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7kgf5v | How do transformers step up voltage without essentially creating electrical energy out of nothing? Or more generally, what is the difference/relationship between voltage and power? | I'm having a hard time separating voltage and overall energy potential of electricity in my brain. A step-up transformer apparently raises voltage but lowers current, and I am completely failing to understand how that is possible if everything else in the system remains the same. I feel like I'm misunderstanding a fundamental property of electricity. Does the voltage drop if continuous current is drawn from the system? | Engineering | explainlikeimfive | {
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"Power = Voltage times Current Energy = Power / Time Energy can not be created or destroyed, but can be changed in form. Going from low voltage and high current to twice as much voltage and half as much current leaves you with the same energy and power on the input as the output. As long as you are feeding power in continuously the output voltage should remain the same(unless you change the load) Transformers work just like gears or levers do. If i give you a short wrench then you can undo a screw without moving your hand too much but it will take a lot of force. If i give you a long handle on the wrench then you can use less force but you have to move your hand significantly further. The work done in both cases are the same, you traded force(voltage) for distance(current)"
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7kic8n | How does using a revolving door "save energy" as compared to a normal door? | I live in Toronto and there are these signs at Yonge Dundas square which encourage people to use revolving doors instead of normal doors to "save energy". How does using a revolving door save energy? | Engineering | explainlikeimfive | {
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"It reduces the amount warm air going out/cold air coming in. This helps reduce the cost to heat the buildings.",
"As well as what other people have said about allowing wind to blow in and out of a building I'm sure I've read something about if a building is extensively cooled, particularly in a hot country, the air inside the building is denser than outside, so has a tendency to want to leave the doors rapidly, even to the point of preventing a normal door closing properly.",
"Revolving doors are designed in such a way that airflow is reduced compared to normal doors, so less energy is spent trying to offset the temperature differential from cold or hot air coming in. In moderate climates where a building doesn't necessarily need to run air conditioning/heating, it can be negligible at best. URL_0",
"The volume of air that enters or exits a building when a revolving door is used is much less when compared to opening a door. The revolving door exchanges only the volume of air contained between the doors. Opening a door usually lets a blast of air to come in or go out"
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7kkv2v | the difference between blacktop, tarmac and regular roads | Engineering | explainlikeimfive | {
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"I don't know where you are and what constitutes 'regular' roads. Asphalt roads vary, essentially the different types have different quantities of stone (cheap) and bitumen (expensive). Types include bitumen macadam, hot rolled asphalt and stone mastic asphalt. These are all considered flexible pavements and the thickness of the layers are often around 2.5x the size of the stone in it to aid compaction. Concrete roads are made of concrete with layers of reinforcing mesh, with joints at certain intervals to allow it to expand and contract which could otherwise cause cracking. Sometimes cuts are made to ensure cracks happen uniformly. Both are generally supported by compacted graded crushed stone."
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7kl2j9 | What's the difference between winter, all-season, and normal tires? | Engineering | explainlikeimfive | {
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"summer tires: awesome in summer, disaster in winter winter tires: horrible in summer, awesomeness in winter all season tires: meh in summer.....aiiight in winter the difference is in the tread depth and design and the stiffness of the rubber. winter time is also colder than summer time, so rubber is naturall harder in cold. so winter designed tires are designed so that in cold temps, it's still able to grip the road.",
"The difference is in the composition of the rubber and the tread pattern/design. Rubber tends to get very hard and brittle in colder temperatures, which is bad for grip. Winter tires are made of rubber that stays softer and grips better at lower temperatures compared to a normal or all season tire. The key though with winter tires is in the tread design. Winter tires have very deep treads, and lots of them, in order to dig through the snow and find grip. A tire with a shallower tread design would float on top of the snow (ask me how I know). They also have serrated [siping]( URL_1 ) that allows for much better grip on snow and ice. The rubber wears very quickly in the summer though, and the tread design means they are louder than a tire that is design to be quiet. The polar opposite of a winter tire is a summer performance tire. These often have a few shallow treads in order to maximize the amount of rubber contacting the road. And have rubber that is extra soft and grippy in warm temperatures. These are usually overkill outside of racing applications and might even be dangerous in the rain. A normal tire probably is an all season tire. It attempts to be an \"all around-er\", providing a compromise between noise, wear, and grip at all temperatures and conditions. Some do this better than others, and how \"good\" they do all of these things can vary between manufacturers or individual tire lines. Generally these are good enough to be on a car year round, but it'd be best to stay home if you expect slippery conditions in the winter. On our cars we use Blizzaks in the winter on a spare set of rims, and for the spring/summer/fall an all season that I try to cater to noise, rain traction, and how much life I can get out of them. URL_0 has good informational articles and videos if you want to know more."
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7klq03 | How is oxygen maintained in the ISS? | Is there a better or energy efficient way? | Engineering | explainlikeimfive | {
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"text": [
"They get O2 by separating water and venting the H2 overboard. Water is very low cost, easy to move around and store, and mostly oxygen (by mass). The key is to not let it leak out."
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7kmm80 | Now that winter is here (UK), and water pipes are more susceptible to bursting, how do water providers detect a burst water main underground? | They always seem to dig a repair hole in the exact location of the breach. How can they detect it so precisely? | Engineering | explainlikeimfive | {
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"text": [
"I would guess an abnormally wet piece of ground or water bubbling out of it would be the clue..."
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7ko31z | Digital Aliasing and the Nyquist Frequency | What is aliasing? What are some examples? What is the nyquist frequency in relation to aliasing? | Engineering | explainlikeimfive | {
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"The real world is analog, things like sound and radio are continuous oscillations. While quantum field theory is true, most all real-life things are much, much too large to have discrete quantum behavior. When you sample something digitally, you are making a discrete measurement at a specific time and using that to represent the continuous signal. This is never correct, the real world is analog, but it's often plenty good enough. The Nyquist Frequency is all about knowing when it's good enough. Let's say you sample at 1000 samples per second. If the signal is 60 cycles/second, like wall electricity, you have each sine wave represented with 16-ish values. That's 8 for the positive side of the wave and 8 for the negative side. That will produce a very good representation. At 250 cycles per second, you're down to 2 for the positive side and 2 for the negative side. This could be 0, 1, 0, -1, ... which looks a lot more like triangles than a sine wave; or it could be .6, .6, -.6, -.6, ... which looks wrong in a different way. At 500 cycles/second, you've got 1, -1, ... or 0, 0, ...; barely right at all. At 2000 cycles/sec, you get .6, .6, .6, .6, ... or -.3, -.3, -.3, ... Absolutely wrong. And 4000 cycles/sec is exactly the same wrong. These are \"aliases\" of each other. The Nyquist frequency is last frequency where you barely get the right shape. For out 1000 samples/second measuring device, this is 500 cycles/sec."
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7kwvp3 | How did someone just come up with parts to make an engine? | How did someone way back then just come up with parts to even form a engine and know that'll it'll need gas and oil to run? | Engineering | explainlikeimfive | {
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"They didn’t. We started with very simple steam engines and then improved them slowly over the next 150 years or so. Very few inventions just come put of nowhere",
"A person way back when didn't just slap together a modern internal-combustion engine. It started with steam engines, and someone realizing that the pressure steam creates could be used to create mechanical motion. That system was refined over some time, and later on people started experimenting with the idea of using combustion itself to create the motion, rather than the middle step of heating steam. We knew that moving mechanical parts rubbing against each other needed lubrication (oil) for a long time."
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7kyhdo | Since we almost have self-driving cars, why would it cost hundreds of billions of $$ to have trains slow down at known corners on a well-defined 2-D route? | Engineering | explainlikeimfive | {
"a_id": [
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"Originally it was required that the technology be added to all rail lines by 2015. Then Congress passed an extension at the request of rail businesses to where it wasn’t required until the end of 2018. I don’t know if it was a cost factor or just trying to avoid a safety regulation but obviously it was absolutely needed!"
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7kyyha | Why would we ever care about the distinction of a Newtonian fluid and a non-Newtonian fluid? (I put this with an engineering flair because I want to know if there’s any practical use, not theoretical) | Engineering | explainlikeimfive | {
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"Imagine you're trying to fill a mold with a material. You'd likely want to do that as fast as you can. Well, what happens if the material doesn't behave like a Newtonian fluid? It becomes much more difficult to predict how the mold will fill without extensive experimentation. You can also get neat things like URL_1 which lets us do URL_0",
"For one example, [liquid armor]( URL_0 ) can be made only of a non-Newtonian fluid."
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7kz217 | How does a level work? | Engineering | explainlikeimfive | {
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"A level has a tube filled almost completely with liquid, and a smallish bubble of air. The liquid will go to the lowest point, and the air will go to the highest point. If a surface is higher on the right than on the left, the air bubble will go towards the right. If a surface is \"level\" then neither end of the tube is higher, and the air bubble will stay in place.",
"Assuming a bubble (liquid) level: any liquid will find equalibrium to Earth's gravity and thus the bubble will move as it's angle to the gravitational field is changed. In a zero G environment, the bubble doesn't move."
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7kzqyi | How is water supply pressure high enough at the end of the line, while not being too high close to the source? | Engineering | explainlikeimfive | {
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"The pressure is not much higher near the source. You may ask, then why isn't it quite low near the end? Two reasons. 1. The pipes are fairly big, commonly 20cm or more in diameter. These carry water well, without much pressure loss per km. 2. Often the supply continues to run downhill, adding more pressure along the way.",
"Finally! a ELI5 topic I can respond to! For a transport system involving a pump, the point of highest pressure (or head) is right at the pump outlet. We take this value, give it a safety margin (say, around 10%), and assign it as the design pressure of the entire system. So the entire line is designed to handle the highest pressure. As far as the first part of your question is concerned, the losses in head are fairly negligible for water lines since the pipes are such a huge diameter. The only real factor that would diminish a system's ability to transport water to the end of the line would be if there's an unexpected source of consumption somewhere along the way (i.e., leak)"
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7l2eca | Why does "safety glass" break into square shards and does the size of the pane effect the size of the shards | Engineering | explainlikeimfive | {
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"Safety glasses is usually tempered glass. When the glass is molten, one side is rapidly cooled, it makes a tight skin before the rest cools. That tempering is what make the glass break into small squares instead of shards. Safety glasses may also have layers of plastic embedded in the glass one on top of it to prevent the small squares from falling apart."
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7l2m0h | How Dual-Clutch Transmissions and Continuously Variable Transmissions use clutches but do not stall. | Engineering | explainlikeimfive | {
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"standard manual transmissions leave the operation of the clutch to the driver. dual clutch tranmissions have a computer thats controls the clutch thru vacuum and hydraulic systems. the computer doesn't make the mistake of misengaging the clutch .",
"Dual clutch transmissions are basically a sequential manual transmission controlled by computers and therefore automated and programmed not to stall. If you are able to override the computer, then yes, it can be stalled. CVTs are like automatics and use a torque converter and will not stall as if it were an automatic. However it is not strictly true that CVTs cannot be stalled as nothing prohibits you from installing a foot-operated clutch to the CVT(same with automatics), in that case, it can still be stalled",
"First, DCT: These transmissions use two clutches - one for even gears and one for odd gears. This is what helps make them so fast. As you are about the upshift or downshift, the computer \"readies\" the other clutch's gear by selecting the higher or lower gear depending on whether you want to go up or down a gear. When the next gear is connected, and the computer is ready to shift, it can very quickly release one clutch and engage the other. Then it can select the next gear again on the disengaged clutch. You save the \"gear change\" time consumed by a normal manual transmission. If we had more legs, we could do the same thing with 2 clutch pedals. That answers why they are fast and desirable, but why don't they stall? Well, the computer-controlled clutches do the same thing humans do while driving. When you come to a stop, the car selects first gear, but disengages the clutch. It can hold it's position using the brake (even if you aren't pressing it enough, like on a hill), or by slipping the clutch like a human might do. This can cause extra wear on a clutch, but it's pretty much the same way humans drive a manual transmission. The computer decides when you want to stay still, creep forward slightly, or move forward and continue accelerating. Then the computer modulates the clutch appropriately just like a human so that the car does this. This technology is still improving, and many people complain of \"jerky\" driving behavior especially in parking lots or with a cold car because the computer isn't as smooth with the clutch release as a human might be. CVTs: These actually use a torque converter typically. The ones that don't (like a motorcycle) use a clutch to follow the same principles as a normal manual transmission. CVT is all about the gears (not the clutch engagement of those gears). To understand how CVTs work, picture a typical multi-speed bicycle where you have front and rear gears. You know that by moving the derailleur in or out on the front or rear gear sets you can adjust for high power and fast acceleration with a low top speed, or low power with low acceleration but a much higher top speed. The whole time though the chain on the bike remains the same length (I know that fixed gear sizes actually mean the derailleur needs to pick up some slack, but I am simplifying the explanation). A CVT works on the same principle. Instead of using a chain, it uses a kind of belt that always stays in the same place. Both of the \"gears\" the belt rides on are actually like cones where one end is very small and the other end is very wide. Picture them like the small gear and the large gear on the back of the bicycle. By moving the cones towards or away from the belt, we can change the diameter of the front gear to be larger at the same time the rear gear is smaller (the belt stays in the same place). This would be like going to a large gear on the front of the bicycle, and a small gear on the back of the bicycle, except because they are cones the change is \"continuous\" instead of in steps like a bicycle. The result of all this is that we change the gear ratio in the transmission continuously, so as the car accelerates (higher MPH) we can adjust the gear ratio to keep the engine at the same speed (RPM). This is more fuel efficient and produces more power across the MPH range. EDIT: Added some paragraph separation so it doesn't look like a 5 year old typed this.",
"some CVTs and DCTs use electronically controlled clutches (or similar tech), which automatically engage the clutch when the engine revs above a certain limit. these cars are notable, because they do not inch forward when you release the brakes while the engine is idling in drive gear. some CVTs and DCTs use torque converters, similar to how traditional automatic transmission vehicles. in both cases, the system actively prevents the engine from stalling."
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7l7ixg | Why is plumbing so difficult to get access to if it's so temporary and disaster-prone? | Engineering | explainlikeimfive | {
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"Simply put nobody would buy a new house that had visible plumbing and they likely will die/sell it long before the plumbing gets that bad. General lifetimes for different plumbing materials. Brass 40-70+ yrs Copper 50+ yrs Galvanized Steel 20-50 yrs"
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7l8uys | What's the difference between Cement and Concrete? | Engineering | explainlikeimfive | {
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"text": [
"Cement is just a binding agent that isn't really use alone, it is present in Concrete and other mortar."
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7lchhc | What is the science behind overclocking a CPU? | What actually happens behind the scenes, inside the computer for it to overclock? Edit: Went to sleep and came back to crap ton of answers. I appreciate it truly and will read each one. Thanks! | Engineering | explainlikeimfive | {
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"Imagine 500 workers in your company. Each worker fills out a form, their work. You give them 10 minutes for one form, since some guy has calculated that to be the best \"base clock speed\" of 3000 forms per hour. You actually sell your company to other people and they perform as advertised, but every company you sell has DIFFERENT workers (obviously). It is still kind of the same company though. It turns out, your workers fill out the form in 8 minutes on average and then meet in the hallway to chat. One of your customers thinks he can 'overclock' his company: he tells all the workers they only have 9 minutes to fill out the form. Works great, there were still resources left in that company and now you have a company that gives 3300 forms per hour (10% increase). One of the customers friends got wind of the overclocking and tries it with his company. It's horrible: the workers take 9 minutes on average to fill out a form, so on average they should meet the 9 minute requirement, but they have no more time to chat, get depression and burnout. Eventually a worker quits because he had enough. This is where your company becomes unstable and locks up, e.g. the overclocking went too far, not enough untapped resources were available, mistakes are made that cannot be undone, etc. The 'potential' for overclocking is different for each model and even differs with each CPU sold. If you increase the clock speed, some signals can get lost in transit if the physical layout of your CPU is 'bad' (this means that one of the circuit paths during the lithography process was less than ideal, too thick or too thin for example) so you also need to increase voltage, but THAT in turn increases temperature and also, since each circuit path is an antenna, the influence one circuit path can have on another. This can go to a point where to circuits cancel out each other's signals when they 'transmit radio signals' too much. That 'interference' is what cannot be overcome by any means other than designing the CPU differently. In essence, there's potential to do stuff faster. How MUCH is determined by the quality if the design AND the individual 'print' of your CPU. To get your CPU to a stable processing speed that is higher than what the manufacturer intended is tricky but can usually be done reliably without damaging the component by 1. increasing the frequency until failure 2. increase voltage to strengthen signal 3. repeat 1+2 until failure because of interference The reason a manufacturer picks a certain clock speed is simple: yield. One printed wafer gives a certain percentage of functional dies (the heart of your CPU). Each die is tested to run at the base clock speed. The better the design and the better the manufacturing process as well as how carefully chosen the clock speed is: more dies per wafer = more cash. The idea is to get the best die per wafer that can reliably be produced with as few losses as possible.",
"Nothing is perfect, but some parts of the processor chip are better than others. The chip company, on the other hand, wants to have about 3 speeds of parts for sale. They test all the parts, to see how fast they can run without making mistakes. The parts that work best get the high speed rating, the middle parts get the middle rating, etc. You, on the other hand, only have one part in your computer. You can choose to provide better cooling than the chip manufacturer requires. As a result, you can choose to slightly increase the speed of your CPU to make a faster computer. It's a bit of work, and it gives you a non-standard configuration, but it might be worth it.",
"Processor manufacturers practice boxing. They have one assembly line that makes all their CPUs of some kind. Then they test them. You see, manufacturing at the atomic scale isn't a perfected process, so lots of flaws make it in. If your CPU has 4 cores and one is dead, disable it and sell it as a 3 core CPU. This is why Intel has such variation in their product offering. The CPU you're running is discounted because it's mostly broken. The CPUs that make it through manufacturing fully functional are the top end offering and the most expensive. Among this testing process, they see how fast a CPU can change state, because there are some trillion-plus transistors that all have to switch at the same time, and your CPU can only go as fast as the slowest one. All this is ostensibly true. If their process improves and they make more fully functional CPUs, they may hamper the device intentionally, so they have commodity offerings and they can capture that segment of the market, lest they go to a competitor for a CPU in their price range. So all this is locked in to a CPU by physically breaking connections. Unlocking the CPU means reestablishing these connections that enable, at the very least, higher clock rates. The improved performance comes with a risk of reduced reliability and stability. It also means the device will run hotter, because faster switching speeds are accompanied with additional power consumption. There are overclocking motherboards, but they increase the bus speed, which is the speed your memory is running at, which is much lower than your CPU speed. This can give a good boost in performance because your CPU spends most of it's entire life idling, waiting for data to arrive from memory. This also comes with increased power consumption, and heat, and reduced stability and reliability. System memory, RAM, is made from banks of tiny capacitors which hold a tiny charge, and writing data to one requires either charging or discharging it. This takes time. If you run the bus speed too fast, then this transition can't happen fast enough, and you end up with memory corruption, false 0s and 1s."
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7ldwuu | why is the tail wheel on an airplane usually tiny? | It seems like it wouldn't be robust enough to handle much weight. | Engineering | explainlikeimfive | {
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"There’s not much weight on the rear of those aircraft so the smaller wheel works fine. The smaller wheel also saves weight.",
"The center of gravity is almost over the front wheels, so there is very little weight on it. You can easily lift the tail of a single engine aircraft with one hand. You do not want a tail heavy plane (a front heavy plane flies badly, a tail heavy plane flies once). Also, you don't want anything heavy in the tail. 1 kg in the tails means you need 5 kg in the front to balance it, due to the leverage of the long tail. If you look at a taildragger landing or taking off, you'll also notice that the tail is only on the ground at low speeds. As soon as it gets some speed, the tail lifts and the plane becomes horizontal. That said, for these reasons and a few more, taildraggers are being phased out. They remain in some applications (aerobatics (weight), bush flying (robustness), glider towing (works better with the towing forces) and a few more), but most new aircraft use a nose wheel. They are less likely to \"nose-over\", and the pilot has a better field of view during taxi (if you look at old warbirds, which have a huge engine, you often see them zig-zag during taxi, because the pilot can't see straight ahead)."
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7lf8qu | Why do Guitar strings go out of tune Sharp, and not Flat? | Engineering | explainlikeimfive | {
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"Your strings have gained tension due to the change in temperature and humidity causing the wood of your guitar to expand and contract. Metal strings don't expand or contract enough to cause detectable tuning issues alone. The wood of your guitar, however, does. The truss rod does the best job it can for keeping your neck at the right angle relative to the body, but it's not perfect. A slight movement of the neck backwards (towards the z axis relative to the body of the guitar) will cause your strings to go sharp enough for your ear to discern. You can test further this by playing open strings and pushing on the headstock in different directions perpendicular to the body of the guitar--just don't push too hard. As relative humidity changes, the wood of the body and neck of a guitar will expand and contract in two ways: tangentially and radially. Tangential movement lies parallel to the growth rings of the wood while radial movement is perpendicular across the growth rings. Another thing to consider is that different species of wood are more hygroscopic than others. This simply means that one species, take Maple with a radial growth coefficient of 0.00353 for example, will absorb more water--and thus move more--than another species like Cherry that has a lower radial growth coefficient of 0.00248. So, while the neck of your guitar gains or looses moisture, the wood will expand and contract relative to one of the two directions I explained earlier. This movement in either direction can very well be enough to cause more tension on the strings, thus bending them sharp."
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7lirir | Surveyors who survey land and roads before a new construction project. What are you doing? | Engineering | explainlikeimfive | {
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"They are measuring the land (the actual dimension of plot, etc.) and the topography, or changes in elevation. They need to do this so they know exactly what work needs to be done, make sure they comply with set-back and other zoning considerations, know how much dirt needs to be cleared to level the site, and so on.",
"I was a surveyor for a time. If you are talking about a road or construction, they are marking off exactly where everything is supposed to go. Both location and elevation. The place where a road is supposed to go is surveyed before any plans are made. This lets them know what space is available, etc to place the road. Then a plan is made that says, \"the road should go right here\". The surveyors come back and put in stakes and other markers that let people know, \"The center of the road should be here at this height\" and other things about where construction should occur. As they go, new surveying is done to make sure everything is where it is supposed to be. Also, when someone buys a piece of land, they also mark off where the piece of land is that the person is considering buying. The way all of this is done is by comparing to things that you know where they are. The little tripod thing- it shoots out a little laser light that reflects off a mirror on a stick held by a second person. They find location by determining the angle that the laser light was shot and the time it takes for the light to come back. The laser shooting thing is called a theodolite. Here is a pic URL_0 The mirror thing is called a traverse prism. It is usually on top of a stick held by a person. Here is a pic URL_1 If you have any specific questions, please do ask. I'm pretty sure I can answer them. Be happy to tell you about any of the specifics of pretty much anything.",
"Roads and pipes and things need to be built at certain slopes to allow drainage to happen according to plan. So all the water that builds up on a roadway during a rainfall can roll off the road and into the storm drains where it can be properly carried away. If the road is sloped wrong the water may pool up and cause a serious hazard to traffic. When the road is being made, layers of sand and gravel are laid down and compacted. Surveyors measure the height of the land and the slope and tell the equipment operators where to shave a little off here or add a little there, until the numbers are all correct. There are markers all over the place, laid down in the past by surveyors for the government, that have known heights above sea level. These are used as a constant reference point to gauge the height of the measuring stick. There is a telescopic device on a tripod that the surveyor looks through and the assistant holds a very tall ruler and stands at the spot where they want to know the height of the ground. The surveyor looks through the telescope and reads the numbers on the ruler and through some simple math using the number obtained from the known marked point, the exact height of that particular location is now known.",
"Mapping. Imagine you want to build a curb, sewer, bridge or even just lay down some new pavement. You want to design them accurately so they're easy to build and match into the existing conditions perfectly. Remember not everything you build starts on a clean plot of land, likely there are lots of man made objects you need to avoid or tie into. So to get your existing conditions, you need survey. Accuracy of topographic mapping (flying a plane and taking a picture) is accurate depending on the height of the plane, but say +-0.5 feet. That's usually only precise enough for large scale grading, not bridges, pavement, utility work. So you'll need higher accuracy. That means boots on the ground and survey usually by GPS. So you'll have a surveyor with a big rod, the bottom end is a point, the middle has a small computer, and the top has a super accurate GPS. This instrument gives an accuracy of +-0.005 feet in all directions. The surveyor will walk the entire site and mark all objects and a grid for anything in between. The surveyor will see an object, determine what the object is (say a manhole lid) then describe the object by inputting a code into the computer, then physically put the pointy end on the object to measure it's exact coordinates. Once you get all the coordinates and codes, you send it back to the office to process and produce a map of the site. As you can imagine this is a laborious process for big sites, but to make an engineer's work easier and more accurate a good survey is where it all starts."
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7ljjd0 | How does a whetstone sharpen a blade? | Engineering | explainlikeimfive | {
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"text": [
"By scraping off the metal that's sticking out above a flat plane. By using two flat planes on either side of a blade you can form a sharp edge where the planes intersect."
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7lmx52 | Twin-Jet vs. Quad-Jet, and why the latter has a declining usage in Aviation Industry? | Engineering | explainlikeimfive | {
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"There are organizations who make rules about aeroplanes, so that the people who fly on them will stay safe. One of the rules is about how far an aeroplane is allowed to fly over the ocean away from land in case something goes wrong, so that it can get back again. Many years ago jet engines weren't very reliable or powerful, so plane makers had to use four of them to get across the oceans quickly and safely. Over time, new kinds of jet engines got more powerful by blowing more air round their outsides. So powerful in fact, that just two would do the job for even huge aeroplanes. Now it was no problem to cross the atlantic on just two engines - and of course it was much cheaper too! But in the beginning, they weren't sure how reliable just two engines could be, so the safety people made a law called ETOPS that said you had to stay within 60 minutes of land at all times, and be able to fly for that long if one engine failed. This wasn't very useful because it meant taking more indirect routes across oceans, staying near the land quite a lot. So some places still needed four engines to get to, while a few could use two. Over time, those new engines got ever more reliable and the safety people began trusting them more and more. They changed the law from 60 minutes away from land, to 120 minutes, then to 180 and recently to even 370 minutes! If you are allowed to fly 370 minutes away from land on two engines, then you can go pretty much anywhere you want in the world - so four engines aren't needed for safety any more except for the very biggest aeroplanes - who need them more for the power than reliability. And that's why you don't see many four-engined aeroplanes any more - because twins are much cheaper, and have become so unbelievably reliable that we trust them to fly more than six hours across the ocean, even with one engine failed."
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7lnu5i | why do Falcon 9 Iridum 4 exhaust plumes look so weird? | Engineering | explainlikeimfive | {
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"The change occur when it changes from stage 1 to stage 2. The second stage engine is design for use in vacuum and have a different nozzle. It ignites at 80 km where the pressure is less the 0.02% of the pressure at se level. If your look at the [video from space X]( URL_0 ) of the launch the difference is obvious after the separation a few seconds into the video.",
"Good guesses, that's basically right. The stages separated, and the second stage engines kick in. These are \"tuned\" for use above the atmosphere, so the plume is extremely wide. Back up one second: what makes a \"normal\" rocket plume is air pressure. Stuff leaving the rocket wants to expand in all directions, but the outside pressure keeps it in a relatively tight cone. As you get higher up, this effect weakens, so plumes in or near space are very wide."
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7lo4r5 | How is concrete poured/set underwater when making bridges? | Engineering | explainlikeimfive | {
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"When they can or are required to, they remove the water from the area by putting down something around the intended concrete volume to keep the water out, essentially like a \"moat of air\" that's either open on top or fully sealed. [It's called a cofferdam if open]( URL_1 ). When they can't or it's not cost-effective to do that, they can use underwater concrete, which is usually poured via pipe into prebuilt forms. The heavier concrete displaces the water as it fills the form. In many bridges, particularly ones that cross deep water, they manufacture the posts and stands for the bridge elsewhere and move them to their locations. Requires some pretty damn big transports to do this though. [Here's how the parts look for the \"Confederation Bridge\" which connects Prince Edward Island across 12 kilometers of the Atlantic Ocean to New Brunswick in Canada.]( URL_0 ) I saw some of this in action and it was pretty impressive engineering. When the conditions are right, for some really big projects like dams, for example, they divert rivers to other areas until the structure is ready."
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7lpu9w | Why do you put gemstones in clockwork? | So, plenty of automatic clockwork for watches (wrist and pocket alike) use Sapphires and Ruby's in varying amounts (some use 3, some use 7, some 15 for instance). But why? Not only am I asking about their function, but why use gemstones instead of something like precision-engineered titanium or other hard-and-light materials? | Engineering | explainlikeimfive | {
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"One reason is that they are very hard, and this means they take a LONG time to wear out, but that's already been said. The other reason is friction. Since they are so hard, they can be polished into an extremely smooth surface. When used as bearings in a watch, this translates into very low friction. This accomplishes two essential goals is watch design. It minimizes energy loss due to friction, allowing the watch to run longer between windings. It also makes the movement much more consistent, translating to better accuracy.",
"Because some gems like sapphire are really resistant to abrasion. So you can use those as bearings that don't wear as much as a metal bearing. But eventually its market. Because a 11 Ruby clockwork must be better than only 5, right?",
"The rubies are bearings for the various moving parts. They're both durable and low friction. Sapphire (typically white / clear), on the other hand, is used for the \"crystal\" over the face of better watches. Sapphire is super hard and almost impossible to scratch other than with a diamond. Source: I own a dozen mechanical watches."
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7lpzto | How is it possible for AC current to move from point A to point B? | If the electrons keep switching directions, how do they travel from point A to point B? | Engineering | explainlikeimfive | {
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"They do not. In an AC line, the electrons move less than 1 meter before the current reverses direction. But *all the electrons throughout the wire* move back and forth together, like a mob in a very crowded room.",
"The electrons don't, current does. Think of hose filled with water, the water is the electrons, but when you turn the water on it instantly flows out the other end, the water didn't instantly travel the full length of the hose, but the pressure did, and it pushed the water at the other end out. You could have two hose and alternate what one is one and what one is off to get the water to flow back and forth from one hose to the other and back. The water would move back and forth, and work can be extracted from the flow. But in that case the water is just moving back and forth a few inches at the time, and isn't moving in any particular direction over the long term. That's what AC power is like, the electrons are moving back and forth a very small distance, and not going anywhere, but the fact that they are moving is enough to extract power from it."
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7lrkv9 | The recently released footage of the “UFO” filmed by US Fighter Jet Pilots. So if it’s not aliens, what is it? | Engineering | explainlikeimfive | {
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"When the US launched a raid on Osama Bin Laden, Seal Team Six breached an ally's border in a top secret stealth helicopter that had never been seen publicly before. The only reason anyone found out about it was because the helicopter crashed and though they attempted to destroy the helicopter with explosives, it wasn't fully destroyed. The most likely explanation is that, just like the US uses top secret drones, satellites, and other aircraft to spy on it's allies, other countries also use top secret locally developed equipment to spy on the US as well. China, Russia, India, Israel, etc. are all possible origins of this aircraft. UFO simply means it's unidentified, not that its extraterrestrial. But it's a lot more fun to think about aliens visiting than countries spying on each other.",
"We don't know, its Unidentified. However, it 'could' be...light reflected off of optics or glass; forged video and audio; human created aircraft; slow moving meteor, time-travelers. It could also be misleading if any of the statements made by the pilots or video readings were mistakes in judgment, like wind speed and direction. This video is of the vintage, that I would expect the pilots would have coming forward and claim to have seen it or been the ones recording it. The fact this hasn't happened (yet) gives me some pause in the veracity of the video. Even if they do come forward in the future, any number of explanations make more sense than aliens.",
"It's an experimental surveillance balloon drone that uses dynamic supercavitation to make rapid changes in velocity and direction. These drones use both lighter-than-air gasses, a local low pressure atmospheric manipulation, and heat, to maintain buoyancy. This is why the object appears warm, with a surrounding bubble of cool air. The drone is only capable of operating at high altitudes with extreme wind (hence the 138 MPH winds cited in the video.) These drones are launched from submarines and are controlled using various methods. Newer systems use a main controlling drone that communicates with the rest of the networked swarm for less latency. This eliminates the need for the submarine to maintain direct control, and much of the decision making is left to pre-programmed flight path and AI that is designed to adapt to environmental situations. Spreading the drone swarm over a large enough area, satellite communications become viable, and human controllers are permitted. Some drone systems (aerostats) are tethered to an underwater extraction vehicle. When the drones are spotted, the submersed vehicle fills underwater ballasts and quickly descends. The drones, likewise, deflate their own lifting gasses, thus filling the surrounding supercavity vacuum, and creating a rapid decent. An envelope of pressurized air is created before re-entry into the water, however, newer systems forgo retrieval and instead are designed to be destroyed upon impact. This explains several things: 1) How did the vehicle make such advanced and rapid maneuvers? (supercavitation) 2) Why did the vehicle appear to have such a strange heat signature? (vacuum combined with low-pressure zone) 3) Why was the water below the craft behaving in such a unique manner? (submersible craft for either release or extraction) 4) Why was there a \"fleet\" of them noticed on the ASA (radar)? (swarm ability for better communication and surveillance) 5) Why did this event occur in the ocean, during a military exercise? (typical military testing itself) 6) Why did the craft operate in such windy conditions? (supercavitation is only capable in these conditions with current technology) 7) Why did the craft turn sideways? (retrieval stance requires maneuvering towards submersible) 8) Why did the Pentagon scramble some of the pilots language? (\"Is that one of our #@$% & @?\" < -- secret vehicle code name)"
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7lsptj | How do they make stainless steel truly stainless? | Engineering | explainlikeimfive | {
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"text": [
"It isn't \"truly\" stainless and can form minor amounts of rust or at least unsightly corrosion. Depends on the quality of the \"stainless\" steel and the conditions it's exposed to. In general, it's \"stainless\" because it's a mixture of metals that cause it to form a protective, hard layer of oxide as it corrodes which prevents oxygen from reaching the metal underneath and continuing to corrode more. Normal steel and iron have such big problems with rust because they corrode into a form of iron oxide which is porous and allows the underlying metal to continue to rust as well."
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7ltvzf | If an airliner is flying at 30,000ft the outside temperature is around -30F, so why do airliners need to run A/C instead of heat while at cruising altitude? | Engineering | explainlikeimfive | {
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"Basically the engines suck in air and compress it before mixing in fuel and igniting it. When you compress air, it gets hot. Turbofan engines compress the air so much it heats up to oven-like temperatures. In order to pressurized the cabin, airplanes \"bleed\" a small amount of this high pressure air from the compressor sections of the engines, but it has to be cooled so that it doesn't cook the passengers.",
"A person produces about [100 watts of heat]( URL_0 ). That's the same heat as a 100 watt lightbulb. Or to put it another way, a basic [space heater]( URL_1 ) equals about 15 people. What's the point of this? A big plane with 200 passengers on it has 20,000 watts of heat to get rid of. That's a lot! Way more than will go out through the walls. If you've ever been in a crowded meeting room, you may have noticed that it can get hot even in the winter. Same thing on planes."
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7luq51 | When a plane has a loss in cabin pressure for a long time and the oxygen masks run out of oxygen why can't they descend to 8000ft and open a window or door so that the pressure equalizes? | Engineering | explainlikeimfive | {
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"That is pretty much what they do, except without opening a door or window. Oxygen masks in the passenger cabin are only intended to give enough oxygen while the aircraft descends to a height where they're no longer needed. Once they're down at that height, they can allow the cabin pressure to equalise without needing to mess around opening doors. If they did open a door, then suddenly they'd find that there was an incredibly strong wind ripping through the cabin.",
"I have been on a flight where this happened. The pilot said only \"put on your oxygen masks and prepare for emergency\". It was terrifying and I thought I would die."
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7lx49w | Why do leather belts start out straight, but after being worn a lot, get curved? | Engineering | explainlikeimfive | {
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"When one bends over or even sits, the back belt loop pulls down on the belt where the pants would want to gap. Over time, this stretches it out and causes it to curve.",
"A straight flat belt fits around a cylinder perfectly. Chances are you're not cylinder, because you have a bum, and maybe some belly. Your girth is bigger at the bottom of your belt than at the top of the belt. ( A contoured waistband is curved instead of straight, but most ready to made clothes have straight waistbands because it takes less fabric.) When you sit down your body becomes longer in the back and shorter in the front. The pants will rise in the front and make accordion folds, while the back will pull down lower and the straight waistband wants to stick out from your body. In this position you aren't anything like a cylinder.",
"Your hips are not a perfect circle. A leather belt will reshape itself around your bodies natural curvature.",
"the belt gets conditioned into a curve from being held in that position for long amounts of time, or multiple periods of use (E.G. from wearing it). you can achieve a similar result when conditioning a new baseball glove (rubbing conditioner the leather, putting ball in mit, then wrap a few rubber-bands around it.) baseball players do this whenever getting a new glove because it helps them catch the ball easier. Hope that helps :) Edit: changed the phrasing, and minor grammatical corrections."
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7m811c | How do speedometers work on boats? | Engineering | explainlikeimfive | {
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"text": [
"Besides GPS, a ship uses a speed log to determine speed. There are multiple types of speed logs: - Impeller log: A small device with a propeller is towed or attached to the ship. When the ship moves along the water, the force turns the propeller. The rotational speed of the propeller is proportional to the speed of the ship - Pitometer: A tube faces the direction of the ship and another tube faces 90 degrees. When the ship moves, the water pressure builds up in the forward facing tube while the 90 degree tube remains at static water pressure. The meter calculates the difference in pressure between the two tubes, which is proportional to the speed of the vessel. - Doppler log: The Doppler log emits a sonar wave (TX). The wave travels out, bounces back, and returns to the receiver of the log (RX). If the ship is still, the TX and RX have the same and frequency. However, due to the Doppler effect, the forward motion of a ship compresses the waves closer together, changing the frequency. The change in frequency is proportional to the change in speed. Finally, on larger ships, you can determine the speed by doing calculations using the engine RPM, the pitch, and the load. This will give you the mathematical speed, but won't account for friction and other variables.",
"The classic analog speed sensors are just little paddle wheels on the transom or bottom of a boat. There are also pitot tube versions. Now we just use GPS for speed over ground. In the old, old days, they would throw a piece of wood(log) tied to knotted line overboard and count the knots. Thus, knots for speed.",
"It depends on what you mean by speed. Speed over ground, or the rate at which you cross from one geospatial point to another, is determined by GPS. Speed through the water, or the speed at which the water is passing by the hull, can be determined a few ways. Olden times, a log on a regularly knotted rope was thrown overboard. The number of knots to pass over the gunwale corresponded to the speed in \"knots.\" Today, a number of methods including a small free-spinning prop (flow meter) and doppler are used. If you don't need to be terribly exact and you know the vessel, many of us just approximate based on engine RPM."
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7mke5c | Why is forward parallel parking not effective? Why does it have to be reverse? | Engineering | explainlikeimfive | {
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"Cars rotate on the rear tire while the front of the car swings. You can front park but you'll have to hop the curb to swing the front into the right space. By backing in, you can precisely position the vehicle in the space. Source: former FedEx driver. I backed up a big truck a *lot*."
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7mne80 | how do the sights of mortars (the weapon) work? | Engineering | explainlikeimfive | {
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"> how do the sights of mortars (the weapon) work? They aren't exactly \"sighted\" in the same way as other weapons. They are a method of indirect fire so they are designed to fire at things which cannot be seen, making traditional \"sights\" impractical. Instead mortars are targeted using calculations as to the mortar's location and the location of the intended target, then setting the direction and angle of the mortar tube according to calculations about the trajectory of a mortar round. What this means is that targeting is done with radioed instructions from a distant observer, along with references to a map and a table of range values."
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7mo28p | How do cellphones slow down "naturally" after 2 years or so? | Engineering | explainlikeimfive | {
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"They don't. I explain this to my customers at least twice a week. One of the biggest misconceptions in the world of computer technology is that it slows down as it gets older. Computers (including mobile devices like phones) don't slow down with age. They are exactly as fast today as they were (x) years ago when you purchased it. That 2.5GHz computer you bought three years ago is still running at 2.5GHz. Technically, the term you're looking for isn't \"slower\" but \"less responsive\". It is an accurate assessment that computers et al often get less responsive over the years. So why are they less responsive with age? If you discount legitimately accidental programming bugs then you have a few reasons: 1. Additional code to the existing operating system, generally in the form of OS and/or security updates. Any time you add additional code, the device has to spend time executing that code. Security updates, OS updates, maintenance patches, etc all contribute additional code that the device has to process. This takes time away from other tasks, like registering a mouse click or a finger tap, so your device feels less responsive. 2. New OS installation. As with the additional code issue, new OS's typically have more features and functions than the OS it replaces. This is additional code that your device has to process. 3. OS degradation. All OS's crash, even phone OS's. Sometimes when this happens the OS can be damaged which can result in unpredictable behavior. Take something simple: setting the clock. Let's say the (simplified) code for setting the clock is \"every 2 minutes, reach out to URL_0 and set the clock\" and normally this works perfectly and invisibly. But then there's OS corruption and the code turns into \"every 2 seconds, reach out to URL_0 and set the clock\" which means the phone is going to be doing little more than setting the clock all the time. Or even \"every 2 minutes, reach out to jknwjkdhsiuh and set the clock\" which will result in the phone making potentially hundreds of DNS requests to jknwjkdhsiuh which doesn't exist, so the phone basically gets locked into an error loop. 4. Apps that overextend the capabilities of the device. Pokemon Go was released in June 2016, just a few months before the iPhone 7 was released. It was quite playable on an iPhone 6S, but on my iPhone 5 it was ridiculously slow. It worked, yeah, but it was slow and it sucked battery life like there's no tomorrow. The app is just too big for the iPhone 5 to run efficiently -- but the app was never designed to be run efficiently on the iPhone 5 in the first place. Apps are generally designed around the current, and perhaps the next, generation of hardware. If it runs on older hardware then, yay, but that's more of a happy circumstance than an intended result. So how do you avoid this? Simple. Don't upgrade your OS after a new hardware revision comes out. Don't install any new apps or update your existing apps after a new hardware revision comes out. If your device crashes, clean-reinstall the OS and repeat. Your device will remain as lively and responsive as it was the first day you took it out of the box. And as far as the Apple thing goes, that's another misconception. Apple *did not* slow down **old** phones. What Apple did was, they programmed the OS to identify dying batteries and in response throttled CPU performance so as to allow the battery to power the phone throughout the day (rather than dying in the early afternoon). Yes, old phones accounted for most of the affected devices because their batteries were naturally older. But if you had an iPhone 7 or 8 with a dying or defective battery, you would have seen exactly the same thing. IMO Apple didn't do anything wrong with this programming decision. What they *did* do wrong, IMO, was when customers came in to complain about \"slow phones\" they didn't direct them to have a new battery installed, but instead directed them to buy a new phone. That's a really shitty and evil thing to do.",
"Default your device back to factory settings and then see if it acts the same way. Usually, I find that there a rouge apps running in the background sucking up available memory / cpu cycles (that even a restart of the device doesn't clear).",
"The kind of battery technology we use right now, at least, is only good for a certain number of charges. Afterwards, it's capacity starts to drop, as does it's output. A lot of the time what people really need is a new battery. Most also use solid state memory, which also has a limited number of writes and rewrites before it starts to suffer damage and lose some speed and capacity. For now, planned or otherwise, phones do need to be replaced every few years if you want optimal use from them, and, planned or not, updates do partially drive that process."
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7moqkj | How do machines place each individual pixel on a screen? | There are a LOT of pixels on screens now, millions. I really wanna know: how can machines can be so precise and so fast to place millions of lights on a machine? Does it take a long time? How does it not make many mistakes? | Engineering | explainlikeimfive | {
"a_id": [
"drvink9",
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"text": [
"The pixels are put on the screen in the display factory. All the pixels that aren't in the right place or don't work are not sold to customers. (Actually, most displays are allowed to have 3-6 failed pixels.) Your computer is simply sending color data that the display circuitry turns into voltage to control the crystal polarization that lets a fraction of the available backlight out.",
"First, your computer just does math at a speed you you cannot imagine. A 3 GHz processor, like an average desktop computer, can theoretically make as many as 3,000,000,000 calculations every second. That's more than enough to draw 2,073,600 pixels 30 time a second. (1080x1920 resolution at 30 frames per second.) This is further aided by having a graphics card, which contains its own processor that's optimized for drawing things on the screen. The CPU (brain of your computer) can delegate the graphics portion of a program to the graphics processor, (GPU) and focus on other processes in the program. As for mistakes, they happen all the time, you just don't notice them very much, as any given frame is gone within 1/30th or less of a second. You you've had graphical glitches in games or even just stuttering frames on you screen, you've seen a time where the program running might just be too much for the hardware to handle. Edit: if you're asking about the manufacturing side of things, remember that each pixel isn't a distinct light, but an adjustable filter made out of liquid crystals with a backlight of LED's behind them. There are far more pixels that LED's in a display, so its not as if each pixel has to be placed individually."
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7mqp11 | Liquid screen protectors | I see adds for liquid glass screen protectors for mobile devices. How can this provide any impact resistance in comparison to something like a sheet of tempered glass? | Engineering | explainlikeimfive | {
"a_id": [
"drvxu9u"
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"text": [
"They don't really provide a lot of impact resistance, it's mostly just scratch protection. They'll soften a few blows but their main value comes from preventing the tiny chips that quickly grow into giant screen cracks."
],
"score": [
4
],
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7mqsc8 | How did the nature documentary planet earth get such incredible footage ? | Are the cameras planted? Some of them it feels as if the camera was on the animal almost- it's amazing that the animals are not bothered by the cameras. | Engineering | explainlikeimfive | {
"a_id": [
"drvyj73",
"drvzhwy",
"drw4znt"
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"text": [
"Start with really good camera's and phenomenal lenses. Add in a good documentary cameraman. Tell him to go film nature for a year. Then trim out 99.99% of the footage and cherry pick the most amazing shots.",
"There are quite a few behind the scenes videos from blue planet 2 Below is a link too one such video URL_0",
"Did you watch planet earth 2 yet? They demonstrate very well how the material is acquired in it!"
],
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28,
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"http://www.thevideomode.com/news/behind-scenes-videos-show-blue-planet-ii-filmed-5539/"
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7mvegk | Since metal is a conductor, why are electrical boxes made of metal? | I just got one out of the wall of our century old house and, not entirely trusting the electrical work done by past owners, I kind of was afraid to touch the metal since there is wire running out of it... (This explaining the question!) | Engineering | explainlikeimfive | {
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"text": [
"Electrical boxes are made out of metal *because* metal is conductive! The metal of the box is grounded/earthed so that if it's touched by a live wire, the electricity will be safely redirected away from anything that could be harmed by it (blowing a fuse or tripping a breaker in the process). A plastic electrical box could melt and catch fire when exposed to a large electrical current.",
"The box is *supposed to be* tied to ground so that if there is a miswire and something touches the box then it will short to ground and trip the breaker, cutting the power and making everything safe again. The wires in the box should be properly insulated as well, this keeps them from touching things they aren't supposed to and keeps the electricity only in the wires that it is supposed to be in. Metal boxes are also really inexpensive. You take a sheet of steel, fold it a few times, throw in a few rivets and you've got a box. This is much easier than injection molding a plastic box which really wasn't an option until relatively recently."
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7mwnba | Why do some lights hum? | Engineering | explainlikeimfive | {
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"text": [
"It's typically old fluorescent, LED or halogen lights which can't run straight on 110 / 230 V AC and therefore have a big transformer or ballast, basically big copper coils. Those cause a hum because when you run an AC current through a copper coil, it creates an alternating magnetic field, which makes the whole thing vibrate. Modern LED and CFL lights don't do that because they use more efficient electronic circuits for that purpose. These also have copper coils, but they run at much higher frequencies so we typically can't hear them. If they do, it's a very annoying, high pitched sound.",
"Older, non-electronic fluorescent ballasts often make noise when the steel plates (laminations) in the core of the inductor get loose or the magnetic field causes nearby sheet metal to vibrate. Ballasts used to be sold with various audible noise ratings. Newer bulbs also contain inductors which can buzz if used with dimmers.",
"Are they on a dimmer? A modern light dimmer works by turning the power on or off part way through a cycle. This results in a sudden inrush of power into the light 120 times per second. This inrush causes things to change shape quickly which makes them ring or buzz depending on how they're built."
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7n8ev7 | how do hotels have enough hot water for all their guests. Big hotels like Las Vegas and such? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Hotals don't usually have to preheat water. There are flowthrough water heaters that heat the water while it is running through the pipes. So as long as there is power, there is warm water available without needing to build up a reservoir.",
"They have really big water heaters. I work at a hotel of 80 rooms & we have four water heaters on the first floor. Never any complaints from guests. At a 15 floor 200 + room hotel, we had one giant heater in the basement. That one sucked. Ive also worked at places with a couple heaters on the roof, another with heaters on each floor.",
"Im in the maintance department at a 17 floors 380 room hotel. Usually you have boilers and a holding tank. Boilers heat the water and store it in the holding tank which can hold around 500gallons or such. You then have hot water risers that send the water to the guest rooms. Because these buildings are so large you have a recirculation line for hot water. So essentially the hot water is constantly flowing even not in use. This is so you have instant hotwater when you need it. You usually have pumps on the supply and return lines, depending on water pressure to circulate. If it did not constantly flow, the further you are from the boilers/holding tank the longer it would take to get hot water. This would be because as its not being used it was start to cool down. Then you would have to run the water till it gets hot again. There are also a ton of factors that play into a hotels water system that can royally screw with it. If it takes longer than 15 seconds to get hot water, theres a problem.",
"Plumbing and HVAC designer here... There are many options to heat water for large buildings. The simplest is to have a large water heater for each wing/floor. This can get expensive real fast especially if you have a situation like a Vegas hotel. The most popular is to have high temperature boilers and large storage tanks in a central location. You can heat the water up to around 180°F and then mix it with cold water through a thermostatic mixing valve to make 120°F water. This makes the 180° water last longer and you don't need as much storage. Another mandatory piece of equipment in almost all commercial applications is a recirculation pump. It pumps a designed amount of water from the hot water pipe at the furthest fixture back to the water heater. The amount of water pumped is determined by a set of calculations that take into account the size of pipe and pipe material. Constantly recirculating the water keeps the water in the pipe hot and you don't have to wait for hot water for very long."
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7n9s01 | How does gear shifting works? | I'm talking about cars. I watched some 3d presentation of this but still confuses me. Thanks! | Engineering | explainlikeimfive | {
"a_id": [
"ds0bcv8"
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"text": [
"[This post helped me understand more than anything else, hope it helps you too.]( URL_0 )"
],
"score": [
3
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[
"https://www.reddit.com/r/mechanical_gifs/comments/7fkc6a/how_a_gearbox_works/"
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5rfnyd | Why does the FCC require devices to accept interference? | Engineering | explainlikeimfive | {
"a_id": [
"dd6tmvy"
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"text": [
"According to my research, this used to be a question on the FCC first class license exam. There is a hierarchy of certifications, based on the utility of the device to the public good. At the top is civil defense and emergency communications. Nobody can interfere with them. They can interfere with just about anyone and get away with it. Then comes public safety, such as aeronautics comms, police and ambulance. Nobody should interfere with them, but no guarantees. Pilots occasionally note some interference from government comms, but can't do much more than switch to another frequency. Further down the list are public broadcast stations, radio and TV. They are also serving the public good, unless you look at their bland content :-) Normal people should not be interfering with TV broadcasts, this means your power drill or computer interfering with your neighbors soap opera is a bad thing. If your neighbor complains, you must stop using your drill or switch off your computer. At the bottom of the shit pile is consumer electronics. If a TV transmitter is interfering with your gear, tough shit. You have to accept the interference. No complaining. Your device also can not create any interference with any of the more privileged services such as airplane radios or emergency comms."
],
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11
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5rinw3 | Why do they launch boats sideways instead of forward when first launching them? | It also looks like they just roll straight in, do they not use any mechanism to slow the boat down? | Engineering | explainlikeimfive | {
"a_id": [
"dd7l3rf"
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"text": [
"Boats are designed to have their weight supported for the entirety of the keel length. If you tried to launch long boat pointy bit first, you'd have a time when the front is in the water, the back is still on the dock and the middle is unsupported. This (potentially) kills the boat. And there's no real need to slow one down, since they're designed to withstand many assloads of force, at least in the directions they're designed to handle force."
],
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31
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5ro2sf | If oil comes from the ground, then why are oil leaks from a pipe back into the ground such a big deal or does it only apply to leaking in water supplies? | Engineering | explainlikeimfive | {
"a_id": [
"dd8qxq8"
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"text": [
"Oil comes from *deep* underground and so leaking into the surface is a problem despite it in concept being the same region it came from. All the surface stuff from water supplies, plants, animals, etc. are unaccustomed to encountering oil and will generally be negatively impacted. It is sort of like saying \"Poop comes from people so what is the big deal dropping it on their face from time to time?\" Well, that isn't where it usually goes and it causes *big problems*."
],
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12
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5rt1s3 | Why do you have to wait a few seconds before starting a Diesel engine car? | Engineering | explainlikeimfive | {
"a_id": [
"dd9whpr",
"dda4jw0"
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"text": [
"Diesel is hard to ignite. If the diesel is cold it will not even ignite in the engine. So diesel engines comes with electric glow plugs that can heat up the fuel before it enters the combustion chamber. These glow plugs take a little while to heat up. So when you turn on the ignition the glow plugs are connected. You may have a light that turns off when the glow plugs have heated up. You can then start the engine with the heated fuel. If the weather is cold you have to wait for longer and if the weather is hot or the engine have recently run you may not need to wait at all.",
"To explain this, I think it makes sense to explain how gasoline works in comparison, first. People, myself included, generally seem a lot more comfortable with it's operation. Gasoline would be considered \"lighter\" than diesel, meaning it will boil at a lower temperature than diesel will. This is pretty much how the two are separated. If you imagine a big pot of gas and diesel, refineries turn the heat on, and at a certain temperature, the gasoline will boil off just like steam when you boil water. The vapors are \"caught\", cooled back down into a liquid, and you have gasoline in one container and diesel in your original container. A lot more goes into it than this, but this is a start. However, this exact method of separation is really the key to the difference. At room temperature, gasoline readily gives off vapors. No extra heat is necessary. So when gas and air are injected into the cylinder, the spark plug ignites the vapors already present, and this is what drives the piston. Diesel, on the other hand, does not give off a lot of vapor at room temperature. One would say that it's boiling point is too high to do so. So if you add a spark, there isn't anything to ignite. Liquids don't burn, the vapors do, thus we need to add heat to vaporize it. The interesting thing with diesel is that it is added to the cylinder with air as little tiny (atomized) droplets. The piston then compresses the space in the cylinder. When the air and diesel are compressed, all the little gas and air particles run into each other because there isn't as much room, and when this happens they generate heat. The heat from the compression vaporizes the diesel, which we needed, and it actually heats the fuel up so much that it ignites on its own, and drives the piston. Where letting your engine warm up comes into play is when its cold and the heat from compression is not enough heat to vaporize the diesel. It needs a little extra boost of heat. Now I'm not actually a car guy, so I'd be curious to know if technology has improved any such that new cars don't require the same TLC. Diesel and gas haven't changed (much), so maybe there isn't much technology can do aside from insulated or gently heated fuel tanks or something. I work at a refinery, so that is my two cents on the process as it relates to diesel and gas, but I'd love to hear a real car guy's thoughts. TLDR: Vapor pressure"
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5rwewe | Why does nitrous make a car go faster? | Engineering | explainlikeimfive | {
"a_id": [
"ddaoawn"
],
"text": [
"Nitrous Oxide is a chemical that breaks down into oxygen and nitrogen when heated by the combustion creating a large amount of oxygen which then allows you to burn more fuel and make more power."
],
"score": [
5
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|
5rx1a6 | Can someone explain binary numbers and how they're associated with every alphanumeric in our keyboard? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The binary number system is a base-two system. The system most people use is a base-ten system. A base ten system is based on powers of ten. Each position is multiplied by a power of ten to get the resulting value. For example, the number 101 is actually 1 * 10^2 + 0 * 10^1 + 1 * 10^0, which equals 100 + 0 + 1, which equals 101. Binary is based on powers of two. The binary number 101 actually represents 1 * 2^2 + 0* 2^1 + 1* 2^0, which equals 4 + 0 + 1, which equals 5. That's the basics of binary; how computers use binary is complicated, but it basically boils down to the fact that in binary, the only possible values are 0 and 1 (unlike in base-10, where the values range from 0 to 9). Computer engineers have taken advantage of this, and have set the computers up so that if there's electricity on a given wire, that counts as a 1, and if there's no electricity on a given wire, that counts as a 0. When you press a key on an analog keyboard, you're completing a switch. The switch sends electricity down a series of wires (called a \"bus\"); each key corresponds to a different series. Originally, alphanumeric characters were represented by a system called ASCII, which assigned a given graphical character to a given 8-bit (that's 8 digit wide) binary number. I think most keyboards use Unicode or something else now, but the principle is the same. Completing the switch sends a specific pattern of electricity down the bus; the computer knows to display the correct symbol in response to that particular pattern."
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|
5s1mgp | What places on Earth is natural silicon found and why is it used in computer chips? | I know silicon is used as the common semiconductor in computer chips, but why silicon and not another semiconductor? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Silicon is rather common and can be extracted from minerals fairly easily. The reason it's used so commonly in electronics is because it has the ability to be easily \"doped.\" Doping semiconductor material introduces imperfections that make it a better insulator or conductor. This allows silicon to be used to make NPN and PNP transistor gates and other complicated electronics to a very fine scale. ( URL_0 )",
"Because silicon is literaly everywhere! Its the second most abundant element in Earth's crust, only oxygen is more common. For example quartz is silicone dioxide and most sand is made up of silicates (silicon oxides)."
],
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5s1xnc | Why aren't laptops functionally designed to be on laps? | Engineering | explainlikeimfive | {
"a_id": [
"ddbtxpv"
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"text": [
"Laps were not specifically designed to support laptops very well so I guess that settles the score. On a serious note: Although you can put any laptop on your lap, heat production will make it uncomfortable fast. Newer machines do not produce as much heat as older ones so we're getting there. In the meantime we'll just call them tabletops, ok? 😁"
],
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5s2zz3 | Why are the connections for the vent in a clothes dryer so frustrating and seemingly inefficient? | Installed my brand new dryer this afternoon and realized just how much I hate using the brackets and heat vent. I don't understand why, in 2017, we don't have a better method for attaching the vent to the back of the dryer. Why can't the vents have brackets pre-installed on the ends so that that they lock into place with a half turn on the back of the dryer and floor? | Engineering | explainlikeimfive | {
"a_id": [
"ddc1bj4",
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"text": [
"You are tackling this as a novice. The experienced people have done it scores of times and it is much easier for them. But I agree with you. Purchasers of appliances should know before had just how difficult installation is. But we do not see that information presented to us. A lot of electronic equipment has become much easier. I now expect setup to be a few simple steps. I just had to purchase a thermocouple for a heater. Because it resides inside a flame its lifetime is finite. It will have to be replaced again over and over while the heater will last a lifetime. I did not check how easy that would be when I bought it. One fine thing about youtube is that many people put short videos up about doing these things. A woman learned to build a house just watching youtube. One of my goals is to produce very short videos showing routine maintenance jobs at my house which only happen every few years. Youtube will store it and I can refresh my memory next time.",
"Because it's cheap, it's universal, and it's good enough. How often does the average homeowner change this out? Once a decade if the dryer fails, or whenever you move?"
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5s32n7 | Why are objects smaller than they appear in rear-view mirrors? | Engineering | explainlikeimfive | {
"a_id": [
"ddc1hpx"
],
"text": [
"Passenger-Side mirrors are often convex, in order to provide a larger field of view. The convexity also, however, shrinks the objects seen in it. Basically, if you are bending a mirror such that it shows more real-estate, then anything in that real-estate is going to become a smaller part of the whole."
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5s8tsl | How does keeping your vehicle plugged in overnight help it start on a cold morning? | Engineering | explainlikeimfive | {
"a_id": [
"ddd7g6t"
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"text": [
"ASE/Lexus certified Master Tech here. This is a multi part answer, and I'll do the best I can. Engines rely on lubrication from engine oil to be able to run. Engine oil is responsible for preventing wear, reducing friction, preventing corrosion, and is used as a hydraulic fluid within the engine. Because of all of the properties it has to achieve, even the lowest-viscosity oils available are rather thick. Ever heard the expression \"slow as molasses in winter time\"? As viscous(thick) liquids cool down, they become more viscous, gradually getting thicker as temperature drops, until the eventually freeze. Engine oil does not exactly \"freeze\" in any conditions you'd likely find in nature, but it does get quite thick when it's in very cold climates. They make special oils with very low viscosities for cold-climate operation, but even those have a hard time in climates where temperatures are below 0* F. If oil within an engine becomes too thick, it cannot do its job properly and damage to the engine or poor performance could occur. The device in question is called an Engine Block Heater. It is basically a powerful electric blanket that plugs in to household power, and it warms the engine block constantly. The warming prevents the engine oil from becoming too thick, so when you go outside to start the car, it's much easier to start, and prevents damage from extremely cold starts. The increased engine temperature also helps with combustion, or the burning of fuel /air inside the engine. Engines run most efficiently at a certain temperature, and when they start at a very cold temperature, much more fuel is used and wasted to achieve combustion. Engine block heaters are not commonly sold built in to vehicles, and are an accessory that must be added if needed. In very extreme climates, diesel-fueled vehicles also use heaters inside the fuel tanks to prevent the diesel fuel from becoming a gel in the extreme cold. This is because diesel fuel is much more viscous than gasoline, and behaves similarly to engine oil in cold temperatures. It's kind of like insulating your plumbing pipes in the winter to keep them from freezing."
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5sbhcp | Why would a certain street lamp turn off as I pass under it? | Engineering | explainlikeimfive | {
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"text": [
"Street lights are turned on by a light sensor. Your car is turning it off with it's headlights. This is an indication of a faulty light sensor and you should report it to the township.",
"Older ones also overheat and shut off periodically so if you are noticing them a lot you'll see them turn off every so often",
"I had no idea anybody else noticed this, and I am too creeped out to google anything. But I agree with others, it's probably just that we notice the ones that turn off and flicker since they stand out. We don't notice the ones that work.",
"The ones that do it all the time are probably broken. The ones that you notice are just that, the ones you notice. You don't notice the fully functioning street lamps because they're doing their job correctly. The ones you do notice that suddenly turn off when you go under it just *happened* to short circuit/get burnt/get falsely tripped off at that moment. Sorry, you're not psychic, nor is your car (though that would be dope). You're just noticing it happen because it's something out of the ordinary.",
"Did this happen once, or has it happened more than once under similar circumstances? What were those circumstances?",
"I told reddit about this being my lame super power a couple years ago. They came through. URL_0",
"On my daily route to my last job there was one street light on an overpass that very consistently went out as I approached it. This happened for years. For all I know it went out every 5 minutes but it was still strange at the time.",
"You're probably finding yourself under a high pressure sodium-vapor lamp. As they age, they start to cycle repeatedly. This cycling is caused by a lack of sodium in the bulb, which is lost over time due to the reaction created which is what makes the arc, producing the light. What happens is that the light will start up, but as the arc reaches full intensity, there is not enough sodium left to maintain it, and it basically flames out and starts all over again. Source: I work for water and power. We change lots of street lamp bulbs (mostly to LED now... they don't have this problem). *Edit: Sorry, that wasn't quite like \"I was five\" was it. OK maybe 10. Like you were five: Lightbulb turning off at just the right time because it does that, turns off and on as it's dying. There. :-)"
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5sdbko | Why is the leaning tower of Pisa actually leaning? | Engineering | explainlikeimfive | {
"a_id": [
"dde7vwk"
],
"text": [
"The leaning of the leaning tower of Pisa is due to both a wrong assumption and poor engineering. When the second floor of the tower was being built, the soil under the tower began to sink. This was because of a very weak 3 meter foundation. The construction temporarily stopped because of the war going on at the time. Construction was resumed after a century when engineers decided to compensate for the tilt by building the upper floors having one side larger than the other. This is the reason why the tower has a curvature to it. Some engineers also try to do stuff with the soil underneath which caused the tower to lean even more. The later engineers didn't want to touch anything because of the fear that the monument would topple. In due course of time it became famous because of the tilt and people decided to keep it that way."
],
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|
5sdl3r | Why is it so difficult to create accurate hot-cold water controls for toilet use? | I assume we are all familiar with [this problem]( URL_0 ), right? Why is it so hard to get right? | Engineering | explainlikeimfive | {
"a_id": [
"dde8zms"
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"The range that you find 'ideal' is relatively narrow compared to the range of temperatures delivered by your hot and cold water pipes. Temperature sensors lag actual temperature by a noticeable amount. Hydraulic systems react to slowly to mechanical changes. Changes in temperature cause changes in pressure that can impact your hot/cold mix. This combines to create an engineering problem where it's nearly impossible to create a stable control system for use in a consumer environment. If the temperature in the pipes shift, your system probably doesn't notice for 2-3 secs and then spends the next 6-7 sec oscillating towards a compensated value - at which point something changes again and you're back in that loop. If you wanted to create a hot-cold water control that worked the way you want, you have to start with water that is precisely controlled for temperature/pressure so that it always delivers the same amount at the shower head. That eliminates the need for a feedback loop with temperature/pressure sensors and you'd simply be able to dial in a temperature and keep it there. Obviously, they can do this in industry. But for your average consumer, redoing the plumbing in their house to accommodate such precision doesn't have enough value-add over simply using mechanical controls to vary the hot/cold mix manually."
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5sdope | Is it cheaper to automate processes than to outsource them to cheap labour? | Engineering | explainlikeimfive | {
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"It really depends on the product, the process and the size of the run. If you are trying to perhaps, bottle beer, or box cereal, a simple, constant product and process, automation makes sense if demand is high. You really don't want workers putting bottles of beer in six pack holders all day, and then placing them into cartons. On the other hand, if you are making short run products, 100 of these, 50 of those, then automation becomes less important and flexibility becomes more important. For example, if you only make 20 jet engines a week, but the engines are of four different types than only certain aspects can be automated. However, if you want to eliminate unskilled labor, like fork lift drives, box closers, packagers, assemblers, and demand for the product will exist for a long period of time, then automation becomes cheaper than unskilled labor.",
"This question is probably best answered using the concept of 'Net Present Value', which is essentially the value of future cash flows in 'today's money'. It is calculated by reducing ('discounting') future cash-flows (cash money after all costs) by a certain rate that reflects the cost of borrowing money from somewhere *and then* deducting your initial investment cost (the cost of buying your machinery or equipment used in producing a good or service) from this. This can give you and objective 'value' of a project in today's money and can be compared with other projects to see which is best. In the short-term, outsourcing is often cheaper as automation involves an up-front investment (called 'Capital Expenditure'). If the cost of this investment is not recouped by future cash-flows from producing and selling your good or service, then the same project offering short-term cost savings by outsourcing costs of production could be a more attractive alternative. In the longer-term however, the cost savings made by automating production often outweigh the initial investment as the project has longer to recoup that initial investment and the cost savings (particularly wage costs in developed economies) tend to significant. This is a generalization, and is dependent on a number of factors (such as average wage costs, tax rates, depreciation rates, residual value of the machinery, the labour intensivity of producing your goods) but is a key reason why so many manufacturers in developed economies have either turned to automation (e.g. Japanese Car Industry) or a combination of automation and 'offshoring' (moving production to a foreign country) (e.g. Nike's production of shoes in Asia). If you are interested, this scenario can be compared through using a 'discount cash-flow' (DCF) model (there are plenty of explanations of how this can be done on youtube). Good to finally use my Finance Degree for something other than answering emails!",
"In my experience it is enormously cheaper to outsource because there is zero investment. To automate requires capital investment for machines and time to switch over which is itself downtime. There are still vast populations willing to work for peanuts compared to Americans."
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5si95n | Why do solar panels expire? | Engineering | explainlikeimfive | {
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"I don't think they expire like food. However, the 'active' parts that do the job of converting light to electrical energy are very thin and fragile. They eventually degrade and fail.",
"Like anything they suffer from ware and tear. This results in loss of productivity (eg solar cells dying, the glass getting worn and becoming more opaque, etc). Companies tend to guarantee that a certain % of output will remain after a period (typically 80% after 20-25 years I think). But in reality solar panel technology is advancing very fast so today's panels might keep generating plenty of power for much, much longer."
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5sihzw | All I've ever seen my entire life are #2 pencils. Why is #2 the most popular? | Engineering | explainlikeimfive | {
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"It's hard enough to write cleanly and soft enough not to just stab holes in the paper. If you get into art or mechanical drawing, you will be exposed to different hardnesses of leads.",
"That's the type used for writing in school and all the other types of pencil are primarily for art or other niche purposes (architecture drafting, etc). When scantron tests became so widespread, it wouldn't work with lighter pencils so they mandated the dark #2. This led to #2 pencils being pretty much exclusively sold except for art stores.",
"It has to do with the hardness of the lead. Harder pencils write really nicely, and don't smudge, but as a byproduct they also don't erase very well. Also if it's too sharp or your paper is too thin it'll just punch through the paper. Softer pencils write really pretty and smudge in an artistic way. It's a great asset to apply shading and wipe effects. However, that means they will smudge for no reason, which makes for a shitty drawing if you don't know what you're doing. Number 2 pencils are just right. They write and erase well, and resist smudging on a clean hand.",
"True! At work we have a couple #3 and a few #2.5 pencils and the difference in the hardness of the lead is truly infuriating if you're not expecting it."
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5slgq3 | Why are the windows on aeroplanes not square? | Engineering | explainlikeimfive | {
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"The sharp corners of square windows would create areas of high stresses which would lead to cracks in the fuselage. The first commercial passenger jet had much more square shaped windows and the hulls started failing after just one year due to metal fatigue caused primarily by stress concentrations. If you're curious check out the de Havilland Comet for more details, diagrams, and pictures. The same basic principles apply to all metal so you'll see similar round copes and openings in I beams, tanks, etc. For a simple metaphor, imagine 1000 cars on a 6 lane highway reducing down to 2. You don't just immediately close 4 lanes you slowly merge them together."
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5srpm3 | What happens when a generator is running but no load is being applied? | For example; a portable gas powered generator. When the generator is running it is capable of powering a fridge. What happens when the same generator is running but no load is applied? Is electricity still being made? | Engineering | explainlikeimfive | {
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"> Is electricity still being made? Yes. There's voltage, but no current. Static electricity is a different example of accumulation of potential without a load. Voltage is sometimes called \"potential\" because it *could* make current flow if a load is connected. Since no load is connected, no current is flowing and no electric *power* is generated. Power is voltage times current.",
"Short answer: with no load generator is easier to turn. It gets more difficult to turn (and takes more energy) as the load increases. essentially it has to do with inductive reactance in the coils of the generator. in simple terms, a magnetic field moving near a conductor will induce an electric potential within that conductor. when the generator is spinning with no load you still have electromotive force (voltage) but no current flows and in an ideal generator no *power* is produced. P = VI (ohms law). The amount of torque required to spin the generator's rotor is proportional to the amount of load. the more load the more *work* to spin the rotor one revolution. The rotor will be \"easier\" to turn with no load. Its all physics. so you have basically an electromagnetic coil spinning inside of some other coils, and really a generator is not much different than an electric motor (in fact many types of AC motors will function as generators, producing a voltage when you spin them while *off*) current flowing through a coil of wire produces a magnetic field and the north pole will attract the south pole of another magnet. With alternating current the polarity reverses cyclicly so when the rotor poles gets close to the stator coils, the direction of current flow and thus the magnetic poles reverse so they dont just get close to each other and stick (3 phase AC is really useful here). If you spin the rotor and attach a load instead of a current source, a rotating magnetic field is produced, which induced an AC voltage in the coils. (the term AC voltage just made me wonder, alternating *current*, well thats just what its called i guess) The rest is a lot of physics, and math. Basically a lot of electrical engineering technical shit that hopefully somebody that knows more about it than me can explain in elegant simple terms that ur average person thats not an electrical engineer or can understand; I'm a computer science student but I dont know everything about electrical circuits (but wants to know everything there is to know about everything), especially when it's not digital logic. Explaining technical stuff in a way that ppl just \"get it\" is hard."
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5suh9p | Analog to Digital Converter | ELI5: How is an analog to digital converter work? Am I wrong in assuming the output as a digital bit i.e. 1 or 0? Can you cite an example? | Engineering | explainlikeimfive | {
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"Input: a continuous signal, like a voltage Output: a binary number that indicates the measurement of the voltage. Usually a number of bits, like 8 bits or 32 bits. A tape measure is a simple example of an analog to digital converter (a physical one). You give it a physical distance, and it tells you the closest numerical measurement of that distance."
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5sv2i2 | Why are cars that use automatic transmission less energy efficient than those that use manual transmission? | Engineering | explainlikeimfive | {
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"For the most part, this is no longer true, fuel economy is a usually a wash between a stick and an automatically. It used to be true, because: * automatics weren't as good as humans at deciding when to shift * automatics were often sold with fewer gears * automatics added weight to the car The technology for automatic transmissions have improved to the these are no longer big factors, and some automatics now get a little better mileage.",
"Automatic transmissions are less efficient than manual transmissions because they use a torque converter to exchange the power of the engine to the forward motion of the car. A torque converter works much like two fans facing towards each other where one is blowing and one is not. The energy from the blowing fan makes the non-blowing fan turn. Anyway, it is a less efficient process than using a clutch in a car to transfer the engine power to the forward motion of the car because there is less energy wasted.",
"An automatic transmission tries to get you on the appropriate gear for your speed and acceleration without your input, but it is controlled very specifically, so if you do a lot of speeding up or slowing down, it can jump you up or down a gear multiple times, giving you less than optimal gas mileage. On a manual transmission, as long as you don't screw up, you can stay on the same gear even if you have to slow down a little, allowing a more consistent fuel consumption."
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5sx41m | Why do American school busses not have flat fronts? | Engineering | explainlikeimfive | {
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"Some do. As to the visibility, most school busses have an arm that automatically swings open from the front of the bus to force a walk forward to get around it. Also, most bus routes are built to have the children not crossing the street if possible.",
"For starters, most school buses with a nose are older models. Flat front designs are fairly modern. A lot of school districts simply can't afford to update their models to the newer version/ it's cheaper to buy the older design. Secondly there are somewhat naive concerns with flat front buses due to where the engine is located. Having under the kids = parents are afraid of engine problems harming their children. Finally, and this ties into the first point, it's easier to make sure the fleet stays homogeneous for repair purposes and for aesthetic reasons."
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5sx53n | What do 'Space Coordinates' look like? When NASA points a rocket at Jupiter and punches (trajectory solution) into a computer, what are they actually inputting? | Engineering | explainlikeimfive | {
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"JPL has a [great web page on this subject]( URL_0 ). > Spacecraft navigation comprises three main aspects: (1) Designing a reference trajectory which describes the planned flight path of the spacecraft; this is the task of mission design. (2) Keeping track of the actual spacecraft position while the mission is in flight; this is the work of orbit determination. And (3) creating maneuvers to bring the spacecraft back to the reference trajectory when it has strayed; this is the area of flight path control. It's not just \"coordinates\" for the destination, but which of he infinite number of paths between the two points you want the craft to follow. Since stopping is as hard as getting going, they tend to work in terms of loops.",
"Try playing kerbal space, it will give you a really good idea of how orbital mechanics and space flight works",
"They're calculating how much velocity they need to send the rocket to its target, when to launch it or perform other maneuvers, and the exact direction to point. All of this is managed using what's called inertial guidance. Inertial guidance is a system that calculates an object's (in this case a spacecraft) speed, direction, and location by remembering the starting values and making changes based on those initial values. It keeps track of it's orientation using roll, pitch, and yaw, so for example if the rocket started with a pitch, roll, and yaw of 0 degrees, and then pitched up 40 degrees and later down 10 degrees, it would know it's at 30 degrees. Same applies to velocity. Essentially those are the only things the rocket itself needs to know to get where it's going: Which direction to point, and how much thrust to apply in that direction."
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5szvfg | Why does modern electronics and appliances have a rounded/curved shape while older electronics and appliances have a squarish/block like shape ? | Engineering | explainlikeimfive | {
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"Ergonomics partly. The other part will be influenced by advancement of technology. Parts get smaller and more compact (and cheaper!), and that means people started housing things in whatever shapes they could produce, whether for comfortability, aesthetics, safety or otherwise - **in a competitive technological market, why wouldn't you want to produce the sleekest looking device that's also safe and comfortable to use?** The machines that produce these parts and the housing, now including consumerised 3D printers, along with the software that goes with it, also got much better and more efficient. Different materials with various properties become more readily available, whether it's your aluminium cased, glass backed phone or your brushed steel toaster with thermoplastic dials. - - - In summary, technology got better, smaller, cheaper and more readily available. Customers have more choice and so designs will tailor to their customer base as trends change.",
"If I remember correctly, I believe older electronics required more space and had mostly rectangular parts such as tube televisions and Macintosh computers. It's for roughly the same reason most tower PCs are rectangles and not, say, a pyramid. Things like phones and laptops no longer need as much room and can fit a more ergonomic and, frankly, sleek design."
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5t2gnk | Why do most of the 4-leg robots (see: Boston Dynamics) have their knees look backwards? | Engineering | explainlikeimfive | {
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"Because they are not knee, they are Ankles. The robot reproduce the articulation of a 4 legged animal. Human are bipedal so we use our heel and toes to walk and run. 4 legged animal usually only use their toes to walk and the ankle is higher and help to run.",
"\"Backwards\" is in the eye of the beholder. A horse has two sets of knees and the front ones operate the opposite of the back ones. Which one is \"backwards?\"."
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5t39rh | What's the difference between surface air missiles on US Navy Destroyers? | Reading about current USN Destroyers, and they have an assortment of SAMs onboard. What's the difference between SM class, Tomahawks, and ESSM? Since they're all surface to air, why not just have one missile? | Engineering | explainlikeimfive | {
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"The SM class are general-purpose surface-to-air missiles. They're designed to be used against planes, helicopters, drones, and other missiles, hence the SM \"Standard Missile\" name. The ESSM (\"Evolved Sea Sparrow Missile\") is specifically designed to be an anti-missile missile. It's much smaller and much faster, meant to intercept incoming missiles before they get close enough to damage the fleet. The Tomahawk is a ship-to-surface cruise missile, not a surface-to-air missile. It flies low and slow, and has a range almost ten times greater than the SM."
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5t84l8 | How do train crossings know a train is coming? | Engineering | explainlikeimfive | {
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"Rail tracks are split into sections. The sections have a small gap to the nearby sections to electrically isolate the sections from each other. The two tracks are also isolated from each other. Each section then have a small voltage applied across the tracks in addition to the main supply. When a train moves over the track it short circuits the tracks. This will then be able to trigger relays in the crossings to close the gates and control the signals. The simplest crossing is just a yellow light that is lit when it is safe to cross, this light is just hooked up directly to the rails.",
"The crossing (lights/gate) relay is always powered. The train shorts this power to ground causing the (lights/gate) relay to de-energize. Once this happens the normally open contacts of the relay close powering the lights and or gate."
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5t9ngp | Why Moor's law saying that amount of transistors will double every two years. And that is about how it goes. Why it is so linear? | Engineering | explainlikeimfive | {
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"The processor industry chose to use Moore's law as a goal to achieve, so they managed to achieve it. By doing so they are able to design chips and circuits knowing how many transistors they will have available before the technology to make that circuit exists. There's no actual law, it's just what the industry has strived for. That being said, Moore's law is soon to meet it's end. We are running into physical limits, as in transistors are reaching the size of dozens of atoms, and we can only get so much smaller. Advancements will shift to new materials allowing faster clockspeeds, more efficient circuit designs, etc.",
"It isn't linear, it's an exponential growth. It might look linear if you're looking at a logarithmic plot. An [article]( URL_0 ) from Investopedia: > Because Moore's law suggests exponential growth, it is unlikely to continue indefinitely. Most experts expect Moore's law to hold for another two decades. Some studies have shown physical limitations could be reached by 2017. The extension of Moore's law is that computers, machines that run on computers, and computing power all become smaller and faster with time, as transistors on integrated circuits become more efficient. Transistors are simple electronic on/off switches embedded in microchips, processors and tiny electrical circuits. The faster microchips process electrical signals, the more efficient a computer becomes. Costs of these higher-powered computers eventually came down as well, usually about 30 percent per year. When designers increased the performance of computers with better integrated circuits, manufacturers were able to create better machines that could automate certain processes. This automation created lower-priced products for consumers, as the hardware created lower labor costs."
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5tavrt | How can a 737 land on a snow covered runway perfectly and I it's hard for me to drive on snow? | Engineering | explainlikeimfive | {
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"A 737 can only land on a 'snow-covered' runway if it's significantly longer than the published runway length for the aircraft at the landing weight. The jet will use full reverse thrust for nearly the entirety of the stop; they also have anti-lock brakes to prevent too much skidding, so whatever stopping power the brakes can add is used to the fullest. For the most part, a runway is kept as clear as possible with plowing + de-icer so the plane is really just landing on a wet runway. To the guy who says that 'no tire can be expected to provide traction,' jets have to be certified to stop entirely without reverse thrust (on a dry runway) and many airports restrict the use of reverse thrust for noise consideration. Reverse thrust will decrease stopping distance by 20% or so, it doesn't do the whole job.",
"Because the tires and brakes on a 737 aren't really expected to grip all that much, they just provide a buffer between the fuselage and ground. Most of the stopping force is extended airflow speedbrakes and reverse thrust. When you're going 150 miles an hour, and weigh 64000 lbs, no amount of tire surface area can be expected to provide traction."
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5tdg70 | How does Solar Power convert energy from the sun to electrical power? | Engineering | explainlikeimfive | {
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"The PV cell has what's called a p-n junction of two semi-conducting materials layered next to each other. Semi-conductors, as the name suggests, are able to conduct electricity but do not do so all of the time, unlike regular conductors like copper and aluminium. Instead a semi-conductor requires a little 'nudge' in order to become conductive, and depending on what it's made from, that nudge may come in the form of enough heat, enough voltage or - as with a PV cell - enough light. The p-n junction is made up of a positive and a negative layer; you can think of the negative layer as having an excess number of electrons that it is looking to get rid of, and the positive layer as having an excess number of 'holes' that it's looking to fill. When the energy contained in sunlight hits the negative layer, it provides enough energy for the electrons to jump the gap across the junction, thus allowing electricity to flow around the circuit"
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5tf1b1 | What Americans mean when they say their infrastructure is crumbling. Which parts of US infrastructure are broken, and why were they allowed to go defunct? | Engineering | explainlikeimfive | {
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"Roads are probably biggest example. Major highways get much of their funding from per gallon taxes on gas. But the federal gas tax hasn't been raised since 1993 and many states haven't raised theirs in years either. So with inflation and increased fuel efficiency of cars, there just isn't as much money available for maintaining highways. In Michigan, they're closing a section of a major highway into Detroit for 2 years so they can do major repairs of a bridge. The bridge had gotten so bad that holes in the road were going all the way through and concrete was falling down onto roads underneath. So in this case, it is literally crumbling. In 2003, some tree branches falling on power lines in Ohio caused a blackout that affected over 50 million people. In my city, the rail cars used in the public transit system are 30+ years old and there are no current plans or funds available to replace them. The current fleet is kept running by salvaging parts from broken trains. Over the past few years, the state has cut funding for public transit, leading to reductions in bus and rail service.",
"A significant part of the problem, not yet mentioned, is that the U.S. had a binge of infrastructure building in the early and middle of the twentieth century. But that created a huge amount of infrastructure that then had to be maintained, a costly consequence that seems not to have been considered at the time.",
"In many states, the funds typically used for infrastructure repair come from a general fund and tend to get redirected to other issues. Lawmakers tend to do this because maintaining roads is boring and gets relatively little praise even though it's very important. A prime example is a set of bridges in Rhode Island. One bridge is maintained totally with tolls collected from drivers who travel over the bridge. It's in really good shape and always has been. The other bridge never had tolls and was maintained by the state department of transportation. It had to be replaced due to safety reasons about halfway through it's projected lifespan because it wasn't properly maintained. While lawmakers thought they could get away with deferring maintenance on the bridge they ended up spending many times the \"saved\" amount building a new bridge.",
"Roads, Bridges, Phones, Power, Water, etc. All the infrastructure is decaying. As to why? Government not wanting to spend money on it, and private companies not doing so.",
"There is not a single category of infrastructure in America where the majority of the country is not in bad shape. Roads, bridges, electrical grid etc. Probably the largest reason is that those public works have always been sold to the public and funded solely on construction costs, with nothing in place for upkeep/repair/replacement. Those costs are huge, and no one in government wants to be the one to require the increase in taxes or decrease in others services needed to fund it. So the can gets kicked down the road until a bridge collapses, and then funding is approved as emergency. As an example, here is a report on structurally deficient bridges from 2016. URL_0",
"During the depression, the president put a huge income tax in place. I don't want to pretend like I have current money equivalent. If ya made 10k a year it was a small percent 50k or over it was higher 100k it was higher.... If you made more than 100k.... The NEXT 50k you made had a MUCH higher bracket... Kinda like that...but the first 10k was taxed the smallest, even for the wealthy... Well when america's good guy, actor, and already very wealthy man with very wealthy friends became president....he stopped that and changed the tax code.... Basically....the money that the government got from the taxes on the very wealthy went to making sewers, roads, bridges, railroads, power grids....etc....and also put many of the unemployed to work, while also bringing basic utilities to nearly everywhere, which fixed a lot of sanitation issues, which means there were less sick people, less poor people, less people living in harsh conditions, and the country blossomed. The basic idea was that (to put in current terms) who the heck needs MORE than a million dollars a year to live comfortably? NOBODY who isn't doing stupid and ridiculous things like buying a gold plated airplane? But when already rich actor became president, he struck all that down and declared that if the rich guys have more money, they will spend more money and that money will slowly and eventually make the poor man have more money. But now we all know that isn't and hasn't worked and we are at the point now that many of these roads, bridges, pipes....are rotting and we don't have money to fix them.",
"This is basically a consequence of the United States' extreme tendency for privatisation. Phone lines, railways, some roads, and other public necessities are often sold off to private for-profit companies, which aren't required to really act in the public interest so long as the service is provided. Likewise, the government isn't interested in fixing the problem, because any solution would take years to implement- by which time it's a different government's issue. So, the politicians ignore it beyond bandaid solutions, because they won't be around to get the credit for the job.",
"One thing not mentioned here is the lobbying by businesses who have an interest in one thing or another. The trucking & tire industries lobby to limit railway funding at the expense of the public good. I am sure there are other examples, but the famous one is General Motors [killing streetcars in San Fransisco]( URL_0 ).",
"Currently 1 in 4 bridges in the US are either functionally obsolete or structurally deficient. That places people that travel over them at an unacceptable risk of injury / death should an event like the I-35 Bridge collapse in Minneapolis. Bridges typically have a design life of 50 years. Government has ignored the fact that bridges are going to need replacement and thus haven't funded for such."
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5tk2v6 | How does Glock get away with having a safety mechanism built into the trigger, instead of an external one like almost every other gun company? | Engineering | explainlikeimfive | {
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"Because they make an excellent handgun that people will buy. Not everyone is terribly concerned about having an external safety on a handgun.",
"They \"get away with it\" because there aren't any regulations as to what safety devices a gun must have, except in California, which requires an integral magazine disconnect which means the gun won't be able to fire if the magazine is ejected (don't ask me why; I don't know why this would make a gun \"safer\" than a gun without it)."
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5tlpe4 | How can Motorcycles hit and maintain ~10,000 RPM's, whereas my 6 speed car feels like it's about to fall apart at 7500? | Engineering | explainlikeimfive | {
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"Stroke length - the distance from the bottom on the cylinder to the top- plays a huge part of this. The shorter the distance the less speed the piston has to have and the less rotational G force applied to the piston. 80's indy cars had over bore engines that could turn over 18k rpm. Meaning the diameter of the piston is most larger than the stroke of the crank. (Rod length that connects the two makes no difference in piston speed, but on side load it does. Totally different subject) Stroke is torque, rpm is horsepower. Indy cars going around a track don't need much torque because horsepower carries them around a track more efficiently. A street car uses torque to take off from a stop and gain better fuel economy. A motorcycle doesn't have the wieght disadvantages a car has. So they don't need the tq a car has. If you need any more technical data and math to go with this I can supply it.",
"General rule is basically: longer the cylinder stroke is, slower the max rpm. Longer cylinder stroke means cylinder moves more per revolution compared to shorter stroke. Also forces and accelerations endured by cylinder are higher. That is why car engines have usually lower max rpm than a motorcycle. Ship engines run with much lower rpm and rc car engine can run over 20000rpm.",
"I like to use the analogy of a twig. Take a long twig and apply a force to each end in compression. The twig will bow the break. However take a twig the is shorter and it will require more force to break. The same logic applies to the connecting rods in the cylinders of the motor. Motorcycles tend to have short strokes. My FZ-1 has 1000cc of displacement but only travels 58mm or 2.28in. That is a pretty small stroke and keeps bikes connecting rods acting like the short twig.",
"Smaller engines have shorter piston strokes, essentially. If you've ever watched a Formula 1 race, you've observed that the cars have a high pitched whine, like motorcycles, despite being 8 or 10 cylinder engines. Same principle at work.",
"If you looked at the *actual speed* the parts inside the engine are traveling and also the acceleration as they change direction, they may be *relatively* similar. Because the smaller engine parts travel shorter distances each cycle, they are (potentially) not moving faster in absolute terms. A motorcycle engine may be built to withstand higher forces for performance reasons but in short, it actually doesn't need to be."
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5tqm9d | the difference between the dam in Oroville failing versus the spillway failing. Or any city dam/spillway. | Engineering | explainlikeimfive | {
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"The dam itself is made of a single comparatively thin vertical core wall of concrete and clay reinforced on both sides by enormous amounts of earth (40,000+ trainloads worth that took eleven years to move). This structure is strong enough to hold back the enormous pressure being exerted by the water in the main channel, however it is NOT designed to be overtopped. If water flows over the dam proper, it would cut a channel through it like a knife through butter, all the way down to the natural river bed. [As enormous as the artificial dam is, it is still much thinner than the hills surrounding it.]( URL_0 ) Which is where the spillway is. As bad as the erosion is on the spillway (and it is bad), it is still happening at a rate MUCH slower than if the dam itself was overtopped.",
"The Dam holds back all of the water. The main spillway is to the left of the dam wall itself. It is an entirely different structure from the dam. It is where all of the water is supposed to go, since the main spillway has a nice concrete chute for all the water to go down. Weee!!! The emergency spillway is a 30 foot tall wall built even further to the left of the main spillway, built as a last-resort just-in-case thing to prevent water from EVER going over the dam itself. If the emergency spillway were to fail, up to 30 feet of water would drain into the Feather River uncontrollably. If the dam would fail, about 770 feet of water would drain into the river uncontrollably. Fortunately the emergency spillway has stopped flowing now that the main spillway has increased its output.",
"TLDR/ELI5 timeline from my POV is: Cracks filled in 3 years ago, not fixed, floods caused re-failure of spillway few days ago, they reduced overflow through spillway to prolong lifespan, this action now compromised whole dam as it's overflowing an emergency spillway (never used in 50 year history of the dam) and also the overflow of the overflow (aka a car park) and only getting worse as more rain is scheduled. This water simply removes top soil and loose rock, destabilising the walls of the dam above it, causing them to collapse if this continues. If rain stops, you're lucky. If not, it's gone. Hence they are evacuating because they know this is the truth."
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5trzlb | Why is the United States' infrastructure in such disarray? | Engineering | explainlikeimfive | {
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"text": [
"Because politicians love big shiny new projects that they are responsible for. This has happened for centuries. Each pharaoh built a huge pyramid for their grave. Roman emperors built huge baths, aqueducts, et cetera. Maintenance is always in the background. No politician is content to say. \"I carefully maintained what the others before me did.\" We love new highways. Every thirty years they must be rebuilt. In my state a salesman really increased the use of concrete in the Interstate system with the simple argument, \"Don't you want a nice concrete highway?\" It cost a little more. But he got the money spent for the concrete. Thirty years later it is far more expensive to repair and replace."
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5tvui0 | How can the Oroville Dam is overflowing when California is experiencing a prolonged drought? | Engineering | explainlikeimfive | {
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"text": [
"[This nice graphic]( URL_0 ) shows the status of the reservoirs relative to their capacity and normal level. This shows surface water not in drought conditions. The time to refill the underground aquifers is much longer.",
"Drought is an extended period of lower-than-normal rainfall. It doesn't mean that it never rains. Think of it this way. If you stop eating, and only have one meal every four days at an all-you-can-eat buffet, you are still malnourished.",
"In the last two months, much of California has received significantly more rainfall in a shorter amount of time than average. This results in a lot of surface water pooling in some reservoirs and leading to floods. You can see a weekly layout of the California drought over the past five years here: URL_0 Notice the last row of entries.",
"California stopped being in drought conditions two months ago when massive storms started raining on most of the State. The Dam is overflowing because it rained so much that it filled the Dam, then rained so much that the primary spillway was not able to handle it and the secondary \"emergency\" spillways which are earthen are also not handling the volume of water and are failing (may have failed by this point). Now it will take longer for underground sources of water like the Aquifers to replenish, but all surface sources are filled/overflowing."
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5tw9hl | What caused the Deepwater Horizon catastrophe? | Engineering | explainlikeimfive | {
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"text": [
"1) BP Co man tried to be cheap & reduced the number of pipe centralizers by a significant number. 2) Halliburton was hired to pump cement to solidify the pipe. Head cementer noticed the discrepancy & noted it to the Co man. Insufficient centralizers can cause a poor cement job since the pipe bends & moves as it goes downhole. 3) Co man told him to \"shut up & do his job\". Signed cementer's joblog & notation. 4) Cement in a well job goes down the inside of the pipe then back up the outside of the pipe. Water is pumped behind the cement to clear the cement w or without a rubber plug. 5) As the cement came up the outside, the pipe had bent & was touching the freshly drilled hole so the cement went around the pipe THICK on the other side but NOTHING on that side. Just as the cementer had predicted. 6) After the pipe was perforated to allow product to flow into the pipe, no cement at that point in the pipe allowed it to shake & erode the hole. 7) Very quickly the metal pipe burst allowing pressurized petroleum to escape OUTSIDE the pipe & blast up the outside of the hole outside the cement & all pressure control mechanisms on the rig. Pressure ratings on pipe require proper counterpressure such as hardened cement. - I got this during my 10 years in the oilfield including 6 in cement w several ex-Halliburton engineers & Senior Cementers who were given the full briefing when this happened."
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5twwla | Where does water pressure come from? | In municipal water supply, such as my faucets at my home, where does the water pressure originate. Or, what creates the pressure to allow it to flow to our homes? | Engineering | explainlikeimfive | {
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"I'll just try to elaborate a bit. There are only 2 common ways to increase the pressure of any fluid (including water). Pressure is equal to the density of the liquid times the height, it doesn't matter how wide or deep the pipe is, the water pressure at the bottom of a 2 inch diameter tube that's 100 feet tall will be the same as a 2000 inch diameter tube that is 100 feet tall. So water is either collected at high elevation (rain collecting) or pumped to a higher elevation (tank at the top of a tower). Pumping is the second method to increase pressure, which is pretty obvious, using electrical power, to turn mechanical parts that apply force to the fluid to increase pressure."
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5tx4gr | Since both light and sound could be measured by their frequencies, does that mean they are essentially the same, only that sound is in the audible frequency range and light in the visible frequency range? | Engineering | explainlikeimfive | {
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"text": [
"No, though both sound and light are types of waves, they are fundamentally two different type of waves. Sound waves are compression waves; they involve atoms physically moving and interacting with each other. The atoms \"push\" each other, so to say, like people in a crowd. This also means that sound requires a medium; there must be atoms to push, after all. Light, on the other hand, is much more fundamental—it requires no medium. It occurs to due to excitations in the electromagnetic field, which is inherent in physical space, and extends infinitely everywhere."
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5txo5d | How do rewritable disks rewrite themselves? | Engineering | explainlikeimfive | {
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"text": [
"Re-writable disks use a thin layer of metal alloy (silver-indium-antimony-tellurium for CD-RWs, germanium-antimony-tellurium for DVD-RWs) which has two states - a dull, amorphous state, and a shiny, crystalline state. By turning on the laser at full power, the alloy melts, and cools into the amorphous state, which is used to write information to the disk. By turning on the laser at partial power, the material is heated, and cools into the shiny crystalline state, erasing the disk."
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5tzzc4 | Why are cab-over trucks virtually non-existent in the US, but used almost exclusively in other countries? | Engineering | explainlikeimfive | {
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"The USA is a spacious country. Design trade-offs that reduce the truck's length are not as valuable when you have lots of room. And the USA is a large enough market to have its own truck designs. Note that other very spacious countries (Australia, Canada) also have lots of non-cab-over trucks.",
"Cab-over trucks are shorter, and so more useful in countries who have bad/small road systems. But the tradeoff is that you have bad aerodynamics and use more fuel to drive. The US is spacious and designed for car and truck travel with larger roads. This means that we can have the longer, more aerodynamic models for our truck which will operate more efficiently.",
"We have max total length of 25 meters and 64 metric tonnes here, so a cab-over makes room for a lot of cargo. In the US, the weight limit is less and only the trailer is limited in length. It has nothing to do with power or aerodynamics.",
"To add to the other disadvantages mentioned, cab-over trucks are less safe for the driver, because they are closer to the point of impact in a crash and not protected by the engine. I think cab-over trucks are still quite safe in crashes compared to small cars, but this is just one of many small reasons to avoid cab-overs if space constraints don't make them necessary.",
"Countries have limits on the size of trucks. In the US, the length limit is on the trailers. In the EU, the length limit is on the trailers plus the cab. So in the EU, it's better to have shorter cabs, because every extra foot you put in the cab is a foot you can't use for revenue-generating cargo space. In the US, if you make the cab a couple of feet longer, you don't have to make the trailer shorter.",
"A lot of countries have more restrictions on the overall length of the vehicle. Even if there is no legal restrictions there are tighter corners and smaller intersections on the roads which makes it hard to maneuver a long truck. A cab-over have the advantage of being shorter but have more drag. This helps close maneuvering but have higher fuel consumption on the open road. Another difference is that lorries with trailers are more common outside of the states. The lorry might have the same size frame as a standard American tractor but with a short cab-over there is room for a cargo room on the chassis where the fifth wheel usually goes. Then there is a shorter trailer behind that. This have the disadvantage of having to uncouple the trailer when you want to unload the cargo and not being able to quickly move the cargo to another truck. However you can get more room in a more maneuverable vehicle. American trucks on the other hand is going the other way and is adding long trailers to their already long 18 wheeler which makes it hard to maneuver and almost impossible to back up. However this is nothing compared to the Australian road trains that are able to pull lots of trailers after each other but need special turning circles and only drive on straight roads."
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5u0ezs | Why do products have such seemingly arbitrary numbers and letters? What goes into the naming convention? E.g "HP Pavilion 15-bc200" or "Sony Bravia KD-55XD8505". | Like why is it called "Sony Bravia KD-55XD8505" instead of just "Sony Bravia" or "Sony Bravia X" or something? | Engineering | explainlikeimfive | {
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"This will vary by manufacturer and product, so there's no general answer. It's safe to assume the digits and letters represent features and options within a model series. I can give one example that makes sense and is specific to Taylor acoustic guitars, e.g. 514CE-N. First digit: 500 series. Second digit: Number of strings and type of top wood. \"1\" is 6 / softwood. \"2\" is 6 / hardwood. \"5\" is 12 / softwood. \"6\" is 12 / hardwood. Third digit: Size. Dreadnought, concert, orchestra, etc. If the \"C\" is there the guitar has a cutaway on the treble side of the upper frets. If the \"E\" is there the guitar is acoustic / electric. If the \"N\" is there it's a nylon classical. So something like 256E will be 200 series 12 string spruce symphony electric. Assuming that one really exists.",
"Usually it just denotes that items position in a lineup, what features it has, what generation of product it is, and so on. The naming i s arbitrary unless you know what those numbers and letters mean, which is usually why they have a marketable name out in front, like Bravia. The rest is technical.",
"Because Sony makes a shittone of Bravia TVs and calling them all the same thing would lead to confusion. Look, per Sony's website there are 21 Bravia TVs and many of those models come in 3 or 4 sizes. So there's potentially 100 different Bravia TVs and that only includes this years models. They've been selling Bravia TVs since 2005 so there's likely thousands of combinations of features and sizes. It might be that the complex model numbers are confusing. In the case of Sony, they DO mean something it's just that the average consumer might not be aware of what they mean. Take your example: KD-55XD8505 KD notes that it's a Bravia TV, as opposed to a Sony camera or something. 55 is the size of the TV. X means it's an 4K Ultra HD screan. D notes the year, in this case D means 2016. 8505 notes the exact panel and features within that size and model year. Generally the nigher the number the more features it'll have. For the informed consumer, this tells them a lot of information about a TV. The average consumer need only know it's a Sony Bravia. This is opposed to Apple's strategy. Look at iPads, there's a world of difference between a gen 1 iPad and a current gen one, but they are all branded the same \"iPad\". If you walk into some backwater electronics store 2 weeks after a new iPad comes out, how do you know it's the new one vs the old one. What if you're buying on Ebay, how can you tell. I'll give you a hint, there's actually a model number there. My iPhone just says \"iPhone\" on the back. If you look at the fine print under it, it says \"model A1533\" I can look that up and know it's a 5s GSM model intended for the North American market. The A1453 is a CDMA intended for the US and Japan, A1457 is for the UK, Europe and the middle east, A1528 is for China and A1530 is for Asia Pacific. And that's just the 5s model, there's also the 6, 6 Plus, 6s, 6s plus and SE PLUS all the ones that came before! These models exist because the conventions of the cellular networks are not the same country to country."
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5u394g | How are engineers able to build subway tunnels under already built infrastructure? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"There's loads of technology. The old fashioned and cheap (still used where possible) method is cut and cover. Dig a big trench, build the tunnels and then cover them up. [Here's them doing it in 1861, London for what is now part of the tube]( URL_2 ) [And here's a modern version for a road tunnel in Scandinavia]( URL_3 ) However, for digging under buildings and such there's another technology - tunnel boring machines. [Here's one of the TBMs used in the newest London underground expansion, Crossrail]( URL_1 ) They're basically giant worms pushed by hydraulics. The front head turns slowly, grinding the ground in front. Conveyor systems carry the sludge away. [Little trains]( URL_0 ) bring precast concrete tunnel segments, which are placed against the wall and bolted in place by a giant robot arm. This is pretty efficient, provided the ground is stable. Unfortunately, many large cities are built on river basins or other flat, muddy ground. This requires more advanced techniques. Back in the day (eg Paris metro) they used to freeze the ground by pumping cold liquid through pipes that they pushed in. Then they could excavate a tunnel and build walls before the ground started to melt. A more modern technique is to use a Earth-Pressure-Balance TBM. If you just use a regular TBM ground will just fall down in front of the cutting head, causing a sinkhole above the TBM. In a EPB TBM the cutting head is kept pushed hard against the tunnel head, so that the ground doesn't start caving in. The front of the TBM is sealed, linking seamlessly with the tunnel lining (built from those concrete segments) that the TBM is always assembling as it moves along. Subway tunnels are pretty well mastered nowadays. The main issue is cost control. In the US you're looking at $200-1000 million a km! (Yes, a million dollars a *meter*). Spain on the other hand has managed to build subway systems well below $100 million/km. This is mostly a management/legal problem. Other tunnels can be more difficult though! Highway tunnels are much bigger, so cause more problems. A recent example would be Seattle where the Alaskan Way Viaduct Replacement tunnel caused sinkholes to open in the city, or Boston's Big Dig which cost billions upon billions above predictions. There's always new innovations as well. One big one is the New Austrian Tunneling method (which is really a collection of good practices) which is particularly applicable in hard rock. This basically uses pretty standard-looking earthworking equipment, the top half of the tunnel is dug first, the rocks natural strength holding up the tunnel. Then spray-concrete is thrown on the roof. After that the second team comes through and digs out the bottom half, concreting that as well.",
"Very carefully. There are big drills that chew rock very slowly, deposit it onto a conveyor belt that takes it out of the tunnel. Right behind them is a similar machine that lays some brand of concrete, reinforcing mesh, and usually a polymer coating. At no time is more than a very little bit of the tunnel exposed without reinforcement. The whole process goes very slowly, and only really vibrates at the surface entrance/exit, which is usually in an industrial area anyway. Basically, we know the math behind the forces that would ruin existing surface structures, and make sure we don't do that. Or if it's unavoidable, you design for the outages too, and build repairs into the budget."
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5u5hl7 | why do airplane windows have tiny holes in them? | Engineering | explainlikeimfive | {
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"text": [
"Airplane windows have three layers. The inner layer's job is just to keep your dirty mitts off the real windows. The outer layer has to bear the pressure difference between the pressurized interior and the low-pressure exterior. The middle layer is the one with the hole in it; its job is to be a backup in case the outer panel breaks. The hole is to allow the air between the outer and middle panels to equalize with the cabin pressure, so the outer panel bears 100% of the load. If the outer panel fails, the middle panel will leak - but it's a tiny hole which the pressurization system can easily keep up with. [\\(source\\)]( URL_0 )"
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5u6bda | How can one rocket get over 100 satellites into each of their positions around the Earth? | India just broke the record for how many satellites put into orbit with one rocket. Each one travels at immense speed so must be spread out a lot surely? So how can one rocket achieve this? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"I'll simplify and just consider two satellites. Their rocket launches them together into a certain orbit, and then the satellites split up and need to get far apart. They can use their own engines or one can get help by the launching rocket. It doesn't require much rocket fuel for one satellite to go ahead of the other. One satellite just has to drop its orbit a tiny bit and it will go faster and has a shorter path, so it will steadily pull ahead of the other one. It's a bit like a racing car taking the inside lane. Once the two satellites are far enough apart, they can get themselves back into matching orbits and they'll stay with one leading the other. It takes a bit more rocket fuel for one satellite to get into a higher orbit than the other. But not too much if you only need say a 50 or 100 km difference. And then the two satellites will be in different orbits and the closest they'll come to each other will be the difference in their orbital heights. But it takes a *lot* of rocket fuel if you want one satellite to tilt its orbit round so it's different to another. This is because the satellites are doing about 7 km per second already, so to deflect that speed north or south requires a big push. So while the multiple satellites launched by a rocket can orbit at different heights or get into different positions around their orbits, they must all stay in nearly the same plane. If you looked at the orbits of just those 100 satellites, it'd be a bit like the rings of Saturn."
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5u6to2 | How do you invent new origami sculptures? | I recently saw some instructions for complex sculptures with many steps and asked myself how did the creator of this sculpture come up with this? Trial and error seems impossible, right? | Engineering | explainlikeimfive | {
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"ddrs0pj"
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"text": [
"Origami experts are artists just like a sculptor who works with marble, they have a vision of the finished work and the knowledge of what needs to be done to achieve it. There is an element of trial and error but for the most part creating new works is based off of previous experiences. As for recording the steps necessary to recreate a new origami design, most people work backwards from a finished work. It's much easier to deconstruct and record, since there will be some folds that were made in error."
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5u7q0b | why are american and european electrical outlets different? | Engineering | explainlikeimfive | {
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"Because the standards for generating, delivering, and using electricity were developed independently by different countries.",
"This has been discussed several times before. Electrical systems were developed independently with differing choices along the way. Most European systems chose 50 cycles per second. American systems use 60 cycles per second so simple clocks would be wrong even if the voltage were correct. The US uses 110 to 120 volts while others use higher voltages. Lower voltages are slightly safer. Higher voltages do not need wires to be as large. IF you search you will find more answers."
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5u9ry1 | Why is there a little bulge on top of the positive terminal of an AA battery? | Engineering | explainlikeimfive | {
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"It's so you can get the best contact with both sides in the simplest way. Since the negative side is flat, you can place a spring of some sort on that end and not risk it slipping off. Because the positive nub is smaller, it's concentrating the force applied to the back end by the spring onto a smaller area, ensuring good contact on the positive end without needing a second spring. Since there's only one spring, it's a lot simpler to load than if you had two springs pointed opposite directions. Also it's easier to show pictorially that \"the side with the nub goes here\" than \"the positive side goes here\" to someone with zero knowledge of how electronics work or that there are positive and negative charges."
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5ua0n1 | Why is it so hard to make smart-devices waterproof? | It seems like you can currently get a cheap case for things like the iPhone 6 that make it water-proof. What's the hurdle that stops companies from making almost every device they put out waterproof? | Engineering | explainlikeimfive | {
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"Most small electronic devices have very fine instructions on how they're made so that they fit together and feel smooth all over. This is hard enough even when you're not thinking about people putting the device in water. If you want to worry about having the device be submerged, that's an extra layer of precision (and more expensive quality control) that has to go into how the parts fit together that form the outside, as well as things like polymer seals in the places where water could get in (like at the microphone, or between the lens of the camera and the shell). You could just put a special case all the way around a \"normal\" phone but this makes the device bigger and heavier. You also have to make some guesses as to how deep into water the device may go, because the forces involved in submersion are directly proportional to depth. Other guesses need to be made about the possibility of contaminants or solutions in the water that could get stuck or corrode your seals, like naturally occurring acids. There are other possible things to worry about, but it's all another layer of engineering that has to have its own quality control layer, which just increases the complexity of manufacturing. All, for something that most people think is something you should naturally avoid anyways. Of course it's becoming a competitive point for some products these days and the market is always changing. Who knows, maybe waterproofing will become a default option in the future."
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5uas0x | How do people with houses next to eachother get power from two different companies? (even though they both use the same power line) | Engineering | explainlikeimfive | {
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"You don't get power from a specific company. They provide capacity to the network and you pay for that. You get exactly the same power as everyone else.",
"I used to work for an electricity reseller in Texas after they deregulated. They likened the system to a bathtub. You choose your electric company based on price and/or greenness. They pay the generation companies to turn on their faucets and it all flows into the bathtub. You then get charged for how much you use from the bathtub. A single company is in charge of that bathtub to make sure it doesn't break and so they know how much you used. They pass that information and a small charge for their services to your electric company, who charges you for your use."
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5ubaak | Why do some cars have gas tanks on the left and others on the right? | Is there a reason they aren't they all on the same side? | Engineering | explainlikeimfive | {
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"It's not that there is a reason they aren't on the same side. It's that there's not a reason to have them on the same side. So each manufacturer dies what's best for their factory and design.",
"Researching this I found a few candidate explanations: The filler cap is on the opposite side to the exhaust pipe. Makes sense that it would reduce the risk of igniting spilled fuel, and it might also be mechanically easier to build. As for which side the exhaust is on, that will be influenced by the engine mounting especially for a transverse engine. If there's a lever in the car on the driver's side to release the filler cap, putting the filler cap on the driver's side too is mechanically simpler. But my own car goes against this - UK model Suzuki, so right hand drive, lever on the floor just next to the driver's door, left hand side filler cap. Probably the car designers just put it where it's easiest, considering the rest of the vehicle. Things like which side the driver sits, a transverse-mounted engine, and certain rear lights all create asymmetries in car design."
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5ubvuy | Why are we so amazed at what past civilizations created (pyramids, temples, etc) how did we lose the way these types of mega structures were created? | I can't figure out how word it better hopefully someone understands what I'm asking. Thank you ! | Engineering | explainlikeimfive | {
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"We are amazed because building massive structures without sophisticated machines and tools seems amazing to us today. We haven't \"lost\" anything though. People kept right on building amazing structures right the way through history. The pyramids, the Acropolis, the Aqueducts, hundreds of amazing Cathedrals, etc.",
"The simple answer is we sorta didn't. When people say we don't know how they built the pyramids, it's more about us not knowing their exact methods, not about how they were so advanced and we could never do it today. We do have plenty of plausible theories but we can't say we know exactly for all of them. The amazement is about what they managed to achieve with what they had, not about us not being capable of replicating it at all. Also keep in mind the amount of time and effort that was put into some of these megastructures. They took many decades to build and were huge efforts that often took the resources of powerful kingdoms/states/empires. I'd say it's better to compare the building of the pyramids to something like the Space Race and moon landing rather than to buildings today. Also note that it's not as if these megastructures somehow prove that ancient peoples had better building technology. They would've found it impossible to build the skyscrapers we can put up in a few short years. The Roman ancient roads were an amazing achievement at the time, but they would not have found it possible to build the US highway system. And just because stone tablets will last hundreds of more years than paper doesn't mean that they are somehow more advanced to develop.",
"We could probably build the Pyramids today if we had the motive. It would probably be cheaper than the border wall.",
"I often hear amazement specifically for the size of stones used in ancient structures. As far as I know, the ancients haven't been surpassed in that regard. We could surpass them if we wanted to, but we have modern materials that are easier to build with. So, we don't surpass the massive stones, and we remain awed by the real achievements of engineering that used them. Similarly, entering a structure made all of wood with no nails can impress us for achievements that we do not emulate today. The examples abound of architectural practices that awe is that are out of vogue: gargoyles, stained glass, spires, even large scale brickwork is not seen so much and impresses me when I see the beautiful rows of bricks, and the devil's bridges, and the mud skyscrapers of Yemen, and so on.",
"I've heard \"how did they get so many people to build that?\" on more than one occasion for an ancient structure that would've taken hundreds or even thousands to assemble. Well, to not be to blunt...slavery or forced servitude or conscripted labor. Many of the marvels of ancient times--like the pyramids--were heavily built by ~~slave~~ conscripted labor. **some structures like the Colosseum used slave labor** With slavery now much less prominent, and considered by most modernized civilizations to be barbaric and cruel, we rely on the heavy work to be done with engineering and usually individuals on risk-pay (relatively high pay for unskilled labor based on very high risk of injury or death). Even very large tasks in the last couple centuries utilized a good amount of forced or slave labor until we developed machines to expedite the work. Like the Railroad system of the US. Don't know if that was what you were asking. Edit: pyramids were a bad example, as some pointed out they didn't use a lot of slaves, but conscripted labor. Added the Colosseum example, as everyone will know that, and slaves were definitely utilized. I'm also not saying there wasn't technique involved, but the actual workload used a good amount of forced human effort.",
"Omg I've been Binge Playing Civ 6 and my shallow knowledge of history thinks I have the answer to this.",
"We can still build these structures, the thing that amazes people is the way we would do it today didn't exist back then. I suspect that amazes people primarily because it's so disjointed from the current reality.",
"1. We didn't lose the way these were created. 2. We can and do make much more amazing things today. The typical office building is a more complex feat than a pyramid and something completely impossible for an ancient civilization to achieve. 3. People are only amazed because they don't know 1 and 2."
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5uc4ts | Why do German luxury automobile brands such as Audi/BMW/Mercedes recommend oil changes every 15K+ miles whereas American standard brands like Ford and Chevy still recommend oil changes every 3-5K miles? | I have always owned American car brands and regularly changed the oil at the recommended 5K mile mark as part of the routine maintenance. I recently got a BMW X3 and found out that the recommended mileage before getting an oil change is around 15K. This lead me to ask: What is it about the design of the German vehicles that allow them to go longer without changing the oil? Does the engine run at a slightly temperature than American models? Does it have to do with the fact that I am combusting higher rated gasoline in it(requires premium)? Do they use a superior oil filter? If anyone could give some insight, I would greatly appreciate it because I was genuinely curious and don't know enough about cars to formulate my own hypothesis. | Engineering | explainlikeimfive | {
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"Service contracts. BMW used to recommend oil changes every 5000 miles or so, but then the marketing department got involved and offered free oil changes for the first X years, and once the dealers had to pay the cost of the service the interval magically tripled so you needed fewer of them. The effect is that with the reduced servicing the car will still run fine for the duration of the warranty, but at the end of the warranty period it'll have more wear and tear and may need to be replaced sooner - another win for the marketing department.",
"It's mostly due to advances in petroleum engineering. German cars use full synthetic oil, usually 5w-40 or 0w-40 depending on the region you live. The first number measures the oil at very cold temperatures(0F). The second number measures the oils' performance at engine operating temperature (210F). This is important for oil life. Full synthetic oils last much, much longer than natural oils, since they have been specifically engineered to do so. Additionally by having a high heat tolerance -40 oils don't degrade due to heat as fast as lower rated oils. You could put full synthetic 0w-30 in an american car and go 10,000 miles between changes no problem. But I wouldn't recommend putting -40 in a car that wants -30, it might be a little too thick that what the engine was designed for.",
"Check your owners manual. Many cars today don't go by the 3,000 mile thing anymore. The dealer will, but they sell oil changes so they want you in as often as possible.",
"Here in Europe I had Ford, Peugeot, Citroen and Fiat. They all suggested an oil change at 20.000 km (13.000 miles). Some models even 30.000 km.",
"Don't know how reliable this info is but I notice specifically with BMW that for a V8, the oil quantity is anywhere from 8.5-10 quarts of oil. Add full synthetic to the blend and essentially you have a huge oil storage capacity, thereby making your oil last longer and help your engine stay lubricated. BMW 6 cylinder engines are about 6.9 quarts as well. Whereas other domestic manufacturers seem to have less oil quantities for the comparable engine sizes. That's just what I've noticed, don't know if there's any truth to it. My oil changes on my 2015 Mini (which has a BMW motor) are 8,000 miles and I do oil changes every 4K because I drive hard on it and have a turbo motor."
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5udvuq | From an electrical engineering perspective, how does binary code actually work? | How does the specific arrangement or combination of on and off switches physically translate into anything productive? | Engineering | explainlikeimfive | {
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"On a physical level, it works via logic gates. The principle behind them is that they take one or two bits (which will be a wire with a current going through it or not) and output a single bit. Here are the main ones used for every possible mathematical operation: * **AND** -- Takes two bits and only output 1 if both input bits are 1 * **OR** -- Takes two bits and only outputs 1 if one or both input bits are 1 * **NOT** -- Takes one bit and flips it. Output 1 if the input is 0, outputs 0 if the input is 1 * **XOR** -- Takes two bits and outputs 1 if either bit is one, but will output 0 if *both* bits are one. This gate isn't actually necessary, you can get the same result by combining the above gates. But that's the key, we can combine gates to get more complex operations. With these operations you can perform any mathematical operation on any number, which is the only thing computers ever do. How do the gates work? Well let's imagine that we put a resistor into a circuit. It won't allow a current to continue unless the input is twice the current of a single wire, so both wires feeding into it need to be active. This is an AND gate. On the other hand, if we just connected the two wires together with diodes to make sure the current goes to where we want it to, that's an OR gate. If we have a power source constantly powering a wire, but a breaker switch is activated when an input wire is powered, that's a NOT gate. The actual gates don't work like this on a CPU level, with diodes and breaker switches and such, but the electronic concepts are the same.",
"It is, as you said, a series of switches. In the right combinations those switches form some basic logic circuits. The 3 basic ones are AND - this takes two inputs and if they are both 1 it outputs a 1, otherwise a zero (no voltage). Next is an OR gate. Again this takes 2 inputs but if either of them is 1 (high) it outputs a 1. If both are low its output is also low. Finally we have a NOT gate. This inverts the input. A 1 becomes 0 and 0 becomes 1. Now these can be grouped together into logic circuits that perform computationally interesting operations. String lots of logic blocks together and you have a processor. Now again all the processor does is take +ve and -ve signals on the input pins, passes these through the processor and the result (+ve and -ve) is presented on the ouput pins. From there, transistor amplifiers can take these signals and amplify them into things we can see or hear."
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5ufluq | How exactly do planes compensate for the curvature of the earth when they are flying? | Engineering | explainlikeimfive | {
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"Planes **DO NOT NEED TO ACCOUNT FOR THE VERTICAL CURVATURE OF THE EARTH WHEN MAINTAINING ALTITUDE**. Everyone telling you they constantly adjust down a little bit is wrong. The Earth is curved, as is its atmosphere. An aircraft determines its altitude based on atmospheric pressure. Therefore, we do not define \"level flight\" as being tangential to the Earth's surface, but rather as being an altitude relating to a specific atmospheric pressure. Therefore, if the plane is trimmed for level flight it will ALWAYS remain at the same altitude above the Earth. Picture a plane flying [perfectly level above a point on a curved globe]( URL_0 ). In your question, you're assuming the plane flights horizontally (the first image in that link). However, this would only be the case if there were no atmosphere. A more accurate visualization is to rotate the Earth beneath the aircraft (second image). You see how the surface of the Earth directly below the aircraft is at the same location? Because the atmosphere moves with the Earth, THAT is level flight.",
"Aircraft don't move quickly enough for the curvature to be significant over the minor corrections just to maintain level flight. If the aircraft is kept level it is following the curvature already.",
"They control their flight by aerodynamics, and the atmosphere of course curves with the Earth. So when a plane is 'trimmed' for straight and level flight it will automatically follow the curvature of the Earth. Also a plane isn't a dumb object, it's being actively controlled by a pilot or an autopilot, and they will use either their eyes or instruments to determine the orientation and height of the plane compared to the ground and make control inputs to maintain that straight level flight. EDIT PS: If a plane went fast enough that the Earth's curvature would be significant, it would simply fly as though it weighed less than its true weight.",
"The same way absolutely everything else does. There's two ways you need to compensate. One is flight path and the other is altitude. Flight path is easy. Instead of using flat maps, you use great circle routes. North of the equator, the fastest way to reach a target due east or west of you isn't to go due east or west but to take a more northeast path. This depends on distance, something diametrically opposite would have a great circle route through the north pole. South of the equator it's the other way. As for maintaining altitude, the plane has to deal with two factors: gravity and curvature of the earth. The former is causing the plane to veer downwards and the latter is causing it to veer upwards. Well, as it turns out, gravity is a LOT more of a factor than the curvature of the earth! So, like every other object travelling over the earth, it doesn't have to compensate AT ALL for the curvature, because gravity has already done that. It just has to compensate for what's left of gravity. And sometimes gravity's effect and the curvature' effect are equal. We call that an orbit."
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5ufz7y | How do some mechanics know what's wrong with a vehicle just by sound? | Engineering | explainlikeimfive | {
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"Its usually sound and when that sound happens or what your doing when that sound happens. You can narrow it down to what parts are used for that action and the sound they make when they are breaking. Like a bad wheel bearing on tbe left side will make a rubbing grinding noise when you turn right because more weight is put on the left side. High pitch whine when you accelerate. Is usually a pully if it gets louder when turning wheels its a power steering pump. You just need to onow how are car works and what parts are involved and it become more common sense at that point."
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5ug5g5 | How do 3-D printers actually work? Why can't we just 3D print everything? | Engineering | explainlikeimfive | {
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"The technique used by 3d printers is called \"additive manufacturing\" which means they put down one thin layer after another, eventually making a solid item. We can't use it on everything because it ends up being fairly weak. Think of a baseball bat made of solid wood versus one from particle board. The latter would wear away and snap in half long before the former would show any signs of problems. And, combine that with the fact that 3d printers are limited to materials which can be turned from somewhat liquid to solid fairly easily. You can't do it with something like steel, at least with currently available machines. Once you have the ability to assemble the material on a molecular level, then you'll be talking when it comes to 3d printing becoming dominant.",
"The most common variety of 3d printers works by melting down plastic to create 2D layers (of a small thickness) stacked on top of each other (a program slices a 3d model into those quasi-2d slices). There are a few disadvantages with 3d printing that other manufacturing techniques solve. The first is cost and time. 3D printing is horribly slow, and the material isn't cheap due to processing. For bulk production, an alternative example is injection molding, which has a startup cost, but can produce a lot of an object many times quicker than a printer. The second is accuracy. 3D printers can not produce perfectly smooth surfaces (especially if non-linear) and have a finite resolution. There are many more precise techniques of creating a feature on an object. Another is materials. Commercial 3D printers are only able to work with a handful of materials, and what would be the best choice for an object may not be us bale in a printer. The properties of a product of 3d printing may be undesirable (such as strength) compared to other production methods."
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5uim6a | Why are the vast majority of commercial airplanes white? | Engineering | explainlikeimfive | {
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"There's no single reason but here's a few good reasons for white: - It reflects heat rather than absorbing it, this can a good thing because it reduces parts expanding and contracting which wears them out - It makes it easier to spot damage and leaks - It doesn't fade like colours do",
"Lighter colors reflect sun instead of absorbing it, which keeps the plane cool while it's taxiing on the ground. Less need for A/C."
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