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hjq7g0 | Why exactly are pipelines bad for the environment? | Engineering | explainlikeimfive | {
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"The physical pipeline itself isn't particularly impactful, however a major issue is when they break or fail they cause oil spills which can cause havoc to an area's environment. And they absolutely do break and fail, at least, eventually, maybe. And thats kinda it for the physical pipeline itself. In many ways, protesting piplelines though isn't about the actual pipeline, they are protesting the oil and gas industry and fossil fuels as a whole. A pipleline is an extremely cheap way to transport oil and gas, so having a pipleline makes it viable to drill for it, often in extremely environment damaging ways, and in places that if there was not a pipleline, they may not drill. However on the other side, technically a pipeline is actually still safer than other transport methods, and less energy intensive than things like big trucks hauling out the product. So there's friction on both sides, its somewhat odd that if they are going to drill, a pipeline may be a good option, but if they aren't going to build a pipleline, it makes it much more expensive and dangerous to drill, so they might not ever do it, but if they do, then its less safe than if they would have had the pipeline."
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hjztjl | How do we have automated robots that do extreme precision engineering, but there are still no cooking robots in restaurants? | Engineering | explainlikeimfive | {
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"Robots are expensive, so unless they are going to save a significant amount of money for the restaurant, it doesn't offer any advantage over just hiring a chef. Also, some restaurants do use robots - there's a noodle cutting robot that some Chinese restaurants use. Also if you have a flexible definition of \"Robot,\" things like sous vide circulators are technically robots, and restaurants definitely use those.",
"There are I believe some fast food places that do automate their production lines, but they are few. . As to why we have such a small adoption, the way I see it, there are three main reasons: 1. Robots are best suited for extremely standardized and repetitive tasks. While cooking might seemingly look that way (just apply the recipe right?), it isn't. Not all pieces of meat are the same, and require slightly different times to cook for example. Same for vegetables, which might need to be chopped differently to adjust for variations. Now I'm not saying that it's *absolutely impossible* to create a robot that can do that, because we surely could, but that brings us to the second point. 2. Cost. The sheer complexity of a machine capable of performing all those tasks will make it big, and expensive to buy and maintain. This is sure to put off most restaurants. 3. Desirability. The sheer marketing power of \"your dish was prepared by our fancily decorated chef/homeowner who put their heart into it\" vs \"by our soulless robot\" is pretty sizeable IMO. This is okay in fast food joints. Much less in better/fancier places",
"When I worked at McDonald's, we used plenty of robots. Robots measured the fry oil contaminants and told us when to drain and clean it. Robots knew to cook different burgers at different compression levels and for different amounts of time. Robots made the milkshakes and frappes by mixing the right ingredients and blending them together. What you are really asking here, is what is the difference between machines and robots? All those robots at McDonald's might be better labeled as \"machines\" instead. Do they have a need for something that seems more like a robot?",
"Precise robots require precise inputs. Those robots used in high speed/high precision factories have another automated machine who's entire job is to carefully present the required part in a known position so it can easily be picked up, and each part is effectively identical Cooking is imprecise, baking is a lot more manageable (it's food chemistry) but cooking is hard How do you make a fried egg? How long does it cook? Depends on the exact egg you get. If some eggs are 60 grams while others are 66 grams that changes the cooking time significantly. What do you do if you get a double yoke?? You can get around these issues with fancy($$$$) vision systems and image processing, but it's often cheaper just to keep the meatbag at the grill than to try to replace him with a robot",
"There are many cooking robots, even one that makes sushi. You don't see them everywhere because humans are more versatle, easier to program/train, and cheaper.",
"You're comparing unlike items. A restaurant is an artisan, hand-made experience. Precicison engineering is a mass-scale automated identical process. However the food industry DOES do that mass scale automated process! In mass food production facilities, which often look very much like those engineering plants full of advanced robotics.",
"There are cooking robots in factories for prepackaged foods, where there's much higher volume, and less variation. It's a lot easier to build an automated line to make 100k of the same product a day than to make a few hundred each of 10 different products a day. For example, the hamburger buns at your burger place were likely baked in an automated factory with a tunnel oven. I haven't been to any restaurants that have that much room for an oven, or that need that many hamburger buns in a day. Also, how would a cooking robot handle modified orders (extra cheese, no onion, etc.) or food allergies?",
"There are millions of robots in food factories cooking, sorting, packaging every pre-prepared meal you've ever eaten. To use them in small scale restaurants isn't profitable.",
"Robots arent very smart. They do exactly what you tell them to do. Which is why you have to be generously specific with the command you need to give it. So for example, lets say you want to use a cutter to cut a circular hole on an aluminium sheet. The instructions would look something like this. * find the raw part located a, b ,c * pick it up * move it fast to this and this position * fix it * close lid * start the cutter * move the cutter to the point where i want start cutting the circle * start cutting in circular fashion * lift up the cutter * stop it and move it back. * remove workpiece * move it to its next location. And this is the most basic rundown of things. There will be codes involved everywhere. And youll always have to be very very specific with the instructions. Now I want you to try and think of a coding in \"making scrambled eggs\". Find eggs, find specific pan, hit the eggs with gradually increasing amount of force, stop when the cracking is noticed, ensure no shells are in the pan, if they are, discard, if no proceed. I could go on, but I think youre getting the idea of why its difficult. And were only talking one simple recipe here btw. Its very hard to code in decision making in robots. Not that it cant be done ofc. People make experimental robots all the time thall do it for you, but thats what they are, experimental robots. Their viability today is limited at least in the pantry. besides, why even go through all the problems and make robots when humans can do the easily and for cheap. Robots are very helful dont get me wrong here. Theyre great when you need to do something repetitive but while maintaining same precision, or doing something work in hazardous conditions. Like welding robots for example.",
"There are cooking robots. Like this - URL_1 There are also robot bartenders. Like this - URL_0 But in general, the major problem is that because of the shear number of ingredients, judgments and actions that you could only offer a very limited menu which would leave your guests very disappointed. Also, you have problems with allergies because you couldn't easily change out contaminated parts.",
"Chefs are cheap to run, work long hours with little maintenance and are efficient at menial tasks. Who needs robots? Source: chef of 20+yrs.",
"You kind of answered your own question - they are good at precision engineering. Food is imprecise - the ingredients are all different sizes and shapes. Tesla was aiming for 100% robot assembly but found with anything flexible, like wiring, it was easier to just hire a person than accommodate the robots who did a bad job. Plus a robot can't tell (yet) if something looks or tastes good to eat.",
"When a robot breaks everything in the kitchen will have to stop. When a coworker doesn't show we just work harder and get paid the same while we grumble under our breath that it isn't worth it but at the end of the night we cheer to ourselves and get drunk, slowly spiraling into alcoholism while we destroy every relationship we've ever had. Eventually we either become addicts or burn out from exhaustion and depression and lack of sleep. Our lives crumble around us. We may one day wake up and clean ourselves off... Maybe even pull up those old boot straps and Don the apron once more with a sense of pride that we are the only one who can do this job!",
"Chefs in Finland are paid 12 euros an hour for example. Gotta be pretty cheap and reliable robot to beat that",
"Even at small restaurants there is too much variation between menu items and customer requests for automation to be feasible. Not to mention that there are huge variations within the equipment depending on how busy it is.",
"Most of these responses are off. I think the answer is speed. Cooking doesn't require minute precision and can't be improved beyond some point. The limit isn't how fast you can add water do a pot, its how long the egg takes to cook. Why would you turn 25 sec. of preparing the pot into 10 if the proces still costs about 8 min? Cooking takes time and in the meanwhile, the machine does nothing. People who stand still are cheaper.",
"Pre cooked food is mass produced by robots, restaurants are a bit different because the order variations.",
"Robots that work in a factory dont think like you and me. They run something called a program, which are like a set of intructions that the robot runs exactly as it says. A factory robot moves around and doesnt have to worry about things around it, because the factory is a serious and controlled place, so there isn't random things like toys or trash laying around in places where the robots could be working. Because of this, the robot has a place where it can follow its program exactly because there's nothing unexpected to stop it! In your kitchen, there's all sorts of different things, and people have lots of different kitchens, so you would need a program for each kitchen! Combined with the costs of making the many different programs for a robot, the cost of the robot, and how you need a space just for it, it's costs a whole lot more money to use a robot than a person.",
"Imagine a car with wheels is racing a car with human like robot legs. Might sound funny but obviously the wheel is superior in this task. Now imagine you want to climb over boulders and the legs have an advantage over the wheels. If the problem is repetitive (sorting ripe tomatoes from unripe ones for example) and high volume then the robot option is the way because the cost of making it can be made up over time and the performance of it also beats the cost of paying people to do the task. Once set up the thing should run with minimal maintenance. The down side is that this will *only* sort tomatoes and can't be used to sweep the floor or pick up the mail or answer phones etc. A restaurant needs a lot of those alternative functions like cleaning and customer service. The ability to simply change a menu by giving your cook and new recipe vs what a robot would need, if there were new ingredients for example, is another reason to choose people for this task. tl;dr - There are not cooking robots in restaurants because the needs of a restaurant are not best met by a robot.",
"There are a lot of reasons, but most of them boil down to money. Robots are expensive. Restaurants usually don't have a lot of extra money, so they'd rather pay workers a few hundreds of dollars each week instead of trying to come up with thousands of dollars for a robot. Also, to have a robot that works with food, every bit of it will have to be certified as \"food safe\" by the government. That makes them even more expensive. Robots, especially ones that operate in places that are full of heat, smoke, steam, and grease, need maintenance. It costs a lot more to hire a robot maintenance person than it does to hire a high school kid who can flip burgers. In addition, you need someone watching, in case something goes wrong. Robots can do a lot of damage if something goes wrong, and if it's working a hot grill, that could include burning down your restaurant. Finally, people are used to having their food cooked by other people. Some of them might not trust a robot to do the same job, and will stop eating there. Some might also stop because they don't like the idea of robots taking away people's jobs.",
"There actually are several restaurants which use robots in their preparation process. They aren't everywhere and can't do everything because it still isn't economical to do so: humans are still often cheaper than robots would be. Just search \"automated restaurant\" for examples. & #x200B; Precision robotics in manufacturing tend to only do very simple and very standardized processes. If you need them to do something else, you need to reprogram and retool them for a new task. On top of that, the end products are things which use a lot of expensive materials, so they can be sold at expensive prices and thereby achieve a high rate of revenue return per automated process. Or, they produce massive volumes which accomplish the same thing. Restaurants, in essence, produce a comparatively small amount of dishes which sell for a comparatively small amount of money. Not to say that a restaurant can't be profitable, but it requires processes that can't be automated to the same extent, economically, in most places. & #x200B; It takes a lot of adaptability to manage many non-uniform ingredients in such a way so as to produce an end dish of high quality. You can mass produce the same end food product and that is done using automation, but they are of, if not lower quality in ingredients, of boring uniformity throughout each iteration of the product.",
"The issue wouldn’t be, as some replies suggested, the varied sizes and shapes of the ingredients. It could probably weigh ingredients, use a meat thermometer and make better estimates about when the desired internal temp will be reached than I could, it might have a better time with heat management on a stove it’s never worked with before than I would, and it would definitely be better at cutting stuff into very equal pieces than I would (I’m an ok home cook for reference). With somewhat greater difficulty it can probably be taught how to identify the exact moment when something is perfectly cooked; it could probably actually tell how well a steak is cooked by touching it, something some people think they can do but they cannot. A robot can indeed be taught how to do specific things orders of magnitude more precisely than a person could. Problem one is it would also cost orders of magnitude more than teaching someone to be a decent line cook and paying them whatever line cooks make. Problem two is it would be totally incapable of intuition and improvisation. You can’t tell it to make a soup of the day out of whatever ingredients are left over, it has no concept of what to do or if it even should do anything if the kitchen’s out of something, and god forbid someone asks for a dish with an ingredient removed. Imagine if it’s making, for example, a dish that starts by sauteing some onions, then some mushrooms, then something else when those are browned. It’s also programmed to add the salt when it adds the mushrooms to draw out the moisture faster. If someone asks for that dish minus the mushrooms, a human could easily make that no problem. With a robot it’s entirely possible it omits the salt entirely with the mushrooms, or burns the onions because it’s programmed to saute the mushrooms for x minutes after the onions are done and before adding the third ingredient, or it just looks for perfectly browned mushrooms in a pan it hasn’t added mushrooms to so it never proceeds. Sure, you can add workarounds for that... Are you going to be able to do that for every single dish, knowing full well if the programmers miss one bug that’s probably going to end in a kitchen fire with the very expensive robot just watching impassively because they couldn’t figure out how to get it to extinguish fire without it freaking out when it sees a gas stove or flambe? And all of that is assuming it doesn’t just stir ingredients everywhere right out of the pan because you didn’t buy the proprietary standardized iPot that costs 500 dollars."
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hk2ys4 | Towing a Tesla. | If you add a current to an electrical motor it will provide physical force. If you apply a physical Force onto an electrical motor it will become a generator. So what happens if you need to tow a Tesla? Could it potentially damage the batteries due to over charging? | Engineering | explainlikeimfive | {
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"You cannot tow a Tesla the traditional way for exactly this reason. Flatbed or using dollies. Plus, you have to use Tow mode which disengages the electric parking brake to get it up on the flatbed. Towing with wheels on the ground will invalidate your warranty. URL_0",
"it can't overcharge because the charge controller will limit the amount of charging. if the battery pack is full, the controller just won't have the motor regenerate any more. yes you can charge it by towing [ URL_0 ]( URL_0 )"
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hk93pb | Does hot water take so long to reach the bathroom/faucet furthest from hot water heater simply because of the distance or because the temperature of the pipe all along the route steals the waters heat? | Engineering | explainlikeimfive | {
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"Both. The pipes are full of cold water that has to be flushed out first. The further the pipes are from the water heater the more water to flush out. The pipes also act as a heat sink for the hot water traveling through them. The amount of heat lost to the pipes is a function of material, length, whether or not it is insulated, etc. Eventually the pipe will heat up to the temperature of the water at which point the air around the pipes becomes a heat sink. This is where insulation helps retain the heat. Not usually a problem for domestic water applications but the pipes in a power plant are insulated to retain as much heat ($$$) as possible.",
"All the water remaining in the pipe between the hot water tank and the faucet has to be flushed out before the actual hot water starts coming ou"
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hkjbh9 | How combustion engines work. | Engineering | explainlikeimfive | {
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"Let's break this down, shall we? \"Combustion\" is the process of burning something. An \"engine\" transforms some type of energy into mechanical energy -- the energy of motion. So, a \"combustion engine\" transforms the energy released by burning into the energy of motion. How does a combustion engine do this? Let's look at [a diagram]( URL_0 ) of a *cylinder,* one of the units of an engine. (This is a depiction and description of a *four-stroke engine;* there are other types, but this will serve as a sufficient primer.) The piston in the center moves up and down within the cylinder cavity, and it's this motion that drives the process. For the purposes of this discussion, fuel and air are put into the chamber through the port labeled \"mixture in,\" in the upper left, as the piston moves downward. This is the *intake stroke.* Next, the two valves seal the in- and outflow ports, and the piston moves up, compressing the fuel-air mixture. This, logically, is the *compression stroke.* Compressing the mixture makes it so it burns much more energetically in the next phase, which is the *Power stroke.* Here, the spark plug at the center makes a spark, igniting the fuel mixture and causing a very rapid, very energetic burning -- a small explosion, if you like. The force of that explosion drives the piston down, imparting mechanical energy to the connecting rod and crankshaft below. The piston comes back up for the *exhaust stroke,* where the gases from the burned fuel leave the engine through the exhaust valve, and the process repeats from the intake stroke.",
"Suck, squeeze, bang, blow Gas is sent to a combustion chamber, compressed, the spark plug fires, and gasses are exhausted."
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hkk0to | How do satellites always point toward earth | Based on what I’ve learned from games like KSP and Spaceflight Simulator, anything in orbit will “roll” relative to the earth (ex if something is pointed away from Earth at one point in orbit at the opposite point of its orbit it will point directly at Earth). Obviously a satellite would need to be always pointing toward earth, so how would it? I’ve also noticed this with the ISS when I watched a timelapse that was taken from the cupola. | Engineering | explainlikeimfive | {
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"You could take that satellite as you describe, and gently spin it in the same direction as it is orbiting. If you get the spin rate just right then the same side will keep facing the Earth. Conveniently there is no reason for it to stop spinning, so it will keep facing the right way. There are various mechanisms that you can use to adjust the spin: thrusters and reaction wheels are common.",
"They just spin around their axis with the same period as their orbit. Since there is very little to no atmosphere to slow them down, a tiny initial kick is enough to get them spinning for a while. [edit] They spin themselves using RCS or gyros."
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hkn2pm | How do they make technology smaller with all of the same stuff? | Engineering | explainlikeimfive | {
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"To manufacture things smaller, you need more precise machinery to make it. But to make the precise machinery, you need more precise tools to make *that*. So there are slow, but steady improvements where the technology we already have allows us to develop better technology. Cost is also a huge part of this. Once machines that could physically assemble small electronics (pick and place machines) became cheaper it became practical for more companies to make small electronics affordably, while before they might have been assembled by hand with a larger size and greater cost. As these machines make electronics cheaply, it becomes cheaper to make the machines as well, and the ability to assemble such small and precise things becomes more widespread. Computer chips themselves are made with a complicated electrical/chemical/physical process that has many factors involved in it. There are only a few companies in the world that produce state-of-the-art processors like the ones in modern laptops and phones. They have a combination of the best knowledge and the best equipment, which is constantly refined to make them better and cheaper (cost reductions mostly come from fewer mistakes happening in manufacturing so more of what they make actually works and can be sold). There are so many precise tweaks and refinements, and so much expensive equipment that if one of these factories was lost, it would take quite a long time to regain those capabilities even if you had people who knew how it worked. Basically it’s a lot of different technologies combining and building upon each other to make things smaller and cheaper."
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hks1a7 | what’s going to happen if I pull the hand brake while drive at high speed (e.g. 70 mph)? How is it different than step on the brake hard? | Engineering | explainlikeimfive | {
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"One thing to note is that since many hand/emergency brakes are cables actuating the rear brake calipers, they are not restricted by any anti-lock brake functions of the car. A very firm application may cause the rear wheels to enter a skid, which may result in the very rapid loss of directional control of the vehicle",
"Your handbrake is cable actuated and not power assisted. It is MUCH less powerful than your foot brake. You can drive at highway speed in dry condition with your handbrake fully pulled up. You'll burn your brake pads and rotors but you will barely slow down the car."
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hl864c | What is the most important algorithm in modern computer science? | Engineering | explainlikeimfive | {
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"Currently in Grad school for computer science. I can't really place just ONE important algorithm. What's more important is the efficiency of an algorithm. With the vast amounts of data being dealt with by companies/organizations/governments, you need algorithms who's growth rates grow slowly as the amount of data increases. In this vein, log base 2 of n efficiency is a great efficiency to shoot for when possible. So think of the binary search algorithm as a good example."
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hld43u | How does putting power back into the grid work if you have solar panels at your house, like if I plug a battery into the outlet that's fully charged it won't suddenly lower my electric bill, so how would renewable energy work in this sense? | Engineering | explainlikeimfive | {
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"There's a \"grid tie\" especially for solar panels putting power into the grid, but it powers your home before doing that, my father recently put up an array and it will cut his power bill in half, so in reality none of his electricity is going back into the grid, it's being used to power half the house. > Most systems sold in Australia are connected to the electricity grid and therefore require a ‘grid feed’ (or ‘grid tie’) inverter. In a grid feed system, electricity produced by your solar system will supply your home and its appliances first, and only feed electricity into the grid if there is any surplus electricity. URL_0 The power company granted him $10K to install the panels (30K job)"
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hldoc5 | Why do fans and propellers have different amounts of blades? What advantage is there to more or less blades? | My younger sister asked me this, please help! | Engineering | explainlikeimfive | {
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"It's mostly a balance between efficiency and power available for the same space taken up, and material strength. Less blades are more efficient. Because more blades in the same space creates more drag. Ideally one blade is the most efficient. One blade however is hard to balance. Two blades have another problem because the still tend to wobble a bit if things aren't perfectly balanced. More blades spread uneven wobble around the circle more and leads to the whole thing being more stable. It's not unworkable and lots of helicopters have two blades. Three blades is a decent compromise between efficiency and stability. That's why you see lots of wind turbines with 3 blades. After 3 more blades are usually compromising efficiency for more power in the same diameter. Each blade individually bears less load so you get more thrust for the same radius propellor before the propellor material isn't strong enough. You also get more thrust for the same RPM, and max RPM is limited because at a certain point the propellor tips go supersonic which causes shock waves which is very bad for the propeler which is already under a lot of force. They tend to explode."
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hlg24y | Why does flipping the tab on my car rear view mirror reduce the amount of light from vehicles behind me? | Engineering | explainlikeimfive | {
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"The rearview mirror of most cars is not like normal mirrors because the surface of the glass is not parallel to the mirror at the back. It is a wedge. The Guide Lamp division of General Motors worked on head and signal lights and also came up with this solution to headlight glare in the early 1950s. Although glass allows light to pass through, some of it is always reflected but you only see this when it's darker in the surroundings. The front glass surface of the rearview mirror reflects only about four percent of incoming light. In the day time, the silvered back of the rearview mirror reflects the scene behind you and some reflects off the glass front and away. The front glass also reflects a faint image of your lap but because the main image is so bright, you usually won't notice it, unless your pants are on fire. At night time, your pupils dilate so you're more sensitive to light levels. By flipping the tab, you change the angle of the mirror so that the headlights bounce off the silvered surface and away from your eyes, while a small amount bounces off the front surface of the glass so you can see a dim image of the headlights.",
"This is actually a super neat trick. The mirror in your car isn't flat, it's shaped like a wedge. (Thick part on top, and the point of the wedge at the bottom) The mirror is actually reflecting two different images at the same time, one from the back surface, which is fully reflective, and one from the uncoated or partially coated front surface which is much less reflective. With the mirror the day position you see reflections from out the rear window on the back of the mirror which is near full reflective combined with a much weaker reflection of the inside of your car, probably the rear seat. The weaker reflection gets washed out so you don't notice it. At night when you flip the mirror up you get a weak reflection out the rear window combined with a full reflection of your cars roof. But since your car ceiling isn't lit at night, and headlights are bright, the reflection of car headlights washes out the reflection of your cars roof.",
"To give a shorter and simpler answer to complement the longer one posted before I’ll break it down into: The shape allows it to reflect light off of multiple surfaces in the mirror and causing the reflected light to be less harsh. Other answer is more detailed and in depth, but this basic understanding should help understanding it."
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hlsfjo | Is it not pointless to 'warm up' the car when it's 90F outside? | Engineering | explainlikeimfive | {
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"I'm curious where you got this information, to warm a car up. As you can tell, it's not really needed any more. It sounds like you have been passed down a wisdom without the wisdom evolving to modern standards."
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hlsgtf | What makes the power go out during a storm other than something damaging the line? | power was out for 2 minutes during a multiple storms recently. city of 150,000 | Engineering | explainlikeimfive | {
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"Power transfer stations are equipped with surge protectors which will open circuits to protect the grid from a lightning strike. They need to be reset, which is sometimes automatic on a time delay, sometimes controlled remotely by the grid operator, or reset by hand (rare in the US)."
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hlwvhq | How a four-stroke engine lubricates when the piston is stroking upwards? | In two-stroke engines there is oil everywhere, and I get that there is lubricant when the piston goes down. But how does it lubricate on the way up whilst always staying below the piston? | Engineering | explainlikeimfive | {
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"While the piston is up, there's oil being splashed on the cylinder walls from below. Then, the piston moves down. The piston rings glide over the oil, and push the excess back down. On the way up, they're riding on the residual oil from the previous step."
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hlxwgt | How did ancient people know how and where to dig freshwater wells? | Engineering | explainlikeimfive | {
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"People tend to live where there's soil for growing crops, silage, or trees. Soil normally sits atop either bedrock or some other kind of impermeable layer (like dense clay). Rainwater percolates down through the soil, and collects atop the impermeable layer forming an aquifer. Basically just about everywhere our ancestors could live would have an aquifer under it, so really it was just a matter of picking a spot at random and digging deep enough. This why dowsers became a thing. Any schmuck could walk around with a bent stick and pretend to use it to find water underground because you almost can't fail at the task."
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hm0cfa | How are ziplines set up between long distances? | Engineering | explainlikeimfive | {
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"Usually they have someone walk the distance with a spool of cable and connect it to the other side. Then they pull up the cable to the height they want. Some times they drag a smaller cable, and use that to move over a bigger cable. In rare cases they throw or shoot a really tiny cable over, and use that to drag over a bigger cable."
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hm2cxy | How do deep space satellites keep their antennas pointed at the Earth? | Engineering | explainlikeimfive | {
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"For precise aiming, you can use reaction wheels, which are basically flywheels attached to motors. These can get saturated when they hit maximum speed, so satellites also have small thrusters that they can use for larger corrections. Running out of fuel for these thrusters is one of the big reasons satellites have a finite life in orbit. Satellites in low orbit will reenter in a few months to years, while geostationary satellites use the last of their fuel to park in a higher orbit, so they don't pose a debris hazard to operational satellites."
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hm9tpw | How do boats allow propeller shafts to rotate while ensure water is not coming into the hull? | I image if the shaft can rotate, it means the connection to hull is not 100% sealed. If it is not sealed, then water can come into the boat. There has to be a part in the boat where the water is completely stopped from reaching but still allows shaft to rotate. How does it work? | Engineering | explainlikeimfive | {
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"There are various forms of devices called \"shaft seals\". The simplest means is that there is something called \"packing\" in the space between the rotating shaft and the stationary tube around it. The packing is often much like string, often with something like graphite dust or wax added, and then compressed into that open gap with something called a \"packing gland\". It's very much the same as how you can use a tap or bib for a garden hose without water shooting around from around the stem (the axle on which the handle rotates). More complex seals will sometimes involve arrangements like a series of rubber barriers, each of which fit rather snugly around the shaft. This can allow in some leakage, but it's simply pumped back overboard.",
"Lots of o-ring seals along with either water or oil lubrication or both in layers. No one seal will be perfect, but if you have enough of them the amount of water ingress should be enough for a bilge pump to deal with. In larger shafts they'll pressurize the water/oil used for the seal and bearing lubrication so that the water will naturally want to flow out the unsealed end of the propellor shaft and not up into the boat. [Here's an example of the type of configuration]( URL_0 ) (they're all different yet somewhat similar). The water inside the shaft housing can be pressurized or the oil inside the inner housing or both. Also it helps to know that no boat is 100% leak proof. Boats leak ALL THE TIME. Steel ships have bilge pumps running constantly... if you've ever seen a stream of water being thrown from the side of a ship at dockside, it could be some generator/electronics cooling outflow or the bilge pump.",
"All of what people are explaining is fine, and true, but also realize that a \"prop drive\" is not that common for a lot of boats. Many personal boats use what is called a stern drive, or an outboard motor, both of which produce the rotation outside of the hull of the boat.",
"Another thing to understand with the above explanation of the packing material and packing nut is that the packing material is designed to absorb water and use it as a lubricant and coolant. For my boat we are told to snug the packing nut down so we see a drip every 20 seconds when the shaft is turning. There are dripless shafts also but the same principle is applied where water and the packing is what lubricates and seals.",
"Depending on the size of the shaft, different methods can be used. Seals, hydraulic bearings, oil, grease. Or a mixture of these. Hydraulic bearing is just a small tolerance space in which pressurised liquid like water is used to stop water from flowing in the the bearing system. But ships are designed so that certain areas can or have to be flooded. But generally we can say that the solution is tight machining tolerances and combination of seals. Because you dont want to just prevent water from coming in to the ship. You also want to prevent it from getting in to the bearing system, because it can disrupt the lubrication process. Along with prevent your lubrication from leaking out."
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hmo58j | How does a flywheel work to stabilize an electrical grid? | [This article]( URL_0 ) describes a "world's first" flywheel being built in Scotland to "mimic the spinning turbines of a traditional power station" to maintain grid stability. So how do traditional turbines (hydro and steam, I presume) maintain stability that a flywheel is useful to mimic them, and why are renewable turbines (wind) not useful. Is this the same problem that Tesla's Australian battery is tasked to solve? | Engineering | explainlikeimfive | {
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"Here's an important line from the article you linked: > The task of keeping the electrical frequency of the grid steady is becoming more challenging because Britain’s growing stable of renewable energy projects do not use the same giant spinning turbines that typically help to keep frequency stable. The spinning turbines in fossil fuel plants usually rotate at 50 Hz in the UK (60 in the US). Because generators produce one full cycle of AC in a single rotation (the voltage goes up to +320V, then down to -320V, then back to zero), this 50 Hz rotation was responsible for making sure that the AC in the entire electrical grid was at 50 Hz. A lot of equipment relies on this frequency being fairly precise, or else it can't function correctly. When power is drawn from a turbine (for a small scale example, imagine turning on the lights), the coils of wire inside it will actually generate a magnetic field opposing its movement. Which means that when a whole lot of power is drawn all of a sudden, or if some turbines go offline (which is what happened during the blackout), the turbines can actually slow down because they have to push against this magnetic field. When the turbines slow down, the AC frequency drops, and if it drops enough then they have to disconnect people's power to reduce the load, which is the cause of the blackout. The UK has been switching over to wind energy more and more lately. The turbines in a windmill do not oscillate at a steady 50 Hz, which makes it harder to keep the grid at a constant frequency. Basically, the flywheel is connected to a generator, and they will use a motor (powered by the grid) to spin the flywheel at 50 Hz. It won't actually generate any new electricity (since it's powered off the grid), but it will help to keep the grid frequency at 50 Hz by acting like a generator turbine."
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hmst0t | how can a car be 2 seats and a tiny gap wide but a bus is 4 seats and an aisle wide yet they both fit in the same sized lane. | Engineering | explainlikeimfive | {
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"Another thing is that the side walls of busses are straight up/vertical, whereas cars taper off, so the roof is less wide when the base. This has some structural benefits, but not for seating room of course",
"Here is a photo of a bus next to a car for visualization [Photo]( URL_0 ). And here is a photo of a highway where you can see that the lane is way more wider than the car while the truck in the right nearly takes up the whole lane width. [Photo]( URL_1 ) So just because two vehicles fit in the same lane doesn't mean they are the same width. Edit: The truck doesn't 'nearly' take up the whole width but it takes more width than the cars.",
"Because cars take up less than half a lane, and a bus takes up most of it. The normar car is about 2 meters wide, and a lane about 5 meters wide. busses are generally 4 meters wide. The only extra thing you need is narrower seats - and busses have very narrow seats.",
"ELI5 why are some things bigger than others? Seriously don't get the questions asked here sometimes.",
"The maximum width for a vehicle on U.S. roads is 8.5 feet. I don't how many metres or decibels or whatever the hell you call them in UK Land.",
"The vehicles themselves are not the same width. In the US, lane size minimums are defined by the federal DOT but actual lane sizes are dictated by state DOTs. For example, I live in Texas (and am a former employee of the Texas Department of Transportation) and our current \"rural highway\" standards for new construction are 12 ft lane (3.65m) with 8 ft shoulders with a speed limit of 70-85 mph. Only part of I-10 between Ft Stockton and Junction and part of I-20 between Ft Stockton and Odessa have 80's, and SH-130 between San Antonio and Georgetown has an 85 (but the toll camera's have been tested up to 220 mph so don't think you can out run them in car). Anyway, my pickup is 72 inches (6 ft) wide. It won't seat three adults across comfortably, but it will sit three across (in the front row and three across in the back row). Most US busses are 8 ft or 8.5 ft wide (designed for 4 adults with an isle or six children with an isle). My Jetta...is a standard Jetta so two adults and one child."
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hmugri | How has the ISS managed to stay in orbit for over 20 years and not be obliterated by random space junk moving faster than a bullet? | Is it just pure luck? Or is there some sort of mechanism or system in place to divert or destroy the junk before impact? | Engineering | explainlikeimfive | {
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"At orbital speed, any small object will just immediately disintegrate on impact rather than stay intact and penetrate like a bullet. That means that it is enough to have two or more layers between space and the crew - a collision might punch a hole through the outer layer, but probably not through the second because all its momentum is spread out over a larger area. But if any large object hits the ISS, it might destroy the entire thing and kill its crew. For that reason, they track space debris with radar, and if it is estimated that it will pass the ISS (or any other satellite) too close for comfort, they will use their thrusters for evasive maneuvers. In addition to that, at the altitude that the ISS is orbiting, there is still a very thin atmosphere. Anything flying up there is slowing down and will eventually fall back to earth. Which means that the ISS has to use its thrusters anyway to maintain its altitude, which can be combined with evasive maneuvers. It also means that debris at that altitude cleans itself up after a while. Debris is a much greater problem at higher altitude, above 500 km. There, the atmosphere is so thin that all that junk will basically stay there forever.",
"ISS and the spacecraft that is docked has trusters that is used to do debris avoidance maneuver. There was one done [last Friday]( URL_0 ) when a docked Progress cargoship raised the orbit by 900 meters So large space junk it tracked from the ground and actively avoided but for dust size, you build it so it can sustain impacts. Here is an [image of an]( URL_1 )[ impact on the cupola windows.]( URL_1 )",
"The ISS purposefully occupies a very low-altitude orbit. At its height, there is enough residual atmosphere to induce a tiny amount of drag. This slows down orbiting objects and eventually causes them to fall into the atmosphere where they burn up. The ISS avoids this fate by getting the occasional speed boost from visiting spaceships.",
"OP - there is some small atmosphere there, which helps clean up debris. Furthermore, due to the fact that as something halves in size, surface drops to 1/4 but weight to 1/8, small particles have a much greater surface to mass relationship so they drop speed much much faster. In short, a particle 10000x smaller loses speed 10000x faster, everything else being equal. So in effect that atmosphere scrubs small particles, the smaller the better. Also air resistance - which is what decelerates them - grows roughly with square of speed, so the very fast particles burn up their speed fast. The ISS, being comparatively massive, loses speed slowly and just needs some regular boost.",
"I believe smarter every day has a cool video on this but: Anything large enough to penetrate the hull is tracked and manually avoided. Anything too small to be detected that hits a spacecraft will first hit a (i believe) a kevlar weave that is not meant to stop the object but burst it into many pieces and absorb momentum. Afterwords the shrapnel of the object travel another 6 inches or so and strike a aluminum sheet that is strong enough to stop the ,now slow and small, shrapnel. Astronauts often report hearing the pinging of small impacts on the hull. Very unsettling Edit:spelling",
"Simply put, because as much junk as is up there, it's STILL basically empty space. Even including intact and functioning gear (such as the ISS itself) the difference in \"density\" in orbital space between now and when we first started chucking stuff up into space is so small that in most other disciplines it would fall beneath the noise floor for your measurements. Let's take Geosynchronous orbit as an example. That's up at an altitude of 22,236 miles, which means it is a circle of 139,713 miles in circumference. Now lets make an assumption that every geosynch satellite is the size of a city bus, which google says the largest ones come in at 45 ft long. It would take ~16.39 MILLION satellites to end up with a ring of physically touching material. How many geosynch satellites are there currently? 402. So generally speaking the statistical likelihood of a collision is very small even if we do nothing. But it does still happen occasionally regardless, which is partly where US Space Command comes into play. They operate ground radars which track just about every bit of material up there larger than a few millimeters in length. The world's satellite operators (even 'enemy' nations) all have contact info on hand and if their satellite is at risk of running into something (another satellite, or just junk) they will call them up and warn them about it. It's one of those duties where it benefits everyone, even enemies, to work together on because nobody really benefits from satellites shattering up there. In the case of these messages being received, the parties involved will figure out an agreeable system for who moves and in what direction.",
"Finally something I can answer! Satellite engineer here. The ISS travels at about 4.8 miles/second, so even small, stationary debris has a lot of relative momentum. To protect the ISS from damage, it has something called micrometeorite and orbital debris (MMOD) protection. It usually consists of two layers of material: the outermost layer slows down the debris, and the middle layer breaks up the debris so the impact on the innermost layer is spread over a large area. Some spacecraft have many layers of this design. The Air Force can detect any debris in low earth orbit larger than about a grape. If it detects debris in the path of the ISS, they notify mission control and steer the spacecraft out of the way. If the debris is too small to detect, its up to the MMOD protection.",
"It's been able to stay in orbit due to the gravitational pull around Earth which is keeping it from flying away into space and the space junk is located both beneath the iss and above it. Sometimes it will encounter space junk flying near it and the astronauts have to take evasive actions but that is the best thing they could do for many years because a means to fully tackle the problem hadn't been invented yet. [ URL_7 ]( URL_1 ) The good news is that in the last few years, there is a solution and it's going to be released in 2025. [ URL_3 ]( URL_2 ) If an astronaut gets a puncture in their suit, they would last about 15 seconds before fading out of conciousness. There is no oxygen in the depths of space. [ URL_0 ]( URL_0 ) Chis Hadfield says it smells like burnt steak. [ URL_5 ]( URL_5 ) [ URL_0 ]( URL_0 ) What they do with space junk is most pieces will burn up in the atmosphere but the larger pieces can land back on the surface. Some pieces that stay in space are abandoned vessels or satellites. [ URL_4 ]( URL_6 ) & #x200B; Some countries like China have shot missles at their defunct satellite which added to the problem instead of solving it by creating thousands of small pieces upon impact. The bad news is that sometimes a piece of junk can come close to the station, and risk smacking it. If the hole is small enough, they seal off that area and patch the hole. If it's a larger piece they might have to evacuate the iss. The junk though isn't in one spot up there like the great pacific garbage patch, it's everywhere in a sort of giant belt and it's moving. If it's a serious enough threat to the station, the astronauts have emergency spaceships to escape the iss in case of emergencies. To grab all of that junk and dispose of it would be financially large and risky because if the vessel towing it, gets smacked by a stray piece of junk it could puncture a hole into the craft or suit of a astronaut and after symptoms are finished, depending on the circumstances it varies. Some astronauts are frozen in space, other's can be mummified if they're near a heat source even because they're no oxygen in space at all. One man in 1965 survived a pressure issue and said the saliva on his tongue boiled after he lost consciousness in 14 seconds.",
"Quote by Douglas Adams: “ “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.” Chances of intersect are small - lots of bits but much more space for bits.",
"short explanation is iss travels really low on earth's orbit (where any \"junk\" falls down to earth) and slowly falls down to earth so they use propulsion to prevent that.",
"I don't have the math behind this, and maybe someone in the comments can get closer, but probability distributions IRL create events that are difficult to comprehend in normal human terms. According to Nasa, your question is easily answered and [Google did a good job:]( URL_1 ) 10% a year, over 20 years, is still difficult to get a strike on because 20 years is not very long in terms of sample sizes when you're talking about 1 object (regardless of the huge surface area the ISS takes up). Combined with the ability to constantly change the primary variable (ISS location) via thrusters, it's no wonder we've never seen a collision incident in the tiny amount of time it has been in orbit. Brown did a really good job developing visualizations for probability distributions: [ URL_0 ]( URL_0 ) When you start to compound the probabilities for the ISS getting hit, year over year, the math becomes incredibly un-intuitive and you can come to conclusions that don't match real life results. [The Bayesian trap is a good example of this.]( URL_2 ) Long story short... Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is."
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hn0j8f | how does a backup generator hook up to the house? | I'm now reliant on a nebulizer. When the power goes out, as it has been doing frequently these days, I panic. I've got a portable unit that plugs into the car's lighter, but I need to get a generator. Must I get an electrician to hook it up? How does this work? Thanks. | Engineering | explainlikeimfive | {
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"i think you're confused. if it plugs into the cars lighter, then that implies it's drawing power from the car battery through the 12v lighter outlet. a backup generator connects into the home power grid and supplies power for all the home outlets when the main power lines from the power company go down. and yes, you need to get a electrician to connect this to your home. another thing is you can get a portable generator that runs off gasoline/propane which you can plug into as well, but that won't connect to your home power grid and won't power the home outlets.",
"A whole house standby generator is a motor, typically powered by natural gas (presuming you have gas service) or fuel (which is a hassle for someone with limited mobility to refuel), which turns an AC generator. It's the size of a 6-person dining room table, sitting outside your house, near the power meter. It connects to your house with a auto-cutover switch, which detects that the power is off, starts up the generator, disconnects the house from the power lines, and finally connects your house to your generator. This keeps the lights and HVAC on, but it's thousands of dollars and must definitely be hooped up by a licensed electrician. There are forms you have to provide the power company, they have safety concerns and want to be absolutely sure that your generator can't connect directly to the power lines and shock their workers. Depending on the power consumption of your nebulizer, a backup battery might easily drive it for the duration of a multi-hour power failure. The advantage of this approach is that you plug the nebulizer into the BBU and the BBU into the wall. This doesn't take any electrician service calls.",
"Well, I'm not an electrician, but there are two basic ways to do it. First, is just run extension cords from the generator to whatever you need to power, fridge, nebulizer, etc. Cheap but super annoying. Second is to get an electrician to modify your household electrical panel to have either a manual or automatic switchover. When your generator is tied into your regular household electrical system, it's important to have a disconnect apparatus in place, so that your generator doesn't \"back feed\" it's electricity to the lines coming from the telephone pole to the house, or some poor linesman who is repairing the telephone pole after the tree limb falls on the wire will get electrocuted. So this disconnect can be manual, when you go flip a kind of giant circuit breaker, or automatic, where there is a device that senses if the power from the street goes dead and will flip the switchover device and start your generator for you. Obviously manual stuff is cheaper than automatic stuff. Another thing to consider is how much do you want to power? Every device uses a certain amount of watts, it's always printed on the device. You need to total up how many watts you need to power, then pick an appropriately sized generator. I'd say whatever the amount of watts you want to run, multiply that times 1.5 at least to make sure you have some room for expansion. You don't want the generator maxxed out all the time. There are also plug in devices which can determine how many watts a device uses. So buying a generator, a socket mounted on the wall where you can connnect your generator to your house, and a disconnect switch can run a few grand. A fully automated system which can run your entire house, with a permanently mounted generator and the whole works can cost tens of thousands of dollars. So it all depends on what you want and need out of it. Another option you might consider is getting a bunch of car batteries and wiring them up to an inverter. That will turn 12v DC from the batteries into 120v AC like your house uses. You would need to keep the batteries charged of course, but if the amount of watts is low and you don't want something you need to keep refilling with gas all the time, it might be a better option. Make sure you get a float charger and deep cycle batteries."
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hn3wyh | Why do some appliances need fuses? | Engineering | explainlikeimfive | {
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"Fuses are fundamentally overcurrent protection devices...aka safety devices. But in design they can also mitigate mismatched loads. They intend to remove power when a system faults for any number of reasons. Circuit breakers also perform this function."
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hniiyu | When a car engine is listed as having some amount of liters (like a 3.2 liter engine), what does that actually mean? What does that affect, and how? | Engineering | explainlikeimfive | {
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"Liters, cubic inches or cubic centermetres (cc's) for smaller motorcycle engines all reference the displacement of the area inside the piston cylinders where the gas and air mix and explode to provide the force that moves the pistons, and thus moves the car. In general, the more explody gas action from more cubic inches or liters or whatever, the more power you get from an engine. However there's lots of nuances to it. There are ways to get a relatively small (like 1.4L) 4 cylinder engine to produce almost as much (horse)power as a larger 3.6L V6 engine for example, likewise a modern 3.6L V6 engine from today may have the same amount of horsepower as a big 5L V8 from 15 years ago. But stuff like torque and energy efficiency and compression ratios and turbo/super charging is a bit beyond the ELi5 level.",
"From a recent discussion with my son. \"ELI9\" ;-) The engine's pistons work like legs on pedals on a bicycle, and cars usually have 4, 6 or 8 of these \"legs\". Instead of you using your muscles to push the pedal down, each of these \"legs\" in the engine is attached to a little chamber where fuel and air are mixed up then exploded. That explosion makes the leg come down and turn the crankshaft, just like your leg pushes the pedal. The liters, cubic inches, cubic centimetres, etc. refer to how big those explosion chambers would be if you added them all up. So a 4 cylinder 2 liter engine has four \"explosion chambers\" that, but together, would hold a carton of milk (2L). All else being equal, bigger chambers allow for bigger explosions, and more powerful pedal pushes.",
"Think of an engine as an air pump. That’s the amount of air pumped through every time the engine cycles. That’s because the liters listed is the sum of the volumes of space traversed by the pistons as they go up and down. If you had an imaginary 1 cylinder 1.0 Liter engine, the piston would be about the size of a liter bottle and would move up and down about as much as the liter bottle is tall. (Edit; thanks to u/RedFiveIron for teaching me that air isn’t cycling through each rotation of a four stroke engine. I changed my description to “cycles” instead of “rotates”)",
"Most of the top answers are close but not accurate. The displacement is not the total volume of the cylinder or combustion chamber (then multiplied by number of cylinders), but rather it is the difference in volume between the combustion chamber at it's largest (piston furthest from the cylinder head) and at its smallest (piston as close to the cylinder head as it goes in that engine). Even at its smallest, there is some volume in the cylinder, and that volume does not contribute to displacement. So, essentially, it's a measure of how much the air/fuel mixture can expand when ignited (which is done at or close to the smallest size of the combustion chamber), which is why it is so closely related to output power, because that expansion driven by ignition is what produces the power in the first place.",
"The amount of liters refers to the total displacement (aka volume) of the cylinders. The cylinders are what actually provide the propulsion by burning gasoline."
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hnm1r9 | In modern aircraft, why are jet engines mounted on pylons away from the wing or body, while propeller engines are integrated directly into the wings or body? | Modern passenger jets, business jets, military transporters, and most other turbojet & turbofan powered aircraft (with the exception of fighters) mount their engines on pylons that stick out from the body or down from the wings ([examples here]( URL_1 )). Doesn't the pylon and nacelle add weight and drag? Why wouldn't they be built into the aircraft as much as possible to reduce the aircraft's frontal area and mass? Meanwhile, turboprop & piston engines are almost always integrated into the wings or fuselage ([examples here]( URL_0 )). Intuitively, this seems way more optimal. Why can't this be done with turbojets? It has been done in the past (see the [de Havilland Comet]( URL_2 )), so what was wrong with that solution? | Engineering | explainlikeimfive | {
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"The only jet engines you'll see incorporated into the body of the aircraft are low bypass turbojets like those used on the Comet, high bypass turbofans are massive Pylon mounting of turbofans comes with several important benefits. You don't have to integrate a 70\" fan into your wing design. The engine is closer to the ground making it much easier/cheaper to service. You don't have to radically redesign your wing or entire aircraft just to change out the engine. This last one is probably the biggest. Through the years aircraft engines have gotten bigger, and the ability to upgrade the engine and source slightly different engines from multiple vendors greatly extends the lifespan of the plane. The original A320 could come with a CFM engine with a 68.3\" fan or an IAE engine with a 65.3\" fan. More recently they started offering A320s with new engine options(A320neo) which have a 78\" or 81\" fan. But because these engines are all mounted on a pylon, the wing and core of the airframe has remained the same through all of this which greatly reduced development and manufacturing costs Engineers like leaving options open because it potentially saves you a lot of time, money, and effort in the future",
"Have you seen the SIZE of modern jet engines? Unless you build a flying wing concept that can encompass one of those absolute units, on pylons they go. Interchangeability also plays a factor, as you can swap engines/manufacturers easily from a pylon setup, without having to rip the entire airframe apart."
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hntxmd | Why aren't all the truck wheels on the road? | Im talking semi's with trailers, sometimes they dont have all the wheels on the road. Like one set is lifted up, why? | Engineering | explainlikeimfive | {
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"It mostly has to do with weight. Fewer wheels mean less friction, less moving parts, and better mileage. However, under very heavy loads, the trucks need that additional support on the road to evenly distribute the weight.",
"Pavement engineer here. Truck loading is what damages the pavement, and is what we design our pavements to support. Passenger cars are so light in comparison, we do not use them when calculating the materials needed and their thicknesses. There are laws for each state in the US as to what the maximum allowable weight per axle is, and even then, you can apply for an overweight permit and haul more if needed (that’s when you see the trucks with OVERWEIGHT LOAD signs on them and flashers.) We have permits so we can tell the overweight trucks which roads (bridges) are safe for them to take and which ones can’t handle the loading. As for truck axles, the trucks know what load they have and how many axles have to be on the pavement to carry that load. Each single axle (axle plus 2 tires) typically in America carries a maximum of 18,000 lbs. This even has an abbreviation called an “ESAL”- an “Equivalent Single Axle Load.” So nerdy engineers like me would say “how many ESALs does that truck have” or “how many ESALs a year do we expect to travel this road” when we design the pavement or bridge. So, if I’m carrying a bunch of soil from A to B, and it weighs 40,000 lbs, I know I will need to have 3 axles down (each axle carries 18,000 lbs, so 3 x 18,000 = 52,000.) If I only had 2 axles down I’d be in violation because my truck would be carrying 40,000 lbs when my axles down can only handle 2 x 18,000 = 36,000.) BUT let’s say I get to B and dump the soil and now I am headed back to A with an empty truck. Now my truck, dry, weighs 15,000 lbs. I only need 2 axles down to carry that weight. So newer trucks are designed so that I can pick up the extra axle and save wear and tear on the expensive tires, and ride back to A without having them down on the ground. Sorry to do math in a reddit post. Also, “designing pavement” I realize sounds weird to people (don’t you just throw down asphalt?) but it’s actually a neat science of planning all of the necessary layers (soil, then sub grade, then aggregate, then layers of concrete or asphalt on top).",
"Because the amount of weight you can carry depends on how many axles your truck/trailer has but it handles and turns better with fewer axles so they put them down when loaded and up when empty",
"I've one set of trailers that comes through my job, that automatically raises all but the rearmost axels when empty. For the empty run, this means less resistance and saved fuel, less wear on the brakes, tires and suspension. The expense for the system is repaid in fuel and parts over time. I also have other common trailers that have a manually controlled lift axel, and when the trailer is loaded lightly, it is not lowered."
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hnv65d | How does peer-to-peer energy trading work? | I was imagining if my neighbor could use my solar panels when I am on a vacation. Is it possible/feasible/practical? | Engineering | explainlikeimfive | {
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"In theory you connect it to the power grid through your electric meter, and any excess power is sold back to the electric company. In practice there’s a whole lot of red tape and hoops to jump through, it’s like the US is trying to discourage people from doing this",
"Not really practical at the moment, it would be quite expensive to have a setup that connects your panels to your neighbor’s power main safely installed. Your best bet is to sell the power back to the power company or run some bitcoin miners or something. Peer to peer trading as far as I can see is pretty much also you just putting your excess power back onto the grid but another customer buys that capacity off of you directly and the power company just takes a cut for the fee of using their power lines."
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hnxve5 | How do Japanese bathhouses keep their water clean? Is it a closed system like a pool or does the water replaced constantly? | Engineering | explainlikeimfive | {
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"In addition to water constantly flowing in and out of the communal pool, there is the expectation that people wash themselves on small stools outside the pool. This prevents soap and large amounts of dirt from entering in the first place.",
"As an extremely black male, I have seen this first hand in a hotel in Osaka. The water is constantly flowing and replaced with new water",
"In most places, fresh water keeps flowing in and replaces the old water. Some places that don’t have access to natural hot springs will have to recycle the water and there are machines that do that."
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ho6zbk | If pill capsules are only half full, why is the other half of the pill a long dome shape instead of just a flat cap? | Engineering | explainlikeimfive | {
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"Its curved at both ends the same because as you swallow it, you can't control which direction it goes down your throat. It would be difficult to swallow it if the flat side went down first. So having both sides be exactly the same ensures easy swallowing. In addition, they create the capsules in bulk. You can actually buy them from places if you want. So the companies that make them in bulk have no idea how much stuff is going to be put into them. The companies that are using them for their meds buy the size closest to what they need. If there is extra room, it's no big deal."
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ho86u0 | Why do cars have that weird blue tint at the top of their front windshield? | Engineering | explainlikeimfive | {
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"The tint strip on the windshield is actually known as a shade band. Its purpose is simple: to provide protection from the sun’s glare in that pesky spot just below your roof line and just above the visor. That spot is notorious for being difficult to block when you are driving into the sun shortly before sundown. The reason the shade band is only four to six inches in height is so it doesn’t obstruct or obscure your vision when you are driving in normal traffic. If the shade band stretched any further down, it could cause a distraction to some drivers or make it hard to see traffic lights at an upward angle."
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ho9ua0 | how do carburetors work? | Engineering | explainlikeimfive | {
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"A carburetor is a basin of gasoline with a little nozzle in it that leads into the pipe through which the air is sucked to the motor. Because of the pressure, some gasoline is also sucked through the nozzle and into the airstream, where it makes the air a combustible mixture. The basin is refilled by a valve that floats on the gasoline. When the basin is low, the valve opens and lets some more gas in from the tank. Idle is done by setting the throttle valve in the airstream to open just enough. Edit: check out some technical drawings for better understanding"
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hockjz | When are Allen keys better than cross or Phillips head and vice versa? Are there any other types? | Engineering | explainlikeimfive | {
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"text": [
"Allen keys are better than Phillips at all times. Use a Robertson bit if you want a better screwdriver bit. Phillips is suitable for anyplace you don't mind stripping a screwhead."
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hom5hz | Why are train stations and rails covered in pebbles/rocks? | Just rewatched Train to Busan, and wonder why the ground are covered in pebbles? | Engineering | explainlikeimfive | {
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"It’s called [Track Ballast]( URL_0 ). Good quality track ballast is made of crushed stone. The sharp edges help the particles interlock with each other. Track ballast forms the trackbed upon which railroad ties (sleepers) are laid. It is packed between, below, and around the ties. It is used to bear the load from the railroad ties, to facilitate drainage of water, and also to keep down vegetation that might interfere with the track structure.",
"One thing is that rocks and pebbles help stabilize the ground. When train goes on the rails and the ground is made of sand or something else that is fine particles, the vibration from the train can make the rails sink under the train. But when the ground is made of rocks and pebbles, the rails won't sink. I don't know if there's more to it, that's just one thing I've heard."
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hoxcbb | "db" in physical Noise Levels, Analog Audio Equipment, Digital Sound Software. What are these and how they relate? Why are conversations at "60dB" and why is a Digital Software scaling it from negative to zero? | If in Digital Sound Software there's a meter from -60 to 0, what's the best "range" (for the lack of knowledge) of sound someone can record at? Considering that people who will listen to that recording can adjust their speaker volumes up and down. | Engineering | explainlikeimfive | {
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"A dB is a deci-bel meaning 1/10 of one Bel. It refers to a certain standard of measuring pressure or power. If your recording software has meters that show -60 to 0 dB, it shows how much headroom you have left or available before distortion occurs- record so that average levels are somewhere between -24 and -14dB without ever hitting 0dB. That dB is referred to as dB(FS) meaning “tenths of a bell below full scale” and an average of between -24 and -14 will correspond with 0dB on a VU (Volume Units) scale, the oldschool kind with a needle that moves.",
"0 is nominal sound. Thats the volume of the source, without any additional amplification or reduction. So you can add decibels or subtract them, which is why 0 is on the middle of a soundboard fader. Decibels also refer to general sound. You can't really explain what it is without getting into sound pressure level and such. But its basically a measurement of \"loudness.\" A normal conversation between two people = 60db. A jet engine is about 140. Just know that while you record something, it has an inherent value in db. Then, when you put it through an audio system, if the system is set to 0, you're going to hear it at the same volume that you recorded it in."
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hp1d3s | why must coal be used for generating electricity? Generating electricity is mainly about turning the generator right? Then why cant we use other methods like manual power? Some might say its not consistent and good enough but cant they use gears? Thanks in advance | Engineering | explainlikeimfive | {
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"We use a *ton* of other methods. Geothermal, hydroelectric, wind, nuclear, ethanol(?) But for the amount of power we need to generate in a centralized fashion (on the scale of a conventional plant) you'd need so, so, so much manual power. You'd need an entire pocket industry of workers willing to run on hamster wheels all day long. It's just not necessary when we have a bunch of other ways of generating that energy that doesn't waste people's time.",
"Because there's massive amounts of the stuff and massive amounts of power is what we need. 400 W is the best an athlete can do over an hour. ( URL_0 ). For comparison, your typical nuclear plant outputs 1 GW of electrical power 24/7. That's 2.5 million humans doing vigorous exercise. It just won't satisfy our power needs to rely on muscle power.",
"The amount of manual power required would be pretty ridiculous for how much electricity you get out of it. How much manual power do you think you need to compare to a turbine being spun by river water coming through a dam?",
"Coal has traditionally be used because it has a lot of energy per ton (and they do burn this stuff by the ton), and you get it by just digging it out of the ground. Its hard to match the combination of power and low costs. A person, btw, can generate about enough power to run a single 'fridge. There's no way the people in a family could actually power their home just from manual power. New methods -- methane, wind and solar -- have only recently been cost-competitive with coal. Methane's really only there because we have lots of it thanks to fracking; wind and solar depend on new materials to be competitive."
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hp4cs4 | Isn't nuclear waste hot and releasing neutrons or electrons or whatever? Why can't we just throw nuclear waste in a chamber surrounded by water to heat it up and generate power? | Engineering | explainlikeimfive | {
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"There's a large gap between \"radioactive enough to generate power\" and \"radioactive enough to give you cancer\". Most nuclear waste is stuff like containers that nuclear material was stored in, or gloves and suits used by people handling nuclear material. That stuff is in the \"radioactive enough to give you cancer\" range.",
"Nuclear reactors run on *very* thin margins, money-wise, because of all the safety features they need and because they're heinously expensive and slow to build. If you built a reactor to run on burned-down fuel you'd have all the expenses of a normal reactor but your electrical output and revenue would be sub-par. Secondary reason - if you had some fuel bundles from Reactor A and some other ones from reactors C and G, their isotope contents are going to be different and that will make your reactor run weird. You could get hot spots, cold spots, spots that react faster or slower to control rod changes, spots that burn off xenon faster or slower. That might all be manageable, but it makes the system less safe. Compared to all those hassles, fresh fissile material isn't all that expensive."
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hp4dci | High rises steel rust under rain during construction. Will there be any structural issues? | I often see high rises during construction sitting in rain and storms for months especially in places like New York. You can often see rust forming. Aren’t those rust going to cause structural issues? | Engineering | explainlikeimfive | {
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"Not a structural engineer or materials scientist by any means, but from what I know, that is simply surface level rust that doesn't affect the structural integrity of the steel beams.",
"The rust you see is just surface rust, similar to the underside of most vehicles. Structural issues would only develop if water was sitting on it constantly with no way to escape.",
"To start, rust is bad because it has a different density from iron, expanding and causing cracks that furthers the corrosion by exposing new surface. Second, many metals form protective oxide layers, like aluminum, which is harder and prevents any further corrosion. Steel is an alloy of iron, and some versions handle corrosion better than other steel alloys. To most structural steels, some surface rust patina is considered normal and mostly an issue with welding and finishing. Structural rust fractures should only happen if corrosive conditions persist in some spot for an extended time, which could be due to pooling water or galvanic reactions with other metals. URL_0 an example of steel meant to form a rust patina."
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hp4do0 | Why are houses in the US made of wood/gypsum boards but houses in India made of concrete/brick? | Engineering | explainlikeimfive | {
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"Only the wood studs are structural, the gypsum boards (also known as drywall) exist only to divide the interior of a building up. They are screwed into the wood studs and hang off them. The joints are taped, mudded (not actual mud), and then the surface is sanded and painted. Another way to do it is to plaster the entire wall, it depends on what kind of wall product is being used. The walls on the outside of a house is some kind of wood product like Orientef Strand Board (OSB), that's covered in a vapor barrier, and then a siding material covers that. If you see any modern brick buildings in the US there's a very good chance that the brick is only a veneer and not structural. The advantage of drywall is cost and installation. Drywall is a cheaper material, and it's quick to install. The void between studs are used for insulation on exterior walls, so no need to find or build in space for insulation as the construction method naturally leaves voids.",
"Wood construction is used in North America because wood is cheap and available. It's also very common to have brick and stucko/ concrete houses. We also don't have the same high heat and humidity in the more North areas, so wood buildings perform well."
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hp9qzn | Why is it that Retention/Detention ponds aren't built for swimming? | From an outsider's perspective, it seems like they're just small, man-made lakes. People swim and fish in man-made lakes all the time. What's different? Couldn't you just make retention/detention ponds the same way? | Engineering | explainlikeimfive | {
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"Retention and detention ponds are for drainage - they’re also called storm water management ponds. They are typically filled with runoff water from parking lots and other parts of a property and after a rain storm likely aren’t very clean. By storing water there, it keeps the dirty runoff from other clean bodies of water. A detention pond serves the same purpose as a retention pond but does not always have water in it. It’s often dry until a heavy rain. TL;DR That water is gross and you don’t want to swim in it. Edit: forgot some details. Their purpose is to filter the water so that it gets back into the water table clean. And they also prevent flooding.",
"Great explination by Crying; I design these things for a living, so I’ll just add that most of these are made as small as possible to meet water quality and detention (flooding) regulations. Every square foot taken by the pond is a square foot the developer cannot sell (his product). To that end, they maximize the function of the design and have no interest in making them any kind of swimming amenity. Plus the last thing in the world they want is the liability of someone getting hurt or drowning in their pond. So a lot of developers and municipalities actually design them to keep people out. I worked for a developer once who put up a “Protected Copperhead Habitat” sign to keep people out. These things also usually have a “littoral shelf” around the water’s edge that serves 2 purposes; shallow bench that allows vegetation to grow (deters geese) and shallow mucky area that is difficult for a human to walk through. So you have to really try to get through that and out to the deep part if you want to swim. Kid falls in, water’s only 6” deep, they can get out."
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hpadwt | What is "damping" (car suspension) | Hi. I'm becoming interested in cars and how they work. What is damping and how does it affect suspension and what does it do? (or dampening, idk if they are 2 separate words or are interchangeable) (I'm only 13 so a really simplified answer would be appreciated, I don't understand any sort of complicated physics) Thanks in advance. | Engineering | explainlikeimfive | {
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"You know how if you were to hold a slinky (those plastic, coiled-up things that \"walk\" down stairs when you start it off) in the air and let part of it fall toward the ground, it will oscillate up and down before it finally comes to rest? Car suspensions would behave the same way if there was no damping/dampening. The damping/dampening is performed by a shock/strut. A shock/strut slows the movement of the car relative to the springs, so the car doesn't continue to bounce up and down after going over a single bump.",
"It's similar to a screen door with a spring to pull the door closed but also a shock / strut / damper to keep the door from slamming.",
"Suspension springs cause the car to bounce when going over a bump. The dampers stop the bouncing motion again.",
"Damping provides resistance to movement. The faster the movement, the higher the resistance. This is different from a spring that will apply a force proportional to the distance it has been moved from its neutral position. Imagine a pendulum hanging freely, it will swing from side to side for a long time. Now put the end of the pendulum in a bucket of water, then pull it to one side. The pendulum will slow far more quickly as the water provides damping. Replace the water with honey, and this time the pendulum will take ages to return to its rest position. An undamped spring system will oscillate repeatedly, which would make a car undriveable. If the damping was too strong, the car would take too long to recover from hitting a bump, and badly affected by following bumps."
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hpawve | What are the limitations of using an inkjet printer to make PCB at home? | I have heard of a few copper or silver printing inks that can do this but not much else as a mainstream type of product. What are the limitations of using a home printer to make PCB boards? Is it the ink, the printer paper or plastic that need research? I dont understand why i can buy a material to print on and special pcb ink to make pcb's at home. Thanks for you help. | Engineering | explainlikeimfive | {
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"Quality and cost, mostly. You can make a decent PCB at home, but it's usually cheaper and easier to use a service for anything other than extremely basic stuff. A service does it all; they don't just print the board, they can print both sides aligned properly (which can be a HUGE pain), they drill the holes, they make the vias (connections between layers), etc. They can also make multilayer boards, which is borderline impossible to DIY."
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hpl9cc | "Why do Torque Wrenches use Nm?" | Would someone explain how torque wrenches use this unit of measure? it doesn't seem to apply as a newton is a measure of acceleration and a torque wrench is used to set a specific amount of twisting force (to a bolt or nut for example). How long it takes to turn the torque wrench is not part of using it. The Newton would imply that it is. a gram/meter or kilogram/meter I would understand. Like the lbFt, they measures how much pressure is applied at a specific distance from the center of rotation. | Engineering | explainlikeimfive | {
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"It's one Newton of force applied on a rod 1 meter in length. The longer the radius the bigger the amount of torque",
"Newton is a measure of *force*, not acceleration. The newton-meter is the standard measurement of torque. If a torque wrench is set to 1 Nm, then this means that it will slip when you apply 1 newton of force one meter down the handle of the wrench, or half a newton at a distance of two meters, or two newtons at half a meter."
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hptz3l | Why do mobile phones need to be moved specifically in an infinity shaped pattern for the in-built compass to be calibrated? | Engineering | explainlikeimfive | {
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"text": [
"The compass detects magnetism, but it drifts. There is always changing local magnetism, like magnets in a phone case, or just innacuracies in the magnetometer that build up. But the phone has many other sensors - most important is acceleration sensors that detect movement and gravity, and gyroscopes that detect direction. The phone can detect errors in the magnetometer (compass) by comparing them. As you move your phone around, it can detect, using those gyros and accelerometers, how it is moving in space. As any innacuracy in the phone's magnet sensor will stay the same as you move it, it can detect what magnetism remains static and what changes. It can subtract the stationary magnetics and be left the changing ones - and the magnetism that changes as you move the phone around is going to be the Earth's. In addition, as the phone moves right around, it knows that the magnetic fields should also, turning right around in lockstep with the rotation it is measuring from the gyro. If the phone is close to a big piece of steel, that will show up as an attraction of both the north and south poles, out of step with the rotation. The software can detect and correct for this, too. Moving the phone in that figure-8^* pattern is used to get it started. Once you are using the compass and moving around, the phone keeps correcting. > ^(This was figure-98 in the original post, which was a typo. This note is added so as to not orphan the joke thread below.)",
"Not just phones, I had a car back on the day that had a compass in the rear view mirror and to calibrate it I had to find an open parking lot and drive in a figure 8 several times."
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hq39d8 | Why has a better method for producing power not happened yet. Why are we still using steam to move a turbine? Are there not more efficient methods? | Engineering | explainlikeimfive | {
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"Steam is a wonderful working fluid. No other material has the heat range, low cost, and safety. Even when we get fusion reactors, they are going to boil water to make steam.",
"The short, ELI5 answer is: because steam is *just that good*. * Water is cheap, quite literally cheaper than dirt. * Water is safe--completely non-toxic and requires no special handling. * Water is liquid at temperatures that humans find comfortable. * Water boils at temperatures that are easy to achieve. * Water expands *1700 times* when it turns to steam. * Steam is non-toxic, non-corrosive, and non-flammable. There are ways to make electricity that *don't* start with something getting hot, like wind power, solar power, and hydroelectric dams. And yet, whether it's an old-fashioned coal fire or a space-age fission reactor or a future tech fusion reactor, when your power plant gets its power from \"a thing is very hot\", you're going to find steam . . . because *steam is that good*.",
"No, that's pretty much it. There aren't actually that many ways to make electricity, and spinning a turbine is a really effective way to go about it. You can make a lot of steam out of not a lot of water, and get a lot of force out of it.",
"No, not really. Aside from Solar (which does straight to electricity but is inefficient in other ways) and wind/hydro (which use wind/water to spin the turbine directly). Most ways to produce electricity start with heat being generated, and the best way we have at a large scale to turn heat into electricity is a steam turbine."
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hq3rjj | How do seatbelts “sense” that the belt is being pulled abruptly and lock the belt so it does not extend? | Engineering | explainlikeimfive | {
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"text": [
"You know those flying-chair rides at amusement parks, where the seats are hanging on ropes and the whole thing spins? As it spins faster, the chairs fly outwards, and the faster it spins, the farther out the chairs go. [ URL_0 ]( URL_0 ) Seatbelts start with a setup like this, but put the whole thing inside a larger tube, so the parts that fly out when it spins hit the outer tube, stopping it from spinning any more. There are teeth on both sides on it so it catches really well. If it spins slowly (like when you adjust it), the inner part doesn't fly out far enough for the teeth to catch. Elevators also have a similar mechanism to stop them if the cable breaks.",
"The centrifugal force from the reel being pulled quickly would throw out hinged arms or suchlike that would catch on the static part of the reel housing and stop it rotating.",
"The seatbelt reel has pins where if the reel spins too fast, they lock the reel via centrifugal force. If the reel spins slowly during normal operation, the pins won't lock up because there isn't enough centrifugal force. Hope this helps a little better."
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hqh033 | Ok how do people make does rope bridges across great gaps before modern tech | Engineering | explainlikeimfive | {
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"text": [
"Well, either some poor schmuck climbs all the way down the gorge and all the way up the other side trailing a rope behind them, or they shot a spear or arrow across the gorge tied to a string. Either the spear or arrow embeds into something or its caught (or they pull it back across and try again). Then the string or vine is pulled across tied to a heavier rope and so on. Once you have that first string or twine across you can keep pulling across successive and multiple other ropes so long as their weight doesn't snap the previous one(s). It could also be that the first rope is thrown across at some point much narrower, but for whatever reason isn't conducive to building a bridge at that point, then a person on either side walks the rope down the gap to the point where you want to build a bridge. Once you have your main supportive ropes across, its a simple matter to start laying down wooden or bamboo stays, anchor ropes etc."
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hqqsqd | Why do trucks have those large bolts protruding from the front two tire rims? | I’m not engineer or truck driver. But I’ve been a passenger on a road trip all day and noticed, when passing a truck, that the front two tires have these massive bolts sticking out of the rims. Why are these bolts there? Is it a manufacturing thing? Why aren’t they on any of the other rims of the truck? I’m bored and I need answers! | Engineering | explainlikeimfive | {
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"text": [
"They are the lug nuts that hold the wheel on. They use the same wheel on the front and the back, just flipped inside out. That way the spare tire fits the front and rear",
"The front wheels are generally identical to all other wheels on the rig. The front wheels only have a single tire installed to keep space available for steering mechanisms while all others would have a second tire covering the excess length of the lugs you see."
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hqy2v7 | Why are kettles so loud when they start up and become quieter as the water starts boiling? | Engineering | explainlikeimfive | {
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"\"This hot water around the heating element forms tiny little bubbles which then rise up through the kettle, but as these bubbles rise, they rise into an area of colder water. So the bubbles cool down and condense and kind of implode, and the bubbles sort of slaps against itself making a really loud noise. But as the kettle heats up throughout so all the water inside the kettle is one temperature. As these bubbles form and rise through the water they don't reach an area of colder water, so they actually make it all the way to the surface and then they pop on the surface. But this popping sound on the surface is a lot more gentle and quiet than the sound of the bubbles kind of imploding on themselves within the kettle\" URL_0 .",
"As the water is boiling, forming little bubbles of steam and as they rise up in the colder water they shrink and collapse and then smash into one another and make lots of noise. So it gets a lot quieter once bubbles get all the way up to the surface and they stop cavitating."
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hr7dn0 | How do Morse code straight key machines work? | I saw this video - URL_0 And I’m wondering how in earth the man does this and how the machine is able to keep up. Thanks! | Engineering | explainlikeimfive | {
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"fy2cln2"
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"text": [
"That machine is literally just a bar with a spring, and every time the bar is pushed down it closes the electrical circuit and sends a pulse for as long as it's pushed down and when it's no longer pushed down the spring pulls the bar up again opening the circuit. It's really just a switch and that man simply has training and experience to do this that fast without error."
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hr8ztd | Why is "hand made" considered better and more luxurious ? Would a Toyota Corolla have better quality if some of it's current automated assembly line tasks are taken care of by a human with a tool ? | Engineering | explainlikeimfive | {
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"text": [
"It usually denotes that it's made with artisanal skill. And yes for some goods it's not necessarily a good thing.",
"Well unless you are willing to pay 100k for a corolla, that's not a very good idea. Handcrafted means quality only because someone has to take the time to make it, check it, and correct any issues. All of this takes skill and time, significantly raising cost for what? Handcrafted doesn't necessarily mean better built, just more attention to detail. When it comes to quality control, you want consistency and nothing is more consistent than any robot designed to do one task repetitively.",
"Sometimes it's not about the pure functional usefulness of an item, but the uniqueness and artistic quality provided by skilled human labor. Certain goods might also be so niche that they are only made by such craftsmen, and in small numbers, which adds a sense of exclusivity. Just knowing that they own something that very few others do is very valuable to some people."
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hrcbxm | Why do crash test dummies have those black and yellow checkered circles on them? | Engineering | explainlikeimfive | {
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"text": [
"The circle serves as a reference point to track how the dummy moves in a crash. It can be hard to tell a cheek from a chin in a video of a featureless dummy disintegrating, but if you have a brightly colored, high-contrast reference point it becomes much easier to track, for example, the movement of the dummy's head upon impact.",
"They're easy to track in the camera footage so you can tell exactly where the dummies are and how fast they're moving so you can tell how badly a real person would be hurt in the same crash."
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hrhm85 | Why are elevators/lifts and their shafts have to be a Faraday cage and does it have to stay that way? | Engineering | explainlikeimfive | {
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"text": [
"They don't \\*have\\* to be one. It's merely the nature of the elevators being made of metal. I don't think anyone would want to ride in an elevator made of thin plywood. Elevators are built for safety, not for the convenience of someone who can't deal with being out of cell service for 2 minutes.",
"The shafts are reinforced concrete, with rebar 6\" to 12\" apart, so not a Faraday cage. The elevator cab/car is a metal box, typically stainless steel, and that is a Faraday cage. Metal is strong, fire-resistant, and easy to clean, but the cab/car could be made of something else. Elevators were being made long before cell phones were invented and i don't know of any elevator manufacturer that is making a cell-friendly box."
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hrnhir | Everything eventually breaks and/or needs maintenance, so why do key locks seem to be working forever? | Was thinking this, your car, tv, computer, gates, fences like everything eventually needs maintenance or it breaks down. But some of these padlocks, door locks, etc. with a key they seem to be working forever without ever breaking down! How? | Engineering | explainlikeimfive | {
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"text": [
"It's not something you use all day every day, just a couple of times a day so wear is minimal. They are also built with high tolerances for error so it takes more wear before malfunctions.",
"For one they are protected from the elements due to mechanisms being protected. Secondly they are not used nearly as often as you'd think. Aside from deadbolts on front door of a living space, average use would be maybe .5 or less per day. Plus the forces put on the mechanism is fairly low since it's a twisting motion. Combining those, you have an all metal encased mechanism that has little wear and tear. 10,000 uses (which is not high for machined parts) would over 30 years if used daily. A padlock that gets used maybe once a week on a shed could easily last over 100 years if moisture doesn't get at it. The worst thing you can do to a lock that will cut down its lifespan outside of letting it rust is to use the wrong key on it too often. Messes up the tumblers, which is why sometimes a new key for an old lock feels \"sticky\" at first because the lock is used to a rounded worn out key.",
"they do break. But if you only use the mechanical parts once every 3 days or so, thats different than having brake calipers pressed in and retracted 400+ times a day. everything breaks if you use it enough.",
"Locks do fail just like everything else. Being made of stainless metal, being partially protected from the elements, and not being used very often compared to most other mechanical devices certainly does help on their longevity but they do often start failing after a few years of abuse. However when they fail they usually fail by accepting more keys then designed. And the user does not notice this too much because their key still fits and they do not usually have a set of similar keys to test. So the locks will still appear to work as they are able to lock and unlock just as normally. However what the user does not notice is that more and more keys will be able to unlock the door and eventually even a screwdrivers will fit."
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hrrd3l | How do we communicate using electromagnetic radiation? | So I understand that, with radio for example, there’s a transmitter that takes information and sends it out, and a receiver that takes in the information and does stuff with it, but how does that work exactly? How do the electrical signals get converted into, essentially, the same thing as light? How does electromagnetic radiation even carry information? Why do we only use certain bands of the electromagnetic spectrum for communication? TIA | Engineering | explainlikeimfive | {
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"Electromagnetic radiation IS light. With things like radio, it's a frequency of light so \"red\" that our eyes can't perceive it. The way information is transmitted using light (EM waves) is by *modulating* it. That is, the EM carrier wave is changed in some way to make it also contain the information wanted. There are four main ways to modulate light: [AM, FM]( URL_0 ), PM, and switching. With Amplitude Modulation, the carrier wave's amplitude (strength) is changed slightly according to the content of the information you want to send (the \"baseband\" signal). With Frequency Modulation, instead of changing the carrier wave's amplitude, the frequency is changed a little bit to encode the baseband signal. Phase Modulation is a little bit harder to describe. It's kind of similar to FM, but not quite. And for some communications systems, like in high speed fiber optics internet, the light is simply turned on or off rapidly to represent a digital version of the baseband signal. With some communications schemes, more than one of these techniques is used simultaneously so that more information can be sent. We only use certain bands of the EM spectrum for certain things when broadcasting over the air so that they don't interfere with each other. In the USA, the Federal Communications Commission (FCC) allocates certain frequency/wavelength bands for different things. And very very low frequencies aren't used much (except by the military for talking to submarines, for example) because they can't carry much information very fast. Very very high frequencies are hard to create and capture.",
"There's the simplest method: Morse code. I'm sure you learned about it - it's the simplest method for communication with radio or light. Dots and dashes, produced by turning a signal on and off. Now, that's well and good, but if you turn a radio on and off a bunch, you're going to produce a lot of static and honestly you just aren't going to move a lot of information by doing that. Instead, you can make it slightly brighter/dimmer or you can shift its frequency slightly. You can do both of these things *way* faster than you can switch it on and off. This was first applied to transmitting sound, by shifting the frequency/'brightness' of the radio waves in time with the sound waves. However, we have since developed a whole bunch of different standards for transmitting binary information and numbers by shifting frequency; we chose frequency over 'brightness' because brightness changes when you move or something partially blocks the signal but frequency does not.",
"without getting too much into the weeds, electromagnetic waves propagate through what we call the electromagnetic field in a very similar way to how ripples propagate through water. The electromagnetic field exists everywhere in spacetime, much like water exists everywhere in the ocean. Imagine dipping your finger into a pond. There will be some gentle ripples. Now, if you thrust your finger into and out of the water, you will create more ripples which follow the pattern of your finger movement. In this analogy your finger is an antenna, because if someone (receiver) were able to analyze those ripples, they would be able to tell exactly how you (transmitter) moved your finger in the water. The pressure your finger puts on the water is analogous to voltage. Applying a difference in voltage to an antenna will cause the electrons within it to move, which is what causes the ripples in the electromagnetic field. The peaks and valleys of these ripples are then interpreted as information. This is the fundamental idea behind transferring information through waves."
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hrrw0n | what's the difference between a motor and and engine? | Engineering | explainlikeimfive | {
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"text": [
"A motor is any machine that converts some form of energy into mechanical work (movement). An engine is a specific type of **motor** that converts thermal energy to mechanical work. All engines are motors but not all motors are engines. For example, an electric motor is not an engine but a combustion engine is a motor."
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hs3md5 | How do the dispensers at gas stations know when to stop disbursing fuel? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"In the pump nozzle, there are two tubes. One that the gasoline flows through called the *spout* and a smaller one that is connected to a vacuum sensor and connected to the gasoline tube called the *vacuum tube*. Both tubes have openings at the end of the pump nozzle. It looks something like [this]( URL_0 ) As the gasoline flows through the *spout*, it \"pulls\" air through the *vacuum tube*, with air entering the *sensing port*. When the gasoline in the tank reaches the *sensing port*. No more air is able to enter and more force is needed for the gasoline to go up through the *vacuum tube*. The rest of the air in the vacuum is pulled out of it into the *spout*. This creates a vacuum in the *vacuum tube* and the *vacuum chamber*. This causes the *diaphragm* to be pulled which cuts off the flow of gasoline. How the gasoline pulls air up through the *vacuum tube* is known as the *Venturi effect*. I won't explain it since is a bit more complicated than an ELI5. If you want to know more about it, you can look it up.",
"There is a small tube that runs along the inside of the gas nozzle and comes out at the end of the nozzle. When the end of that tube goes under the fuel, the flow of fuel is shut off. But how does the tube shut off the flow of fuel? We will go through it step by step. Imagine you are sucking air through a drinking straw, and then you lower the end of the straw into a drink. You will feel a difference, right? To make it more obvious, imagine you lower the end into something thick like honey. You will really feel it now. Maybe if you suck really hard on the drinking straw in the honey, then the sides of the straw will collapse. Why would that happen? Because the pressure inside the drinking straw reduces. So now we have invented a way of detecting if the end of a tube is under the surface of a liquid: the pressure reduces in the tube. We can use that invention in the fuel pump. We can use the pressure reduction in the tube to suck a valve closed, and that will shut off the flow of fuel. Actually it's a little more sophisticated than that: the low pressure moves a diaphragm, and that movement triggers the spring-loaded valve to shut closed. But basically the low pressure is making the fuel shut-off valve to spring shut. (And when you pull on the pump trigger, that opens up the valve again, and loads up the spring ready to be set off again.) So, all that remains now is the question of where does the suction in the tube come from to suck in the air? Surprisingly perhaps there is no actual air pump as such in the system. What happens instead is that when the fuel is pumping, the pipe that it goes through has a narrowing in it. When the fuel is pushed through this narrowing, it speeds up and its pressure reduces. This is called the Venturi Effect. You might think that the pressure would increase there, but it's one of those weird results of physics that it actually decreases instead. So after the narrowing, there is a low pressure region with some empty space in it, and our little tube connects to that region, and that is what sucks the air into the tube.",
"Most gas nozzles have something of a pressure sensing function in the tip. Basically if any fuel but the fuel going out gets close the tip of the nozzle, it feels it and stops."
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hs5663 | How does SawStop recognize my finger? Does it recognize flesh in general? | Seen this here and am utterly amazed! [SawStop Reddit]( URL_0 ) – full video [here]( URL_1 ) | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Capacitance. Same principle as your smartphone's touchscreen. Your fingers are full of salty liquid (blood) that is easily detected by a weak electrical field, and the system can react very quickly when it senses the proximity of human flesh.",
"It's explained in the video. A very small static electric field is applied to the blade. Your finger, just like a hot dog, will create a capacitance when it comes into contact since it is a conductor. Exactly the same principle that applies when using your smartphone The impressive thing with the blade though, is how fact the mechanical aspect of it engages to save your finger. The capacitive sensing aspect of it is quite reliable."
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hs6wbj | Besides Neural Networks, what other ways to build AIs or ANIs are there, what other theoretical models of AIs we have? | Engineering | explainlikeimfive | {
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"text": [
"Try evolutionary/genetic algorithms, where you start with a bunch of potential solutions to a problem, encode them in a pseudo-genetic way, evaluate their fitness, select a subset based on various factors, breed them to produce a new generation of algorithms then repeat the process until you reach a solution that satisfies your criteria. Basically have your algorithms compete in natural selection. Now that's spooky.",
"Artificial Neural Networks attempt to simulate how your brains actually work. They are build using networks of artificial neurons, and they are trained by feeding in a data-set and having the neurons automatically adjust to improve their performance. At the fundamental level, this turns into a massive number of matrix multiplications and some fairly ugly math to actually do the learning. While the idea has been around for a while, it's only been in the last 30 or so years that computer hardware has been able to do it efficiently. Another approach is to build your AI like a conventional program. Natural language processing is a good example of this. Chat bots, like the classic ELIZA, do the same kind of language processing in the same way that compilers and interpreters do. It's just a regular program that goes through the instructions that it's programmer work line by line. It's creating by hand instead of being generated through mathematical processes."
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hsdomr | Before digital image technology, how did newspapers turn the original illustrations for comic strips into casts for serial printing? | Or did they have some other technique than creating casts? It hardly seems like individual, non-recyclable metal casts could be cost-efficient. | Engineering | explainlikeimfive | {
"a_id": [
"fy9undm"
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"text": [
"Sieve printing. Basically similar to photography, but you print on a fine net that gets solid where light hits it. Make 4 for the c, m, y k elements and you can even print in color."
],
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3
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hsge58 | What is the origin/reasoning behind the 5 point star-like shape on the bottom of plastic soda bottles? Wouldn't a flat design be more stable? | Engineering | explainlikeimfive | {
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"text": [
"It's not for stability. The curves strengthen the bottom and let it hold up to pressure better.",
"In addition to what everyone else said... Plastic bottles used to have hemispherical bases which is the best solution for containing the pressure and ease of moulding, but obviously couldn't stand up on its own. So it had a second piece glued on to provide a flat base. Obviously this is more expensive to produce with extra steps required, so once technology had improved suffieciently they moved to the one-piece solution with 5 'feet' as a compromise between stability, efficiency and cost.",
"a flat design would bow out from the pressure inside the bottle, or need to be several times as thick."
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hsknf0 | I live in a extremely hot area (115 degrees F) I understand that the pipes run underground and the dirt insulated it to keep it cooler, but, the water coming out of my sink will get as low at 65-70 degrees, which seems cooler than should be possible just by insulation from the ground. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"You'd be surprised, is basically the answer. Go down just a few metres, and the ground is almost the same temperature anywhere.",
"Google geothermal cooling and heating. Super interesting way of heating cooling homes/buildings."
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hszsli | What do surge protectors actually do? | This morning after a large clap of thunder it appears some of my electronics that were plugged into a surge protector are no longer working. the surge protector obviously was not able to protect them, so what do surge protectors actually protect from/do? | Engineering | explainlikeimfive | {
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"A surge protector reacts to a higher-than-usual voltage, and diverts as much as possible of it to ground. When it does, it will inevitably damage itself. The diversion wears it off, so to speak. It can't do that forever. And it can't do that for very long if the voltage is very high. After it's worn out, it no longer protects. It sits there passively, but can't protect against anything. Industrial surge protectors are sold as modules, where the protective pieces that are worn out can be replaced without cutting power. What happened to you is either that the surge protector got a spike that it just couldn't handle (and the outcome would have been the same no matter if you had the protector or not) or that you have had it silently protect you so many times before that it didn't last through this last one properly."
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ht1x8e | How do car batteries work? | Hi all, I always wondered how a car battery is able to charge cell phones, radio, dashboard and all other things that requiere electricity, and not need to to be recharged for a couple years. Why does it not die out sooner? Can someone please ELI5 on how it's able to achieve this curious feat? Thanks! | Engineering | explainlikeimfive | {
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"A car battery will recharge itself while you’re driving around using the alternator in your car (basically an electric generator). It uses up a significant portion of its charge every time you turn over the starter motor but this is replenished within seconds/ minutes.",
"Your car battery is only used when the engine is not running, and principally it exists to deliver the amperage necessary to power the high-torque electric starter motor that cranks over the engine, which starts the self sustaining combustion cycle. After the engine is started, the combustion cycle drives what is called an engine accessory; these are all the components driven by the belts off the front of the engine. Most of these components are pumps: the AC condenser pump, power steering pump, water pump - for the engine cooling system, sometimes a smog pump for emissions... One such accessory is the alternator. This is a device that produces an alternating current, and it produces more than enough power to both recharge the battery, and run the entire electrical system of the car - most importantly the ignition system, but also the very energy hungry headlights. Alternators are self-regulating, in that they produce nominal power output once they spin at a minimum speed, and from there will lower or raise their output to compensate for changes in their rotational speed. This is why, when using jumper cables to start another car, it doesn't help to rev the engine of the supplier car. Some of this power produced by the alternator will be used to recharge the battery. The power in the battery is stored chemically, and those reactions are reversible to a point. The average life of a battery that sees regular use is around 7 years. Cars that won't start have an old battery that can't deliver the amperage necessary to turn the starter motor adequately. If a running car dies due to an electrical failure, seemingly cured by a jump, the alternator itself has failed, and the vehicle is actually just running off the battery. You can get a few miles out of just a battery."
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htwqn9 | Why do bicycles make that clicking sound when moving but not pedalling? | Engineering | explainlikeimfive | {
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"There's a ratchet mechanism that allows the wheel to turn without pedaling. It lets you coast comfortably without the pedals spinning. There's a bunch of teeth kindof like a gear, and a spring loaded pawl that clicks up and down when the ratchet spins one way, and locks in place when the ratchet spins the other (relative to the chain). Stunt bikes don't have one of these and the chain is directly connected to the wheel which let's the rider control the speed by pedaling in reverse."
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hu3cfn | How are skyscrapers built to not destroy the city in the event of an earthquake? | I always look up to the sky and think if the tall buildings fall, they better not smoosh the entire city. So how do they fall so that the debris etc don't kill people. And if they do, why are they allowed to be built? | Engineering | explainlikeimfive | {
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"In most cities it’s the wind that’s the controlling factor, which is designed for in its own way, but focusing on seismic design for now: 1. The USGS, or local equivalent overseas, produces maps that show expected seismic ground motions. These are basically controlled by the size of and distance to nearby fault lines. The engineer will look these up on a map, or type the zip code in, and get their ground motion values. 2. The effect of these is dependent on the ground conditions. Hard rock is good, soft soil is bad, with grades in between. The geotechnical engineer will tell the structural engineer what the ground type is. These are then combined with the values above to get the ground motion at the site for design. 3. The building type affects how much force it takes. Stiffer buildings generally take more force, flexible buildings take less. In high seismic zones you run into the issue that you make it strong enough it gets too stiff, which makes it pick up more force. So instead you design your lateral system with special detailing to provide “fuses” - selected weak points where you can control exactly Which, where and how members will fail in the event the earthquake is stronger than expected, which controls the failure mode so the building might get damaged but shouldn’t fall down. For example they might design “notches” into beams so that the beam might bend a lot, but it’s physically not strong enough to fail the connection to a column or fail the column. This means the floors might be bent out of shape in a severe earthquake, but won’t collapse. All these things allow the building to absorb energy from the earthquake in a “ductile” manner, things bend and stretch, but won’t snap. 4. They can do more extreme measures - base isolation - there’s a set of giant springs and rollers at the base that let the ground move underneath the building. This is expensive. They can also put dampers through the building - basically a plunger in a tube of viscous goo that will absorb energy from the building movements.",
"They don't fall. Skyscrapers have heavy weights inside attached to springs, whose entire purpose is to soak up the vibrations of any reasonable earthquake. If the earthquake is severe enough to overwhelm those and knock the building down anyway, the destruction is going to be so severe that the debris from the collapse won't affect things much."
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hu62e9 | How do lock companies prevent making duplicate locks? | Engineering | explainlikeimfive | {
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"In general, they don't. If you have a typical lock on your door that is sold at any hardware/ home improvement store, there are thousands of people with the same lock and key as you. A typical 5 or 6 pin lock will have between 50,000 to 100,000 unique key combinations, but many of them aren't actually useable because they would be straight or mostly straight.",
"Your assumption there are no duplicates isn't correct. Duplicates get shipped all over the world. A six pin has almost 50000 possible pin combinations. More if they have more precision or more pins. Even if they shipped one to every person in the USA the chance of you and a neighbor having the same key is small, but would happen. The idea is very few people are running from house to house hoping their key os that 1/50000.",
"For common household locks, there might be a few thousand possible combinations. Keys don't have to be unique: just varied enough that carrying a few random keys and trying them on a random lock isn't a viable strategy (at that point, picking the lock becomes a far more reliable option). In fact, many lock manufacturers create locks with matching keys so that they can be purchased together so all locks in a house are keyed alike.",
"They don't need to make every single one unique, just rare enough that statically it's unlikely to work another. Locks typically have a number of pins inside and each one can be set to a number of positions. So say there are 5 pins and each can be set to 7 different levels -- that's almost 17,000 possible variations. So what are the odds than any particular key is the exact same of those 17,000 variations and will open a particular lock?"
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hudvjv | What's happening when an engine sputters and almost stops, then picks back up like everything's fine? | Engineering | explainlikeimfive | {
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"Usually it’s due to air in the fuel line. Sometimes it’s due to a blockage in the fuel line or a spark lug missing a spark during fuel injection, either from a timing issue, or not enough power from the alternator or some debris in the gap."
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hugcb4 | how do they make Milk out of almonds? Is it possible to make Milks out of other unconventional plants? | Engineering | explainlikeimfive | {
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"It isn't actually milk. It's more like almond juice. They crush up almonds and mix them with water, then put that almond-y mixture through a strainer, so that all you're left with is the almond-flavored water. They call it almond milk because it has a similar texture to milk, meaning that it feels like milk when you drink it. But it's more like an almond juice really. Same with soy milk, and oat milk. They're not actually milks like we get from cows or goats.",
"So basically you blend the almonds with water then strain out the almond pieces and the resulting liquid is the milk",
"Here ya go: [ URL_0 ]( URL_0 ) They also make milk from rice, oats, soy... The list goes on! :)",
"its not milk at all, while they market it as such technically milk is a fluid produced from the mammary glands of animals. plant milks are just produced to resemble milk, they contain no lactose, its usually a juice or extract. almond milk is probably one of the simplest and oldest out there (over 500 years old) its pretty much just almonds and water heavily blended as far as im aware, id imagine some other, newer plant milks are much more heavily processed"
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hujumj | Why aren't airplane wheels equipped with some system to make the wheels catch up with the 'speed of the ground' before they touch it? | Engineering | explainlikeimfive | {
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"The benefits just aren't worth it. Tire wear from catching the runway isn't nearly a problem as would developing an electric motor to spin the tires, making sure the gyroscopic effect from a massive wheel train doesn't rattle the plane, making sure the brakes can keep up with that entire system, carrying batteries for that motor to do its job which would increase weight, etc.. Tires do their job well enough as is, plus they're inflated with inert nitrogen gas which doesn't risk fueling a fire like normal air would, so punctures are not only rare but not very risky if they happen anyway."
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hv1gok | How does the fuel gauge on your car work? | More specifically, how does your car work out how much fuel is in the tank and display that to you on the dash? | Engineering | explainlikeimfive | {
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"It does so using a fuel sensing device. A floater is attached to a variable resistance component. The floater will move upwards in the tank when filled and downwards when drained, which changes the voltage across the resistor. That voltage is then interpreted as a fuel quantity depending on your tank size and other parameters."
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hv84u0 | How is it that just a few millimetres of insulation in space suits is enough to protect astronauts from the extreme heat/cold of outer space? | Engineering | explainlikeimfive | {
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"Vacuums are really terrible at conduction, so you dont need a crazy thick layer of insulation. When we insulate something on earth its either in air or in a liquid, both of which transfer heat (conduct) a lot better. Basically the cold air or water \"steals\" your body heat a lot more than a vacuum would",
"Temperature is a property of matter. The vacuum of outer space is, by definition, largely devoid of matter. For this reason, it is inappropriate to think of the vacuum of space as having a temperature. What is true is that objects in the vacuum of outer space are often at the extremes of temperature. The reason for this is the fact that you do not have any air or water to help spread heat around (aka, \"convection\"). An object exposed to sunlight in space heats up just like an object exposed to the sun on earth, but on earth the air will carry away some of that heat. When we insulate things on earth to try and keep them hotter/colder than the surroundings (homes, food, etc), we either surround them with vacuum, or we do our best to keep the air from easily moving (styrofoam, fiberglass, blankets). An astronaut's suit is typically white so that it does not absorb much heat energy from the sun to begin with, because the biggest concern in space for a human is generally getting rid of excess heat produced by the astronaut's body. The sunlight is a little brighter without the atmosphere absorbing stuff, but in general it's not a ton of energy from the sun, and in Low Earth Orbit (where the ISS is), you only have about 45 minutes of direct sunlight max as you circle the planet. The astronaut's suit includes a water cooling system that helps to combat the fact that they are basically in a vacuum thermos. Because our bodies are used to being able to dump our excess heat into the air around us and we get hot when we can't (imagine being wrapped in blankets), the heat has to go somewhere. The ISS itself gets rid of excess heat the only way it can in a vacuum environment: by radiating heat energy in the form of infrared light into the darkness of space. The ISS uses ammonia-filled fins that are kept in shade to do this. They use ammonia because it can hold onto more heat energy drop per drop than water. Scenes from movies where someone is exposed to a vacuum and instantly freeze are very, very unrealistic. If you were exposed to the vacuum of space, you would not have a great time, but as long as you didn't explosively decompress, you'd more or less stay your same temperature for a while and even survive if you were able to be rescued within a minute or so. Could get some localized cooling due to evaporation of water from your eyes and mouth, but nothing like freezing solid and breaking apart.",
"Space is not actually either hot or cold. You know those thermos flasks that keep your cool drinks cool and your hot drinks hot? They use vacuum as an insulator to keep heat from transferring inwards or outwards to the drink keeping it the temperature it is. The vacuum of outerspace will keep things exactly the temperature they are without allowing heat to transfer out in either directions the way it would for objects touching other objects like the air. There are other ways you can transfer heat though. Things like simple infrared radiation the sort of thing you can see with thermal cams and infrared sensors. A warm object in space would give of this sort of radiation until it cooled of to the level of the background radiation of the universe at which point it would give off as much as it received and stay the same temperature. This radiating heat away process is rather slow though. A human body that generates a lot of heat normally would quickly overheat if the only way to transfer heat away was radiation. Another important point is that there is a huge source of radiation in space called the sun. Sunshine will heat you up. For satellites made out of solid stuff like metals and plastic and ceramics etc this is where it ends. You have to look at how much energy you receive from the sun to heat the thing up, how much heat it generates by running its machines and then find a way to radiate all that heat away with something like big metal fins to keep things stable. For humans however we have another problem. Humans aren't made up out of just solid parts. We are rather squishy, with lots of liquid components in the mix. Liquids behave in weird way in extremely low pressures. Our normal human way of getting rid of heat by sweating out liquid is not going to do us any favors in a a vacuum. Space suits mostly need to keep our body from being exposed to the vacuum and under pressure and ensuring that we don't overheat. With suits designed for walking around on moons and planets we have a different situation, because unlike the vacuum of space those have a temperature and mostly not one that is good for humans to live in. On the moon where there is no atmosphere you only get heat transfer via the soles of your boots that touch the ground, but on Mars or similar it would be more complicated.",
"Fun fact: you know how in many movies if you get launched into space without a suit you almost instantly freeze? Well, that’s false. You would die of suffucation. Heat gets transferred by contact. In actual space the atoms floating around are indeed very cold, but there’s so few of them touching you at any given time that you are losing heat very slowly, unlike on earth where, be it water or air, there’s always a lot of matter touching you. Edit: ok, I was simplifying in the spirit of an eli5... you would die an horrible death based on a mix of suffucation, organ failure and internal pressure boiling you from the inside. But you definitely wouldn’t become a popsicle in the short term and would be very very dead long before becoming one.",
"Heat transfers in 3 ways: Convection - a fan blowing on you to cool you off Conduction - you touch a hot surface with your hand and your hand feels warmer Radiation- warmth is projected. Like when you warm your hands near a fire. In space, there is no wind so there is no convective heat transfer. In space, there are no surfaces or molecules to touch (it's a vacuum), so there is no conduction. The only method of heat transfer that works in space is radiation. Thankfully, this type of heat transfer isnt very fast and it's pretty easy to keep the suits cool when they are in sunlight.",
"Heat and temperature are two different things. Temperature is a measure of how fast some molecules are vibrating. Heat is how much energy is contained there. If you set your kitchen stove to 500 degrees, you can reach inside it with your bare hand for a few moments as long as you don’t touch anything. The air is 500 degrees but it isn’t very dense — the air molecules are far apart so not many of them touch you. But if you grab the metal wall of the stove you’re going to get a nasty burn instantly. The metal is much more dense. The temperature is the same, but the metal holds much more *heat*. It works the same way with cold. And in outer space, the atoms are very very very far apart.",
"**Real ELI5**: **Space doesn't have a temperature because there's nothing there.** What the suits really protect astronauts from is the **vacuum** (*our bodies need to be pressurized to keep working*) and **radiation from the sun** (*which would cook you really fast without an atmosphere to protect you*). There are other details, but that's the gist.",
"You need some stuff to conduct the heat away. The temperature tells you which way energy will flow, but the material tells you how well it will flow. This is why 40 degree (F) air means putting on a jacket and 40 degree (F) water can fucking kill you. Water is a lot better at conducting heat than air. In space, there's essentially no material outside so you don't really have to worry about conducting heat away, just radiating, which is much, much slower. You basically have to \"glow\" your heat away in space. So a little layer of insulation on top of that can be all you need. If anything it's actually harder to stay cool!",
"It's a matter of your understanding of space and heat. There are two types of heat.. conductive and emissive. ON EARTH, all hot objects both conduct heat (as the surface molecules bang into other molecules and transfer energy) and emit heat radiation (as infrared radiation). That is.. to be clear.. a pot of boiling water (conduction) and a powerful infrared laser (radiation) will both burn you, but using different mechanisms. In space... you don't have air, you have no particles really bumping into each other, so you have nearly zero heat loss by conduction. That is.. as you understand hot and cold, it's not ACTUALLY cold in space. I will illustrate. To jump in a volcano, your instincts will tell you that the magma will touch your suit and give it tons of heat, and the suit will give it to you, so you need something THICK to give you time to cool the suit. In space, nothing is touching you. You have very little to worry about with conduction, which is a really efficient way to move heat. However, the Sun is emitting tons of radiation.. not JUST infra-red, which is also heat, but x-rays and microwaves and gamma rays, which will be converted to heat when they touch your meats. So the trick is not to worry about conduction, but reflecting as much radiation off you so it isn't absorbed and cooking you. Addendum: Note that if i shot you into the vaccuum of space, you WOULD feel cold.. this is because the water you emit, on you, and in you, will react to the low pressure and essentially boil, taking heat from your surface as it boils off. Theoretically, if you were in an unbreakable plastic bubble, you would feel no temperature difference until the sun came up.",
"the thing that's confusing you is the widespread mistaken belief that space is hot or cold. Hollywood relies heavily on the instant freezing nature of space, and it's factually not true. heat moves in 3 ways: conduction, convection, and radiation. inside a vacuum there is no conduction or convection, so a mass will only lose heat through radiation which is a very slow process. Ovheating is a much bigger problem for astronauts for this reason. their own body heat would suffocate them inside the suit without mechanical cooling. this [wikipedia]( URL_0 .) article has some details on the complexity of the system used for cooling.",
"Space is cold in the same way that a single grain of sugar on a big empty plate is sweet. Sure, the average taste of the food on the plate is sweet, but you're unlikely to run into it, and if you do there's so little of it it doesn't matter much.",
"There are 3 types of heat loss: 1. Conduction. This is 2 masses touching each other. 2. Convection. This is air moving across the surface. 3. Radiant. This is why sunlight feels warm. In space, conduction and convection are effectively non-existant. So all you have to do to insulate in space is block radiant heat loss. That can be done by any material that blocks light in the infrared spectrum.",
"\"just a few millimetres\" - have you ever seen a picture of an EVA suit? They are big and bulky and thick, not just a \"few millimetres\" > The garment was made from thirteen layers of material which were (from inside to outside): rubber coated nylon, 5 layers of aluminized [Mylar]( URL_2 ), 4 layers of nonwoven [Dacron]( URL_3 ), 2 layers of aluminized [Kapton]( URL_5 ) film/Beta marquisette laminate, and [Teflon coated Beta filament cloth]( URL_4 ) they also had complex cooling systems to prevent overheating during EVA [ URL_0 ]( URL_1 )"
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hv8xqa | How are advanced high precision tools made from (what I assume) are less advanced and less precise tools? | Engineering | explainlikeimfive | {
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"Imagine this: you have a motor that has a +/- 0.5 turn slop. If you tell it to turn 45 times, you’ll get somewhere between 44.5 and 45.5 turns. If you connect this to a small gear that turns a big gear in a 100/1 ratio, you can reduce this. The small gear turns 44.5 or 45.5 times and the big gear turns 0.445 to 0.455 times. Your accuracy increases from .5 rotations to .005 rotations. Precision manufacturing takes advantage of dramatic gear/belt ratios a lot to shrink the inaccuracy of the control systems considerably.",
"If you're interested in the progression of precision and how our ever more precise manufacturing/measurement enables our continued advancement, this is a great primer: [The Perfectionists: How Precision Engineers Created the Modern World]( URL_0 )"
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hva5ya | Why are so many battery chargers/power bricks designed to block adjacent outlets? | Engineering | explainlikeimfive | {
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"Space is required for the components to convert high-voltage AC power to lower-voltage DC power for a device, mainly the transformer. [Here is a picture of the inside of a power brick]( URL_0 ). Why then do you see some (apple chargers for example) that are so much smaller? Generally speaking, the less power the device provides, the smaller the components need to be. You can either orient the components so it takes up space to the sides, the top/bottom, or outward. If you choose the sides, it won't work with a lot of power strips. If you choose top/bottom, it will work... if the power outlet is oriented a particular way, and even then you can only put one of these bricks on a standard 2-gang outlet (as the second one would block the first outlet). If outward, then it makes it a pain to plug in areas behind furniture and makes it more likely it'll get knocked into accidentally. For a deeper dive, see the first answer to the question here: URL_1",
"Because most companies buy their power supplies from outside vendors. They tell their purchasing department \"we need 100,000 120VAC transformers that deliver 12V/1A DC\" and the purchasing department finds the **lowest cost** supplier that can fulfill the order. Nobody cares if the transformer is well designed to fit a power strip. They just want the cheapest thing that can do the job. Higher end devices that cost more and have higher profit margins may be willing to spend a few cents more per device to have something that is branded, or ergonomic, etc"
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hvacrn | Why do some electrical prongs have holes and some do not? | What purpose does it serve? | Engineering | explainlikeimfive | {
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"If you were to take apart an outlet and look at the contact wipers that the prongs slide into, you would find that they have bumps on them. These bumps fit into the holes so that the outlet can grip the plug's prongs more firmly. This detenting prevents the plug from slipping out of the socket due to the weight of the plug and cord. It also improves the contact between the plug and the outlet."
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hvmj8p | How are the giant crucibles that are used to make and move molten steel and iron manufactured? | How do they, and the furnaces, not bend and melt? | Engineering | explainlikeimfive | {
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"They use crucibles or refractories typically made of ceramics. Ceramics are clay (extremely finely ground rock) mixed with water and heated. They have melting points higher than most metals. Iron melts at 1375°C; most ceramics melt at over 2000°C. Tungsten melts at 3400°C, the highest of all metals. Tantalum hafnium carbide melts at 4000°C, the highest of any known ceramic. Now, you may be asking yourself, how do we melt *those* without melting their container? The answer is: we don't. Most things with super high melting points don't get melted. Instead, we use powder metallurgy to shape and combine them, which involves very high pressures to squeeze things together."
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hvny7m | How does spinning a turbine generate electrical energy? | I get how spinning a wheel generates mechanical force. What I don't get is how wind or water (or steam, etc.) generates electrical energy when you spin a turbine inside a dynamo. What gives? | Engineering | explainlikeimfive | {
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"The simple explanation is that if you move a wire in a magnetic field, it jiggles the electrons in the wire. An electrical current is moving electrons. See Faraday's Law of Induction for more.",
"A wire loop will get an induced electric current flowing in it, whenever it's placed in a changing magnetic field. It's due to one of the fundamental physical laws related to electricity and magnetism -- one of the four Maxwell equations. Now all you have to do as an engineer is cleverly arrange magnets and wire loops, so that the turning motion brings many wire loops through regions with magnetic fields in different directions, or so that the turning motion [spins a magnet design through regions that're surrounded with coils of copper wires]( URL_0 )."
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hvnzhr | How are gun scopes accurate at all when they are placed above the barrel, and sometimes even placed at least a few inches above the barrel. | Engineering | explainlikeimfive | {
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"Gun scopes are adjusted for specific ranges. The line of the scope and the bullet are not parallel, but slightly tilted together so they cross at a point. The lines are flat enough they're basically touching for a certain bit of length before and after the distance you set it for But yes, scopes are not accurate at all ranges at the same time. They have to be set for the range, which is why you see people fiddling with the nobs on the side of the scope",
"Gun scopes have little thingies built in to adjust them so they line up with the barrel. Doing this is called zeroing. However the bullet will be pulled down by gravity and drop. In addition it will be blown around by the wind. And whole mess of other things like the spinning of the earth or humidity become problems if the shot is far enough. That means the best the scope can do is put a bullet at a particular range at a particular wind condition. And any little thing might make it off The actual long range sniper scopes have a bunch of other notches and lines to help the shooter figure out where to point to actually hit the target. And snipers have to do a lot of mental math. But it’s still very very hard."
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hvom8k | Why can't light switches just figure out which is the right wire? | Been wiring lots of light switches in an old house and it's frustrating to find wiring that's not consistent. I've also seen some dimmers that didn't seem to care which wire was the line and which was the load. Is it a design choice or could someone actually design a modern light switch that doesn't care which wire is which? | Engineering | explainlikeimfive | {
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"Yes, it is possible. I've been installing Lutron Caseta smart switches and one of the things I love about them is that they can figure out which end is the line and which end is the load, you don't have to worry about it.",
"Most switches simply connect a hot wire to a neutral, or make a contact so the circuit \"makes a longer live wire.\" So, they do kind of \"just figure it out,\" since that's all you need to do. The problem is the switch itself needs to be bonded to a ground, which is usually inside the switch box. If you hook up a hot wire to your ground, you've bypassed the switch, creating a short to ground. Does that help?"
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hvvhzw | How does an anchor, which weighs much less than a ship manage to steady an entire ship even during storms? | Wow, this post really blew up it has exactly 0 upvotes Edit: thanks for the gold Edit2 : wow platinum Edit3: stop with the awards please i already have 3 billion years of premium | Engineering | explainlikeimfive | {
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"There are two types of anchors - anchors and sea anchors. An anchor is dropped so that it catches on the bottom. If it catches onto something solid, it holds the ship in place because the anchor cannot move. The anchor has to be sturdy and attached to the ship with a strong chain. A sea anchor is not really an anchor. It floats underwater and has to be dragged around when the ship moves. This simply provides drag which makes it harder for the ship to move. It works because ships traveling over the surface have so little drag compared to their size, that the additional drag of the sea anchor underwater is significant. It is really the difference between traveling over and through the water."
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hw2xgh | if lightning has so much power in it, why aren't we looking at it as a renewable source in areas that frequently get strikes? | Engineering | explainlikeimfive | {
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"Because it's not actually that much, in addition to being very infeasible. A lighting strike might have on the order of a gigajoules of energy. That's around a $1 of natural gas. 1 GJ is 278 kWh (energy unit used for electricity), which is about $30 of electricity. That's not excalty great, but lighting strikes the earth almost 50 times per second. That's almost a trillion dollars worth of electricity! Except, most of it hits the middle of nowhere. Those that do hit human occupied areas, are not going to continue hitting the same place. Reality is, you'd get very few strikes actually hitting a lightning collecting setup. But what if we put those on every building? Well, that would take all the money in the world pretty much, it would be absurd. The energy is very fast (high power). So dealing with it takes some heavy and robust setup. And what do you do with that high burst of power? It hits powerlines and goes into the grid all the time already. The power burst is too fast, so all it does it break things when it gets on the power grid. You'd have to charge something and then slowly release the energy. Energy storage isn't cheap or economical, and even then you'd probably need two layers of it as batteries aren't going to charge at the speed that lightning strikes without blowing up. There's a reason why your phone takes an hour to charge, depsite the fact the wall outlet could deliver enough energy in seconds."
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hwha89 | - How does a light with two switches work? Like the light at the top of the stairs might have a switch at the bottom and at the top | If one switch is on and the other is off the light is on, but if both are on or both are off the light is off. How does it work? | Engineering | explainlikeimfive | {
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"In order for current to flow, you need to have a complete circuit. A normal light with a single switch is just one loop of wire. When the switch is off, the loop is open. When the switch is on, the loop closes and completes the circuit. For the double switch lights, it's still a complete circuit, but it has two switches. In between the two switches there are actually two paths - let's call them Path A and Path B. Instead of opening the loop or closing it, each switch controls whether it is connected to Path A or Path B. When they're on the same path, there's a complete circuit and the bulb lights up. So if they're both on Path A, the light is on. You can turn the light off by flipping one switch, because now one switch is on Path A and the other is on Path B. If you want to turn the light on, you can flip either switch - putting them both on Path B, or putting the first switch back on Path A.",
"It uses multiway switching techniques. It is easier to understand with pictures than explaining. This [wikipedia article]( URL_0 ) shows in pictures some ways to implement this, the most common is the traveler system, which uses two three-way switches.",
"The key is that there is two wires between the switches and when you flip the switch you change what wire it is connected to. If both are connected to the same wire the lamp is on and if they are connected to different wires the lamp is off. Look at the illustration on Wikipedia below because it is simpler to get than any text. It is clear that if you flip any switch when it is off the result is that the lamp is on [ URL_0 ]( URL_1 )",
"[Ask This Old House]( URL_0 ) answers this pretty well. For a great little visual, start watching around 2:30. :-)"
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hwlmaq | Why are telephone poles made of wood, and street lights made of metal? | Engineering | explainlikeimfive | {
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"It just depends on your area. There are plenty of places where the wooden \"telephone\" poles also have a metal street lamp bolted onto them so one pole does both jobs. You generally see wooden telephone poles in the suburbs and rural areas where its not worth it to run underground wires, but the metal street lamps are fed by underground wiring generally in cities where you can't just dig down 8 feet to set your wooden pole in, you need to bolt something to a concrete footer, that something is a hollow metal tube. Different poles for different requirements"
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hwr2nb | How does a switching mode power supply work, how does a MOSFET work, why is it used instead of other types of transistors, and why are SMPS more efficient than linear power supplies? | Engineering | explainlikeimfive | {
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"I'll work from the bottom up Linear power supplies have no way to trade extra voltage for extra current, any amp that comes out has to go in, they can also only go down in voltage. So if you have a 12V input and need a 5V output, you have to drop 7V across the transistor in the middle. If you want a 5A output that's 35 watts of heat for 25 watts of useful power. Ouch! Switching power supplies work to pass power through rather than current, they can trade voltage for current or vice versa. Basically all of them work by running current through an inductor to store energy in its magnetic field, then flipping a switch so the inductor discharges to the other side. You can bring the voltage up or down using this method since a charged inductor will ramp up it's voltage until it can discharge. Switching supplies are preferred because you've only lost power to the non-ideal parameters of the components (your caps and inductors have resistance you generally ignore). You can make a DC-DC converter with efficiencies above 95%. Our 25W of output power earlier would have 1-2 watts of heat dissipated in a high efficiency switcher You also don't have to use MOSFETs, they're just easiest to understand because they work the most like basic switches. You can build switching supplies with FETs, BJTs, IGBTs, or any switching device really"
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hwuug4 | Would aerodynamics on a spaceship matter? ie, Circular vs square, etc... | Engineering | explainlikeimfive | {
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"since it has to be launched from an atmosphere, yes it's very important. once it's in space it doesn't matter, but to get it there it better not fall apart halfway up, right angles are bad in general going fast through atmosphere. they found this out originally because planes in the 50s~ had rectangular windows, and the corners were prone to cracking, which is why all plane windows now have beveled corners",
"Only if you're moving incredibly fast because space isn't completely empty, there are still individual atoms and molecules and little dust particles floating around. It's a few million particles per cubic meter near Earth, a few thousand at the edge of the Solar System and a few dozen at most in intergalactic space. However, shape *does* matter even if you don't need to worry about aerodynamics. A sphere is the most material-efficient shape because it gives you the most volume for a given surface area (=material used). It's also the strongest shape. But on the other hand, angular shapes like cubes, tetrahedrons and octahedrons are much easier to construct and generally easier to work with.",
"The aerodynamics only matter if it's going to be coming up and down through the atmosphere. If it's built in space and never lands on a planet, then it doesn't matter how aerodynamic it is because there's virtually no atmosphere in space. Most things we put in space are big bulky squares and they just have an aerodynamic cover that they get rid of once they're already up. That said, there is a tiny bit of atmosphere in space. Particles from the sun push on things in space; the James Webb telescope has a bit that sticks out just to act as a little sail and keep that wind from spinning it around. And even though aerodynamics don't matter, symmetry does, because you need your engine behind the center of mass or you're just going to do space donuts when you hit the gas."
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hwwy82 | Why are road bike saddles more comfortable? | To me it seems logical that if a saddle has more padding and more surface to sit on, it would be less painful for the pelvis, however this type of saddle can only be seen on commuter bikes. Road cyclists, who ride for much longer, are equipped with very narrow, slim and hard-looking seats, whose shape I'm assuming is more ergonomic, but I can't imagine sitting on that for a whole day and yet if that's the standard, then it must be much more comfortable than those big cushy saddles used on city bikes. How come that's the case? | Engineering | explainlikeimfive | {
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"A proper road bike saddle puts weight on your sit-bones. This allows for good blood flow to all your soft tissues, and once you get used to the pressure on your bones, is quite comfortable. Other seats squish your sensitive soft tissue more and block blood flow."
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hx9wlj | What are the different components of the sounds you hear when you turn on a car? | Engineering | explainlikeimfive | {
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"The first thing you hear is the starter motor trying to get the engine going, once that happens, next you hear the engine. What makes some cars quieter than others is mostly just sound deadening. Some cars have more of it than others, and depends on where it's placed. There's also intake and exhaust systems to consider, depending on what kind of muffler and resonator, it changes the sound of the car.",
"I’m not sure if this is exactly what you’re looking for, but I’ll give it a shot. The very first thing, you may not even hear it on newer cars, but the fuel pump whirring to prime the system. This normally gets muted by the sound of the starter motor: a small electric motor that connects a gear to the flywheel which is a large rotating mass attached to the engine right before the clutch. Then you’ll hear the start of combustion, hundreds of small burns (technically not explosions, but think of it as explosions) start happening to actually provide you power. Some cars rev up higher just for fun, but also to deal with excess pressure in the fuel line, smooth out airflow in the exhaust, and to start to get all your fluids where they need to be. The exhaust note is largely determined by the exhaust headers as they determine exactly when the exhaust pulses will come (the headers are actually what give Subaru’s their distinctive sound, **not** the engine), but the piping itself also plays a large part in the exhaust note, along with your resonator, which just helps to produce certain frequencies so that they can be muted (muffled) by your muffler. All of this is heavy and inefficient, so some cars opt for less turns, higher flow resonators and mufflers and catalytic converters and so on which produces a louder, crisper, harsher note. You’ll also hear squeals out of some cars, this isn’t normal, it’s loud belts that are used to drive accessories like the alternator, AC compressor, and water pump. You may also hear a tapping/knocking sound; this is usually internal components that are damaged/worn and need to be addressed"
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hxc053 | why is mining nickel efficiently difficult and valuable? | Tesla just offered a giant contract to whoever can efficiently mine nickel- why is this process so difficult and inefficient? | Engineering | explainlikeimfive | {
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"The top two ores of mining nickel ore are through a chemical reaction. Most of it is mixed with other elements that require expensive elements to react with the other elements without reacting with the Nickel itself. And the mining byproduct is also toxic. [ URL_2 ]( URL_1 ) [ URL_3 ]( URL_0 )",
"IIRC my uncle was telling me the mine he works at in Quebec mines Nickle and ships it by ocean barge to get refined. The nickel ore veins have a percentage of Gold and the Gold alone pays for the entire operation. The Nickle is 100% profit.",
"Because 1st world nations eschew mining developments due to nimbyism leaving mining to happen in 2nd and 3rd world countries that don't give a shit about efficiency or the environment. There's lots of good nickel mining in USA and Canada but new mining will tend to happen in less regulated regimes, because while people will gladly say no to mining in their area, they will not say no to the goods they want that ultimately get made anyway by getting the materials elsewhere. Out of sight, out of mind.",
"mining nickel is fairly easy and efficient depending on whether it is mined in a open cut mine or a underground mine ( underground mining tends to be a lot more expensive and slower due to ground support needed ) . Depending on ore types, processing into nickel concentrates can be very simple and efficient or can be horrendously complicated and expensive but still very efficient . Refining nickel into metal is the difficult and expensive part due to the amounts of processes and materials needed to turn nickel concentrates into metal and treating and reprocessing the wastes from refining is the inefficient part that all refining company's are always looking to improve .",
"It would actually be really interesting for Mr. Tesla to invest himself in a mining company because mining co's are fairly slow to innovate and he would add an interesting new approach. But the challenges of opening a new mine are staggering. The fact is that building a new mine is not a very safe investment for many reasons. Much riskier than starting an electric car company. Let me give an example. When Tesla builds their car factory, they have by then built many prototype cars, many prototypes of all of their parts and components, designed their assembly process exactly, established all of their quality requirements and their chain of supply to get the needed components in suitable quantities, price and quality. While it may be questionable if the factory will be able to sell as many cars as they claim, or be profitable doing so, is still in question. But the fact that they can build the car they say they can build with this factory is fairly certain. After completing the factory, if Teslas were not popular and did not sell well, there is still the possibility to retool to make a different car, or a better version of a Tesla. Now consider a company that owns the rights to a large metal deposit that begins several hundred feet below the ground and extends some 500m down. They have drilled holes down to explore what is under the ground, many, many holes in fact, and they think are confident they know the extents of the ore body, ie it's rough physical dimensions, how the mineral content changes within that to some extent, how they can mine it, etc. They have already spent maybe a billion dollars buying the rights to this when it was a less studied deposit, and maybe a few hundred million doing engineering studies, drilling campaigns, environmental studies, permitting studies, etc. This has taken 10-15 years thus far. NOW after all that work, the company has to apply for their water permits, their environmental permit, file their reclamation plans, operating permits etc. They have to go to public comments and spend years convincing the public that they CAN do this safely, and they WILL meet and exceed the legal requirements, and they will go above and beyond to protect the environment in ways that no other mining project has yet done. This can go years, and may or may not be successful. Even if they DO get their permits to operate, and have sufficient cash or investors to spend the next billion dollars over 3 years to actually build and start up the mine, there have been many cases of citizens groups filing a lawsuit and a judge revoking the permit and sending them back towards the beginning of that process somewhere. (There is an argument of course that diligence is important here and I don't argue that- but we can't shift the rules so dramatically at the end of the game if you know what I mean). Anyway, even if they HAVE successfully gotten through all this, and built and opened their mine, they have continuous technical challenges. Their mine plan might not work as expected. They might have planned to use an open pit mine but the ground is not as stable as expected. They might have planned to mine underground but the rate of productivity in preparing the underground workings to access the ore body is crippled by rock instability they couldn't foresee from their drilling (see [Oyu Tolgoi mine in Mongolia, happening now]( URL_2 )). The ore could have harmful inclusions that were not detected in drilling that interferes with separating and concentrating the valuable minerals in the milling process on the surface. Or that contaminant could render their concentrate product unsaleable (for example too much arsenic in a copper concentrate makes it unsalable, or too much silica in an iron concentrate, too much copper in a nickel concentrate, too much lead in a zinc concentrate). The ore could simply be lower in grade than expected or harder to process with sufficient metal recovery. Or, maybe they don't have any such problems... but in the several years it takes between starting to build the mine and mill and getting it started up in production, commodity prices have dropped and they don't make enough money to stay in operation. Putting the example of building a Tesla factory in the context of the mining example, this is like if Tesla decided today they have done all the correct diligence to build a factory and economically build and sell Tesla electric cars. They think it will take them 2-3 years to build that factory but it actually takes them 15, because they have to fight off 10 lawsuits and rejected construction permits along the way. Once they successfully build the plant and start it up, it turns out that many of their electric motors that were supposed to be a particular size are not actually the size they though they were, and there's nothing they can do about it. The batteries they are building, which in their sample runs reliably yielded about 100 kWh, actually only produce 20-50 kWh in half of cases. They thought they would have 19\" tires but it turns out they can only get 15\" tires. And they thought they could sell a Tesla for $75k but now it turns out the market price for the commodity electric sports car is only $50k due to tradewars between the US and China causing an excess inventory of electric cars on the market. In the real world, for Tesla, most of these problems are quite far fetched and if they arose are solvable by R & D and improving/correcting problems. In the case of a mine, you are stuck with what you have in the ground. You can't change your supplier, it is what nature gave you. By the way Tesla also doesn't have to worry at their factory so much about attracting their workers to a far away remote place (maybe even fly in/fly out in 2 week shifts), keeping them safe in a fairly hazardous operation, and protecting the environment from disaster. (not to downplay safety of workers but this is much easier to manage in a factory than in a mining environment). A good recent example is [Nemaska Lithium in Quebec]( URL_1 ). Everyone thinks lithium is a slam dunk moneymaker, surely, what with electric cars.... Well Nemaska Lithium got all the way through this process to the point of having all their permits, having the mine ready with their process plant in construction and having bought much of their equipment. But, they burned through their cash more quickly than expected due to engineering and construction delays, defaulted on their first supply contracts that they weren't ready to sell product for in time, and went bankrupt. Lithium prices were dropping anyway too. Before that, Quebec Lithium, a different company and different mine, got alllll the way up into operation, but couldn't produce any product successfully, and they also went bankrupt. I believe that operation was since bought up, restarted, and gone bankrupt again, just in the last several years. The same kind of rushes are taking place in graphite mining, also related to Tesla and electric cars. See this video (which I really love btw...) [ URL_0 ]( URL_0 ) I hope this at least provokes some thought for y'all. Cheers."
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hxde5t | How do they put in new cables without digging in the ground? | We recently got solar power and they ran new cables through the ground. The thing is they didn’t dig a trench, they just put it through some tube that went through one end out the other! | Engineering | explainlikeimfive | {
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"Dig down in one place that isn’t developed, and then using a long drill (similar concept to oil drilling in some ways) they just dig horizontally. Alternatively, you can dig on a slight incline and connect from the other side, but this isn’t as ideal",
"Directional drilling is the answer. URL_0 link to a you tube video that lays it out in about 3 min.",
"Was the tube already installed? If not, they may have used something like a tool like this: URL_0",
"They either snake cables through an existing conduit, or they horizontally drill. In the case of your power lines, I would guess that they horizontally drilled."
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hxgy89 | Why is it when I'm driving on a road, the suspension is great; When the car is on a tow truck, the suspension is very bumpy? | Engineering | explainlikeimfive | {
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"Well for one, you shouldn’t be riding in the car whiles it’s being towed, at least no city I’ve ever lived in is that normal. If you mean riding in the cab of the tow truck, it is probably because the suspension is already being weighed down by the weight of the car, reducing the suspension already."
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hxk0xa | Why so some guitars have 24 frets and some have 22 frets? | What is the use of having 24 frets, are they better than 22 frets? The only difference I know is that in 24 frets you get 2 octaves . | Engineering | explainlikeimfive | {
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"That’s basically it: with 24 frets you can get a full two octaves up from the open string, if that’s something you’re going for. A 24-fret guitar probably also allows for a bit more room for your hand if you’re playing anything past the 12th fret. Whether this matters kind of comes down to the style of music you play. If you play metal or some other kind of stuff where you’re really high up on the neck a lot, you’re probably going to look for a 24-fretter, but if you play in a punk band like me a 22 is likely fine.",
"With 24 frets you get, well 24 frets, with 22 frets the neck pickup can be further away from the bridge and has a subtly different sound."
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hxpwtn | why is it so hard for Tesla to get their fit and finish up to the standards of other car companies? | Yes I have searched and I couldn't find an answer. I can understand why perfect paint jobs are hard, they just are. However, with things like panel gaps being bigger in some spots, or interior panels not lining up correctly, how does that happen? I would think that all these body panels and interior panels are stamped or molded on the same machines, so shouldn't they all be exactly the same and therefore fit together the same? | Engineering | explainlikeimfive | {
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"Cars are incredibly complicated assemblies. The major traditional manufacturers have spent decades working out how to do this. You are correct that stamped parts coming off a tool will be very similar, although tools do wear over time. The variation can also occur when parts are assembled. If you have 0.5 mm variation in how two parts meet, an assembly that has ten parts could result in a 5 mm variance, which would be enough for a hole not to match up with a mating part.",
"An mechanical engineer took apart one of their cars, essentially it boils down to Tesla innovating too much in areas they don't need to. Using excess screws in certain areas to create their own unique shell and avoiding tried and tested methods.",
"> I would think that all these body panels and interior panels are stamped or molded on the same machines They are. I did metal stamping on progressive die presses and single stroke presses a couple of years. The tools wearing down(individual pieces of the die). Lack of coolant on certain parts of the metal as it goes through the die. Slight variance in the steel you are stamping. These are just some of the factors in what will give some variance. Each individual part isn't measured either. Depending on how long the run of parts is, you have a first piece quality check and a last piece, but you might not get another check on everything during that run. So any little variance that come up is hopefully within the specs they are expected to be in. Then you have how much of a variance the part is allowed to have. To give you an example I worked for a place that made ceiling trusses. The variance for those boards was 1/4 inch. So if two boards were both 1/4 inch short, you were looking at a half inch gap. Now with the auto parts the biggest variance I've personally worked with wasa couple tenths of a millimeter and as far down as a couple of hundredths of a millimeter. But any little variance, especially if everything is hitting on the short side will add up.",
"Aside from trying to reinvent the wheel during production Tesla is also under a huge amount of pressure to keep production up. For the established car makers their production numbers are important but they don't make the news when they don't manage to meet them. When everyone is looking at your production numbers you will decide to send a car to a customer instead of sending it back after quality control so these issues can be fixed. You reach your target, media reports this and shareholders are happy. Customer has to go in for a service and it is still fixed and might not be entirely happy, but that barely seems to affect share prices.",
"I worked for a company picking up the cars from the port and bringing them to the dealership/service centre on a truck. So many cars were in bad shape from the factory and had to have repairs/bodywork done. Also I remember when we started delivering the model 3 when it was brand new and I put the paperwork on the hood of the car for the manager to sign and he said and I quote \"we can't sign paperwork on the hood of these because the paint is so thin and poor that it'll damage it\". After having driven 1000's of these cars from brand new ones to the oldest ones I can tell you that the tech in them is good but the car is an absolute piece of shit."
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hxutdg | What stops an internal combustion engine making more power with more revs? | For example an engine may have its maximum power output at say, 5500rpm. If it can rev all the way up to 8000rpm what stops it from generating even more power, ie. More revs = more fuel/air = more horsepower? | Engineering | explainlikeimfive | {
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"Power is the torque × the speed. Power (watts) = torque (Newton-metre) × speed (rads/second). Imperial units are a goddamn disaster, but the same holds with a bunch of nonsense factors. What is torque? Angular force. The gas expands in the piston, creates pressure, exerts a force on the piston, and then the crankshaft converts this all the spinning motion and torque. If you had a constant torque, you would be correct. Power would linearly match speed. If the engine goes twice as fast, twice as many cycles occur, twice as much gas is burnt, and there is twice the power. The torque, or the force, however is not constant. The speed that the torque peaks at is actually well before the higher speed at which power peaks at. Even though torque starts dropping, it's offset by the increasing speed so power keeps rising, albeit slower. The peak power is the higher speed at which to torque starts dropping faster than the increase in speed. The transmission ideally tries to keep the engine between these two points. Why does torque drops? Well, firstly, friction. The engine spinning faster causes more friction loses which reduce its torque/force. Even if you push the same, if there's more friction, you push with less net force. Secondly, air. The engine pistons at low speeds actually struggles to suck in enough air though the valves, which keeps the torque lower. At medium speeds, it sucks in air quite well. At high speed, the air becomes all turbulent and the engine starts sucking in less again in addition to more friction.",
"Air resistance increases exponentially with air speed. Resistance isn't a problem at low or medium engine speeds, but the faster you try to suck in air through the intake and force it out the exhaust the harder it is. Eventually, you get to a point where each intake stroke of the piston starts taking in less and less air reducing your power output."
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hxy13p | What determines engine power and torque? | Engineering | explainlikeimfive | {
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"More fuel and air makes bigger and more bangs. The torque you get from the transformation from linear motion in the pistons to the rotational motion of the crankshaft. Power is a function of torque at a given RPM. To get more air in to the engine you can have bigger valves and/or keep the valves open for longer. You can also force more air in to the engine through a turbo for example The get more fuel in you just need a bigger pump and/or fuel injectors that can flow more fuel.",
"Torque is a measure of how strong the twisting motion from the engine is, this is mainly determined by the volume of the engine since bigger cylinders hold more air and fuel and create bigger booms that can push harder Power is a function of torque and RPMs. High torque means the engine can push really hard, but being able to push 200 pounds up a hill at 1 foot per minute is less useful than being able to push 50 pounds at 10 feet per minute, the second combination is 2.5x more powerful. Engine power is determined by the torque and max RPMs. Small light engines like F1 cars have can spin really fast so you get a lot of power from relatively low torque, while big heavy diesels give a ton of torque but simply can't spin fast so they produce less power than you'd initially expect The number of cylinders in an engine isn't a good way to compare them. Formula 1 cars had V8 engines that out out 1500 HP but they'd suck in a big pickup because they lack torque despite both being V8 engjnes"
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hxyj9n | Why is it almost always when a car accident happened, the windshield wiper will get activated? | Engineering | explainlikeimfive | {
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"text": [
"It's the easiest thing to trigger since it sits on a lever. Anything flying around, including the drivers' hands, is bound to flip it on.",
"I believe it is because the person in the car panics and moves their hands away from the wheel, hitting the wipers, or the wheel turns and takes the drivers hands with it, turning on the wipers"
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hy04k6 | How do clothing and outfit manufacturers determine the right proportions and shapes to use on 2D sheets of fabric? What is this process called? | I would like to learn more about this, and am wondering what this process is even called. Are there any tricks involved? How much of it is math involved vs just measuring and expanding. I feel like it can get complicated with many things working together with complicated shapes and how we human beings on earth with human being bodies just have these big branches off of our central body meat. Edit: It's called drafting. | Engineering | explainlikeimfive | {
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"I think what you’re referring to is pattern making or pattern drafting. Years ago this was a skill taught to tailors and seamstresses and they could take a set of numerical measurements and turn it into a basic pattern or “sloper” that when sewn together produces a 3-D garment. I learned the introduction to this process in college during a costume design and production course. It was clearly a skill that would take years to master although I was able to learn the basics in a couple of semesters (I already knew how to sew, though, which is a different skill set entirely.) Later I worked with a couple of master patternmakers on theater productions and it was fascinating to watch them work. Since the 90s there have been computer programs that draft patterns based on a set of measurements and that’s the way many patternmakers work now."
],
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7
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hybn5z | how are zip lines across canyons (or large gaps) built? | Engineering | explainlikeimfive | {
"a_id": [
"fzbontw",
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"text": [
"I know for dams and such, a lightweight pilot rope is sent across, using various methods, dragging it across by boat, an arrow, or even a rocket. URL_0 . I think it would be similar for a zip line, take a lightweight rope across, and then use that to pull up a heavier line, repeat until you have the final weight line installed.",
"In the modern world, you have access to helicopters and cranes. Both of which can either lift the main cable or you can lift over a lighter cable, and use that to pull over a stronger bigger cable until the desired cable size is reached. For example here is a helicopter pulling wire for power lines. URL_0"
],
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"text_urls": [
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"https://pdfs.semanticscholar.org/c47c/6d1dc26a945f02bc606a8662be73ca09dc02.pdf"
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"https://youtu.be/UqtXCV14LSo"
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|
hyc0cq | The purpose of a neutral wire? | Hi, sorry if it has been asked before but i read some of the post but I still dont really get it. Correct me if I am wrong for anything i say! In a balanced three phase system, a neutral wire is not required. But exactly why?? I saw some diagram that the 3 phase essentially cancels out each other, but how is that actually happening? I saw in another post that imagining an DC circuit is a closed loop where electricity flows, in an AC circuit the electricity is alternating really quickly back and forth. Is it because the 3 phase meets each other at the source and cancels out each other?? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"If you've ever looked at the image of a 3 phase sine wave, you'll notice that for any given peak of one phase, the other two are of the opposite polarity. So the current going out on A phase is returning on B and C phase. If you express it as a ELI5 math equation, the 100% of A phase is returning at 50% on B, and 50% on C simultaneously. This is repeated continuously for all the phases, so the neutral is zero as long as they are balanced and have no 3rd harmonic component. But not all loads are balanced, so the neutral is often necessary, but is usually reduced in size since it carries a reduced current."
],
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hyj1p3 | why are straws not recyclable and why can't they be made out of the same material as plastic cups? | Engineering | explainlikeimfive | {
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"You know I actually was curious about this a while back too with the whole no straw movement... You won't believe the reason: When you throw a straw into the trash / recycling bin, all that stuff eventually makes it to a sifting machine of sorts and will attempt to separate out the plastics that can be recycled... Straws are too light and cylindrical that they often fall off / over / out of the conveyor belts and then will be just swept away and piled back again with general trash, dumped to a dumping ground. Since these straws are light, they often times end up flying away from the dumping site too and end up in the ocean.",
"The biggest problem is a lack of consistency. In my state, some councils tell you to put them (and bread clips) in milk bottles and put the lid on. In other councils, they tell you to take the lid off the milk bottles when recycling. This just leads to consumers not knowing what to do, and recycling the wrong way, which leads to things not being recycled despite being put into the correct bin.",
"They typically get thrown away with the trash. Or just thrown on the ground. Reduce, reuse, recycle. Don't use it if you don't need it. Use it again if you do need it. Recycle it once it is garbage. People are fixated on the recycle part, when that is the least effective. Don't like reusing a plastic straw? Find your own straw.",
"Just a reminder to my American fellow humans from an eastern European person. You may not be aware of it, but vast majority of drinks can be consumed without a straw. It may sound unbelievable, but there exists this ancient way of drinking a liquid from any sort of cup by putting your lips to the rim of a cup and slightly tilting the cup to your lips. Try it, it works!",
"Plastics in general are pretty rarely actually recycled it’s extremely unprofitable and way cheaper just to make new plastic. Most recycled plastics these days just end up in the trash anyway",
"As a mechanical recycler, the reason I don't purchase straws is the difficulty in granulating them. They are impossible to Granulate with existing technology."
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hylhy0 | Is there a scientific reason why records might sound better than CDs? | I keep hearing that records have better sound. Is that psychological or is there something about records that captures/reproduces sound better? | Engineering | explainlikeimfive | {
"a_id": [
"fzdh3o4"
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"text": [
"CD vs vinyl? Perhaps. Many people claim that the 16 bit/44KHz bit depth/sampling rate for CDs is audibly poorer quality than analog vinyl. But I think this might be a pretty small group of people and only if they have fairly expensive equipment. Many modern high quality digital recordings are 24bit/96 KHz sampling and my own opinion is that vinyl is not likely to be superior from a sound quality reproduction standpoint. Still, there is nostalgia - in which case it is more of a subjective attitude than a truly measurable objective reproduction quality statement. Some people are \"used to\" the distortion, noise and the RIAA equalizer (used in vinyl) circuits so that is their preference - which is not a statement of quality. Vinyl recordings (due to mechanical limitations of the media/pickup) are equalized through a filter during playback which generally means it is quite far from a \"perfect\" reproduction which would be defined as faithfulness to the original recorded sound."
],
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