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cldc77 | How do access specifiers work under the hood? | how does the compiler understand that a particular variable isn't accessible somewhere? For eg:- we have protected int a; public int a; How does the compiler know that a is accessible somewhere or not. | Engineering | explainlikeimfive | {
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"The compiler (or interpreter) will keep an \"environment\" while analyzing (or running) the code. Among other things, the environment will hold a list of all known visible identifiers (added as the analyzer processes declarations, int a), and when the analyzer sees an identifier is read (int b=a) it will look up its environment to see if that identifier is there. When going into a function or other new scope, a new child environment may be added on top of the current one where local variables will be stored (so it can find local variables there and global ones in the parent), and then when the scope exits, the child environment will be removed. The environment can also hold meta-data about the variable, such as public/protected and can do additional checks to see whether the specified variable should be visible from the current scope."
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clexxk | - How do ice machines make crunchy ice? | Engineering | explainlikeimfive | {
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"If you’re referring g to “sonic ice” when I worked at Jimmy Johns we had a similar machine instead of the classic mold , cold, dump style it poured water thru a super cold short metal tube and it froze. So instead of ice ever so much time it was continuous. The quick freeze creates the cracks that is common in them"
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clfcvc | How is concrete poured for roads with steep inclines? Wouldn’t it all just run down hill? | Engineering | explainlikeimfive | {
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"Concrete can be mixed to various consistencies, there isn't just one recipe. Concrete mixes have a variable called \"slump\": Imagine filling a traffic cone with wet concrete, then lifting the cone away to see how far that cone of wet concrete collapses under its own weight. Stiffer concrete falls less, or has a lower \"slump\", while runnier concrete collapses more and has greater \"slump\". Specific jobs work best if the concrete is mixed to a specific slump. For paving hillside roads, they just order a mix with slump that's low enough that the concrete won't wander off before it sets up.",
"concrete on an incline uses techniques like using less water (so it's thicker to start with), rebar (metal bars driven into the ground) with the concrete poured over it, framing (like a wooden frame to form the sides), and metal latticework that is laid inside the concrete as it's being poured. all of these things help support the concrete, as it sets and after."
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cljm13 | How do phones know which side is up? | I.e: when you flip your phone 180 degrees how does it know to rotate your screen? | Engineering | explainlikeimfive | {
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"They have a special chip that has a tiny moving silicon piece inside (like a spring). The silicon piece has a special shape such that it jiggles only when the phone is moved back and forth in one direction. When that happens, it allows electric current to flow and let the phone know that its moving in that direction. They combine several of these chips to determine how a phone is rotating.",
"They contain a device called a 3-axis accelerometer, which detects acceleration in any direction. Since gravity produces a constant acceleration of approximately 9.8 m/s/s downward, the phone looks for that acceleration and determines where 'down' is. Up is of course the other direction.",
"What biggsteve said. The 3-axis accelerometer is a flat-out marvelous gadget that militaries would have killed for thirty years ago: a single solid-state chip smaller than your little fingernail with no moving parts. [ URL_0 ]( URL_0 )"
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cll2p8 | How does a self-sharpening blade sharpens itself? | Engineering | explainlikeimfive | {
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"Self-sharpening blades have a metal strip along the entire length of the cutter. When the cutter moves through the thing you're cutting, that metal strip is rubbed against the cutter and sharpens. If you're cutting something like paper, it'll work really well. There's some debate whether or not this kind of thing actually works or if it's just a marketing gimmick. There's some evidence for both sides of the argument, so really take it with a grain of salt. It's generally going to be better to just sharpen your blades from time to time."
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clnuws | Does an empty fridge use more energy? | So I'm staying at a friend's has his fridge filled with books. I was pretty curious so I asked why and he said because a filled fridge has less air circulating around so it uses less energy. At first it made sense but I guess not entirely(?)so I went online to search and all answers say pretty much no. But let's say we are talking about modern fridges, could my friend be right? Edit: I don't mean HIS fridge is completely empty, it's just for the formulation of the question. | Engineering | explainlikeimfive | {
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"When you open a fridge you let out the cold air and let in the warm air. Now your fridge needs to extract the heat. If your fridge is empty you will let in a lot of warm air. If it is half filled with books you will let in less warm air so the fridge has less heat to extract and so is less expensive Your friend is correct",
"Something dense like a book, has a lot of thermal mass, and the fridge has to remove all the heat from it before you see any savings from the book taking up space, so that less warm air is let in when you open and close the door. he would be better off filling the space with empty plastic containers. If he is adding and removing books as he fills or empties his fridge, he is wasting energy, not saving. But, if he rarely uses it, and just keeps the same books in there all the time, he might be saving a few pennies a day."
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clrln5 | How are very large construction materials transported? | This thought began with transportation of street light poles and football stadium lights, but this question extends to any of the large materials used in buildings. For example, a long metal pipe or pole used for structural integrity, or a glass window spanning one whole wall of a building floor. How are those transported places? The point here is that those materials are too large even for a conventional truck. | Engineering | explainlikeimfive | {
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"ELI5: We don't transport the big stuff. We make them by gluing small pieces together! First of all, we do not transport huge materials (not usually). That would be expensive. Those glass walls you see are made with a group of small pieces. The reinforcement that goes in the structure are usually made out of 12m long bars. For the large construction materials, we use specific trucks or even helicopters. But as I said, that's not usual! That is for very specific kinds or constructions"
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clyg3h | Why do rechargeable batteries deteriorate over time? | Engineering | explainlikeimfive | {
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"When using a battery, bits of one end dissolve and travel to the other end (or in most household batteries, from the inside to the outside). Recharging forces them back using an electric current, but they’ll never go back as cleanly as they first started. Over time the electrodes continue to deteriorate, and the battery becomes less effective. If something goes wrong (e.g. you try to recharge a non-rechargeable battery, or the control for a lithium battery breaks) it’s possible for the material being deposited to form a thin connection to the other side. This shorts out the battery, creating a lot of heat, and probably causing it to explode.",
"It's like everything in life, nothing lasts forever. In simple terms, batteries are said to \"age\", just like everything ages. The compounds that make up the battery, the chemicals, deteriorate, become different compounds, and are no longer able to charge and discharge cleanly. So, over time, the compounds no longer work, and the battery stops working like in the beginning."
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clym6j | the process of using electricity to create cold air (e.g AC, fridge, freezer) | Engineering | explainlikeimfive | {
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"You can't create cold, you can only move heat. So a pump compresses a gas and compression causes it to heat up. That heat is put into the external environment through coils exposed to the air. When gasses expand, they basically cool, so you expand that gas inside tubes an insulated area, the refrigerator box. Basically you're taking heat out of that space into the gas. But, you always have to give up that heat to the environment or you won't have a refrigerator. It's a way transferring heat through compression and expansion, using a pump, which uses electricity.",
"The electricity doesn’t creat the cold air as such. The electricity powers the compressor that’s at the back of a fridge or freezer that pumps Freon which is a refrigerant, so basically coolant. It takes the warmth from the inside and disperse it it through the pipes at the back of the fridge or freezer. That’s why the pipes at the back are warm (my basic understanding anyway), if you have a fridge or freezer in your room, you may here it “click” when it turns on and hums. Hope that helps."
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clymlg | How does G-suit work? | Does it hold your blood in place by pressing on your body or what? | Engineering | explainlikeimfive | {
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"Yep. When a person is subject to extreme g-forces, the big problem is that the blood pools in their legs. The force of gravity pulls the blood downwards and prevents it from circulating up. It also works in reverse, because an outside turn can cause the blood to rush to the head, but this is less common. The G-suit has air bladders that inflate to basically pinch your blood vessels. That prevents the blood from moving into the legs, so that blood above the waist stays there."
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cm26p3 | What is the purpose of bed supports/platform frames? Why not just have the box spring and mattress by themselves? | Engineering | explainlikeimfive | {
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"Bed frames are often just to get the bed off the ground and for decorative looks. Depending on the type of mattress, you may or may not need or want a box spring, and the support from a bed frame may be perfectly fine. A solid bed frame can often take the place of a box spring in many mattresses. However, a box spring also raises the bed a bit higher, which some people like, again often for decorative reasons.",
"Having the bed elevated makes it easier to get in and out of bed when you're older, and also the height differential and headboard are useful for sex"
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cm3ybk | How do ballistics labs trace a bullet to a specific gun? | Engineering | explainlikeimfive | {
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"When you discharge a firearm, it does a lot of things to the **cartridge** to shoot the **bullet**. First, the **cartridge** is made of 4 main parts: 1. The **case**, which is the brass part that is ejected after you shoot it. 2. The **primer**, a very sensitive explosive that goes off when you hit it hard enough. 3. The **powder**, a less-sensitive explosive that provides most of the energy to move the bullet. 4. The **bullet**, the part that is actually shot out of the firearm and strikes the target. Each firearm, even those of the same model, is slightly different. Just like how you can tell which typewriter a document was typed on based on how each letter is worn down, you can tell which firearm a shot came from by looking at how it affects the various parts of the **cartridge**. When you pull the trigger, many things happen. First, the **firing pin** in the firearm strikes the **primer**. This puts a little dimple into the **primer** and triggers it. Now the **firing pin** is aligned slightly differently and worn down differently in each firearm. Even the springs get weaker over time. By test-firing a **cartridge** in a suspect firearm, you can see how it strikes the **primer** and compare how similar it looks. Next, the **powder** ignites. There are many different kinds of powder with different properties. It doesn't all burn up when you discharge a firearm- some is left inside the firearm, and some might be left on anything near the **muzzle** when the **bullet** leaves the **barrel**. By comparing the powder residue found on-scene with any that might be in the firearm, you might be able to make a comparison. When the **powder** ignites, it makes the **case** expand. Again, every firearm's internals- in this case the **chamber**, which holds the **cartridge** when it's being fired- is unique. Brass, the materials most **cases** are made of, is a great material because it stretches to fill the **chamber** when you fire the **cartridge**. Since each **chamber** is different, with unique dimensions, microscopic marks, and other tell-tale signs, by comparing a test-fired **cartridge** with any empty **case** found on scene will give you a great comparison. After the **powder** ignites, it produces hot, expanding gas that pushes the **bullet** down the **barrel**. Now, most **bullets** are slightly larger than the internal diameter of the **barrel**. This is so that when they are fired, they get squished into the **barrel** to form a tight gas seal. Now many things happen here, both to the **barrel** and the **bullet**. First, the **bullet** is squished into the **barrel**. Most **barrels** that fire **bullets** will have spiraling grooves cut into the inside, to make the **bullet** spin as it travels- this is called **rifling**. Each **barrel** is once again unique and has slight differences in **rifling**, which leaves a slightly different pattern of scratch marks on the **bullet**. Again by firing a test shot, you can recover a test **bullet** and see if the marks made match up to what you recovered from the scene. As the **bullet** travels down the **barrel**, it's going at a ridiculously high speed. Some amount of material from the **bullet** might rub off on the inside of the **barrel**. You can compare any residue found with the **bullet** recovered from the scene, though that usually doesn't tell you much. Now the **bullet** leaves the **muzzle** and travels to its target. By examining the **bullet** itself that you recovered from the scene, you can usually determine what **caliber** it was and what type of **bullet**. If you find a box of the same ammunition at the suspect's home or where you found the firearm, it's circumstantial evidence but could help point you in the right direction. Now the **case** is ejected from the firearm. This is done by a special part called the **extractor**. Depending on the design, it can leave a noticeable mark on the **case**. Again, the **extractor** differs slightly between all firearms due to design, tolerance, and wear and tear. By retrieving a **case** from the scene of the crime and comparing it to test-fired ones, you can make a pretty good comparison. The **case** itself contains a ton of information- usually the type of **cartridge**, and the manufacturer. Even if it doesn't have any of this data, police can compare it to a long list of known **cartridges** to determine what it originally was. Now if you find a box of that exact type of ammunition at the suspect's place or where you found the suspect firearm, you might consider that suspicious. Finally, the basics! Rarely you'll find fingerprints on a **case** that match fingerprints on the firearm.",
"Rifling is the spinning groves the make a bullet spin and increase accuracy. This rifling makes a unique set of marks on a bullet as it passes sown the barrel.",
"Each barrel has unique filing patterns from the tools used in it's creation. These patterns are similar to fingerprints, as there are no two that are exactly alike. When a bullet is fired, the projectile expands and fills in the grooves of the barrel. These markings are left on the projectile and can be compared to another round fired by the ballistics team under a microscope to see if the grooves line up"
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cm4mpz | What do water towers do? | Engineering | explainlikeimfive | {
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"Store water & create some pressure in the pipes (because of the height the water is stored at).",
"The point is so you don't have to turn on a pump every time someone in your city turns on a faucet. You pump a whole bunch of water up high using a large, efficient pump, and then you let gravity trickle it down to all the faucets in all the houses. It's the same principle as the tank in an air compressor. The compressor fills the tank with pressurized air, and then you can use a little at a time for your air tools or painting or whatever."
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cm8jme | How are underwater tunnels for cars reinforced to make them safe from the incredible water pressure above and more importantly how are the monitored to ensure they aren’t weakening? | Engineering | explainlikeimfive | {
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"Most underwater tunnels are not actually in the water, they are dug a good distance under the seabed. The Channel Tunnel between the UK and France is about 40m under the seabed, so the earth above it helps absorb the water pressure. Laying a tunnel on the sea floor would be very risky as any small leak would cause the tunnel to flood."
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cma4tu | What would happen if I used diesel fuel in gas engine or the other way round? | Engineering | explainlikeimfive | {
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"Diesel fuel relies on compression for ignition, hence why diesel engines don't have spark plugs. If you put diesel into your car it wouldn't run. It's basically a thin oil rather than being volatile enough to run the gasoline engine. I was a mechanic and had a lady put diesel in her car. It just stopped running and was towed in. Drained it out, added gas and it ran. Roughly at first, but then it was fine.",
"Modern diesel engines rely on the fuel to lubricate the fuel injectors and the pumps. Adding gas to a modern diesel engine will result in thousands of dollars worth of damage to high pressure fuel pumps and fuel injectors. The pump will almost certainly shell out sending bits of metal to the injectors destroying them."
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cme90c | Why do some trains make a loud “violin-like” sound when they accelerate and decelerate? | Engineering | explainlikeimfive | {
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"That's an electrically powered train with AC induction motors. These motors can produce huge amounts of torque at low rotating speeds. One side effect is that the high currents they use to do this alternate in a speed that's low enough that humans can fear it. You're hearing the harmonics caused by starting current in the motors vibrating other metal objects near the motors. As the train goes faster the currents go down and the rolling noise drowns out the motor whir."
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cmito3 | Why does it feel like shower water pass from too cold to way too hot when you move the dial 1 micrometer? | Engineering | explainlikeimfive | {
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"This is entirely personal based on your setup. It depends on what kind of mixer and handles you have. Longer handles will have the outside move farther per every degree of rotation. Moving a 3 inch handle one inch will be under 30 degrees, but moving a one inch handle one inch will be over 45. Also some mixers do adjust very coarsely, with big changes in output temperature for smaller input (handle) changes. Some have two handles where you adjust the flow of hit and cold separately. Some only let you control both with one handle, which is obviously harder to fine tune. In some the entire range of temperatures is traversed in only like 60 degrees, while in others it goes the full 360.this is up to he specific construction you have",
"The human body is pretty sensitive to temperature changes and it's a pretty narrow range of degrees to go from \"cold\" to \"acceptable\" to \"hot\" and as other users have pointed out, tap valves don't have good mixing valves. In Fahrenheit, the human body is 98.6. If I set my hot tub to 97 degrees, it feels cool to me. I generally set it to 102 degrees which is \"warm\" (to me), but if it gets to 104 it's \"hot\" and 106 is unbearable to get into. A four degree change is all it takes and water can be anywhere from around 55 degrees (direct from tap) to almost 130 (based my tap and using a meat thermometer). Combined with what other users have said about shitty tap valves and the ability to mix cold and hot water streams, this is why it's so difficult to get \"just right\". Probably not the most scientific explanation (and yes, obligatory bragging about having a hot tub), but trying to ELI5."
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cmtp28 | Why do steering wheels automatically recenter themselves if you stop holding them during a turn? | Engineering | explainlikeimfive | {
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"It's actually caused by the caster angle of the front wheels. When you turn the car is actually lifted a bit higher due to the geometry of the steering system. When you release the wheel, the weight of the car wants to force the wheel back to straight. This is also helped along by something called trail. The point of contact of the tire to the road is behind the axis on which the wheel itself turns. This means that as the car is moving, the wheel is being pulled straight by the motion of the car."
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cn5co2 | How do smartphones measure remaining battery capacity? | Engineering | explainlikeimfive | {
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"2 main ways. A battery is like an inflated balloon. You can pump it up with air to inflate it. Then, you can release that air and use the air pressure to do some work—say, blow out a candle. If you inflate the balloon all the way, the force of the air that comes out is high. If you inflate it halfway, the force is weaker. So you could measure how inflated a balloon is by measuring the pressure of the air as it comes out. *Voltage* is what we call pressure when it's electricity. Voltage is electric pressure. The voltage at the battery terminal is higher when the battery is more charged for the same reason the air pressure is higher in a more well-inflated balloon. There are more electrons pushing into each other trying to get out. The other way you could measure the remaining air in the balloon is to count how much air came out. If you put 10 breaths worth in there, and it takes 1 breath's worth to blow out a candle, and you used the balloon to blow out 5 candles—youve got 5 breaths worth remaining. *Coulombs* are what we call breaths when it's electricity. Coulombs are a measurement of electrical charge. At a given voltage, they can do a specific amount of work in a circuit. Some battery systems count coulombs by keeping track of how much work was done. This way is harder to do, but can be more accurate than measuring voltage.",
"It's one of the sensors. Perhaps the most interesting one: It is a micro electro-mechanical Ouija board. The planchette is chemically carved out of silicon, much in the way the tuning fork in an accelerometer is fabricated."
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cn8rwc | What produces noise in an MRI? | I got an MRI today. I had read that the noise during the process is quite substantial but even with hearing protection on, it was so loud I couldn’t even think straight! I know the ELI5 version of how an MRI works but why is it this loud? | Engineering | explainlikeimfive | {
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"In an MRI machine there is a VERY strong magnetic field and a set of coil. There you have the same component in a speaker so when an electric curreent go though the coils a force is applied on them and they vibrate. Which make noise.",
"The MRI machine uses very strong magnetic pulses. The pulses cause little reflections from the conductive bits inside your body, that's what the scanner records during the magnet's \"off\" time. All well and good, silent in theory, however, the machines themselves are made of conductive things. Strong magnetic fields can create forces inside a metal, even a non-magnetic one like copper. Those forces press and flex the metal parts of the machine in different directions, At high enough force levels, everything metal can shift a tiny bit, just enough that when the magnet snaps off it vibrates, like a wine glass it you pluck the rim. Combine all those sounds, and you're not thinking \"harmonious melody\" you're thinking \"noisy machine\"."
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cnfakk | why do electric car engines accelerate faster than gasoline car engines? | Engineering | explainlikeimfive | {
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"In a nutshell: Gasoline cars use a combustion engine to turn a transmission, and the engine has to “spin up” in a sense. Electric Vehicles typically (not all) use a battery to power an electric transmission which is designed to turn as soon as it’s given power, so there’s no engine lag.",
"The faster an internal combustion engine spins the faster it combusts gas and the more power it makes but it takes a bit to get the engine spinning that fast and their is a comparatively low range of how fast it can spin so it has to shift gears a lot to stay in this power range. An electric engine produces full power right off the bat and it has a much higher range of how fast it can spin so not as much or no shifting gears which wastes less time and energy.",
"Odd; all the answers so far miss the answer. Gasoline engines have relatively low torque but all sorts of horsepower. Because they work by triggering a series of explosions in a row to turn a shaft, an ICE car needs to turn that shaft at high RPM and low gear in order to get the mass of the car moving. Once momentum is high enough, the car shifts, and the same amount of force is applied to the new momentum. With electric motors, the force on the shaft is more direct, which means more torque. Because of this, the force/torque of the electric motor can overcome the car's (lack of) momentum without the gear shifts. The electric motors just push until the car speeds up, spinning faster as they are able, with the energy that isn't able to be expended as motion being expended as waste heat.",
"Because of the way an internal combustion engine produces power, the amount of torque (rotational force) it produces starts off low, peaks somewhere in the middle of the RPM range, and then falls back down. Electric motors on the other hand can produce their maximum torque immediately. The torque still drops as you spin the motor faster though. That higher torque means you accelerate much faster at the start. Even at their least efficient, electric motors can often out-perform internal combustion engines in terms of torque. [ URL_0 ]( URL_0 )"
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cnfgyl | Why do toilet paper manufacturers make the paper so that you need to fold it so many times instead of having one proper square that can handle a regular wipe? | Engineering | explainlikeimfive | {
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"Toilet paper needs to break down quickly in the sewer system; thick toilet paper would be too durable and would not only clog your toilet, but the whole system. It's a problem we instead now have with \"wet wipes\" doing all of what I just said.",
"Sometimes its runny and you need a lot of squares sometimes it's barely left a trace at all and you need one or two. If they made them more heavy duty it would mean all those times where you just needed a little you would still be using a lot."
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cnkp4j | Why is it such an issue if Google has information on everyone? | Engineering | explainlikeimfive | {
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"The thing is not really what they do. The thing is what they *could* do. As long as they ju just manage to figure out that you are one of the guys in their early 30's who live in Chicago and happen to be shopping around for a new car - and make a local Mercedes dealer pay them $.30 for showing an ad on your screen - it's not that much of a deal. But what if they figure out exactly who you are? And figure out who your dad is? And figure out that he has a chronic illness? That you have a 80% risk of also getting trouble with in your 40's? And sell that information to an insurance company just as you are shopping around for life- or health-insurances? Figuring out who you are is often not that difficult either, considering how you probably already told them. If you have an android phone. Or use gmail. Or Google Chrome. I'm sure this is a thin line they are trying to walk consciously and all that. But...you know. What if they overstep? What if they figure something out that is really none of their business? And what if they find a way to sell that information? You have to remember that selling information, that is a huge part of their business. It's not that worrying when they sell the help with showing ads for people who actually want similar ads. But...you know. If you are a bit keen on conspiracies, you tend to ask yourself if they really stop there.",
"The rabbit hole goes way deeper than Aldis vs Walmart. With all the information they mold the way you think by steering your ideas. Check the netflix documentary for starters. We are being manipulated every second online.",
"It's not just about someone knowing stuff about you, it's enabling manipulative people to abuse that information. From an older post of mine: In a world where corporations have all the information they want about anyone, there are endless ways to increase the money made form selling you things. Examples, ordered by creepiness: Every 4 weeks right on time you need to buy new wet wipes. Seller recognizes that and ups the prices for you alone when that time comes. You are looking for pink paint in smaller amounts but your profile says your a dude and your engaged. With that they will probably conclude you are about to have a kid and will conveniently show you ads for a bulk sale on diapers. You buy a book on Amazon titled \"How to deal with addiction\" in ebook format. You are repeatedly looking at page 36 - 59, which contains the chapter about how to deal with nicotine addiction. You close the ebook app and open Google. Before even typing anything, it suggests you \"numex nicotine patchers sale\". End of quote. You see how a person can be manipulated by just knowing stuff about them? Imagine what decisions got taken away from you when you thought YOU were in control. Tell your parents that."
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cnnwts | - why do small electrical appliances (beard trimmers, razors, toothbrushes, phones) use so many different types of connectors? | I understand that there are different plugs/transformers to take into account voltages, amps or whatever (I'm bluffing because I don't really understand that either) but surely life would be simpler if I could just use one USB charger for everything? And wouldn't having a simple USB socket on everything work out cheaper for manufacturers? | Engineering | explainlikeimfive | {
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"theyre not bound by the e waste management ruling that forced phones onto the same standard the law basically was modified mid 2000 to cut down on miscelaneous chargers as they were causng lrge amounts of ewaste, till then they were even more varied than otherapliances... all the circular charging ones also are generally sized based on voltage to prevent incorecct voltage being used",
"If they used the USB standard for everything, those things would need their transformers to be built into the device. Having the transformer outside the device is a way to reduce size and weight. The proprietary connectors ensure the correct transformer is used. You can think of a transformer as a set of gears on a bike. If you have a big gear at the pedals and a small gear on the wheel, the wheel is going to turn much faster than the pedals and need more strength from your legs to do it (this is good if you want to go fast). If we switch the gears, the opposite happens (this is good for going up hills). If you put the wrong set of \"gears\" on an electrical device, you could burn out the device, or it just wouldn't work in the first place.",
"USB is by definition a 5V supply. Not everything wants to run on 5 V. There are a lot of 12V and higher devices."
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cnw47p | Why does sloping armour increase its thickness? | on tanks and armoured vehicles there is this thing called sloped armour where the armour plate is at an angle. So when a shell hits it, its less likely to penetrate the armour than if the plate was at 90 degrees. I know that there is a formula for it. But how does it exactly work? | Engineering | explainlikeimfive | {
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"There are a couple factors at play here First is the apparent thickness. The round wants to punch straight through the armor. It can't really make the 45 degree turn it would need to to punch through in the short direction. The result is that a round hitting [this armor straight on]( URL_0 ) would have to punch through the 200 mm of steel to get to the passenger compartment, but the tank only has to haul around the 100 mm layer which gives it far better armor for the same weight. Short of magically transforming all of its momentum, a round headed straight at that tank can't take the short route. The second is ricochet chance. If the shell hits the armor dead straight on then its not going anywhere but into the armor, but if it hits the armor at an angle it can bounce off into the sunset leaving the tank relatively unscathed. If you have a nice pointy round that flies well and looks like a traditional rifle bullet then you have a very narrow window where the round will punch into the armor rather than bounce off, you really want a blunted tip that'll dig into the armor which is why many rounds had [ballistic caps over the tip to make them fly well but a blunt end underneath]( URL_1 ). The blunt end underneath will also tend to catch in the armor and rotates the shell up so its facing a bit closer to that 100 mm line in the above picture, this is called normalization and reduces the effectiveness of sloped armor. Source - a bit too much /r/warthunder",
"When a bullet hits a perpendicular surface, the full force of the object is put directly into the object. When it hits a slopes object, some of the force is translated in the direction of the slope so there is less force going directly into the surface."
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cnyt59 | How do people pick locks with hairpins? | Engineering | explainlikeimfive | {
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"Hair pins are actually pretty large and many locks are two small to fit them. With that house keeping out of the way... You might be able to open some (read very few) locks by raking with a hair pin. Raking means quickly moving a jagged object over the pins in the lock in hopes of getting them to set. Otherwise, if you have a large enough keyway and the right shape hair pin you might be able to set the pins individually like you would in a traditional pick. There hair pin pick is likely a Hollywood/et. Al creation. You can check out the lock picking lawyer on YouTube for more information than you could ever want on locks."
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co6k1g | - Why are rechargeable AA batteries 1.2 Volts while the non rechargeable ones are 1.5 Volts? | Engineering | explainlikeimfive | {
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"The voltage depends on the chemistry of the device in that form factor. Some types of rechargeable AAs deliver as much as 1.48 volts; others max out at 1.25. Anything below 1.25 on a fresh cell is considered out of spec. As the anode gets further corrupted from recharge cycles, the efficiency of the battery will degrade further, affecting both voltage and amperage."
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co8rf3 | Why are there large tanker trucks that spray water all over at construction sites, what do they actually do? | Engineering | explainlikeimfive | {
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"They spray water all over the site to keep the dust down! It's only a light misting. Not enough to make it all muddy.",
"Those are water trucks. They are spraying water onto the dirt. When dirt gets dry, it gets dusty. When the wind blows, the dust goes all over the place, and then people call the city and complain. If you keep the dirt wet, you don't have dust problems."
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coiu85 | Why did early planes have more wheels in the front and now most wheels are in the back? | WW I and WW II planes had two wheels up near the wings and a single wheel by the tail. Now, commercial and military planes have most of the tires in the middle of the plane with fewer up near the cockpit. What was the rationale for both and why did we change it? | Engineering | explainlikeimfive | {
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"Lots of reasons. It was not practical at all for the pilots but it was very practical for the designers. The shape of a low wing airplane lends itself well to a taildragger configuration. The wings are natural mounting points for retractable landing gear (needed if you want better range and speed, incredibly important in a fighter). The nose and tail have to be proportioned such that you can fit a massive heavy engine up front (not to mention machine guns, ammo, and fuel) and still have an aircraft which is either slightly nose heavy or neutrally balanced about the center of lift at the wing. This meant you tended to need a long tail sticking far out. Adding a little weight to the tail in the form of a tail wheel helped add a little ballast to the aft end of the aircraft, and prevented you from adding EVEN MORE weight up front in the form of a nose gear. Excessive nose weight causes constant elevator up trim to be required for forward flight, which causes extra drag. Excessive tail weight causes a positive feedback loop in the controls that can make an aircraft stall uncontrollably (there is a saying that “nose heavy airplanes fly poorly, tail heavy airplanes fly once!”) This was a huge pain for pilots, and still is. Taildraggers are their own separate type certification for pilots. The steering is not nicely linear like you are used to in a front steering vehicle, small steering inputs can get very high rates of turn, and it’s not uncommon for a beginning pilot to experience a “ground loop”, where you spontaneously do a spin on the ground while taxing. Visibility is also severely impacted. Most taildraggers don’t have visibility of the runway on takeoff, you are looking out the sides of the aircraft to judge your distance against centerline. Eventually you get enough airflow over the elevator to purposefully lift the tail wheel off the ground, switching you to steering with the rudder airfoil and leveling the aircraft for visibility and angle of attack management at takeoff. Landing is equally blind. There was a time late in the war when Germany had exhausted its supply of trained pilots, and the fresh pilots were experiencing higher casualty rates from landings/takeoffs of tail dragger aircraft than from actual combat! Edit: forgive me, i completely neglected the second half of the question. Modern aircraft evolved different propulsion methods, namely 'jet' type aircraft, which have engines either wing or tail mounted. This alleviated the above design constraints. You also can go out of your way to make a tricycle gear aircraft ANYWAY, just because of its inherent benefits. Obviously taildraggers still exist but they are so much less practical that modern aircraft design just pushed away from those initial concepts for quality of life and practical reasons.",
"Nosewheels vs taildraggers evolved differently due to advantages and disadvantages in form and function. Control, landing/takeoff, and propeller length/clearance are some factors. Check out this link from FlightSim: URL_0"
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colchq | Do you have to tune brass/woodwind instruments? If so, how and why? | Engineering | explainlikeimfive | {
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"Yes. In the case of brass instruments this is usually done by slightly varying the length of the tubes within the instrument to keep it producing the proper notes. This is necessary because there is no single perfect configuration of the instrument that will keep it tuned in every circumstance. Suppose for example your band moves from a room temperature practice room to play outside at a Christmas parade. The air temperature is drastically different, the brass instruments change temperature and resonate differently, etc. You need to retune or everyone will sound bad (except the trombone master race, playing is tuning).",
"Yes, using a saxophone as an example, you tune it every time you play by adjusting the position of the mouthpiece which alters (shortens/lengthens) the length of the airway and thereby adjusts the pitch. Most woodwind instruments have similar methodologies, brass instruments tend to have an adjustable portion of their body (called a slide if memory serves) to perform this function. Tuning is required every time you play because of many factors - how you assemble your instrument, the humidity, temperature and atmospheric pressure of where you are and likely more that I can't think of atm.",
"A flute is tuned a few different ways. One is by embouchure: rolling the flute slightly in or out changes the pitch. Another is to pull the head joint in or out from the body. A third is to unscrew the cap at the tip of the head joint, turn the head joint so the lip plate faces away from you, and stick the end of the cleaning stick in--there is a line on the stick that should be perfectly centered. If it isn't you push on it with the stick from either inside or inside where the cap was to center it."
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cowos9 | Why aren't motorcycle-style engines (small displacement, high RPM, high HP) used in small sports cars like hot hatches? | Engineering | explainlikeimfive | {
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"Because motorcycle engines are: A: generally too fragile for what’s needed for a heavier vehicle B: very low torque for a heavier vehicle. Example, a Hayabusa can have over 160hp, but only puts out around 97 ft lbs of torque. C: they’re really not that high horsepower. Even at 160hp, that’s nothing for a car. My base model 2012 Focus had 160hp. Bikes are super fast with that much power though because of the power to weight ratio."
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coxctc | How do luxury cars have better shock absorption than ordinary cars? What prevents the passengers from feeling the shocks from crappy roads? | Engineering | explainlikeimfive | {
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"The shock absorbers have 2 main parts: the spring and the damper. The spring's job is to convert the strong hits of the road into a soft motion, while the damper's job is to stop the spring from ringing the car up and down like a carnival ride. The damper also has 2 parts: a chamber and a piston that moves inside the chamber. The way it slows down the shocks is that that there is oil in the damper and also there are holes on the piston. When the car hits a bump for example, the piston wants to move inside the chamber, this motion compresses the oil and pushes it through the holes on the chamber. So all that energy that the springs have and makes the bouncing motion, goes through the damper where it gets used up by the piston moving through the oil. The quality of the shock absorption depends on several things: - The shape, material and number of turns of the spring - The oil's thickness/viscosity - The shape, size and number of the holes on the damper's piston - A few other, less relevant things All these things influence the way it absorbs the shocks, manufacturers have to find the \"golden middle road\" for the optimal absorption. Cheaper cars get less optimal shock absorbers, while luxury cars of course get the better ones.",
"Adding up to the other answer: Modern luxury cars have road surface scanners in the front and electronically adapt the dampers, making them harder or softer depending on the surface of the road. You can actually see them in some cars in the grill. Mostly I see them on luxury Mercedes and new Audi A6 / A8 models, but I‘m from germany so those cars are also very popular.. You can probably google Magic Body Control, which is the name of the Mercedes technology as far as I just found out."
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cozg1v | When a fire occurs and the fire department taps into a fire hydrant, does the water pressure in surrounding buildings drop? | Engineering | explainlikeimfive | {
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"It really depends on where they draw the water from. In a big city, most buildings have their own water tanks/pumps, so they won't be affected. In more suburban or rural areas, it depends on the local infrastructure and if the system is built to handle that kind of flow.",
"In my city, fire hydrants are fed from water towers. Drinking water is supplied with pumps from a pumping station. The systems are not connected.",
"Yes it drops thought the system. If the engine draws more volume then the pipe/Hydrant can provide from the internal pumping pressure if the system. The engine can draw water itself and actually cause vacuum at other open sources. Aka you open you faucet next door to said fire and get nothing but air because the pump next door is now literally sucking the water from your pipe now that you opened an outlet. They require certain businesses to put backflow preventers on their supply lines to prevent this. Pressure also changes throughout a town based on elevations and where the pumping starting are."
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cp0rqw | Why do engines need to be exercised? | Engineering | explainlikeimfive | {
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"By never running an engine for a long period of time will allow oils and other lubricants to dry out and set in. This will lead to corrosion which will damage the engine and gaskets and other rubber parts to dry out and crack. By running the engine every now and then the engine will be lubricated preventing corrosion and mechanical parts getting stuck etc."
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cp1i0u | How do toilets work? | Engineering | explainlikeimfive | {
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"text": [
"The open bowl part of the toilet that you see is basically one end of a \"U trap\". Imagine instead of a tube running straight out the bottom of the toilet into the sewers it instead goes back and upward a little bit before going back down. This means some water will get trapped in the lower spot which is good because it blocks smells from the sewer from coming up into the room. The second part of the system is a water supply, either a reservoir filled relatively slowly in domestic dwellings or a high flow supply in commercial buildings. Either way when the toilet is flushed a few gallons of water are released all at once and fill the bowl enough to push water over the other side of the U trap and down into the sewer. During this the contents of the bowl are carried along with the rest of the water into the sewer."
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cp1swd | What causes the shower to make that high pitched screech when you turn up the heat a bunch? | Engineering | explainlikeimfive | {
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"text": [
"Bernoullie's principle states that a faster moving fluid is at a lower pressure than a slower moving one, so the speed of the water through the pipes lowers pressure enough for the hot temperatures you're requesting with the shower knob to turn some of the water to steam which is then heard as a screech."
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cp8qjl | What does CC and horsepower actually mean in cars? | Engineering | explainlikeimfive | {
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"CC means cubic centimeters and describes the volume of the engine cylinders. Horsepower is a measure of the rate which work can be done. 1 horsepower means that you can move 550 lbs 1 foot in 1 second. 2 horsepowers would either be 1100 lbs/1 ft/1 second, 550 lbs/2 ft/1 second, 550 lbs/1 ft/0.5 seconds or any combination thereof.",
"Im surprised that nobody has mentioned yet the fact that a power level of 1 **hp** is approximately equivalent to 746 watt (W) or 0.746 kilowatt (kW). If you're into physics, that makes more sense.",
"To expand on CCs, when an engine is, say, 2000 cubic centimeters, that means that each piston \"displaces\" 2000 divided by the number of cylinders it has. So for a 4 cylinder engine, each cylinder would displace 500cc. What displacement means is the volume of the space within the cylinder that the piston moves through. To get that number, you take the bore of the cylinder (the diameter), then use good old pi to figure out the area, then multiply by the stroke of the piston (how far it moves up and down in the cylinder). So each time a piston cycles in our 2000cc four cylinder engine, it displaces 500cc of air, and does this four times a complete engine cycle, for 2000cc of total displacement.",
"As others have pointed out, CC refers to engine displacement. You also commonly see this measured as cubic inches as well as liters. For example, you might see a 1960's Ford Mustang advertised with a \"289.\" This refers to an engine displacing 289 cubic inches. You might also see a later-model Mustang advertised as a 5.0, referring to 5 liters (more or less) of displacement. In short, larger engines displace more volume. As any gear head will tell you, when it comes to performance [there's no replacement for displacement]( URL_0 ).",
"Others have broken down the technicalities of cc and hp, but if you're around car guys, it's shorthand for \"how powerful is your car?\" CC (cubic centimeters, or its American cousin, ci, cubic inches) is almost always directly related to power. The bigger the number, the more powerful your engine. Back in the muscle car days of the late 60s and 70s, you could roughly equate one cubic inch with one horsepower, so a \"Chevy big-block 350\" would make roughly 350 HP. These days you're more likely to hear displacement referred to in liters instead of cc or ci (smaller engines in ATVs or motorcycles will still use cc). There's not much of a direct one-to-one for liters-to-horsepower as current engine technology is much more advanced than the 70s, but it's not uncommon for a 6-liter V-8 engine to make well over 400 HP if it's naturally aspirated (over 700 if it's boosted with turbo or superchargers like a Dodge Hellcat). A Dodge Viper can make about 650 hp with a naturally aspirated 8.4 liter V-10.",
"Horsepower is a measure of \"power\", which is a term in physics that describes doing one job in a period of time. The shorter the time, the more \"powerful\" that machine is. For example, I can carry two buckets of water at the same time, one in each arm. My mom can only carry one bucket, using both hands to hold it. If we need to fill up the same tank with water, I will finish faster because I can carry twice the amount. I will fill up two buckets, and she will only fill up one. After three trips, I filled up 6 buckets, and she was only able to carry 3 buckets in that time. If we need to fill up 10 buckets, and each trip takes 1 minute, I will finish in 5 minutes (5 trips), while she will finish in 10 minutes (10 trips). I was able to do the job faster, in a shorter time, therefore, I have more \"power\". If my mom has a 5 HP engine, I have a 10 HP engine."
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cpcvjq | How are dams and dam walls built? | Engineering | explainlikeimfive | {
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"text": [
"Usually the river is diverted first. A channel is dug around the construction site and a temporary earthen barrier is dumped into the river to push flow into the channel. The dam is then constructed dry. Once complete, the temporary barrier is cleared to allow the original flow path to resume. The temporary channel may be abandoned or filled back in, or it may be kept in place as part of an emergency flood management system."
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cpicaz | how do you dig a large, level, deep hole? | If someone is building an underground car park, for instance, how do they dig a hole that's so large and level? I might need to dig 50m down at some points, 48m at some and 51m at others. How is the depth measured and tracked on a large scale? [Clearly the answer is measure from the centre of the earth.] | Engineering | explainlikeimfive | {
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"Construction surveying, which has been around since antiquity, is the answer. Basically the guys who designed the car park created a surface in a 3D drafting program like Civil 3D. The surveyor goes out with a total station, which is a computerized device used for precisely finding the position and elevation of a given point (it's that thing you sometimes see by the side of the road that looks like a really fancy camera on top of a tripod.) The surface will be loaded into the total station. The surveyor will walk around with his reflector, and at various points he'll get the total station to shoot a signal at the reflector. This tells the surveyor what the ground elevation is at that point. Since the surface is loaded into the station, it'll also tell the surveyor how much material needs to be removed to get to the finished grade. Once the surveyor knows how much cut there is, he puts a wooden stake in the ground and writes Cut on it, and how much cut. Like C0.5 means cut of 0.5 m to finished grade. The operators will then come in and excavate, and then they'll level the pad, and the surveyor will come in again to check and make sure they're at the right elevation before they start pouring concrete. As for how they know they're at the right elevation? They calibrate the total station to a point of a known elevation, which is called a survey monument. You've likely seen them in the sidewalk. There's usually a metal lid about 200 mm in diameter that says \"Survey Monument\" on top.",
"Well, a car park is not level, by design. Has to be sloped for drainage, and a parking garage is sloped a lot to provide a ramp to other levels. And very few applications are large and precise enough to require accounting for the curvature of the planet, and most of those are on the surface (e.g. runways). There are tunnel boring machines which use a laser running the length of the machine to tell if they're drifting off target. As for measuring large distances accurately, you use a total station theodolite, and trigonometry."
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cpicoc | What physical properties of a hard drive allow it to have a certain amount of digital storage? | Engineering | explainlikeimfive | {
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"At its base, data is still written in bits. 0's and 1's. String 8 bits together and you have a byte. That's the same kilobyte, megabyte, and gigabytes that we use to measure how much data something uses. You'd probably be able to write a few hundred bytes on a letter page. To fit more data, you either make the lines smaller, or add more pages. That still applies to hard drives today. The concentric rings on a hard drive are still basically 0's and 1's written down in lines, but instead of paper, ink, and text, a hard drive will read and write magnetic 0's and 1's on microscopic lines on rotating disks. Hard drive capacity depends on how small those lines are (which is why drive capacity has increased over the years as tech gets better) and how many disks are in the specific hard drive. The latter is why specific lines are different product lines have multiple capacities, but usually a multiple of the lowest capacity. (Like 1, 2, and 4 TB lines)"
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cppwqh | How do they paint mass produced dolls and action figures? Are they just hand painted by lots of people, if not, what kind of machines do the painting? | Engineering | explainlikeimfive | {
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"Fine details get stamped on by a tampo printer, which uses a silicone dome to stamp paint onto contoured surfaces. Larger areas of color get airbrushed on. A mask (basically a mold of the toy with the areas to be painted cut out) is fitted onto the toy, then it gets airbrushed, either by hand or robot arm. You can see both processes here - airbrushing at 1:20, tampo printing at 2:36 URL_0",
"Depends on what kind of item it is. There are certain machines that will stamp on a color, then the next color, and so on. It's evident in some toys when things don't line up correctly (say, the eye white is in place, but the iris is a little off). More expensive figures, like big anime figures, are typically hand painted with airbrushing and masking tape in pieces, then put together. Some statue figures are painted in one piece."
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cpt4dq | Why are standard drinking cups shaped the way the are, wider on the top and more narrow toward the bottom? | Wouldn’t it make more sense to have the cup be a consistent width throughout? Or, even make the cup wider at the bottom to make it more stable when sitting on a surface? | Engineering | explainlikeimfive | {
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"It’s easier to stack a cup that’s wider at the top than one that’s the same width the whole way up or one that’s wider at the bottom. It also makes it a little easier to drink, but I don’t think that’s as much of a reason as the stacking since just making it wide enough to drink easily the whole way down would also work.",
"Slippery cup + wet hand = dropped beverage. So, cups have this design so that as gravity pulls the drink downward, the flaring taper counteracts that effect keeping it safely in place inside your hand. If the taper went the other direction, as you squeezed your hand tighter, you could actually force the cup through your closing fist (kind of like squeezing a slippery bar of soap and it popping out of your hand. Also, it's WAY easier to store 100 cups if they all fit inside each other, than if they have to be individually placed on the counter. Uniform width, and fat bottomed cups can't stack inside each other. Edit: Typo",
"Cups are made that way so they are easy to release from the molds when they are manufactured. Also, it makes the cups stackable.",
"While some of these reasons are true, the main reason is that stacking the cups takes up less space during transport and storage, saving money for the manufacturer, distributor, and retailer.",
"When molding plastic it helps to have a \"draft\" or an angle, so when you pull the 2 halves of the molding tool apart, they separate easily without rubbing on the part being made, like the Cup. It simplifies the tooling and reduces the amount of time per mold cycle by speeding up the release. It also helps with stackability of the items."
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cpt4ol | Why do cables between pylons have slack in them? | Cables between pylons always dip but surely a lot of money could be saved if they were pulled taut. | Engineering | explainlikeimfive | {
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"One big reason is thermal expansion. Normally this effect is small, but when you’re talking miles of cable, a big change in temperature can make a noticeable impact on the length of a cable. On hot days when there’s a lot of load cables tend to sag a bit more, it’s something utility companies have to monitor to avoid damage. If you made the cable super tight, especially considering most of this kind of maintenance work is usually done in the summer when it’s warm, when the cold causes the cables to shrink in the winter it can lead to damage or snapping. It also makes the cables a bit more resilient in general. If the cable is super tight and something like a heavy branch falls onto it, it’ll snap right off. If it’s got some wiggle room that force is spread out a bit more and the cable might rock or shake but is less likely to snap entirely.",
"They're pulled as taut as they can be. There's a couple reasons for the slack. 1. any cable, no matter how tight you pull it, will have SOME slack, that's just physics. 2. Imagine they were in fact pulled as tight as physically possible without breaking, like guitar strings from pole to pole. This would cause constant stress on the pylons, or telephone poles, or whatever they're strung between, which could lead to bending, breaking, or other structural damage over time (imagine an old guitar neck that's been warped cause it was left strung for years in storage). It's much easier to re string cable, than it would be to repair/replace the pylons themselves. 3. Also, having no slack means there's no wiggle room for unforeseen circumstances. High stormy winds, seismic activity, heavy snowfall, vehicle collisions; any number of things could cause strain on the stretched cables. Without any slack the % of times the cables would snap and detach from the pylons would skyrocket, and you'd have downed live power lines, which are super unsafe. Imagine if every time a car struck a telephone pole, the power lines hanging above snapped and came tumbling down with the collision. If that could be avoided most of the time by introducing a little extra cable between them, seems like a pretty easy choice to make.",
"Any rope or wire of any material that stretches to any amount will have some sag in them. You would need a materai that do not stretch in any way to have a straight wire but not material like that exist. So all wires will have some slack and the amount depend on the length between the pylons and the amount tension and strength of the wire. The strength and mass of the wire is also very important. You also need margins so the force of the wind or even ice that form on the cables will not result in a cable tha So the design is a composite between strength of the materia vs the cost and the cost of the pylons. Use the calculator at [ URL_2 ]( URL_2 ) and 300 feet length, 32 ft/s\\^2 in force perpendicular. With a wire from [ URL_1 ]( URL_0 ) take a 1/4 inch wire with a mass of 0.11lb/ft. If you use the Minimum Breaking Strength of 5480 lb\\_f the sag is 7 feet and you use a extra 0.4 feet wire. If you use more force you cant be sure that it will hold and you haven't margin for wind At Safe Load of 1100 lb\\_f the sag is 35 feet and the wire is 11 feet longer (3%) The number are for steel wires but they are bad conductor. So power lines use Aluminium-conductor steel-reinforced cable that have lower strength compared to mass so you will have more sag. If you add more steel the wire can have less sag but cost more so you optimize cost vs extra cable needed and we get what is used.",
"Cables expand and contract when they get hot/cold, they also are blown on by the wind and have birds land on them. A taut rope is way more likely to snap, so it would cost them more long term in material upkeep than it would to add a foot of slack into the system."
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cpuwxt | Why are Jeeps stopping and starting at every intersection | Engineering | explainlikeimfive | {
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"Fuel economy standards. Car companies face this \"problem\" and that is that governments have regulated that fuel economy standards new cars must produce. Most of these standards are applied based on averages of all cars that the manufacturers make. Some manufacturers have responded by moving more and more models to hybrid drives (such as Toyota). Others have gone even smaller but added turbos left and right, like Honda and Ford. They do some hybrid drives as well, but it's more common to see a civic with an engine under 2L but a turbo added. Other manufacturers have added additional technologies that make the same old engines get better ratings. One of the things that's been done is that the engine shuts itself off rather than idling. Most people notice this at stop lights when the car next to them turns before accelerating away. GM does this and so too does (I think) BMW. To be clear. All manufactures are doing a bit in all of these areas. You can find a ford that has start-stop technology and you can find a GM that has a turbo or a hybrid drive.",
"The new cars turn off when they idle at lights for a period of time. I guess it's supposed to help in fuel efficiency but I would think it just beats on the equipment more. I turn it off when I drive a car that has it",
"This is called a Start-Stop System. Many new vehicles feature these systems to enhance fuel economy. An idling engine is many times just wasting gas, so there's no reason for the engine to be running. When the conditions are right, (Stopped, catalytic converter is hot enough, AC is not running) the car will turn off the engine. As soon as the brake is released, the engine will start back up. Unfortunately, on Jeeps and other FCA vehicles, you cannot permanently disable this feature. Many people don't like the start-stop systems because it causes a small delay if you want to accelerate quickly from a stop. Hybrids don't have this problem as they have electric motors that can move the car without having to start the gas engine. Most hybrids can also run the AC without needing the gas engine, so you still get the start-stop benefit with your AC turned on."
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cpxeg4 | How do Seabracher watercraft keep the engine running without getting flooded with water, even when submerged for short periods of time? | My best guess is a large airbox with a diapraghm and a water trap with a bilge pump? | Engineering | explainlikeimfive | {
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"From their [website]( URL_0 ): > The Seabreacher is only meant to dive just beneath the surface for brief durations. You typically do not go lower than 5-6 feet, and it will also depend on your level of experience as a pilot. Most people are under for about 5-10 seconds at a time, and almost always have a portion of the snorkel above the waterline. ... You also need to consider the snorkel/dorsal fin, which is your air intake for the engine. Diving below snorkel depth will only cause the engine to stall, and then the boat will always pop back to the surface."
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cq0cd1 | how do lights, and light switches work? | Engineering | explainlikeimfive | {
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"There's a circuit that connects the light to the electricity. Basically the light switch breaks that circuit to turn the light off, and reconnects the circuit to turn it back on again",
"Lights have been explained here before, but basically the electrons in the wire excite electrons in the light which vibrate and release light. The switch is just something that either connects or disconnects wires depending upon its position. You can find diagrams of this online, or dissect an old one you have lying around."
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cqc8xm | why are helicopter blades so narrow? My ceiling fan seems to have wider blades and pushes air down. | I recognize there’s a huge difference in scale between these two machines, but would wider helicopter blades help or inhibit lift? | Engineering | explainlikeimfive | {
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"they aren't. maybe you will realize how big they are if you see one up close. also they are not flat at an angle like a fan, they are basically shaped like wings .",
"Your fan can pull air up too if spinning the opposite direction. The big problem is weight and strength. A wider blade weighs more, needing more thrust to achieve lift, more horsepower to spin the blade and the assembly needs to be stronger to hold it all together. That's just one half of it, I am not qualified to speak about aerodynamics.",
"Ceiling fan blades are made for low cost, acceptable performance, and acceptable weight. Weight isn't a big deal when you're mounted to the ceiling. Helicopter blades are made for minimum weight (for flying), optimized performance (for high efficiency flying) and acceptable cost (in a machine that costs $1M). These are two almost completely different trade spaces."
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cqffal | If a solenoid, a relay, and a switch all do essentially the same thing why do they have different names? | Engineering | explainlikeimfive | {
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"They are different things. A solenoid uses electrical power to move a metal object in a limited linear direction. A switch however takes a physical motion and uses it to open or close a circuit. Combine these and you have a relay which is a solenoid that takes electrical power to convert it into physical motion and then a switch to use that physical motion to open or close a different circuit. So a relay consists of both a solenoid and switch. However you might often hear tradesmen mix these terms."
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cqp3ua | What was the big insight that allowed the wright brothers to 'discover' flight? | I know there were hot air baloons before hand, but why did it take so long for people to understand or intuitive things like air speed over the wing, or even wing design? For example I thought Leanordo de Vinci experimented with gliders? & #x200B; Many thnks | Engineering | explainlikeimfive | {
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"There were two major innovations. First, improved engine technology made powered flight realistic. Second, they were able to steer the plane by changing the shape of the wing in flight by using cables. Many of their innovations came about in trying to understand how to control the plane during flight. In history, the question of “why did it take so long” almost never has an answer. We can’t say why a person DIDN’T think of a certain idea. However, there are factors that slowed development until the industrial revolution. Literacy was poor, most people practiced subsistence farming, communication was slow and difficult, educational opportunities were few, and not many people had the financial means to sit around inventing things. The Wright brothers had all the advantages of the industrial revolution (scientific method, improved tools, education, communication, etc) but - most importantly - they had countless examples of things that didn’t work. The Wright brothers spent a huge amount of time looking at failed projects and trying to understand why they failed. A history of failed attempts is precisely what made their success possible!"
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cqtafd | For dishwashers, washing machines, etc: why does ECO washing take longer than the normal one (even 4+ hours)? Shouldn't it be quicker? | Engineering | explainlikeimfive | {
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"Using less water and less water pressure, also usually using cold water. This means that the machine must run longer in order to achieve the same level of cleanliness as a \"normal\" cycle. Go rub some peanut butter on your hands and try to wash it off with cold water that's coming out at a trickle. You'll get it.",
"Heating the water is more expensive than anything in this machines, to save energy they have to run longer but with less warm water",
"Not sure. Not heating up water as much and instead having a longer wash that’s colder that is more efficient but takes longer to do the same job?"
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cqu7i3 | Why do pilots in airplanes have different type of seat belts compared to passengers? | Engineering | explainlikeimfive | {
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"The lap-belt in your passenger seat is designed to keep your butt roughly in the seat during extreme turbulence or worse. But not to keep you from flopping all over. If the plane is getting thrown around violently you will get injuries... just not as severe as if you weren't wearing the belt at all. The pilots have to not only stay in their seat, but their arms and legs have to remain roughly oriented to the controls - won't do to have a severe turblence jolt shove you sideways when your arms are on the controls - the shoulder straps minimize this. Yeah, you could put 3 or 5 pt harnesses on the passenger seats too, but noone would ever wear them properly. Its hard enough to get people to keep on a simple lap belt (ask any attendant), let alone anything more strenuous. And lets face it. If you're ever on a plane where a 3 or 5 pt harness is saving your life, its really the pilot, maintenance and aircraft builders who are gonna save your life at that point.",
"Pilot's need to be able to remain in their seat no matter the situation so they are able to regain or maintain control of the craft. A 5-point harness will hold them in place no matter the orientation of the craft."
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cqyl9n | How do stop lights with on-road weight sensors work, exactly? | How does it know when to change and what to prioritize? I.e. the first car that got to the intersection, left turn arrows first, one side first, etc.. is it on a timer and takes the sensors into account or what? | Engineering | explainlikeimfive | {
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"Well, for one, they often use electromagnetic metal sensors instead of weight. But typically that data is fed to a computer, and different computers are programmed differently. In some cases, for instance, the computer may always keep one direction green, but change when a car is detected."
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cqz1qt | Under sea power cables | If the problem with Solar power is that energy can’t be easily stored why don’t we build big power cables under the sea from areas where there is a lot of sun, ie around the equator, especially the Sahara. My thinking is that we have big communication cables connecting the U.K. and US, why could this not work for power? My initial thoughts are bandwidth/ capacity issues and politics/geopolitics | Engineering | explainlikeimfive | {
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"They do exist already: URL_0 - NorNed is a 580-kilometre long high-voltage direct current submarine power cable between Feda in Norway and the seaport of Eemshaven in the Netherlands. The NorNed cable is a bipolar HVDC link with a voltage of ±450 kV and a capacity of 700 MW URL_3 - The Basslink electricity interconnector is a 370 km 500 MW high-voltage direct current (HVDC) cable linking the electricity grids of the states of Victoria and Tasmania in Australia, crossing Bass Strait, connecting the Loy Yang Power Station, Victoria on the Australian mainland to the George Town substation in northern Tasmania. Others are there and more are being developed: URL_1 and this is the longest one: 3800 km between Australia and Singapore - URL_2",
"It is very inefficient to transmit power over distance. Most power stations are within a few dozen miles of their most consumers. Sending power across entire oceans would be so inefficient that it would be easier to just use other power storage systems (batteries, pumped hydroelectric, flywheels, you-name-it)."
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cri5ue | when a skyscraper is being built, how do they keep the crane on top at all times? | Engineering | explainlikeimfive | {
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"There are three ways cranes can make themself taller. 1. The crane will build itself up grabbing more pieces of itself and placing it on top of itself. Or from the inside it can bring more pieces up like an elevator. 2. The crane sits inside the building or attached to the outside of the build. The crane builds a few floors. And then uses the building to move itself up like and elevator. Than it builds a few more floors and repeats. 3. A helicopter drops the crane on higher floors and/or moves the crane(s) around. There a cool videos on YouTube of this."
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crm6ev | How do they manage to constantly provide hot water to all the rooms in big buildings like hotels? | Engineering | explainlikeimfive | {
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"Finally a question I can answer! Engineer here. Basically, most hotels use industrial size water heaters, at least one large storage tank, and a return pipe. So you have 3 domestic water pipes instead of 2. Cold, hot, and hot return. Pumps constantly circulate the hot water, it is either going to get used, or go back to the tank. The tank is then sized for peak water flow, which would be early morning showers when the hotel is fully booked. So you can have a few hundred gallons of instant hot water available, then during non peak times, the water in the tank is heated. The same types of systems are also used in office buildings, albeit a much smaller scale. A mid or even a high rise office building rarely has showers, and usually only have one or 2 sets of restrooms per floor. Sinks in public bathrooms usually don’t use a lot of hot water. Edit: thanks for the silver! Edit 2: thanks for the gold! Edit 3: a lot of people have been asking if the hot water return is recycled water that has gone down the drain. No, it isn’t, that would be nasty. Return water simply means water that has not been used. If the water does not get used by a faucet, it gets returned to the tank. Once it comes out of a faucet, it’s not going back in.",
"They use recirculating hot water. You can even get this in your house, for the cost of a special pump. The hot water pipes form a loop, and the pump slowly circulates the water through the loop. This means the water gets hot almost instantly, which saves water. A boiler adds heat at the rate that cold water flows into the system, sometimes with a separate water heater stage.",
"It's pretty simple. Bigger buildings = more pipes and bigger heaters. Many places (mainly in Eastern Europe) provide hot water to entire cities, not only big buildings. Heat that would normally be lost during normal power plant operation is used to heat water to \\~40 degrees C. Contrary to what you might think, it's pretty efficient as large pipes don't suffer much from heat loss.",
"It also depends on the country. In my country there are a lot of apartment blocks. So, hot water and heating (also done with hot water) are not produced by the building - instead it is produced by special facilities that each deliver it through underground pipes to a certain area of the city. In winter, in order for the water to be hot when it reaches the building, it needs to leave the facility at super high temperatures.",
"Shorter answer. Hot water is continuously recirculated to the hot water tank for reheating rather than being left to cool off in the pipes. Nicer homes have these recirculation pumps now.",
"I have never seen individual on demand hot water units in hotels. I could see them being used in other countries, but I have never seen them in the USA. It is almost always more efficient to have a central system.",
"Giant industrial water heaters. Often they operate as continuous flow heaters, where the water heats up as it flows through the pipes.",
"I work at a hotel. We have 5 industrial sized heaters for 80ish rooms. If the water isn’t hot; turn up the gas line. Job complete",
"I stay at the same hotel and often in the same room for years now, so I've found fluctuations in the hot water to be fascinating, and had this same thought. There's no doubt hot water is far hotter at night than it is in the morning, when I assume most people are taking showers.",
"Think of it like an electric kettle that you use to boil water in the morning for coffee. There is a small coil that electrify runs through that heats up and heats the water. In a big building that electric coil could be several different things but all serving the same purpose. Could be an oil/gas heater, electric heater, large boiler that uses hot water or steam, but all serve the same purpose to heat up that kettle full of water. Now think of that kettle as being a massive tank. Your water is stored in that tank and heated by a heat source (paragraph above). It uses a thermostat (similar in your home) and when it drops below the set point it will get heat from its heat source. Now that you have a huge tank of water that is always hot you run a pipe that goes to all the taps that require hot water. Add a pump and that water will always be moving. When hot water gets used the tank fills with cold water and gets heated up. The cycle repeats",
"Massive boiler engineering rooms you the hotel room staying public never see because it's usually in the basement. If you wonder about the Air conditioning it's massive chiller plants also located down in the basement. There is a large underground complex under most large hotels that are serviced by maintenance people you are likely never going to see during your stay.",
"Some older buildings have hot water tanks on every floor. Some larger high rises have mechanical areas every few floors and on the top floor to help boost and/or reheat water, when distances from basement would allow water to cool or require considerable pressure. I run a facility where hot water is also re-circulated and stored in 4 reservoir tanks, with 2 dedicated boilers that turn on as soon as temperature starts to drop."
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crmsvi | Why do modern CPUs have more core and not just 1 really big one? | What hinders them from making 1 really big core instead of like 8 normal cores. Is there something in physics stopping them or just cost? It seems like with multiple cores you need programs wich need to utalise multiple cores, wich is not always the case. | Engineering | explainlikeimfive | {
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"Because Pentium 4s proved that was a bad idea. Most instructions in a CPU take more than 1 cycle so rather than waiting for each one to finish before issuing the next, the scheduler will try to fill up all blocks in the core at the same time so it can get more done in parallel(Instruction level parallelism). The more instructions you stack in a row the deeper the \"pipeline\" of the CPU and the better the single core performs, this was the source of most single core processor improvements until the middle of the Pentium 4 era. Part of pipelining is assuming the results of any IF statement you come across. If you guess right then you're several instructions ahead and doing well, if you guess wrong then you need to clear the pipeline and start again, this is a big hit. The longer the pipeline the bigger this hit. Pentium III had just 11 stages in the pipeline, Pentium 4 \"Prescott\" chips topped out at 31. Unfortunately its really hard to predict 31 instructions in advance so longer pipelines became a liability rather than a helper. So how do you move beyond this? What if instead of trying to execute 31 instructions at a time, i have two schedulers running unrelated threads that are keeping all my parts busy? This reduces the hit when one of them gets a branch prediction wrong and lets me keep all the parts busy. Congrats, this is Hyperthreading and provides Thread Level Parallelism Well what if we add another Adder? Maybe another floating point unit? How about another memory module? Well then you've just added another core! One that can work on a completely unrelated task and isn't impacted by bad branch predictions like one massive core would be. This is a multicore processor and provides even better Thread Level Parallelism, and you can slap a second scheduler in each core to hyperthread it for even better performance!",
"The size doesn't matter for the most part. A processor's job is essentially to compare two numbers, the speed of the processor is about how many calculations it can do per second and to some extent how fast the pipeline can feed it with new numbers. For a while, people thought they'd be able to build faster and faster processor cores, but eventually they ran into what's known as \"crosstalk.\" A processor and the pipelines that supply it are basically very tiny wires stacked side-by-side, and when you run too much energy through a wire too fast, it starts to give off electromagnetic interference that messes up the signals from the wires around it. So since it becomes impractical to build a 5+ Ghz processor core, we work around it by stacking multiple cores in a single processor.",
"Software developer here, To add, yes, you need software that can utilize multiple cores. Luckily, you have it in spades: your operating system can schedule processes to run on multiple cores. Back in the day, only one program ran at a time. In the 80s, people ran the DOS operating system on PCs, and there were other computers that had a mere BIOS, that was sort of an operating system, sort of hardware. But DOS is the example I want to talk about - when you ran a program, the operating system basically unloaded itself from the system nearly if not entirely, to make room for the program. When 64 KiB of memory is all you have, you have to be accommodating. Software, then, typically included their own built-in hardware support. Fun times... Then there was this idea that came from the Mainframe era of the 50s, 60s, and 70s. I don't remember when it was invented, but we called it multi-programming, what we call more commonly multi-tasking. Computers were essentially 1 core, though we didn't think about it in those terms, 1 core was the foregone assumption. The OS takes a bit more prominent role, and it lets a program run in the CPU for a time slice, maybe as long as 25 milliseconds, then it switches it out for another program. By switching out programs quickly, you can get the illusion that multiple programs are running at the same time. It's funny to me to think about how moving the mouse generated an interrupt, which stopped your program long enough to update the screen buffer to draw the damn thing in it's new position, that wiggling the mouse could be very disruptive to overall performance. Then came along superscalar processors. This is the whole instruction pipeline thing you've heard other people talk about - multiple instructions executing at once, in different stages of completion. Well, if you have a fast instruction stuck between two slow instructions, it might finish before the end of the pipeline. Or maybe you have a bunch of instructions in the pipeline that do one kind of work, leaving a whole section of the processor idle. This is where hyper-threading comes into play. When you look at your task manager, you have that one view of how much work your cores are doing. Not all those cores are true \"physical\" cores, some of them are \"virtual\" hyper threading cores. Basically, if there's any computing that can be done, and resources available to do it, the virtual core can steal that work and get it done. As you can imagine, the stars have to align to utilize virtual cores, so you can't expect to ever really see them pegged. Multi-tasking is still used today across your physical cores. In the biz, we call utilizing more cores as vertical scaling. Got a bunch to compute? Use more of the CPU. One strategy is the oldest, and that's to spawn more processes, more instances of the program running on that system. You can divide the work among them, they can communicate and coordinate with each other, and each process can utilize its own core. The other thing you can do is threading - this is where one instance of a program exercise multiple, concurrent paths of execution that have to be scheduled by the OS to run on cores. There are certain advantages to how the data gets shared among the work units that makes for an efficiency boost, but this isn't always a desirable design choice. It adds complexity and instability. If the program crashes, it takes all that unsaved work with it, whereas if you split it between processes, such a loss can be smaller, the program can be made simpler, and the whole system can be made more robust. Then there are fibers, which are even smaller units of work, that the program manages the scheduling across threads. These are really good at saturating CPU pipelines with work, because threads are a much bigger unit that can become quite idle. Some of these fiber systems are actually easier to manage than threads! Check out the Go programming language, aka Golang. It's currently the 9th most popular language, and I love it, it's what I always wanted C to be, it's so much fun to program in, and it's all about fibers - it's built into the language, whereas so many languages it's an afterthought because they're older than the concept of threading and fibers themselves. Horizontal scaling is running more processes across computers, and using a load balancer to dish out work among them. We would love it if we went back to one core, and it just got really fast! It would make programming and programs so much simpler! But as Herb Sutter, a famous programmer said, the free lunch is over. There was a time that if you wanted a faster program, you just bought faster hardware. But alas, we caught up to the speed of light. I live near Intel, in Hillsboro OR, and I'm surrounded by quantum physicists. No really - my neighbor. AND his wife. AND my landlord! Can't get a beer around here without talking to a fuckin' quantum physicist. Anyway, as they tell it, we're just about as small as we can go. The problems they're trying to solve include the wires that span the width of a single core are TOO LONG, and they just can't get the signal down the wire in time. Another fun problem is when an electron sporadically pops into existence on an adjacent wire, which is a separate problem than electrons leaking off one wire and onto another. It's possible to make astoundingly fast transistors that don't also melt. The record is in the hundreds of gigahertz by some team in Champaign-Urbana, some transistor made of gold and was some 2 atoms across. But now you need to put ~32 billion on a single chip, like the AMD EPYC Rome architecture, and you gotta make them all switch at the same speed. They can only all go as fast as the slowest transistor."
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crn2d3 | how are helicopters able to turn or climb or decent? It’s basically just two fans spinning? | Engineering | explainlikeimfive | {
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"Helicopter use the main rotor (big fan on top) to provide lift (climb) & tail rotor (small fan on tail) to provide yaw & counteract the torque of the main rotor (which way the nose is pointed & stop the cabin spinning on the spot) When the main rotor pitch (angle the big fan on top away from horizontal/parallel to earth) is changed, some of the lift is directed in that angle - e.g if the big fan pitches forward then some of the lift energy is sent behind the aircraft instead of straight down - this causes the aircraft to move forward but also lose altitude (height above the ground) so the pilot has to increase thrust (spin the big fan faster) to maintain altitude when the aircraft moves Imagine the big fan as putting out thrust like a rocket, when you tilt the rocket to 45⁰ forward it will move horizontally forward & up in that direction Now reduce the thrust of the rocket until it no longer have enough energy to climb away from earth at 45⁰ but is also still putting enough downward thrust to stop from falling - the rocket will then move horizontal to the earth on a 45⁰ tilt - this is basically how the main rotor on a helicopter works I flown my father's bell 47G helicopter since I was 16 so feel free to ask me more in DM if you not understand Edit: notwithstanding the rest of my answer, it important to know that helicopters do not actually \"fly\" - they just so ugly & ridiculous that the earth actively repels them",
"Each of the “fan blades” act like wings on an airplane. The middle part on the shaft changes what angle the spinning wings are facing and therefore what way and how much lift is being generated."
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crpi0b | Why do they spray water everywhere at a demolition site? | I’m currently walking home, and happened to walk by a demolition site with water being sprayed everywhere. | Engineering | explainlikeimfive | {
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"Keep the dust down. We use a water truck in our yard at a concrete facility. So I’m assuming same principle.",
"The dust that comes from smashing buildings is really not good to breathe. To minimize the dust, the spray the area down. The water sticks to the dust and causes it to clump up, and therefore be unable to float around in the air. It's not 100% effective, but it is a decent reduction in dust.",
"On that note, dust in large quantities is super dangerous You wouldn't think it, but depending on the small particles in the air, dust can cause breathing problems in people (and in rare instances cancer) all the way to being a fire hazard (ie grain silo fires or saw dust cannons)"
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crswph | How does a gas car work? | Engineering | explainlikeimfive | {
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"Teeny explosions push the piston, which pull on a central rod, making it rotate. That rotation powers the locomotion.",
"Sucking air and gas in the cylinder (stroke 1) then compressing it (stroke 2) them burning it (stroke 3) then releasing the exhausts (stroke 4) [Wiki link + nice gif]( URL_0 ) When the air/gas mixture is burned, it is basically a small explosion that presses the piston down with force. How much power you get out of an engine is decided by many factors like what type of gas you use, like what octane number you use. Higher is in almost all cases better (this also decides how long you engine might live). If air is forced into you engine (Turbocharger/Supercharger), cylinder size and number etc. plus lots of electronic stuff. A Diesel engine is almost the same but instead of an sparkplug it uses glow plug (if I understood this right, diesel/air mixture ignites itself due to higher compression)"
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crtoqs | What is the purpose of "cruise main" on a car, and should I avoid always having it on? | Engineering | explainlikeimfive | {
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"Cruise main just means your cruise control is on but not set to a speed. It doesn’t hurt to have it on, just means you only have to push the set button instead of turning it on then setting it to speed."
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crtqae | why is the chocolate soft serve machine always broken at every fast food restaurant? | Engineering | explainlikeimfive | {
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"Usually they aren't broken, they just need to be cleaned. The machines need to be emptied out every X number of hours and washed and the staff generally hate doing it because it's a pain in the butt. Sometimes the machine is generally broken, sometimes it's being washed and won't be working for a couple of hours yet, and sometimes the staff just refuse to clean it (perhaps because it's been too busy that day) so they can't serve what's in it."
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crwdiu | How do people build things like oilrigs and bridges over water? | Engineering | explainlikeimfive | {
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"Oil rigs are weighted floating pontoons (heavier on the bottom than on top to prevent capsizing) that are anchored to sea floor - the pontoons are built closer to shore then towed to postion before being anchored - then the rest of of the rig is built on top of the pontoon by cranes taking construction materials delivered to the rig by ships",
"Oil rigs are built like boats, they float on the water and get anchored to the location they want to drill at. The footing for large bridges are normally built by damming the area and pumping all the water out."
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crxbtn | What is sabbath mode on kitchen appliances and what is the purpose? | Engineering | explainlikeimfive | {
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"For Jews who keep Saturday as the Sabbath, they are not allowed to cook or turn on any electronic devices. This mode makes it so they can use these appliances without desecrating the Sabbath. I am sure that you can find a lot more information out there, but this is the basics."
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cryczj | How the power source of Voyager 1 and 2 function, which made them kept going for almost 40 years (and still going) ? | According to Google it have something called "Radioisotope thermoelectric generators", but couldn't understand how are they able to produce limitless energy to keep going. | Engineering | explainlikeimfive | {
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"The power source is just 4.5kg of plutonium-238. This radioactive substance breaks down at a predictable rate, half of it decays in every 87.7 years, into Uranium 234, which has a very long half life and so can be considered stable. The decay produces alpha radiation, fast moving helium nuclei, which will run into other atoms, bouncing off them, shaking them up - which is another way of saying, heating them up. This heat is used to create electricity using thermoelectric couples - similar thing to peltier devices - a kind of diode that produces a voltage as heat moves across them. As the satellites are now 42 years old, this means that they now provide 72% of the heat they did at launch, and they produce less electric power than that, as the space radiation degrades the thermocouples. Because of this, many instruments on them have been shut down; they will continue to shut things down as time passes. They hope to keep at least something running at least to to 2025.",
"But unlike the first comment made it seem they have virtually nothing in common with nuclear reactors. Radioisotope thermoelectric generators (RTGs) use isotopes like plutonium to generate heat passively without fission. Plutonium decays permanently and because of that decay it preduces a lot of heat which is in turn used to generate electricity with peltier-thermoelectric panels.",
"They use Plutonium-238 in an Radioisotope thermoelectric generator (RTG) as you mentioned. It's kinda like a nuclear plant, but way more basic and simplistic. In a normal nuclear reactor you fire neutrons into uranium fuel to split the uranium atoms into two smaller atoms. Splitting atoms creates a ton of energy and in theory you can split all the atoms in a very short period of time by creating a chain reaction of fission events, ie nuclear bomb. RTGs are way simpler, they just take a radioactive material and waits for it to decay. While splitting a big atom into two approximately equally sized ones creates a ton of energy, just waiting for a big atom to give of small decay products will still creates a steady trickle energy and you don't have to do anything since radioactive elements will decay on their own. Specifically for RTGs in spacecrafts they use Plutonium-238, because it's half life is 88 years so half of the material will decay over 88 years and you will lose half the power output over 88 years, which is a good fit for most space missions. You can really pick whatever isotope that has the best half life to fit your mission but the total energy released is pretty similar across all elements so if something decays over 500 years you would 5x as much of it to get the same power output. One important criteria is that the material decays with Alpha decay, since that's the biggest decay product, a helium atom that will get you the most energy per atom and it's the easiest type of radiation to block. How you actually generate the power is also very simple, one side gets hot from the fuel and the other side stays cool, with the heat difference you can generate electricity in various ways."
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crz84l | why do crackers have holes in them? | Engineering | explainlikeimfive | {
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"If the holes weren't there, the crackers would puff up from steam while baking. The holes help release the steam, preventing the crackers from puffing up.",
"It’s called “docking”. Keeps steam from puffing up the pastry.",
"It is thought that poking holes on crackers will help baking in the oven, as well as allow the dough to rise beforehand, in an even manner."
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crzjzs | What is happening when you downshift gears to accelerate in a manual transmission car ? (how does the lower gear provide more rpm and power) | Engineering | explainlikeimfive | {
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"It works similar to the gears on a bike, in simplified terms. The largest cogwheel, the lowest gear, makes it easier to turn the wheel once. One turn of the pedals means like half a turn of the big gear, meaning that you have to pedal really fast to get any speed, but it is really easy to get it to turn slowly. A higher gear is a much smaller cogwheel, meaning that one pedal turns it like twice. This means you need 4 times the force of the lowest gear to turn it just once. However, the same amount of pedals in the lowest gear also gives 4 times more force if you have the higher gear on. Hope this makes sense, I'm not a native English speaker.",
"This is a video from American automobile whatever, which beautifully describes this concept. URL_0",
"Engine power is a basically calculated as torque x RPM. While torque varies depending the speed of the engine, it's usually consistent enough that RPM control is the main factor in determining how much power the engine gives you, especially with the gaps between gears. Obviously gears control the ratio of engine rotation to wheel rotation. This varies by car, but 1st gear might give you a (net) gearing of something like 12 engine rotations to 1 wheel rotation, whereas your highest gear might be more like 3 to 1. Lower gears give more torque but less speed, and higher gears the opposite. Law of Conservation of Work and all that. Selecting a lower gear means the engine RPM goes up significantly, which means the power it is capable of delivering also goes up. This gives better acceleration, hill climbing power, etc. Aside: Automatics are largely the same, they just change gears automatically for you. Pushing down hard on the gas pedal will make the transmission realize you want power and downshift a gear.",
"The lower the gear, the more revolutions of the engine is *required** to move the car a given distance, which means that if the car is already moving some distance per minute shifting the gear down increases the rpm automatically. Each of those revolutions involve pumping gas and air into your cylinders and lighting it on fire, producing energy. There's a limit to how much gas and air will fit in a cylinder, so if you're already at that limit (\"pedal to the metal\") the only way for your car to produce more power is to fill and explode the cylinder more frequently, so higher rpm = more power up to a point**. *) Unless the clutch is engaged, your tires are sliding across the road rather than rolling, or some other part of the transmission is disconnected. **) at some point the internal friction of the engine reaches a point where it starts consuming more additional energy than the engine produces with increasing revs, and/or your valves are no longer able to keep up and instead of lighting gas on fire in your cylinder you squirt it into your exhaust."
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crzrlg | Why is it sometimes suggested that some battery-operated products should only be charged to a certain percent instead of 100%? | Engineering | explainlikeimfive | {
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"When you charge and discharge a battery, some of the chemicals in the battery will be consumed in side reactions, and get trapped so they can't be used to store and provide power any more. These side reactions happen more when the battery nears full charge, and when the battery nears empty. So you can keep a battery lasting longer if you avoid either fully charging it, or fully discharging it. They also happen more when the battery is hot, so anything you can do to keep the battery cool also helps."
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cs52ce | How do designers keep aircraft flight controls from getting the blue screen of death or crashing while mid air? | Engineering | explainlikeimfive | {
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"There are a few major ways to keep mission critical electronics from crashing: * Be so simple that even if you do crash you can recover near instantly - *The computers on the Apollo spacecraft could reboot in a fraction of a second* * Have non-identical backups for your main system - *The space shuttle had control systems that were constructed in different ways so if one went bad, the same error wouldn't affect the other* * Put it to a vote - *SpaceX uses three computers that are running in parallel, and if the output of any one system isn't identical, recognizes the error and reboots the faulty system.*",
"They have specific requirements, and they test that the code works in all the likely cases. It's the opposite of \"Marketing says we need to get our product on sale first, even if it doesn't work, we can always issue patches later that are backwards compatible, even though that might make it really hard to really fix the problems, because users are a dime a dozen.\" That's why the Boeing Max8 MCAS problem is so newsworthy. A major airplane maker put a feature in to maintain \"just like an ordinary 737\" even though it had a lot of unexplored performance envelope. The \"not fault tolerant - pilots will be the failsafe\" solution has been in the 737 for ages, but that depends on pilot expectations being the same. Violating those expectations for marketing reasons is very rare in aerospace.",
"There are several standards that are adhered to and validation processes that mission-critical software systems can undergo, depending on their purpose... DO-178 is for aircraft systems, but there are others for medical devices, etc. For the most stringent, coverage analysis is done and each line of assembly code (the lowest level that they look at, as far as I know) is assured to place the system into a good state after execution. There are standards-compliant operating systems, graphics libraries, etc. Validation is expensive, understandably, but even code that doesn't crash doesn't necessarily work as imagined... there are famous examples involving rockets, etc.",
"There are two important parts to this and a third lesser important (but still very important) part. Part 1: Specific Hardware. * What does this mean? The software developed for a given plane design ONLY needs to work for that plane and that design alone. If you are upgrading the Boeing 747 with a few improvements then the bulk of the software may very well be the same as the previous software with only changes made to the parts concerning the altered hardware. Your 747 engine software doesn't need to know how to handle an engine meant for a 737 and so none of that code is in there. There's no If Statement asking \"What kind of engine is this? Should I use the 747 module?\". The code was specifically designed to work with THAT model aircraft and nothing else. * Why is this important? This is important because in computers/phones/etc that software has to support a variety of hardware states. Apple TENDS to have a reputation of their equipment being more stable and that is almost entirely because their hardware is locked down. For any given iPhone you'll have the 2-4 versions Apple puts out and that's it, so the new version of the iPhone OS is designed FOR those phones. Now an important point here is that a lot of the issues iPhones develop later in their lives are because the newer OS, which you get, is meant specifically for the newer phones. It'll be backwards compatible with the older hardware for a few generations, but in general they only take the effort to make sure that basic functions still run at all and won't brick the phone. As a terrible example, lets say the new camera software expects some feature that your old phone doesn't have. They'll make sure the lack of that feature doesn't crash the camera software, but they won't necessarily make sure that the safety systems that prevent the crash from happening don't slow the phone down with software inefficiencies that the newer phones CPU can handle without trouble. However more on the Microsoft side, Windows is designed such that basically every combination of hardware you can conceivably make SHOULD work, but it isn't guaranteed to work perfectly, simply because there is no possible way they can make sure of that. GPU A and CPU A might work wonderfully together, but GPU A and CPU B might have a TINY little mismatch that happens only in extremely rare circumstances only brought about by a singular random event inside of a video game you play such that one will send a message to the other that the other just can't handle and things come crashing down. * What are the implications? Purpose build software for a specific piece of hardware ALWAYS works better (assuming proper engineering standards are applied anyway). Think of it from a practical standpoint of converting data from one type to another. In some hardware you might have a \"least significant bit\" (which digit is the 'zero/one' space) where the bit in question is the first bit (ex: 1000) and in others it will be the last bit (ex: 0001). If your software has to handle the possibility that the hardware given to it could be one or the other, then when a number arrives in the computer, before it can do anything else, the number gets passed over to a piece of code which interprets that number to make sure it matches how the computer works (ex: if you have 1000 and the computer is expecting the opposite direction, the number must be reversed before the computer can use it), before the number is used. This is true EVEN if the number is correctly formatted. This little extra operation doesn't take much processing to do, but it IS less efficient than just knowing for sure that the number is arranged one way or the other. If you only have to do this once every few minutes, it's no big deal, but if you have to do this hundreds of thousands of times every second of operation, it adds up to a lot of wasted calculations that you don't have to do if you KNEW that the number was ALWAYS organized in a particular way. Finally, all this together means that your software knows EXACTLY what is possible from the hardware. If the hardware CAN throw a particular error or spit out a particular output, your software WILL be able to handle it because you designed it to do that. In a situation where you don't know what hardware is plugged in, you have no proof that your software will be able to handle (or even understand) a given error message or input from the hardware, because you don't know all the possible inputs you might get. **tldr: By having a VERY constrained hardware set, the software can be designed EXACTLY to handle what that hardware can do. This means no matter what the hardware does, the software can do something with what it's told instead of freaking out and crashing.** Part 2: Limited Actions. * What does this mean? Your phone and your computer have effectively infinite actions that you the user can direct it to do. This doesn't mean that you can ask it to add any number to any number (though that is part of it), it more means that you might want to install a particular game and play it, or go online and look at a random web page that the programmer of your phone/computer had never seen before. The specific number of individual actions that you can make your system do are too large for any team of coders to anticipate and test for, they have no idea what you might want it to do, so they do their best to handle the average cases. In the case of planes, they know EXACTLY what all the things a pilot can do are and they know EXACTLY how these actions are allowed to interact. They don't have to anticipate that the pilot might want to plug in a disco ball in the cockpit and try to have the throttle lever control how fast the ball will spin or the flaps lever control how bright the spotlight on the ball is, because there is no possible way for a pilot to DO that. * Why is this important? By knowing EVERY action a pilot can take in the plane, it becomes possible to ensure you accommodate them. Depending on the circumstances you may not be able to accommodate all of them with specifically designed code to handle that action, but you can guarantee that there is some default behavior that is acceptable. Ex: Maybe you don't have code that handles specifically what to do when the pilot pushes the 'cabin lights' button while also adjusting the throttle, but you can code the 'cabin lights' button to always toggle the lights no matter what else is going on, and you can code the throttle controller to always adjust the engines based on the position of the throttle no matter what else is going on. And thus you have handled the scenario of what happens when the pilot pushes the cabin lights button while adjusting the throttle without actually writing code specifically to deal with that scenario. With a phone, it might be possible that the software you are running takes control of your volume buttons and uses them for some purpose (brightness say), meanwhile it cares about touch inputs on the screen to control the USB device plugged into the phone. Maybe the creator of the software you are using never anticipated that the users would have the dexterity, or reason, to be poking at the volume buttons while tapping the screen while the USB device the software was meant for was not even plugged in. This could cause the software to hang in a loop as it tries to figure out what to do. Meanwhile in a panic you try to minimize the app, only to realize that the volume buttons are still 'grabbed' by the software because your phone hasn't realized the app is crashing and is just steadily caching every volume push waiting for the app to take the inputs, and in a panic as you are pushing the various buttons you somehow manage to overflow the volume-button cache on the phone and the phone makers never expected that would be possible, and so the new value goes beyond the allocated memory space and changes a value needed for the OS which becomes a value that the software never expected to see and so the phone stalls and crashes. With a phone or computer, the programmers cannot know that this scenario might happen and take actions against specifically it. (Not a perfect example of course, the phone programmers should always expect that somehow the volume input cache might overflow and throw in some safety programming to handle it, but you get the idea.) * What are the implications? This means that generally speaking, no matter what the pilot does with the controls, the plane knows what it should do in response. There's never any possibility of confusion where a combination of inputs/actions from the pilot are unexpected or unhandled. As such the programmers have made sure that no matter what has happened, the plane has an answer to it. The answer might not necessarily be terribly meaningful in the grand scheme of things, but it is an answer that is logical given the inputs it has been provided. A given scenario might be best handled by the plane simply refusing to change states. Ex: The plane has some sensor on the landing gear to know for sure that it is on the ground and the pilot sends it a command to retract the landing gear, the plane might just do nothing. Note: It is always a best-practices thing in the case of 'do nothing' to provide some feedback to ensure the user knows that [the system heard you, the system doesn't care.]( URL_0 ) **tldr: Because the programmers know EXACTLY what all the possible actions of the pilots are, they can program things to handle ALL of those actions.** [1/2]",
"The short answer is that they do a lot testing and any problem the test find is not just fixed but analyzed and policies enacted so there's less chance of happening again in the future. You can find more information in [They Write the Right Stuff]( URL_0 ) an article about the people who wrote the Shuttle software.",
"for those kinda of system you have a few options: 1: make them simple, os simple in fact that evne if they do crash they cna recover faster than it may lead ot issues(not good if you need to preserve data for instance, but generally good for stuff like sensors) 2: assymetric redundancy: aka having a system with a back up, but said bakc up works in a different manner so niether cna be affected by the same kind of error. 3: have multiple system working in tamdem and copare their output for istance many miliatry aircraft have 3-4 flight computers on board, if one of those start outpuuting weird data it get evaluated and if found erroneous its rebooted. also worth noting that misison critical systems that you cant afford ot have failing. go thru much more rigorous testing."
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csbp0s | How are ships stabilized in high waves? | What keeps the ships from toppling due to high waves in sea? | Engineering | explainlikeimfive | {
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"Primarily, a heavy keel. The more mass you an concentrate below the waterline, the more stable your craft. Secondarily, keeping it pointed into the swell. A boat pointed into the wave is much, much more stable than one getting broadsided.",
"Usually ballast. The hull or body of the ship goes way down under water where you can't see. The very bottom and middle part of the ship is usually called the keel. It is packed with super heavy material called ballast. On old ships it was rocks or lead or special weights. Sometimes water tanks are used. On modern ships sometimes the keel part extends far below the bottom of the ship's hull in a big counterweight looking thing. All that weight at the very bottom of the ship keeps it from flipping over or capsizing. The heaviest parts always want to be at the bottom.",
"Typically, the [shape of the hull]( URL_1 ) is designed to keep a ship upright. When a ship lists (turns sideways), its center of mass stays the same (everything is tied down inside), but the shape of the part of the ship that's in the water changes (like in [this picture]( URL_0 )), so the center of buoyancy changes. The shape of the ship underside is designed so that the way the water pushes at the ship [returns it]( URL_2 ) to the upright position. You can see in the left diagram (a) that for a properly-designed hull shape, when the center of buoyancy goes to the right, the forces of gravity and buoyancy will act together to rotate the ship back upright. The (b) diagram is a poorly-designed and poorly-loaded ship (top heavy); the combination of gravity and buoyancy will rotate the ship even more."
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csbsns | Why is the sound of a car going over a bridge so loud compared to normal asphalt? | Engineering | explainlikeimfive | {
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"Because bridges have guardrails which reflect the noise of your car back too you. It’s not that your car is necessarily louder on the bridge you’re just hearing more of the noise it makes.",
"It's the echo from an elevated structure. Also the materials used to build that bridge as opposed to a gravel or dirt base. of course if you're talking about a lift bridge it's the steel grates used."
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cscgxq | why does gas mileage change between city/highway? | I just bought a new car and it gets 28 MPG in the city and 32 MPG hwy. why is it different?? Because you’re stopping and starting less? Accelerating less?? Please explain | Engineering | explainlikeimfive | {
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"Stop and go on city streets, and relatively constant speed on highway. Less gas to maintained speed that to go from a dead stop. Short answer, acceleration uses more gas than maintaining a constant speed."
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cscz2f | What changes in how the engine works when switching between different driving modes like Eco, Sport, etc.? | Engineering | explainlikeimfive | {
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"Nothing much really, between normal and sport(+) the only difference is that your car will shift later up open the exhaust valve to make more noise(if you have a sport exhaust) stiffen up the suspension. You don’t habe over all more power or something and everyone who says that is an idiot, you just get the power sooner and the car feels mire aggressive.",
"Engine mapping is the answer. Engine mapping tells the engine: \"if the driver is using X% throttle, give him Y% power\" Now, you may think that pushing the throttle to 30% will give you 30% power, but many times this is not the case. In normal driving mode, 30% throttle may equal 25% power, 70% throttle equals 80% power and so on. (I'm just making the numbers up) If you switch to sport, at 30% throttle you may get 40% power and at 70% throttle you may get 90% power. Essentially, the same throttle input results in more power, which can appear to make the car more powerful, but the car does not actually produce more power Here is an excellent video on the topic. Also, keep in mind I wildly simplified it, as lot of other variables are involved, not just throttle input (rpm are also important, for example) URL_0"
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csoj4h | How has the Voyager not hit any space debris and gone off course? | I'm under the assumption that scientists were able to calculate a route with the least amount of debris possible. (By debris I mean comets and various materials that are floatingg into the vacum of space). But I'm curious to know how do we know we didn't send the Voyager straight into the path of a comet field at some point in time? | Engineering | explainlikeimfive | {
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"“Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space.”",
"Stupid auto mod.. Space is big. Very big. You have to try to hit things. Yes, there was likely some luck involved, but for the most part it is empty.",
"That's like saying how can a ship sail on the ocean without hitting another ship. The ocean is a huge place, but space is millions and billions of times larger, comparatively. Plus there isn't that much debris out there. Debris tend to get captured by a gravity well, or run into something."
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csyxea | Why are car keys double-sided? Why aren’t all keys double-sided? | Engineering | explainlikeimfive | {
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"* It costs a little more to make keys double sided. * It's not worth the extra cost to make something like a house key double sided because most people who use them will be looking right at them when they are inserting the key into the cylinder. * Car keys, on the other hand, are almost always used by someone who isn't looking at the key when they put it in the cylinder. Now it's very much worth the extra cost given how often people stick their keys into the ignition and how cumbersome it would be if the key only fit one way.",
"Car locks become harder to pick as they have pins on both sides of the tumbler. More specifically, it's pretty much impossible to single-pin pick a car lock. More people look to break into a car than break into a house, it's worth it for that little extra security. Also, for the longest time car keys were single sided. We also had separate keys for the trunk/doors than the ignition key."
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ct2fe5 | How does a helicopter tilt forwards, backwards and to the sides? | I imagine it rotates by using the little rotor in the back, but how does it do the other moves? | Engineering | explainlikeimfive | {
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"It uses something called a \"swashplate\". The angle of each of the blades of the main rotor can be adjusted to push more or less air, and they can be adjusted very quickly in the middle of a rotation by the swashplate. For example if they want to tilt forward the plate is adjusted so the angle of attack of the rotor is greater in the rear of the rotor's travel, pushing more air and tilting the craft.",
"> I imagine it rotates by using the little rotor in the back The rotor on the back is there to counteract the torque applied to the body of the helicopter by the propellers. Without that, the helicopter would spin the in opposite direction of the main rotor."
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ct6gof | How is it that when you follow the left wall of a maze, it will always lead to an exit? | Engineering | explainlikeimfive | {
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"This also works with the right wall. But it only works on mazes that are \"simply connected\". This means that all the walls you touch need to be connected to the outer edge of the maze. If that is the case, following the left or right wall you will always end up at an exit, because these mazes are \"knotted strings\", which if stretched out will result in a simple circle with 2 holes (or more) which are the exits. If the maze is not simply connected, and the goal is in the middle of the maze, then you can't use this technique, as you'd have to release the wall at some point to get to the other walls which are not connected to the outer edge of the maze."
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ct8epl | Why do pens stop working mid sentence, not allowing you to write on the space where you were writing, but working if you write somewhere else? | Engineering | explainlikeimfive | {
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"Grease from your hand as you rest it on the paper ahead of where you are writing. Because it acts as a lubricant, there is not enough friction with the paper to make the ball in a ball-point pen rotate and pull the ink from the reservoir behind it.",
"Typically because there's something on the page there like a thin layer of wax or other substance that prevents the ink roller from rolling properly, or prevents the ink from sticking.",
"Because in somewhere else, you make fast and sudden movements which clean the tip and temporarily increase the heat that helps to draw more ink from the cartridge. Same as when you give a hot breath to the tip."
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ct8w38 | Why does engine power peak in the middle of an engine’s RPM range? | Why wouldn’t a higher RPM lead to more power? Why does a torque / horsepower curve peak below redline? | Engineering | explainlikeimfive | {
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"Its all about efficiency. As the piston moves down it sucks the fuel/air mixture into the empty space, the more air you can cram in there the more power you make (an engine is essentially an air pump). So if their is more time for air to enter the cylinder you get a stronger explosion which moves the cylinder downward faster during the combustion cycle creating more power. It also depends on how the engine is designed, the camshaft controls how long the valve stays open (duration) to let air in during the intake stroke as well as how much the valve opens (lift). A larger lift has less impedance for air to enter and a longer duration allows air to continue to rush in (to a point). If you have a camshaft with high lift/duration it will shift power higher in the RPM range at the expense of low end power/stability. This is why drag cars have that lopey unstable idle. As RPM increases the fuel/air charge has less time to fill the cylinder which results in less power per stroke, but horsepower usually peaks out higher in the RPM range than torque because you have more power strokes per minute. This concept is known as volumetric efficiency, the measurement of how efficiently an engine can fill the volume of the cylinder",
"Engines are usually optimized for mid-range power output. No sense in optimizing a car for high revs when your average driver rarely takes it that high.",
"Engines are more efficient at lower rpm's (to a point). That's cuz the expansion of the hot air in the cylinder isn't perfectly efficient. The slower you go, the more efficient it is. But on the other hand, the higher your rpm's the more power-strokes of the cylinder you get per minute. The optimum balance between the two is at peak torque, usually mid-to-high-range of the engine. Where that peak is, whether its 4k rpm or 8k rpm, depends largely on the design of the engine."
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ct9ihv | Gradient Descent and Backpropagation | Hey y'all. I'm an ML Research Engineer/Student giving a presentation about ML to a bunch of others who don't know ML. I wanted to see how the greatest minds on Reddit can explain this concept as simply as possible. Cheers! | Engineering | explainlikeimfive | {
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"Many problems in machine learning are influenced by statistical optimization. Much like optimization when you are picking an apartment for example, you want to weight different combinations of factors that are important to you with the overall objective of minimizing cost. In neural networks, the principle is the same. You want to find a function that best maps your input data to the output labels. This is a prediction problem and so you can measure error, how off your prediction is. Ideally, you want to tweak your network so that it generalizes well to new data while also capturing the pattern between the input and output with the lowest error possible. To do this, you need to solve an optimization problem that requires that you determine what optimal combination of weights for the neurons gives the lowest error. Let's say that we have two weights. We can visualize this process by having the weights on the X and Y axes and the error on the Z axis (insert simple plot of a 3D topological function). As you can see, the point where the error is lowest is the point where the two weights are at P or Q. This procedure of exploring the 3D landscape in a somewhat random fashion to find the valley is called gradient descent. In a neural network, however, you don't have two weights but 100s or 1000s. Backpropogation is a procedure that allows you to update all weights at once by layer while minimizing cost. This is typically done over multiple trials in which the error continues to decrease as the network gets better and better. Eventually, the network might converge on an optimal set of weights. Hopefully you have not overfit and the network generalizes to new data it's never seen before! So just like in the scenario where you want to find the optimal weights of factors you care about that minimize monthly apartment cost, in the case of neural networks you want to find the optimal combination of weights that minimize error between associating the input to output over repeated trials. EDIT: On second thought, the apartment analogy might not be so good since many times the weights are fixed (like you have to have a 3 bed 2 bath etc). But I suppose there could be a case where you just want the cheapest place and factors that give you the lowest price is what matters. I am too tired to think of a better analogy right now but I may update this answer tomorrow."
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ctb0ak | How do blimps control their altitude? | I've been trying to think about how this would work, but honestly, I'm stumped. Once they're up in the air, they can't add more weight to counterbalance the lift of the blimp so that theory is out. Depending on the gas used for lift, adding heat to gain more lift would be super dangerous. How does that work? | Engineering | explainlikeimfive | {
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"There's two smaller balloons inside the main balloon called balloonettes. One in front, one in back. These balloons are filled with air. When they want to sink, they pump air from outside into these balloons making the whole thing more heavier/more dense. If they want to tilt forward/back, they pump air into one, but not the other. More or less equivalent to a submarine's ballast tanks."
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ctbd29 | How a piano is tuned. | Engineering | explainlikeimfive | {
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"There are devices for measuring the proper note, either electronic these days or in it past carefully calibrated \"tuning forks\", two metal tines of a specific length to make an accurate resonance when struck. A note on the piano is played and the sound compared to the fork or measured by the electronic tuner, and the appropriate adjustment determined. Adjusting the piano is as simple as opening the top and turning a tuning peg on the appropriate wire. This will increase or decrease the tension and thus the produced note. Repeat for every key and the piano is tuned.",
"A piano tuner opens the piano to reveal the harp, where all the strings are housed. Each string is held in place by a really strong bolt or peg (a piano holds enough tension in the strings to tear itself apart) and some keys play up to 3 strings at a time. The tuner then plays a note and uses an electronic device and their ear to set each string to the correct pitch. Then they move on and do the same thing for the other 87 keys. It’s like tuning a guitar on expert mode."
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ctch8u | Chicago has poor conditions for building due to the swampy soil underneath the city, so how are tall buildings like the Hancock and Sears/Willis towers built in these poor conditions? How were older buildings like the Tribune tower and Wrigley building built? | Engineering | explainlikeimfive | {
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"For very tall buildings they will usually drive a bunch of long steel beams up to a few hundred feet down to bedrock. The foundation is poured on top of those beams as support.",
"As a result of what the other posters are saying, Chicago has a huge underground. Back in the 80's and 90's my mom took the train from the suburbs to a stop right under her office building. When she would go to lunch, she would walk underground to several restaurants. There's a whole underground \"mall\" thing there.",
"A little bit of history here, too - back before they could drive pile into the bedrock, they used to make “floating” foundations. The wet sand of Lake Michigan was too deep for them to reach bedrock originally, but Chicago still had some of the tallest buildings around because of the shape of the foundations they put in. So imagine a snow shoe. You know how they make it possible to stay on top of snow by distributing your weight over more ground? That’s basically how they did it before they could reach the bedrock. They made huge, pyramid-shaped corner foundations that would “float” on the sand. The pressure from the building helped keep it from moving around, and the area kept it stable/kept it from sinking. This doesn’t answer your question, but is directly related because it is an issue Chicago has been dealing with since its foundation (no pun intended). “The Great White City” is a great read if you wanna know more about Chicago’s history/planning along the timeline that the serial killer H.H. Holmes was active. Especially if you are, like me, a casual historian.",
"Piles driving, they drill a bunch of hollow steel tubes until it hit the bedrock, pour concrete or whatever else in there, pour another concrete foundation and sit it on the piles then put the building on it. No matter how swampy the soil is, you drill it far enough you will hit bed rock, they do the same when building bridges across rivers.",
"Oh something I can answer! I'm a structural engineer that was the lead on the 2006 Wrigley field bleacher addition! The soils at Wrigley were actually perfectly fine for shallow spread footings. In fact, the whole stadium bears on shallow spread footings. We called them wedding cake footings because of their shape...a practice that isn't used anymore. Fun story, the fifteen foot tall wall that surrounds the bleachers along waveland and Sheffield was demolished as part of our work and replaced. We didn't have drawings for it so we didn't know what to expect for the footing. We assumed it would have been at least four feet wide to keep it from tipping over in the wind. Nope. Turns out it was an 18\" wide 'bank pour'! The constructors had dug a shallow trench with a shovel and poured concrete in it to make a level surface. No reinforcing, no dowels to tie them together. Everything I learned in school is a lie! I do have old drawings of the main field I could post if anyone actually makes it down to my post and reads it.",
"We went on a field trip to Chicago and I remember learning one of the bridges has hundreds of feet more foundation on one side than the other because the bedrock was so much farther.",
"I’m not an engineer or anything but my understanding of large buildings is that they dig down to the bedrock and set the foundation on that whenever possible so the building won’t shift or sink. Since Chicago is so low lying it didn’t drain well, so in the 1850’s and 60’s they raised all of the buildings roads and sidewalks in the city with jackscrews so they could add drainage systems.",
"Chicago area native and professional deep hole driller here. I am a fourth generation driller and my family has being drilling this area since the 1910s. Just weighing in my two cents that the soil really is not swampy. I've drilled all over in Chicago from as north as Rogers Park to as south as Inglewood and can say the soil is relatively the same across the city. Chicago's modern storm sewage system keeps most of the water from settling in the soil which keeps the soil largely stabile. The most trouble I've found is debris from the fire going as deep as 15 to 20 which include bricks, slabs of concrete and sometimes wood and garbage. Close to the lake front is about 25 feet worth of sand on top which carries the ground water from the surface to the clay and gravel layer underneath. Limestone bedrock typically comes in at about 80 to 110 feet citywide which is relatively shallow compared to areas just north and north west. Shale comes at about 350 feet deep with a final formation shift of sandstone at about 650 feet depending on where in the city you are. You can find all well, well water and geological survey information for free for Illinois online at: URL_0 You can find geological information, well yield, Karst information etc here. Edit: mobile phones auto correct is fun.",
"I did an architectural boat tour in Chicago last year. There's this one building that was built on a small plot so the base of the building is very narrow. A few stories up the building widens out. This made the building very unstable and it would often sway in the wind to the point where it may collapse. The solution was that they put huge water tanks in the top floor so when the building sways, the water sloshes to correct it's position. Thought it was really cool. Also, the people working in that building often have to take motion sickness medication.",
"Before a building is erected, geotechnical engineers and geologists go to the site to inspect the conditions of the ground. The geologist concerns with the type of soil, their layers, age and types of rocks, faults, and any defects in the rock layers like cracks. The geotech engineer typically builts on that data and determine what is the load that the ground could support, how much settlement is expected, if the settlement is even, drainage of the soil, and then recommend solutions. If the ground could easily support the building, say something like a house, then maybe the recommendation is a shallow foundation. Basically like a snowshoe for the building to sits on. If the ground is weak, too much settlement is expected, or if the building is tall, then the solution is deep foundation. Think of those coastal houses on stilts or the piers at the beach. They work in two ways: friction and load transfer. As you go deeper into the ground, the soil pressure increases. This pressure clamp the pile tight and prevent it from sinking (and rising). These works great with some exceptions, notably liquefiable soil or if the ground retains too much water; water is not known to have good traction. The load transfer pile type looks like a flair bottom jean, it is wider at the foot. This type is typically suitable if friction is unreliable and if there's a stronger layer underground that could support the building. Factoid 1: Piles are absolutely necessary for tall buildings because of wind. Strong winds cause buildings to lean. On one side, there'll be a stronger downward force, and on the other side, there's an uplift force. Friction forces on the piles counteract uplifting while shallow foundation usually ineffective. Factoid 2: In places where the ground swell with water or freezes, simple concrete slab foundation don't do the trick as the swelling of the ground tends to crack the slab. In these cases, usually the slab is \"float\" on top of the ground and not anchor to the sides. This allows movement of the slab and prevent cracking. This also cause doorways to get sticky.",
"They explain the underground beam process in a book called Devil in the White City. I highly recommend reading.",
"Maybe unrelated - but other cities have similar issues. Take old Amsterdam for instance - they've solved it in the same manner, by hammering poles down into the soil until they reach a sturdy rocky/clay layer that'll support the buildings. And this is still being done to this day, which is why you often hear a dull thumping near construction sites, those are the poles being hammered down. & #x200B; 'tis a foolish man who builds his house on sand - but only without the proper preparations.",
"Geotechnical engineer from Chicago here. Typically when you have crappy soil conditions like this you need to use deep foundations to support your structure. This can mean drilling several small holes about 6 to 8 inches in diameter, inserting long circular steel bars into the holes (called micropiles), and finally pressure grouting the holes up to grade level. For big buildings, you might have hundreds of these things drilled. Another way is drilling large cylindrical drilled shafts (called drilled piers) down to, say, 100 feet, inserting a large rebar cage, and pouring each pier with high strength concrete. You can also use driven steel piles which are used pretty frequently for things like bridges. These systems rely on the \"skin friction\" between the concrete/steel/hardened grout and the surrounding soil. If you can imagine the outside surface area of these piles/drilled piers all the way down to 100 feet down, that is a lot of contact between the soil and piles! Basically what you get is a massive amount of resistance that prevents the foundation from \"settling\" or \"sinking\" due to the building's loads. You also get resistance from the \"end bearing capacity\" at the bottom of the drilled piers, which, at large enough depths, usually means bearing on stable rock.",
"The book “The Devil in the White City” by Erik Larson does an excellent job explaining how Burnham & Root went about solving this issue when designing the first skyscrapers. They created artificial “bedrock” by making overlapping layers of steel beams then just pumping the whole thing full of concrete. Because the weight was then distributed it acted like a snowshoe does, instead of normal post foundations which drill down tubes till they hit bedrock",
"The template for building skyscrapers is based on how they built tall buildings in Chicago during the late 1800's when the city was very up and coming and competing with New York for dominance. Basically they built the foundations so well that they realised you can build really high on top of them. If anyone is really interested in the story then read 'The Devil in the White City'. It is set around the worlds fair in Chicago in 1893 and follows the building of the fair and Dr. H. Homes, a serial killer operating in Chicago at the same time.",
"Giant concrete surfboards to distribute the weight over a larger area. No I’m not kidding.",
"Hancock building they (I think case foundations) drilled caissons (hollow steel pipe) into bedrock, then they drill a socket into the rock, fill the whole thing with rebar and concrete. Then they form a concrete cap around a cluster of caissons and place columns on top",
"Gothenburg in Sweden has this exact problem. The entire city is built on more or less mud. The tall buildings (specifically Läppstiftet/The lipstick) are twice as long under the ground as the actual building sticking up.",
"I worked on a skyscraper in Chicago. The foundation was over a hundred 95 foot long steel piles driven into the ground until they hit bedrock (pile driver makes a satisfying PING! When that happens). The ends of the piles were tied together with rebar and concrete.",
"Pretty much all the land from Chicago to the Wabash River in Indiana is/was swamp land. You should read about what the did to the Kankakee River to basically drain all that land in between. The Kankakee marsh use to the the richest hunting and fishing ground on the planet.",
"If you've ever heard of a machine called a pile driver- the wrestling move being named after that machine- then that's how it's done. Long support rods are driven through the ground by impacts from the driver and come to rest on bedrock, and the foundations for the structure rest on the pile, so rather than the foundation's weight being settled on the wetlands, it's settled on the firm stone underneath."
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ctdhcf | How come the operating pressure of gasses is can be lower than atmospheric pressure? | I recently had my gas pipes changed and found out the operating pressure of cooking gas is around 30 millibar. Which seems impossible considering 1 bar is the atmospheric pressure. Am I missing something? | Engineering | explainlikeimfive | {
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"Pressure is measured in relation to another pressure. Your gas line is 30 millibar or about .25 psi above the surrounding atmosphere.",
"There are different ways to measure pressure. When measuring atmospheric pressure we measure absolute pressure which is the pressure above absolute vaccuum. However for most practical purpuses like the rating of a gas line to seperate the gas from the atmosphere it makes much more sense to measure the pressure relative to atmospheric pressure. Especially as the atmospheric pressure can vary depending on the weather and your altitude. So in a high pressure area near the sea the atmospheric pressure might be 1030mbar which means your gas system is rated for an absolute pressure of 1060mbar. However if you get to a low pressure region on a mountain then the atmospheric pressure can be 980mbar so your gas system will operate at 1010mbar absolute pressure."
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ctf6cj | Why can’t blueprints be of another color? | Engineering | explainlikeimfive | {
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"text": [
"Traditionally, blueprints are actually reproductions of a design rather than the original design. The original would be drawn normally with pen and paper, then copied with what is effectively black sharpie onto a glass pane. For mass reproduction, the glass pane would be placed over a piece of paper that's been coated in a chemical that turns blue when exposed to UV light, and placed under a UV light. The areas that are covered up by the black lines on the glass would stay white, while the uncovered parts would turn blue. Excess chemical would then be washed off and the paper would be dried. A video of the process can be seen [here]( URL_1 ). That process was used prior to other methods of document duplication (photocopiers and the like) and in today's world of computerized engineering they exist only in name. Modern engineering drawings ([example]( URL_0 )) are computer-generated and are black-on-white or even in full color.",
"Old blueprints were reproduced by a method called cyanotype. It is a chemical process similar to photography, except simpler and less sensitive. Its main ingredient is a blue inorganic dye. Hence all blueprints were blue. Now cyanotype is no longer used, and blueprints can be of any color."
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ctrz1i | How can one key work across multiple doors that don’t have the exact same lock? | For example, my house key also opens my apartment’s garbage room. | Engineering | explainlikeimfive | {
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"exn4ikl"
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"text": [
"Locks usually have small pins that are cut in two at a specific height. Different heights are how a key is matched to a lock; the split is aligned with the edge of the rotating lock cylinder. In master-keyed locks, one or more pins have two cuts instead of one. Either cut being aligned with the edge of the cylinder allows it to turn, effectively making the lock work with two different keys."
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ctsgn2 | Why do some buildings look really cool, but seem really impractical, ie having gaint holes in them? | Engineering | explainlikeimfive | {
"a_id": [
"exnhcm7"
],
"text": [
"Can't speak for every building, but those little design quirks can actually serve very practical purposes. For example, you pointed out that some buildings have giant holes in them. That can actually counteract excess swaying in the wind. Here's a video if you'd like to find out more: URL_0"
],
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ctweqh | How does regenerative braking allow my car battery to charge and store energy? Or is it just a marketing gimmick? | In school I learned that braking is a waste of fuel as the kinetic energy transfers to sound and heat (which is effectively a loss, right?). So how does regenerative braking recoup some of that energy into the car's battery? | Engineering | explainlikeimfive | {
"a_id": [
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"The way electricity is usually generated is you take an electric motor and spin the shaft. This causes the magnets inside to rotate next to the coils, which induced an electric current. So basically an electric motor can be used two ways: you can hook it up to a battery and use electricity to spin the shaft, or you can hook it up to a battery and spin the shaft manually and charge the battery. You might see where this is going. Sine electric motors can be used in \"reverse\" to create an electric current, some engineer got the idea that since the wheels on an electric car are hooked to an electric motor, why not set up the cars battery to harvest the electric current created by slowing down? So when you press on the accelerator, the battery drains as the motors soon the wheels. But as soon as you let off the pedal, the car will begin to use the deceleration of the vehicle to recharge the batteries. It's not a lot, and like you say, some of it is lost to friction and heat, but it's a clever way of extending the life of the batteries."
],
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cu36qg | Why do some battery powered items need to be off when being charged, and other can be turned on while being charged? | Engineering | explainlikeimfive | {
"a_id": [
"exqrmtn"
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"text": [
"Its been a while since I've encountered a device that couldn't charge while in use (mobile electronics anyway) - can you provide an example? It would come down to the complexity of the device and its corresponding power monitoring chip. More expensive PM chips are capable of doing both. Since using your cell phone while charging is a critical feature, the additional cost and complexity is worth it. In simpler devices it may not. On one hand, maybe because charge-while-use isn't a typical use case. Back in the day of cordless vaccums and cordless phones, the use-while-charge use case wasn't really possible, so they never designed for it; and now that it is the additional cost/complexity doesn't jive with the low cost nature of the appliance. From an engineering perspective charge-while-using requires some serious circuitry; keep in mind the operating current of the device will likely be an order of magnitude less than the charging current - battery usage draw is slow and continuous, but you want charging to be fast, ergo: high current. So the PM chip has to be able to either handle both current levels simultaneously ($$$) or isolate between them (and thus only handle one case at a time.) ( $)"
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cu9t89 | How do airplanes navigate when going through dense clouds? | Engineering | explainlikeimfive | {
"a_id": [
"exsi6fh",
"exsdq0o"
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"text": [
"There are two ways pilots can fly. VFR, or Visual Flight Rules, is when a pilot navigates using mainly what they can see. VFR flight cannot be done in bad weather, such as rain or snow, with low cloud levels, or by airlines*. The other way pilots can fly is IFR, or Instrument Flight Rules. This allows pilots to use ground radar, radio frequencies, and GPS to fly, and requires the pilot to file a flight plan with the authority (FAA in the US). Flying IFR has the advantage of allowing a plane to fly in all but the worst of weather, but the plane is under the strict direction of ATC (Air Traffic Control) for the duration of the flight. Aircraft without proper radar and radio systems cannot fly IFR, nor can a pilot without the proper training to do so. *to the best of my knowledge. Source: worked in general aviation for 2 years, airlines for 2.5 years.",
"Small planes like a single-engine Cessna generally aren't allowed to fly in these conditions if they don't have the proper instrument navigation equipment like GPS or radio-navigation aids. Commercial planes aren't using visual navigation in the first place, they're almost always using GPS and radio navigation. In addition, all planes have basic things like altimeters to measure altitude, bank indicators to measure whether the plane is turning, heading indicators or compasses to track the plane's heading, and an attitude indicator to measure the plane's orientation relative to the horizon."
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cuekm6 | Why is “dead” weight heavier than the weight of someone who is conscious? | Engineering | explainlikeimfive | {
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"text": [
"Whenever you lift an object, you need to apply two forces. One is simply to oppose gravity. This is dependent solely on the mass of the object. The other is the resist the torque causing the object to become unbalanced. Consider the difference between lifting a broom in the middle vs. lifting a broom by the end. The latter is significantly more difficult despite the fact that the mass (and force of gravity you need to oppose) is the same either way. The reason is because when you lift the broom by end, you also need to exert a significant force to prevent it from rotating downward in the gravity field. In contrast, when you lift it in the middle, the fulcrum point means that the torque on the broom cancels out (gravity is pulling both ends down equally). With dead weight, you need to find a place on the body that is both near the center mass and available for gripping. Moreover, you need to hold the body in such a fashion that it doesn't spread out and change the torque characteristics (torque is dependent on how far mass is from the center, so extending your arms and legs increases the torque required to rotate you). In contrast, a conscious person is almost automatically performing this task for you - they are focused on ensuring that their center mass is the point where you're lifting and that there's no rotational torque on their body.",
"A conscious person will cling to you and help to distribute their weight. A unconscious person is a big floppy hard to balance weight that you have to control, but a conscious person can help alleviate a good deal of that.",
"It's not necessarily heavier, just less managable/maneuverable. Like the difference between trying to carry a floppy garbage bag full of water versus a straight weight bar designed for lifting weight. When you carry conscious people they tend to tense up making themselves a little more \"designed\" for carrying."
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cugjpe | how they make touch screens sensitive to finger and not other stuff? | Engineering | explainlikeimfive | {
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"text": [
"There are two types of touch screens. Resistive and Capacitive. Resistive types are the ones you see on DSs, old palm pilots and PDAs and credit card machines. They use a Grid of lines to detect when the two resistive mats have been pressed together, these are also the type that typically use hard styluses. These screens will react to any pressure placed on them. The type most commonly found on phones and laptops is capacitive. It uses the capacitance (your finger interacts with the electric field beneath the glass and causes a signal) these screens require an electrically conductive “stylus” like your finger or those pens with the funny domed end. The reason it reacts to mainly your finger is because your finger is just “the right amount” of conductive to trigger the screen.",
"Modern touch screens are capacitive, they detect changes in an electrical field just above the screen caused by your finger.",
"Just like to drop some extra knowledge. There are actually many different touchscreen technologies. It isn't *just* capacitive or resistive, though they account for the vast majority of touchscreens. Occasionally, I have to deal with surface acoustic wave touchscreens. I believe they pickup changes in how sound waves resonate through the screen.",
"screens are capacitive, meaning they have an electrical current/field running through them, and when something \"meaty\" touches them, the change in voltages on that spot tells the computer what coordinates were touched (water would work too, but it's less precise). When capacitive screens were new, I remember reading that South Koreans would use little stylus shaped sausages on cold days because they couldn't touch screens with their gloves (then they could eat the sausages).",
"You can operate an iPhone with your nose. Good to know if you’re wearing gloves and need to tap the screen."
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cuj0yn | How does air conditioning work? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Your air conditioner compresses some gas with a motor, which makes it hot. It transfers some of that heat into the air outside of your house/car/refrigerator with a radiator, which cools down the compressed gas. Then it allows the cool, compressed gas to expand. Just like when you compress a gas it gets hotter, when you decompress a gas it gets cooler. But since it radiated some of that heat outside already, the cool gas gets colder than it was originally. Then that cold gas can absorb heat from inside your house/car/refrigerator, cooling the air. The cycle then repeats."
],
"score": [
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cuvnbz | The pool noodle hole | Why do pool noodles have a hole going straight through the middle to the other side. Wouldnt it be just as effective without any holes? | Engineering | explainlikeimfive | {
"a_id": [
"exzgs2i",
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"text": [
"One of the reasons is that you can put a rope through them and use them to divide the pool into sections or lanes.",
"You can buy connectors to join them together And using less plastic does save a bit of money on manufacturing costs But the real reason is just simply that the machine that originally made them put the hole in them and by the time they took off as a product people were used to them having a hole in it so the design has stuck. It's entirely possibly (but I wouldn't know for sure) that they're still using the same machine to make them The pool noodle was originally a backer rod - which is used in construction to help join two materials together by providing an expansion foam you can apply a sealant too (making the seal more stable) - the inventor of pool noodles noticed that people would regularly just fuck around with the pool noodle sized backer rods so decided to add a bit of color to them and actually sell them as toys."
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cux050 | How do two devices on the internet agree on a transmission rate? | I’m teaching a high school intro to computer science course and this question came up, but I can’t find an answer at the very low level that we’re talking about. We know that the most basic level of the internet is a wire with an electrical current. You can set or read the wire voltage as high or low, and interpret that as 0 or 1. The only way to consistently send/receive messages is to have an agreed timing protocol of when to read and when to set the wire. But in the real internet, devices all communicate at different connection speeds...so there are clearly multiple timings. How is that decided? Ideally at the physical/binary layer. The best I can imagine is sort of like radio systems, where there’s a default channel (timing in this case), and then on that channel you both agree to change to a different frequency. That would also explain why transfer rates fluctuate during the same connection or download, since a computer could be switching timings several thousand times a second if it was needed for the best speed. But can anyone verify that this is an accurate analogy? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Across the Internet they don't sync up transmission rates. The Internet is packet switched, there is no direct connection. One device sends data in packets, which is received by a router, and then retransmitted to another router, and so on until it reaches the intended destination. Generally speaking Internet protocols have to be tolerant of packets not arriving with consistent timings. Or even packets not arriving or being corrupted along the way. It's only necessary to sync up with with the device that's the next step along the way. So your PC has to sync up timings with your router, and your router has to sync up with your ISP.",
"In analog days (ie a modem on a phone line), you can hear the handshake. That infamous dial up tone. Eeeee....rrrrrr..shahshshshshs....perhaps more IS the handshake. It's saying \"56k okay?... No response.. 33.6k okay?... No... 2400bps?? Ah yes confirmed.\". This includes bit rate (raw speed), and error correction settings. Once that is established there is a serial connection. In the digital world there is usually a 'clock' signal which is used to sync things. Think of a phone line with an extra line that plays a drum beat. You send 1 bit per beat, so if you skipped a beat then it's assumed to be a 0. So essentially you are syncing to the beat. The number of beats per second is the bit rate."
],
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cv1h9i | Why do different homes have different water pressures? | I assume it is powered by pumps but how do they work? | Engineering | explainlikeimfive | {
"a_id": [
"ey1aphs"
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"text": [
"Frequently rather than pumps you have water towers. Giant containers of water are filled at the top of these towers and connected to the water system. Since all that water is pressing down into the pipes, it creates pressure for any home that is below the level of the water tower."
],
"score": [
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cv7jeh | What is the ideal size for a fighter pilot and can fighter jet cockpits be customized to fit taller/larger pilots? | Engineering | explainlikeimfive | {
"a_id": [
"ey2bvme",
"ey2bsbj"
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"text": [
"The size limitation is mainly your sitting height and your legs due to the ejection seat. If your legs are too long then they're likely to be broken during ejection. The seat raises and lowers on a linear actuator, but on certain aircraft there are clearance issues with the canopy since engineers want to to sit lower in order to reduce radar cross section and improve aerodynamics, but pilots prefer it to be higher to improve visibility. Ideally pilots would be on the smaller side to keep less blood from pooling to their extremities during high g maneuvers.",
"Honestly as long as your eyes are good, you’re set. Passing that, 5’ 6” is preferred at minimum, weight doesn’t seem to be too much an issue because armament and fuel additions to the jets far exceed any weight you could possibly have on your frame, but you’re not going to be obese and pass survival and physical fitness courses."
],
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cvdj82 | Why do bike pedals only move the back wheel? | I noticed this with rc toy cars too, why is this? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Because the drivetrain only connects the back wheel with the pedals. If you wanted to connect the front wheel, you'd basically make it impossible to turn since turning the wheel would make it rub against the chain, which is a terrible idea.",
"They do make two-wheel-drive bicycles, but they require a shaft drive for the front wheel, otherwise it would be unable to be turned. Significantly more difficult to build, therefore more expensive, therefore not usually found outside of specialty shops or the internet.",
"Penny Farthing bikes (old timey bikes) had pedals directly attached to the giant front wheel. The wheel had to be large to give a human enough torgue to get the wheel turning. The invention of the bike drive sprocket and chain drive allowed bikes to have much smaller wheels and took the form that we have today. The front wheel isn't powered because it would be impractical to run a chain to a wheel that can turn side to side. Basically making the front wheel a driven wheel would make it impossible to turn the bike.",
"despite all technical problems, a second driven wheel does not give you any benefit energy whise. A bicycle is far from being friction-limited between the wheel/road interface. The limiting problem on the bike is it's awful air resistance."
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cvdtgh | How do some images on twitter change colors when saved/opened? | URL_1 First picture is the post explaining second picture is a screenshot of the picture off twitter third picture is the saved picture in my gallery, the paint on the hand is white, but on imgur, the paint is darker. original post: URL_0 | Engineering | explainlikeimfive | {
"a_id": [
"ey3jkdp"
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"text": [
"That portion of the image is actually transparent, as a result the color you're seeing is the background of whatever app/platform you are viewing it on. It should be noted only certain file types are capable of this."
],
"score": [
6
],
"text_urls": [
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cvfh6w | How are the pedals of a bike able to not spin while coasting on a bike? | Engineering | explainlikeimfive | {
"a_id": [
"ey3twz8"
],
"text": [
"Bicycles have [freewheels]( URL_1 ) which allows the wheel to spin without turning the cogset. [Here's]( URL_0 ) a short video showing the ratchet mechanism. It shows how it works when you \"backpedal\", but if you imagine the yellow part turning clockwise, you can see how it would not engage the blue part, which is where the chain is attached."
],
"score": [
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"text_urls": [
[
"https://youtu.be/bAL_nWjuhOI",
"https://en.wikipedia.org/wiki/Freewheel"
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|
cvgiod | Why do some cars accelerate from 0-60 faster than from 5-60? Shouldn’t the rolling start always be faster as both cars are in the same gear? | Engineering | explainlikeimfive | {
"a_id": [
"ey426ft",
"ey4m5ui"
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"text": [
"When you do the 0 - 60 you rev the engine to the RPM where it produces the most power and then dump the clutch. This is very hard on the car, but produces the fastest acceleration. The complaint against this is that it's not how people drive, so 0 - 60 times don't represent how a car feels when you drive it. For 5 - 60, the engine will already be in gear and at very low rpm. So this tests the engine's power across the entire rpm rage. This is more what you will experience when you need to accelerate onto an onramp. AWD cars, like Subaru STI, get much better times for 0 - 60 since the AWD helps the car accelerate without wheel spin.",
"5-60 would be the test you want also if competing against an electric car. Electric motors have maximum torque between 0 and 1 RPM. All internal combustion engines are extremely weak at very low RPM so an electric will leap way out off the line."
],
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