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gxah41 | how can dolls close and move their eyes side to side? | I've seem a lot of doll that close their eyes when they are laying down or that can move their eyes side to side when shaked. I've tried dismantling one to understand it, but l really couldnt make anything of it. | Engineering | explainlikeimfive | {
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"It is just gravity. For the eyelids imagine a hemisphere of eyelid that goes around more than 90 degrees but less than 180 with a weight on the back edge. That back edge is pulled downward when the doll is upright, keeping the eyelids open. But when the doll is laid horizontal the weight pulls the eyelids shut as \"down\" is now 90 degrees different than before. Similar methods can be used to make the eyes move from side to side."
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gy4z32 | why does rolling the batteries around inside a tv remote that's gone flat suddenly make it work? | Engineering | explainlikeimfive | {
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"Battery corrosion. Spinning them knocks off a little corrosion so there’s metal to metal contact again.",
"45 years old and never questioned why this happens. Just like blowing air in the game cartridge. Don't question the battery and game gods when it works!",
"Am I the only one who didn’t know this was a thing?",
"Something I’ve done for almost 20 years and never even considered to wonder why I was doing it. Also taking batteries out and putting them in each other’s slot.",
"So, a TV remote, as simple as it is, has a microcontroller onboard- a really dumb, 8-bit thing. It's designed to operate off 3.0v nominal. At some point, like 2.2v, it's liable to start to malfunction and go into a shutdown state which draws essentially no current, at which point the battery might recover back up to 2.22v, and it could technically restart and blink its LED, but we design these reset circuits with \"hysteresis\" so it won't keep restarting constantly while sitting on the threshold. It will stay in a reset state. Removing power and reapplying allows it to reset, and run briefly."
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gyiztw | How does an aircraft carrier carry 60 planes? | [ URL_0 ]( URL_1 ) The most I see is about 30, and that itself fills up most of the deck. But they are stated to have capacity for 50, 60, or even 70 aircraft. How so? | Engineering | explainlikeimfive | {
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"Many of the planes fold up and are stored on the level below the flight deck, commonly called the \"hangar deck\". They are brought up as needed using large elevators.",
"The inside of the ship also has maintenance and storage decks for storing additional aircraft. Here's an example picture of that - URL_0 They have elevators that they use to move the planes up to the flight deck or down to the storage deck."
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gys5zx | How do we paint giant words on streets/fields? | The Mayor of DC had "Black Lives Matter" painted in enormous letters on the street leading to the White House (which was awesome). How do those giant letters get reproduced so perfectly on such a large scale? | Engineering | explainlikeimfive | {
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"This can be accomplished with the use of surveyors tools and good measurements. You can basically pick a font and scale it up to the size of the street. Surveyors tools, like laser distance finders, can help you find all the vertices. Then you use a guide line (string between the points) to either paint or mask.",
"You can use a scaled grid system. If the printed letters have a grid of say 1/8\" inches and the corresponding street grid is scaled up to say 3 feet and each large square contains the same content as the smaller square you've enlarged the text (or any other image content). The grid can be drawn on the street with rulers and chalk (or the afore mentioned surveying tools and lasers) and then the image transferred and paint applied."
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gywnfs | How does a manual transmission work? What does a clutch even do? | Engineering | explainlikeimfive | {
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"A manual transmission has two shafts, and on each shaft there are gears (the actual cogs). How you move the gearstick determines which set of gears are connected, and that's what makes the car reach different speeds or accelerate differently, with the same engine RPM. While you are disconnecting one set of gears and connecting another, it is important that the two shafts spin at the same speed - otherwise the gear teeth can shear! Now, one shaft is connected (through a bunch of joints, differentials etc) to your wheels. Its speed is dependent on your speed on the road, and can't be easily changed. That means you want to be able to adjust the speed of the other shaft - the one connected to your engine. This is what the clutch does: it lets the input shaft (and its gears) spin at a different speed from the engine. The clutch is a series of circular plates with high-friction material on them, and a big plate on the end with springs on it, to push all of these plates together. Every second plate is connected to the engine, and the rest are connected to the gearbox's input shaft. When the clutch plates are pushed together firmly (by the end plate and springs), then then they all spin at the same speed. If they're not pushed at all, they freely spin at different speeds. As they are gradually pushed together, they rub against each other and match each other's speed. This is why you are taught to let the clutch pedal out smoothly, not just to drop it.",
"The clutch disconnects the output shaft of the engine from the input shaft of the gearbox. It's bad to try and change gears while all the load (torque) of the engine is being transmitted through the gears, so you disconnect it for a short period of time."
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gyyoqu | How does NASA/other space organizations take photos of the ISS? | Engineering | explainlikeimfive | {
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"arriving and departing spacecraft, as well as from the [cupola]( URL_0 )"
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gz5idy | Why do ships have circular windows instead of square ones? | Engineering | explainlikeimfive | {
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"The joke answer is so that the water doesn't hit you square in the face. The real answer is that shapes with sharp corners are structurally weak. Arcs and circles are very strong shapes. If port holes were squares, the openings would get damaged and worn out sooner.",
"For the same reason that airplanes have round(ish) windows. The structure of a ship is put through a lot of changing stresses, both in the sense of the ship being heaved and twisted by waves, and in some cases having actual water pressing against the portholes. The corners or square windows are a point where stresses can build up - it's a weak point. Circles or circular shapes are better at distributing forces equally. The same is true in airplanes, though there the pressure is from the inside, as the outside pressure drops. Early jets had square windows, and it caused several accidents as the uneven stresses over many many flights led to metal fatigue and finally failure.",
"Round windows are less prone to cracking compared to square ones. The angles of square windows are the weak points, whereas the force is spread amongst the outside of a circle evenly.",
"for the same reason planes have rounded windows instead of square ones. a square window has a corner and that is a stress point. a rounded window spreads the pressure and does not lead to stress fractures.",
"All the answers on structural integrity make sense but one thing is missing: water. Windows on ships, specifically, are round because they're easier to seal. Water would most likely come in at the corners where two sealing strips meet. A round window allows for one continuous seal. (Same with airplanes, except with air). This seems more significant to me than structural integrity: the small number and small size of windows addresses that issue.",
"The De Havilland Comet was the worlds first commercial jet airliner, designed in the late 40's and going into full operation in 1952. There were a catalogue of issues with the Comet, partly because of the company rushing to beat US competition to the 'jet liner' market, mostly driven by the UK aerospace industry being congested with several major wartime producers scrambling for market share in the new post-war landscape meaning there was a lack of cooperation and De Havilland refused to use the more powerful and advanced jet engines available on the market (made by Rolls Royce), so the plane was underpowered and the airframe was stripped back to the absolute minimum to reduce weight, including going as far as not painting the plane, because of the weight of the paint. The Comet went into full operation and for a time (a short time) it was seen as a success, partly because of its high-tech design, silver/chrome appearance (because of it having no paint) and because of lots of marketing with big 50's celebrities using them to fly between the US and Europe. Within the first 12 months of operation 3 Comets were lost to in-flight breakups, and it was because the plane had square windows, the combination of the light airframe (because of the weak engine power) and the structural weak points in the corners of the square windows resulted in mid-air explosions. De Havilland would flounder about until 1958 when it'd relaunch the Comet, but by then Boeing had released the 747 which was better and more efficient than the Comet and De Havilland would be absorbed by Hawker in 1960 (the people who made the British Hawker Hurricane in WW2) as a part of wider consolidation of the British aerospace, Hawker would go on to form BAE in the 70's. So long story short, same reason - square windows don't deal with structural stress very well and both ships and aeroplanes suffer cyclic stresses which overtime will cause hairline fractures which will develop into catastrophic failures.",
"Was literally just reading about this in a book about sailing. Basically the answer is what most people mentioned; the fact that the shape is stronger and so on. Another plus point is that if for whatever reason the glass shatters and the boat starts taking in water, a square window may be much harder to plug. Rounder windows are much easier to contain if they are breached, even if it was just temporarily stuffed with a pillow to ride out the bad weather.",
"A circle is much stronger than a square. This is important on an airplane, boat, or space-ship. I suspect houses have square windows because they are easier to build. Houses are built with either blocks/bricks or wood frame, which means it is easiest to make any entrances a square shape to fit into the linear building materials. It would be really hard to make a circular window frame out of bricks or planks of wood! Ships and airplanes are built differently, typically with sheets of metal as the outside, so it is just as easy, if not easier, to cut a circle hole than a square one.",
"Oh wow how interesting! So no difference between having a square with rounded edges and a circle? Because windows on a plane aren't really circular as much as just curved around the edges. Does the shape also change depending on where the pressure is coming from (i.e, inside the vehicle/ outside the vehicle)?",
"Maybe I'm being stupid, but it might be the same reason manhole covers are round. So they won't fall in. They might protect from a wave from smashing it and pushing it inside the vessel.",
"Unlike the windows at your house, windows on ships need to take a real beating. Water pressure alone is a force to be reckoned with. Circles are a better shape for this. You actually see this in tons of places. Next time you see an area of concrete that is patched over, take a closer look. If they did a good job it will be a circle. If they didn't do such a good job it will be a square, likely with cracks along the diagonals if it has been there long enough. Imagine some long, flat piece of metal or wood supported on both ends. If you push down in the middle, it is going to sag a lot. Now use a shorter piece of metal or wood, with the same thickness as before, and repeat. Sags a lot less right? Now do it with a piece of glass (don't actually). If you the glass is long enough, it is going to shatter or at least crack. Glass is brittle, and there is a pretty low amount it can sag before it breaks. So if we are going to make a strong window, we have a restriction on the length from the center of the window to any point along the edge. If we use a square, the distance from the center to the corners is going to be longer than from the center to the sides. So our biggest square window size is limited by the length of the diagonal. But we want more window viewing! If only there was a shape that was equidistant from the center to the edges. Oh wait circles! Circles are the same distance from the center to any point along the edge. So we can have the biggest window possible while still staying under this rule of longest allowed length. This isn't the only reason. But it does a good job of intuitive illustrating the premise.",
"A circle has infinite points, a rectangle has 4. Less points = more stress. Hull warping and twisting = stress. Stress will find the easiest outlet to relieve itself.",
"Im nlt sure for ships, but I think Airplanes do because of those De Havilland Comets that explosively decompressed from their square windows and pressurized passengee cabin in tje 50s killing everyone on board back in the 50s, but that's just my opinion.",
"The load, e.g. from water and air pressure, distributes much more evenly on round surfaces than on rectangular ones. Right angles concentrate tension inside and usually are the first to break. Same reason why we drill holes instead of filing them (i.e. making round holes instead of rectangular ones) for screws and bolts.",
"Finally something up my alley. Everything has a value of stress that it can withstand. Sharp corners act as stress concentrators. These concentrations make cracking easier. Think of cracks as the corona virus and concentrators as distance. The more people (sharper edges) in a place , the greater the chance of getting the virus (cracks)"
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gz6pfh | Why and how does putting a hairdryer in a bathtub electrocute you? Why wouldn't the electricity take the shortest path to ground through the water? | Engineering | explainlikeimfive | {
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"Electricity only takes the shortest path with no resistance. If there are multiple paths exist with none zero resistance, then more electrons go trough the path with less resistance and less electrons go trough the path with more resistance. However electricity goes trough all paths in second case.",
"Pretend that electricity is the flow of water instead of electrons for a minute. If there's a big tub of water high up, and multiple pipes flowing down, the water will go through all of them. Some pipes are bad, so it's harder for water to get through them (resistance is higher), but the water will still go there proportionally to how hard it is to get through. With electricity, it goes proportionally with how resistant it is to electricity. So a large portion will go with the shortest path of least resistance, but some will go through you.",
"Electricity takes the shortest path with the least resistance. Your wet body (Avg 1.1 K Ohms) has less resistance than tap water (Avg 182 K Ohms). So electricity prefers to travel through, not around the body."
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gzbg06 | Crinkle crankle walls, how do they work? Why are they sturdier than straight walls with only one layer of brick? | Engineering | explainlikeimfive | {
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"The wave pattern of the wall gives itself support - if you were to lean against the wall it distributes your weight along the other bricks forming the curve. A flat brick wall does not have this type of distribution without outside supports."
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gzf9nq | assuming they are primarily steel structures, how are 5g masts susceptible to arson? | I keep seeing news stories where these structures are intentionally burned, but it seems they should be sufficiently resistant to fire, at least near the ground. | Engineering | explainlikeimfive | {
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"Only the antenna is made of just metal. The base of the tower contains wiring, computer hardware, cooling systems, hardwired connections to servers, and a lot of other things that are *very* susceptible to fire. And, just so it’s said, the fears over 5G are pointless and based on people having a bad understanding of science. While the frequencies used in 5G *are* more energetic than previous generations, it is still far less than even the light from a red LED. You get more exposure standing near a running microwave than from being near a tower. And even if you didn’t, it’s harmless, as it is non-ionizing radiation."
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gzq01t | What does it mean when people say a song is "mixed well?" | Engineering | explainlikeimfive | {
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"Music recording since the late 1950's has been what is called \"multitrack.\" Essentially, each instrument (and each singer) is recorded on a separate audio channel. When all of the parts have been recorded, the audio engineer mixes them together to create the finished song. Part of mixing is adjusting the volume of the different tracks. You want instruments to come to the front of the mix when they're playing the lead, and fade to the back when they're playing in support. Motown songs are well-known for having very good mixes. [Listen to this]( URL_0 ) track. It starts with the bass and the drums. The bass is really loud for the first few bars, and then it fades when the guitar comes in. The guitar fades when the horns come in, and the horns fade right before the vocals. But there's a little drum fill between the end of the horn and the start of the vocal, and they increase the drum volume so that you can hear the fill. It's an extremely tight mix - each instrument (And Stevie's voice) gets highlighted at the right time."
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h06zil | How do high speed spacerafts deal with potential space debris and stones in space? | Because at high speeds, the force exerted by even a millimetre sized particle would be exponentially high. Do we just hope that nothing hits us or keep track of objects before it hit us? I've always wondered | Engineering | explainlikeimfive | {
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"we (as in NASA and ESA mostly) keep track of every particle that is larger than 2-3 cm diametre (roughly 1\" for those weird ones using the other system). the actual value might differ, it was in this neighbourhood when I still worked in that field ~10 years ago. this is actually insane. we track tiny tiny pebbles in space from the ground and in the worst case tell the satellite to evade this pebble. but even the smaller particles pack quite a punch at the speeds we're talking about here, which are often in the 10-20km PER SECOND range. (bullets from guns/rifles usually are in the 0,5-1km/s range) for my work we simulated those impacts in a lab (with a friggin huge light-gas-gun), and yes, even a small aluminium piece with < 1cm diametre will punch a considerable crater in anything it hits. the main way to protect yourself from these tiny particles is that we use \"walls\" to surround the important equipment. a honeycomb-like structure where you have 1 outer metal plate, followed by mostly empty space and then another metal plate (held together by the honeycomb-structure in between them). the particle punches through the outer plate, fragments and then the slightly slowed and smaller particles hit the inner plate and dont penetrate that one. This way you got a tiny hole on the outside and a (mostly) intact inner plate. the likelyhood of another particle hitting that exact hole on the outside are basically zero (I think a satellite gets hit by 1-2 such particles per year overall) If you used one thicker plate with the same weight as this structure, the particle would just punch through and you'd suffer damage. (and the primary limiting factor for bringing equipment into space is the weight, less so the actual size). that still leaves the solar panels, you cant really coat them in this way. and the impact of a tiny particle actually \"melts\" the material where it impacts and creates a plasma for a few milliseconds. this can short-circuit your panels. that's why most newer satellites (we had to understand this phenomenon first) have \"breakers\" so that the damage to the solar panels is limited to the actual impact crater (this is easily 10-15 times the size of the particle) and not the much larger \"short-circuited\" area (which would have been in the range of 50-100 times the particle size). hope this answers your question edit: I'm gonna link you a few pics: URL_3 < -- the honeycomb-panels that are basically the satellite's \"walls\" URL_2 < -- how the panels protect URL_1 < -- impact in a solar panel URL_0 < -- why thicker metal plates are inefficient",
"Kinda both. The big chunks we can keep track of, and try to avoid. And helpfully space is big. Very big. Even if just in low earth orbit. However... The smaller things we can't keep track of. And there you can only really pray your not hit. Given the chances are still low. Because space is so big. That is only a major concern for humans in space, satellites can be replaced. But every satellite taken out by debris causes more debris. Something called kessler syndrome. Its when the amount of debris keeps causing more and more debris until spaceflight is impossible.",
"Anything large enough to be tracked is tracked, but a lot of debris is too small to track and sometimes things [do get hit]( URL_0 ). Critical areas do get [some protection, typically from Whipple shielding]( URL_1 ).",
"All parts of the spacecraft is designed to be bulletproof. They usually have layers of aluminium and kevlar in a design created to break up and deform any incomming debris and then capture it before it punctures the hull. This is very similar to modern tank armor designs. At this point the International Space Station is covered in tiny impact craters which is an issue for astronauts on EVA as these impact craters can have sharp edges that might cut the space suit. For bigger debris with more energy the spacecrafts is relying on ground based radars to warn them in time for them to change course. However after the cold war ended there have not been as much money available for these radar systems as they were primarily used to gather military intelligence on satellites and warn against incomming weapons. So many of these radars have been abandoned and others are in danger of having to close down due to a lack of funds.",
"Basically they [track]( URL_0 ) it. There is a lot. Most of it is in LEO (low earth orbit). Depending on size/weight, any lower and it gets sucked back into the earth any higher it can lose orbit and fly away but there is a zone packed with potentially dangerous clutter. So yeah they have to plan launches and missions to avoid the dense areas."
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h0ba04 | Why do modern graphic cards require a separate power connector? Why not get power from the motherboard slot? | Engineering | explainlikeimfive | {
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"When the design groups came together to standardize the slots on your motherboard, the lines (the copper traces on the motherboards) providing power were sufficient at the time. So the standard was set by the committees, specifications published. This way there is a standard that everyone can follow so the consumer isn't locked into using one kind of hardware in their computers. As graphics cards advanced, the lack of power was limiting, but the data lines were perfectly fine, so as a work around, power connectors were added to the cards. This allowed the cards to conform to standards and still work. So, why not add a new standard? That's expensive for starters. All of those groups have to get back together and come up with a new slot and specifications (size, height, etc.). Also, routing power like that on copper traces on the motherboards requires them to be redesigned. The width of the copper traces needed to carry that much current need to be big, and would introduce more heat and noise to the rest of the board. In the end, the work around of just adding a power connector was easier.",
"The PCI-E x16 slot on a motherboard can offer up to 75 Watts of power. Major graphics cards require more than that. Each 8-pin power adapter can give it an extra 150W.",
"A modern graphics card needs *A LOT* of power, up to 300 Watts. The slot on the motherboard was designed to provide 75 watts of power as that would take care of most things while minimizing the size of the power traces on the board. All the slots on the motherboard get their power from that 24 pin power connector, but if you need to pull 300 watts through it then you need to add more pins or you'll overheat the ones you have So the options you're left with are either to add more pins to every motherboard connector and *hope* the power supplies can deal with it, or give graphics cards a secondary power connection and the power supply can choose how many they want to offer which lets them stay inside their limits. Note that we did this with CPUs before graphics cards. There is a separate 8 (formerly 4 pin) connector near the CPU which provides the power for it as it can need up to 200 watts which again was more than the main connector could handle.",
"Because it doesn’t provide enough power. The PCIe slot where it is inserted providers about 75W of power. The 6 pin connector from the power supply also provides 75W. Then there’s another smaller 2 pin plug providing 25W so a 6+2 pin connector can put out 100W. For example, the RTX 2080 has a max draw of 250W and it has two 8 pin connectors so 75 from the slot, 100 from one connector and 100 from the other for a total of 275W.",
"The power used by the components inside a computer is DC, direct current. For DC electricity, \"more power\" means more voltage and/or more current. If you increase the voltage, you need thicker insulation between the wires. If you increase the current, you need thicker wires, otherwise they get hot. As the others have said, video cards require a lot more power than what the PCI connector can supply. If you look at a [PCI connector]( URL_0 ), those wires are too close together to support higher voltage, and too thin (they're just a very thin film of copper / gold plated) to support high current. So, low voltage and low current = unable to deliver high power."
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h0hdke | How come diesel engines don't need spark plugs unlike gas engines ? | How come diesel engines don't need spark plugs unlike gas engines ? | Engineering | explainlikeimfive | {
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"Diesel engines are built differently A diesel engine takes in air, compresses it until its really hot, then at the top of the stroke it sprays in the fuel which combusts and pushes the cylinder back down. This direct injection is what made diesels work reliably, you cannot build a diesel engine without direct injection. Gasoline engines would take in a fuel/air mixture, compress that, then set of a spark at the top to cause the fuel to combust and push the cylinder down. If you just squeeze until the fuel detonates then you have a very unpredictable engine that will occasionally burn the fuel while the piston is still on the way up damaging the engine Modern fuel injected gasoline engines could get by without a spark plug, but that would also require much higher pressures than they currently run at which leads to a stronger(aka heavier) engine than they need if they just use a spark plug and run at higher RPMs",
"The idea of a diesel engine is if you compress diesel gas it'll heat up and explode, and you can use the motion of the engine from the last puff of gas to compress the next puff of gas. With a gas engine it explodes because you put a little tiny fire in it to make it explode."
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h0jv77 | How do TOW missiles and other tracking projectiles work? | Engineering | explainlikeimfive | {
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"There is a lot of variety of missile guidance systems out there. Going through them all would be quite a chore. The TOW missile is remote controlled. Meaning that the shooter is able to steer the missile after launch. The missile have an infrared target on it which gets picked up by the sights of the TOW launcher. There is then a small computer that calculates what control input needs to be made to steer the missile into the center of the crosshairs. These control inputs is then sent through a thin wire that is unspooling behind the missile to the servomotors on the missile itself. So the shooter only needs to fire the missile and then point in the direction of the target and the missile will hit the target."
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h0rt6o | How do these massive metal ships float on water? | Engineering | explainlikeimfive | {
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"Because the are hollow and contain lots of air. The metal part is denser than water but the air part is a lot less dense then so a ship with a watertight hull that keeps the water it will float. As long as the density of the ship is less than the water it will float. If you let water in the ship will sink. In practice so you make the ship density a lot lower than water so a large part is above water. If you use Archimedes' principle you will found out if you hade the same amount of water as the volume of the ship below water they would weight the same.",
"Why does anything float is really the question. It's rather simple: the weight of the water being displaced by the object is greater than the weight of the object. Boom."
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h0ucxp | why Sweden plans to build charging system for electric car into roads instead of just using charging stations alone | Engineering | explainlikeimfive | {
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"To allow for long distance driving without stopping. This plan isn't unique to Sweden this has been suggested around the world as the future of road transportation. The problem with electric cars is that recharging the battery is a long and slow process, and speeding it up carries risks to battery health and difficult to pull of safely. While putting fuel to the tank of a car is matter of minutes. So a solution to this the thought of adding induction coils to the road so the vehicle doesn't have to use it's batteries or better yet, is able to charge it's batteries while driving long distance. The idea is to compensate for the issues of electric cars, and to give it an edge over fuel."
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h0w71w | Why aren't we using hydrogen as fuel when it seems like the cleanest option for cars? | Like, you can easily separate O2 and H using solar power and as far as I know, Hydrogen doesn't produce any other elements (besides water ofc) when burned. So why not use hydrogen? | Engineering | explainlikeimfive | {
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"The main reason is efficiency of the fuel cells in the cars themselves, although Hyundai and Toyota have some really nice hydrogen cars with good ranges. The [Toyota Mirai]( URL_0 ) for example uses 0.7kgs of hydrogen on 100km, and can carry 5kgs of it, that's a range of 715km! The Hyundai Nexo is similar. The infrastructure is even easier to build, since regular gas stations could get funding when they build a hydrogen pump and you don't have to cope with the massive amounts of electricity every day when people get home from work. Making hydrogen is a little tricky, but possible. It is already a byproduct of many large-scale chemical processes and could be easily harvested. When green energies like solar and wind have peaks on especially hot days with a good amount of wind, the overproduction can easily be used for electrolysis and storing energy. Yet, after transport, electrolysis, more transport and then combustion in fuel cells, hydrogen has a low overall efficiency, possibly meaning less harvested energy than invested energy. They are drivable today and in some years, they will be affordable for countries and a broad range of the population instead of being an upper class vehicle.",
"A couple of issues. Firstly, hydrogen is extremely flammable and is difficult to safely store large quantities aside from cylinders designed to hold high pressure gasses. Secondly, there is not a system in place for refueling a car with hydrogen gas the way there is for gasoline. Thirdly, hydrogen does not release that much energy when it burns, so the amount that a car would consume is quite significant. Fourthly is the weight, a cylinder to safely hold a large quantity of hydrogen is extremely heavy and to be able to hold the amount of hydrogen necessary would also be extremely large. This means current vehicles couldn't be refitted to use hydrogen, the structure of the car isn't compatible with the necessary safety features. I'm sure there are other reasons, these are just the ones I'm able to think up off the top of my head."
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h0yv96 | .How forensic analysts match a bullet to a gun? | How do ballistics/forensic analysts match a bullet from a victim or found on the scene to the EXACT gun that fired it?? I mean a 9mm bullet can be loaded into any 9mm firearm right? So how do they know exactly which gun that fired it? How do they match it? | Engineering | explainlikeimfive | {
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"Quite honestly poorly. Studies in recent years have shown that ballistic analysis is highly flawed and unreliable. But to answer your question. The barrel of a gun has grooves etched into it called rifling. These grooves are used to spin the bullet when it is fired. That spin makes the bullet travel straighter. The theory is that if you have two bullets fired from the same gun, the grooves created by the rifling should be identical.",
"Because some guns differ even if they're both 9mm. Glocks are atypical and use hexongonal rifling where most other guns use land and groove. That easily differentiates Glock vs non Glock. The main thing is to match the wear patterns. As guns are used, the rifling wears. Like fingerprint, each wear pattern is random depending on the ammo previously used, debris, tooling imperfections. That shows up on an intact bullet. Get the gun that you think fired the fatal bullet and shoot another bullet thru. If the wear pattern is close, then you can reasonably say it's probably the same gun that fired the fatal bullet",
"So, if you replace the barrel after using it (and maybe the firing pin), will that be enough to throw off the analysis?"
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h16cd1 | Why are cities, towns, ... built on top of other towns during history? | My town is built on a settlement which, estimated is 2000 years old. How does this work? As far as I know people always lived here (old Roman and medieval roads were found) but the town now lies several meters higher than the original one. I would suspect that old buildings are taken down and a new one is raised. Does sediment, dust, ... stacks meters high over a period of 2000 years and wouldn't people dig out old buildings? Or did they purposely mound the entire town? | Engineering | explainlikeimfive | {
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"The reason they stack higher and higher is because of demolition. Construction equipment and dump trucks didn’t exist back then, so if a building collapsed or was demolished, and you wanted to rebuild there, it was easier to just knock down the building where it stood, smooth out the debris, and then build on top of it."
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h16vc8 | Why is a building called a "building" when it is already built? | Engineering | explainlikeimfive | {
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"ftqcghv"
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"text": [
"In English, we use gerunds, verbs ending in \"ing\", to create related nouns. You paint a painting, draw a drawing, and build a building. In this sense, \"ing\" can be seen as meaning \"that which is made by\", especially in an artistic sense, but there are more utilitarian examples, like a covering (a cover for an item) or a sighting (the event of seeing something)"
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h7agpn | How are underwater tunnels built? | Engineering | explainlikeimfive | {
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"There are several techniques, but the most common way is to make concrete rectangles, like a box with no top and no bottom. Then you lay the rectangles on the bottom of a trench across the river bottom, making a rectangular tube. Then you bury the tube and pump sealant into the seams. After the sealant cures, you pump out the water.",
"Two major ways. For really long major tunnels, they dig deep underneath the bottom of the water to where there is solid rock. Then they just break up the rock there with a big tunnel boring machine, take the rocks out of one end and build up supports. Otherwise they dig a ditch, sink down concrete sections, seal it up, and take out the water.",
"its kind of crazy that the first underwater tunnel wasnt completed until the 1840s! i think the real key is knowing where and how to find the perfect geology to support it. its the thames tunnel btw and brunel is quite well known for improving safety standards for his workers. for the tunnel they used a sort of 2 or 3 floored rolling scaffold with a roof and basically dug it out by hand"
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h7cdlu | How does water become pressurized in a faucet? | Engineering | explainlikeimfive | {
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"See those water towers around town? water is pumped up to them and then gravity provides the pressure to the network",
"The whole system is pressurized by the weight of the water itself. The system depends on wether you’re in a city or town or rural area. Or if you’re using municipal water or are on a well. But the whole system is pressurized, which is why water will shoot everywhere if you start unscrewing a random pipe. The most common way to do this is with water towers, in which the water is pumped high up, and then the weight of the water sitting up in the water tower is what pushes the water through the system to your faucet."
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h7qdz2 | why is it easier to cut sheet metal in one direction than at 90 degrees to that? | I often have to cut sheets of aluminium with a jigsaw at work, it seems the saw cuts more easily in certain directions. Does the metal have a "grain" similar to wood? | Engineering | explainlikeimfive | {
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"Yes metal has grain. It gets aligned in a particular direction during the process of producing sheets (stretching, rolling etc)",
"Yes. Sheet metal has grain, and this influences a lot of behavior and has to be taken in to account when cutting and bending precision parts. This is why sheet metal tends to the rolling direction marked on it, and plans might call for certain orientation. For example it takes a lot less firce to cut and bend along the grain, than across it. When cutting with laser or plasma, the grain has to be compensated for to get accurate parts. When I operated a laser cutter, at worst case on a 8mm aluminium I had to give +0.5mm on the lenght axis to hit tolerances. There was so much shrinkage due to internal pressure from the grain. I'm a steel fabricator by trade, and the grain direction affects a lot of things, from bending to welding, and resulting tensions. If you look closely on high grade cold rolled metal, you can even see the direction of the grain."
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h7x1jn | Why do door locks have two turns for locking, turn once-locked, turn twice-superlocked? What's the difference and if one is more secure than the other then why are there options? | Engineering | explainlikeimfive | {
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"Multiple turns increases how much of the bolt is sticking out of the door. This makes it harder to break the door down, because you end up having to take more of the frame out to free the bolt. There are options because it's hard to make a lock that will move the bolt a large distance with only the relatively small movement that turning a key provides.",
"From what I could find, it’s to prevent lockpicking. It requires what basically amounts to two instances of the locking mechanism being actuated. It theoretically could be done with a pick, but would be very hard because this is usually a deadbolt accessory, meaning the turning of the pick to undo the lock would also be much harder. Secondly, it prevents “bumpkey” infiltration because bumping pretty much just destroys the lock on a door. However with two layers of security, the second lock would not be able to be done the same way because the internal instruments would be damaged in a manner that would make it impossible to align the “teeth” on the inside of the lock again"
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h820nc | When a switch is off, where does the electricity go? | When you turn off your light switch, where does the flowing current go? Does it build up? Is it wasted? If so does that mean that off power points just waste electricity all the time? | Engineering | explainlikeimfive | {
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"The classic water tap parable works here as well. You've got water lines which are pressurized in some way and depending on the water pressure and the diameter of the tap, you get some water flow. When you close the tap, few things can happen depending on the pressure system - if you get your water from the water tower(battery), closing the tap does nothing and water will stay still. If your pipes are pressurized via pump(generator in the power plant), you might get an increased pressure and the pump might break. Of course you switching the light switch won't do anything to the powerplant, but if there's a big failure in power lines and an unexpected decrease of the load, the generator in the powerplant would start spinning faster which could lead to a failure, because there's no way to quickly disconnect it from the turbine that's applying force to it. So in power plants, there are usually dummy loads for this case where power can be diverted. In a real power grid, it's much more robust and complicated and scenarios like this can be prevented without affecting the frequency in the network.",
"Actually electricity is just the movement of electrons u turning off a switch basically stops electrons from moving in a circuit and without electrons moving the light switches off",
"When there is no voltage in a wire, the electrons inside it move around randomly like they were shaking. When we apply a voltage on the wire, we basically push the electrons from one side and the randomly moving electrons start to move to one direction. This is electricity. When the electrons don't have a path, they don't move because they have nowhere to go."
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h83mpz | How does an u-boat dive? I know its something to do with filling tanks with water or air but how does that work? | Also while writing this I got to think about how does a sonar work and how does u-boats detect each other? Not sure which flare I should use | Engineering | explainlikeimfive | {
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"#Ballast A U-boat, or submarine, surfaces and dives using *ballast tanks,* compartments that hold water or air to alter the buoyancy of the submarine. At the surface, the ballast tanks are empty, rendering the craft *positively buoyant.* When the crew wants to dive, they will partially fill the ballast tanks by opening vents and valves, rendering the craft *neutrally bouyant.* In this condition, the submarine can use its forward propulsion combined with the hydroplanes at the stern and aft to drive it down into the water. When the time comes to resurface, the crew will use tanks of compressed air to blow the water out of the ballast tanks, making the craft positively buoyant again. #Sonar You know how sometimes you can hear an echo if you shout in the right conditions? That's essentially how sonar operates. A sonar *pulse* is a high-energy, directed wave of sound, projected from what amounts to a speaker somewhere in the submarine. This pulse of sound is swept in a circle, hence the green line you see in movies. Sound will bounce off an object and return to the underwater microphone, and that is represented as a blip on the sonar screen. There's also *passive sonar,* where the submarine just listens to other things making noise. It's less sensitive than active sonar, but it's also harder to be detected.",
"Think of a submarine as flying in water and not air. The vanes on the side of the submarine flip up and down to make it fly up or down. Very much like how the flaps on an airplane flip up and down to increase lift. URL_0 But that only works if the submarine is moving, just like an airplane. Once they reach a desired depth, tanks on the sides of the submarine called ballast tanks are filled with water or air. At shallower depths, more air, less water. Except in emergency situations, they don't use the ballast tanks to surface or dive. Kind of like how a scuba diver adds or releases air in their bcd vest. Adding air or releasing air to change the buoyancy."
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h84nmf | How toilet systems were built. How on earth does a city withstand the amount of waste flushed down everyday? | Engineering | explainlikeimfive | {
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"text": [
"If you're asking about the collection system: big pipes and gravity, occasionally a pump station. If you're asking about removing the poo: There's a set of big ole concrete ponds somewhere downhill(basically). Those ponds have capacities measured in millions of gallons/day, or MGDs. They make swimming pools look cute. The solids are seperated from the water in a series of increasingly fine operations, until about 12 hours later, we have water that's cleaner than the river we release it into. It's a pretty refined process by now. A lot of pumps, a few big air pumps, 3 or 4 people walking around looking for problems, and we can clean 100 MGD on a slow day. 100 MGD equals about a million people's wastewater."
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h8agog | what is built into the freeway? | What are the repeating markings in the freeway? Not the lane markings, but they in the middle of the lane, approximately where tires would cause decay. There are some on I-90 near cle elum washington. I assume they are something to help the integrity of the road, but what? And why specifically here? | Engineering | explainlikeimfive | {
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"if you mean the grooves on the side/shoulder of the road, the are called \"rumble strips\". They make a godawful noise and shake your car when you drive on them. They are there to alert a distracted (or asleep/drunk/etc) driver that they are drifting off of the road.",
"They’re there to prolong the useful life of the concrete panels that make up the freeway. > To extend the life of the freeway, often more than 10 years, adjacent concrete panels are tied together with steel bars. That helps the panels last longer because they are more stable and remain aligned, Holter said. To install the steel bars on older freeways, crews grind grooves into adjacent concrete panels, insert the bars, then cover them with concrete. URL_0"
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h8zxxu | If motion is relative in space, why would a spinning spaceship imitate gravity? | Engineering | explainlikeimfive | {
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"Most of what we talk about in terms of \"relative motion\" is only valid for **non-rotating** inertial reference frames Rotation changes everything You cannot detect speed, but you can detect acceleration! And that's exactly what a spinning spaceship creates. You can also differentiate between spin gravity (centrifugal force pushing you into the deck) and thrust gravity(engines are running pushing the floor straight up at your feet) As you're standing on the deck the floor is moving up towards your feet pushing you upwards(which feels the same as a pull downwards). This is because you want to travel in a straight line but the floor keeps catching you because it(and you) are rotating so your velocity keeps changing."
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h91q1u | Why are all planes not biplanes? Especially cesna's or small prop planes? | Question 1: With my 5 year old level knowledge of the physics of flight, I would think that having two set of wings like early biplanes, would give you double the lift for a given amount of thrust. Why did biplane airplane designs go away in favor of single wings? & #x200B; Question 2: Also, related question....why hasn't anyone designed a novelty airplane with twenty 1ft long wings, instead of two 10 foot long wings... could something like that fly? I'm thinking it couldn't, but why not? & #x200B; & #x200B; & #x200B; | Engineering | explainlikeimfive | {
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"For faster planes, the air resistance of the spars and wires connecting the wings becomes too much. It's better to have wings that are twice as long, with the truss giving them stiffness inside the wings.",
"> I would think that having two set of wings like early biplanes, would give you double the lift for a given amount of thrust. A biplane configuration will give you more lift for a given speed (although it does not give you double the lift, due to aerodynamic interference between the two wings). It also offers higher structural rigidity for a given weight. However, it also generates a lot more drag, which means you need more thrust to maintain a given speed. Early aircraft were usually made of wood and fabric with weak engines. They couldn't fly very fast, so they needed a lightweight yet rigid wing that would give high lift, while drag was not such a big issue due to the low speeds involved. As aircraft technology improved and speeds increased, monoplanes became the dominant configuration due to their higher efficiency. > Also, related question....why hasn't anyone designed a novelty airplane with twenty 1ft long wings Short wings are less efficient than long ones. There's not really any reason to build an aircraft with so many wings, but that's not to say that ideas like that [have not been tried]( URL_0 ).",
"When planes flew at 80 mph, you needed all the lift you could get from that speed. Two (even three) wings were common. But two wings give double the drag too. Especially when they have a lot of curvature to get all the lift they can out of that speed. If you get a plane up to 200 or 300 mph, you still need a lower landing and takeoff speed so you don't have to use miles of runway. If you have enough speed to get off the ground at 80 mph, then you have an embarrassing amount of lift at 200 mph. So you want thinner wings, that can work with a wider range of \"angle of attack\", and have more accurate shapes because they are made of metal, not from plywood and canvas. You also have engines that are much more powerful for their weight, so you don't need so much lift, and you have propellers that you can change the \"pitch\" of, so they can be efficient over a wider range of air speeds. Lots of short wings would not work because they would mess up the airflow around each other, and they would also all be close to the fuselage, which also messes up the airflow, and puts them in the backwash from the propeller too. You really want the wings to be way out on their own, in clean air."
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h92t1r | If aircraft runway overshoots are the most frequent type of landing accidents, why aren't runways made much longer? | Of course real estate costs are high but nothing is more valuable than saving lives. Isn't the purpose of all regulation to prioritize safety compensating for pilot error, poor weather or aircraft fault. [Source]( URL_1 ) on statistics. More [info]( URL_0 ) on runway overshoots in the past year alone from u/Ozimandius80. | Engineering | explainlikeimfive | {
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"> Of course real estate costs are high but *nothing is more valuable than saving lives.* That's a slogan, not a resource-allocation strategy. Airports have a limited budget, and they can't just spend as much money as it takes to make their runways longer and longer. As things stand runways are generally as long as will fit in the available space.",
"> but nothing is more valuable than saving lives. Money is. Companies literally calculate if the cost of implementing certain safety features would be higher or lower than just tanking the projected number of lawsuit settlements stemming from the lack of it over the operational life of products. Also sometimes runways physically do not fit. It's easy to say \"just find 4 kilometers of almost perfectly flat ground\" and another is actually trying to do that in a hilly area. Remember, if the airport is 700km from the city you want it to service, you might as well just drive.",
"Under normal circumstances, no plane should ever be landing on a runway that isn't long enough to accommodate that type of plane. There are very strict guidelines and documentation that every pilot knows and knows to look for while planning their route. Every runway already has dedicated space on the runway for overshoots to allow for aircraft that are unable to stop in time, and runways themselves are marked with stripes and special lights to guide pilots down to land on the correct part of the runway so they have space to stop. On top of that, *very* few runways have narrow margins for error and even the part of the runway meant for normal use is almost always much longer than it strictly needs to be. So in order to completely overshoot the runway and end up on, say, a road near the airport, something has to go wrong that already has safety features to prevent *and* go wrong so catastrophically that it isn't stopped by the safety features in place in case all of the other safety features go wrong. There are two realities here. The first is that you *cannot* prevent something from ever going wrong. If pilot error can happen with a runway half again longer than it needs to be *and* with additional emergency space, it can happen with a runway twice as long. A longer runway won't stop a plane from sliding off due to excessive wind or ice. There are already a lot of ways to prevent overshoots and nothing is going to stop them entirely from happening. Which means what you're really doing is mitigating risks, not eliminating them. The second reality is that air travel has a cost. Land has a cost. The busiest airports in the world are usually surrounded by major cities or other natural barriers that make extending the runway prohibitively expensive. It's not *just* the runway that has to get longer: all of the area *around* the runway has to be leveled and cleared of obstructions like buildings or trees. Some runways can't be made larger because the space to do so doesn't exist. Runway pavement is expensive because it has to withstand a lot more punishment with a much narrower margin for error than most other kinds of pavement. And for what, to *maybe* prevent an additional one or two accidents from happening out of tens of thousand of flights? It's like asking why every car doesn't have a five point harness instead of a seatbelt. A five point harness is safer and more secure than a seatbelt, sure. Someone who won't wear a seatbelt isn't going to wear a harness. It won't stop the car from getting crushed by a runaway semi. It won't prevent any of a hundred possibilities. And for the normal conditions of a normal car driving at a reasonable speed, it's not that much safer than a seatbelt. Similarly, a longer runway would be safer, but it won't stop most of the things that lead to overshoots and it won't stop any of the accidents unrelated to overshoots. It'll just make flying more expensive, which would probably mean airlines cutting costs elsewhere.",
"Most frequent =/= most deadly. Sliding off the runway generally is not a deadly crash. And during take-offs, the plane is positioned to be able to use the full length.",
"Why do cars go faster than 20km/h? Speed is one of the main risk factors for a car and collision at very low speed in rarely. You would save almost all died in traffic accidents with that change. You should argue that if you think \"nothing is more valuable than saving lives\". You will soon see that people likely even you see the problem because travel time will be a lot longer. If you can change something there are most of the time advantages and disadvantages. So clearly most thing there is other stuff more important that saving lives. 1.35 million die in road accidents each year worldwide you can compare that to the 84000 dead in total in aircraft accidence since 1970. Car accidents is 3700 dead per day or 10 Jumbojet crashes per day. So if you think \"nothing is more valuable than saving lives\" start to argue for very low-speed limits. & #x200B; The airplane runway is expensive and takes up a lot of lanes that might not be available. So extending them will result in higher ticket prices. But runways has been extended and widened the question is to what length do you extend them. It is like everything else an evaluation of risk vs benefit. Even if you had longer runways I am not sure that it would stop all accidents. Most are because of pilot mistake where the com in as speed or in the wind where they should not land so would even longer runway result in fewer accidents or pilots that continues with more bad landing because the thing they have more of a margin. An option is an engineered materials arrestor system after the runway. They will stop airplanes quicker then a regular runway but the might damage the landing gears as they are concrete that crumble so a bit like if you drive a car into a field of snow. I think something that the pilot knows to avoid so it does not just increase the number of risky landings.",
"Just making runways longer won't stop planes from going off the runway. You could make a 1000 mile long runway and planes would still go off the runway. They can go off the side of the runway, they can bounce off the runway and keep going before landing again really far off the runway. Some runways do have a material at the end of the runway to stop planes from going off. A better use of resources would be developing more ways to prevent planes from entering the condition where they would go off the runway in the first place. Your suggestion is reactive to a problem rather than stopping the problem before it happens. It would be like suggesting we make planes stronger so when they crash fewer people die instead of preventing planes from crashing."
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h98tej | What's the go with one handle taps? How do they make the water hotter? do they open up some other valve? | Engineering | explainlikeimfive | {
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"The open valve let's in both water sources from a T intersection. Turning it to one side let's in more of that source and blocks off more of the other, changing the temperature"
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hag2f1 | How were measurements like inches and centimeters replicated hundreds of years ago? | Engineering | explainlikeimfive | {
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"There was a master bar with the measurement standards marked on it. People made copies of it, and sold the copies. People used the copies, or made their own copies and sold those. Eventually, everybody got a pretty good copy.",
"Inaccurate :-) The inch (and related local names like \"duimbreedte\" which literally translated to the width of the thumb) is the width of your thumb. So if you are working on building something and measure it and are looking for a piece of wood that size, then it will be easy as the width doesn't change between you standing at the house and you standing in the forest. But if you work between people? \"Go get me a plank of fifteen inch in length!\" will be in generally the right size unless you have small fingers and the fetcher has thick fingers. So they invented measurement tools for that, for example the \"duimstok\" (literally \"thumb stick\" just google it, currently it's just a foldable measurement tool), so that people within a project had the same right size. So things got standarized over time, most often city by city and province by province and country by country. So you have measurement units like the ounce which have different values depending on which country and which kind of object you are measuring and the feet which differed too depending on location. After a while the scientists who were communicating with peers in other countries got fed up with this and decided \"we need to fix this properly\" and came up with a standardized and reproducible way to define the units and since then life is much easier for students, scientists and people in general."
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hal4t9 | Installing new set of tires on car | Engineering | explainlikeimfive | {
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"You could, but it'd be a bad idea. The *wheel balance* is necessary because wheels aren't made perfect, as much as people try. Wheel balancing involves spinning the wheel and tire on a sensitive machine, then adding weights to correct the imbalances that exist. *Wheel alignment* refers to how the wheels are, well, aligned with respect to the arms on which they're mounted and the road. Because the alignment is done with the wheels on, every time you move wheels from one arm to another, it's recommended to realign them. Failure to align can result in faster tire wear, or a perceptibly bad ride."
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hao5dj | If a wind turbine (or any generator) is producing electricity but no one is using it where does the electricity go? | Engineering | explainlikeimfive | {
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"Nowhere. The effort needed to turn the wind turbine is equal the produced power. The more load is needed the harded is to turn the turbine. If you disconnect the load it will be very easy to turn the turbine. There still be voltage but there will be no currect. In real life you have to stop such a generator the prevent damage. This is valid not only for wind turbines but any other generator eg. in nuclear power plant. Let's say that eg. power lines to power plant is damaged and the plant is cut away from grid. Then the reactor has to be stopped and steam is vented away from turbine. Withtout load and still huge steam delivery to turbine it would speed up and damage.",
"In a small off-grid setup using batteries and a wind turbine you need a dump load to get rid of the excess energy once the batteries are full. A simple way of doing this it to use a electromagnetic brake to slow the rotation of the blades, this both uses power and slows down the rate of generation."
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hb7zk9 | How the gasoline makes a car to move | I would like to understeand how gasoline its transform into energy basically and makes a car to move, and obviusly, in which moment "dissapear" LOL. Grettings from Perú :D | Engineering | explainlikeimfive | {
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"basically what happens inside the engine is that air/fuel mix, create a tiny explosion that pushes the pistons which eventually causes the wheels of the car to turn. you control the rate of the explosions by the accelerator petal which opens an air valve to let more air in and the amount of fuel injected is controlled by a computer.",
"I would recommend watching a YouTube video(s) of how an internal combustion engine works. It’s much easier to comprehend with visuals instead of a description.",
"In gasoline, there is a certain amount of potential energy stored in the chemical bonds of the gasoline molecules. To extract this energy, we combine the gas with air and spray the mixture into a sealed cylinder. A piston inside this cylinder compresses the mixture (this improves the efficiency of the whole process). When the cylinder is at max compression, the air/fuel mixture is ignited, forcing the piston back down. This motion is used to drive the car forward. Chemically, gasoline consists of *hydrocarbons*, molecules containing Carbon, Hydrogen, and Oxygen. When this is mixed with air (more Oxygen) and ignited, the combustion process results in Carbon Dioxide (CO2 - Carbon and Oxygen) and water (H2O - Hydrogen and Oxygen). The water is in gaseous form, so it and the Carbon Dioxide are spit out the exhaust."
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hbci6e | How does a key that doesn't look symmetrical work from both sides of the door ? | Are there two identical mechanisms on each side or is the system inside made to work for both directions ? In all schemas I've seen it looks like door locks and keys would only work in one direction only yet I can close my door from outside or inside ! | Engineering | explainlikeimfive | {
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"Your first guess is correct - the lock has two matching cores on each side. You can see both sets of pins in [this image]( URL_0 ) of a transparent training lock. (That one is likely keyed differently on each side, but a regular lock would have matched cylinders)."
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hbdy6v | How do companies fill glass bottles with carbonated drinks with bottlecaps without the bottle breaking from air pressure within? | Engineering | explainlikeimfive | {
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"The glass is simply so thick that is can sustain the pressure inside. Glass is a surprising stong material. Glas is brittle so do not get deformed a lot but shatter when you apply a lot of force. A material that gets deformed is ductile. If you compare to steel you can have both softer that get deformed or very hard and shatter. A common example of brittle steel is a drillbit the does not bend but shatter. You do not add the carbon dioxide after you have the liquid in the bottle like in a soda streamer. The carbon dioxide is added in another container and is in the liquid when you fill the bottle. You fill it with a tube inserted in the bottle almost to the bottom so you fill it from the bottom to top so the air can escape."
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hbi5bz | How did they prevent engines from rotating too fast in the old days? Did engines have some form of rev limiter or did the operator just have to be aware of how hard they're pushing the engine? | Engineering | explainlikeimfive | {
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"In the old days, engines were fitted with what's known as a governor. This term is still used today on modern engines. Let's go back to steam power. You make steam in a boiler, and then send it through some pipes and valves (which are beyond the scope of this explanation), until it reaches a piston, like in a car engine. The steam pushes the piston, which is connected to some rods which make the crankshaft (long rod which is connected to a big wheel) turn. The more steam you put in the piston, the more force the steam applies, and therefore the faster the wheel turns. Here's the clever part. You ever notice how if you spin an object on a string, it flies outwards? This is from an effect called Centrifugal Force (From the perspective of the object being flung out). Well, the faster you spin the object, the larger the force on it becomes. Some clever people worked out that if you spin a pair of metal balls from a freely-suspended (nothing stopping it from moving outwards) point, the balls will move outwards, and because of the way geometry works, slightly upwards. This upwards motion increases the faster you go, because the balls move out further, because they're spinning faster. Therefore, you can use this upwards motion to control the speed of the engine. If you decrease the amount of steam going to the engine (by adding a valve controlled by how far up the metal balls go), when the engine starts going too fast, the balls go higher, and the steam gets decreased, which slows down the engine again. Here's the really clever part: This sort of thing is a secret balancing act. The engine naturally reaches a point where the steam going in is constantly being reduced when it goes faster, and increased when it goes slower than a set speed. The engine 'acts' to slow itself down or speed itself up, and by adjusting the set point where this happens, you can accurately control the speed of the engine. Since this equipment with the metal balls is 'in charge' of the speed of the engine, the metal balls 'govern' the speed of the engine. Therefore, the metal balls equipment is called a Governor."
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hbj2tp | Why is japan's transit so good and massive for such a large country when countries like usa and canada isn't nearly as sufficient and lacks in most states? | Engineering | explainlikeimfive | {
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"Japan is a very small country compared to the US. Additionally, high speed rail is very expensive and will still not meet the needs of the majority of people.",
"Japan really isn't a large country. It is about 1/26th the size of the US. In addition, Japan generally has one direction of travel between cities. Other than the train lines to Nagano and Niigata, it might as well have a line drawn up its east coast. Comparatively, the US is a large 2 country with population centers all over that need to be connected. Also, much of North Americas rail lines were originally built for commercial shipping. The primary owners of many lines are freight companies, which means they get to tell passenger trains to wait their turn. Since Japan is almost entirely coastal, there wasn't really a need for shipping via train, so the primary tenants of the rail networks are passengers and not freight.",
"Japan is the size of California, yet has 126 or so million people. That means that the people of Japan live in very dense cities, not all that far apart. Japan has a very high GDP for it's physical size as well, meaning that they can afford to spend money to get those people around. With densely populated cities it is easy to build rail systems that can serve the vast majority of the people in the country, without spending even a small fraction of what it would cost to do the same in the US. If you look at a population density map of Japan, you'll see basically a single line of large coastal cities in the southern half of the Japanese islands, where most of the population is located. It's a very, very small area to have to serve with high speed rail, and that means that it can be done relatively cheaply, compared to the US with people spread out and spread all the way across the continent.",
"Well for starters, Japan is extremely small. They may have a lot of people, but the entire country only has an area of 146,000 sqmi (about the size of Germany). The USA has an area over 3.17 million sqmi. Geography is one simple reason. Places are very far apart in the USA which makes air travel far, far superior to any form of public transit system for interstate travel. A further reason is cultural. You'll notice a distinct trend as you move west in the USA. Cities get VERY large. Not just in terms of population, but it terms of land area. As a house in the suburbs became the symbol of American success cites expanded out instead of up. The major urban area of Phoenix for example is over 60 miles across. Commutes of 20mi+ are very common. Not practical for mass transit use. Mass transit is slow and even with rush hour traffic it is typically much faster to drive than to take public transit. Vehicle ownership is also seen as a measure of success in America. While very common for someone in Japan, Korea, France, or Germany to not own a vehicle, not owning a vehicle is seen as a hard negative trait in the US. People would think you are unsuccessful or lazy or poor. Vehicles are also much cheaper in the US than in other countries both in terms of purchasing cost and in cost of ownership. Americans also highly value independence and the car is seen as a method of that independence. Being able to go where you want, when you want. All these things combined have lead to the US building it's cities and infrastructure without public transit in mind. And once you have a city with 5.7 million people and a heavily established road+highway arterial network, making changes to add for public transit becomes logistically almost impossible. Also many cities don't view it as profitable, since because of the cultural reasons mentioned above, they tend to see low use."
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hbjv3d | How do bathroom taps switch between hot and cold water just by turning the handle? | I figured the taps with independent dials for hot and cold just tap into different pipes for hot and cold water. How does the mechanism translate into taps with handles you can rotate? | Engineering | explainlikeimfive | {
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"There are two pipes feeding the faucet. One is hooked to the hot water line and the other to the cold. The faucet is a valve. Every manufacturer designs theirs a little differently, but they all work on the same principle... inside the faucet there is a device with holes in it (someone mentioned a ball in another comment - Delta works that way, but not every faucet does). The handle turns that device so that holes will line up with either the hot, the cold, a mixture of both, or none at all. When the faucet is turned off, those holes are blocked and water cannot get through. This same principle applies to any hot/cold single-handled faucet, whether it is on a sink, a tub, or a shower."
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hbmxpl | How do they fix the internet cables on the ocean floor if they break ? | Curiosity.. | Engineering | explainlikeimfive | {
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"Pretty much how you would expect. - They locate the portion of the cable with the issue. They can do this by sending light pulses down the cable and seeing how long it takes to get a reflection back - They send out a repair ship - The ship either uses a submersible to grab the cable (shallow water - < 6,500 feet ) or a long cable with a hook on it to grab the cable - The haul the cable up and make repairs.",
"They pick up the ends and splice them back together. Specialized ships have been constructed with all sorts of undersea equipment to perform these tasks. Sometimes it's hard to get the ends near the break, so they add in another length of cable.",
"Three short answers 1) they lay a lot of redundant cables, so swap to another until the spares run out 2) they don’t, and reroute through someone else’s cable/system 3) very expensively, the same way they laid it in the first place. With modern tech, they can likely know within a fairly workable distance where the actual break is, so they can sometimes patch it in place."
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hboh30 | - Why can't they create phone screens that don't crack? | I had always taken good care of my phones, but my last two I have had drops (they were in a case), but the screen still cracked. Thankfully this last one wasn't as bad. Is there a reason they can't create a screen material that won't crack? | Engineering | explainlikeimfive | {
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"There are smartphones with screens that don’t crack, they simply make the screen with plastic instead of glass Only problem is plastic gets scratched really easily and feels cheap, which is why it’s very rarely use Generally materials that are hard are also brittle, so they might not scratch, but they do crack, and also viceversa is true",
"The problem is that there are conflicting goals. The ideal screen would have perfect durability, clarity, hardness, be weightless, and not cost anything. All while being thin enough for touch sense to work. Polycarbonate does not break but it scratches. Steel is hard and durable but not clear. The glass used is actually a fairly recent development. It could be made more durable by making it thicker, but then it’s heavier and less responsive to touch. They create phone cases that don’t break if you want to give up cost, bulk, and weight to improve durability."
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hbslrg | why do all cars slightly move forward when your foot is on neither the gas nor the break? | Engineering | explainlikeimfive | {
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"In simple terms if you’re driving an automatic and the car is in gear the engine never really stops running and generates enough force to move the car forward",
"This would only happen on a car with an automatic transmission/torque converter because once you put the car in drive the spinning of the engine even at idle is transferred to the wheels through the TC ever so slightly. If the car is an automatic with a cvt they're electronically controlled and won't engage until the gas is pressed. A manual transmission car will just stall because the connection between the engine and wheels is more direct and the idle rpm would not be enough to move it.",
"Not all of them. Might be that you're on a slight incline forward. But your formulation makes me guess you only refers to automatic cars. If you're in D(rive) then the car clutch will stay engaged to be ready giving you that slight move. If you change to neutral, then there will be no drive. Edit, damn bilingual autocorrect",
"> break **B** **R** **A** **K** **E** \"break\" is smashing something into tiny pieces. This doesn't happen with \"all cars\". This only happens \"naturally\" with automatic transmission vehicles that use a torque converter... I guess the ELI5 explanation is that it \"leaks\" a little bit of power from the idling motor to the wheels, so the car will be pushed forward slightly when set to \"Drive\" as long as the engine is running. Manual transmission vehicles don't do this. The engine will stall if you try to come to a complete stop with the clutch engaged (or you'll damage the clutch). If you disengage the clutch it's like being in neutral in an AT vehicle, and it won't creep forwards. Electric cars and vehicles with fancy things like a CVT (continuously-variable transmission) normally wouldn't do this... but because people are used to it with regular automatic transmissions (and it can be helpful for parking) they actually fake this behavior and deliberately transmit a small amount of power to the wheels when you take your foot off the brake. IIRC in some electric cars you can toggle this behavior on and off."
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hbu8b2 | Why didn't Zeppelins/Blimps become popular means of transportation? | Disclaimer: English is my second language For quite a while I've had the idea idea that if zeppelins where popular they would probably be like the cruise ships of the sky, you know, awesome sights, taking 1-2 weeks to arrive at your destination, and I'd think it would be awesome. Why didn't they get popular? I guess the Hindenburg accident might have been a big contributing factor to the loss of popularity, but hey, the Titanic sank and we still have cruise ships sailing the seas. Edit: Thanks a lot for your answers, I guess the real reasons are the cost and low speed | Engineering | explainlikeimfive | {
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"[The cost of helium is too damn high! ]( URL_1 ) Also, here's a good story about a guy with a plan to bring back airships, but [the cost of helium is still too damn high. ]( URL_0 )",
"They were popular for a while. But the combination of disasters such as the Hindenburg and the fact that airplanes were much much faster they fell out of use.",
"In the early 20th century, they were decently popular, though pretty expensive to operate and required large areas to land or dock. Like you mentioned, disasters such as the Hindenburg did a lot to damage their popularity at the time. The reason they didn’t bounce back: airplanes were being improved much faster. Of course blimps and zeppelins were still used, they played some surveillance roles during World War II, but planes were much more effective in most regards. Eventually larger passenger planes took over the air market and there hasn’t been any huge financial reason to bring them back yet, though there are some [plans to develop better blimps for shipping cargo]( URL_0 ). Though they will probably not be used for general travel in our lifetimes, there is a chance they will be brought back for other purposes.",
"Money, I'd say. Obviously, we won't be using hydrogen anymore. So that means helium. Which is crazy expensive in the amounts that a luxury airship would need.",
"The Hindenburg was not the decisive reason. Over time, a lot of ships have sunk and a lot of planes have crashed, but those things still thrive nowadays. There were other problems: First, they were expensive to build and maintain, given the huge amount of Helium they need. Therefore it was only ever an option for rich people in the first place. But they did not really accomodate rich people. Sure, the ads showed they they could lift a grand piano, giving the impression that there was no limit to the possible luxuries. But do you know what weighs a lot more than a grand piano? Freshwater for the showers for the passengers. So you have rich customers who pay a lot of money, and are only allowed to use a few literes each in the shower. That doesnt fit together. Being trapped in just a few rooms for several days was also not all that appealing, especially considering that you spent the nights in the \"upper floor\" that had no windows. In the end, Zeppelins were trapped in a market nieche between much more luxurious ships and the emerging, much faster commercial airplanes. There was just no way to operate them economically.",
"one other thing I feel people of mist is that time is often at a premium in our current world and planes are much faster than blimp so even though they're not as cost-effective it doesn't matter because times worth so much.",
"No idea, but if I had to take a wild guess at it, I'd say it's because we already invented the airplane, and blimps/Zeppelins were just too slow to be practical. Not to mention the not so good ratio of weight to lift and the fact that they weren't exactly agile in any sense of the word.",
"I [took flying lessons]( URL_0 ) in a Zeppelin once. I learned a lot about how they're operated. First, as others have pointed out, the cost of helium is just too much. Other limitations: * They just can't fly very high; the Eureka had a service ceiling of 8000 feet. * They can't fly very fast; 55 knots top speed (although the Hindenburg could do 84 mph). * They're at the mercy of the weather; flying had to be postponed one day because of the wind. * They don't carry much. The Eureka was as long as a 747, but only carried 12 passengers with no luggage. The Hindenburg was 3x as long as a modern Zeppelin, and carried around 140 people (passengers + crew). The bottom line is that as amazing as they are, and I would totally get one of my own if I was a billionaire, they're just not practical compared to modern airliners by any metric at all. The only real market that Airship Ventures had was well-off people who wanted a Zeppelin ride and could afford one. Once that supply of customers ran out, that was all she wrote."
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"https://www.citymetric.com/transport/why-blimps-and-airships-died-out-and-how-they-might-make-comeback-722",
"https://www.theverge.com/2012/11/16/3654280/airship-ventures-ceases-operations"
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hbw2t8 | The function of polarized sunglasses compared to regular sunglasses. | Engineering | explainlikeimfive | {
"a_id": [
"fvbi6ly"
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"text": [
"Polarized lenses can reduce glare, especially the bright reflections off of glass, roads, or water. Light can be represented with waves. When those oscillating waves hit materials like water, then the light that reflects, at some angles from the surface, will tend to have mostly one direction of oscillation. A polarized lens will mostly block light with one direction of oscillation, typical of road glare or water glare. If you tilt your head sideways, with your ear aiming toward the ground, your lenses will pass the light that they'd been blocking just a moment prior. That lets you compare the \"glare\" view and the \"no glare\" view. Edit: clarified tilt direction"
],
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4
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hc31f8 | Why is there a small hole in the side (and the lid) of my pen? | Engineering | explainlikeimfive | {
"a_id": [
"fvcj5mg"
],
"text": [
"The hole on the barrel creates the same level of air pressure inside and outside of the pen, allowing the ink to flow into the point. The reason that some pens have a hole in their cap is to prevent the cap from completely obstructing the airway if accidently swallowed."
],
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47
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hc723i | How can R2D2 heads spin 360 degrees arbitrarily without tangling the internal cables? | People build these all the time, and it seems like there's something mechanically clever happening. Not being a mechanically educated person I haven't figured out the correct search terms to actually take me to the content that explains this. | Engineering | explainlikeimfive | {
"a_id": [
"fvdh0f7",
"fvdhao6",
"fvd9jee",
"fvdqnmq"
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"text": [
"There is a ring of copper, and a tab that connects to that copper ring to maintain a connection. It is similar to how a subway or an electric train maintains an electrical connection. [Here is an example]( URL_0 )",
"As the previous user mentioned, the answer is slip rings. There are MANY kinds of slip rings but I’ll explain the simplest and most common. The most common is that there are brushes that rub against a metal shell. These brushes rub against the shell while the shell is allowed to spin freely. The brushes have an electrical current running through them to allow for the transfer of energy. In this way, the head is able to freely spin without the base needing to spin with it.",
"Slip rings. Whenever you need continuous rotation, you run the wires to a slip ring at the point of rotation. It's a standard engineering part, available off the shelf from parts suppliers.",
"Have a joint in the cable at the point it needs to rotate. The end of the wires in this joint touch but are not solid connected like a cable. Imagine 2 brush / yard broom heads touching each other. Each bristle on the brush head can conduct data/electric power. These heads rotate against each other. Every bristle that touches keeps the connection alive. grab to hair / dustpan brushes - touch the bristles together and rotate - imagine each bristle/fibre transfers power & data - :)"
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hcc54b | How a bullet proof vest works and why knives are more effective against a bullet proof vest. | I was told knives are super effective against bullet proof vest and I've always wondered how those vest work. | Engineering | explainlikeimfive | {
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"text": [
"So bullets penetrate things like your body because they are moving really really fast. They aren't actually sharp, or have any real cutting power... they just move fast enough that it doesn't matter. Kevlar acts sort of like a net. Catching the bullet and spreading out it's energy over more area slowing it down enough that it can no longer go through you or the kevlar. Knives penetrate things because they are sharp. They cut through things. Kevlar is basically just a man-made cloth with some nifty properties, cutting through cloth is something knives were meant to do. It would be harder than cutting through a cotton t-shirt but a kevlar vest won't stop a knife for long.",
"Bullets get stopped because they hit the kevlar fibers head-on, kinda like a tennis ball hitting a tennis racket. Knives can separate the fibers and pass *between them* (or actually cut the fibers), much like a needle passing between the strings of the same tennis racket. The main thing with kevlar is that the fibers can withstand *impact/stretching* and not snap. They can be *cut* with ease, kinda like how a rubber band can be stretched far without snapping but you can cut it with plain old scissors",
"There are no bullet proof vests just bullet resistant ones shoot a vest enough times and the bullets start to get through. The fibres are designed to spread the force out and go with the force of the bullet until the force is dissipated and the fibres spring back into position while a non stab vest will help, the knife can cut these fibres stopping them from spreading the load."
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hce1jd | With automatic transmissions, what is the difference between ‘1 speed automatic’ and any other number of speeds? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"I’ve never heard of a 1 speed automatic... that’s just direct drive with a gear reduction. Unless you mean in the context of CVTs (continuously variable transmissions/transaxles). Instead of a sequence of gears (much like a mountain bike), CVTs use a belt stretched around a cone, and the belt moves from the wide end of the cone to the narrow end and back depending on the driving conditions. It never feels like it shifts, though, because it’s gradual instead of stair-stepped. But if you mean “2 speed” “3 speed” or any other number, it’s just the number of drive gears a transmission has in it. Lower gearing (higher numerical ratio) helps cars accelerate and drive up hills, while higher gears reduce the strain on the engine (and save fuel) at cruising speeds."
],
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5
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hce1ls | How is it that when you peddle a bike forward the rear wheel spins forward but when you peddle backwards it doesn't? | Engineering | explainlikeimfive | {
"a_id": [
"fveiixq"
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"text": [
"There’s a clutch built into the crank assembly that allows “freewheeling”... it’s like a ratchet that only applies force when turned in one direction. Not all bikes have them."
],
"score": [
9
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hcgh1a | Why do escalators have that shoe shine like thingy on the edge of it? | Engineering | explainlikeimfive | {
"a_id": [
"fvexuum"
],
"text": [
"It’s actually called a skirt guard to avoid small items from entering the machine on the tiny gap between the steps and balustrade. 🙂"
],
"score": [
39
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hcpeto | how do they initially test airplanes to know if they're ready for their first flight? Especially functions that only matter once already in the air. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Aerospace Engineer here: Aircraft designs (aero performance, structural integrity, flight controls, propulsion systems) go through very rigorous system verification and qualification procedures. It usually will start with lab test of a single component (engine, wing, etc...), then more tests when integrated as part of a larger system (engine test with the actual design fuel system, wind tunnel test, static wing loading failure test). Eventually all systems are “verified” that they function as designed, and the entire aircraft will go through more rigorous ground testing before its first flight. First flights aren’t without risk, but if engineers/test pilots doubt its safety, it won’t go flying till those issues are addressed.",
"If your question is about newly designed airplanes: engineers run finite element analysis (FEA) of the structure to make sure it doesn’t break, computational fluid dynamics(CFD) to make sure it generates appropriate lift and drag, and to ensure that the aerodynamic stresses tested in the FEA match real life aerodynamic stresses. They also do real life tests like putting scale models of parts of the plane (or even the whole plane scaled way down) in a wind tunnel, to help verify the CFD. They also do lots of things like analysis of the comms system to make sure it can talk to people far away, power budgets, cabin air circulation, and much more."
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hcs25c | If energy turbines (hydroelectric, wind, wave current etc) are essentially spinning magnets past copper wire, why do they have to be so big? Or rather, why cant a smaller scale turbine spinning really fast do the same job? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Short answer: they could in theory. Longer answer: the larger the turbine the more energy you can collect using a given turbine. Since the expensive part of a turbine is the core(the spinning magnets) having it gather from a larger area is more efficient. Like using a funnel to fill a bottle. If you hold a bottle under a waterfall you're gonna fill the bottle slower than if you used a funnel to fill the bottle and you \"missout\" on less water."
],
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hcyt4a | different types of concrete on highways, typical black-colored vs. the light gray on flyovers and bridges | Engineering | explainlikeimfive | {
"a_id": [
"fvi1scd"
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"text": [
"The light gray material is concrete. It is a strong structural material used in bridges or “flyovers.” The black stuff is asphalt. It is a flexibility and cheap material that can take a lot of repeated loads over and over again. It is used mostly on roads."
],
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16
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hd3a33 | How does an air conditioner and refrigerator differ in process of cooling? | I read stuff in the internet but I'm having a hard time fully grasping the technical terms and ideas. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"They do not differ. The difference is what you cool and where you put the excess heat and the temperature goal A household refrigerator is all on one part that cools down the inside so you do not need fan to push the air and it hears up the surrounding room. An AC is intended to cool down houses so you need to deliver the heat to the outside so most have the evaporator on the outside with pipes to the inside with coolant to an evaporator you blow air through. If you instead look at smaller portable AC the are a single unit with an air duct to lead the warm air to the outside and a fan that pushed are to cool down the room. They are just like a refrigerator the difference is that you have consolidator with a fan and a duct and the evaporator is designed for a fan and higher airflow instead passive air in a refrigerator If you look at commercial walk-in refrigerator have fans push air around and are in many way an AC for a room that cools it to a lot lower temperature."
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hd3n96 | How did hillside castles get built in medieval times so close to the cliffs | Engineering | explainlikeimfive | {
"a_id": [
"fvizxvg"
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"text": [
"I’m gonna blow your mind when I tell you that they weren’t so close to the cliffs when they were built. They were built elsewhere and [then moved closer to the cliff. ]( URL_0 )"
],
"score": [
4
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hd4m41 | Why will a well-maintained engine break one day or an other? Why can't they run forever? | I'm talking about car/motorcycle engines that receive irreproachable care and proper use throughout their entire life, even these won't run forever will they? What will be the reason they will seize someday even if they had been given all the care they need? I know some manufacturers build better engines that last way longer than others (Honda has a very good reputation in the motorcycle world) but why even the best Honda engine won't run forever? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"No matter how much care you afford your engine, its full of moving parts rubbing against each other. Even with always receiving fresh oil to minimise friction, eventually things will wear, in particular piston seals, cylinder bores timing chains, cams, etc.. That being said, with the right amount of mechanical skill, its possible to replace all of these things, even the cylinders can be resleeved. I don't know of a single part on an engine that can't be replaced, but then you have a theseus ship problem of if you replace every part of an engine is it still the same engine?"
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hdk94x | Why are granite countertops such a big deal? | I keep seeing granite countertops listed on real-estate listings, home improvement/remodeling project ads, etc. Why is this particular amenity so popular and considered such a plus? What are the alternatives and why are they inferior (at least, inferior enough not to be explicitly mentioned like granite countertops are)? | Engineering | explainlikeimfive | {
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"they're considered a luxury over the cheap plastic counter tops. they're much more attractive and durable than plastic counter tops. and \"solid\" granite (or other natural stone, like marble, quartz, etc) countertops are extremely expensive. but a lot of the times the \"granite\" counter top is just a thin layering on top with the bottom part just wood or other material, kind of like how jewelry has the \"gold-plated\" variety vs the \"solid\" gold variety.",
"I'm not a contractor, but I am a geologist, and I've been helping my mom redo her kitchen. First of all, granite can be really pretty, and adds a lot from an aesthetic standpoint. It's on the expensive side, but it's also stone, so it can handle having a hot pot set down on it better than most other materials can. After all, what's even a 500°F cast iron skillet when granites form somewhere around 1500°F and up? It's also relatively difficult to chip or scratch once it's installed unless you're really putting some effort into it, so it's durable. Most of the alternatives are man-made products. Laminate, solid surface, and even wood countertops don't deal nearly as well with heat, though they tend to be cheaper. Engineered stone, marketed under different brand names, is what my mom eventually went for. It's less expensive than granite, and more resilient to heat and scratches than the solid surface ones. They don't quite have the aesthetics, but there are some that dont look too bad.",
"Granite countertops are not the best available, nor are they the worst. Granite is, however, currently quite trendy, in the US. When many home shoppers see \"granite countertops,\" it makes a home seem more appealing and desirable. And there are many other such features that are seen as trendy and desirable, such as \"barn-door-style sliding doors\" and \"farmhouse sinks\" and \"stainless-steel appliances.\" When people see certain features mentioned in a home description, they are more likely to want to see and maybe purchase the house, which leads more people to install and advertise such features, before listing a house for sale. Ultimately, it's simple salesmanship--giving the people what they want. If you're still curious, here's a good article from Zillow, explaining certain currently desirable home features. [ URL_0 ]( URL_0 )",
"You can take a hot pot off the stove and set it on a granite countertop with no damage. This is much better than a plastic countertop, which would be instantly destroyed. Granite comes in pieces big enough that the whole counter could be one piece, or at least only a couple of pieces. This is much better than tile, the other heat resistant option, which has grout lines which can be very difficult to clean. Granite can be very pretty, with interesting rock formations in it, which it better than man-made quartz countertops, which share granite's other desirable properties. Frankly, a lot of people prefer quartz, but htat's a regional trend and highly subject to change.",
"It’s a signal for luxury/high end kitchens. There are a few other terms that signify trim level, like stainless appliances (and even high end brands like Viking, Sub Zero, Bosch), crown moulding. They change over time however, and now seeing something like quartz counters may be seen even more favorably. It’s because it’s often too hard to descent qualitative aspects in photos",
"Granite has a number of advantages...and a few disadvantages. Advantages are a smooth surface that doesn't give off a ton of heat (so even if you put a hot pan on the countertop you're unlikely to burn yourself) and is resistant to heat and all kinds of abrasion. The disadvantages are that it can crack and it's porous (so it needs to be resealed every now and then to prevent it from staining or becoming a magnet for bacteria). An additional disadvantage is that if the countertop is a complex shape then it will have to be made from multiple blocks of granite. That generally makes it superior or equivalent to most other countertop materials (certainly superior to laminate, wood or marble). For pure utilitarianism a concrete mix (you can get a really nice finish on concrete if you mix it with the right materials) can usually match all the advantages of a granite countertop. \"Concrete countertop\" doesn't sound very nice when you're trying to sell the house though. For commercial kitchens steel is usually the superior choice, since it's easier to keep hygienic. The disadvantage of steel is of course that it will show any stains or deposites. If your tapwater is somewhat alkaline a steel countertop is basically cleaning hell (which is a pro in a commercial kitchen but not that desirable in your home).",
"Lol any counter top that isn’t plastic or laminate and is a solid slab of stone of considered a “luxury”",
"Assistant architect here. Granite tops are mostly aesthetic, just like other types of stone tops, like marble, terrazzo or quartz for example. The reason for picking this over other options is mostly for the grain pattern or veins on the natural stone, making it uniquely beautiful as these patterns are difficult to replicate especially for marble veins. There are artificial ones, which are passable (more like large format ceramic tiles actually) but for something which you will sit or use up close like a countertop, sometimes the printed grains and veins can be seen. A nice veined marble can look good in a well designed kitchen and the same one can be tacky as heck in a badly designed one, so this is personal taste and professional execution. As for feel, it honestly feels like a solid product with a nice cool touch, part of why people would like to use natural stone if they can afford it. As for how it is mounted on the counter, normally a 20mm piece would be used, not really that thin, and then there are edge details which can be done to magically make it look much thicker than it actually is. Any thinner isn't really recommended, also a bit difficult to source from my experience, and any thing veneer-like is more a question of why the heck is that used on your counter? Your other options are the artificial ones like artificial quartz or corian. Those function comparable to the stone above, heatproof, impact proof etc, but the patterns and grains tend to be more subtle and consistent as it is difficult to replicate natural veins, but still, it's possible to make a nice kitchen with this. Functionally, the good quality ones are similar to natural stone, a possible plus side is that the man made ones tend to be much more stain resistant than the natural ones, as natural stone has pores in it which if not sealed well, can allow for wine or water to seep in. There are also composite panels, which in a way can be an option, however I feel that they aren't as strong as natural stone or artificial quartz, with regards to heat, and in a design sense they don't feel as nice to the touch. All this being said, granite is often emphasised as a big deal because of the cost and feel of it as well as the uniqueness of the stone's grains and patterns, giving the kitchen that premium magic; and it does, only if the interior and spacial design helps make it work too."
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hdo05k | How do soft produce not get bruised up during harvest and transport to the supermarket? | Engineering | explainlikeimfive | {
"a_id": [
"fvmagnl"
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"text": [
"Ah so here’s the sad truth about produce. Unless it’s local, produce is harvested before it is ripe and is then allowed to ripen while in transit and while waiting to be sold. As a result it’s quite firm during the transit process and only softens once it arrives."
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hdr2x8 | Why aren't zinc-air batteries used for cars, instead of lithium batteries? | It would seem that zinc is more easily available, cheaper and more eco-friendly. Am I missing some disadvantages which prevent it from being used in cars on a large scale? | Engineering | explainlikeimfive | {
"a_id": [
"fvmq29u",
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"text": [
"From [this 2018 article]( URL_0 ): \"A limitation in zinc air batteries is the electrical potential of 1.35-1.4 volts in practical cells—about half of what is available in a lithium-based battery. Another challenge is setting up the infrastructure for stations that could supply fresh metallic zinc in a slurry, while removing and storing or renewing the spent zinc oxide. This is not insurmountable. But for now, it is easier to supply electricity from the grid through a charging station to a lithium ion battery—the technology that seems destined to dominate electric vehicles, at least in the short term.\" It's from two years ago, so presumably some progress has been made. But no breakthroughs have been reported or seem imminent.",
"Zinc-air batteries is simply not ready as a technology for large scale market. There is still some technical hurdle to fix . The concept is old (1840), it was first sold on the market in 1932. Those batteries had high energy, but very bad power output. This meant that they were mostly used in low power, long endureance products. Those batteries were also non-rechargable. The first commercial rechargable zinc-air battery was in 2012, but this one had 14 to 9 times less energy than older zinc-air batteries. Basically, Zinc-air batteries have the potential to be better and probaby replace lithium-ion battery in the future, but some technical problem stop them from reaching this potential. Research will continue and maybe in the future we will be ablet o reach capability level that make them good enough, we are just not there yet."
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hdthzc | How do astronauts get back to earth from the moon? | So I understand how they get to the moon kinda. They have a massive launch from the earth and the thrusters break off into the atmosphere right? So how do they launch back to earth from the moon without those things? | Engineering | explainlikeimfive | {
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"text": [
"The Moon's gravity is much much weaker than Earth's, and they were moving a lot less mass. The Apollo moon lander had a rocket that shot the little box with the two people in it off of the moons surface and up into lunar orbit. The command module would then dock with it, transfer the people over, ditch the excess weight, and burn its little rocket engine to head home. Now because Earth has soooo much more gravity than the Moon you don't need to get terribly far from the Moon before you're back in Earth's sphere of influence so they were able to use that smaller fuel tank and rocket that were in the service module (the part that had a problem on Apollo 13) to boost themselves from the Moon back towards Earth It would have taken a much much larger rocket if they wanted to land something heavy like the command module on the surface and get it back to Earth, but since the Lunar Lander didn't have to worry about the heat from reentry it could be super light which meant a small rocket and fuel tank were all that was needed to get it back off the moon",
"The moon's gravity is far weaker than that of the earth, and there is no atmosphere to slow the ascent of the craft. As such, it required far less fuel to lift off the moon and to escaped a lunar orbit. This also means that you don't need as large of a spacecraft to accomplish this goal, which further helps the fuel situation.",
"The Moon’s gravity is much lower than the Earth’s and it has no atmosphere to create drag, so it takes much less thrust to escape from the Lunar surface. Also, when you launch from Earth, you’re carrying all the hardware and fuel you need to: * Reach Earth orbit * Propel yourself to the Moon * Insert youself into Lunar orbit * Land on the Moon * Launch from the Moon * Propel yourself back to Earth * Survive reentry of the Earth’s atmosphere When you launch from the Moon, all you’re carrying is enough fuel to get back to the command ship in lunar orbit."
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hedkwv | What are the advances of ARM versus x86? | Engineering | explainlikeimfive | {
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"text": [
"ARM is cheaper and easier to design custom chips with (Partly for licencing reasons: x86 is owned by intel), and more power efficient. For a long time x86 gave better performance on the high end, but this is changing and we are starting to see ARM designs capable of giving x86 a run for its money in this space.",
"Gotta remember that x86 is backwards compatible with every other x86 CPU made since the 1980s. A modern Core i7 can run DOS programs written for the 286 without special emulation software (not that I would encourage it). Bugs and poor decisions made back in the day will come to haunt the future. By contrast ARM is a lot more modern, designed with lessons of the past learned, and overall a much simpler CPU and instruction set design. It's also a significant fundamental design change. x86 instructions are part of the \"complex instruction set computer\" (CISC) family which means that a single instruction can be quite complex. One instruction can fetch data from memory, act on it (eg: add numbers together) and save the result directly to an internal CPU storage bucket called a Register. ARM is a \"reduced instruction set computer\" family member, meaning the set of available instructions are significantly smaller. For example the above x86 addition operation would have to be at least 2 instructions: fetch from memory into register, and add registers together. But it simplifies a lot of facts such as each CPU instruction is a fixed number of bytes whereas on x86 each instruction could vary in size, typically 1-4 bytes but larger does happen. This is a significant part of why ARM CPUs use a lot less power."
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hehh55 | How do bike gears work to combine front and back? I know how to use them and the basic idea of torque, but how do the front and back work together? | Engineering | explainlikeimfive | {
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"text": [
"The front and back gears are doing the same thing, but in reverse. The final gear ratio determining the speed and force is determined by the ratio of the gear sizes in the front and back. So using a small gear in both front and back is the same as using a big gear in both front and back. So even though you have 21 gears there are a lot of them that are very similar. But you are not supposed to use all of these similar gear combinations. Having the option of using a big gear in front and a small gear in back as well as using a small gear in front and a big gear in back gives you a big range of speeds which is why you have the choice of gears both in the front and back. Another issue is that the chain is not flexible enough to comfortable cross across all seven gears in the back so you need to use the big gear in the front to have the chain going streight to the small gear in the back. So you are supposed to start off in gear 1-1, then go to 1-2, 1-3, but then switch to 2-3 and then continue for 2-4, 2-5 and then maybe 3-5 and on to 3-6 and 3-7. This gives you a total of 9 usable gear combinations. However different bikes have different bikes have different gear combinations and you have some of your own preferances so it might vary."
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hejb07 | How do locks have unique keys even though they are produced in huge numbers? | Edit: thanks for the answers! | Engineering | explainlikeimfive | {
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"For common house locks, they don't have to be unique. There just have to be enough combinations that the chances of a random key combination working on a random door are low enough where it's not an unacceptable risk.",
"Along with the answer \"they don't\", a lot of locks are also produced with keyways that can be reconfigured to take different keys (called rekeying), so they can be produced in large quantities and then rekeyed later so they don't conflict with other locks in the same location.",
"As others have said, they don't have unique keys. Most locks that we interact with on a day-to-day basis function by having a rotating cylinder that controls a locking mechanism, and inside that cylinder are 4-6 pin-stacks; that is, a spring-loaded pair of pins that are stacked on top of each other. There is a visible line where these pins sit on top of each other, called the shear line; when the shear line of all of the pins in the cylinder lines up with the space between the lock cylinder and its housing, the cylinder is free to rotate, otherwise the pins halt its rotation by, well, being a solid object wedged between a moving bit and a non-moving bit. The trick is that, if you imagine each pin stack as a single pin that has been cut at some point along its length, each one is a different length; on their own, the pins are all long enough so that even when fully pressed in/springs fully compressed, they won't go all the way into the housing, some will still be in the cylinder stopping the mechanism, and so the only way to get the lock to turn is to align the pins correctly. If you imagine that each pin has 10 possible points for a shear line, and a lock has 5 pins in it, then you essentially get (pardon the pun) security on par with the PIN for your debit card: a number of a set length that is hard to guess, but not unique. The end result is that if you take your house key and try it on about 100,000 different locks from the same manufacturer, your key is very likely to open at least one of the other locks. But it is very *un*likely (but not impossible) that your key will unlock the door of anyone within a block or two of you. Just like if all PINs were truly random (which, they aren't, but that's another story), and you had several tens of thousands of cards to try, one would eventually have the same PIN as yours, but most of us only interact with a handfull of debit cards other than our own in our lifetime. EDIT: number of pin stacks; 5 is common, but they can be anywhere from 4-6 typically.",
"I had a 92 Jeep Wrangler and my key would start my neighbors 92 Jeep Wrangler as well. I was friends with the guy so we just had a good laugh but it was mildly concerning. Especially when he parked my Jeep on the other side of the street when I was home one day and I didn’t hear him do it. I thought I was crazy",
"In the RV business we have the 'dungeon masters' keyring. It's every key that opens a specific brand of lock, there are about 100 unique keys, one of which will open any lock made by this brand.",
"Now that you’ve been told many times they aren’t unique I’ve got a little story! I worked for Volvo semis as a mechanic and went to pull a truck in, I got the description which was basically “red Volvo and model#” went to a red Volvo and same model tried using the button unlock which didn’t work so I figured it was dead (very common) so i put it in and it unlocked! I pulled the truck in began my pre inspection and began trying to find the issue the customer explained and nothing was wrong at all. Finally I double checked the vin # and it was the wrong red Volvo. This one had been in for only a service. So that’s the day I was told Volvo semis only have 32 key combinations. That’s the story of how I discovered this was a thing.",
"sometimes lazy contractors will just batch buy locks and at minimum make sure that the same key doesn't open the same lock on the same floor. I've heard of people with the keys to 301 being able to open the locks to 401, 501,601 but not 302 or any other doors on the third floor.",
"Fun fact, for things like forklifts, scissor lifts, and snorkel lifts, the keys are almost always identical (at least withan a particular brand). They dont even bother to make them different and [you can even buy them online]( URL_0 ).",
"Like other people have already answered, they aren't unique, but unique *enough*. As for how, the most common lock you probably know is a pin-tumbler lock. They contain a few sets of pins inside (typically 3 to 6 sets of 2). The length of those pins is what's different between locks. Everything is cheaply mass produced. Only choosing the combination of lengths & cutting the key for it gets a little more complicated. [How a pin-tumbler works and how it's picked]( URL_1 ) [In-depth talk about key types, key reuse, etc]( URL_0 )",
"My Dad's ability to enter the pits for an important auto race on time was being thwarted because the only available entrance was blocked by large Mercury station wagon. After fruitlessly trying to find the owner. His crew then tried to slide the car out of the way. No dice. In desperation he stuck the key to my mom's' Ford Fairlane, still sitting in the driveway two thousand miles away, into the door lock of the Mercury. It opened, he started the car drove it a few hundred feet to the nearest safe parking spot, carefully locked it back up and managed to get into the track on time. His only regret was that he was not around to see the owner of the Mercury trying to figure out how his car had re parked itself."
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hekp52 | How do we get cold water from our taps? | I understand we simply heat the water for hot water, but what process do we use to get cold water? I'm not talking about refrigerators or water coolers, rather actual taps and showers and whatnot. | Engineering | explainlikeimfive | {
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"The reality there is that cold water isn't really cold water; it is just unheated water. Water pipes feeding your house usually run underground, and the water in those pipes tends to be well insulated and stay cool but still liquid all year long.",
"Once you get deep enough into the ground it stays at around 50 to 55 degrees year round. It's not really all that deep, 10 feet or so. Most water supply pipes are buried and because of this the water stays at around 50 or 55 degrees year round giving you cold water from the tap. If you have a significant length of pipe that runs above ground the water will heat up to the temperature of the environment. That is why if you turn on a hose that has been sitting out in the sun the water coming out of it will be warm at first."
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hekwmv | How do ancient/ non electric pumped fountains work? | Online, all it says is gravity from a high aqueduct but nothing about what would make water cycle through a fountain. wouldn't it overflow/ or is it like a sink that has a hole to let out at a level so it doesn't overfill, or is it recycling at all? please help me understand! | Engineering | explainlikeimfive | {
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"A reservoir on a hill, pipes to a fountain, and then the water would drain out to a canal, stream or river. Since the reservoir took a long time to fill up, you didn't run the fountain continuously, you only turned it on for special occasions, like a party or celebration."
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heoq0t | How do large naval guns not capsize ships? | I've read that the yamamoto class battle ship could fire a 1.5 ton round over 26 miles. How does that amount of force not knock over the ship? EDIT: This is more of an explain like I'm 20. Sorry. I cant find the answer anywhere. | Engineering | explainlikeimfive | {
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"It is not enough. The power (I would not use the term power but I think we all get what you mean) is way too little to move the ship in real. I have found quite nice article when they prove it. It is simplified but it really does the job. [ URL_0 ]( URL_1 ) Do not forget that the ship is \"sitting\" in water and to move the ship sidewise you have to move huge amount of water too."
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heskzn | What is three phase electricity and how is that different from “normal” electricity? | Engineering | explainlikeimfive | {
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"Think about holding a rope in your hands. Someone tugs on it from one end and keeps pulling. You feel heat generated from friction. This is analogous to Direct Current (DC). The energy transferred from the rope to your hand is constant. Now imagine someone tugging back and forth between the two ends. First it tugs one way, generates heat from friction, pauses, then tugs the other way, again generating heat from friction. This is analogous to Alternating Current (AC). The energy transfered from the rope to your hand is not constant. There is a pause between each tug. (AC) is how we transfer energy through electricity for most applications, and is exclusively how we transfer energy through electricity over long distances. It comes with significantly less energy loss. The problem is most uses of electricity need that energy delivered at a constant pace, such as DC. Well now imagine there are two ropes in your hand. As the end of one tug is approaching, the second rope starts its tug. By the time the end of the secind rope tug is coming up, you've begun the opposite direction tug of the first rope. While the energy transfer is not constant, it is a lot more constant than the single rope case, while maintaining the benefits of AC not having as much energy loss. Three phase electricity is three ropes, whose timing is evenly spaced out to provide even better constant energy transfer"
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hetxgh | Why do some countries 120V and others 240V? | Engineering | explainlikeimfive | {
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"Most of the world adopted electricity after WWII when copper was scarce. 240V allows you to transfer more power using less current which allows you to use smaller wires to transfer the same amount of power; the US was electrified before most other countries and there was no copper shortage. 120V is also safer than 240V; it is much more painful and dangerous to be shocked with 240V vs 120V.",
"Electricity was not standardised and each country implemented it differently. Some countries like Japan even have separate electricity grids (60 Hz vs 50 Hz) based on which company started the network where. 240V is more efficient at the distribution level (ie after the electricity is stepped down) due to the smaller current. There is less power loss in the transmission cables that way. The difference is minor (about 0.5%) but it adds up over an entire network. For that reason the US does have a 240V distribution network, they just split the incoming electricity into 2 halves (180 degrees out of phase) when it enters the home. This results in a negative and positive phase of maximum amplitude of 120V."
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hf4c3t | My buddy has a scooter. It ran a good 3 minutes without a spark plug wire. How did it do that? | Engineering | explainlikeimfive | {
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"Internal combustion engines operate by compressing a mix of air and finely distributed fuel in the form of vapor and tiny droplets. The compression of the fuel-air mixture heats it up and aids in the combustion usually triggered by the spark plug. However it is possible for the compression itself to heat the mixture above the point where it ignites on its own. This is what diesel engines do as they don't use spark plugs. Normal engines can end up doing the same thing (predictably called \"dieseling\") when something is wrong with them.",
"That is a runaway engine from the sounds of it. Runaway without spark is caused by the plug or dome heating up to a temperature that will combust the fuel on contact, the engine will then continue to run until something stops the reaction. Normally when a runaway starts this is how it goes. 1:Turn off key/hit kill switch (nothing happens) 2:Freak out a little bit 3:Cut spark (that diddnt work, plug is so hot) 4:Have existential crisis as you think your machine is going to self destruct. 5: Turn off fuel (Will work however compounds the issue temporarily, engine starts to run lean, lean running engines run even hotter, possibly causing more damage) 6: Cut the air supply(Small engines you can put your hand over the intake, larger machines like a runaway diesel can eat a phone book and spit it out the other side and keep on running). 7: Huge relief or despair as you narrowly avoided a seizure or just cost yourself an engine.",
"Maybe it's a twin cylinder and was running on the one remaining one with spark? Twins will run surprisingly well with only one cylinder firing....they idle fine and will rev up a little but will of course lack power.",
"It was a runaway because of lack of maintenance. 2-stroke engines need to have their top-end serviced every 50 hours. A runaway 2 stroke requires two things: Heat and a lean condition. Heat is supplied from glowing hot carbon from lack of cleaning. The lean condition is from excess air being sucked in from a bad seal somewhere. The engine needs to be rebuilt or it's going to seize up completely if it hasn't already.",
"A build-up of carbon in the cylinder can hold enough heat to keep the engine going, like a [glow-plug engine]( URL_1 ). I'd recommend adding some [engine cleaning fluid]( URL_0 ) to the next tank of fuel to see if that changes anything."
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hfckh8 | How the hell are dams built? | Engineering | explainlikeimfive | {
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"They dig a channel or channels and divert the flow while they build. Then they plug up the channels they made. [Look up the construction of the Hoover dam. It's dam interesting.]( URL_0 ) Edit:Spelling Error.",
"Dams are built by tons and tons of beavers that work together in unison to create a self flooded area."
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hff36b | With modern CNC machining, which is designed for repeatability and consistency and is controlled by computers, how can each gun barrel be completely unique, and produce unique rifling marks on a bullet? | Engineering | explainlikeimfive | {
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"The true answer is, they're not and a gun doesn't necessarily give consistent markings. \"barrel matching\" is incredibly inaccurate. It's getting discredited more and more. URL_1 \"As with fingerprints, not enough research has been done to quantify the probability of error in ballistics matching. So it's impossible to say with certainty that the marks made on bullets as they are fired are truly unique to an individual gun. Currently, ballistics examiners are aided by computer databases such as the ATF's National Integrated Ballistic Information Network, but lab techs always rely on their own visual inspection to make the final call. The Association of Firearm and Tool Mark Examiners only requires an examiner to find \"sufficient agreement\" between bullets in order to conclude that they came from the same gun. Those judgment calls can cause false results. Last September the Detroit Police Department's crime lab was shut down after an audit by the state of Michigan found a 10 percent error rate in ballistics identification.\" URL_0 After years of research, Dr. David Klatzow’s monumental work regarding ballistic fingerprinting is finally published. Titled Defective Science, it is a must-read for any citizen concerned with justice and law enforcement. In it Dr. Klatzow thoroughly debunks the pseudoscience of ballistic fingerprinting. \"The theory behind firearm identification is that microscopic striations and impressions left on bullets and cartridge cases are unique, reproducible, and therefore, like “ballistic fingerprints” that can be used to identify a gun. If investigators recover bullets or cartridge cases from a crime scene, forensic examiners can test-fire a suspect’s gun to see if it produces ballistic fingerprints that match the evidence. URL_2 But bullets and cartridge cases that are fired from different guns might have similar markings, especially if the guns were consecutively manufactured. This raises the possibility of a false positive match, which can have serious consequences for the accused.\" (The paper then goes on to identify a much more accurate computer-driven 3D method instead of the current eyeballing, but it gives a probabilistic answer instead \"match or no match\")",
"The CNC machines can be off by a few micrometers, and the metal could have a different grain pattern which makes it cut different, and if the gun was used before it could have microscopic amounts of damage. It all adds up and even then it’s not a 100% guarantee they can tell if it’s the exact gun.",
"The problem comes down to the metal. Each price of metal has grains, similar to wood. These grains are very very tiny, and differ in size shape between different metals. When the metal is cut, each grain is cut slightly different, and this impacts the overall bore of the gun barrel. Does this make sense?"
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hfi2vt | the difference between EMF and RF radiation | Engineering | explainlikeimfive | {
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"I assume you mean electric & magnetic field radiation and radiofrequency radiation. Radiofrequency radiation refers to a type of electric & magnetic field radiation. Types of EMF radiation are determined by the frequency of the waves of energy that make up the radiation. The waves of energy are categorized by frequency according to the electromagnetic spectrum. RF radiation is made of radio waves that have very low frequencies. Meanwhile, gamma radiation is made of gamma rays, which are very high-frequency waves. Visible light that we can see and interpret colour from is another form of EMF radiation. We can see different colours of visible light because each colour of light is made up of certain frequency wave. For example, blue light contains higher frequency waves than red light, and our eyes can tell the difference which is why we see different colours."
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hfi41a | Why are trains more efficient because of length but airplanes aren't? | One of the cited reasons for why a train is more efficient than airplanes is because of the long length of the train, reducing the drag. That would suggest that longer airplanes should be more efficient. However, the total drag of airplanes eventually goes up with increased length due to increased friction drag. Why is this not the case with trains as well? EDIT: I mean in terms of ratios, as these links show: [ URL_0 ]( URL_1 ) (page 16) [ URL_4 ]( URL_4 ) EDIT: I found this website which claims similar efficiency for planes and aircraft, but idk how correct it is: [ URL_2 ]( URL_3 ) | Engineering | explainlikeimfive | {
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"When airplanes fly high the air becomes thinner and requires more engine thrust(Fuel) to keep it up, keep adding weight and you'll need a lot more fuel to battle gravity. A train doesn't worry about gravity nearly as much. A train has high torque and low horsepower, to get a train to move you must only break the standing friction to get it start rolling. It will take a large effort from the engine to get everything moving but once moving will not longer need nearly as much fuel.",
"A train is fighting air resistance and rolling friction from the wheels. If you double the length of the train, the rolling friction will double, but the air resistance will remain (roughly) the same. An airplane is fighting air resistance and gravity. If you double the length of a plane, the air resistance remains roughly the same, but the amount of gravity you have to fight doubles. The way you fight gravity is to provide more lift from the wings, and the added lift from the wings is at a cost of more air resistance. The way an airplane provides upforce is to either increase the size (or alter the shape) of the wing... flaps can do this in real time on airplanes... or to go faster. Either of these options increases air resistance.",
"> However, the total drag of airplanes eventually goes up with increased length due to increased friction drag. Does it increase faster than the plane's volume? I suspect it does not, and that the reason planes aren't sky snakes has more to do with balance, rigidity and lift issues."
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hfm35u | How do internet cables that go under the ocean simultaneously handle millions or even billions of data transfers? | I understand the physics behind how the cables themselves work in transmitting light. What I don't quite understand is how it's possible to convert millions of messages, emails, etc every second and transmit them back and forth using only a few of those transoceanic cables. Basically, how do they funnel down all that data into several cables? | Engineering | explainlikeimfive | {
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"In the earliest days of wire-based communication (analogue), there was only one signal on the wire at a time. Later, we learned to pass multiple signals by using different frequencies/wavelengths for different signals. In it's simplest forms, imagine that instead of shining a white light down a wire for one signal, you're shining red, green, and blue lights. By measuring the amount of red, green, and blue light at the other end, you can separate the signals. That's the principle, just scaled up and with a bit of fiddly detail at each end. This gives us (with current technology) up to about 80 signals per strand of fiber. A cable can have dozens of fibers, so that's potentially a few thousand signals in a cable with a hundred fiber strands But as you say, there are millions of data transfers... this part is fairly easy though. Although the signals appear to be fully simultaneous, we don't actually have a constant connection along each possible pathway: what we do is break our data up into chunks called \"packets\", and put an address on it of where it needs to go (your IP address). That might sound strange, but think of it like sending things in the mail. Instead of having someone drive back and forth and give the message, we put them in packets, and send them down the road with an address on it. Think of our cable as a road network. We make a road (a strand of fiber) and then we give it 80 lanes: those are our multiple signals. Now imagine we can overlap those signals so all 80 lanes are just one lane where the cars don't interfere with each other. And then for each lane, we can send lots of individual cars (packets) down one after another, with their own destinations. We don't need to make a full connection (lane) between each pair of destinations, we just send everything down the shared lanes and let it split off when it needs to. And then we combine a whole bunch of these roads (fibers) into one cable. So imagine we have 100 of these roads next to each other.",
"A key feature of fiber optics is the ability to multiplex multiple wavelengths of light onto the same strand of glass. Think of it like a prism- the one beam of white light can be broken down into multiple beams of colored light. Each of those \"colors\" (the light used in fiber operates at wavelengths invisible to humans) can carry as much data as your modulation scheme allows for- say 1Gbps to make it easy. Using dense wavelength division multiplexing (DWDM) we can fit 80 of those wavelengths onto one strand. And of course most fiber cables are multiple strands- lets say its a small cable with only 12. Doing the math, that's almost 1Tbps of bandwidth on a fiber cable. Real life applications can carry even more, it all depends on the equipment being used. As our technology improves we'll be able to modulate more data per wavelength and pack more wavelengths per strand.",
"You mentioned \"only a few of those transoceanic cables\" -- there are far, far more than a few. There are a few hundred, some longer than others but all serving the same purpose.",
"Hi! Here is a good link ( [ URL_0 ]( URL_0 ) ) on what the fiber looks like. It is super durable because, well, there is a lot of things that can go wrong at the bottom of the ocean. In essence, there are normally always one or two cable ships laying undersea cable at any given time, sometimes to fix lines that broke and sometimes to give more bandwidth. From what I have read before, to solve attenuation every 100KM or so there is a repeater device. There isn't only one or two wires in a cable bundle, there can be hundreds. The cable is huge, but the wires themselves are the width of a human hair. I can't find the exact number of wires in the undersea cable but from looking at the picture they must have at least 48 pair. So, quick explainer, on the internet you typically have one wire for send and one wire for receive. So if you want a 10Gb connection between two pieces of electronics, you would need two wires. So if you have a 48 wire cable, then you get 24 different send and receive pairs that can be put into electronics. Technology has come along and we know how prisms work. For example, I have residential F/O service in my house. They gave me 1 wire. So how do I send and receive? The technical answer is 'coarse and dense wave multiplexing' which is a complicated way of saying you can send a communication in one direction on one wavelength (or 'color' for short) and receive on a different wavelength. The colors are a handy way of talking about it, but these electronics can use the non-visible spectrum as well. I think, the last time I purchased multiplexing optics, I was able to get 10 10Gb pairs on one wire. So for that undersea cable, assuming it is 48 pin, it is 48 x 10 send/receive pairs. How the data actually flows? That is a topic called 'digital signal processing' (DSP) and you will need to ask another ELI5 for that.",
"I'd like to know how they are laid? Ship has a giant reel on the back laying thousands of miles of cable? How does that work?",
"Gee, everyone talking about DWDM and stuff when that is really almost irrelevant to the question. Yeah, sure, having n wavelengths on a fiber reduces the number of fibers you need by a factor of n, which is great, but if you have hundreds of millions of \"connections\", it having a thousand \"channels\" rather than a hundred \"channels\" does not really answer the question. **The real answer is: Packets!** What you perceive as a \"connection\" of sorts, at the network level, just isn't. You might be thinking of how traditional telephone networks worked, where a pair of copper wires was (more or less) connected up between caller and callee to establilsh a connection. That is not how modern computer networks work. Modern computer networks are what is called **packet switched** (as opposed to **circuit switched**). **As far as the network is concerned, there simply are no connections.** In the particular case of IP (Internet protocol--the thing you use for websites and email and instant messaging and what have you ...), how that works is that every device connected to the internet has a unique number identifying that device, also known as the IP address. And that really means every device, your laptop or smartphone just as any one of Google's or reddit's servers. Now, when you(/your device) wants to send some piece of data to any other device on the internet, all it has to do is to label it with the address of the device it wants to send it to (that's then called a packet) and transmit it to its upstream internet router. That router will look at the address to determine which of its available links (\"cables\") would be the best (fastest/cheapest/whatever) choice to get the packet to the device that has that address. At the other end of that link, there will usually be another router that does the same thing. And then another one. And another one. ... until, at some point, it reaches the router that the destination device is connected to, so the router will transmit it to that device, which will then, presumably, somehow do something useful with it--and also, oftentimes, send another packet in reply. For that to work, the sender of a packet also adds its own address to any packet it sends, so the recipient can use that address to send back a response. However, the size of packets on the internet is limited, commonly to around 1500 bytes. So, if you want to transmit something that is larger than that, what you have to do is to split it up into small pieces and transmit those as individual packets--and you have to add some information to the packets that allows the receiver to put them back together, of course. But the important part here is that, as far as all those routers are concerned, there is no connection. They see a packet with a destination address, select a next-hop link to transmit it to, and forget about it. If you do some hour-long download, the routers don't know and don't care, all they see is individual packets, millions of them. And really, there is no reason all those packets would even necessarily take the same path through the same cables or routers. All that matters is that all those packets get to their destination, somehow. Or, well, most of them at least, because even that isn't guaranteed, some fraction of packets do just get dropped for various reasons, in which case the sender will simply have to retransmit if they don't hear back from the recipient in time. So, the answer to the question is that those fiber links simply have an extremely high speed, and the routers connected to them simply push through them any packets that arrive in whatever order they arrive in. If your submarine cable has a capacity of 100 Terabit/second, say, that means it is capable of transmitting about 8 billion packets of the typical maximum size per second--and as far as the routers and cables are concerned, those could all be from the same \"connection\", or they could be 8 billion different \"connections\". In practice, usually, there would be a few million \"connections\" using that link during any second: Some people transfering data between datacenters or if you have a gigabit connection at home, you might be transferring ~ 80000 packets per second, someone else using a dialup modem in a rural area might be transferring only ~ 4 packets per second. All of those are just mixed as they arrive and transmitted through the cable, one after the other.",
"I don’t have a simple ELI5 answer, but I did want to share with you a great article in wired by Neal Stephenson (sci-fi author) where he travels the world learning about and telling the readers all about these transatlantic fiber optic cables. There are so many interesting details, give it a read. URL_0 “Information moves, or we move to it. Moving to it has rarely been popular and is growing unfashionable; nowadays we demand that the information come to us. This can be accomplished in three basic ways: moving physical media around, broadcasting radiation through space, and sending signals through wires. This article is about what will, for a short time anyway, be the biggest and best wire ever made.”",
"Imagine the cable fiber communication works similar to how Morse code lines work. They send data via lights on and lights off (0 and 1) instead of the regular _ . from Morse code. Specialized machines (routers, but waaaay more powerful than the one you have at home) code and decode this 0-1 into usable date. Remember that light travels incredibly quickly (about 0.01 seconds in a transatlantic fiber cable, example Yellow/AC-2), so the 0 and 1 make it from one side to the other really fast. Now imagine that on top of this you can use red for one line of messaging and blue for another, and yellow, green, etc. So that you can use several lines of communication for each fiber. And also note that Everytime they make a transatlantic cable they use a LOT of single fibers because if you are on the bottom of the ocean puting one fiber or 100 is almost the same cost. That's how you get data speeds of up to 160 terabits per second across the ocean (see MAREA transatlantic communication cable)",
"So many answers here, but none of them are explained like you're five. I'm sorry OP. Here's an actual explanation to answer your question: The cables are really big.",
"Multiplexing. I'm not sure what exactly is used but I've used DWDM on circuits before for heavy bandwidth intensive use cases. Here's a WIKI on DMDW. It can send 160 different channels on one fiber pair. [ URL_1 ]( URL_0 )",
"The ELI5 answer is let's say you watch a cat video on Youtube, that cat video is sent to you from the Youtube server in the form of billions of 1s and 0s on a single strand of fiber. The server and your computer have an agreement beforehand, 0s are transmitted as \"light off\", 1s are transmitted as \"light on\". So 101010 would be transmitted by light on fiber as light on-light off-light on-light off-light on-light off. That cat video you just watched, it's encoded in billions of 1s and 0s. And the strand of fiber that connects your computer and the Youtube server is capable of turning itself light on-- > light off billions of times per second. So those billions of 1s and 0s are transmitted in just a few seconds on this strand of fiber. Sounds cool right? Let's say your brother wants to watch a Justin Bieber music video using that same strand of fiber. The principles are the same, the Youtube server sends the music video in the form of 1s and 0s and transmits this video on the strand of fiber to your home. Sounds understandable. But how about if you and your brother want to watch videos at the same time? It turns out different wavelengths of light don't really mix. For example ultraviolet light (fancy name for sunlight) and infrared. Using this same strand of fiber you send both a ray of sunlight and a ray of infrared at the same time. At the destination, you will still retrieve the same exact rays of sunlight and infrared intact. They don't disturb each other despite sharing the same media. So if you use one wavelength of light, and your brother uses a different wavelength, both of you can share the strand of fiber. The cat video you watch and the Justin Bieber video your brother watches are transmitted at the same time and arrive at the destination intact. This is called Wavelength Divison Multiplexing. Wavelength Divison Multiplexing is heavily used in undersea cables to enable multiple concurrent data transmissions on the same cable. A more hardcore version of WDM, Dense WDM (DWDM), enables more concurrent transmission on the same wavelength space. As a rough example, if between wavelengths of 100 to 200 WDM can accommodate 5 concurrent transmissions, DWDM can handle 10.",
"Really the answer is Packets. The same way you can have an ethernet connection and get e-mail, be watching a video on a web browser and playing an online game all the the same IP address. It happens the same on the transport end except a much larger bandwidth so more things can happen at the same time.,",
"It all comes from the Shannon-Hartley theorem, which says that maximum transmission rate is proportional to the number of frequencies (“light colors”) that cable allows passing through, and increases when the noise descresses (a more “pure” signal). More colors, more data can simultaneously pass. Currently we’re talking about 20 Tbps, or 20 thousand simultaneous 4K Netflix movies per cable. URL_0",
"There is not just a few of these cables. Here's a world map showing the various transmission cables laid on the sea floor: [Undersea Data Cables Map Image]( URL_0 )",
"1. The cables are huge, and there's a lot of them 2. They use fiber optics, which means they communicate through light. Light can have different colors, so if you use 6 colors instead of 1 color, you multiplied your bandwidth by 6.",
"You know how a prism of light splits white light into a rainbow of multiple wavelengths? We can do something similar with an optical fibre - this is called multiplexing. If you imagine drawing one of those bouncing rays down the optical fibre, what angle did you make at the very start? Vary that angle by a small amount and you can see that you can create a new path that does not interfere with the first."
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hfmr9p | What's the difference between an alternator, a stator, and a generator? | Engineering | explainlikeimfive | {
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"A stator is the part of an electric generator that doesn’t move, it is stationary. Both an alternator and generator have a stator inside. A generator is a device that turns rotational motion into electricity. An alternator is a type of generator that outputs alternating current.",
"A generator generates electricity from mechanical motion, the lots of designs of them An alternator os a type of generator that produces alternating current, this is where it gets the name. A stator is the stationary part of a rotation system and the rotating part is a rotor. An alternator and all other generators will contain both a stator and a rotor. So an alternator is a type of generator and one part of it is the stator.",
"An alternator is a kind of generator that produces AC, that is current with alternating polarity. A stator can be part of both a generator and a motor, and is the static part, opposed to the rotor, which is the moving part in a generator. Both are working together. In a motor, the current flowing in the stator will make the rotor rotate. In a generator, the rotation will induce a current in the stator and produce electricity."
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hfpqhv | How do houses in a town all have water pressure? | Engineering | explainlikeimfive | {
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"[Water Tower]( URL_1 ). They pump the water into a reservoir up there, and gravity pulls it down and pressurizes all the pipes in town, because of the way [pressure applies to all points in a liquid]( URL_0 ).",
"Water towers. Water demand is not continuous. If it was, then a giant pump would make sense. But its hard to engineer a pumping mechanism that can handle various inconsistent rates of flow. Plus its also hard to engineer a pump that can press against the resistance of a town size plumbing network continuously without breaking and yet still be instantaneously responsive. So, instead, you have a water tower that suspends a body of water high above ground. Gravity now becomes the force that provides the water pressure to keep water in the pipes AND it can be immediately responsive to various rates of flow as demand change fluctuates AND the water is available even if there is a power outage (although backup generators are usually present). The benefit of this is now you only need a single constant speed pump to keep the water tower full, a little like the tank ~~bowl~~ on your toilet. Once the tower is full, the pump shuts off. When below a refill threshold, the pump turns on and runs continuously at the same speed until the tower is full and it shuts off. Other benefits are the pump can be solar-powered or only run at night during low demand periods etc. In the case where you're on a well and not on a municipal water grid, you probably have a pump that fills a cistern somewhere outside or maybe inside (attic?) of your house and the water pressure is from that cistern (+gravity) or however pressurized your water pump is capable of."
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hfrn4m | For electrical work, why turn off electricity by the circuit breaker if you already turned off the wall switch? | Engineering | explainlikeimfive | {
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"The circuit breaker is where the electricity gets fed throughout the house. If you just turn the switch off on the wall, the cables in the wall are still energized (have an active current going through them), which is really dangerous. Same reason why you need to shut the water off to your whole house if you want to do any sort of plumbing work, it's not enough to just turn the shower off, for instance.",
"A big reason is that relying on the switch means you're assuming the switch is wired correctly. I've seen setups that had switched neutral instead of switched hot. It was also standard a while back to run the power to the box, and then send \"switch loop\" wire switch, so even if the switch is off there is still a live wire in the box (this is less popular now but still allowed). There is also a psychological aspect. Other people in the house are a lot less likely to flip a breaker without thinking.",
"If you're replacing a switch or an outlet electricity is always present. If you're replacing a fixture controlled by a switch someone could come by and accidently turn on the switch which would shock you. If the circuit is improperly wired electricity could always be at the fixture waiting for the switch to complete the circuit."
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hfu9oh | How do old fighter planes (world war 1 & 2) shoot at enemies from the front without destroying their propellers? | In movies they look like they are shooting through their propellers as they are spinning around. Wouldn’t that destroy the propeller and cause the plane to crash? | Engineering | explainlikeimfive | {
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"The guns are connected to the timing system on the engine so that they only fire when the propellor is out of the way.",
"The guns were synced with the rotation pf the propeller. So the bullets would only fire if the prop was not in the way",
"Through the use of a [Synchronization gear]( URL_0 ) The propeller spins wayyy faster than the machine gun fires the synchronization gear was setup to pull the trigger whenever the propeller was in a safe spot as long as the pilot had the trigger pulled. Most of the time the gun wouldn't be ready (clearing the last round or loading a fresh one) but it would fire as soon as the next safe window came around. It would shoot a bit slower than one out on the wing that wasn't restricted by the propeller, but it wasn't a huge difference."
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hfxt7j | Why do aeroplanes feel slow from the inside although they are moving so quickly? | Engineering | explainlikeimfive | {
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"This is in essence the theory of relatively. One of Newton’s laws is force =mass*acceleration You only feel force when you are accelerating or decelerating. This is true in any vehicle, even a slow one. If you ride a bike, and you slam on the brakes, you’ll feel thrown forwards. If you ride a car, you can feel an acceleration, or deceleration. But at constant speed, you don’t feel anything. Someone asked earlier, this does not have to do with evolution. This is because of a reference frame. When you’re going 60mph, or 600mph, or 1000s of mph around the sun, if it’s constant, you won’t feel anything. This is because no force is acting on you. Everything in the car, including the air, the seats, and the chassis are moving with you so you feel like you’re not moving",
"A couple of reasons. Firstly, we don't feel velocity, we only feel changes in velocity. This includes acceleration (taking off), changes in direction, and deceleration Once the plane is up to speed, you feel nothing because you are moving with the plane. Secondly the ground is 35,000 away, which makes it appear to move slowly. This is called parallax. If you look out the side of a car window in motion you'll see that objects in the distance seem to move slower. Looking at the ground in a plane is the same effect."
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hfz2q6 | How do the red and blue 3D glasses work? | Engineering | explainlikeimfive | {
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"The red and blue glasses basically filter the non red colors out of the red eye and no blue colors out of the blue eye. This causes the blue eye to see blue image and red eye to see red image. On the movie screen, the red and blue images are almost identical, although taken by separate cameras an eye distant apart. This color separation technique simulates a 3D image by giving the two eyes images of from different viewing positions (the two cameras)"
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hfz4oa | Can entropy be reversed? | Engineering | explainlikeimfive | {
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"One of the most visualizable explanations may be \"a measure of how spread out things are\". Localized systems have low entropy, uniform systems have high entropy. For example. if you sorted red and green marbles into left and right edges of a box, they're highly localized, but if you mix them, both types are as uniform as possible. Since that's the high entropy state, they don't unmix spontaneously. > And why can't it be reversed Entropy can be decreased, but only by increasing it somewhere else. You can unmix your marbles by sorting them again, but you'll generate some heat by doing that, which is entropy at the molecular level.",
"Entropy describes how chaotic a closed system is. This chaoticness increases over time. Like, picture a sand castle. It'll eventually trickle down until it's completely smushed into the surrounding sand. It decays from a high order state into a low energy chaotic state. Can it be reversed? Locally, yes. You can take energy from outside the system and spend it to rebuild the castle. But where does that energy come from? Earth as a system is not decaying, because it's constantly fed energy by the sun, which rebuilds our sandcastles by fuelling plants, animals and eventually us. But the sun doesn't get energy from anywhere. Once the sun burns up, that's it. It ends up as a smushed sandcastle, with nobody to rebuild it. And eventually, all stars burn up and there's nothing to refuel them. Everything just spreads out, like the flat sand that used to be a sand castle. That's maximum entropy."
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hg3qng | Why aren't people more concerned about space junk? | Engineering | explainlikeimfive | {
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"People absolutely are! At least, the people involved in launching satellites and looking at the sky. Right now, every new satellite that's launched, must have a plan for getting it out of orbit (letting it burn up in atmosphere) once it stops being useful. It's a big problem indeed, and a lot of smart people are working on ways to solve it."
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hg41dj | How do emergency bulbs work? | Engineering | explainlikeimfive | {
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"text": [
"Emergency bulbs are powered by an internal battery. When the power is on, the battery charges and the light is off. When the light is off, it uses the battery and turns on"
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hg5o4f | Is there some kind of storage for electrical power? | every country is making their own electricity, but there is probably more of it than the people need. How do they store that remainder? | Engineering | explainlikeimfive | {
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"Other than batteries, excess electricity is used to pump water uphill to a reservoir, so they can use it for hydroelectric generation during peak times. Countries also sell electricity to neighbouring countries, although that's not really the on-the-spot excess.",
"Most energy producers try not to generate too much more electricity than their customers will use at any given time, but they do store the resources to generate electricity. Coal fire electric plants only burn as much coal as their is a demand for at the time, hydroelectric dams only let enough water through to spin the turbines enough to meet electricity demand, and natural gas plants only use as much as needed at the time. Solar and wind do not have these stable resource reserves, so they're forced to use really big batteries, which is a pretty big detriment to their usefulness due to the limited capacity of the batteries they use. Nuclear doesn't really store energy normally because a reaction is essentially either happening or not, and shutting it down takes a long time, but they produce so much energy so consistently that the energy going to waste isn't that big of an economic loss. Of course there have been recommendations to use the excess energy during times of low demand to power mechanical energy storage methods such as running a pump up a hill and letting the water flow down through a turbine during times of higher energy demand.",
"Yes, batteries. Tesla installed a massive battery in Australia because it was having trouble handling peak power consumption. It stores power during the day and releases it at night: URL_0",
"Short answer is they only make what they need. Yes there is some storage, but it is tiny relative to the amount that needs to be produced. On the grand scale, a grid is managed to ramp supply up and down to meet demand as it changes. That is why it is critical to have a variety of ways of making electricity because not all produce at some time of day (eg, solar), at same cost or with the same amount of lead time (eg, nuclear power plant takes a long time to turn on and save little money when shut down, so usually try to just leave running; burning natural gas turns on/off quick and the fuel is the expensive part so can be used for changing demand). But yes, increasing need for actual storage particularly for solar and wind protects because they produce most of their power at times when demand is not at its peak (peak is evening in developed world when people are at home). Others have answered about a few ways to do that."
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hg9ata | How do Vinyl Records work? | Engineering | explainlikeimfive | {
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"Sound is just vibrations. Vinyl has grooves with bumps corresponding to music, so when record player needle rides the groove, it vibrates to the bumps in the groove, those vibrations then are amplified and that's what you hear."
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hgbgwy | How does the liquid in soap dispensers turn into bubbles when you press it down? | Engineering | explainlikeimfive | {
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"text": [
"there are little bitty screens in the dispenser that mix air in with the soap as it's being dispensed. This video shows the mechanism: [ URL_0 ]( URL_0 )",
"Because the tiny mouths in the filter blow bubbles inside the soap as it comes out. They like it when soap is a soft cleansing cloud."
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hgdewf | How does the ISS keep their oxygen at acceptable levels? Do they keep a huge tank and refill everytime someone comes by? | Engineering | explainlikeimfive | {
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"The oxygen is made by electrolysis of water where you went the hydrogen to space. You have a small amount of oxygen in pressure tanks. The reason you split water is that it is simpler to transport to ISS and store there. IF you have oxygen as a gas you need very high pressure and heavy container to contain it. If you store it in liquid form oxygen needs to be colder then 90.19 K (−182.96 °C; −297.33 °F) so a lot of energy would be needed to keep it cool. Your transport is as water as you can keep it as a liquid at the normal internal temperature of ISS. The other part you need to do is to remove carbon dioxide and you use scrubber for that. If you are in an enclosed gas-tight space what will kill you is carbon dioxide poisoning not lack of oxygen. Adding oxygen does not help you need to get rid of the carbon dioxide. You would not survive long in a 100% oxygen environment than in normal 21% because of the carbon dioxide rise at the same rate.",
"The ISS specifically creates oxygen on the fly using electrolysis. The atmospheric system captures water from the air or from waste water, and directly converts it into hydrogen and oxygen. The hydrogen was initially vented, but at one point they were talking about using it to combine with CO2 in the air to make water and methane, the water would be reused, and the methane would be vented, getting rid of CO2 in the process as well.",
"It’s not coat effective on the ground. Electrolysis isn’t efficient. It is cheaper than carrying extra o2 up there though."
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hgey8q | How is large cargo transported in submarines? | But the entrance is so small. | Engineering | explainlikeimfive | {
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"There is a unit called a \"deck skid\" mounts over the hatch and allows large heavy items to control slide in at an angle. Source: I make submarine parts.",
"Submarines are not usually intended for carrying cargo. With rare exceptions, they're warships, not freighters."
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hgwgks | Why are motorcycle engines much louder despite usually being smaller? | Engineering | explainlikeimfive | {
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"Most cars nowadays have mufflers built into their exhaust system, which lessen the amount of noise coming from the exhaust. Some cars also have soundproofing around their engines to dampen sound coming from there. Motorcycles have none of those things, so even though they’re far smaller engines they sound louder to us.",
"Cars have more muffling built in, plus the pipes are longer so the sound waves have more time to diminish before exiting the pipe. Plus many bikers buy custom exhausts to make their bikes even louder"
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hh7ud0 | How do nails (like the hammer kind) work? Like how do they keep things together? | I've looked it up and I just don't get it | Engineering | explainlikeimfive | {
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"I think to add to the previous comments, this isn't simply a case of friction between two surfaces, because if that were the case, a nail resting on top of a plank of wood would be just as difficult to remove. When the nail is driven into the wood by the hammer, the wood immediately around the nail compacts to make way for the incoming nail. You can think of the wood like a spring, compressed between your fingers, it wants to return to its \"uncompressed\" state and the spring therefore pushes on your fingers til you let it go. Because the wood also wants to return to this uncompressed state, but the nail is in the way, the wood applies significant pressure to the nail. This pressure increases the friction between the two surfaces making for a strong bond.",
"The angle it's hammered in at helps too. Imagine if you pulled a nail out in the direction you hammered it in, you'd think it could slide right out. But imagine if it was hammered in at 45° and you pull it \"straight\"; the side of the nail pushes really hard against the edge of the hole it's in and the whole nail would have to bend to come out, so it really doesn't want to move."
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hh9t7q | Why does some furniture use Phillips head screws, while other use hex or torx? What are the advantages between the many different types? | Engineering | explainlikeimfive | {
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"a slot screw can't be tightened with a lot of force, usually you'll slip or snap the bit. But you'll see it in common things where a lot of hold isn't needed due to being easy to find things to use as a flat head. Philips Heads are common when needing to screw in multiple screws, but they aren't ideal for things of high hold where you need to make sure they go in tight and have to be removed and reused multple times I.e beds, as the heads can easily strip making them hard to remove or impossible to reuse again. Furniture will more oftenly use hex because one, Allen keys usually give access to tighten things even in small places and at angels including the lack of need to make sure you apply pressure to the bit when tightening or loosening the screw unlike flat or Philips heads where you need to apply pressure while screwing in a screw, while the hex is also deeper and a lot harder to thred usually finding the Allen key will thred before the actually screw head.",
"Locking forces and uniqueness. Phillip's is a generic every day format, useful for wood screws and self locking plastic fasteners. Hex allows greater locking forces. Torx is a specialist type, usually to prevent every day adjustments.",
"My understanding of Phillips heads is that they were developed for automation. They self center on the bit, and have better cam-out (ie slipping that can cause damage) than a slotted/flat head screw. There are beliefs they are designed to cam-out at torques that would otherwise damage aluminium used in aircraft construction, thus allowing for simpler tooling to protect the aluminium. However it wasn't mentioned in the original patents, so it might just be an unintended side-effect. Pozidriv is similar to Phillips head, but has additional slots to improve its cam-out point, allowing more torque. These are a lot more common these days. ____________ URL_0 Has a big ol' list of screw head types, and some brief descriptions of them"
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hhnf3i | Why are there not space shuttles for sending nuclear waste into space rather then dumping them on our planet where they are toxic for millenia? | Engineering | explainlikeimfive | {
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"Challenger. That's the only answer you need. If it were carrying a cargo bay of high grade waste half of the country would have been irradiated for centuries.",
"Underground storage is waaaay cheaper. 6500 tons for $1B. For that price, you could shoot maybe a few tons out of sphere of influence of the Earth(and hoping it won't come back) URL_0",
"Currently there is a massive cost barrier as well, getting anything off this rock costs a lot of money. In the future they could feasibly shoot them off into the sun or just out into the void but would require significant leaps efficiency for that to be more viable than just chucking in a hole in the ground.",
"Expensive, dangerous, and dumb anything in orbit will eventually come back down again. Tons of nuclear waste eventually burning up in the atmosphere and coming back to earth as a shower of radioactive dust or rain is a very very bad thing"
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hiwv46 | Why are there no SSDs with more capacity, if 1TB MicroSD cards are a thing? | Engineering | explainlikeimfive | {
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"You use an SD card every now and then for a few minutes; you use an SSD for long periods at a time. The SD card doesn't have to be particularly robust, but the SSD needs to be *massively* more reliable. Look at it this way: an SD card that fails after 5000 hours of use lasts damn near forever. An SSD that fails after 5000 hours of use means that your desktop is hosed in 7 months. Additionally, an average SD card transfers data at, what...20 MB/s? 80 MB/s? Something like that. An average SSD transfers data at more like 500 MB/s, with M.2 SSD drives being more like 3000 MB/s. All the things that make SSDs more reliable and faster take up room and increase price.",
"32TB SSDs have been around since 2018. But they are very expensive. They are aimed at the enterprise market. I have a mess of 7.6 TB SSDs at my job. And those are already a couple years old. The newest models I can get I think are 32TB for those arrays.",
"I don't know all the technical details behind it but while it has a large amount of storage for it's size, it's very slow. You can get a $300 M2 1TB SSD that reads at over 3500 MB/s and writes at over 2000 MB/s (compared to 160MB/s and 90MB/s respectively), so the cells used in the MicroSD probably focus more on capacity than speed. However that's not quite a direct comparison because that speed is only available due to the interface, normal SATA SSDs are quite a bit slower but still much faster than the MicroSD. I wasn't able to find endurance info on the SD card but I know SSDs are often also built for high endurance (like server-usage for 5+ years), which takes away space that could be used for higher capacity.",
"They exist, they're just very expensive. This company makes a 100TB drive. They're aimed at big companies that need to store lots of data. I have 5 slots in my PC, if I had 5 of those I'd have 500T of storage. I've had 5TB of storage for like 5 years and haven't filled it, and I have a lot of games. [ URL_0 ]( URL_0 )",
"SSD are wrappers of simple Flash memory MicroSDs are simple Flash memory with nothing else wrapping it Flash memory itself has a very finite lifespan based on \"write/erase cycles\" which means every time you write new data, you take away lifetime points. **SSD is a wrapper technology intended specifically to minimize how many low-level write/erase cycles are applied to Flash memory cells by buffering data into SDRAM.** So SSD has **duplicate memory** which takes up physical space) and it also has a lot of extra logic (more physical space) to even out all the memory cells mapped to addresses so that write/erase cycles more. This requires having a lookup table which is also a form of (duplicated) memory. So an SSD has many times **duplicated memory cells for every cell of non-volatile Flash** which each take up space that in a non-SSD like a thumb drive or MicroSD isn't there. All that extra memory takes up space and reduces how much memory space you can have for the same price of components. The other advantage of a SSD is by caching to SDRAM also speeds up access to the memory compared to direct writing Flash memory. How fast does Flash memory directly age out to failure? Well typically they start to fail at 10\\^(5) cycles. So if your CPU is clocked at 3 GHz (3 x 10\\^(9) cycles/second) and if Flash actually ran as fast as SDRAM, you'd age out to FAILURE your Flash memory in less than 1 second. But thankfully (?), Flash does NOT operate remotely as fast as SDRAM - Flash memory write/erase take 100s of microseconds to 10s of milliseconds. So only for that reason you don't age out Flash or MicroSDs in just a second.",
"... & #x200B; They do exist...they are just exorbitantly expensive... [ URL_0 ]( URL_0 )",
"Note that the 1TB MicroSD card is priced at about $400. From that price you would expect the price of a 20TB SSD to be around $8000 which puts it way outside the range of any consumer product. So no manufacturer would market it on places like Amazon but rather markets them for their enterprise customers who can actually afford the drive. And looking up a few internal pricing catalogs for the enterprise market I can see several options for double digit terabyte nvme storage devices. They are even a bit cheaper then the price for a comparable MicroSD array and that is before any haggling which could reduce the price to less then half. For an enterprise spending $2000 for a 20TB drive is no big cost in the grand scheme of things. The drive will pay for itself multiple times over during its lifetime. However the manufacturer knows that regular consumers are not willing to spend that much money on a disk. So they do not market them for consumers.",
"Longevity. The way current huge SSDs work, like 2 TB big ones, is that each cell holds 4 bits, that is, 16 distinct values. Imagine each cell as a bucket full of water. Every time you read the cell, you need to fill the bucket, see how much overflows, empty the bucket, then fill it to the original amount. After a while, the bucket gets damaged and can't hold distinctly different amounts of water. That is, instead of holding 16 different amounts, it can only hold 15 or less. That means you go to the next power of 2 down, or 8. Over time these cells degrade so that less and less data can be stored on them. AD cards can deal with this by no being active for long times, thus ignoring the damage because it takes too long. SSDs can't ignore this, so they have extra space in them that goes unused until needed. They are usually built with 20% extra space. There are also other methods, like my Intel SSD will use 1 bit per cell on heavily used data (like OSes, commonly played games, etc.) to stop (or at least severely slow) degradation.",
"There are SSDs with mroe capacity. I've worked with ones that go up to 12TB but they are server grade ones that use U.2 connections and are super expensive..."
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hj5cqm | How do these glasses work? | [link]( URL_0 ) What are these glasses doing to block out all of the tv picture? | Engineering | explainlikeimfive | {
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"Those are LCD screens and those are polarized glass lenses. Polarized stuff work by by blocking light that is twisted in a certain way. For example, light that has bounced of something on earth and is causing glare. LCD screens work by shining light through a polarized filter, so it's blocks all the light unless it's twisted in a particular way. It then goes through another filter that blocks all light unless it's twisted another way. This makes a dark bit of screen. To make that bit light up, they have some liquid crystals twist it to the correct way. But the end result is that all the light coming off the screen is twisted in a single way. And the guy's glasses lenses are blocking that way. If he held the glasses in a different way, the light would come through."
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hjcdjd | How do bike pedals rotate without unscrewing? | I know for a fact that the pedals are screwed on to the crank by a bolt and the footrest rotates with the bolt as the axis. How does the rotation of the footrest not affect the bolt? | Engineering | explainlikeimfive | {
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"Bearings: there's little friction between the pedal and the spindle it rotates on. The direction of the pedal threads is also specifically chosen (left hand thread for the left crank) so that any bearing precession would exert a torque to tighten, not unscrew the pedal.",
"They do, which is why the right pedal has a screw that turns the other way, so it tightens instead of unscrewing But also the friction is very little, which is how the pedals turn so freely and you can pedal backwards without them unscrewing immediately"
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hji93l | Why do some cars (mostly sports/muscle cars) have engines that sound like gunshots going off? | Is this a different type of engine? All engines utilize small explosions, but why do these engines sound particularly loud? | Engineering | explainlikeimfive | {
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"Potentially you may be talking about backfiring if you mean very sharp, distinct pops over the normal sound of the engine. Backfiring is when the engine doesn't combust all of the fuel and it then burns in the exhaust system. It may also cause visible flames from the tailpipe. The typical causes are too much fuel for the available air in the engine or an ignition issue and it's a bad thing in general. However, many vehicles that are set up for a massive amount of horsepower will backfire under certain circumstances. For instance, a vehicle may be set up to get enough air when the turbo is fully spooled up but will backfire when the turbo rapidly drops off and stops supplying enough extra air."
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hjoked | How does Honda make such reliable engines? | Some engines are more reliable than others, obviously it depends on amount of moving parts and things that can go wrong. But why is honda so good at keeping things simple and making their engines last so long and still work compared to their competitors? | Engineering | explainlikeimfive | {
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"Honda isn't without flaws but honda and Toyota tend to keep things simple and what I mean by that is they don't try too hard to innovate something that works well they'll build off of it. For example I have an I-VTECH in my CR-Z while it's in no way fast its reliable and fuel efficient. The VTECH engine works well so they run with it so they mainly build off that foundation. Most of the time (from what I've witnessed) is that many manufacturers dont work as well because they try to \"innovate\" too much meaning they go with cheaper parts or have to change the location of something to fit in a different shaped engine bay. Ford had a pretty big issue with their transmissions back at the beginning of the decade (2010) brought back the fiesta multiple times to have it fixed before Ford just bought the car back off of me. They had gone with a new manufacturer for transmissions and many if them were garbage. Note: not scientific information but my observations",
"Because they've been taking quality and reliability very seriously for well over half a century. Long before American manufacturers were, and still to a much greater extent. They don't just see it as a way to make more money. It is ingrained into their company culture as something *without which they could not exist*. When Japanese auto companies first tried selling cars in the USA, they were a literal joke. They could hardly give them away. So they hired some quality experts who had been mostly shunned by American companies and took their advice. They saw it as the only way they could succeed in a business they desperately wanted to get into. And it worked. The fact that it worked reinforced the decision and they began to rely on their quality and reliability as their competitive advantage. They've not just incorporated a single quality system, they've incorporated multiple systems, and have evolved them over time. One of the important principles of several such systems is to minimize \"opportunities for error\". That's true in both the design and the manufacturing. It's the old engineering principle of Keep It Simple, Stupid (KISS). All engineers learn it, few truly take it seriously. That sounds simple, but it isn't. There are always multiple forces in a large corporation pulling in various different directions. It's not easy to have the principles to let quality and reliability trump everything else. You've got to have the iron-clad belief that they are what makes or breaks you, and most companies don't. Honda and Toyota do."
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Subsets and Splits