangerous? (I get it's pressurized steam, but is there anything else?) * Are pressure cookers just as dangerous? Or Hot water heaters? * Is it just poor maintenance? | Engineering | explainlikeimfive | {
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"Look up ntsb accident videos. Many of them are the result of failure to control pressure, either due to reactions, heat, or mechanical.",
"Pressure is a hell of a beast. I remember a mithbuster episode where they manipulated a boiler so that the pressure increased without regulation and the thing whent through 2 story of a building. Over that there is the fact that if it is not well mantained it can litteraly explode causing great structure damage to the building. A pressure cooker is not as dangerous as it hold less pressure than a boiler and it has only one opening making it easyer to secure."
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bxl8w6 | How are complex functions like trigonometric or hyperbolic calculated on computers or scientific calculators? | Computers either have an integer processing unit and/or a basic floating point unit. Using series expansions must take a lot of time if high accuracy is required. So how is say, tan(34.5) calculated so fast? | Engineering | explainlikeimfive | {
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"Because most calculators of limited power don't use the slow functions. They use specifically chosen approximations, Taylor series, etc. and optimise the algorithm towards whatever the processor does best - e.g. integer operation, fixed-point or floating-point, multiplications, additions, bitwise operations, etc. If you choose the right algorithm it can converge to a calculator-number of digits very quickly, probably only a handful of iterations of maybe a few dozen operations each. Even at 1KHz, that means almost no time at all to converge to something you can display to 10 decimal places, even if you have to prep the numbers involved, use a weird algorithm, and then convert back from integer to float at the end.",
"Simple answer. Because the computer or calculator is running really fast. A simple floating point operation or integer can be done in one clock cycle. And there are dedicated hardware to do special functions, but let's ignore those for now. With high end calculators running 10mhz processors that means they can do 10 million calculations per second. So yeah that's basically instantaneous to you."
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bxmnr2 | How do American 20 amp plugs/outlets safely carry more current than their 15 amp counterparts ? | I'm referring specifically to the NEMA 5-20R socket. Obviously the neutral blade is larger and so is capable of carrying more current but the Live (Hot) blade is the same size as a 5-15 plug so how is it able to safely carry 20 amps ? | Engineering | explainlikeimfive | {
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"They have bigger wires. You have to use 12 gauge wires for a 20A outlet, whereas you can use 14 gauge wires for a 15A outlet."
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by02sc | Why are utility poles made of wood? | In Southeast Michigan, from what I've noticed, utility poles carrying electrical wires, phone wires, etc. are made of wood. On the other hand, light poles are made of metal. Why is one material used for one kind of pole and not the other? Or why not just use the same material for both? | Engineering | explainlikeimfive | {
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"wood is cheap and nonconductive. light poles where the wires are stretched from pole to pole can be wood as well. but light poles where the wires go down into the ground need to be hollow because you don't want the wires exposed to pedestrians, and that's easier with metal since it still needs to be sturdy and thin (since they're often placed by sidewalks that they'd otherwise block)"
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by4ga7 | Why are the back wheels of wheelchairs slightly angled inwards? | Engineering | explainlikeimfive | {
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"That's called camber. Negative camber is when the bottom of the wheels flare out. Negative camber improves handling on turns by increasing the grip on the center of the tire as the forces cause the vehicle to lean on that side. Makes it less likely to tip. Negative camber also provides an outward force on the wheels when going straight that helps it maintain a straighter course."
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by6m2o | How does a property surveyor actually decide where the property lines are? | Engineering | explainlikeimfive | {
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"Land Surveyor here. Typing from mobile. In the U.S.A., and specifically Florida, we use plats for original surveys done, older surveys sometimes being 100+ years old, these surveys were good at the time, but not on par for today's standards. Due to changes in zoning laws and sometimes sub-dividing property, you will find that there is sometimes multiple pins/rods/concrete monuments/wrenches/pine/spoons where a corner of property could be located. I say the older historical evidence is the property corner. For newer corners, surveyors now use a piece of rebar with a plastic cap. This is just for your local evidence. To also determine your property for a single individual, surveyors will look at the block the house is on, hopefully a 4-way intersection (easier to use squares). This way surveyors and the city property appraiser/record keeper/city planner can see how a block was originally designed and measured. This also insures us that if multiple \"pins\" are in a line, that the pins are still reliable; this is if the houses are in a traditional rectangle block. To circumvent future problems, city engineers also ask to put all new peoperty coordinates in a \"state-plane\" system, meaning we have a coordinate where your property corner is at. We find evidence with what you said a metal-detector, old sketches of the house, the math on the sketches (Bearing and distance), neighbors pins, house location, and similar things done on previous surveys and sometimes no found surveys. The problems that occur with this are line-of-sight, encroachments, and people aggravated you are on \"their\" property."
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by882h | How do sea captains "fight" a storm? | On shows like Deadliest Catch, when there's a storm, the captain is showing struggling to keep the ship afloat and (I assume) in the same position. What is he actually doing at the controls to make this happen? | Engineering | explainlikeimfive | {
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"There are a few strategies. Usually they revolve around keeping the bow (front) of the ship pointed toward the waves. A wave on the side can much more easily roll the boat. If you've ever seen surfers paddling out through waves it's a similar concept. Nose on the ship is designed to cut through water. Anyways the seas can come at odd intervals and directions and keeping the boat lined up can be difficult work.",
"Ships are long and narrow, and a large, steep wave will \"push\" a ship. Since ships are designed to sit on the surface of the water, as a wave rolls towards a ship on its side, imagine seeing it from the rear: the low part of the wave gently \"pushes\" the beam, or side, of the boat, tilting it slightly as the ship's hull attempts to \"climb\" to the top of the wave (again, they float.) If the wave is small enough, this happens easily and the ship rolls over it, though significant rocking occurs. If the wave is large enough, however, you may be able to picture the ship being tilted so far on its side as it tries to climb the wave, like a skateboarder or snowboarder in a halfpipe, and the ship can capsize, which is one of the two worst things to happen to a ship (hull breaking in half is the other one.) If, however, you point the ship straight into a wave, now view the ship from the side (\"beam\"). A ship's bow (the nose) is pointed and sharp. It literally breaks the surface tension of the water as the ship moves around, and this is the first line of defense against larger waves. A big wave may push the ship's hull up at first, but the wave's energy is literally split by the bow, greatly reducing how much force subsequently pushes the ship up as the wave continues. The ship *is* pushed up, but it has already broken the surface a little bit more than if the wave had come from the side, and now you can see also that any non-circular or non-square object is harder to \"flip\" or rotate around its longer side. Think of how easy it is to roll a pencil, but it won't flip from the tip to eraser nearly as easily. Same with a surfboard or a boat. So because of the length of the boat, it takes a lot more force to flip it over that way. Even a very steep wave might terrify a crew as a ship seems to go vertical, but a proper, sea-worthy ship may survive a much steeper wave than our intuition tells us. They are still extremely dangerous, and even the largest steel ships, both merchants and Navies, will track and avoid the largest storms. That being said, pointing the ship *into* oncoming waves is the best way to keep the ship floating and right side up once you start hitting heavy waves. Wind and uneven waves themselves can make this difficult, as they may change directions so that not all of the waves are coming exactly in a straight line one behind the other. The wind can also push around the superstructures (the \"sail area\", all area above the waterline) of larger ships, causing them to drift and point in different directions than what the current is pushing on the hull. Both of these matter, and it can be confusing to try to determine if the wind or the water is having more of an impact on a specific angle of the ship. Water is far more dense than air, so generally has more force, but for some ships there is quite a bit of superstructure (\"sail area\") and they can push it around quite a lot. Finally, a ship captain must be aware of all 3 movements of a ship: Yaw, Pitch and Roll. Roll is the easiest to remember, it is how much the ship rotates if it were like a rotisserie, or a pencil; pitch is the angle from the bow to the stern (front to rear) relative to a flat, calm sea (or tangent to the ocean floor, since the earth is round); and finally yaw is the compass rotation of the ship looking down from above. If the ship is yawing to one side it will \"crabwalk\" through the water. So there is quite a lot to consider when in truly big waves. Source: I was an officer in the Navy.",
"Several good comments have talked about survival by heading into the swell, but if you’ve lots of open oceans and are not worried about getting to a destination on time, another strategy is to Run before the Storm - that is, turn the ship around, have the wind coming in over the back and (if not a sailing ship) speed up to approximately the speed of the waves, if you can (not a significant issue if you can’t). It means you essentially surf with the storm. The advantages of this if you can do it are that it’s a lot more stable and a lot more pleasant for everyone on board. With the wind behind you, the relative wind over the deck(ie the wind you feel on your face) is much less, and provided there’s no cross swell (waves coming at random angles) the boat doesn’t move around as much. The disadvantages are that unless you’re in the open oceans, you can run out of sea fast! Source: sailed a lot as a kid. Of course, the best tactic in a storm is to go and sit in the pub/bar/tea shop. Why be there at all, if you can possibly avoid it? As you can see, I was a fair weather sailor! Edit: punctuation.",
"As a Bering sea Fisherman I can add to this. The waters we fish in the northern latitudes not only bring about some choppy and rough wave action, but the approach the captain must take to each buoy (boo-e) depends on the tides (current) and the wind as well. Our bags that are in the water are easier to pull up onto the boat with the correct approach. I have fished in 30ft+ waves with winds up to 60-70mph. With a favorable approach it's possible for us to keep fishing. With an unfavorable approach it is deadly and almost impossible. TLDR; Captains don't \"fight\" the storm, they have to go with flow."
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byae87 | how do samd bags hold back water ? | Engineering | explainlikeimfive | {
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"A proper sandbag works in three ways: 1. It’s not over filled, so the sand bag can conform to the shape of the wall you’re building. This lets the sand “fill” the gaps that would otherwise exist in between full bags, and grants full coverage of the area. 2. It acts like a trap for silt, soil, and clays. As the water moves into the sand, all the “murk” it’s picked up from the streets, ground, river banks, etc, get caught in the sand. These particles fill in the spaces between the sand, making a more complete barrier. 3. As flood waters try to move through the bag, they’re slowed down. This forces most of the water to go around the bag, greatly slowing the amount of water the sand actually has to deal with. So, in short, as the water tries to get through the sandbag wall, it meets a lot of “solid object” in its way. Only so much water fits through the sand at one time, greatly reducing the amount that can get through. Enough sandbag layers will slow the amount to a trickle. That trickle deposits sediment and such into the sand, which begins to plug up the gaps in the sand. This further reduces the amount of space that water has available to squeeze through. Sandbags are not watertight, however. Generous flooding will often produce a bit of leakage through the sand wall. The goal in this case is to slow it to a point that any damage is superficial at best."
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bydbqb | Why do window AC units use so much energy? | Engineering | explainlikeimfive | {
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"Window units are actually terribly inefficient. Because they are classified as an appliance the energy efficiency requirements are considerably less strict than with residential hvac systems. Additionally your apartment is presumably older and therefore not well insulated this adds a great deal of thermal load to the space. In general the best option is to leave the system on all the time. Turning the unit off causes the humidity to rise and the structure and its contents to increase in temperature.",
"In addition to the points other have made, it might be more efficient to leave the A/C on, instead of turning it off when you're not home. While it might be set to \"cool,\" it should only kick on whenever it starts getting over your target temperature, so it's not running constantly. If you turn it off when you're not gonna be home for like 9 hours, it'll have to work harder when you turn it back on to get it back to that target temperature. It might use less energy if it you leave it on, and it runs periodically, each time trying to overcome a smaller temperature differential than that 9 hour temperature differential."
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byhp4o | How does a spoiler in a car work ? | Engineering | explainlikeimfive | {
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"You know when you're driving down the highway on a nice day and you stick your hand out the window and feel the air moving around it? You tilt it up and the force of the wind almost lifts your arm for you. You tilt it down and it pushes your hand and arm towards the ground. The spoiler works the same way. It has that downward tilt, which pushes the back of the car towards the ground and gives it extra traction.",
"Faster you go, the more air blows onto it. The spoiler is angled I'm such a way that the air blowing over it pushes it down into the ground, creating what's called downforce. That allows you to have more grip in the tires as if the car was heavier than it actually is.",
"A spoiler is a device that spoils the flow of air. So if something would create turbulence and therefore drag you can place a spoiler in place to reduce the turbulence. Spoilers can work in different ways. One area where turbulence would normally occur is on the back of the car. In slow speeds the air will pass over your car and down behind it. However if you increase your speed the air will start separating from the surface and go straight back. This creates a zone of low pressure air behind the car sucking it backwards. So a carefully designed spoiler in this area will usually help reduce the drag on the car. It can for example push the air down behind the car or create turbulence that makes it easier for the air to go around the corners of the car. Note that you should also not confuse a spoiler with a wing. Wings are intended to create down force that helps the car around high speed corners and will actually increase the drag on the car as opposed to spoilers which will decrease the drag.",
"I’ll start by clarifying that there’s a difference between a wing and a spoiler, and they don’t do the same thing. The first two responses got it wrong, but it’s something that is commonly misunderstood, so they’re not alone. Wings are used to push the car into the ground, which generates more friction on the tires, increasing grip/traction. This is “aerodynamic downforce.” Essentially, an airplane wing turned upside down. Wings generally stand off the bodywork of the car. Spoilers work to disrupt air flowing close the car in ways that aren’t efficient or desirable, including turbulent air near the car that causes drag, reduces overall downforce, and/or too much noise. One key location for spoilers is the rear, where the spoiler works to free the air swirling around the rear window, and at the back of the the trunk that would otherwise pull backward on the car (like eddies in a river). Another way to think of it is that, by messing-up the air that’s close to the car, the air flows around the car are much smoother (“laminar”), so the car performs better. Spoilers are all over the car, too - in the front air dam, on the underside of side mirrors, etc. Spoilers can generate their own downforce too, but its often secondary to the job of disrupting other bad air. Spoilers are generally closer to the bodywork than wings, and are often molded into the trunk lid and fenders. Does that answer your question, or are you asking also about how wings and spoilers actually use air to create negative lift (wings) or reduce/disrupt/increase/redirect air and air pressures? [edit] I thought of another, more ELI5 way to describe what a spoiler does: think of a river flowing over a hole. The water will want to fall into the hole, but since there’s water in the hole already, it’ll push some of that hole water out and up in a rough way, mixing with the smooth water and swirling around (turbulence), causing the water flowing around it to slow down. But if you were to add a flat stick (spoiler) before the hole, it’ll kick water up and away from the hole, smoothly (laminar), so it passes over the hole faster (with less drag). A spoiler works in a similar way on a car.",
"Spoilers are for turbulence. Wings are for downforce. Dont get them mixed up. The spoiler on a road car is designed to reduce turbulence. The less turbulence on a car the less drag. Lower drag means lower fuel consumption. They have nothing to do with 'pushing the car down'"
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byidn5 | I understand how igloos stay insulated as a result of building fires inside them, but how do the emissions from the smoke get ventilated out of the igloo without suffocating its inhabitants? | Engineering | explainlikeimfive | {
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"Normally you dont put a fire in an igloo. The purpose is not to make the igloo warm, but to make it not cold. So around -5 to 0 celsius is fine."
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bywmk6 | Why are most eggs, egg shaped and some eggs are spherical? | Engineering | explainlikeimfive | {
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"'Egg-shaped' (ovoid) eggs have the advantage of *not* rolling in a straight line - particularly useful if you're a bird that nests on high ledges, cliff tops, etc - in these types of birds, evolution has had the effect of ensuring that only the genes of ovoid-egg-laying birds survive to the next successive generation.",
"Birds and most reptiles hold their eggs inside them for a longer period, resulting in eggs that are larger in comparison to their body than the eggs of things like fish and amphibians. So the traditional egg shape one thinks of associated with chicken eggs is mostly an adaptation necessary to fit through a comparatively small cloaca compared to the size of those eggs. For creatures like fish and amphibians, almost all development, including fertilization, occurs after the eggs are laid, so the egg can afford to be very small. And for a very small object, a spherical shape is the most efficient since it minimizes the amount of surface area per unit of volume."
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bywp1i | Can you accidentally open the emergency exit door on a plane mid-flight? What would happen if you did? | Engineering | explainlikeimfive | {
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"Almost all doors on airplanes open inwards. This is also the case with the emergency exits. During a normal flight the cabin of the airplane is pressurized. The pressure inside the airplane is keeping the door shut with a very high force. So any human does not posses the strength to open the emergency exit in flight. And even if you had the strength the door handle and the door itself would not handle the forces and would be destroyed before it would open. If you were able to do this then all of the air in the cabin would rush out the hole. If you are standing close to the hole and is not secured in place then you might be pushed out with all the air. It is also possible for debris of the emergency door or slide could go back and hit the tail plane damaging it. Other then this the loss of cabin pressure would pose a danger to the crew and passengers due to lack of oxygen. The pilots will normally put the airplane into a rapid decent in order to get into thicker air with more oxygen. They will then fly to the nearest runway and land. There have been several cases where similar things have happened, none involving any doors opening inwards, and these types of accidents are normally quite safe.",
"No you can’t, the doors are designed so that the door forms a sort of wedge and can’t be pushed out. That’s why when you see someone taking the emergency doors off in a movie (like sully) they pull the doors inside the cabin, rotate them, and then they throw them outside. If somehow you managed to break through all the metal reinforcements around the door and essentially punched a hole in the side of the aircraft, your results would vary with altitude. Let’s assume we’re at 30,000ft. At this altitude you would experience explosive decompression and a lot of things would be thrown outside the aircraft. Assuming you managed to get your safety belt on and didn’t forcefully dismount the aircraft at altitude, you’ll now notice it’s exceptionally hard to breathe. This is because the air is too thin at this altitude and all you’re getting is nitrogen. The oxygen masks will deploy, and if you’re still conscious you’ll (hopefully) put yours on. Your pilots will attempt to maneuver the severely crippled aircraft down below 10,000 ft, to breathable air. The aircraft skin will have been ruptured when you blew the door out and will peel back, reducing the control the pilots have, and eventually the aircraft will just plummet to the ground/ocean"
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byx0gf | How a gyrocopter works | I read that it gains lift by upward moving air spinning the autorotors and giving it lift... But the way that sounds, it seems as though the gyrocopter needs to fall in order fly. But if it's flying, it's not falling... Can you see why I'm incredibly confused? | Engineering | explainlikeimfive | {
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"Falling is a relative term. If you get sucked into the air by a tornado, you're still falling through the air toward the earth, but the air around you is moving so quickly that you \"fall up\" faster than you \"fall down\". You're not wrong to think the autogyro has to fall in order to fly, but it falls in a very specific way. The rotors are tilted, and that means the direction of the air \"looks different\" to the rotors than it does to a person. As long as the vehicle is moving forward in the air, the tilt of the rotors means the air is also moving up through the rotor disc, generating lift. So, the vehicle actually \"falls forwards\" to generate lift, instead of falling down. That's why they usually have to get moving forwards before they can take off, even though they sort of look like a helicopter, which can most certainly just go straight up - an autogyro has to fall forwards fast enough to generate lift so it can fly."
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byzh7l | What's the difference between a number 2 pencil and a pencil that isn't labeled number 2? And if number 2s are almost always required why not just only make number 2 pencils? | Engineering | explainlikeimfive | {
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"The number describes the hardness. Different numbers are made mostly for artists, who want different effects when they draw with pencils.",
"It's the hardness of the graphite core. A number 3 pencil will have a much harder graphite core. URL_0 > pencil’s location on the HB graphite grading scale depends on the hardness of its graphite core. The hardness of the graphite core is often marked on the pencil — look for a number (such as “2” “2-1/2” or “3”) — and the higher the number, the harder the writing core and the lighter the mark left on the paper. As the pencil core becomes softer (through the use of lower proportions of clay) it leaves a darker mark as it deposits more graphite material on the paper. Softer pencils will dull faster than harder leads and require more frequent sharpening. Hope this answers your question",
"The #2 specifies the hardness of the graphite inside the pencil. The harder the graphite, the lighter the color that gets made. #2 pencils are usually specified for machine-readable documents because that's what the scanner is set for. Other grades/hardness of pencils are used for other items, such has carpenter pencils being much harder because they have to be drug across materials like concrete."
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bz5lvl | Why is zipper merging (when a lane ends) better? | Engineering | explainlikeimfive | {
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"It's effective for the same reason stop signs are effective - and by that I mean it's effective only when EVERYONE does it. If everyone knows to let one go on one side, then one on the other side, repeat, it all works efficiently and quickly. But the problem is that everyone is kinda doing their own thing - and when some people are merging \"properly\", some people are randomly holding back to let others in that have no business merging in at that moment, and some people are trying to jam themselves in way back at the start of the merge, it all falls into chaos. Zipper merging isn't MUCH better than other methods, but it is a proven effective method when done properly. We just lack an effective way to get everyone on the same page, and unless everyone is doing it the same way, no matter what that way is, it will always be chaos.",
"It is absolutely the best way to deal with traffic. Traffic during congested times can be measured with physics similar to fluid dynamics. Think about a pipe. The place where the pipe gets narrower causes greater pressure, and in turn, slower flow. The sooner you make that narrowing, the earlier the traffic slowing occurs. Therefore, utilizing all lanes for as long as possible creates the best traffic flow."
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bzamp4 | Why do instruments sound different if sound is just vibrating air? | Engineering | explainlikeimfive | {
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"It all has to do with what they call timbre. Different instruments may be capable of playing the same note or pitch, but they all do it differently. Not only is the pitch (or frequency of the note) being sounded, but also other frequencies get sounded, too. These might be overtones, or multiples of the intended frequency, or other non-multiple frequencies. Which additional frequencies are sounded, and their relative strengths compared to the pitch frequency, color the overall sound. That is the instrument’s timbre. The timbre is a function of many properties of the instrument. An instrument that creates sound through cavity resonance, like a clarinet, will excite different frequencies than an instrument that creates sound through vibrating a string, like an electric guitar. And then different models of the same instrument can excite different frequencies through the use of different materials, or different playing skills, or slight changes in design, etc. Hope this helps!"
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bzfkkz | How come they use heavy lead-acid batteries for conventional cars? | Why do they use the heavy and bulky lead-acid batteries in conventional cars, whereas they use lithium in fully electric/hybrid cars? | Engineering | explainlikeimfive | {
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"Because lead acid batteries are cheap. Most of the time when a internal combustion engine runs, it doesn't need a battery. You only need it to get it started. Your alternative is to use a $500+ lithium battery that you only use maybe a few times a day for few seconds Ev's and hybrids use the battery all the time as you're driving. So capacity and weight make up in performance.",
"They're also almost indestructible. If they are cracked in an accident, they'll just leak. A lithium-ion for instance can explode if subject to enough shock..",
"They are cheep. They last a long time and can be repetitively drained and filled , which is hard on other battries. They stand up to drastic temperature changed well. They are cheep and reliable.",
"Lead acid batteries are easy to use, just connect the battery to the dynamo in the engine to charge them and you are set, & #x200B; Lithium ion batteries are tricky beasts, and require more advanced electronics to maintain, and make them safe",
"Lead-acid batteries are cheap, durable, and can put out tons of amps. Amps are important for starting engines. Lithium batteries are still expensive and not quite as durable, but can also put out tons of amps. & #x200B; So possibly in the future, Lithium batteries will be cheap enough. But not right now."
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bzovlr | Why can an electric car (like a Tesla) still be beaten in a race by a classic car? | I saw multiple videos about a Tesla family car beating all the competition on a 100 meter or so track. After that the classic engines gained on them. Why is this? Isn't an electric motor able to just gain speed until the battery runs out since there are very little moving parts like in a classic engine? Correct me if I'm way off. Thanks! | Engineering | explainlikeimfive | {
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"An electric motor is limited by the amount of current the power supply (which is a combination of the batteries and the associated control circuitry) can deliver. Why you're seeing Tesla cars beating muscle cars and drag-strip type cars has to do with the fact that an electric motor delivers maximum torque when it is dead-stalled, whereas a gasoline motor doesn't hit the peak of it's torque until well into middle RPM range. This is what allows you to stomp on the pedal in a Tesla and go from zero to 60 in a heartbeat while the guy in the gasser is still waiting for his engine to hit the sweet spot in its torque curve."
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bzq947 | how does the fuel gauge in vehicles know how much fuel is remaining? | Engineering | explainlikeimfive | {
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"A float in the tank goes up and down. As it goes up and down... It is connected to a resistor. So full will read x amount of resistance and empty y amount of resistance. Values in between are simply divided up equally. The gauge in you dash basically reads that resistance and outputs it as a needle reading that points to a number. Full empty etc. Basically if you take the wire coming from your fuel tank and apply a resistance to it... You can trick your fuel gauge. This is also how they test the fuel level sensor. The manufacturer tells the mechanic what resistance range it should show. They use a multimeter device and it shows the value.",
"Unless you’re on a motorbike. Open the cap and slosh the bike around. If your face gets wet, you’ve got almost a full tank.",
"There is a float in the tank, and it’s height in the tank registers the amount of fuel remaining."
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bzxily | How can a half-built house be left in the weather with no issues? I’m talking about a wood frame with plastic in the rain type of thing. | Edit: this really blew up but i can’t read 200 essays about wood treatments so thank you to everyone who contributed ❤️ | Engineering | explainlikeimfive | {
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"Construction materials are typically rated to a certain amount of exposure to the elements to allow for construction time. Thats why construction scheduling is so important, so that sensitive things arent ruined before the building is up. Ive seen thousands of dollars worth of material discarded because it sat too long in a building that wasnt sealed Wood framing can go quite awhile exposed before there starts to be a real concern. But it depends on climate and whatnot. Source: work in architecture",
"All building materials arrive on site with a specific moisture content. They can get wet until the building is ‘dried in’. Once the building is dried in, you have to wait for the moisture content in the framing to return to the proper level before sealing everything up with drywall and insulation from the inside. Framing getting wet isn’t a problem, it only becomes a problem if you seal that moisture in before it has had a chance to return to proper levels.",
"(In southern Ontario) a framed house is fine for a while in the rain for a few reasons. 1) That plastic wrap shit, usually Tyvek, is hydrophobic 2) we try to get shingles on quickly to minimize how wet it gets, especially the horizontal surfaces because puddles can form and that's the real issue. 3) wood only warps when wet if you make it. If it's laying perfectly flat, it will dry flat. To a certain extent, the framing of the house is fixed in place, there isn't any major warping that can really happen. Plus, it shouldn't be sitting exposed for too long in the first place. 4) going back to #2 for a moment, puddles are an issue because they are constant. That wood is soaking indefinately that's when it starts degrading the wood, mould, etc. Wood getting wet and drying isn't a huge deal aside from the threat of warping.",
"The most sensitive things in a building regarding moisture is the insulation and the electrical work. Typically the order of operations allows a roof to be installed and at least an air barrier (plywood with tyvek building paper) barrier before insulation and electrical is done. If enough moisture is allowed to let the framing materials to get wet than many contractors will use fans and heaters before the drywall stage, but after roofing and siding, to correct the house to the proper humidity and moisture content. Most plywood has an amount of time lt can be exposed before it degrades, and lumber can be dried. We always try to wrap our buildings before we let the plywood sit exposed. Once it's to \"lockup\" with doors and windows in, and roofing and siding on...the finish material can be safely installed. 50% of what we do is weather proofing for our buildings, when you see framing up in the rain, that's half way done. I'm a carpenter.",
"Ex carpenter here. It’s not the rain that matters in rough framing. As long as things have time to dry it’s fine. Generally right after the rough in the roof gets done so no more direct water comes from above. You might be surprised but its sun exposure that does a number on wall studs. Generally the lumber can still be a bit too wet when delivered so it isn’t finished moving. You can get some nasty bows after a few days of baking. But that’s what the back out crew is for. They go through and rip out or straighten bad studs before drywall.",
"Back in 2008 when the housing market went and fucked off, there were some unbuilt homes near me. It was just the basements. They remained exposed for almost 3 years. There was no rebuilding the basements or anything. How'd they manage that? Wouldnt there be damage overtime?",
"Any wood in direct contact with cement must be treated since concrete always has some level of humidity. All the other wood sheds water rather well. Also all the 2x4 or 2x6 and such are in a place that is exposed to air and can dry quickly. The only thing that is a problem is OSB plywood. On a vertical wall it still sheds pretty well but when we do a roof the goal is to cover it the same day because it can't shed as well and it will definitely swell and make it impossible to fit the spacer clips on. Also the last thing you want compromised in any way is the roof that will see plenty of abuse over the years.",
"That plastic (usually tyvek or zip) also adds a lot of weather protection. That's why it's there, to be an additional barrier for the wood should any moisture get under the siding hat will be put over it. I would also guess that if a frame were left bare in the rain they wouldn't add the side panels until the sun has dried it out. If you added the sides with a big puddle sitting on the foundation, it would be trapped in there.",
"I’m a home builder here in Portland Oregon where it rains half the year. We build all year round. We frame it and don’t care if it gets wet. Then once the roof is on I bring in specialty crews who use moisture meters and see where the water is accumulated. We use fans, heaters and dehumidifiers to suck all the water out of the wood framing to the appropriate moisture content and then they certify it. It needs to stay wet awhile for molds and such to start growing. We pull the water out way before that happens. In fact we do this even in the summer sometimes if we don’t use kiln dried wood and we do get water out. That’s because the framing lumber comes to us green and “pond cured” as we call it where it’s basically been floating in water till recently and is still real heavy.",
"don’t renegade mormons, like colorado city, never finish their houses so they don’t have to pay property tax?",
"It's not always the case that there are \"no issues\". The IBC strengthened the inspection requirements once the reasons behind the Berkley balcony collapse came to light. URL_0",
"Maybe someone here can answer my question then. How is that I can buy perfectly straight lumber at Home Depot or Lowe’s but when I take it home, the next day even though it was laying flat, it’s now warped like crazy!? How does this happen and why does this not happen to the frames of houses?",
"Back when I was working construction (coastal NC) it was common for projects to come to a halt for one reason or another, usually lack of money. Given that this was the big building boom of the 70s, we'd just move on to the next house, leaving the unfinished house to \"weather in\" as we called it. You'd run into a pal at a bar and he'd say \"Didja finish that house in Oyster Pointe?\" \"Naw, we're letting it weather in.\" Similar to \"doing road work\" after being sentenced to pick up trash for community service.",
"Simply enough, water doesn’t produce mold. Water in a sealed environment does. The wood can get wet as long it can also breathe. That being said, I’m a young builder and I originally had a huge issue with this. I now understand that it is ok to do but ultimately, I’d try and avoid it as much as possible. Not to mention, much of today’s material has built in waterproof membranes, making it even easier to avoid. Edit: Just realized what sub this was. Hey 5 year old, go smell your sponge by the sink. Does it stink? If not, it was properly wrung out before left to sat. Now earn some chore money, wash some dishes with this perfectly clean sponge and leave it soaking wet this time. If you come back to it in a couple hours, it’s gonna be pretty stinky. The stink is mold. Now unlike the sponge, the mid-construction house that got wet is also open to the sun, which will dry it out. Much like wringing out the sponge originally would achieve. Mold has a much harder time growing in an area with no moisture.",
"\"with plastic\" Does this mean the housewrap you see on buildings. If that's the case housewrap is a weather-resistant barrier to protect the wall assembly from the rain and it allows water vapor to pass to the exterior.",
"Wood comes from trees and trees live wet. Wood can easily dry up to a certain extent, as long as the wood isn’t out for months on end you can dry it. This is also why after a water loss you should try to dry out wood flooring instead of replacing, they can take some moisture and dry it out before being damaged",
"There are impacts, and anyone who has bought a brand new house knows them. Over the first 12 to 24 months of new home ownership, wood framing loses a great deal of its moisture content and something called settling occurs as the wood dries unevenly. This results, usually, in nail pops, doors being out of square, and small cracks along drywall seams. Most new home builders offer an inspection and free fix at that one year point, where they come in and fix all the nail pops, calk all the exposed drywall seems, repaint, and adjust any doors that are out of square.",
"Basically i see 3 issues. 1. Rain will fuck up isolation materials like rockwool or the likes(styrofoam is a non issue). It takes ages to dry out and will make it lump together and be bad in general. So it cant be in direct rain for any period really. Wood can last a long time, even untreated, but mostly you use some chemicals to keep wood from rotting away. Especially the wood that is meant to be outside(outer wall) is chemically treated. Wood skeleton will not be exposed and doesnt need protection other then ventilation and a outer wall. 2. Sunlight is a factor but its a slow process for it to become problematic. Mostly in regard to plastics this could become an issue. 3. Wind can knock shit down and blow out the plastic barrier(very bad). So in regards to seeing some wooden house with a roof and no real outer wall just maybe some sheet of fabric(dont know the english term) the house can stand like that for a long time no issues. It will get damp and have moist problems but it could still stand for a long time."
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c00cne | What is a box spring for? | Engineering | explainlikeimfive | {
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"For bed frames that do not have supports across the middle. Some bed frames are just the outer rectangle connected at the head, foot and maybe once across the middle. Set a mattress on that by itself and when you sit on it it'll push through the frame. Putting a sturdy box spring on it first prevents that. If you have a platform bed frame or bed frame with sufficient support in the middle then a box spring is not necessary.",
"They also allow for airflow adding the mattress - the material is thin for a reason. Putting a bed directly on plywood, as someone suggested, can lead to moisture issues. Most \"box springs\" today are actually foundations - which is designed mainly to support the mattress, allow moisture and airflow on the bottom of the mattress and to leave your bed at the correct height. Box springs used to have actual springs that provided additional support for the mattresses. Mattress technology has come a long way and that is no longer needed. Bed frames that don't use foundations use slats which, again allow for airflow around the mated while supporting the mattress correctly. All Queen mattresses and larger must also have a centre support, regardless of what you are using (foundation, slats or just a sheet of plywood) without that support, the mattress will sag and your warrantee will be voided. The scene spray should be just slightly shorter than the short on the sides so that there is a small amount of give. Fun fact - most mattresses have 10+year warranty but should really be replaced every 7-8 years because you may not realize that your mattress isn't spring you correctly because your used to sleeping on it, but they tend to be less supportive at the end of that 10 year period. Fun fact #2 - unless something goes really really wrong, the mattresses today are made so that they will never actually sag down to a point where warranty could be claimed on it...even if the mattress is completely ruined. They are designed to never \"fail\" from a warranty point of view."
],
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21,
10
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|
c030n7 | Why do some countries have visible electricity cables above ground whereas other countries have the cables underground? | Engineering | explainlikeimfive | {
"a_id": [
"er0agp2"
],
"text": [
"The key issue is the expense. Installation is far less expense if above ground. Also if the cables are going to need regular access for repairs/junction boxes etc. & #x200B; Another factor with things like pylons is cooling. The cables stay relatively cool compared to burying them. & #x200B; There was an interesting mini series on UK TV a couple of years ago following the installation of some massive pylons across some hillsides etc."
],
"score": [
7
],
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|
c059yw | Why dont we use XLR outputs on guitars? | Engineering | explainlikeimfive | {
"a_id": [
"er1j43s"
],
"text": [
"There's no advantage to switching to XLR (except maybe that it locks in). & #x200B; There is a pretty big disadvantage that guitars, amps, and pedals, are all designed to use 1/4\" already. Also lots of gear that uses XLR is meant to be used with microphones or at least mic-level devices. Guitars are not mic level, so mixing and matching guitars, amps, mics, and mixers, could end up causing some headaches because of mismatched levels. & #x200B; Some may argue that XLR means that the signal can be balanced instead of just regular mono and this might reduce noise in the cable. The thing is, 1/4\" can be balanced too if you use the right cables and the right 1/4\" connectors."
],
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7
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c06s6b | How toilet systems were built. How on earth does a city withstand the amount of waste flushed down everyday? | Engineering | explainlikeimfive | {
"a_id": [
"er25ugt",
"er1z40i"
],
"text": [
"A sewer system is a network of pipes that mostly flow down hill (your home's is above the sewerline which is above your neighborhood's sewer line which is above the major sewerlines, which is above the sewage treatment plant), which is a big tank that lets waste be digested by bacteria until the sewage is back to being water and nutrients where it's released. It was built slowly, neighborhood by neighborhood. Once you get the treatment plant location built, and lay the major sewer lines, it's not that hard to plan for a new connection from a neighborhood and build the neighborhood lines and lines from each home into that. Part of the permitting process will be approval from the local sanitation department that will approve of the system to handle the planned additional load.",
"Can you be more specific on what your want to know? Do you want to know how the physical sewers are built ( your first sentence) or how wastewater collection and treatment works in general (your second sentence) or both? I can answer either but how the system is built and how it works are two different questions."
],
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c0azpw | why MRI machines make so much noise. | My boyfriend got an MRI of his brain the other day and will not stop talking about all the noises it made and has been obsessing over the “Why” of it. Can someone ELI5 so I can give him the answer he so desperately needs? | Engineering | explainlikeimfive | {
"a_id": [
"er38p6w",
"er3s59s",
"er3b40k",
"er3e75o"
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"text": [
"because on the inside of the machine, the large metal coils are vibrating when electricity passes through rapidly, creating a magnetic field, which causes the banging noise. the louder the bang, the more the vibration, the more detailed the scan.",
"There are multiple coils inside of an MRI that produce magnetic fields for various purposes in various ways. 1) the 'primary' coil. This is what is known as a superconducting coil. It's made of proprietary alloys, cooled to about 4Kelvin (-452°F or -269°C) to prevent loss of current via heat and 'cannot be turned off'. This is your 1.5, 3, 7, or 12 Tesla magnets (commonly, they do have other levels of tesla). This is the magnetic field that is used to image the body. (Edit: for comparison, the magnetic field of the earth is about 0.5 Gauss... there's 10,000 Gauss to 1 Tesla!) 2) gradient coils. These are water-cooled electromagnetic coils, inside of a resin shell shaped like a tube, that's just on the other side of the tube a patient sees. They are powered by about around 600 amps and used to manipulate the primary magnet field in such a way to produce spatial information (x,y and z axis to build the actual image being taken). (Edit: there is typically 1 gradient coil for each axis, so 3 gradient coils in the whole assembly, each sucking up 600amps!) The primary magnetic field does not make noise. It's at a constant level, just being shifted around by the gradient coils during a scan. The gradient coils are basically giant speakers without a diaphragm... well, YOU are the diaphragm. The air is a diaphragm. Absolutely do not do this, but if you took a piece of aluminum sheet into the magnet while the gradients were pulsing, the field and noise actually knocks the aluminum and it feels like it is being physically contacted! Much has been done to reduce the noise of a machine... after all, they're scary enough for many patients. But at the end of the day, a 600 amp (x3) speaker tube big enough to fit a large person is going to create some noise Maybe if we sucked all the air out of room.... Source: clinical imaging engineer",
"I think ICP said it best. “Magnets, how do they work?”",
"Got an mri a couple of weeks ago after 2 herniated discs. Was no where near as bad as i had been told it would be"
],
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35,
18,
6,
3
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c0cheb | Why does it say "DO NOT PUSH" on the back of dumptrucks? | Engineering | explainlikeimfive | {
"a_id": [
"er3l7in",
"er3l7x3"
],
"text": [
"Quite clearly because you are not supposed to push it. Seriously though, it depends; that is, the trucks I've seen typically have it written on the metal bars on the back which presumably would give out under the force of another truck. There could also be risk to the hydraulics should you over exert energy (push) on them. Generally speaking, the trucks are not designed to take any hit, no matter how slowly applied, to the back of their frame. Lots of moving parts in pressed metal that would get bent out of shape about being bent out of shape.",
"On construction sites, other equipment will often push a dump truck along as it does its work. Think of an asphalt spreader getting hot asphalt from a dump truck. Some spreaders are designed simply to push the dump truck along as it takes its material from it. But the truck needs to be designed for pushing and it must be in neutral. Other cases involve dump trucks getting stuck on a muddy building site and getting pushed by a dozer."
],
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5,
3
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|
c0htmn | - Why kitchen sinks take more time to get hot or cold than bathroom sinks? | Engineering | explainlikeimfive | {
"a_id": [
"er4pkjo",
"er5hd15"
],
"text": [
"Has nothing to do with kitchen or bathroom, only depends on the distance the water has to travel from the heater to the output.",
"This is likely has more to deal with your house in general. In most US homes, there is a central water heater. The further away from the water heater, the longer it takes for hot water to reach the faucet. If a bathroom and kitchen faucet are the same distance from the water heater, the kitchen will actually warm up faster as they almost always have higher outputs (Measured in GPM, gallons per minute); Meaning more water flows out of the kitchen faucet than the bathroom faucet."
],
"score": [
15,
3
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|
c0libr | We cast things out of steel or other material, but before that we didnt have those 'machines for creating another machines' and had to use more primitive tools. How our ancestors managed to craft something that it looks impossible to make without machines we have today? | Engineering | explainlikeimfive | {
"a_id": [
"er5kmmd"
],
"text": [
"You did it by hand and simple machines often powered by human/animal or running water. Blacksmiths shaped metal with hammers and fires. That is how metalworking was done back in the day. Simpler machines made from wood was often used. Metal have historically been quite rare and wood, stones, clay etc is was was used in the past Casting metal with lower melting temperature is not hard. [Lost-wax\\_casting]( URL_1 ) when you shape the object in wax, pack in in sand and clay and then you heat it up and the wax melt and can be reused. You then pour int molten metal like bronze that you can make on a fire in a burned clay container. So you need wood, clay, wax and the metal to do that. The metod have been used for 6 000 years and you have complex statues like [Dancing\\_Girl\\_(sculpture)]( URL_0 ) from 2500BC So it is stuff that is easy to find and wax can be bee wax. The most uncommon was the bronze but there was mining of metal deposits thousands of year ago. They mined metal that was closer to the surface with high metal concentration. Deposits like are rare and almost all have been completely mined out so metals is harder to get today. Look for example a [Primitive Technology]( URL_2 ) where stuff is made by hand with stuff he find in his surrounding . He manage for example to create small amount of iron with stuff from his surrounding."
],
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6
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"https://en.wikipedia.org/wiki/Dancing_Girl_(sculpture)",
"https://en.wikipedia.org/wiki/Lost-wax_casting",
"https://www.youtube.com/channel/UCAL3JXZSzSm8AlZyD3nQdBA"
]
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|
c0oz3y | How do those top down, 360° car cameras work? | It's messing with my head. How the hell does that work? | Engineering | explainlikeimfive | {
"a_id": [
"er6cmza",
"er6ctnz"
],
"text": [
"My wife's car has a camera in the front bumper, camera under each mirror, and a rear camera. It basically takes the image from all 4 cameras and puts them together to simulate top down view. I assume it's similar with all cars with this feature",
"A combination of at least four cameras fused to one picture via software, the car itself of course is a model. If this already freaks you out check out the drone like outside view of new BMWs, with 3D Models of the car. Edit: Doug DeMuro shows it in his reviw of the new 8 series and the Rolls Royce Cullinan I think."
],
"score": [
4,
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c0pc4m | if vehicles have the ability to go from 2WD to 4WD/AWD, why aren’t there cars that let you change from RWD to FWD? | Engineering | explainlikeimfive | {
"a_id": [
"er6fu6n",
"er6g97v",
"er6g0we"
],
"text": [
"There are, so there's that. It's just not practical in pretty much any application so it's very rarely done. There's almost never a need for it except in very specific off road conditions.",
"There was a truck during WW1 that was called FWD. it was classed as a four wheel drive but could switch between front only, rear only, and 4wd. [wiki for it ]( URL_0 )",
"Subarus have driver controlled center diffs. You can select the ratios in which the power is sent. Newer AWD systems automatically adjust the power distribution between front and back also due to road conditions and drivers habits."
],
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14,
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"https://en.m.wikipedia.org/wiki/FWD_Model_B"
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|
c0qftc | How does the gravel under train tracks stay level so the train doesn't make it slide? | Engineering | explainlikeimfive | {
"a_id": [
"er6rcsj",
"er6sfxp"
],
"text": [
"More than anything, the tracks themselves are made using strict guidelines. This helps to keep the weight distributed well across all the wood at the bottom and in turn the gravel/dirt underneath it. The gravel also does a very good job of holding the dirt underneath in its place keeping it from moving around.",
"It's not just a massive pile of gravel, its built up layers of various sizes of aggregates and sand layers, with the very heavy and large sized \"ballast\" that the ties sit in on the top. This makes it very solid as a foundation but can be susceptible to washing out over long periods of time without proper maintenance in the form of tamping which vibrates the ballast layer to compact the rocks down. Usually more ballast is dropped beforehand. Also, those ties and rails are *very* heavy and take a lot of force to move once set in place. Outside of acts of nature and major accidents they generally aren't going to go anywhere."
],
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10,
7
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|
c0wzei | Why do passengers on an aircraft have to recline thier seats, pull the windows and stow away thier trays when taxiing, taking off and landing? | Engineering | explainlikeimfive | {
"a_id": [
"er8g5ld"
],
"text": [
"If something's going to go wrong on a flight, it's more likely to be during takeoff or landing. The intention is to have your seat upright and tray table stowed for better protection of impact, and to leave more room so you can quickly exit your row. The window shades are supposed to be open so first responders can see in to assess damage and rescue, and so you can see out to see if it's safe to exit the aircraft on that side."
],
"score": [
107
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|
c11olg | How do toilets keep a consistent water level? | Engineering | explainlikeimfive | {
"a_id": [
"er9utpf"
],
"text": [
"The bottom of the toilet is shaped like a “U”, so fills with water. If any more water is added, it overflows over the back into the drain."
],
"score": [
3
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"text_urls": [
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|
c13bu9 | Why are there no guns with more effective explosives than gunpowder? | Engineering | explainlikeimfive | {
"a_id": [
"eracxsm"
],
"text": [
"I think you are seriously mistaken. Firearms haven't used gunpowder since [cordite]( URL_0 ) AKA smokeless powder was invented in the late 19th century. The only guns you'll find today that use actual black powder are antique and replica muzzle-loading rifles."
],
"score": [
5
],
"text_urls": [
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"https://en.wikipedia.org/wiki/Cordite"
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c15pnk | An article today said using your phone battery below 20% and charging it routinely above 80% reduces battery life...what causes this and is it the same process at both ends of the range? | Engineering | explainlikeimfive | {
"a_id": [
"erb4b5a",
"erbkdh4",
"erb5uzi"
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"text": [
"ELI5: Discharging a battery too deeply causes its structure too break down, increasing the potential for a short circuit. Overcharging has a similar effect, but can also result in the battery catching on fire. Discharging from 80-20 slows the breakdown. Full Answer: When discharged below its safe low voltage (exact number different between manufacturers) some of the copper in the anode copper current collector (a part of the battery) can dissolve into the electrolyte. The copper ions then in turn can stick on to the anode during charging by chemical reduction and cause dendrites. The dendrites might cause a short circuit inside the battery. So basically discharging too much is as bad as charging too much. But the dendrites caused by overcharging is formed out of lithium. Normally the battery pack should have some sort of supervisory circuit that disconnects the cells from the charger or load when the cells are above or below the recommended voltages.",
"Was this article from the 90s? Almost all modern phones regulate themselves to avoid battery damage. Also important to note, that when your phone says it's at 100%, it isn't actually 100% maxed out. And when it says it's at 1%, it absolutely isn't going to completely run out of power. Those are just numbers to provide representation of when to take your phone off the charger, and when it's going to shut itself off.",
"Isn't the 80/20 thing BS? Or at least the science behind battery technology is too finicky to say?"
],
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c1chaq | How on earth does the power supply to an entire Country fail? | Engineering | explainlikeimfive | {
"a_id": [
"ercadrx"
],
"text": [
"There is a problem with turning the power back on again that makes it difficult to do it: Many appliances in a normal home are consuming a lot more electricity for a while when you start them up. Fridge? Needs more electricity. Freezer? Needs more electricity. Some tv start up, realise that they are not supposed to do anything and hibernate again. And so on. Not to mention that a fridge that has been turned off for a day will have a pretty rough time cooling down the food in it again. It will consume a lot more electricity in the upcoming day than it usually does during a day, just because it has to catch up. Now, imagine that a whole bloody country does this at the same time. It'll demand so much from the producers that you literally can't turn it all on at the same time. You have to turn on a section at a time. And pay attention to the load you get, and then carefully pick a section to turn on after an hour or two. And still pay close attention to the load. And at the same time you run into other problems. When you turn on power, it's a really large circuit breaker that has to be moved. I'm gonna bet you that if you open 20 really large circuit breakers that haven't moved in a decade, then one or two of them will probably fail. Or at least be bit cranky. And some of the large breakers are fully manual. How...how do you manage to get personell out to that breaker, when gas stations can't sell gas to the company vans and cellphone towers are knocked out for lack of electricity? There is a lot of practical problems that...are not necessarily solved in advance. Not all the line workers have satellite phones. Not all the depots got their own fuel depots with a hand-cranked pump for emergency refuelling. And... Well. Yeah. Once it's blacked out, you face a lot of practical problems with the restarting procedure, if you wait for too long before you get started. As for the question on how things fail... that is a good question. But it literally only takes that a very, very, very large power line gets disconnected before there is a fault on it. Or that a large producer has a failure. I haven't read up on what the problem actually is, but it's usually one of those two. There is a problem with production or there is a problem with transmission. EDIT: I browsed a news article or two about it. The problem appears to be that the consumption is so large that the producers can't meet demand. Producers can't maintain the goal frequency on the production. Voltage goes down. Voltage goes up and down violently when the producers try to meet demand and can't. Eventually, lots of equipment will start to disconnect, because when the voltage does that, it's...an obvious problem. In a perfect world, it means that the production units will have a less rough time keeping up. In a real world, it can mean that the producers loose *too much* consumption, and force them to do an emergency shut down because of that instead. And once a large producer shuts down, it'll give too much load to all the others. And the vicious circle continues. It's all a matter of failed load balancing. Production can't meet demands. And whoever it is that has balancing as their job failed at it. Or reacted a hint too slow. And now they have to start up slowly. From scratch. One consumer area at a time. one production unit at a time. Probably for days."
],
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13
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c1infv | Why do printers make so much noise before and after actually producing a document? | Engineering | explainlikeimfive | {
"a_id": [
"erdhi1e",
"ere0tza"
],
"text": [
"Howdy there, printer technician here. There are several parts in the machine that get \"synced up\" before pulling the paper through. It's easy to get deep in the weeds on the types of printers and how they work, but the most common method is by using a laser to draw the image on a spinning tube, the toner attaches to that drum as it spins, and then the paper is pulled past the spinning drum and through a heated roller that melts the toner into the paper. So, before the paper even gets picked up the machine has to 1. Spin the hexagonal mirror that the laser bounces off of to write to the drum--this is the initial high pitched whine you hear 2. Clean any leftover toner from the last print off of the drum--this part usually sounds more \"rumbly\" 3. Move new toner to the drum to be put on the next page 4. Make sure the heated roller is up to the exact temperature to melt the toner without burning the paper--most machines have ceramic heating elements that take a few seconds to warm up ...and on top of all that, there are anywhere from 4-10 ventilation fans that all turn on to make sure the above processes don't get too warm.",
"For inkjet as well they like to purge a little bit of ink if it hasn't been used in a while, it's a lengthy and noisy processes that wastes some of your precious ink, but it protects your printhead and makes sure your prints come out properly."
],
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27,
3
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c1io1j | How would a Dyson sphere actually work? | Engineering | explainlikeimfive | {
"a_id": [
"erdl2x1"
],
"text": [
"Let's get this out of the way, the \"dyson sphere\" that is a solid structure entirely encasing a star is almost certainly not going to work. Even Dyson himself dismissed the idea. He was talking about a Dyson swarm when he was talking about it. As to how it would work, we don't know because we haven't seriously tried actually building a power plant in space that beamed down power to earth or any other remote object. The current scientific best guess on how to start on that is a Space-based power satellite. This is a satellite put in an orbit around Earth that's always in the sunlight (either sun-earth lagrange point 1 or a sun sync polar orbit). The atmosphere soaks up alot of the sun's energy, so we can bypass it. So we take the energy in space, turn it into a beam of microwaves, shoot the beam at a collecting station on Earth, the beam isn't as affected by the atmosphere, so more energy gets through to the collecting station. Once we get a hang of that and aren't microwaving people to death accidentally. Then we can think of doing it long range. Most likely we'll build a bunch of really simple mirrors in orbit around the sun. Turning it at a more complicated solar power plant. This is pretty much exactly like a [concentrated solar power plant]( URL_0 ) on Earth, except it'll be using a microwave or something like it to beam power to where it's needed. **TL:DR mirrors - > concentrated solar - > LASERS (well MASERS technically)**"
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4
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c1kfvp | what are the needs of capacitors in many electronic circuits ? | Engineering | explainlikeimfive | {
"a_id": [
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"erdu7rf"
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"text": [
"Basically, signals are noisy, there’s lot of things that can cause noise, so we use capacitors to keep the noise down. In an ideal world, there would be no need for many of the capacitors in electronic circuits. There is a relationship between current flowing through a wire and magnetic fields. This is essentially how electromagnets are made, by taking advantage of this effect and magnifying it. This is called inductance. In a perfect world, wires are perfect conductors meaning they don’t have any resistance and they don’t have any inductance. But in reality they do have a bit of both these things. So when signals are changing (especially at high speeds) the inductance causes more and more issues, because the magnetic field keeps developing (stores some energy) and going away (releases energy). This is where most applications for capacitors come in. Capacitors store energy as well, but to put it simply they behave opposite to inductors. So if we put the capacitors at the end points of a signal, it will make a shorter path for the electrons to flow and lower the resistance and inductance. Without capacitors, this “parasitic” inductance and resistances can cause noise (variations in the signal that we don’t want). In digital circuits, If it’s big enough, it can even make it so that one transition between 0s and 1s be read as multiple. We also use different size and value capacitors on one signal line because different capacitors can reduce different frequencies of noise, which is why we can’t just stick one big on on there and call it a day. Also if the capacitance is too high, the signal might not be able to transition at all because the capacitor stored too much energy. The noise doesn’t always just come from the inductance of a wire. For example, wires that run next to each other can create noise in the other one because of the magnetic field that it creates when current runs through it. Radio waves (electromagnetic waves), and even tapping (piezoelectric effect) can introduce noise into a signal.",
"among many others, mainly two things: 1. filters: for example, filter out interference by filtering out high frequencies in the signal 2. voltage spikes prevention: if there is voltage spike in the circuit, it could potentially damage some parts. Capacitor is there to be charged by this spike, thus effectively removing it"
],
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c1ovu4 | Why haven’t we gone to a specific screw type yet? | If you look up screw heads you’ll find that there’s a ton of different designs. The designs are meant for preventing slipping and stripping. They also involve different torque. So my question is why are there so many different kinds of screws? Wouldn’t there be a superior design that would handle the problems above? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Different screws are needed for different applications. Some are designed to be \"security\" screws, some are designed for higher torque, others are made just to be cheap, and some are made for convience.",
"> The designs are meant for preventing slipping and stripping. Phillips are designed to slip when too much torque is applied so that you don't damage the thing you are screwing into when screwing by hand.",
"> So my question is why are there so many different kinds of screws? Self answered questions are the best questions: > The designs are meant for preventing slipping and stripping. They also involve different torque. > Wouldn’t there be a superior design that would handle the problems above? No, not really. You can't design something that gives you a ton of torque, but at the same time will cam out to prevent damage to the material due to over tightening. That doesn't include all the new security types that pop up every few years. Instead you choose the correct screw head type for the application. Phillips for things where over tightening will damage materials, Roberston or Torx when you want high torque and no slippage, and slot headed when you need to vent by yelling and swearing at your project."
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c1vvwr | What the heck does that third prong on a Western Hemisphere power plug do (the "ground") if it isn't necessary for all electronics? | Hell, I've even seen people rip them off to fit 3 prong plugs into 2 prong extension cords. I'm sure it's not safe, but I dont know why and why they would be necessary sometimes and sometimes not. | Engineering | explainlikeimfive | {
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"It's a safety feature on electronics that have a metal exterior, to prevent people from getting shocked, in case the wiring inside gets messed up and touches the case. It grounds the actual metal exterior. I guess it's only necessary if you value your safety, LOL. How and why it works is actually really interesting! URL_0",
"So you have a drill you are using. The motor has two wires going to it: the hot and the neutral. They do the normal circuit for the drill. Now there are parts of that drill that are conductive and exposed to you, the human. To try and help you from being a dead human they ground the casing/metal of the tool. That ground wire runs from the metal bits you can touch directly to the wall, through a dedicated wire to the ground bus and from there to ground. If the power wire gets shorted to he case/metal bit and there is no ground wire, YOU become the human ground wire. The current follows the least restrictive path to ground. In this case you. If it passes through you heart, well that could make you dead. No on our three prong plug device that metal you are touching has that low resistance direct connection to ground. So that shorting current will go through the wire and not you! So you may get a small bit of current but much less likelihood of being killed. ie a little bzzt instead of CPR while we wait for the ambulance. Now the two prong plug with the size difference. Nope not a birthmark of the appliance. With two wire systems one is the hot the other is the neutral. The hot wire always has voltage on it. If you measure that side of the outlet to ground it will be 120V. The neutral side will read 0 volts to ground. now your standard plug with no size difference can go in either way. So let's say you have a nice hair dryer. That hair dryer circuitry on the inside has a switch that is at one side of the electrical connections in the dryer. With same size plugs you plug in one way and all of the internal wiring and heating elements are at 120 volts since the switch is on the \"backend\" of the circuit. Plug it the other way around and the voltage is only up the switch. It's at the front end of the circuit. That bigger prong only lets you plug it in so that the switch is front end and you only have voltage up to he switch connection. It is also to limit the ability of the electricity to kill you or start fires. So Safest is 3 prong. Second safest is two prong with off sized prongs. Lowest safety is the standard one size jams in however you want it to plug.",
"Double insulated is the answer, if it's not double insulated the exposed metal parts of the appliance need to earthed, the earth/ground prong should never be cut off if it's there it needs to be there",
"It’s a safety feature that appliance manufacturers starting using in the 70’s. Let’s say you drop a toaster with a metal exterior and it gets dented. Unbeknownst to you, the location of the dent on the toaster is directly over an exposed wire in the toasters circuitry. The inside dent of the metal toaster is now touching the exposed wire where the dent is. When you plug in the toaster and move it, the electrical current will is not going to toast your bread, instead it is going to travel through YOU. However, if the manufacturer had the foresight to install a wire connecting the inside of the metal frame to the ground (the third prong), the current will instead travel through the ground wire and trip a breaker instead of shocking you. The toaster example isn’t something that would be likely to happen today as 99.9% of toasters made today have plastic exteriors (for your safety). But any appliance you see with a third prong has it as a safety measure in the circumstance that the circuitry should fault in an exposed part of the appliance."
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c20xh9 | Differences between putting some 87, 89 or 91 octane gas in a car | Engineering | explainlikeimfive | {
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"Gasoline is not a single chemical; it’s a mix of lots of different components. There is no universal recipe for the ideal blend of components for all engines. Different blends or recipes for gasoline might all work OK across a range of engines, but each engine is designed for a blend with specific properties. All engines are designed to squeeze or compress gasoline with air in the cylinder, then ignite the compressed mix at just the right time with a spark. The octane number of a gasoline blend describes how much compression the gasoline can take before it detonates (ignites) on its own without needing a spark. Some engines, usually high performance ones, are designed to compress the fuel/air mix extra hard; these engines need gasoline with a higher octane number, or else the fuel will detonate early and not produce power smoothly for the car. You can use gasoline with a higher octane number than it was designed for, but people seldom do that because in engines designed for “regular” gas, high-octane fuel doesn’t provide significant benefits but costs more than lower-octane gas.",
"In general, pump the gas that is recommended for the car. Pumping a higher octane than recommended brings little, if any, benefit to performance but will cost significantly more. Cars that need high octane fuel usually have high compression ratios and are more than likely, high performance vehicles. The high octane is needed to prevent pre-ignition of the gas/fuel mix in the cylinders. Pumping lower octane than recommended runs the risk of pre-ignition which can be very damaging when it occurs.",
"This depends heavily on the design of the engine. Octane basically means how \"easy\" it is to make the fuel detonate. The higher the octane, the more compressed it needs to be in order to detonate efficiently. Car engines are designed to function most efficiently with a specific octane, usually 95 RON (EU numbers being used here - not familiar with US standards). The design of an engine with regards to fuel revolves around the *timing* of the engine, specifically when the spark plug fires during the compression stroke of the piston in each cylinder. When a piston compresses the injected fuel, it makes it easier to detonate - and the spark detonates it. The higher the octane, the later in the compression stroke you want the spark, because it's harder to detonate it under a lower pressure. On an engine designed to work with 95 RON fuel, it will be set to a specific point during the compression stroke. If you then take 97 RON (higher octane) fuel and put it in that car, it will still fire at the same point during the compression stroke. In most cases, this will make absolutely no difference to the performance of the engine, because it's still firing at the same time, and the fuel detonates in the same way. You might get *slightly* more energy released from the fuel due to the higher octane, but the difference will be negligible. The opposite applies if you put low octane fuel into a car designed for *high* octane fuel. The spark will fire \"too early\", and you will end up with lost energy due to inefficient combustion. tl,dr; in the vast majority of cases, it will make no difference, as long as you are using the same or higher octane that the car was designed to use. Some higher octane fuels contain more effective detergents, which can possibly improve engine life."
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c23rku | How do breaks squeak if/when they need to be replaced, but do not squeak when working normally. | My breaks on my car started squeaking and I know that means I need to replace them. I'm just wondering how the mechanical system works. | Engineering | explainlikeimfive | {
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"There’s a little piece of metal that sticks up next to the pad called a chirper, and when the pad gets short enough for the chirper to touch the rotor it makes the squeaking.",
"Most brake pads have a little piece of metal that rubs on the rotor to make the squealing noise while you still have a small amount of pad left. If your pads don't have this, it's the metal backing off the pad rubbing on the rotor. If you live somewhere that sands the roads, you can get sand, or debris, between the odds and rotors that make the same noise.",
"There's something built into the break pad so that once you've worn through the good part of the pad it starts making noise... kind of like how on receipt paper in registers, you'll see blue line when it gets near the end of the roll."
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c24guf | Why do the colors on a computer screen change depending on the angle at which you look at them? | Engineering | explainlikeimfive | {
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"This only occurs on TN (Twisted Nematic) LCD Panels. It is due to the method in which the LCD twists light through a group of horizontal and vertical lines in order to block or allow light to pass. When you look at it at sharp angles, you're seeing the light that is between the two layers. This light is not seen when looking at it straight on. Higher quality TN panels typically do not exhibit this behavior except at extreme angles. Lower quality ones, especially those found in laptops, tend to show this very easily. & #x200B; The reason TN panels are still used is that they're both energy efficient and cheap to manufacture. This is why they're often found on laptops and TV's. Computer monitors and phones tend to use IPS for better viewing angles and picture quality."
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c2galm | - Why and how does a plane dump fuel in emergency landing situations? | I understand that they need to be a lighter weight to land. How does the process of dumping fuel while airborne work? Edit: sorry my question was worded horribly. What happens with the fuel if it is dumped while airborne. If a plane is flying over a city and needs to dump fuel how does that work? | Engineering | explainlikeimfive | {
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"Air planes have a maximum landing weight that's less than the take off weight. The assumption is that when you land you'll have burnt off the fuel and be the appropriate weight. Sometimes you're not, like if you take off, realize there is an issue and need to turn around and land back at the same airport. You'll open a port, usually on the wings and spray fuel into the air. It gets misted because of the speed.",
"As a sidenote to your question, it's worth noting that if the plane is still airworthy, then generally, they'll fly a holding pattern until the fuel load is reduced, rather than dumping."
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c2hacv | Why are there multiple methods for measuring electricity? (Volts, amps, watts, etc.) | Engineering | explainlikeimfive | {
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"They mean different things. Instead of electrons, imagine you're measuring a water pipe. How wide is it? That's resistance. How much pressure is inside? That's voltage. How fast is the water flowing? That's amperage. The water is turning a waterwheel as it passes, how much energy is that using? That's wattage.",
"Because they each measure a different aspect of electrical current. Volts = The pressure of the electricity (Such as water pressure or PSI). A lot of pressure doesn't necessarily mean a lot of water will come out. Amps = The amount of electricity (How much water can a pipe puts out, gallons per minute, etc.). A lot of flow doesn't mean high pressure. Watts = A combination of both volts and amps to measure the total amount of power. Volts \\* Amps = Watts. Ohms = How much resistance a wire has. This is similar to using a more narrow pipe that would restrict water flow."
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c2ljvl | Why do cars have a "power range" | I know a decent bit about cars, but it is still a mystery to me why cars have more power at some points in their rev range than other parts of it. For example I'm told that diesel engines are really powerful at low revs and small displacement engines need to be revved higher to have power. Why is this? | Engineering | explainlikeimfive | {
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"This is explained by \"volumetric efficiency\". If we assume a particular temperature, volumetric efficiency can be taken as a a ratio of mass of air drawn into the engine vs. the theoretical mass-draw capacity of the engine. At the point of maximum torque, the engine’s volumetric efficiency is also the highest, meaning that the engine is sucking in the maximum mass or volume of air it possibly can. After this point in the RPM band, the torque reduces due to the air flow losses in the valves and mechanical losses which dominate at higher speeds. These factors reduce the volumetric efficiency and thereby the torque. & #x200B; Power continues to increase as it is a product of speed and torque. At one point closer to the engine’s upper RPM limit, the power peaks and starts to reduce as the rate of fall in torque is greater than the rate of increase in RPM."
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c2lwbg | What is a Watt per meter Kelvin? Also, what does a materials' thermal conductivity tell me? | Engineering | explainlikeimfive | {
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"Thermal conductivity tells you how well a material conducts heat. Watt per meter Kelvin is a little more difficult to visualize. If you have a large window versus a small window, the large window will let more watts of heat out in the winter, right? And if it's thinner, that will let more heat out, versus a thicker window. Also, if the temperature difference is big, more heat will be let out. So you combine all of these, and your number for thermal conductivity is in watts (energy transfer rate) per degree kelvin (difference in temperature between one side and the other) per meter (cross-sectional area of the material divided by the thickness of the material). W/mK.",
"It tells you if the material is a good insulator or a bad one. Thermal conductivity is the ability of a material to transport thermal energy heat conduction. It just tells you how much energy a material is able to transfer from one side to the other. I'm currently on the road. I will try to explain it better when i get home."
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c2puoi | Why do re-entry vehicles enter the atmosphere in the least aerodynamic orientation? | Engineering | explainlikeimfive | {
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"When you're flying you want to be aerodynamic so you can reduce drag and move as fast as possible. When you're re-entering the atmosphere, you want to be as un-aerodynamic as possible so you can maximize drag and slow down. Also re-entering with a blunt shape creates a detached shockwave in front of the vehicle, rather than on the vehicle. The shockwave is where the temperature and pressure are the highest, so you want that zone as far away from your vehicle as possible.",
"They want to Aerobrake. They are using the atmosphere to slow them down enough so they can use weaker retrorockets and their parachutes are less likely to be destroyed. They want to hit as much atmosphere as possible to slow down as much as possible. The heat isn't ideal, but can be dealt with."
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c2wlm6 | What actually physically happens when hard drive "fails"? Does it just ''wear out''? | Engineering | explainlikeimfive | {
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"In a platter drive (the older, typically larger capacity ones), they have one or more thin discs of metal on a central spindle, and one or more arms with a sensor that act almost like a stylus on an old vinyl record player. When those drives fail, one of the following has typically happened: - Physical failure of the central spindle - Physical failure of the sensor arm - Failure of the sensor - Failure of the input/output socket or circuitry therein On newer, solid state drives, it will be a problem with the chip or the board that the chip is mounted in. There are no moving parts.",
"The disk drives that have failed on me have done so for two reasons. Most often, some small bit of crud breaks off the surface of the platter or gets into the sealed compartment, and drifts between the platter and the head. That chips off a tiny bit of platter, which destroys that sector (data chunk), and means that there are now two bits of crud in the disk. When drives get very old, sometimes the lubricant on the spindle bearings (that allow the platters to spin) gets thick and sticky. As long as the drive is spinning it can overcome the sticky, but once it's turned off the motor can't spin it up again. For reasons entirely beyond me, chilling the drive will allow it to start. I've had one critical drive do that, and my co-worker has had a second. When the computer is old enough that spares are short, you get creative."
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c2xop9 | When a car is stationary, where does the engine’s power go? | So I know that the combustion moves the pistons which turns the crank shaft and sends power to the wheels via the drive train (is that right?). But when the wheels aren’t moving, such as when the car is in drive but stationary, where is all that power going? The engine is still running, and the crank shaft is still turning, so somewhere along the line some parts must be slipping, or not turning when they normally would, right? Basically I’m a little confused as to how the mechanical rotation of the engine is translated into “power” or applying pressure to rotate the wheels. | Engineering | explainlikeimfive | {
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"That is where a clutch comes into play. When you are idle the flywheel disengages from the clutch plate and stops the engine from transferring power to the drive train. When you start moving again, the clutch and flywheel press together and power is transferred back to the drive train. There is some slippage there. That is how a clutch gets worn out. It is rubbing against the flywheel."
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c32xt4 | So I’m pretty sure everyone has slipped in the tub or almost slipped. Why are standard shower surfaces and tubs not made out of non slippery materials? | Engineering | explainlikeimfive | {
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"My understanding is that the surface itself is pretty non-slip and it’s the soaps and shampoos and conditioners that we use that can make them slippery. I use a body wash that turned it into a slip-n-slide. PainfulAF! I see the tubs that have a textured surface on the bottom and they are usually filthy cause the dirt gets in the crevices and hard to clean. Not sure I was any help of why this one thing moved me to comment when I rarely do 😂😂",
"Smooth surfaces are easy to clean, while rough surfaces collect nasty gunk in the cracks. Also tubs made of porcelain may have trouble making and holding subtle features tending instead to be formed of a melted glaze.",
"Biofilms and soap residue collect on the tub surface over time, and this is usually what you're slipping on. A clean tub usually has surprisingly good traction for all its smoothness, and a quick scrub with a dilute bleach solution every now and then will keep the slippery stuff from building up. Gloves are recommended because even diluted bleach can damage the upper layers of your skin. It's nothing serious usually, but it'll be annoying for a while."
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c35dz7 | airplanes cruising altitude when flying over mountains | I recently took several flights across the Andes mountains and the flights seemed to be close to the mountains at cruising altitude and were mostly turbulent. I read somewhere that the optimal cruising altitude for a jet is about 35k feet... does this altitude need to be adjusted when flying over high mountain ranges? Do the mountains cause additional turbulence? | Engineering | explainlikeimfive | {
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"So I'm not a commercial pilot, but a private pilot. Mountains come with eddies, also known as mechanical turbulence. Basically, as the air passes over and around the mountains, it is disrupted and so causes swirling action that can affect planes. I don't believe that altitude changes much over high mountain ranges, as cruising altitudes are actually set by a standardized law, but I'm pretty sure they're avoided if possible. There's no reason to subject the pilot and the passengers to additional stress.",
"35,000 is over a mile higher than Everest (29,029 ft). No adjustment required. Actually, this may not be entirely true. Flight levels are based on direction. Flights north and south are on different levels as are east/west flights in order to prevent mid-air collisions."
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c37gt3 | The difference betweens cars that are V4, V6, V8, etc. | Engineering | explainlikeimfive | {
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"V is the layout style. the number is the # of cylinders. V means that the cylinders form a V shape with equal number on both sides of the V in pairs of 2. the other common engine designs is the inline \"l\" where all cylinders are vertical in a line. the flat/boxer \"h\" where all cylinders are mounted horizontally towards each other in pairs of 2, or the \"W\" which uses two rows of \"V\" that is used in designs with larger number of cylinders, ie 8/12 cylinders. each design has it's tradeoffs and advantages.",
"The number of cylinders that an engine contains is an important factor in the overall performance of the engine. Each cylinder contains a piston that pumps inside of it and those pistons connect to and turn the crankshaft. The more pistons there are pumping, the more combustive events are taking place during any given moment. That means that more power can be generated in less time.",
"For a given combustion chamber total requirement- cubic capacity (example 2 litres) the pistons can be sized with a diameter and stroke length to give the capacity. This could be a single piston or multiple, the configurations of v4, v6, v8, v16 could all deliver the same 2 litres but by having smaller and larger diameter pistons engine character can be change this allows for smoother running, less fuel, higher torque, faster revolutions, the ratio of (total size of piston diameters added) and the total size of the inlet and exhaust valves also come into play a 60 valve 12cyl by 5valves would also add considerable complexity to engine design , and is normally reserved for large high power units. - edit - Oh I forgot the V can also be either hot allowing for the turbo to be centred within the V (unusual) but compact or classic."
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c3ac83 | If lightning is drawn to metal and the tallest objects in a given area, why doesn’t it always strike airplanes? | Engineering | explainlikeimfive | {
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"It does often strike airplanes. Lightning is trying to find the best path to go from a negative area to a positive area (charge wise). Generally the earth is a big positive area so it likes to go down. It finds air hard to travel through (and metal easy to travel through) so it finds something else to crawl down to get there. There can exist positive areas in clouds and a bunch of lightning does go from cloud to cloud. Airplanes tend to try to avoid being in thunderstorms though, thats more so the reason that lightning doesn’t always hit planes, because the planes aren’t there often.",
"Airplanes aren't grounded to anything to complete the circuit. Although they do often get struck by lightning and it passes through on the way to the ground."
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c3ee5b | Why a wobbling ceiling fan never balances itself | Engineering | explainlikeimfive | {
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"It wobbles because it is out of balance. That won't change without human intervention. You can tape a penny to the top of a blade to fix it. Some trial & error will be needed."
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c3ge3i | What is it that a step up transformer does to increase voltage? (please correct me if I'm wrong) | Where does the extra voltage come from? How does it still follow the law of conservation of energy? | Engineering | explainlikeimfive | {
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"Think of it like the electromagnetic equivalent of a gear ratio. Two gears of different sizes will rotate at different speeds when connected. Anyone who has ridden a bike or driven a car understands this. If you place a few coils carrying low voltage as the input, near *many more* coils of the output wire, that will induce a higher voltage in the output. Here come the numbers: Let’s say we want to build a step-up transformer. You wrap the input wire around the core 5 times. On the other side of the core, you wrap the output wire 20 times. (The core is basically 2 bars very close to each other.) The ratio is 1:4. To make the math easy, our input is 100 volts, 10 amps, 1,000 watts. In that case, the output will be 400 volts, 2.5 amps, and still 1,000 watts. (If you ignore resistance, Volts * Amps = Watts) So, it doesn’t violate conservation of energy because it has less current in the output (lower Amps), and the power (watts) remains the same. Edit: An important detail: Most transformers do this process several times inside one machine. So it’s not just two bars with coils on them, it’s like 50 sets of two bars, wired to one another. So the transformers you see on the street are more like 50 transformers wired together, each one multiplying the voltage from the one before it. Tl;dr: Step-up transformers are trading amps for volts, maintaining the same wattage."
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c3jenz | Why, with all our advancements in telecommunications and phone technology, has phone call audio quality stayed virtually the same as ten or twenty years ago? | Engineering | explainlikeimfive | {
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"In simplest terms; because the telephone system is an internetwork of individual links, it is limited by the least capable link in the system. Think of having a road between two cities that starts out as a five-lane Interstate highway, drops to a dirt road, then goes back to a five-lane highway and then arrives at the destination - the traffic is limited to the capacity of the stretch of dirt road in the middle. In standard telecoms that limitation is the enduring use of [G.711 encoding]( URL_5 ) to convert analog sounds from the two ends of the call into digital information that will be carried over digital [trunk circuits]( URL_2 ) in the middle. Those circuits, at least in North America, are built around the [T-carrier architecture]( URL_0 ) (with the ulaw variant of G.711), which has a hard limit of 64kbps of information per circuit which, skipping over a whole bunch of technical stuff, translates into only carrying sounds between [300 and 3400Hz]( URL_6 ) \\- everything else within the typical range of hearing of 20–20,000Hz is simply discarded. Various methods of delivering [wideband audio]( URL_3 ) over conventional digital telephone networks do exist (eg. [G.722]( URL_1 )), but if the call will eventually terminate on a conventional analog telephone (or cellphone) then the extra effort to capture and transmit that extra audio information just goes to waste as the signal must be [transcoded]( URL_4 ) to meet the capability of the lowest common denominator in the end-to-end circuit. On the other hand with pure VOIP calling, for example with Skype-to-Skype calls, most of the internetworking issues are eliminated as the sound is transmitted entirely as a stream of data which is controlled exclusively by the two ends of the call, and so the system can transmit as much audio spectrum as the designers wish. & #x200B; edit: goodness, gilding? I'm flattered!",
"If you talk about landlines or anything that is talking to landlines: That is a dead technology, don't expect anything there. If you talk about VoIP: That is much better than years ago, with a better sampling rate and wider spectrum they capture. However, that is part of the problem, the biggest problem is the transfer of the voice of the speaker to the microphone: Some microphones are crap (cheap headset), or not at the right place (laptop, or not close by the mouth) or interference with the environment (wind, background noise). There is only so much technology can fix :-/ You won't get movie quality because that's rerecorded in the studio.",
"TL;DR you’re limited by the lowest common denominator. To get the amazing call quality you can get over 4G, you need everything between you and the person you’re calling to be capable of handling the high quality calls. If even one link in the chain isn’t capable, you’re going to be limited to the capability of that link",
"Of all the things that cell phones do better than land lines, the sound quality was so much better.",
"That's patently untrue. HD Voice / VoLTE has vastly superior audio compared to anything else prior. I do miss the old landlines, where you could hear yourself talking in the earpiece tho.",
"phone network operators are today internet service providers (simplified a little) - millions of calls go through their data network every sec. so they want to keep costs down and that means limiting the per-call bandwidth as much as possible - that in turn entails high compression of the audio which leads to poor audio quality. basically the operators want the audio quality to be just good enough - anything more than that is a waste of their money. TL;DR it's from the same reason we don't go to the moon anymore (at least not manned missions) even though we could do it - economy. the operators are trying to max profits, not audio quality.",
"The audio quality of a mobile phones is based on following aspects: note this applies to both devices, originating and terminate end. - bandwidth assigned to the voice channel - vocoder technology used - microphone quality of mobile phone - speaker of device Now, the best technology to measure Voice quality is based on a set of standards, which for VoIP technology, is PESQ (google it). PESQ measures the variance of signal and creates a score using various large database that has relative voice metrics to what it listens to. It scores it based on a 1-5 score. 1 means not understandable and 5 being it sounds perfect (original audio from originating device) Since the 1990s, the quality has improved by 1 point. In 2G and 3G technologies, it was 3-3.5. In 4G, it has been improved towards 4.2-4.5. Note this is log scoring, so as you get closer to 5 it’s a huge incremental improvement. One commenter brought up a good technical specs on the G.711.",
"Audio quality on smartphones (especially iphone) is great. The noise cancelling is incredible too, but people don't even realize that it's doing it but these phones have lots of microphones for that purpose. & #x200B; The limitation is the speaker quality on the tiny phones",
"Lol, you clearly weren’t making many phone calls 20 years ago. Quality has undeniably improved.",
"I dunno what phone you use but phone call quality has increased a ton for me in the last decade. Lots of the calls I have now are the HD audio calls.",
"because it hasnt. compare a voice quality from old school landlines/early cellphones to the hd voice quality of today. OP you are clearly ignorant to the fact the voice quality has indeed changed over the decades.",
"Because it has been studied which frequencies are necessary to make speech understandable and only those frequencies are being transmitted to save bandwidth. We could easily switch to higher quality but there is no need. I suspect higher quality audio will be a thing when VoIP becomes easier with the new 5G networks. I am bewildered by some of the answers here claiming that the reason the quality is limited is the infrastructure. No, that is not true. The infrastructure has been *designed this way* based on the needed frequencies. We have created these limitations on purpose to save the cost."
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c3p7y6 | How are bridges that span long distances of water (e.g., Seven Mile Bridge in Key West, FL or Lake Pontchartrain Causeway in Louisiana) built? | Does the water determine the materials? How do those working on it get out there? How do the materials brought on site? Seems like any mistake would be a lot harder to deal with because of the environment. | Engineering | explainlikeimfive | {
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"This doesn’t give exact details about those bridges but it’ll provide some basic insight to how bridges in large bodies of water are constructed. [Here]( URL_0 )",
"Typically what will happen is a coffer dam gets set up. Basically its just some thick sheets of metal driven into the seabed.Once its set up you can pump the water out and have people start building the base. These will be the piles you see sticking up out of the water. Now that thats out of the way you can bring in your crane barge and lay some girders. These are the steel beams you see running the length of a bridge. Now you can start building a work platform to build on top of, or just start laying some prefab concrete across the spans.depending on the type of bridge After that it really is just like most other projects"
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c3wy55 | How do those “push and twist” drug bottles work? | Engineering | explainlikeimfive | {
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"They utilize a thread with an interruption on the bottle and a small bit of spring tension on the cap. Unless the cap is pushed down it cannot interact with these thread to come off."
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c3xi86 | How do those windows, wich you can turn non transparant with a switch, work ? | Example: URL_0 | Engineering | explainlikeimfive | {
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"There's a film of liquid crystal inside the window, specially constructed and treated so that the crystals inside respond to electric current. When there's no current, the crystals go out of alignment, and their random orientation blocks light. When you flip the switch on, a low-voltage electric current forces the crystals to align, letting light pass through. [This website]( URL_0 ) can tell you more.",
"It's interesting - the ELI5 answer is \"liquid crystal film between sheets of glass, electrically activated, lol\", but the ELI10(?) explanation has to do with polarized light and how liquid crystals twist light polarization when energized. The invention of LCD displays for things like calculators is an interesting story. I've been waiting for LCD window shades for decades, and I think we're getting close."
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c41zb4 | How do digital cameras focus by me just holding down one button? | Engineering | explainlikeimfive | {
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"They analyze the data coming from the sensor and adjust the focus until they get the clearest image. When you're out of focus, the level of similarity between pixels is high, as the image comes into focus, the similarity between pixels drops. The camera adjusts the lens until it finds the point with the lowest similarity between pixels.",
"There are different ways a digital camera does this. The most popular method is \"contrast autofocus\". With contrast AF the camerasoftware evaluates how sharp the image is. Then the camera focuses a bit and checks again if the image got sharper. So it's basically the camera cleverly focusing around until the software says \"stop here, this was the sharpest image I have seen\". The software detects sharpness by measuring the contrast. The higher the contrast, the sharper the image. An other method is \"phase autofocus\". While contrast AF is cheap since it only requires software, phase AF requires an additional sensor, making it more expensive and therefore less widespread. But it has some benefits over contrast AF. The phase AF system uses a clever optical mechanism to project the desired image section multiple times on the additional sensor. The clever part is, that the projected images are further away from each other on the sensor the more the real image section is away from being at focus distance. So the image distance on the sensor is a measurement of the defocus. This way the camera immediately knows how much and in which direction it has to adjust the focus. Without trying around. Phase AF is often found in expensive premium cameras. Edit: typo; typo"
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c49cua | How does defusing a bomb work? | Engineering | explainlikeimfive | {
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"The problem with answering this question is that there is no single way to design and fabricate a bomb. By far the simplest method is to intentionally blow it up with the surrounding area evacuated. Robotic vehicles in the military are design to do this. If the situation calls for actually defusing the bomb, then a bomb disposal team may try to take x-rays of the bomb, review the innards and formulate a plan to defuse the bomb. The exact methodologies they may use are trade-secrets for obvious reasons. More sophisticated bombs may be undefeatable however. For example, the [Harvey’s Resort Bomb]( URL_0 ) of 1980 featured: • 30+ switches on the exterior that had to be flipped in a specific sequence to lengthen the timer and disable certain sensors. • A tilt sensor. If the device was moved without staying level, the bomb would explode. • A float valve. If the device was flooded with water in an attempt to disarm it, the bomb would explode. • Spring loaded screws. If any of the screws on the exterior were turned, the bomb would explode. • Pressure sensors. If you tried to pry the top off, pressure would be relieved and the bomb would explode. • Conductive metal foil. A thin metal layer surrounded the inside of the bomb. If drilled or sawed through, the bomb would explode. After scanning the bomb with an x-ray, the FBI tried detonating a small shaped-charge on the top of the bomb that would destroy the circuitry and leave the main bomb charge untouched. The idea was to destroy the device circuitry before the electricity running inside of it could compete the circuit and detonate the bomb. However, the bomb creator actually had a few sticks of TNT placed throughout the inside of the bomb that went unnoticed in the x-ray scans to prevent exactly that from happening. When the FBI detonated the charge, they ended up setting off the main charge of the bomb and destroyed the entire building.",
"Bombs aren't that complicated IRL. They are composed of: * power (to set off the detonator) * switch (to send power to the detonator) * detonator (to set off the explosive) * explosive Typically, to \"defuse\" a bomb, you can simply remove the detonator (or its ability to detonate) from the explosive. I movies, they are probably cutting the wires going from the switch to the detonator."
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c4b0gt | Why is it that during a storm, power always seems to flicker or go off. Why? | And why have no countermeasures been taken to prevent power outages Edit: I realize my error in the title... | Engineering | explainlikeimfive | {
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"Well storms are associated with lightning, and high winds, both of which can cause power outages. Trees being felled causing lines to short out, lines swinging violently enough can potentially short out, lighting strikes causing surges, blowing transformers, they're all things that would cause the power to flicker and die."
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c4k80i | Why do railway tracks have stones around? | Engineering | explainlikeimfive | {
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"The stones are called Track ballast. They are there so water can drain away from the track and doesn't cover it. They are also hard for plants to grow on, so you don't have to clear bushes from them as often.",
"Prevents vegetation growth= reduce fire Diverts rain water=prevent track washout Locks rail ties = keeps tracks stable Distributes load= keeps tracks in good condition.",
"Railway tracks are laid in a bed of gravel. It supports the tracks well enough, while being really convenient. If you laid them on the soil, the weight of the trains would push them into the soil, leaving the line twisted. If you cast them in a bed of concrete, that would be really expensive, and the forces involved would soon crack the concrete, and the rails would move and spread. (High speed rails are often cast in concrete, but it's really expensive concrete, and the trains and rails are carefully built not to destroy the rails.) The bed of stones spread out the weight of the train across a good area of soil, so it won't sink. The rails are allowed to vibrate or shift as, say temperatures change and the rails become longer or shorter; and if the track becomes a little uneven, you can use a machine - a tamper - to lift the rails, shake a bit of the stones back under the ties (or 'sleepers'), and tap it back down to level.",
"The primary purpose is to provide resistance to movement. When trains accelerate and brake they cause a lot of forces on the track. The same can be said for going around a curve. There are also a lot of dynamic forces that occur due to heating and cooling because of the climate. A secondary feature is to better distribute load and allow for water to drain.",
"Otherwise, a heavy storm would wash the dirt out from under the track and you’d have a real bad time. Even then, in flash floods, you get washouts sometimes.",
"Ballast does several jobs. & #x200B; 1. Maintains track position, by its very nature, formed and compacted granite is hard, and resists lateral and vertical loading 2. Allows drainage 3. Cheaper than laying it in massive slabs everywhere 4. Maintainable, your slab cracks and you're screwed, your ballast moves and you can re-pack and re align with tampers, stone blowers, kango guns 5. Hard wearing, see #1 by it's nature it lasts a damn long time 6. Ease of transport - can be moved by had with shovels, in tonne bags, on wagons...",
"infrastructure engineer here. the main (or first) role of the stones is to distribute the load of the train (live load). if the stones (ballast) would not exist, the sleepers (the transversal cincrete /wood beams on which the rails are placed) would be placed directly on whatever soil the tracks are going through. soils are diverse from one place to another, sometimes you don't have the same type of soil in 500m. This means they behave differently under loads (either live loads or for example exceptional loads - earthquake, floods etc). if you have a very rocky soil that doesn't react with water for example, next to an area rich in clay soil, that swells up, your rail tracks will deform. if the tracks are placed on the same type of bed (tge ballast/stones) the deformation from various environment factors, is diminished immensely. Put in very few words, the stones help with the load distribution and also the stability of the whole system. PS: they are calculated (diameter of stones, placement, etc) depending on the load projected to circulate on the track but also depending on the soil bed they are being placed on, so the results (deformations and reactions) under loads is optimal(around the same values) from km 0 to the end of the track. They also serve to drain water as presence of water causes stability issues. Stopping grass from growing is not a purpose, it's more like a good side effect of the technology."
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c4n0xr | How do anti-tank weapons kill tank crews after penetrating armor? | So I've read a lot of explanations on how different anti-tank weapons work and how they penetrate armor, but I was wondering how the crews are affected by them. Are they killed by shrapnel, pressure or heat? Is there a high survival rate for struck tanks? Thanks in advance. | Engineering | explainlikeimfive | {
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"Anti-armor explosives have shaped charges that use explosives to force a concave piece of metal (like copper) into a molten jet of metal that pierces the armor. Once through, it is still molten and moving supersonically, introducing hot metal, plasma and a concussive, expanding shockwave to the interior. Soft, squishy humans react poorly to those sorts of things. As well, some anti-armor rounds cause large scabs of interior metal to fly around at high rates of speed.",
"Tank crew member in the early to mid 90s here M1, M1A1, and M1A2. Several ways to be killed inside a tank. If the armor is penetrated with a sabot the shrapnel from what was once the armor plating is just a fine mist and catches fire burning and shredding you all at the same time. ( a main gun round has phosphor on it and burns for tracing ) If the armor is not breached then all the equipment bolted to the inside ( gun sights, radio, ammo storage, safety shields, target computer ect...) has a chance to break free and either crush you or shead you. The concussive force is also real bad for your health. ( think blast lung/ gut) Some rounds are designed to breach the armor and set off a shaped explosion inside the crew compartment.",
"APHE(Armor piercing high explosive) rounds were common previously and would penetrate armor then detonate inside the tank doing severe damage to the equipment and killing the crew Composite and Sabot rounds punch a hole through the armor and send bits of the armor into the passenger compartment as a shotgun blast. These can disable the tank without killing all of the crew HESH(high explosive squash head) rounds are designed to hit the side of the tank, squish and spread their explosive across it, then detonate which sends the inside layer of the armor shooting into the tank(spalling). They don't penetrate the armor but can kill the crew. HEAT (high explosive anti tank) rounds often have a shape charge head. They detonate carefully laid out explosives behind a sheet of copper to create a high temperature, high speed jet of metal that cuts through the armor. If it makes it through you now have hot molten metal spewing around inside the tank. This is bad for the crew",
"Depends on the round type. Some bounce around inside, some release an explosive. Also, shockwave/ shrapnel is an issue because humans are quite squishy and don't do well in those situations. There are a range of very good YouTube videos and documentary on the subject but I'm on my phone and as a five year old that can post on Reddit you can look up a video for yourself as well. I believe in you!"
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c4t15u | How modern tanks are said to be indestructible against WW2 era tanks? | Engineering | explainlikeimfive | {
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"That's a very broad statement, and I'm sure you can find exceptions. Speaking broadly however, there are big differences in weapons, armor, and firecontrol that make it like using a handgrenade to shoot fish in a barrel. & #x200B; WW2 era tanks generally used solid AP or improved solid AP rounds for armor. Solid AP is simply a solid metal round designed to punch through armor using pure kinetic force. Improvements on this will include explosive boosters in the rear or an explosive cap to help cause more damage, but they are all very old ways of beating armor. Shaped explosives were adopted into tank weapons after WW2, and them becoming part of the vehicle mounted arsenal redefined how tanks had to deal with incoming fire. Modern HEAT rounds of the same diameter can roughly go through 3 times the armor of something like a WW2 75mm M3 gun, and because they rely on an explosive effective of the warhead rather than kinetic energy, the distance to the target is less relevant. & #x200B; Modern tanks fire a variety of rounds including HEAT. HEAT uses the explosives inside the round to form a copper or similar penetrating medium into a slug that goes through armor. This is pretty much the default effect used in shoulder fired anti-tank weapons. Sabot rounds are the other most common method. Sabots being a very dense metal like depleted uranium that fires at an extreme velocity. Less common but still in use are HESH rounds that try to thump tanks with a wide explosive pattern to cause a large dent and internal spalling. & #x200B; Modern tank calibers are also generally much larger. A WW2 Panther had a 75mm. A modern M1 has a 120mm. Lot bigger, and they are higher velocity. & #x200B; Modern tanks have better armor. In addition to having better material composites, they also commonly have explosive armor that can prevent damage. & #x200B; This is to say nothing of fire control and imaging. Modern tanks have fire controls and stablizers that allow them to fire accurately fired while moving. Combined with thermal and night vision (often these system are combined in hybrid vision) and a modern tank can run circles around a WW2 tank while shooting at it, and keep doing it in the dark. & #x200B; The way warfare works, you're better off with a pickup truck with a decent AT weapon bolted on the back than you are with a WW2 tank. Even then that is really only going to be effective against unupgraded cold war era tanks and using good tactics.",
"Modern tanks have much better armor that WWII tanks, and also are designed/constructed in better ways that make them more resilient to damage. And modern weaponry has evolved to be more destructive in response. Much of the WWII era anti-tank weapons would not be particularly effective against modern tanks. And beyond just their armor, modern tanks are generally faster and more versatile than older tanks. They not only have significantly better guns, but they have much more sophisticated sensors/targeting/aiming/etc. systems. They have various sensors/camera/etc. that they can use, while WWII tanks would be reliant on their operators' eyes. Modern tanks can see and fire upon enemies at a much further range than older tanks. If a stupid driver drove a state of the art tank through a gauntlet of WWII tanks, there's a decent chance that some of those older tanks could score some lucky hits that would damage the modern tank. But if the modern tank used proper tactics and good decision making, it would be engaging the older tanks from a range where they couldn't even hope to fight back.",
"To claim that they are indestructible to WWII tanks is just incorrect. Better WWII tanks can penetrate the side and back armor of tanks used today because it is not thicker then WWII from armor. But the front armor today on main battle tanks is thick enough that most WWII tanke would have huge problem penetrating it. The same was true back in WWII and the largest take especially heavy german tank destroyed was almost invulnerable in the front but the sides and the rear had a lot less armor and if you hit it there it was not that hard to destroy. & #x200B; The primary advantage a modern tank has is not the armor but the that there gun with the projectile used could penetrate any WWII tank even at long range. The guns are a lot more accurate and you can get over 90% fist shoot hit probability because of thing like laser distance measurement. The optics is a lot better and you have thermal sight that work as good in the dark and dusting the day and show tanke that is hard to see with visible light. Time from spotting a enemy util you can fire and hit it is a lot less today. The guns can also fire on the move with almost the same accuracy but WWII tanks needed to stop to have any chance to hit a target at a distance. Tanks today are a lot faste and are many times more reliable then WWII tanks. So you have the advantage that you can maneuver and choose where to engage. Just running away at high speed and maneuver will make it very hard for a WWII tank to hit you but a modern tank could hit the enemy that did the same thing a lit easier because of fire control computer and could do that while it was itself moving. & #x200B; So a long as you can engage the enemy at long distance there are very few tanks of WWII that can do serious damage to the front. So for example in a tanke combat in a desert the result would be that WWII tank would have no chance. If the combat was in a city or in other terrain where you manage a ambush and can hit the sides from closer distance WWII tank could certainly destroy a modern tank. & #x200B; So the result is that a a combat between WWII tanks and modern tanks would have even larger difference then in the Gulf war when the Iraqi tanks that was a generation behind had no chance. But is is important to remember technology advantages have the most effect in a desert. Tank for example alone in a city is a totally different situation and then infantry have the advantage and WWII infantry with the antitank weapons the had could destroy a modern tank if they could engage if from above. The first [Battle\\_of\\_Grozny]( URL_0 ) 1994-95 when Russia used armor forces in a city without enough infantry support around them resulted in a lot of tanks and other vehicles destroyed. Russia won but is was a pyrrhic victory and there losses was a lot more then the enemy."
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c513ub | What's the different between Gen 3/3+ or Gen 4 nuclear reactor to the normal Gen 2 reactor? What are the advantages? | Engineering | explainlikeimfive | {
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"3+ plants incorporate passive safety features. That’s the biggest difference. Gen 3 plants eliminate large Recirculation piping and reduce the size of the worst possible LOCA because of smaller piping. They are usually simpler. They take advantage of the operating knowledge of the gen 2 plants which are the first plants that had very high power densities. They use more digital or solid state integrated control systems instead of the gen 2 plant analog control systems. Gen 3 plants are more standardized",
"The difference between 3 and 3+ is that 3+ has safety features that 3 doesn't. That plus stands for passive safety, meaning humans don't have to do anything to initiate the safe shutdown, the reactors were built, combination fundamental physics and engineered systems, so they safely shut themselves off if temperatures or reactivity get too high. They also were designed to be more eocnomical, mostly by reducing the amount of material and relative complexity of Gen 3 reactors, and are much more standardized than Generation 2 reactors. However, they are clearly direct descendents of Generation 2 reactors, and both generations are known as Light Water Reactors. Generation 4 reactors have many different design types. They are really some using hotter and more pressurized water, liquid metal, molten salt, and gas. The fuel types and forms can be very different from previous generations, the size, the safety features, really it represents a much more drastic change than the difference between Gen 2 and Gen 3."
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c524p8 | How to CDs work, more specifically, how does sound and picture get transmitted from a little disc? | Engineering | explainlikeimfive | {
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"A CD is essentially a layer of metal pressed between two pieces of plastic. To record onto the CD, a laser burns pits into the metal. If there’s a pit, that represents a 0, and if there isn’t, that represents a 1. This is recorded from the inside to the outside in a tight spiral. To read the CD, another laser is shone along the spiral, and a photo sensor is placed so that the reflected light from the shiny bit will hit it and create a small electric current, representing a 1, and the pits don’t. So this electrical signal is read back to a computer that takes that stream of 0s and 1s and interprets it in some way to pass on to computer memory, and then eventually out to a screen or speaker as a pattern of light or a wave of sound."
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c5csxr | How do some magnets have the ability to turn on and off? | Why don’t all magnets have this ability? Is it based on the material? If a magnet is turned off, is it that the material is demagnetized somehow and then magnetized again? | Engineering | explainlikeimfive | {
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"Electromagnets can be turned on and off by adding current/electricity. Natural magnets cannot be turned on and off. [ URL_0 ]( URL_0 )",
"You are thinking of electromagnets that can be turned on and off. Electromagnets are a non magnetic material like copper that becomes magnetic when an electric current is applied to it."
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c5j8jk | why are jeeps allowed to have no doors? | Engineering | explainlikeimfive | {
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"There's no law stipulating doors on any vehicle, the same as no law requiring a roof on your car. Jeeps are just really easy to get the doors off of, and built for enjoying the outdoors, so they're the only ones you see this with commonly.",
"It's actually not about the doors it's about the mirrors, the law requires you to have enough mirrors to still see surrounding cars, as long as you relocate your mirrors, doorless cars are fine"
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c5pdtt | Why are triangles the most stable shape in construction/engineering? | Engineering | explainlikeimfive | {
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"A quick way to visualize this for yourself is to get 4 popsicle sticks or some other small stick like that - toothpicks would also work (they aren't necessary if you can picture this mentally). Take 3 of the sticks and try to touch the ends together to make a triangle. What you will find is that there is only one triangle that can be made and in order to change the shape of that triangle and the angle between any of the two sticks you would have to change the length of one of the sticks. Now take 4 sticks and touch the ends together to make a quadrilateral. Did you make a square? Or perhaps a rhombus of some sort? What you'll notice is that using those exact same sticks you can make many different shapes by changing the angles without having to change the length of the sticks. For this reason when if you have a square structure it is easier for it to change shape than when you have a triangle structure. In other words, it's easier for the square structure to longer be square than it is for the triangle to no longer be triangle. There are other shapes such as circles which are very strong as well depending on the circumstances and arches which are often used in architecture to distribute weight more evenly, but for the simplicity of being able to use multiple straight lengths of material a triangle is the easiest to build of the structurally sound shapes.",
"Already some great explanations for the triangle, so I'll just add that triangles are not always the most stable shape. It is mainly the most stable polygon. Another very stable shape is a sphere. This can be used to distribute a given load quite efficiently. This is the idea behind building a dome, such as The Pantheon in Rome."
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c5qew5 | How is bamboo turned into pillows, clothing, and other textiles? | Engineering | explainlikeimfive | {
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"text": [
"Just got done cutting some bamboo fleece. Oversimplified, they crush the bamboo, use enzymes to break it down to a pulp. Mechanically separate the fibers from the pulp. Fibers are then spun into yarn. Yarn is turned into linen/fleece/some type of fabric. The bamboo fabric is sent to the apparel manufacturer which will be cut and sewed up.",
"Bamboo is a very fibrous material, so its stripped down into these fibers, softened, and woven like any other fibrous material. It's also super soft and breathable, as well as more renewable than other materials because of bamboos ridiculous growth rate."
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c5t5sg | How do the outfits that competitive Olympic swimmers wear allow them to swim faster? Would they not swim faster if they were completely naked? | Engineering | explainlikeimfive | {
"a_id": [
"es3xf4e"
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"text": [
"Olimpic swimmers wear sleek, often spandex/rubber clothing because it doesnt cause any drag. When you swim, everything on your body has to push against the water. So if you cover your hair (swim caps) and genitalia (pants of any form) the water can more easily glide across your body with less resistance. On top of that... do you reall wanna see a bunch of wet, naked guys in the olimpics? On second thought. Dont answer that."
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c5w2v7 | Why does the engine of a vehicle only require around 1-3 thousand rpm other than for accelerating? | For example riding at a constant 65 in my truck only requires 1.5k rpm, riding at 30 is the same. So why wouldn't you get substantially higher gas mileage on a long stretch going 60 vs going 30? Is the engine doing more work somehow? If so, how? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"You do get better gas mileage at 60 for precisely that reason. The ‘how’ it does it is because of the transmission and the gear your vehicle is in."
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c5xe5y | Besides looking ridiculous, why is it that cars with a lot of horsepower can't tow while trucks with less horsepower can? | Engineering | explainlikeimfive | {
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"text": [
"All the responses so far miss perhaps the most important thing: brakes. With the right gear ratio, even a weak vehicle can get a heavy load rolling, but trucks that are designed to tow have braking capacity that greatly exceeds that of the vehicle alone. A Corvette has big vented brakes to produce impressive stopping specs from high speed, but it’s not going to stop safely with four times its own weight. The Society for Automotive Engineers (SAE) has a standard for this. SAE J2807 is defined as “Performance requirements for determining tow-vehicle gross combination weight rating and trailer weight rating,” the standard measures a vehicle’s ability to safely tow by measuring braking distances, acceleration times, passing ability, grade-climbing ability, and physical load-carrying capability.",
"Two things: 1) torque and horsepower are different things and 2) the frames of trucks are built to allow you to tow more. BTW that ugly Honda 'truck' isn't...",
"It's mostly the ability to control the mass once you have it moving. High horsepower cars are usually built fairly light. They don't have the frame strength to control or hold back the mass of a heavy trailer. Trucks are built with towing in mind and therefore aren't built light. Most have steel frames that go from the front to the back where the trailer is attached. This let's them control the mass of the trailer with much less chance of breaking things.",
"In addition to what others pointed out (torque & structural rigidity) i'll also point out that vehicles designed for towing lots of weight tend to have more granular gearing control. While your average car might have 5-8 gears, a semi truck can have as many as 18 speeds. Even if you don't have a lot of horsepower or torque, you can still pull extremely heavy loads if you have the right transmission. It may take a long time to acquire some speed (it's part of why semi trucks are so slow) but at least they will eventually get the job done, whereas your Maserati will still be right where it started. Regular pickup trucks, even though they have the same number of gears, those lower gears are often geared differently, allowing for better towing at the expense of acceleration. & #x200B; This is a more minor thing, though. What others pointed out (torque and structural rigidity) are certainly the larger factors. But this is the third major thing that comes to mind. & #x200B; Also, to offer more explanation on torque vs horsepower, understand the following: 1. Say you have a 1ft (or 0.30 meter) wrench on a bolt. Torque is decided by how much weight (or force) you can put on the end of that lever. If you're pulling 1500lbs, you're going to need a lot of weight on that lever. 2. Horsepower, like other types of power, has to do with how *quickly* you can do something. A watt, for example, is equal to 1 joule (a unit of work which is something moved 1 meter with 1 newton of force) per second. Depending on the country you may see cars measured by their *watts*. Horsepower is just the imperial version of watts; it's equal to 550 foot-pounds per second. It has to do with rate, not really with force. But as you can tell from the definition of horsepower, it is related to torque. But it is different. To generate more horsepower, an engine needs to have either more torque or have a higher redline (maximum RPM aka maximum speed of the engine). Consequently, you can have an engine with very little torque and just a high RPM and still have a lot of horsepower. But that is not what is needed to turn the aforementioned lever to pull that heavy load. This is just my understanding of this-- really wasn't great in physics class lol! I double checked my information and I think it's correct, but if anyone sees any errors, let me know and i'll make an edit!"
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c5yuqq | Why are electric car battery estimates so much more accurate than laptop and phone battery estimates? | My < 1 year old laptop turned off today while saying it had 7% and 24 minutes of battery remaining. In my limited experience, electric cars just don't do that. They provide a much more accurate estimate of how much juice they have left. Yet both use lithium ion batteries. | Engineering | explainlikeimfive | {
"a_id": [
"es4z7ub"
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"text": [
"Have you edited your laptops critical battery settings? They tend to toss themselves into hibernation when they hit a predetermined critical level of battery by default, usually 4-7% at factory setting."
],
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4
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c5zm70 | How do they know when it’s time to repair a highway overpass or bridge before it’s too late? | Engineering | explainlikeimfive | {
"a_id": [
"es56ivh"
],
"text": [
"Proper and timely inspections are the key. You check for metal stress and deterioration. It’s easier to do minor repair than to build a new bridge. Unfortunately, there’s “never” enough money or resources to keep up maintenance but you can better believe there’s enough resources to float a bond election to pay for the replacement of a bridge and the general contractor for the replacement just happens to be the governor’s best friend."
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c5zrz7 | Why do offshore oil rig leaks take so long to stop? | Apparently, the Taylor Energy leak in the Gulf of Mexico has been going for 14 years and could cost $1 Billion to stop. What exactly is leaking, and why is it so hard to stop the leak? | Engineering | explainlikeimfive | {
"a_id": [
"es58unu"
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"text": [
"So part of it is that Taylor energy basically lied about the amount of oil still leaking. Taylor Oil said it was leaking 3-4 gallons a day, but the government is saying it could be close to 4,600 (or 71,000 I don't know). Oil wells in the ocean need pipes to bring the oil and natural gas from far below ground to the surface where it can be processed. During a hurricane these pipes were broken. Because the broken parts are so far under the water, it's just really really hard to actually get down there to actually do anything. And once you're down there it's really hard to fix anything because it's underwater. In some ways, it's easier to do stuff on the moon than deep underwater."
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9
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c6ombq | How do micro SD cards keep having more an more memory, yet stay the same size? | Engineering | explainlikeimfive | {
"a_id": [
"esa9j2b",
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"text": [
"Most of the size of a microSD card is taken up by the wiring from the contacts to the chip(s). The chip is actually a pretty small part of the card. What is happening is the chip manufacturers are constantly improving their fabrication techniques and researchers are refining the physics so we're able to fit more 'stuff' onto a chip the same size. This is Moore's Law that the other comment mentions. Also if you did make a smaller SD card then it wouldn't fit anything. The card manufacturers together with the device manufacturers agreed on the dimensions of the card. That way the card maker could all make cards which would fit in many different devices. And the device manufacturers could make devices which take cards from anyone. This is how standards in the electronics world work. Companies that try to buck the standard often don't last long.",
"Moore's Law states that the amount of transistors manufacturers can put on an integrated circuit doubles every 2 years or so. This means you can fit more transistors into a memory card, increasing the amount of storage in the same sized card. Moore's law is predicted to slow down as science is getting down to molecular level transistors which actually leak electrons."
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c6p9s3 | Fake car grilles and vents are becoming quite common on newer entry level cars. Why can't they just, not be fake? Why can't they just be actual grilles, whether they serve a cooling purpose or not? And just say throw the air out somewhere? | Engineering | explainlikeimfive | {
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"If they don't have a purpose for them (say, the car doesn't need an intake for a supercharger, doesn't need extra cooling for brakes, etc) then they do more harm than good because they can seriously disrupt air currents and cause drag. But car brands seem think that they look \"cool,\" and they probably do trick a few consumers into thinking the car is faster than it is, so they put them on anyways. However, they don't want to hurt aerodynamics and consequent fuel economy for something that \"looks cool.\" Moreover, they don't want to have to cut holes all over the place; it's easier to just plunk down a fake vent thing than to cut a hole and then plunk down the vent. Finally, there are a lot of places under the hood [where you don't want a lot of water hitting]( URL_0 ), and so they either have to design a vent that doesn't let much water through, waterproof the area, or just make the vent fake. & #x200B; It's part of the reason why Tesla got rid of the air vents. On their first major car, the Tesla Roadster, they used a Lotus Elise car body. The Lotus normally has a 1.8L engine, not an electric motor. When Tesla put an electric motor in it, though, they kept the vents (because it would be a pain to try to replace them), including the large front grill. But as soon as Tesla started making their own car chassis, they did away with the grill and excessive vents, mostly for improved aerodynamics. They could've kept them though, and, in fact, many people argue that Teslas are ugly for their lack of a large front grill, especially with the Tesla Model 3.",
"The more air you move, the more energy it takes to move the car. Grilles and vents move air. If that air isn't doing anything useful then it's a waste of air movement. People buy cars off of asthetics first with efficiency being further down the line of what's important (but efficiency is still important) so engineers cater to both by sticking on fake vents that only slightly reduce the efficiency but greatly \"improve\" the looks."
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c6pxoe | Why when traveling in a moving vehicle we feel the wind/air always coming in from windows but never going out, always wind/air coming inside shouldn't be possible since it will result in high pressure buildup inside the vehicle. So why we never feel wind/air flowing outside? | Engineering | explainlikeimfive | {
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"text": [
"When moving in a vehicle the wind isnt blowing. It is a static column and your vehicle is running into it. The vehicle forces the air outwards, compressing it. For every action there is an equal and opposite reaction. The compressed air pushes back against the vehicle the same amount. If your window is open the outside air pushes against the inside air. If the inside air has nowhere to go then the inside air prevents the outside our from entering and you hear that 'wubb wubb wubb' sound caused by the changes in air pressure as the inside and outside air pushes against each other. If a back window is also open then the outside air pushes the inside air out the back window since the air pressure against the back window is less due to portions of that air column having already passed the vehicle. If both front windows are open then variations in pressure on each window means air is constantly pushing back and forth against each other with inside air escaping whenever it encounters a path of least resistance. Thus wind. If you want windows open without the wubb wubb, open another window at a different amount than yours. Creates a pressure differential with counstant air flow into or out of the vehicle, prevents the wubb wubb.",
"The air leave the car in vents in the back of the car. The can be east to spot on the car on the outside but you might never notice them or the can be [hidden]( URL_0 ) behind plastic part or exit down so you can see them. On the inside they are often hidden behind stuff in the car."
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c6qa7q | When constructing a skyscraper, why are some of the piles (?) that are drilled filled with water while drilling and others are not? | Engineering | explainlikeimfive | {
"a_id": [
"esalbqv",
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"text": [
"Civil engineer here. Water, or a mixture of water and other materials called a suspension, can be used to stabilize the hole until it's filled with concrete. A big issue with bigger holes is to make sure that they don't collapse until the rebar is put in and the concrete has hardened. There are different techniques for different ground conditions. Sometimes you put in this special suspension while drilling and then replace it from the bottom up with concrete after it's finished. The suspension can then be reused for the next hole.",
"Water is a heat conductor and commonly used to drill through certain types of materials without damaging them."
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c74u5k | Why do some US electrical plugs have a "ground" and many do not? | I don't know much about how plugs or electricity works, obviously, but I was taught that one side is the "positive", one side is the "negative", and the bottom (seemingly quite optional) is the "ground". It's odd to me that so few plugs use the "ground", so it made me curious why it exists, and why it's optional. Are there any safety benefits to having a "ground", or safety concerns with not having one? Thank you! | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Positive and negative doesn't really apply here, because they switch back and forth 60 times per second. You have hot and neutral. Hot is connected to one of the phases, neutral is the same potential as ground, but only connected to ground in the main breaker box. stuff that uses a lot of power will often have two hot wires with 240v between them, and the neutral wire is halfway in between. If you have an appliance with a metal case, you connect the ground wire to the case, so that in the event of a failure somewhere, the outside of the device shorts that back to ground and trips the breaker, instead of sitting there at mains voltage waiting for someone to touch it. Two prong plugs are used for double insulated appliances, usually items with plastic shells that won't conduct electricity if there's a failure, but it can also apply to metal items so long as a single fault won't cause an electrocution hazard.",
"The alternating current coming out of a power socket is like a dog zooming back and forth between the positive and negative plugs represented by opposite sides of a backyard. Normally, this is okay if there are no other things in sight of the doggy. But the doggy has a huge prey drive that represents how much electricity loves to flow from high potential to ground. If a squirrel comes within eye contact of the dog, the fence and other people could try and stop it, but it will run through them as eager as possible. With just two sockets, electricity can easily jump through objects (like people) if there is a path to ground. Adding a ground prevents this by providing a direct ground to go through if the electricity leaks in any way. Often, electronics enclosures are grounded. This is like putting a tube for the running path of the dog so it never gets distracted enough to run out. A ground has other advantages such as providing a fixed reference for signals in case certain circuits are noisy.",
"As others have said, the neural is the same as the ground in concept. The difference is that neutral is Ground at the Power Plant and Ground is the ground in your home."
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c753ec | How does a loudspeaker reproduce the sound of a whole orchestra, which is itself comprised of a hundred or so different sound sources, with just one single swinging membrane inside of it? | Engineering | explainlikeimfive | {
"a_id": [
"esd3c62"
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"text": [
"It happens the same way we can hear that orchestra with only one single tiny membrane vibrating inside each of our ears (ear drums) in response to the sound of the orchestra. The various sound waves from all points within the orchestra add and subtract (depending on phase). This “composite” wave form made up of the mathematical sum of all the waveforms is reproduced by the loudspeaker and caused our eardrums to vibrate in a similar way as if we were near the real orchestra."
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c77n5h | How are fireworks manufactured and made to pop out like they do? | Engineering | explainlikeimfive | {
"a_id": [
"esdrb8l"
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"text": [
"Not a fireworks guy, but How It's Made has a really good piece on how they're made. URL_0 Basically, it's a series of explosive charges seperated by time delay fuses. An initial \"lift\" charge launches the firework into the air, after a given time, the burst charge, usually gunpowder surrounded by small metallic stars, all contained in a plastic shell, explodes. The type of metal dictates what color they burn. They're made in a very anti static environment, by specialized technicians. Hope that's a good start!"
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c7c9u9 | what is the cylinder looking thing on power cables and chargers? | Engineering | explainlikeimfive | {
"a_id": [
"eseemlp",
"eseeu29",
"eseeqez"
],
"text": [
"It's the ferrite bead. It's a bunch of winded wire used to reduce noise on the cable, to provide a more stable electric current to the device.",
"Think of it as a muffler for electricity. Engineers use it as an easy way to quiet electronic devices that have resonances or “ground-loop” noise issues with straight line voltage powering them. Imagine an electronic hum or whine being emitted externally or through speakers/headphones etc. It is a cheap and easy way to fix noisy devices without having to troubleshoot and fix one, or maybe several, contributing factors.",
"Ferrite bead/ring. Reduces interference from poor power sources. Usually used on audio/visual stuff to reduce buzzing on speakers/microphone recordings/etc. URL_0"
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c7fg26 | What is the difference between labyrinth and maze? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The two words are usually synonymous, but a labyrinth *can* be a maze with only a single path (such as the labyrinth in the cathedral at Chartres) while a maze generally has multiple, branching paths."
],
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c7lmow | Why do nuclear reactors rely on diesel generators in emergencies? | The more I read about nuclear power plant incidents, the more I wonder why these plants seem to be reliant on diesel generators to keep coolant circulating in an emergency. Is there a reason that power generated by normal operation can't be stored for emergency use? In a large scale battery or something like that? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"> Why do nuclear reactors rely on diesel generators in emergencies? They work. In an emergency situation where failure can lead to an entire city becoming uninhabitable for centuries, that's the only thing that matters. Batteries are fragile and even petrol engines have more breakable parts than diesels (spark plugs, specifically). Add in the fact that diesel generators are cheap, can be easily kept running indefinitely by trucking in fuel, and take up far less space to store a given amount of energy than an equivalent capacity of batteries and they're simply the best choice.",
"It's not safe to rely on the reactor running at the time of the emergency and continuing to be safe to run after the emergency. The safest thing to do is to power down the reactors to minimize the cooling needed and wait for repairs to the grid. Commercial nuclear reactors aren't meant to provide small amounts of power and likely aren't capable of producing the relatively small amount the emergency equipment needs. > In a large scale battery or something like that? Nuclear plants in the US do have battery backups but they are used as a last resort and are fairly small. A battery system large enough to power the coolant pumps for any length of time would be absolutely massive and expensive. Fortunately diesel is very energy-dense and readily available anywhere in the world. One diesel generator replaces a huge bank of batteries and can be refueled while running. The chances of a plant going multiple days without access by tanker truck is extremely small; plant loss of power events happen all the time but never makes the news because it never becomes a real emergency.",
"> Is there a reason that power generated by normal operation can't be stored for emergency use? In a large scale battery or something like that? It can be, that gets you through a couple days. What do you do when you need to keep the coolant pumping for weeks or months? Its impractical to build a big enough battery bank, you'd need warehouses of batteries that are useless for normal operation. Diesel generators are cheap, powerful, space efficient, and work indefinitely as long as you keep pouring diesel and oil in the top. You can even have a couple extra one's that you rotate in so you can perform maintenance on the others. They'll be incredibly reliable and reasonable sized. Remember that almost all nuclear power plants in the world were built before Lithium Ion batteries were remotely common so all the backup storage would be with lead acid batteries. If you need 10,000 liters of diesel(which is a low estimate) to power the generators until the problem is fixed then you'd need 70,000 liters or 2,700 tons of lead acid batteries to get you through the same outage. Its just not remotely practical for an outage where you might need 1,000,000 liters of diesel to cool the core all the way to a safe level"
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c7nsg0 | how the space stations were built. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Old 1960's and 1970's space stations.were generally just one large capsule or a couple of capsules that were launched and docked together in orbit The current ISS (international space stations) is a mutli module space station built.pver the last 20 years of space launches It's a joint project between five participating space agencies: NASA (United States), Roscosmos (Russia), JAXA (Japan), ESA (Europe), and CSA (Canada).",
"The first space stations - Salyut 1, 6 & 7, Almaz/Salyut 2, 3 & 5 and Skylab were prebuilt modules that were launched, achieved orbit and then a crew was sent up. Mir and International Space Station were built out of modules that were launched up into space and then docked with other modules up there. The first part of ISS was the Russian Zarya module"
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Subsets and Splits