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fl8hjh | How is a Hi-point pistol different from a normal pistol? | Engineering | explainlikeimfive | {
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"They really aren't. They are just regular blowback pistols. The reason why they look so unconventional is a result of the shortcuts they've taken in order to keep the price down. The most immediately obvious one is the massive slide, which needs to be like that because it's not made out of steel, but rather some other cheap alloy that is very prone to cracking. TL;DR: They're not different from other pistols, just shit.",
"It's made to a very low price point and has reliably issues. The two that I have shot had issues ejecting rounds. One the ejector wore out after like 100 rounds and wouldn't always pull the casing out. The other one liked to stove pipe not really sure why.",
"Hi-Point isn't a type of pistol, it's just the name of a manufacturer. It's like asking what's the difference between a Ford Edsel and a \"normal\" car. An Edsel is just a make and model of a car that happened to be an ugly piece of shit. Hi-point firearms are just cheap, ugly, unreliable pieces of shit."
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fljonb | Why are fan intensities typically arranged 0-3-2-1? | It seems like fans are always off-high-medium-low. Is there a reason for this? | Engineering | explainlikeimfive | {
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"because you use the cheapest motor you can for the fan and at max power, it barely has enough torque to get the fans going from stop. once the fans are spinning, then you can reduce power/voltage and lower the fan speed.",
"Protects the motor. When I was a fairly young & newish car owner, I burned out a fan motor in the cabin air circulation because I'd consistently turn it on low (from off). The mechanic who replaced it was kind enough to explain to me that he saw lots of this exact thing, for that exact reason, and recommended starting a fan by turning it to high first, then reducing to the desired speed. Have followed his advice ever since and never burned out another fan motor, whether in a car or home fan."
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flmaho | How can companies completely unrelated to face masks or hand sanitizers convert their production to those so quickly? | Engineering | explainlikeimfive | {
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"They aren’t as unrelated as you might think. Most of the companies share raw materials of whatever they’re temporarily making. A company that makes computer stuff has all or most of the raw materials to make medical stuff. Similarly, hand sanitizers are mostly alcohol, you know what has a lot of alcohol on hand? Any company that sells booze.",
"Peripheral manufacturers often make another important component for the hardware, the packaging."
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flphda | How do factories that have nothing to do with producing safety equipment (masks/faceshields/ventilators etc) retool so quickly to produce this in demand equipment? Are there companies with "mask producing machinery" standing by? | Examples: 1. Gaming peripheral Razer [to make masks]( URL_1 ). 2. Tesla offering [to make ventilators]( URL_0 ). | Engineering | explainlikeimfive | {
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"Most plastic objects are made through injection moulding. Without getting into the technicalities, injection moulding machines basically consist of a large high-pressure nozzle that inject molten plastic into a mould. These moulds are designed to be swapped out. The machine itself can pretty much produce any hard plastic part as long as you have the appropriate mould for it. So it really doesn't make any difference if it's injecting plastic in a mould for videogame controller casings or ventilator valves. A lot of mass production machines are designed like this. They specialize in a certain production method like injection moulding, stamping shapes out of sheet metal or frying foods. But what they make specifically is very easily swapped out between products that require the same production method. And some products are still made through mass manual labour. In that case, a company just buys up production capacity in a factory where workers make items by hand. If I bought 100.000 man-hours worth of production capacity in a factory in China, they'll happily make masks instead of soldering electronics if that's what I tell them to do."
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flui0q | Where does the sound of an internal combustion engine come from? | I pretty much know how a ICE works. Air/fuel goes in the cylinder, compression, spark/combust, and exhaust. Something that I cannot really figure out is where does the actual source of the engine sound come from and how engine sounds are unique to every design, such a Toyota vs a Honda I4 or a V6 vs a V8. | Engineering | explainlikeimfive | {
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"The size, and duration of the burn in the cylinder. Also the firing order plays a big part in this. A standard cross plane crankshaft in an American V8, accompanied by a tight lobe separation angle in the camshaft, gives you that 'V8 rumble'. A flat plane crank, and firing order gives you that higher pitched, mellow whine if you will common among Italian super cars, the new C8R and the mustang Voodoo engine. There's also a lot of effect from camshaft dynamics. A cam ground for low end torque if going to be more choppy and have that lope. A cam to take advantage of a 4 valve setup is going to be smoother since naturally 4 valve engines don't become an advantage until over 4k RPM. The camshaft would be ground to exploit this and the sound would follow suit.",
"The majority of the noise you hear is the exhaust stroke. It's the sound of that slug of spent air being pushed by the piston out the valves and through the exhaust piping. Other comments cover the things that shape the sound well. The size and shape of every chamber that this air flows through, combined with the timing of the exhaust pulses in relation to one-another is what defines the unique sound of the engine.",
"Every moving part makes its own noise, add all the noises together and you have each engines signature sound."
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fly7p2 | How glasses/contacts work? | Engineering | explainlikeimfive | {
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"You know how you gotta hold a magnifying glass a certain distance away from a leaf to burn it? That’s how vision works, except the leaf is your retina (back of your eyeball) and it’s not as burn-y. Sometimes the magnifying glass is too close, sometimes it’s too far, but glasses are what adjust it up or down to create that perfect pinpoint of light.",
"There is a lens inside your eye which focuses images for you to see, but sometimes the human eye has some defect - sometimes from birth - that causes it to be unable to properly focus the images. Fortunately you can put another lens outside the eye in front of it to adjust the focus going in so your eye can handle it. Think of a pair of binoculars. There's an adjustment dial on it to focus it and it's made of 2 lenses. One of those is like your own eye and one is like the glasses you wear. Rather than adjusting with a dial though, your glasses/contacts are manufactured to the needs of the wearer with a positive or negative focus of varying intensity depending on the person."
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fm1uzc | If my car requires premium, and the guy at the pump before me bought regular, how much regular gas is my car going to get? | Engineering | explainlikeimfive | {
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"Not enough to make a difference. Know what happens when you mix 87 octane gas and 89 octane gas? You get 88 octane gas. It all mixes together in your tank. Some quick googling reveals that the fuel pump and fuel line at the station hold *about* a third of a gallon of gas. That's not enough to lower the octane rating of the whole tank very much unless for whatever reason you were completely empty and bought less than a full gallon. In any case, premium high-octane gas means it compresses more before igniting. The higher the octane, the more compression it will tolerate. More compression means less *knocking*, which is your engine kind of rattling around because a cylinder fired before it was supposed to. Despite what other comments have tried to say, **yes, some cars absolutely do require high-octane premium gas**. Those engines are engineered *very* precisely and can't handle misfiring cylinders. It will damage the engine. However, 90% of consumer cars are not built with that level of precision and do not require high-octane gas. Putting high-octane gas in a beater won't do anything and may actually damage the engine. Putting high-octane gas in a very good but otherwise normal engine will get you a smoother ride for the duration of that tank of gas, nothing else. It is not \"cleaner\" and will not clean your engine. Even high-end engines that *do* require high-octane gas can tolerate low-octane gas for a bit, it won't instantly destroy the engine. It'll just be a really knocky, rough ride for a while. And certainly a third of a gallon of 87 changing the whole tank's octane rating from 89 to \"88.99\" isn't going to do anything.",
"You're not using the same gas station or custom fuel formula every time you fill your car, so the effect using or not using premium one time will be cancelled out by all the others. I don't think any car that literally requires only premium or super unleaded fuel to run safely would be allowed to drive on the roads or even willingly mass-produced by any car company.",
"First, there is some awful and unsolicited advice here that needs to be made explicitly clear: if your car requires premium - **USE PREMIUM**. Not only will using the wrong fuel void any outstanding warrantee, it will also debase any insurance claim you may have had due to any potential damage. You take on sole liability. No insurance company, upon investigation, is going to pay out because you willfully used the wrong fuel in the car. Further, some cars DO IN FACT require premium fuel. I can speak on behalf of the 350z community that engine is largely intolerant of low octane fuel, and the typical community story you occasionally see in the forums of \"I used the wrong gas\" ends with \"and now my engine is destroyed.\" Many turbocharged and supercharged cars that also require premium are also typically intolerant of lower grade fuel. And unlike the other terrible and wrong opinion here, using the wrong fuel one time is not canceled out by all the right times you do use the right fuel - it's not about accelerating wear in the engine, it's not like low grade fuel in such an engine shaves off an extra 500 miles of life, IT CAN CAUSE PERMANENT DAMAGE. God, the bullshit asymmetry principle at work here, folks. Fucking idiots advising you to potentially wreck your car. YES, some cars recommend premium and can run on regular, NO, if you're here reading this, you're probably not qualified to discern which ones they are. And then again, read above about warrantees and insurance, because that will stand regardless. Obviously, differ to your vehicles owners manual and the teams of engineers who have dedicated their entire professions to designing and testing your car with centuries of collective man-hours to back them over a couple trolls... That said, to answer your question directly, the amount you get can be measured in fluid ounces. It won't be a lot, and again, the automotive industry collaborates with the fuel industry and collectively agrees this is an acceptable practice. To understand why is a bit more complicated. Octane ratings are a measurement of stability vs. a reference - OCTANE, a large hydrocarbon that is the principle molecule in gasoline. The rating is an average, because gasoline isn't pure, it's refined - containing hundreds of different types of hydrocarbons, both smaller and larger than octane, and stabilizers may be added at the refinery to raise that stability - chemicals that aren't even hydrocarbons. Then there's the addition of ethanol, which has a higher stability than octane, but is principally added for emissions. So you dilute an already impure cocktail with more hydrocarbons that are already in your premium fuel, but the amount you get compared to a full tank is small enough to be insignificant and immeasurable in application. The reason for different grades are because engines can be designed to burn fuel more efficiently, but in doing so, requires them to be more stable, more resistant to spontaneous combustion. This is often caused by high compression ratios or compression densities - the more you squeeze something, or the more you squeeze in a fixed volume than you have previously, and you will rase the temperature of what you're compressing. Get fuel hot enough, and it can self ignite, often at the wrong time in the engine's cycle, and this can cause damage to your engine internals. Ideally, your engine would run as low a grade as possible, because it's easier to yield the potential energy locked up in it's molecules, and the engineers have already figured that out for you by documenting in the manual and on the fuel cap what the engine needs. Their choice balances performance with reliability so you don't have to."
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fm4ydi | What are the mechanical/biological functions of a ventilator vs. something like an ambu-bag, and what are the practical difficulties in constructing DIY ventilators? | I read a comment section somewhere where a (self-identified) ER medical staff member talked about an ambu-bag and I did a little reading. It seems as if the downfall to an ambu-bag (which I know is like calling all facial tissues kleenex) is the manual nature of it, but I can't imagine constructing a mechanical bellows would be terribly difficult. If oxygen level of the forced air is of interest, what is the fallback to rigging up a system to supplement the bag? | Engineering | explainlikeimfive | {
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"There is a lot to inflating the lungs, both manually with a bag or automatically with a machine. It's more than breath size and rate. Its inspiratory flow, the \"waveform\" throughout the inspirarory phase, peak pressures, mean pressures and end-expiratory pressures. Damage to the lung tissues can result from over pressuring (barotrauma), too much volume (volutrauma) and even too little end-expiratory pressure (causing shear stresses when there are areas that are collapsed that lie next to areas that are inflated- you can shred the alveoli to pieces). Then there is trying to keep the lungs sterile. Studies on manual resuscitator demonstrate that it's very difficult to consistently ventilate the patient breath to breath for days at a time. Source: Former RT and currently working in \"the industry\".",
"Keeping it clean. It's no good to pump air into someone if the air is full of bacteria that end up killing them. A manual resuscitator, only makes sense when you're in an environment with clean air."
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fm9bvf | how do zippers work? | Engineering | explainlikeimfive | {
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"[This]( URL_0 ) gif is handy. Basically there are a bunch of little interlocking teeth just slightly offset. The actual handle/tab guides them together so that they interlock in a way that is resistant to being pulled apart by normal physical stresses (e.g. moving, bending in clothes)."
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fmaa23 | Why do some towns have water towers? | It seems like only small towns have them, so why are they not everywhere? Also, wouldn’t the water get gross over time? Why store it so high up? | Engineering | explainlikeimfive | {
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"Water towers are great for making sure that water pressure is constant, even as the amount of water being added or removed is changing. Imagine all of your water came from a small river. You have a pump that can take some water out. There are times, though, that you need more water than you can pull from the river. So you pump water at a constant rate into a tank instead, then take your water out of that. The tower makes it so the pipes always are under pressure as the weight of the stored water is pushing down on the water running through the pipes. Most towns will actually have water towers, but they are often hidden on rooftops or inaccessible hilltops. Where I grew up, ours was actually built on what was basically a bump on the tallest hill of the neighborhood. It wasn't actually a tower, but a dome. The bump acted as a tower for it. Big cities don't rely on them as much because it's hard to build towers that big, so instead they tend to have water tanks on top of buildings. The building would pump water up to its own tank, then that would act as a local water tower.",
"Large cities have them too. The water is pumped up into the closed tower after filtration and processing. They are high up to use gravity to provide water pressure at your faucet.",
"Imagine you are in charge of a city and you need to pump water to all your citizens from wherever you source your water. The problem is the water demand varies throughout the day. In order to make sure you can maintain consistent supply at all times of day you need to have enough pumps to supply your entire city during the peak daily demand. Alternatively, you could have just enough pumps to meet the average daily demand and instead of pumping directly into the water delivery pipes you instead pump into a reservoir at the top of a water tower consistently over the entire 24 hours of the day. During peak usage the tower drains faster than its being filled. But the rest of the day the tower slowly fills up so that there is enough in reserve to serve the peak hours. And because of gravity you don’t need pumps to move the water from the tower to the delivery pipes.",
"Lets say you use 100 gallons of water a day, but when you're actively using water you use a gallon per minute. You could buy a pump that can supply the peak load directly, or you could buy a pump a thousand times smaller that pumps into a storage tank large enough to supply one day of water. The same principle applies at a large scale. Pumps are sized for average demand, and the water towers are sized to cover peak demand. Even small water systems like a home supplied by a well use a storage tank, though in that case it's usually a pressure tank with a diaphragm rather than one that uses gravity to maintain pressure. If you have a skyscraper, they probably have booster pumps to increase the pressure for the higher floors.",
"Our plumbing needs water pressure to run - this is the force that pushes water along the pipes and out of or taps. This can be done in multiple ways, but one of the simplest is to use gravity - if your water supply is higher than your tap, then the force of gravity will cause the water to move from the high point to the low point at your tap. A water tower does exactly this - we pump the water up high into a big tank on a tower, where it is stored ready, so that when a user (who will be lower than the height of the tank) opens their tap, the water flows down to them. Water towers are very obvious in small towns in flat areas where they are fairly obvious landmarks, but the same principle is often used elsewhere, just it may not be so obvious. In a hilly area for example, rather than having your water tank up a tower, you can put it up a hill - this means it doesn't stick up so obviously and can be easier hidden, but since all that matters is that the tank is above the users, it works exactly the same. In urban locations they might also hide tanks in other places too - so rather than having a tank on its own tower, why not just sit it on top of a building where it isn't so obvious? Tanks can also be split between multiple buildings, so rather than having one big tank for the town, each building has a smaller tank suitable for its own residents use. The other bit is that we do need pumps to pump water up into the tower in the first place. Using a tower allows you to pump up a load of water at once, then turn off the pump while it is gradually used, but it is also possible to use a continuous pump to just keep pressurising the system constantly without using a tower. There are various different costs and benefits to both systems which mean they are used in different places, which is why water towers are common in some areas and landscapes, but rarely seen in others."
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fmech3 | How can a company like Tesla or Razer, switch from producing their standard products to producing medical equipment so easily? What is the process they have to follow? | Engineering | explainlikeimfive | {
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"Depending on the old and new items, the hardest part is figuring out how to do it. For example, Tesla has to use sewing equipment to make seat coverings, can that be modified to make masks? Razer works with a lot of plastics and electronics, can they make respirator masks? Once you determine how you can help, and modify the equipment to do it, it's just an assembly line, like they'd use to make any other product."
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fmhpq2 | What's the difference between id and class in HTML? Any examples? | Engineering | explainlikeimfive | {
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"A class is used to identify a *group* of related elements. Therefore, it is okay for multiple elements to have the same class. An id is used to identify a *single* element. Therefore, no two elements should ever have the same id."
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fmjse9 | Why is concrete used on driveways cut to prevent heaving, but the same practice isn’t done in basements? | Engineering | explainlikeimfive | {
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"It's not cut to prevent pavement heaving. It's cut to provide controlled fracturing as the pavement heaves. Basements don't suffer from pavement heaving because they are deep in the ground and not subject to freeze-thaw cycles. (Sudsidence is a different issue.)",
"Most basement floors are below the freeze line and aren't susceptible to heaving from freeze/thaw"
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fmnml6 | Why are the GHz speeds in computers the same after such a long period of time? | Engineering | explainlikeimfive | {
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"Rather than increasing processor speed, which is becoming increasingly difficult thanks to things like substrate bleed (which is a whole other conversation), the push hasn't been to increase clock speed (measured in Hz) but rather to simply add more processor cores. As software development has matured and proper utilization of multiple cores to get work done has become commonplace, the value of number of cores has steadily outpaced raw clock speed. Clock speed used to be king because there was only a single \"pipeline\" at work in the processor. Stuff went in at one end, did what it had to do, and came out the other end. The faster you could get through the pipeline, the better. Modern processor architecture has added more and more pipelines running together. By spreading what's coming in across multiple pipelines, it keeps everything flowing more smoothly than trying to stuff it all through one pipeline. Additional factors include decreasing cost and size of what's called *cache memory*. This is memory that's actually on the processor itself and is used to store data the processor is actively using. It's far, far faster than having to write data to system memory and retrieve it. Between increased cache memory and more effective use of multiple processor cores, the importance of raw clock speed has sharply dropped off over the past 10 years.",
"We're hitting the upper speed limit for processors because of limitations like the speed of light, and we are having trouble making things smaller because on that scale quantum mechanics starts doing unexpected or unwanted things. We are overdue for a discovery that will revolutionize computer processing yet again. So for the past decade the focus hasn't been to increase speed, but to increase efficiency. Processors are being made with increasing numbers of cores so they can do more at once, and bus speeds are increasing so the processor can talk to devices and RAM more quickly. All of these things translate to improved performance.",
"A lot of this has already been answered, but let me provide a bit of perspective from closer to the silicon level since I'm currently on an internship working with this issue. While clock speeds are important, they are not the only factor in computer performance. Thus, current designs aren't focused solely on increasing clock speeds. One of the main issues is simply heat. As we increase the rate transistors switch the power required increases exponentially and it gets difficult to cool. A more fundamental issue is that transistors and associated wire have capacitances, or the ability to store electrical charge. This effectively slows down the rate you change your signal- as the electrons in these reservoirs counteracts any changes you make until the electrons it holds is depleted. This makes a nice sharp clock signal flatten out and slows down rise times. Lastly, it is difficult to design good interconnects. Even if we have a really high clock speed, it's not easy to design wires that can carry information at that clock speed. All wires have some capacitance and inductance where energy is temporarily stored in electric and magnetic fields instead of being sent down the wire. Worse still, the magnitude of this energy that is stored is frequency-dependent. This means at higher clock speeds/frequencies a lot more energy is \"lost\" before getting to the end. This means that the magnitude of the signal at the end is a lot less. For example, one thing you see is that at higher frequencies, signals on one wire start leaking to other wires close by- something you obviously want to avoid.",
"The GHz 'speed' is cycles per second, but that tells us nothing about how much the computer can do with each cycle. Modern computers tend to do more with each cycle, and have multiple cores running at once. So even though they don't appear to be getting faster, they get a lot more work done in the same amount of time. Immagine a little car vs a fleet of vans; they all drive at the same speed, but the vans deliver a lot more stuff in the same time. As for *why* the speeds haven't increased, you can improve performance either by speeding it up, or by improving efficiency. Currently it's easier to do the latter. Making anything go really quickly is hard; at larger scales this is generally self evident, but it still applies at smaller scales. At their heart computers rely on moving electrons about; they're really small so they go really fast, but there's still a limit.",
"For something to oscillate past a few GHz, the length of time between two signals has to be short. That time is now \\*not long enough\\* to cross the entire length of the silicon chip. This means that one signal can \"overtake\" the one in front of it, which causes absolute confusion and merry hell as we design chips to be \"synchronous\" (i.e. things happen at the same time everywhere). We don't have asynchronous chips (we can have multiple chips that aren't in sync, but one chip tends to have a single concept of \"a clock signal\" that turns on and off regularly and makes everything else happen). Past about 5GHz, the length of the pulses needed for that clock signal mean that, even at the speed of light, they can't make it across the physical length of the silicon chip before another one starts its journey. Making the chips asynchronous, shorter, or quicker actually makes things incredibly complex and liable to all kinds of problems if there's a bug found later on. Not to mention, the higher the clock speed, the more heat given out (because the power required to make more oscillations is greater), which means more cooling or more problems with heat, and more interference. Pretty much, we've hit a physical boundary that you can only compensate for by making chips tinier and tinier (which has other problems, not least manufacturing), colder and colder (supercomputers are sometimes liquid-helium cooled or similar), or more and more complex to design, produce, run, program and diagnose.",
"We're reaching size limitations. Our computers are so fast that the speed of electricity (a decent portion of the speed if light) itself is hindering them. Thus, we need smaller systems, but smaller systems are encountering issues with being unable to prevent electrical flow due to quantum effects.",
"Lets say you own a deli shop making sandwiches. When you have a large order there are 2 ways to get the job done quicker. One is to make sandwiches faster (ghz). The other is to hire more people to make the sandwich (core). Current technology it is just cheaper to hire more people than to get people to work faster.",
"I'll give you an analogy. Let's say you want to clean your kitchen. Increasing the frequency (ghz) is sort of like you moving around and doing things faster, eg walking, picking things up etc. Now, you can get yourself pretty fast if you drink a lot of coffee say, but you will reach a limit. Now to get around this limit we can do two things in our kitchen cleaning analogy. Adding another person to help you clean is like adding another core. As time has moved on the cores or in the analogy people over time are able to work together better, eg not getting In each others way, blocking the sink. There is a limit with this too, think of trying to clean your kitchen with 20 people, you wouldn't be able to manage that in normal circumstances at home. And the other way to improve performance is how you can accomplish a task. Back to the kitchen analogy. Compare manually sweeping up the dust and crumbs with a brush and using a vacuum cleaner. Or adding in a dishwasher. Lots of the performance gains in processors these days are also from optimizing how they perform common sub tasks that they will run into. I hope that clears it up a bit.",
"Let's pretend your family is moving across town and you have 5000 boxes of toys. The moving truck can only fit 50 boxes at a time which means your dad will have to make 100 round trips. The fastest your dad can drive on the freeway is 65mph. Sure, he could drive at 100mph to make better time but damn it, he loves you too much to risk jail time. So instead of pushing himself to drive faster on the freeway, endangering himself and others, he decides it's a better idea to have your mom drive a second moving truck, also packed with 50 boxes of your awesome toys. Now the two of them only have to make 50 round trips each, halving the initial time it would've taken, all without the risk of a speeding ticket or going to prison! Now imagine how faster the move would be if your parents also recruited your uncle Bob and aunt Sally to drive a third and a fourth moving truck. They would be able to move all of your toys 4 times faster than if your dad had to move everything by himself! To match this speed by himself, your dad would have to drive at 260mph and the U-haul down the street isn't renting out Koenigseggs yet."
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fmrbg9 | How do they demolish buildings in densely populated and built up areas without destroying things nearby? | Engineering | explainlikeimfive | {
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"Depends on the height of the building. For shorter buildings they'll use a simple crane and wrecking ball. Most debris will fall withing the building's footprint. However as you get taller that technique would take forever and the higher the debris breaks off the less control you have of where it falls So at heights they will use explosives. They will target the central structural supports of the building the whole way up. like pulling the center card out of a house of cards, the whole thing will collapse inwards into its own footprint. Now the actual math and planning behind it is very complex and changes from job to job but that's the basic idea behind it",
"Strategically place explosives the the building collapses straight down. The explosives are usually placed around central support beams and after the explosion the structure of building is weakened to the point that it can't hold up it's own weight. It pretty much accordions down."
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fms60m | Who makes national and state park trails? | I just got done hiking a great trail through the Tillamook forest in Oregon. The trail was well kept and very long. Who makes trails like this? Does the park service contract out construction companies? How is it done? I assume most were made decades ago. | Engineering | explainlikeimfive | {
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"It is very common for governments of all levels to contract out private work. They are then maintained by private contract or by park employees. Just like any construction area, there are people who are very good at figuring out the best and most durable ways to do it.",
"The US Department of Interior controls the National Park Service. Park rangers and lower level employees do a lot of the physical labor to maintain trails and keep park guests safe. A number of the original National Park trails and buildings were made by the Civilian Conservation Corps, a government employment program from the New Deal in response to high unemployment during the Great Depression. State parks have their own Departments of Natural Resources, but also rely on volunteer trail workers to help maintain all of the trails."
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fmx72i | Why does fast charging only works until about 50%-60% of battery capacity and charge rate slows down after that? | Engineering | explainlikeimfive | {
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"Imagine stuffing small soft foam balls into a box. Initially it is easy to stuff the balls in as there is a lot of space in the box and there is no need to compress the foam balls much. But as the box fills up and you want more foam balls in it, you have to press harder and squeeze the balls a bit in order to fit. This slow you down.",
"The charging circuitry requires power to be limited when the battery is nearing full, there's less space for energy to get in and forcing it in could be dangerous. This mostly applies to phone batteries (Li-Ion), car batteries can take much more abuse. On modern phones they found different ways to produce the same type of battery so they can force more power by increasing the voltage (and therefore the amperage). But this is dependent on the fast charging standard or the device's manufacturer. Probably yours has an older or simpler system."
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fn6fm5 | Positive vs. negative pressure specifically to hospital rooms. | On surgical floors Operating Rooms(ORs) have positive pressure checks daily to ensure air handlers are working effectively. Why is positive pressure more desirable for surgery vs. negative pressure? Can either be compared to the exhaust fan in my bathroom on a smaller scale? Thanks! | Engineering | explainlikeimfive | {
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"I once spent time in a negative pressure isolation room. The idea was to make sure that my nasty germs did not leak out in an uncontrolled way. As long as the room I was in had a lower pressure than the rest of the hospital, my germs did not get out through the door. The way they made sure to keep my room at negative pressure was to have an exhaust fan pulling air out of the room. That exhaust fan the put the air it pulled in through a filter system that made sure no germs got through. Operating rooms want to make sure that no germs get *in* and infect the poor guy with an open incision. So they keep positive pressure by using a fan to blow air into the operating room. And, like the exhaust fan, there is a filter system on the *intake* side of the fan to make sure they don't have any nasty germs in the air that the fan blows into the operating room. The basic idea is that it is easy to filter air at one point: the inlet of a pressure fan, or the outlet of an exhaust fan. Trying to filter all the air that creeps in at every crack is impossible.",
"Positive pressure means that air will flow from the high pressure area (surgical room) to the low pressure area (the corridors). This means airborne bacteria from the less sterile outside does not get carried into the more sterile surgical side by airflow. Presumably the exhaust fan in your bathroom is designed to vent humid air from the bathroom to the outside - not quite the same intent."
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fn9hz9 | Why can't we just pack more and more ALUs in a CPU to increase processing throughput instead of increasing clockspeeds? Wouldn't the gain be just as significant? | Engineering | explainlikeimfive | {
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"Same reason why 9 pregnant women can't make a baby in 1 month. Say you want to tell a CPU to calculate this expression: **(2 \\* 3) + (5 \\* 6)** That's 3 operations, so if you have 1 ALU this would take 3 steps, but if you have 2 ALUs you can compute **2 \\* 3** and **5 \\* 6** at the same time, and finish it in 2 steps. BUT, if you increased ALU count to 3, you'd still need 2 steps to finish the calculation, because the 3rd step requires the results of the first two. Alternatively, if you had something that can be computed in parallel, then you'd write multithreaded code to take advantage of multiple cores, or GPUs which have even more cores.",
"That's what manufacturers *are* doing, by and large. That's why every fabrication generation with a smaller process is such a big deal - they can now pack more transistors into the same size package. CPUs haven't really gotten much faster in clock speed in a long time. 4ghz processors hit the consumer market 8 years ago and that's still approximately the same top end speed today."
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fntpb3 | How do formation jets fly the same pattern without touching? | Engineering | explainlikeimfive | {
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"Practice and communication by everyone knowing what they are all supposed to be doing and when they are supposed to be doing it. In addition some flying techniques only look close when viewed from a certain point like a display audience.",
"Design your show. Communicate with the others. And then lots of practice. More importantly, see this thread from somebody who got into formation flying: URL_0"
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fo3zev | What is the military grade GPS and why can't we receive its signals just like normal GPS? | Engineering | explainlikeimfive | {
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"You are receiving the military signals. The US military disabled selective access in 2000, and ever since everyone on the planet has had the exact same GPS accuracy as the US military. Prior to 2000, the last few decimal points of the timecode were encrypted, so that only the US military could get full accuracy."
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foa5pe | What is social engineering? | Is it a science or a manipulative technique? Why does it often have negative context? | Engineering | explainlikeimfive | {
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"Social structures can be 'hacked' just like physical and digital structures can - and it's often easier to approach an intrusion problem from this standpoint. Actually hacking into the DMV database is a relatively difficult task. However, pretending to be an IT consultant and tricking those with passwords to the database into revealing them is comparatively easy. That no-tech-skills-required approach is 'social engineering'. As for being a science, no. It's no more a science than selling used cars is a science. It's mostly just being able to interact with people effectively. In terms of a negative context, social engineering is fundamentally about tricking people into doing what you want them to do. While it often involves a degree of research - you need to know who the gatekeepers are before you can trick them into opening the gate - it's little different than any other con game. From the standpoint of the hacker community, it's also often considered a 'lesser' form of hacking. Hacking is, in some ways, a competitive intellectual activity. It's not just enough to intrude into a privileged system but you have to do it in a clever or skilled way. Hacking a shipping database to have the next delivery to your local supermarket directed to your doorstep is cool. Throwing a brick through their window at night and carrying off that delivery is not.",
"Social engineering is altering human behavior through indirect means...usually behaviors the humans are resistant to change on their own. Imposing a high tax on cigarettes can be seen as social engineering to stop people from smoking. It is often seen as negative because the government is deciding what is good or bad and imposing that decision on its citizens. Alternately, social engineering is used to describe infiltrating a computer system using trickery rather than technical vulnerabilities. Pretending to be from the IRS and demanding someone's bank account information is an example of this kind of social engineering.",
"It's a manipulative technique used to get informatiom from people, and the negative context comes from scammers using it to get things such as passwords",
"When you use \"social skills\" (convincing, lying, etc) to make people do something. For example when you send and email to someone telling them that you are the administrator of the system and that you need for them to send you their passwords. Haha",
"I'll try my hand because I don't feel like you have received the broad answer you are looking for. Social engineering is simply applying the social science of human behavior to achieve a desired outcome. Much like a structural engineer applies materials science to achieve a certain outcome. The engineering part is the application of the science part. So, if sociology is considered a science, then social engineering is the application. Is it manipulative? Sure, but technically so is every other form of engineering. They just don't involve people. So there is absolutely an ethical component to social engineering. It has a negative context because the most visible examples involve breaking into stuff by tricking people. We all know that tricking someone into giving us a password is unethical, so even when done for good reason, no one really likes it. It could be positive though. What if I used my knowledge of human behavior to manipulate people into following Dr.'s recommendations during a pandemic? TL;DR: Social engineering is the practical application of social sciences.",
"Essentially manipulating others to do something they may not want to do knowing all the information. Its most commonly used in the context of hacking because actual hacking of finding technical exploits is hard these days and its often easier to fool a human than a computer. For instance I can send you a message pretending to be reddit admin asking you to disclose your username and password due to an issue with the reddit database."
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foi13j | How were ancient huge theatres like Ephesos able to have the spectators hear everything without sound systems? | Engineering | explainlikeimfive | {
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"Acoustics. They were designed to magnify the sound coming from the stage. So that it would be heard. Also,speaking loudly assisted this.",
"I was at one of these amphitheaters in Greece and you could try it out. There was a stone circle down on the stage and I could stand there and my girlfriend stood at the very top could hear me perfectly even just talking normally nevermind loudly. The aucoustics were amazing."
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foqdl7 | How does changing the shower head increase water pressure? Shouldn't the water be coming out at the same pressure throughout my house in spite of what shower head I have? | Engineering | explainlikeimfive | {
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"You have a constant volume and pressure coming from your well or municipality. Changing your showerhead changes the size of the exit hole. Doing that while still pushing the same volume and pressure will increase that pressure as the water tries to escape. Think of it like exhaling. When you exhale out of a wide open mouth air really doesnt come out that \"hard\" now purse your lips and exhale the same and you'll notice a dramatic increase in air moving out of your mouth.",
"The shower head changes the nozzle size that the water comes out. Pressure is force over an area . The force of the water doesn't change, but the area that it occupies does. Smaller nozzle means smaller area, smaller area means pressure increases."
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fpdmz3 | How do diesel engines work? Why would they be preferred? | Engineering | explainlikeimfive | {
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"Diesel fuel burns differently than gasoline. It's a thicker, less volatile fuel that burns more slowly than gasoline (think of the difference between setting a cup of gasoline on fire, and the ease of doing so, compared with doing the same thing with a cup of oil). So, when the gasoline in a cylinder burns, it does so very quickly. It only provides propulsive energy when it burns, so it only provides that oomph for a very short time, so you need to have more repetitions of this to get things moving, hence the higher comparative rev rates of gasoline engines. Diesel burns more slowly, so it ignites and it keeps pushing for longer. So, you don't need as many revolutions of the engine to get the power out of it. This longer push in the cylinders also results in the engine creating more torque. Diesel is also ignited differently. It isn't ignited with a spark like gasoline is. Rather, it is compressed to a very small volume, until that compression creates enough heat to cause ignition. This high pressure means that diesel engines have to built very strong, to withstand that pressure. The end result is that you have a very toughly built engine that revs low and creates a whole lot of pull out of those low revs. So... diesel is preferred in those situations that benefit from those characteristics. And that means hauling, where you have a lot of weight that you need to get moving and keep it moving. You don't need the high-revving horsepower of a gas engine for that. You need that slow-burn torque of a diesel for that. Yank all that weight off the line and just get a head of steam going and keep going. That's hauling, and that's diesel.",
"ELY5 : They are extremely strong, reliable and fuel efficient. They are also eco-friendly due to Diesel Exhaust Fluid being injected in the exhaust to burn off any pollutant (NOX). More in depth : Diesel engines do not need a spark to ignite. Only heat caused by compression. Newer technologies allow for extremely low consumption whilst maintaining very high performance, mainly low end torque. A diesel engine is so strong, they can potentially run out of control and you need a steel plate on the air intake to stop it. Otherwise it would keep running EVEN if you run out of diesel fuel. It would simply run on anything that could ignite even a little bit. That is the reason they are used in freight, towing, heavy machinery and more. You might be interested in reading the Cummins history which is pretty amazing.",
"Gasoline engines were built around the idea that you mix your fuel and your air, put them in a cylinder, squeeze it, then ignite it with a spark plug. Since your fuel and air both get compressed you're limited on your compression ratio(otherwise you blow your fuel too soon) which limits your overall efficiency Diesel engines take in air, squeeze it a lot and then squirt in the fuel which combusts which lets them run at much higher compression ratios (up to 23:1 vs 12:1 for gas). This results in much hotter combustion(which can also product NOx), and the efficiency of an engine is all about peak temperature vs exhaust temperature so running hotter results in better efficiency. The downside is that the engine is experiencing a lot more pressure and forces which requires a more robust design(aka heavier) which makes diesels not great for small zippy things. The big heavy pistons and crank shaft also can't spin as fast so while diesels give you high torque, they can't get up to 5000-8000 RPM to give a large amount of power from that torque. Overall, if you don't have a weight or volume consideration a diesel is the way to go as its more efficient, and can be built to last a longer time since weight isn't a concern. This is why you primarily see diesels used in stuff like stationary generators, trains, and large ships but don't see them used in portable generators, go-karts, and speedboats which are all weight/volume sensitive."
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fphutm | how do engineers determine the weight limits for floors in buildings? | I assume residential structures must have practical weight limits, especially above the first floor. How are these determined? Are older homes stronger (since they likely use heftier materials)? | Engineering | explainlikeimfive | {
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"Building codes specify the floor load minimums for buildings built within the area of jurisdiction. The codes have evolved over time, but most of the changes have been to address earthquake risks, or foundations on expansive soils. If you have a special requirement, like a giant aquarium in some museum, the you have to incorporate that special requirement in the design parameters.",
"There are live loads and dead loads. Dead loads are the actual weight of the permanent structure. Live loads are anything the structure must be able to endure. For example snow is considered a live load on a roof, and varies by location obviously, so there is one way live loads are determined. I believe living space is 40psf in residential homes. I found this... The anticipated loads are influenced by a building’s intended use (occupancy and function), configuration (size and shape), and location (climate and site conditions). From here URL_0",
"Let me add from my experience and 25 years as a Lumber Inspector. A well maintained older house is stronger than a modern one. Reasons: the wood used in a pre 1900 house is likely to be from a 100's yr old tree. The grain in that wood is close, so close, you need a magnifier to see the rings. That make the wood dense with high tensile strength. Modern wood; a tree is cut down after 25 years of growth. Its not the same wood as, say, 1820. Some of the wood used in very old houses is both extinct and a hardwood chestnut & elm for an example. My 1812 house uses true 07inx07inch red pine support posts{they extend into the rooms\\] 04 to a side of a 30 ft long house. That holds up the entire, added later, 02nd floor to the house.",
"Wood is really well studied. We know how much weight you can safely put on a 2x6 or a 2x8 over 8 feet, 10 feet, 12 feet, 14 feet, 16 feet, etc. Generally floors are designed to meet some codified weight like 30 lbs/sqft so to build the house you'd whip open your reference sheet like [this one]( URL_0 ) which tells you that if you're doing 12 foot spans then you'll need to use 2x6s that are 12 inches apart, but if you can use 2x8s then you can put them 24 inches apart. So how do they get to that number in the first place? Well you take a whole bunch of boards of various lengths, lay them on their short edge, then apply a force in the middle of the board until it breaks. Record that force, divide by 4, then you have the weight that that style of board can support across its length. Why divide by 4? Factor of safety! If all of your spec'd numbers are only 25% of what you believe the max is then if your material varies by 10% and someone overloads the system by 30% then you're still okay! When a floor is rated for 30 lbs/sqft it doesn't mean that if you put a 60 pound weight down on 1 square foot that its going to plummet through the floor, it really means that the entire floor could support 30 lbs/sqft so your 10x10 room can support 3000 pounds of weight as long as its reasonably distributed throughout the room, and thanks to the factor of safety is actually wayyyyy higher than just 30 lbs/sqft but 30 is where you can be confident that it will definitely hold under all conditions."
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fpl9ys | why does there need to be a separate wash process for cleaning a dishwasher? Why doesn’t it clean itself during a normal cycle? | Engineering | explainlikeimfive | {
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"Because people are stupid and toss the most disgustingly unrinsed crap in their dishwashers. As such, they need a special function to get properly clean. In most units they -super- heat the water to near boiling, and this can deal with the disgusting that builds up in them. But I've had my dishwasher for 4 years and I've never used the cleaning cycle. Its spotless inside. Because I, like many but not all sane humans, rinse or even quickly prescrub really nasty dishes.",
"The soaps used to clean dishes can build up after many wash cycles. The dishwasher is then cleaned with a soap-removing solution. You can't wash dishes all the time with that, because it doesn't take off greasy stuff like food very well, and it costs more.",
"It really depends how heavily you load your dishwasher. A dishwasher loaded with relatively clean plates may well go its whole life without a cleaning cycle and suffer no ill effects. A dishwasher used to clean heavily soiled plates regularly may need cleaning every month. With modern dishwashers, they use very little water and run at cooler temperatures. This means the cleaning water gets very dirty and deposits can start to form over time, particularly in all sorts of hidden locations like pipes, pumps and spray arms. An empty/light load ran on a normal cycle will clean the dishwasher, but some hard to shift deposits may be left. The special wash cycle is hotter and more intensive to give your machine a really good clean. The special cycle may not rinse and dry properly so is not appropriate for washing dishes."
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fpt4te | How do companies have blueprints to create ventilators? | Engineering | explainlikeimfive | {
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"The FDA has approved designs of various types. Those components can be assembled in whatever form the copyright allows. If Zoll says you can use their design then you can make and build anything they own. A lot of trademark leniency is going into this and many of the ventilators will probably be disassembled, repurposed, or turned into trainers because they're not main-line production pieces. Plus the machine is just an air pump and filters, basically. It moves air in a specific quantity, rate, etc. Pretty simple in itself. Speaking out of my ass, here. I'm a paramedic and play the vent game all the time but that doesn't make me an expert on the legal semantics of building the machines. Lol",
"Company generally dont share the blueprint they design a new one from scratch. They believe it it work but their are no garantee (unless they go to the FDA or some alike administration that say this design is safe you can sell it. This is the problem with most 3D printed ventilateur but its always better to have a ventilator that may work than no ventilator at all. (Except if a patient die because it stop working. It then becom the problem of the company even tho the patient would have died witouth one. Its not fair but its like that...) They are some attempt at making a certified design by the MIT. Their using a hand ventilator that is cheap and aldready certified and strap a mechanism to pump it automatically."
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fpuouj | How does mic and speaker work without feedback from each other? | ^(\[Too many conference calls during quarantine and\]) I don't know why the sound from my laptop speaker doesn't feed into the mic and cause a loop. Is it an intelligent cutoff system? I have noticed that during a conference call, if i use the mic from my laptop and sound is coming from an external speaker there's a feedback loop. | Engineering | explainlikeimfive | {
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"Most systems have an intelligent notice system that \"knows\" what sounds it played and will remove those from what it sends to the other parties. If you remove one of the components like the speakers from the \"known\" sets then the calculation of the removal doesn't work."
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fpvgyy | How are passenger jet engines so quiet when you are inside the plane? | How is it that when we are on the ground, a passenger jet can still be heard when its thousands of feet above the ground as opposed to when we are inside and just hear a gentle "whirr". | Engineering | explainlikeimfive | {
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"In addition to edscape’s answer about the position of the engines, most commercial airliners are heavily sound-insulated. Aircraft manufacturers use materials in the walls and bulkheads of commercial aircraft that can deaden a lot of noise from the outside. If you ever fly in a military aircraft, you’ll notice a distinct difference - the military wants to save weight, doesn’t care so much about passenger comfort, and isn’t willing to pay for a lot of fancy interior material that will wind up getting broken anyhow. Flying inside a military jet, you hear a LOT more engine noise, to the point where many people riding on a KC-135 will wear ear plugs for the duration of the engines running.",
"The sound is generated in the engines and therefore is heard behind the aircraft. Remember you are travelling at huge speed. The drone you hear inside the cabin is the mechanics of the engine working. Rear engined aircraft are even more quiet.",
"Because the plane is largely outrunning the sound. While cruising, commercial airlines travel at a significant fraction of the speed of sound, sometimes as much as 90%. That gives the sound waves more time to spread out and a smaller portion of their energy reaches the plane. In addition, passenger airplanes are designed to insulate sound and prevent it from reaching the cabin. Cargo and military aircraft are much louder."
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fpyczq | How do prosthetic hands work and actually move, when the arm it’s on has no connected tissue or ligaments or muscles to move the fingers? | Engineering | explainlikeimfive | {
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"Connective tissues are necessary to connect the power source (muscles) in your forearm to the fingers they operate. Prosthetic hands use tiny motors in the hand for its power and don't require connective tissue. They do have sensors to muscles or nerves in the arm to trigger these motors.",
"Some are powered by the user's body. For example, a prosthetic hand can have a cable leading up to a harness around the other shoulder. So the user basically \"shrugs\" to close the hand. Other are electrically powered. They have motors or other actuators inside the provide the motive force. These use sensors on the \"stump\" called myoelectric sensors. When the user tells their muscles to move, their nerves still try to send the signal. The sensors pick that signal up and direct the prosthetic to do whatever the user is thinking about.",
"There are prosthetics that are connected, the muscle moves, the muscle contraction transfers through wires and the hand closes. When the muscle isn't there anymore instead the prosthetic detects the electrical current that was suppose to contract the muscle and activates the motor that closes the hand. There are new ones that now detect the brain pattern of the patient wanting to contract the muscle and activate the muscle this way. You think about closing the hand, this fires neurons in a specific pattern, the prosthetic detects that and activates the motor. There's a startup developing brain activated race cars like that, you think \"drive\" and it goes forward, after some training."
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fpz6dp | Why do broken automobile signal light bulbs stay lit but not blink when they're broken instead of just not coming on like a regular light bulb? | Engineering | explainlikeimfive | {
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"Many automobile bulbs have two filaments in them, a dim one (taillights) and a bright one (turn signal) and when one burns out, the other one will still function.",
"It makes it easier to diagnose if the issue is a broken bulb or a broken switch relay. Light is lit by default and doesn't switch means the switch is broken. If the bulb is off by default, you can't tell if the bulb blew out or if the switch is broken. You'll take the time and money to swap out the bulb only to realize it was fine and the switch was the problem!"
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fqi0p6 | Why is it so difficult to make a ventilator? | Engineering | explainlikeimfive | {
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"A basic ventilator isn't all that difficult to make. Jumping from making however many they used to make per day, to making 10's of thousands of them, and delivering them tomorrow is.",
"You could make one that just works in an afternoon. But because it has to keep a person alive in a hospital setting it has to meet certain criteria. You dont want to re-train medical staff to work with it. It needs to be easily sterilized. It has to keep functioning no matter what. It needs to be compatible with other equipment. etc etc. I'm sure there are a lot of \"custom builds\" in the wild right now not meeting all criteria. But something is better than nothing.",
"> **ELI5: Why is it so difficult to make a ventilator?** Making a ventilator isn't difficult. Making tens of thousands of ventilator's is. Imagine I asked you to make 80 thousand PB & J sandwiches by tomorrow and when you balked I asked, \"Why is it so difficult to make a PB & J sandwich?\"",
"There is a fuckton that goes into a modern vent. Yeah the old ones were piston driven with an on off switch and not much else. Modern ones however are turbine driven. They sense oxygen levels, carbon dioxide levels, how often and how much per breath is given and the pressures of both inhale and exhale - to list just the basics of it. Now to reliably detect these things, and then have settings to change them is some serious engineering. URL_0 Here's a link to a commonly used vent, the Ltv1200. Terrible ELI5 but I feel like just handing someone the instruction manual to an actual vent answers this question. I can use them, I sure as hell have no idea how to make them.",
"Without getting too technical, they must be...... 1. Reliable 2. Accurate 3. Good software /fast and smart 4. Easily cleaned/serviced 5. No interference with other devices 6. Nurse proof/durable Simple vents are available, but they mostly suck..... you do not want to try using them on a tough patient. And from what I'm reading, Covid19 is causing alot of ARDS, which is among the most difficult conditions to manage on a vent. Edit: please leave a comment if you downvote. I would like to have a discussion on why you feel my reply did not contribute to OP's question.",
"Because the pump has to be special, a person's lungs inside are delicate like wet kleenex and the air going in has to be just right so it doesn't tear the wet kleenex.",
"it has to be moulded to pretty exacting standards. ie the parts must fit exactly. thats part of the problem. you dont want gas to backflow or leak. source: im working with front-line nurses who have to deal with this sort of machinery...esp now.",
"Two weeks ago I was asking why companies can’t retool to make parts for these while others retool for the assembly. I was told it was jus to complicated, precise and delicate a machine. However long it talked to retool an assembly line, that timeline keeps moving if you don’t get started.",
"And while it's true the the fundamental machine is just pushing an air mix, they have many internal safety features and monitoring pieces - flow, PEEP (positive end-expiratory pressure), they have tube pressure monitoring, tube compensation, and release 'valves' so that if a patient coughs it doesn't blow up their lungs - all sorts of important stuff. Now, do you HAVE to have all those bits? Well, maybe not but maybe those things actually help us manage ventilated patients more successfully. So I would much prefer companies that make good ventilators make MORE good ventilators.",
"I work for a steel seller , die set maker, fab shop. Ford just had us make something for these efforts but it’s just one relatively small part (even though it is as big as a small car) and it’s part of a much bigger assembly line they need to tool for. Given we are a supplier/vendor we have our own issues with keeping our shop running through this. On top of keeping our workers happy and healthy enough to want to continue to show up. This stuff can’t happen overnight it can take weeks/months/years for projects of this scale. Most people see the end product and not really think about how each part that makes up the whole needs to be sourced, made, and/or assembled at a pretty large scale",
"Respiratory therapist here. Ventilators themselves are actually quite simple to make, especially pneumatic types, but they are very basic. Patients with COVID-19 require sophisticated ventilators that can calculate ventilating pressures deliver high amounts of positive end expiratiry pressure (PEEP). Right now one of the biggest problems we face, isn’t a lack of ventilators, but a lack of equipment that we need to run ventilators. We are critically low on temperature probes, filters and circuits. Also you need staff to run a ventilator, also critically low. My medical center (along with Governor Andrew Cuomo) has asked five retired therapists to come back to work until this is over. So basically, you can give us 1,000 extra ventilators but they would be of no use to us with out current lack of equipment and supplies.",
"Dräger is one of the brands that make ventilators (among another trillion medical machines). They have a factory or several that has the necessary machinery to produce, say 100 ventilators any given day. They're known in the medical field, their machines work well. They're probably done in a cleanroom. Now say Musk gets his shit together and offers to make ventilators. He's producing electric cars and solar panels. There are probably clean rooms in Tesla factories, but they're tooled to make batteries. And the rest of the factory is tooled to make cars. A ventilator and a car have things in common (injected plastic, circuits, tubing, a screen) but otherwise, they're nothing alike. So Tesla would need either to mod their machinery (change the mold that makes the dashboard for thirty molds for the casing of the ventilator, reprogram the machines that do the circuitry/screen to make the circuitry/screen for the ventilator, use the cleanroom to assemble the ventilator instead of a battery, get something to sterilize all the interior pieces before assembly). So they need to pretty much change or modify all their machinery to be able to produce ventilators, and that needs time.",
"Engineer here. I’m working with a team of startups in NYC trying to tackle the ventilator and PPE shortage. Long story short, it’s not. The problem is that hospitals aren’t set up to buy ventilators off the street. Their purchasing system is set up to buy tens of thousands from large trusted corporations with FDA approval that meet specific quality standards. They aren’t able to track dozens of different kinds of hacked together gear. My cousin is a hospital administrator and our team has had to work directly with him to go through hoops to get gear in place at the most desperate field hospitals. It’s mostly a supply chain problem. That said, ventilators aren’t simply pumps. People with COVID-19 are expected to live with them for weeks to months. A ventilator has to supply air at a *Tidal volume* that the doctor can control. Regardless of pressure, the same amount of air has to come in per breath—this must be adjusted for the patient’s size. A ventilator has to breathe with the patient breathes and if a sleeping patient tries to breathe manually, the ventilator must sense that and change its pattern. A ventilator *should* have an alarm that indicates faults. It must be sterile. It must have no dead legs (areas where exhaled air gets trapped and can grow germs). There are only certain materials that can be used for months without failure. It can’t generate electromagnetic fields that interfere with pacemakers. Overall, the best companies suited to making ventilators are large companies that have already done it. We’re mostly sticking to PPEs like face masks and gowns."
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fqsof9 | why do tanks use "continuous tracks" instead of wheels? | Engineering | explainlikeimfive | {
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"It increases the surface area in contact with the ground. Essentially, a row of people (the wheels, in this scenario) couldn't stand on their feet on water, but a row of people on surfboards could. By increasing the surface area, the weight that can be supported on terrain like loose sand, which would be a pain to get bogged down in (especially in combat), increases",
"Like someone else said, it increase the surface area on which the weight of the vehicle is distribution. The ground have a limit on how much weight per surface it can carry before you start to sink, so increasing the surface area is important for a vehicle that weight 20-60 tonnes. The second advantage is the traction. Since you have more surface area touching the ground, it's more surface with friction with the ground, which create more traction, allowing the tank to advance in difficult terrain instead of getting stuck. It's stronger. In a normal wheel, you can't really have it made all of metal, because it will slice through the ground and give you little traction, it's one reason why we use tire. But tire are made of material that are less strong than metal and will get damage more quickly over time. In a tank, you can make the wheels and the track in metal and still have traction, while keeping stronger pieces that will last longer. That become more and more important as your vehicle become heavier."
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fr1vje | what's the difference between computer engineering and computer science? | Engineering | explainlikeimfive | {
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"If you can hit the thing giving you problems with a hammer it is computer engineering. Otherwise it is computer science. Edit: This does not apply if the problem is the user.",
"CE generally has a bigger component of hardware (electronics) plus a focus on the implementation (systems) view of the subject. Typical when the word engineering is used, students/graduates are usually expected to have a fair amount of hands on knowledge. CS is focused more on the research and academic end which has a great deal of abstraction and mathematics relevant to the field of computing.",
"Mostly paperwork and process. ComSci (undergrad) is where you learn how to code. ComSci (grad) is where you learn the cutting edge stuff and new ways to make computers get up and dance. Not literally though, that's robotics. I mean more like... make them think good. CompE, you still have to learn how to program, but you also have to learn how to prove that the thing isn't going to crash and kill hundreds of people. So, process documentation showing that you have a plan, that you know what you want to make (requirements), know how you're going to make it (design doc), know that it works (tests), and various other things like... we didn't miss anything (traceabilty matrix linking the requirements to the tests). A lot of it depends on the school. At mine, the engineering department was a fair shade better than the comSci. I went into embedded, so there's more bare-metal development without an OS, more vxWorks and Integrity as opposed to... windows. Embedded linux is coming along, btw. More driver development. More ICD, interface control documents handed to us form the EEs working the hardware."
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fr4lz2 | If short wheel based car handle so well, why are high end sports cars so long? | For example the mini Cooper. Handle incredibly well, lotus elise also short wheel based. Handles great, so why are cars such as lambo, ferrari, mclaren are so long in comparison? | Engineering | explainlikeimfive | {
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"because short wheelbase handles great at low speed. long wheelbase is more stable at high speeds. a mini is great bombing arount a track at 70 - 90 mph but at 180 it would be serious brown trouser time.",
"You have a few concepts correct and many concepts wrong at the moment. If you don't mind, I'll take a little bit of time to explain this all to you. A short wheelbase car handles incredibly well for one PRIMARY reason, and that is that it's a tiny car, and therefore very light. Carrying less mass into a corner means you can redirect nice and quick. Shorter wheelbase does mean snappier turning regardless of weight, but to a point is also means that the vehicle can be MUCH more likely to fishtail or come loose if pushed too hard. Lotus Elise, and Jeep Wrangler, and very famously the old Toyota MR2s have killed many a people because the wheelbase is so short and the weight balance so odd, once the back end starts to come around, it's just gone. A shorter pendulum happens a hell of a lot quicker than a longer one. High performance cars are longer because they need high speed stability, and this stability primarily comes from a longer and wider wheelbase, as they break the back end loose a lot slower and are a lot easier to control. And of course, the demands of aerodynamic styling and trying to make sure a 1000hp power plant fits in the vehicle somewhere add some length as well. Take a look at the length of high speed record holding vehicles at the salt flats, some of those vehicles are 40-70 feet long to provide stability at speeds above 400mph. Then take a look at autox type cars, where speed is less important and handling is more important. Power does come into play, as does awd versus front or rear wheel drive, but usually it's the smaller cars, the Micra, the Miata, the Mini, that carry the most speed through tight and tiny corners. There is a whole bunch more to this, do of you have any more questions reply and I'll continue to try and answer them. Source: Regional Director of a 4X4 club, amateur rally racer, AutoX participant, physics nerd, motorcycle track day participant.",
"Handling is more about stance, how wide the vehicle is. Also the center of gravity (how weight is distributed vertically) and suspension design and characteristics are also significant factors over. Comparing a Mini to a Ferrari is like comparing apples to saw dust."
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frpak1 | How does mirrored glass work? | Engineering | explainlikeimfive | {
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"Mirrored glass is just glass with a layer of reflective material deposited on it. The 2 most common ways this is done is to spray a solution of Silver Nitrate and Sodium Hydroxide on to the glass. (The Sodium reacts with the Nitrate to deposit an almost single molecule thick layer of silver on to the glass).. this means you have a VERY reflective substance bonded to the glass. .. you then paint over this layer to protect it. & #x200B; The more modern / cheaper method is to vapor deposit aluminium onto the glass. it's cheaper, requires no chemistry (you simply clean your glass then superheat some aluminum). the resulting surface is fractionally less reflective and fractionally less durable, but SIGNIFICANTLY cheaper. again, they spray lacquer or paint over it to stop it wearing off, but the effect is the same."
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frtfw1 | Why do drummers put towels and the like in their bass drums? | Engineering | explainlikeimfive | {
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"If the bass drum “rings” too much when it’s played, it can make the entire sound of the band sound unclean. Putting towels or pillows or whatever else in there gives the drum a more “dead” sound that doesn’t ring as much, which sounds a lot cleaner.",
"The towels and pillows will absorb some of the sound that resonates in the drum. It means you have to hit it harder to get the same sound volume but more importantly the resonance will die off much sooner. If you hit an undampened bass drum you can hear it ring for up to half a second later which is far into the next beat. If you dampen the drum it will become quiet much sooner so the tones sound much sharper.",
"There’s already a lot of good responses in here but I’ll add that when a drum head is struck (in this case the bass head is hit with the kick pedal), vibrations move out of the drum head, down the shell and reverberate with the resonant head on the other side. Dampening devices, towels, pillows, blankets and whatever else disrupt these vibrations and shorten the time period where you can hear sound.",
"Makes the sound more of a thud and less of a boom. Otherwise, it would ring out more like a tom."
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frz9w4 | How is anything really considered "level" | So, weird part is I work in a field where levelling is important, and I'm aware of how to make anything level, but I've always wondered how that works. Since the earth isn't flat, everything should have a slight curve. I mean, I suppose on such small scale, it would be effectively a straight line, yet somehow this concept still seems weird to me. | Engineering | explainlikeimfive | {
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"Level implies a perpendicularity between the object and the force of gravity. Or otherwise, the level line is 90 degrees (perpendicular) from the force of gravity.",
"if you truely had a flat board and a truely spherical ground, then level would mean the board is at tangent at the position touching the ground. or conversely, the line that's orthogonal to the board surface would intersect with the center of the sphere.",
"The Earth is curved in general, but it doesn't have to be locally. You can shave some of it off (or add a bit more) to create a flat area the same way you could to a ball of clay. This wouldn't be practical for a truly large area, but the curve of the Earth is gentle enough that it's pretty easy to do for the footprint of any building. In that context, you probably care more about leveling out various other local oddities (hills, ditches, etc) than fighting the curve of the Earth anyway."
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fs19mx | Why do smaller engines with less cylinder displacement (e.g 4 cylinder) can create more or similar power to bigger engines with more cylinders and larger displacement (e.g V8) | Engineering | explainlikeimfive | {
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"There’s a ton of optimization on modern cars to boost power & fuel efficiency while keeping the engine small. Turbo chargers are one. Full synthetic oil is another. CVT transmissions too. One downside though is the complexity has gone up a lot. So these new cars end up being super expensive to repair once they start to break down. CVT transmissions a nightmare repair.",
"Forced induction allows small engines to produce the power of a larger engine. The secret carmakers don't tell you: Fuel burn can often exceed that of a larger engine if you have a heavy foot. Good video here: [Engineering Explained: Why small turbo engines are not efficient]( URL_0 )",
"Are you comparing the engines developed in a similar year? You can take a 2020 turbo engine and compare it to a 1960 v12 natural engine and say the inline 4 makes 300 horses and and v12 only makes 280."
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fs6r1q | Why are electric vehicle engines (like in the Tesla) simpler than traditional petrol engines? | Engineering | explainlikeimfive | {
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"First, there's a lot of systems involved in turning gasoline into a controlled and smooth explosion. Then, all the force from the explosion (going in every direction) has to be aimed so it's all going in the same direction, so it can make the crankshaft spin. Even worse, this only works well when the crankshaft is spinning at a certain speed, so you need a transmission to multiply the crankshaft speed using gears so you can get wheel speed. In an electric engine, all you have to do is run electricity around in circles with a magnet in the middle, and the magnet will spin. Plus, the magnet doesn't care how fast it's spinning, so you don't need a transmission. So instead of having this big machine with a lot of chemicals and tons of moving parts, you have a battery and a coil of wire and a magnet, and basically nothing else.",
"Electric engines work well at different revolutions per minute (RPM), and they are quite simple to construct, with low number of moving parts (basically just one rotor). Gasoline (and oil) engines on the other hand, work well only in narrow rang of RPM, thus requiring extra component - gear shift. In addition the engine itself is quite complex, requiring from 4 to 12 cylinders in different arrangements (eg. V8 is 8 cylinders in V arrrangement, but there's also for example B (Boxer) arrangement). Which are connected through yet another element together. Each of the cylinders needs proper mix of fuel and air pumped into it at the right moment, then ignited at the right moment (via Spark Plug)."
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fs9csj | How does a rifled barrel of a weapon makes a weapon much more accurate? | Engineering | explainlikeimfive | {
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"Rifling spins a bullet, which means it doesn't wobble. It's the same thing that causes a spinning top to stay upright, that causes a spinning bullet to stay pointing forwards. By staying forwards and not tumbling, the trajectory of a bullet is much more consistent.",
"To add to the spin part, watch someone throw a football without spin. The ball will wobble in mid air unpredictably. It’s the same principle with a bullet, except the higher velocity results in loss of accuracy. Spin is achieved by fine grooves in the barrel, the longer the barrel the more time is has to spin up.",
"It imparts a spin on the bullet. This gives them a more predictable and flight path (predictable as in if you fire repeated rounds they should all hit more or less the same spot on the target if they're being shot out of a high quality barrel), resulting in higher precision. Accuracy is essentially the ability to hit what you're aiming at, so a predictable bullet flight path allows for sighting in of the gun. If you fired 10 rounds and got hits that were each 3-4\" apart from one another on a target 10' away this would be pretty hard to do. If all the shots hit within a 1\" group it's much easier.",
"The rifled grooves in the barrel are arranged so that they twist in one direction. When the bullet travels along the grooves, it starts to spin. A spinning bullet is less likely to tumble in different directions as it flies. This is exactly the same as a spinning top. When it stops spinning, it tumbles over.",
"Rifled weapons are not necessarily more accurate. It is more accurate for the simple cheap bullet but not compared to more complex alternatives. Most tanks today have smooth bored barrels and not accuracy problems. The one that still used rifled barrels is to be able to use [HESH]( URL_4 ) rounds or just to keep compatibility with the ammunition of older tank design with the same caliber. If I man not mistake it is the UK and India that still use rifled barrels on new tanks. The move to smoothbore is not because of increased currency but that long thin [sabot]( URL_3 ) and [HEAT rounds]( URL_0 ) work better. Both smooth bore and rifled tank guns have the same accuracy it is all about the ammunition. Mortar has smoothbore barrels too. This is primarily because the are muzzle-loaded and you can have thinner walls and more explosive. The fins on the back provide accuracy and you can in a simple way add propellant rings around the narrow tail to control the range. & #x200B; For a projectile, you like it to point in the same direction all the time so you can spin it that result in a gyroscopic effect so it is hard to turn or you can have fins at that end just like an arrow. In-tank ammunition and mortar shells the projectile has fins on the end just like an arrow and that solves the point in the correct direction problem. Another advantage of spinning is if the projectile is not perfectly symmetrical there will be uneven air resistance. The projectile will move in the direction of less air resistance. So a nonspinning projectile will diverge in one direction. The direction will if you spin change so on average there is no net moment and it will follow a corkscrew path to the target. For small-caliber ammunition, you make huge amount where each cost very little to begin with. So any extra work to make it symmetrical or have fins increase cost a lot. So the simple and cheaper option is to spin the bullet. For a large caliber shell, the cost of manufacturing is already many times higher so making it symmetrical and adding fins do not add a significant amount to the cost. So when long sabots and HEAT round works better you make high accuracy smooth bore weapons. I suspect that you also higher accuracy in the diameter of the projectile so it does not bounce side to side in the barrel. & #x200B; Rifling was developed back when a bullet was just a molded piece of soft lead. Most weapons were muscle loaded and are able to push down the bullet especially with black powder fouling it had a bit smaller diameter than the barrel. Rifles were added on standard military [Minié ball]( URL_1 ) that expanded when fired so it was fast to load as a smoothbore gun. Specialist riflemen existed primarily for harassment because of their longer range, but the long reload time it was not standard weapons. Some hunters also use them befoe because loading speed is not relevant as it is in combat. There has been experiment with [flechette guns]( URL_2 ). So smooth bore small caliber guns. The advantage is higher muzzle velocity, less drag, and longer range. None have been successful, It is had to make it work at that caliber especially in a cost-efficient way. The did not provide enough advantage to start using them. Making them as accurate is not good enough if they cost a lot more the have to be better. So you can today make smooth bore as accurate as rifled barrels but the higher cost of ammunition makes it a worse option except for tanks and mortars where you can add ammunition that works better if it does not need to spin."
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fsiy8c | Why do drill bits that are cutting into metal in commercial or industrial settings remain stationary, while the piece of metal spins? | Engineering | explainlikeimfive | {
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"What you are thinking of is specifically a lathe, which is used for circular cuts and working of a material (there are different types of lathes for wood and metal). Since lathes spin the metal so that it can be cut and shaped on the outside, there's no need to have the drill bit spin as well. Spinning the bit at the same time means more moving parts to fail, more stress on the motor for having to drive those parts, and more stress on the drill bit and worked metal, which could damage or break either. In terms of physics, if the metal or the bit is spinning, as long as one of them does. it's just easier and smarter to keep spinning the worked metal."
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fsp89b | why aren't transistors an And operator? | If both the wire and the control wire are on, it's on, otherwise it's off. Why isn't this the exact same thing as an And operator | Engineering | explainlikeimfive | {
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"That is how an NPN transistor operates, but there are many other kinds of transistors with other functions."
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fswwg8 | Why does a sandwich taste so much better when made by someone else? | Engineering | explainlikeimfive | {
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"I hear this from everyone else, but I prefer my own sandwiches. Not sure what's wrong with the rest of you.",
"When you make a sandwich, or any food really, you get a big whiff of what it smells like. As time goes on your nose just gets used to the smell and perhaps even blocks it out, like your eyes adjusting after taking off sunglasses, your ears blocking out certain sounds when youre trying to sleep, or your wrist ignoring the feeling of wearing a watch. Sadly we can't really specify what we want blocked out vs not, so that lovely smell of a sandwich gets kinda lost on us by the time we eat it. Also our mind has a bad habit of anticipating taste for us, meaning that the sandwich is old news by the time we get it there. [Citation needed]",
"I believe it’s to do with expectation. If you make the sandwich, you know in advance what it’s likely to taste like but if someone else makes it, it’s more of a surprise. Same way you can’t tickle yourself, you know what’s happening so the surprise element of it is moot",
"I think other people are missing the possibility that you are just bad at sandwiches. Do other people enjoy your sandwiches less than normal?",
"> engineering tag also it's mostly because of expectation, as the other commentor said, as well as smell. Because you've already been smelling the sandwich, the taste isn't that surprising. But, when you eat one made by someone else, you haven't been smelling it for as long.",
"It's not the sandwich, it's that someone made it for you. My morning coffee is one of the best parts of my day, and I thoroughly enjoy making it. Grinding the beans, listening to the drip. But when someone else makes it **just the way you like** and then delivers it... Sublime."
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ft0016 | How can two (or more) light switches control the same set of lights? | Why is one switch able to disrupt the circuit, and another can override that disruption? | Engineering | explainlikeimfive | {
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"In a 3-way circuit, there are two wires that run between the switches. Each switch connects to one wire in the up position and the down wire in the other position. [This nice web page]( URL_0 ) shows 3-way and even 4-way switching diagrams.",
"The switches create a [XOR]( URL_0 ) circuit effectively, creating a Truth table like |Switch A|Switch B|Light |--|--|--| |Down|Down|Off| |Down|Up|On| |Up|Down|On| |Up|Up|Off| Following the wires, we can see that the power comes in from the power box and into Switch A. Flipping the relay allows it to take path A (down) or Path B (up). Both lead to the next Switch that provides the same Path A or Path B relay. While both switches are in the same position, the power wire is unable to complete the circuit. Think of the 3-way like 2 railroad tracks, and your goal is to change from a dead end to the next town over path. If you change tracks twice or don't change at all, you won't get anywhere, but you can change ether track to get what you want. If you are interested in a more technical way it works, check out [Electrical 101 - 3 Way Switches]( URL_1 ) Note: Same as MRSaunders"
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ft04ix | How do live bands prevent the singer's mic from picking up the instrument sounds? | It makes no sense to me that the vocalist is in front of multiple speaker cabs, and yet the mic only picks up their voice | Engineering | explainlikeimfive | {
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"Microphones used with live bands are very focused. As in the pick up pattern only picks up things very close and directly straight into the mic. You will notice when a singer is singing from the side or a little under or over the microphone it will barely be picked up. So it’s all about the pick up pattern of the microphone.",
"Today the use of in ear monitors also makes it possible to have a much lower stage volume as the band can hear everything perfectly in their headphones. This makes the sound engineers job much easier until alcohol becomes a factor then guitar players seem to turn up their amps and screw the sound up lol.",
"Live sound guy here! They do and they don't. They *will* pick up things around them because that's just what microphones do, but in general the thing the mic is focused on will be the thing that overpowers the rest of what comes through. Not to mention the microphones themselves aren't usually \"turned up\" all that loudly, making them more sensitive to louder sounds - someone singing into it - than softer ones - like a guitar across the stage. It's your main mix that's far louder, and what you hear in the audience. Also, having mics pick up more than just what the focus on is important for some instruments. Drum kits for example can be mic'd with a very complex array of microphones... Or just two overhead mics capturing the whole thing. You can also tune microphones to specific things and volumes as well, telling the mic to ignore everything below a certain volume level or everything making a certain range of noise, and this further helps isolate just the singer's voice!",
"The mic will pick up little of the stage sound, but the proximity of the singers voice makes it a much hotter signal and overpowers the rest of the noise enough that it becomes unnoticeable to the audience."
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ft3s1s | Something being level vs being flat, scientifically speaking | Engineering | explainlikeimfive | {
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"A teeter totter is always flat, but it's only level when you put a ball on it and it won't roll off.",
"\"Level\" generally means that a surface is perpendicular to the dominant local gravitational field. \"Flat\" means that the points on the surface of an object are all on the same two-dimensional plane.",
"flat is about shape. the plains are flat, the mountains are not. level is about alignment. if you're screwing a shelf to the wall and it's not level, things you place on the shelf will roll off"
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ftbcxc | How distilleries repurpose to make hand sanitizer? | Engineering | explainlikeimfive | {
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"Hand sanitizer is 70% alcohol (140 proof). The other 30% is water and thickening agents. Distilleries have giant machines for making alcohol. They have water, and with some thickening agents, and bottles, that's all they need.",
"Ethanol (ethyl alcohol) is a primary component of many hand sanitizers because of its effectiveness. Basically any entity that can normally produce a 40% ethanol-in-water solution (aka vodka) can probably retool their production to achieve a 60-70-ish% ethanol concentration. From there just add a few other commercially sourced ingredients to thicken it a little and add a scent and figure out some way to seal it in plastic bottles. (Which may not be impossibly different from filling glass bottles)."
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ftkkdj | why is every air tank cylindrical in shape? | Engineering | explainlikeimfive | {
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"Because the round shape distributes the pressure more evenly, otherwise the sides of a square tank would bow out and the joints would be weak points",
"Round shapes can handle weight and stresses better than square shapes. Lots of things designed to take pressure are round rather than square, like egg shells. Compressed air tanks are under some insane pressures inside the tank, usually in excess of 2000 psi (pounds per square inch) when full. Think about that - there's about a ton of force inside the tank on every square inch of the inside surface pressing outwards. That tank has to be tough enough to withstand that, the risks of being handled improperly (ie. dropped) and still be safe/not explode. They're designed like that out of necessity. (Normal air pressure on earth is 14-15 psi in most places.)",
"The same thing as with soda cans. It combines weak points (angles) absence of sphere and easy transportation of cube. So, cylinder is the choise.",
"Same reason why almost all bubbles naturally become spherical; it creates the minimum surface area to volume ratio",
"Not all pressurised air tanks are cylindrical. I have several here at work that are square. A cylinder is most common though because that shape distributes the force the most evenly allowing cylindrical containers to be made from thinner and lighter material than containers of other shapes.",
"Imagine a cube tank, and fill it with a little bit too much pressure: it start to bulge. The corners will actually get closer to the center and the faces center will get away. The cube try to take the shape of a sphere. You can see a sphere as maximal bulging. That's why bubbles are spheres. So, spherical tank are the best at holding pressure, why we don't have that? We do, but they are a nightmare to produce. While cylindrical thanks are trivial to manufacture and are quite good, typically one will have the top and the bottom spherical as those are the \"bulge\" shape they would take."
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ftp5g4 | The difference between an nuclear bomb and a hydrogen bomb. | Engineering | explainlikeimfive | {
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"A hydrogen bomb is a kind of nuclear bomb. Specifically one that uses nuclear fusion to boost the yield (explosive power) of the bomb. The first nuclear weapons used purely nuclear fission (splitting an atom) to produce energy. That gives you a huge bang, but it's pretty inefficient since most of your fuel just gets blasted apart instead of fissioning to make the big boom. Second-generation bombs introduced a second stage with a different kind of fuel that allowed for fusion (smooshing two atoms into one bigger atom). The fusion stage takes the energy from the fission, and uses it to fuse lightweight atoms into heavier ones, which releases crazy amounts of energy. This makes your bomb much more efficient, which means you get a bigger boom from a smaller bomb.",
"A nuclear bomb is any weapon that uses nuclear fission to generate its energy. A hydrogen bomb is a special version; it uses a nuclear bomb (the \"primary\") to compress a special device (the \"secondary\") which contains special isotopes of hydrogen which undergo fusion, greatly improving the yield of the overall weapon.",
"There are two ways to generate nuclear energy: fusion and fission. Fission is one large atom breaking into 2 smaller atoms and some neutrons, and Fusion is 2 small atoms forming one larger atom. Both create a lot of excess energy, although fusion creates much more energy than fission (for the most part). A nuclear bomb uses a nuclear reaction to create energy, then uses that energy to make new nuclear reactions, so on and so forth until the entire bomb’s fuel is consumed and the energy creates an explosion. Because fusion bombs (hydrogen bombs are these) are much more efficient than fission bombs (like the ones dropped on Japan), they create much larger explosions.",
"There are atomic (fission) bombs, that release energy through the splitting of heavy atoms. The bombs dropped on Japan were these, and had explosive outputs of around 15,000 tons of TNT. Their fuel is typically either uranium-235 or plutonium-239. There are also hydrogen (thermonuclear/fusion) bombs, that release energy through both the splitting of heavy atoms _and_ the fusion of light atoms. They work by using the energy released from fission to ignite the fusion reactions, which then usually produce more fission reactions. The first hydrogen bombs, developed in the 1950s, had explosive outputs around 15,000,000 tons of TNT. But you can build them to have outputs more like 150,000 tons of TNT, which is what most modern nuclear weapons are like — small H-bombs, which are very efficient in terms of weight and size, and so you can put many of them on top of a single missile. The fusion fuel can be types of hydrogen (deuterium and tritium), or a type of lithium. Both of these types of weapons go under the mutual heading of \"nuclear weapons.\" There are of course many little complexities (you can have fission bombs that use a little bit of fusion but aren't really hydrogen bombs, because they aren't using the energy from the fusion so much as just using the fusion to generate some neutrons; this is called \"boosting\") not covered by these two categories.",
"Imagine you've got a red balloon that pops so well, it can't stay together long enough for it to pop properly. Now imagine you have a green balloon of a different material that's *really* hard to pop, but when it does pop, it pops a whole lot better than the red balloon. What you do is use the red balloon to pop the green balloon. If you are completely crazy, [you can use a red balloon to pop a green balloon, which in turn pops an even bigger red balloon.]( URL_0 ). EDIT: Red balloon = Nuclear (fission) bomb, Green balloon = Hydrogen (fusion) bomb.",
"Fissile isotopes are radioactive variants of some element that decays when it absorbs neutrons, and releases neutrons when they decay. Fissile isotopes can sustain a chain reaction, where one decay can cause an adjacent atom to decay. If you google it, Wikipedia has a formula used to predict which isotopes are fissile, there's a lot more than you think. The equation will produce nonsense, in that some isotopes don't or can't exist (but that's math for you), and the equation doesn't tell you other properties of the fissile material, which are important for use as a weapon. So, then, to cause a nuclear explosion, you want your fissile fuel to decay as fast and as completely as possible. Chain linear reactions are super slow. One atom decays, causing another atom to decay, which causes another atom to decay... And how do you start this decay process? In order to decay your fuel *fast*, and if you could induce decay in the first place, then you'd be better off just inducing decay in the whole mass of fuel all at once. But we do depend on chain reactions, and that tells you we can't induce decay, let alone in an entire mass. So this is what that equation I mentioned above doesn't tell you: of the fissile isotopes, *only a few* release two or more neutrons. That means the reactions aren't linear, they're exponential. The number of isotopes decaying can double over time, and that's something that just cannot happen with a linear chain. The fuels of choice are Uranium 235 and Plutonium 241. Plutonium 239 also works, just not as well. We don't have a process to reliably separate the two isotopes, so plutonium bombs have a mix. U-233 also works, but not as well, though we can separate it out, so our enriched weapons have low counts of that. Uranium 238 IS NOT fissile, in that it can absorb neutrons without decay. Alright, now we need our fissile mass to undergo chain reactions very fast. The best way we know how to do that is to increase its density. You can do that as we did with Little Boy - this bomb, dropped on Hiroshima, was basically a cannon. The bomb casing was a glorified cannon barrel. The projectile was a 60 pound slug of u-235, and at the end of the barrel was a plug, in the shape of a cone pointing into the cannon, made of another 60 pounds of u-238. The bomb fired the slug into the plug. They slammed into one another, compressing, increasing their density. Radioactive decay is essentially random. And so we rely on that random decay to start the exponential chain reaction. We're talking a few tens or hundreds of random decays causing a city-erasing explosion in a fraction of a second. When the fuel is so dense, those random neutrons that went flying away have a greater chance of hitting an adjacent isotope. That's all it takes. From there, it's just a matter of holding in the explosion as long as you can, because fission releases a lot of heat, and so while you're trying to compress the mass, the heat wants to blow it apart. The longer you can hold it together, the more isotopes you'll convert, the more efficient the bomb, the bigger the explosion. Little boy was only a few percentage points efficient. 120 pounds of u-235 for a few kiloton explosion, modern weapons use about 20 pounds of u-235 for up to megaton explosions. Then you have the implosion style weapons. All modern weapons are implosion style. Plutonium works well for this. There was an initial effort to refine the gun style weapon, because it's damn simple, but there were inherent limitations. Little Boy had a bigger brother, Big Boy, a gun style weapon for plutonium. The project was cancelled early on because the bombs were 50 feet long or so. Modern day implosion style weapons use a hollow pit in the shape of an egg or oval, but all descriptions of the original Teller-Ulam device presume a sphere. It doesn't matter so long as the pit compresses into a sphere in the end. The reason it's a hollow pit is because the geometry, called the configuration is important. A solid lump of plutonium will go critical and just melt from the heat of sustaining its own uncontrolled chain reactions. It'll melt down just like a nuclear reactor gone awry. You have to keep the stuff away from itself to keep it stable. So you surround it in high explosives. But the explosives are layered. Because you can't ignite every point on the surface uniformly, you'll generate shockwaves. So you have fast burning explosives detonate domes of slow burning explosives, until the domes all meet up - at which point you have a uniform shockwave, which then goes to fast burning explosives again. The shockwaves hits a tamper, which is a piece of metal between the explosives and the pit. All this thing does is even out the shockwave. The tamper is air-gapped, so it has space to pick up speed and inertia - the pit is hanging inside by wires. The tamper is made of lead, but sometimes the tamper is u-235 to increase yield, but it can make detonation unreliable. They also inject hydrogen atoms into the center of the pit, they use flash tubes - a type of particle accelerator, to inject X-rays, and surround the whole thing with polyethylene foam impregnated with neutron reflecting materials. The foam itself vaporizes into plasma, lending electromagnetic properties to further reflect and compress the pit. The hydrogen and flash tubes are how you can dial-a-yield, by varying their timing, thus varying the weapons efficiency. All that is atomic bombs and \"boosted\" atomic bombs. Let's talk about hydrogen bombs now, or thermonuclear bombs. To go thermonuclear, you need a second stage. Just as we compressed the first stage with conventional explosives, we'll compress the second stage with an atomic bomb. The second stage consists of a u-238 bucket filled with lithium-6 and -7. Notice the bucket is not fissile, but it is still radioactive, heavy, and energetic. Remember when I said we can't just magically induce atoms to split? Yeah, that's not true. This is how we do it. So by compressing the second stage, the lithium undergoes fusion. In the process, the fusion products are more stable atoms than the lithium, and they cast off excess alpha particles - hydrogen! This fusion process is extremely energetic - these hydrogen atoms are just neutrons. **THERMAL** neutrons. When you energize a neutron and flick it off into space, the amount of energy it carries and how fast it moves are categorized. Thermal neutrons are WAY more energetic than those of our previous fission process. They're moving at 17% the speed of light. They fly right through that u-238 housing like it isn't even there, causing it to decay instantly. This is where the big bang of a fusion bomb comes from. Trying to get the fission to happen quickly and completely impacts the yield of the second stage. This housing blows itself apart from all the heat, and this is where most of the fallout comes from the bomb. How does fission and fusion both release an excess of energy? Because iron is the most stable element. Fuse anything smaller, and you'll get energy, fuse anything bigger, and it'll cost you energy. Split larger elements, and you'll get energy, split smaller, and you'll lose energy. It's why stars go supernova a fraction of a second after they start fusing iron, it's an energy sink that causes the collapse, the explosion of a star is just the rebound."
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ftq1dp | why do racecars have to change tires so often? Usually tires are good for much longer than a day. | Engineering | explainlikeimfive | {
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"Race car tires are quite different from the tires on your car and are experiencing a lot more stress Racing tires are quite soft at temperature compared to a normal tire, the softer tires give more grip than harder ones and more grip means faster laptimes. Even your softest street tire is still going to be on the order of a hard racing tire while many racing series have soft, super soft, and even ultra soft tires. Your touring tire is going to be a solid compound designed to give you 30-75k miles at sustained speeds of up to 85 mph, and cornering forces of about 0.5 gs max. An F1 tire will be experiencing 2 g acceleration, 5 g braking, and up to 6 g turns at speeds of up to 230 mph which will get them far far hotter than your car tire. Racing tires have traded tire longevity for grippiness and its up to the teams to balance the time loss of swapping tires in a pitstop against the time gain of running grippier tires",
"1) Racing tires are under pretty extreme stress during the race, stresses that normal tires don't really experience. Thus, it should come as no surprise that they degrade pretty quickly. 2) If your goal is to win the race, you need optimized performance out of the car, which means you need optimal tires. Even if the tires are still perfectly functional, they may have fallen off the performance cliff and thus you're going to be going more slowly around the track than your competitors on newer tires. 3) It actually *is* possible to design tires that will last the entire race. In many series this is objected to out of cost concerns, but in others the tire degradation is actually deliberate because it helps make the race more interesting. This is doubly true in Formula 1, as the only way to *ensure* teams come into the pits is to swap tires, given that mid-race refueling is banned."
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fuisjt | How does a stud finder work in construction | Engineering | explainlikeimfive | {
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"The stud finder is putting out a very weak electric signal into the wall, and measuring how much comes back (the relative permittivity of the wall.) Drywall has a much higher relative permittivity than the studs do, so you basically just move the stud finder horizontally, and when it senses a big drop in permittivity, it beeps."
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fulqro | how does low litre engines make a lot of power? e.g 2.1 or 2.2 | Engineering | explainlikeimfive | {
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"An engine is basically an air pump. Push more air thru the engine and it can make more power. This typically involves turbocharging or supercharging, which compresses the air going into the engine.",
"Generally the way small displacement engines make a lot of power (compared to bigger engines) is that they spin really fast compared to the bigger engines. Horsepower is calculated by (Torque X RPM )/5225 so the faster an engine spins the more power it makes, even if it makes less torque. Smaller engines have light rotating assemblies and are easier to balance, which makes them prime candidates for spinning a lot faster.",
"Small engines can make a lot of power in several ways. An engine is, at the most basic level, an air pump. Each cylinder draws in air mixed with fuel, burns it to make power, and then pumps it out through the exhaust. The more air (with the right amount of fuel) an engine can pump through, the more power it will make. So the faster you run the engine, the more times per minute each cylinder pumps its air and fuel through it, and the more power it makes. You may have a tachometer in your car that shows how fast the engine is turning. You may have noticed that there is a red line that shows the limit to how fast the engine should be turned. There are ways to make the engine able to turn faster, but they generally involve making the moving parts of the engine stronger. There is a lot more to it, but turning the engine faster is one way to make more power. Another way is to force more air into the engine under pressure. This is what superchargers and turbochargers do. If the air coming into the engine is compressed to be twice as \"thick\" as it would without being pressurized, it will make about twice as much power. Those are the very basic ideas, but of course lots of smaller details, like making the fuel burn more efficiently, are just as important. It's a whole thing."
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fusbzi | When talking about engine sizes in a car, what is "litres" refering to? | Engineering | explainlikeimfive | {
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"Car engines have spaces inside them, called cylinders, which are used to burn fuel and provide power. The total volume of those cylinders is what gives an engine its size.",
"It's the volume of the cylinders of the car. for example, most cars in the EU are 4 cylinders. a 4 cylinder 1.6L has 4 cylinders, each one is 400cc big (0.4L). more cylinder space tends to equal more power and torque, since more fuel can go in to power the car.",
"Gas enters your engine, goes BOOM. This explosion moves the 'piston', how much this moves is measured in litres, and is known as 'displacement'. The more litres your engine can move per boom, the more power it has available.",
"It's the *displacement*, which is the *change* in the volume of the cylinders as the pistons go up and down. If the volume of a cylinder varies between 2 and 3 liters in that process, the displacement of *that cylinder* is 1 liter. The displacement of the *engine* is that, multiplied by the number of cylinders. Displacement is the most meaningful measure of *engine size*.",
"Finally one I can answer! A size of Litres is the measurement of the total volume of all cylinders in the engine. The formula (a bit more than ELI5) is: NoC * 0.7854 * Bore^2 * Stroke * NoC = number of cylinders * Bore = cylinder size (usually a tiny bit larger than piston) * Stroke = how far the piston travels Also, litres (L) can be referred to as engine displacement, often measured in cubic-centermeters (cc) and cubic-inches (c.i.) in the states. Source: me, an Ford Asset graduate and ASE certified technician.",
"An engine is like our heart. Bigger hearts pump more blood, smaller hearts pump less blood. Smaller engines pump fewer litres, larger engines pump more litres.",
"So let's say my engine is a 5.0L coyote V8, does that mean I have the best American muscle car engine ever, or am I running people over quicker? 👀",
"Hey, if y'all don't mind me piggybacking off this question, what's up with the naming of those old muscle car engines? Like the 392 and 429? Is there a rhyme or reason to it or is it just a name like 2JZ or LS1?",
"It's the volume of air that the engine displaces, calculated by: area of the bore hole × crankshaft stroke length x number of cylinders.",
"To those wondering why I didn't just Google this: I already did... and the answers I got were a lot more complicated. I don't know much about cars, so I didn't understand what people meant",
"Displacement! 1 litre = 1000 Cubic Centimeters. 1000 Cubic Centimeters = 61 Cubic Inches. Example: 302 Cubic Inches. 302 ÷ 61 = 4.950 Litres or 4950 Cubic Centimeters or 5.0 Litres rounded off. 4950 ÷ 8 = 619 Cubic Centimeters per cylinder!",
"So what drives such a variance in horse power in the same/similar sized engine? My truck has a 5.7 liter V8 and it makes 383hp. How can something like an upper end BMW with the same size engine create a ton more horsepower?",
"A engine cylinder has a specific area. Then each engine has a specific stroke length. The amount the piston travel in the cylinder. The liter or cubic inches is that volume (Height X area). If you ever hear the term \"stroker\" when referring to an engine, it means they kept the cylinder the same size, but increased the stroke length and therefor the displacement of the engine. For instance the Chevy 383 Cubic inch motor is a 350 CI engine block with the crankshaft of a 400 CI. A stock 350 has a piston stroke length of 3.48 inches. The 400 crank changes the 383 to a total stroke of 3.75 inches. And changes the displacement from 350 to 383 cubic inches. It is a relative measure of the size of the engine since it relates to the amount of fuel you can burn. A larger displacement generally means more fuel/air mixture burnt each cycle and therefor more energy produced. So, in general, a 5.0 liter engine has more power than a 2.2 liter engine. Once you add turbo chargers or other things it can make the smaller engine produce more power, but it does that by increasing the amount of fuel air in each cylinder. So a 2.0 liter, 4 cylinder engine will displace 500 ML of air volume per cylinder, per stroke (or revolution of the engine)"
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fvcm3k | How are HEPA vacuum bags different than face filters? | How are HEPA vacuum bags different than face filters? Just thought of something it makes sense in my head but you guys can correct me if I’m wrong. I too was making masks and was going to use HEPA vacuum bags as filters about two weeks ago but, I stop because something in my head wasn’t 100 sure about it. Last night I came across this video made by this doctor. 1. My logic was to use the outside of the bag to face my nose, why? The inside of the bag is intended to trap all the small particles and what comes out in theory should be clean air right? 2. The average vacuum pressure is 20 kPa ( I just googled it) and if I’m using the outside of the bag to inhale at a lower pressure I don’t think I’ll be dislodging particles into my lungs because if my breathing in pressure is all it takes we would be inhaling fiber glass and other chemicals all the time. Can someone correct me? I hope I made Sense. URL_0 | Engineering | explainlikeimfive | {
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"They were actually tested by the University of Cambridge years ago in a paper that looked into the use of common household materials for emergency breathing protection. Bottom line, they concluded that they're too hard to breathe through. But some of the designs coming out now actually do use HEPA filters specifically designed for vacuum cleaners, such as the roomba line."
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fvdkfx | why do appliances like fans have the off setting right next to the highest setting, instead of the lowest? | Is it just how they decided to design it and just stuck with it or is there some electrical/wiring reason for this? | Engineering | explainlikeimfive | {
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"For some fans the amount of power required to get the blades spinning is higher than the amount provided by the lowest setting. The lowest is enough to keep the blades spinning but not overcome the inertia at the start. Edit: as others have pointed out the fan will typically start but it is hard on the motor",
"Electric motors need a magnet to generate the pushing force. The magnet in electric fans is an electric magnet and only helps create a pushing force when electricity is running through the fan. At low power, there is enough magnetism to keep the fan moving at a slow speed, but not enough to easily start the fan. So it is always started at highest power, which gives the biggest push for starting. You could unplug the fan, turn it to low speed, plug back in, and see what happens. The blade will start turning but it will take visible effort. IIRC",
"This might be more technical than desired, but in addition to the \"inertia\" reason given (starting the motor takes more energy so trying to start it on low is harder) there are also design reasons why it doesn't logically make sense to, for example, turn a knob from \"Off\" to \"low\" to \"medium\" to \"high.\" In an electrical circuit, like inside a fan, \"off\" means the circuit is \"open;\" no electricity can run through the circuit to power the fan. Turning the knob from \"OFF\" to \"ON\" closes the circuit. A circuit has some current and voltage, which we can use to determine the power, and some resistance. The basic way to make a motor turn more slowly is to increase the resistance in the circuit, which reduces the amount of current that runs through it, thereby reducing the power. So if we want to go from \"OFF\" to \"ON\" we need to actually close a switch. If we want to reduce the power we need to close more switches to add more resistors to the circuit, and to go back to \"high\" we need to open those switches again (removing the resistors from the circuit). So it actually makes more sense (for the designers) to design a control knob that performs the same basic function as we turn it in the same direction. It is actually a little bit harder (not impossible, but harder) to design a control knob which starts by closing one switch, then as you continue turning it, opens other switches. I hope this makes sense for the ELI5 sub!",
"Thisis entirely dependent on the brand and model. The fan I have in my room has the off setting at the bottom and the highest at the top.",
"It takes a huge amount of current to start the fan, the highest setting is capable of providing that. Moat newer fans have a starter circuit these days so they don't need to start on the high setting though. But, for example, you can't use a standard dimmer switch with a fan or it won't start properly (and could burn out the motor).",
"Electrical makes sense, why TF are gas ranges like this then??",
"so that it's easier to distinguish when you've turned it off - you sequentially speed up and therefore know you have powered it off without waiting for it to spin down",
"There is typically no resistor on the high setting, which allows the motor to start at full load torque, while the lowest and middle settings include a resistor which would reduce the voltage going to the motor.",
"This is probably an American thing. The first time I went to the US, I thought my fan didn't work because the lowest setting was opposite from the stop, where I expected the highest setting.",
"URL_0 . It takes more force to get the motor to start rotation, but once going the bearing warm up and the impregnated oil in the sintered bronze bearings thins enough to allow the fan to turn slowly. That little surge of torque going from off to high keeps the fan from staying stalled, burning out the motor.",
"All my fans have the lowest setting next to the off setting?",
"I have never seen a fan designed this way. And I've owned a lot of fans. Is this a US thing? Edit: looking at the other answers and thinking about it, I guess the explanation may apply more at 110v than 240, so maybe it is an intercontinental difference.",
"It takes more energy to start something going than it takes to keep it going. Starting at the highest level overcomes that initial stickiness. [EL high school student below] The coefficient of static friction is usually higher than the coefficient of kinetic friction. By starting at the highest setting, you overcome that initial static friction and get the blades moving. From there it is easy to lower the speed to the desired setting.",
"Fans can be started on low setting just fine as they have capacitors installed for that reason (most fans won't start if the capicator is bad even if you try to start it on HIGH setting). This is why on push button exhaust fans you can press low first and it will start the capacitor is what nudges the fan to start. If you have an exhaust fan with a rotary switch, those use what are called a POT (short for potentiometer) these devices are a variable resistor (short explanation is it blocks power depending on its value which is based on where it's turned to). Typically once a POT is turned on the resistance value is very low (let's all the power through to the fan, thus it's the high setting) then as you turn it further clockwise the resistance value is larger thus blocking electricity and slowing the fan down (low setting). There is typically more circuitry involved but that is for a more deep dive depending on the unit. I believe the push button style versions (Off-High-Med-Low) design setup is to mimic POTS as people are accustomed to the functionality of older units that used POTS. My explanation is for ranges(stove/cooktop combo) exhaust fans. NOTE: I know enough electrical/electronics to be dangerous but am not a genius. Also pots can be reversed depending on the model but manufactures didn't use that often."
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fvg862 | How do sewers work? | Engineering | explainlikeimfive | {
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"Well there are storm drains, which take water from the street drains and generally route it to a body of water. Then there are true sewage pipes which route dirty water from your home and other buildings to a treatment plant. From there it is cleaned and then put back into a body of water (or used for irrigation in some places)."
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fvzhp2 | What is the name of this machine and how does it work? | URL_3 URL_1 URL_2 URL_0 Swamps outside New Orleans. | Engineering | explainlikeimfive | {
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"It's a railroad raised bridge building machine. It was likely assembled for this specific project, but the idea is used frequently. In this case it is being used for an upgrade - it assume a continuous track is being replaced but that it can uses track in front of it to move forward. It's half a transport and placement system for prefabricated parts (the yellow bit can move big piers forward and then drop them into place) and a pile driver for .... doing what pile drivers do."
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fw789v | Why do most/all cars have negative camber? | What is it good for? Aren't you just losing an extra surface to have better grip? Isn't it wearing the tires faster and un-evenly? | Engineering | explainlikeimfive | {
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"Hi! I drive a BMW and they are famous for their use of more negative camber than most manufacturers. The short answer is that it was discovered that it makes the car feel like it's biting into the pavement. Think of ice skates. They glide on the ice when you have your feet straight up and down, but if you use the inner edge of the skates blades a little, you also have instant cornering ability. Car owner: \"But this wears the tires unevenly.\" This is a perfectly normal reaction and the reality is that it does, indeed, wear the tires unevenly. BMW: \"We make cars that feel like they're glued to the pavement. You buy tires.\"",
"Imagine a car set up so the tire stays perfectly aligned with the car as it moves up and down. Remember, the car will lean as it turns. In this setup, the outside tire (which has the most weight, and the most grip) will begin to lean with the car. As it moves away from perpendicular, it looses grip. Now, start with the tire tilted in at the top (negative camber). If you start with 1° negative camber, as the car tilts, the outside tire becomes more perpendicular, and gains traction. In reality, most suspensions are designed to gain negative camber as they compress, but seldom enough to keep the tire upright. So, the negative camber still helps keep the tire upright."
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fw7f07 | How do misters (such as hose) work? | Also the kind you see with a setting spray, hairspray, etc. How does the flow of liquid get so fine like that? | Engineering | explainlikeimfive | {
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"Air Flow All atomizers work on the principle of air flow and suction. When horizontal air passes over a vertical tube, it causes the air and liquid inside the vertical tube to be pulled upward. Classic atomizers use a squeeze bulb to store a lot of air that moves quickly over the feeder tube when squeezed. The bulb has two one-way valves located at either end. When the bulb is depressed, the valve leading into the tube that leads toward the bottle is forced open by air pressure while the valve leading to the outside is pulled closed. When the bulb is released, the rubber inside returns it to its original shape, closing the valve leading to the tube, and opening the valve to the outside so that air can fill the bulb. Reservoir and Feeder Tube The perfume rests in the body of the perfume bottle, or \"reservoir.\" The vertical feeder tube is partially submerged in the reservoir and connected to the bottle's lid, which also houses a tube that connects the squeeze bulb and the nozzle. The vacuum created by the passage of air pulls the liquid up into the feeder tube and pushes it out through the nozzle. When the airflow stops, a small amount of liquid remains in the tube and, because of the cohesion properties of liquids, will act as another mechanism to pull perfume up the tube once the bulb is squeezed again. Nozzle The nozzle is the end of the horizontal tube, and is usually made of metal or plastic. When the air and liquid perfume pass through the nozzle, it causes the perfume to break up into small drops and mixes it with the air. The restriction at the end of the nozzle, called a \"venturi,\" speeds up the air and liquid mixture causing the liquid to break up and the air to disperse it widely. Depending upon how hard the squeeze bulb was squeezed, the amount of liquid and its distance dispersed changes. Atomizing \"Atomizing\" does not mean to break down into its component atoms, but rather to break a large body up into small, discrete bodies, typically suspended in another medium. In this case, the liquid perfume is a mixture of oils, alcohols, water and dyes. When the air flow pulls some of the liquid out of the reservoir and mixes it with the air flow, the liquid breaks up into drops suspended in the air, each of which has the same ratio of oils, alcohols, water and dyes. URL_0"
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fw92ik | How do the numbers and things work for haircuts like high and low fade and such. I've heard many thing like the numbers are inches or centimeters but I've never gotten a definitive answer. | Engineering | explainlikeimfive | {
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"The numbers are standard. A #0 is the clippers with no comb giving an almost 0 length Each numbered comb is 1/8 of an inch or 3 mm longer #1 = 1/8 or 3mm #2 = 1/4 or 6mm #3 = 3/8 or 9mm #4 = 1/2 or 12mm"
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fwad6d | How do rocket fuel tanks maintain the pressure to ignite in micro gravity? When the engine isn't on, how is the fuel forced through instead of just sticking to the sides in random spots? | Engineering | explainlikeimfive | {
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"In a tank that wit a liquid and a gas for pressure, the liquid will just flow around in any location in orbit when the engine is not on. When the engine is not it will be pressed down to the bottom just like how you are pressed back in the seat of a car that accelerates. So when the engine is on there is no problem but if you stop and restart it there can be a problem. Even when you change stage in a rocket it can be a problem This is a real problem in rocket design. Soviet rocket designers solved it so the next stage ignite before the precious stage shut down. Russian Soyuz still do that. Early US Atlas rocket had 3 engines in the bottom and drop the two outers around the third whey it was running for just this reason. So it is a real problem. & #x200B; The answer is a [Ullage\\_motor]( URL_0 ) that is a motor that can start in zero-G you can, for example, have a solid-fuel rocket to accelerate the rocket a bit and move the fuel down and then you start the liquid fuel engine. The US Saturn V had lot of small solid engines for ullage on each stage. The drawback of a solid rocket engine is that is can only be used once. & #x200B; Space ship has [Reaction\\_control\\_system (RCS)]( URL_1 ) that is used to rotate and for small maneuvers engines, you can use them for ullage too. The Apollo command module did just that around the moon. This is the common way to do ullage is space, use the RCS system The reaction control thruster can be as simple as just releasing pressure nitrogen from a pressure container or use fuel in a tank that works in zero-g. A fuel tank that work in zero-G would be a tank with a fuel bladder inside the tank and use put a gas as the pressure around the bag. That is often how you make a spray bottle of shaving cream with a plastic bag in the bottle. It is not a good idea for large tanks as it adds mass but perfectly fine for RCS where you use a lot less fuel then maneuver engines.",
"This is an important part of rocket engineering and can vary between rockets. Liquid fueled rockets often have fuel pumps running to generate the high pressure for the combustion chamber. As the rocket thruster burns, the fuel is pushed towards the 'bottom' of the tank by the acceleration of the rocket."
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fwdx4c | Why can't batteries be charged in one go? Like one massive charge and that's lasts a while. | Engineering | explainlikeimfive | {
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"Batteries don't store electric charge. The electricity causes a chemical reaction to occur inside the battery which can later be reversed to create an electric charge. The chemical reaction is not instant and takes some time.",
"You would need a massive battery to hold a massive charge. It's sort of like asking why a pitcher of lemonade can't be filled with a lifetime of lemonade.",
"Others have answered this from the chemical side so I'll address the engineering side. Simply put trying to dump that much energy in one go would overheat and melt the battery, the wires, and any number of components along the path of the electricity. This is due to electrical resistance. Every material we know of so far is not a perfect conductor. Meaning some energy is lost as it travels through wires. Now because physics tells us the total energy must remain constant we know the \"lost\" energy must go somewhere. In this case it becomes heat, much like physical friction creates heat. Electrical resistance heat is why your phone and computer get hot when they are working hard. So trying to force a large amount of electricity into a battery at once would create a large amount of heat from electrical resistance. Enough heat that it would melt the metals in the battery.",
"Batteries store electrical energy in the form of chemical potential, where a chemical reaction releases electrical charge and with the application of electricity be reversed again. Charging a battery is reversing that reaction and, like the limits on how fast the battery can discharge, that reaction takes time to occur. Of course the reaction can be sped up by various methods but there are various side effects. The most pertinent one is excess heat. If conceptually you performed the charging reaction all in a matter of seconds the battery chemicals would produce so much heat it would melt the battery casing and explode out as a cloud of boiling hot battery chemical gas. Obviously this is undesirable, and even lower levels of heat can reduce the life of the battery overall. The battery designers *know* that everyone wants them to charge faster. They aren't ignorant of what people want, there are just technical barriers preventing it with current technology."
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fwquy9 | How gear ratios, long and short gears work. | Half a year ago I got my licence, which made me want to know as many things as I can about cars. The physics behind the working of a vehicle is the most interesting part for me. I've read many articles, and watched videos, therefore I now know quite a lot about the topic, but gears, gear ratios is something that I definetely need a simple explanation of. Thanks! | Engineering | explainlikeimfive | {
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"A gear ratio in a car means that for every one rotation of the input, the output will rotate \"x\" amount of times. A gear is basically a lever, but a bunch of little levers in a circle. That's how torque (turning force) is transmitted. The size of the input gear related to the output gear is what determines how much torque can be transmitted. For example, if the engine is turning at 1000rpm and the rear wheels are also spinning at 1000rpm the gear ratio is 1:1 (this is usually around 4th gear in a car). A gear ratio that has a second number larger than one, eg 1:3 (the output (wheels) spins once for every three turns of the input(engine)), (often first gear) means the wheels are spinning slower than the engine - the car is in a lower gear which will transmit a lot of torque from the engine to the road. This is for when the car is trying to speed up. A gear ratio that has a second number less than one, eg 1:0.8, (often fifth gear)means that the wheels are turning faster than the engine - this is called \"overdrive\". There is very little torque going to the rear wheels in overdrive, however by this point the wheels are already spinning fast and have inertia - the high gear just delivers enough power to *keep* them spinning against friction. It's much easier to keep something moving than to get it moving. Short gears mean that the ratios are relatively close throughout all the gears, which allows you to speed up quicker. Long gears means the ratios are farther apart, allowing you to have a higher top speed with a lower engine RPM."
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fwroi0 | Why is building a ventilator so complex? | Engineering | explainlikeimfive | {
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"[Here is an excellent video]( URL_0 ) that goes into the details. Every since the MIT kids proposed an \"automated bag squeezer\" approach, folks have been saying how easy it would be to build that. While easy to build, this sort of thing would kill people, and that's a bad idea. A good ventilator needs to provide small positive pressure, to hold the air sacs open, detect when the person's muscles call for a breath, push in the right amount of air, pull it back out, and then go back to holding the sacs open. The bag thing will keep you alive for 10 minutes in an ambulance, but using it for days would cause damage a patient can't survive. A ventilator also needs to be able to add oxygen and humidity if it's going to be used for a long time. Ventilators also need to be very fine-tunable, to match their output to the patient. This is the second part of the problem, even with a million ventilators patients would just die from a lack of skilled operators."
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fwt5kj | How do cops match a bullet to a gun | If mike shoots a guy with a 9mm round how do the cops know its mike's gun and not just any 9mm? In movies and tv they always get rid of the murder weapon but why, its not like the cartridge has mike's gun written on it. | Engineering | explainlikeimfive | {
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"It's not an exact science so the results are largely up to whoever is doing the analysis(called junk science). The inside of a gun barrel has rifling: spiral groves that impart rotation on the bullet. The theory behind the analysis is that these are \"fingerprints\" that are unique to a specific weapon. They compare a bullet that's known to have been fired from a particular weapon, they fire it into a giant tank of water and collect it, to a bullet retrieved from a crime scene under a comparison microscope. This microscope puts two images side-by-side so the person can compare them visually. Shell casings get similar tool marks from the firing pin and the ejector that can be compared in a similar manner. On top of that, they have the possibility that they've got fingerprints on them from when they were loaded. The toolmark analysis is often used as definitive evidence and the \"matches\" are often overstated by the technicians. There's been no scientific analysis of whether or not the machines that make the weapons truly leave distinct marks that can be identified from one weapon to the next from the same factory during the same production run."
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fwvr4j | How do AP Bullets destroy tanks? | I read that bullets are just sharp tipped objects fired by gas/explosive charge. If it pierces tank armor, how does it destroy the tank (result in an explosion) if the bullet/shell does not hit the gas tank/engine? | Engineering | explainlikeimfive | {
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"Wow, there's a lot of bad info in here. There are two major types of modern anti-tank ammunition. HEAT, and APDS. HEAT = High-Explosive Anti-Tank. A HEAT projectile is a shaped charge that uses a small shaped explosive that creates a very focused stream of ultra-hot liquid metal when it detonates. This Explosively Formed Penetrator hits the target at a *very* high speed and burns a hole through the armor. The result on the other side of the armor is a bunch of armor chunks and liquid metal being blasted around the inside of a tank. Nasty. APDS = Armor-Piercing Discarding Sabot. Modern APDS, often termed APFSDS (Armor Piercing Fin Stabilized Discarding Sabot), is a solid projectile made out of ultra-dense metal like tungsten or uranium. After being fired from the gun it discards its casing (the sabot) and flies towards the target at incredibly high speed. It relies on extremely high velocity to pierce through the armor of the target like a giant arrow. The result on the target is what you'd imagine when a vehicle eats a 40lb metal arrow at 4,000 miles per hour. Everything turns into a rapidly expanding cloud of very hot fragments. Nobody has used an explosive-tipped armor piercing round (APHE) in an anti-tank role in about 60 years.",
"Bullets aren’t all sharp tipped. What are you referring to? Armor piercing rounds from, say, the p90 aren’t penetrating a tank. But a none explosive round that penetrates could damage the engine or other components. It doesn’t have to explode to be destroyed. Most anti armor rounds used against a tank though aren’t just bullets. They use a explosive shaped tip to punch through the armor."
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fwyou9 | I’m an apprentice electrician and having some trouble understanding... well, how electricity works lol. What’s the difference between Amps, Volts, Watts, and Ohms? | Engineering | explainlikeimfive | {
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"The ELI5 version is that electrons are the carriers of electricity in the vast majority of cases. The main thing to know about electrons is that they carry negative charge and are a fundamental particle (they can't be broken down into smaller particles) of nature. Like all negatively charged things, they are attracted to positive charge, or at least much less densely packed negative charge. So with that basic stuff, Amps is how many electrons are moving on a wire per second. Volts is a measure of how \"crowded\" the electrons are. High voltage is an area of positive charge, or at least much less crowded negative charge than low voltage. Ohms is a measure of how much resistance to flow. If electrons were cars, a two lane dirt road in the country would be high ohms, a 12 lane superhighway would be low ohms. Watts are just a measure of how much power is being created or generated or being consumed. If you have a lot of flow of electrons (Amps) moving from an area of high concentration to low concentration (Voltage drop), you have a lot of power generated or consumed. If you have any questions, feel free to help.",
"Volts = how motivated are electric charges to move from one place to another. Ohms = resistance = how difficult it is for electric charges to move from one place to another. Amps = current = how many charges move from one place to another per second. Current = Voltage/Resistance Watts = power = energy(joules) per second. Power = Current * Voltage Some water analogies: Voltage is a difference in height or pressure. Water wants to go from a high place to a low place, and there's more energy available the bigger the difference in height. Resistance(ohms) is the diameter of the pipe, a wider pipe will let more water flow through per second, at a given pressure. Current(amperage) is the volume of water flowing through per second. Higher voltage or lower resistance will increase amperage. Watts is still power, it's how effective a turbine would be if you put it in the water stream. Though things get more complicated when you're talking about AC, because inductive and capacitive loads don't follow the current = voltage/resistance rule. If you have a power factor of 50%, that 1000w device might actually be drawing 16 amps instead of 8.",
"Electricity is like water in a pipe. Amps is how much is coming through. Voltage is how much pressure is behind it regardless of if it's moving (how much it wants to move, jump from thing to going). Watts is how much comes through in a second. Ohms is resistance, how much blockage is in the pipe."
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fx3eaq | Why huge companies always have servers problems when launching a new product? They should have good expectations of what's to come and already have the experience and the means to deal with it right? | Engineering | explainlikeimfive | {
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"Because it's expensive to build for peak demand. Most businesses will take a hit on having problems at launch time as opposed to having infrastructure that's only 20% utilised ongoing when things go back to normal. Despite cloud, scaling up and down isn't always as easy as some people think.",
"Couple of reasons I can think of: a) They don't. Predicting peak demand is hard. It's not simply a matter of how many users there are. It's connections / sec. It's how long each connection takes up a space on the server. It's geography. It's unforeseen bottlenecks & bad architectures. b) They cheap out. The additional server requirements for launch will fall off pretty quickly, so they try to minimise spend c) Same as b, but they cheap out on the scaling, so when the shit hits the fan, they're not ready to scale up as fast as they need d) The performance testing they do isn't realistic, so their scaling plan sucks. e) They fail to account for the fact that systems running at 95-100% don't always behave themselves the same way systems running at 20-50% do. & #x200B; Words can't describe how many times I've seen shit fail because a server ran out of space and then fell over. Why did things fail? We don't know, the system ran out of log space and the logs are garbage.",
"Until I get some proof on that I want to believe that that's not true and that it's just so that we only hear about the ones with a rough start. Like noone ever said 'did you hear about the smooth launch of game/program/service xy? Damn, they know how to do it'",
"There's a few reason. 1. It's not an infinitely scaleable application. There may still be bottlenecks in some places, such as backend databases with high end amount of registrations or purchases. 2. It's just not worth the cost to handle the top 20% of the load, because the majority of it will happen anyways. Despite the fact that you can't make the sales on day 0, you will still eventually make the sales when things flatten out a bit. 3. Most Cloud providers have resource restrictions in place so that a single account cannot grow out of control. As a business, you want something in place so that you don't accidentally cause your cloud application to rent thousands of extra servers and cause an out of control invoice. If you don't properly estimate how much you'll need, you have to call your AWS or Azure or GCP rep and have them increase this limit, but this is a manual process.",
"Im working for a large-ish company. Its cheaper to prepare for say 10.000 calls/visits/whatevers than to prepare for 20.000. So the company will prepare for 10.000 and (rightfully) expect people to return the next day for another call/visit/whatever. Not to mention even through at launch there would be 20.000 visits/calls/whatevers, after a week that number will be cut in half, so why pay for being ready to receive 20.000?",
"The principle to keep in mind is that a chain is as strong as its weakest link. If you think about it, there are quite a few ‘components’ that make any web service tick. These components have further sub-components - both hardware and software. Think caching and queueing mechanisms as an example. Despite any amount of testing and scalability preps, real life data and circumstances can put spanner in the works in almost infinite variations. Hence the possibility of ‘servers’ crashing."
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fxexw9 | Why does the CPU get hotter when doing more intensive tasks? | Engineering | explainlikeimfive | {
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"Computers are actually much faster than we normally need. This means that usually, your computer does a lot of waiting. When your computer waits, it uses less power (less things get turned on). When your computer does something intensive, however, your computer spends all its time working. Electricity flows through more circuits, often multiple at a time (sometimes you can even get multiple things happening at once - for example, if you're adding 1 to 50 numbers, you can start adding to the next one before you finish waiting for the last). When you have more electricity flowing, the processor gets hotter."
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fxng1t | Latency vs Throughput (Computer Architecture) | I keep hearing that latency measures how quickly something is done, while throughput measures how much of something is being done. But if I were to improve latency, wouldn't I be increasing the amount of work done, thus throughput as well? And if I were to improve throughput, wouldn't that mean the process takes less time, which improves latency as well? How do I choose which is more important in certain workloads? (web browsing, video editing, etc) | Engineering | explainlikeimfive | {
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"You throw a ball to your buddy. The ball takes say 3 seconds to travel to him for him to catch, this is latency. You can throw 1 ball per second. This is throughput. This means that you can throw balls while your old balls are still flying in this case but if you were to throw 1 ball every 4 seconds, this would not be true. Improving latency doesn't always improve throughput and vice versa. No matter how many balls I throw, travel time is still 3 seconds. No matter how close I get to him to decrease latency, I can still only throw 1 ball per second."
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fxv3p9 | Why do some motion detectors have opaque, seemingly textured plastic covering the sensor? | Engineering | explainlikeimfive | {
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"Depending on the style of sensor, the detector may not rely on visible light. In which case it may be protected by a cover that is opaque to visible light but transparent to the frequencies used.",
"Slightly opaque plastic diffuses the light, allowing differences in contrast to be detected from larger angles, widening the effective range of a motion sensor."
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fxw1uf | Why do batteries get worse every time you charge them? | Engineering | explainlikeimfive | {
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"A battery is made up of a material that stores energy (electrolyte) and a material that touches the electrolyte and allows the energy to flow out of the battery (an electrode). Charging and using the battery destroys the electrodes a little bit, and over time this destruction causes it to not work as well. It's kind of like steel rusting. The degradation of the electrodes happens much faster at high temperatures, and charging a battery causes it to heat up, so designing a charger is a balance between heat and speed. Charging a battery too quickly creates a lot of heat damaging the battery, but the user is happy because their phone is charged quickly. Charging it slowly is healthier for the battery, but then the user is sad because their phone takes hours to charge."
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fxxdtp | How do they fix power lines when a tree falls on them? | The wind blew a full dead tree onto power lines down the road. The tree is just laying on the lines but they aren’t fully on the ground. Anyways how do they fix this rather quickly? It looks very complicated and the lines are probably still dangerous to remove the tree. | Engineering | explainlikeimfive | {
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"They shut off power to the line and then rebuild it. Power lines are kind of like tinker toys. You just replace the parts that need replaced. Everything from the wire to transformers. If a pole is broken, they cut it off and plant another one.",
"I can’t give an answer that will be 100% applicable to your exact situation without seeing it and without seeing how the lines are fed, if it’s in town or the country, three phase, single phase, multiple feeders etc... I’ll give the most common answer for most situations though. So if there are some trees on the line, the lines aren’t broken and are still energized I’ll use an insulated 40’ extendable pole with a cutting blade on the end. I’ll also be wearing rubber gloves, then I’ll cut the branches from the tree and just use the blade to pull the, down if it’s safe to do so, for example if there is just one phase (primary, top wire and neutral, bottom wire). In a more complicated situation, if the lines are still energized and not broken I’ll turn on something called blocking, which will cause the line to trip if I fuck something up. Then I’ll park my bucket truck close by, go up in the basket and put cover up (rubber hoses and blankets) on the lines to protect myself then cut the trees down with a chainsaw (still wearing rubber gloves). And I’ll pull the trees out. If the tree fell on the line and knocked out the power it’s all the easier, I’ll physically disconnect the line and leave a hold card so no one reenergizes, then I’ll ground the lines (electrically connect them to the earth) then cut the trees the fuck down. Once all the trees are clear I can add some wire to the broken lines, splice them together, then climb the closest pole, pull of the line and replace out the slack... a little more too it to that with some extra safety shit but that’s the basics. Source: journeyman powerline technician"
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fy4n7l | Why do cars make that electrical wirring noise when reversing? | Just always wondered why but never found out. | Engineering | explainlikeimfive | {
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"The gears are straight cut so they whine. Other forward gears are in constant contact with one another, removing the whirring sound.",
"Lots of cars have a ‘straight cut’ reverse gear as opposed to ‘helical cut’ forward gears. Most rally racing cars have straight cut gears for their forward gears too (dog box). If you watch any rally video you’ll hear that same noise, if you can hear it over the exhaust. Straight cut gears are stronger but obviously loud af.",
"... and they have a higher pitch than your forward gears because they are spinning faster. They’re geared very low, which is why you can only reverse at a few miles / kilometers per hour.",
"When in reverse automatic transmission hydraulic pumps will be at a regulated maximum pressure. The gears inside the pump are straight cut. At or near 300 psi, the pump can make a loud whining noise. Not many, if any automatic transmissions have a straight cut as opposed to a helical cut gearset. Some TH400's had straight cut gears back in the 70's. They were used in dump trucks and motor homes typically. Look up Simpson gear set and Ravinueax gear set. Both are very popular types of gear assemblies used in automatics world wide. Fwiw... I own a company in the drag racing industry that builds automatic transmissions for vehicles that produce well north of 2,000 horsepower."
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fyfl21 | Why does the shower in most bathrooms only have a certain sweet spot for warm but anything else and it’s burning hot or the arctic | Engineering | explainlikeimfive | {
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"Most houses and apartments have a single water heater for all water in the house, which keeps a lot of water heated and available at all times. Showers (and other taps) work by combining hot water from the water heater, and cold water directly from the main water supply. Since the heated water is usually also used for things like dishwashers and washing machines, people usually set the temperature much higher than what would be comfortable to shower at. The range between \"all the way hot\" and \"all the way cold\" is much bigger than the range that is comfortable, so the comfortable range ends up being small and easy to miss. You can lower the max temperature of many water heaters, but you will run out of hot water faster (since you are not mixing it with cold), and things like dishwashers won't clean as well.",
"What I think this guy means is ( and I'm using my tap as an example) when adjusting the flow of water to make a comfortasble temperature for the shower. you can have the tap set at 1 position and it is not warm enough but if you adjust it 1 millimeter further to the warm side it is way to hot. This happens with my tap and it is more than likely that it is just a \"budget\" tap and doesnt mix water well",
"As an aside to the general ELI5, it's also possible the shower valve has been misaligned and needs to be readjusted. It's a small screwdriver manipulated device behind the plate on the faucet, and it controls how much or how little is mixed from the hot and cold.",
"Worn shower cartridge, possibly water that is too hot that is damaging them. They cost about $35 to replace."
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fyrpci | What is the purpose of popcorn on the ceiling? | Engineering | explainlikeimfive | {
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"It scatters light. Makes the room seem more diffused. It fell out of style because the old method of popcorn was bad for your lungs and generally it doesn't look \"clean.\"",
"To hide the joint lines and flaws created when your ceiling was put together. Your trusses aren't perfectly aligned because wood bends and warps. Which means your ceiling material can't be perfectly straight and level. Popcorn and orange peel type textures camouflage the imperfections and misalignments.",
"Just to echo a couple comments here. It's a cheaper alternative to a painted ceiling. The rough/matte finish hides imperfections. You can get away with fewer coats of drywall mud on the joints on the ceiling compared to the wall. Painted ceilings are nicer (in my opinion) but they are more labour intensive as you need those extra coats, sanding, and a paint job. Any popcorn texture made after about 1985 no longer contains asbestos."
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fyyhsv | Why does the body shapes of acoustic guitars have curves on them? Why can't they just be a simple rectangle/oblong shape? | Does it contribute to the sound of the strings? | Engineering | explainlikeimfive | {
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"Curves reflect and amplify sound better. That's one of the reasons why stages and auditoriums are curved, to amplify the sound coming from the stage. You'll also see this in domes. If you stand in one spot under a dome and have another person stand on the exact opposite side. Even if that distance is 100 feet away they will be able to be heard talking at a speaking volume like they're right next to you.",
"They also wouldn’t rest on your leg very well, as anyone who’s tried to play a Flying V while seated would know.",
"If it were rounded, you'd have a lute, which sounds a bit different than a guitar. Box shaped guitars sound very bright, almost tinny like they don't have much bass. Cigar box guitars were very popular for a while. The curves on a regular guitar help keep it sounding too mellow, like a lute, but keep it from being too harsh, like a cigar box. Plus, it just makes it easier to hold for most people.",
"There is nothing whatsoever stopping you from making a square guitar - it would work, it just may have done downsides to it... The biggest one is that the shape of an acoustic instrument affects the way it sounds - when the strings vibrate, the shape and design of the guitar world to resonate and amplify this sound, so by changing the shape you also change the way it reacts to the sound. A simple example is that often a larger first will be louder and more bad heavy than a smaller one, because the larger surfaces that make it up can resonate and vibrate more. By using flat, parallel panels and sharp corners, you will tend to get more harsh sounding resonances - at a corner for example you will have the sound reflecting off two separate faces and combining together harshly, rather than a curved face where there will be a gradual change in sound. There is also the fact that a guitar had to be played by a human - so the shape needs to be practically shaped in a way that is comfortable for a human to play. So a typical guitar is shaped to nicely sit on the players leg without slipping off, and is sized so that an average human can comfortably reach the far end of the guitar neck, and reach over the bulk of the body to play. Combine the quest to make the perfect sounding instrument with the practical considerations of an instrument that is actually playable and you reach the 'standard' shape of the acoustic guitar. As an interesting experiment for those who play guitar, try comparing similar instruments of different sizes and shapes against each other to see how the sound changes - which will be even more obvious of your can get your hands on something like one of the tiny travel guitars..."
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fzxk2s | How is Korea's internet so fast compared to other first world countries? | Engineering | explainlikeimfive | {
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"Most of the population is fairly geographically dense which means less infrastructure is needed. That allows them to deploy high quality infrastructure for relatively cheaply compared to countries that are more spread-out.",
"For one thing, what the others said, that South Korea's population is really dense. But more importantly, South Korea in the 1980's (as far as I remember) already heavily invested in building a widespread digital infrastructure consisting of fiber optic cables. To explain why this is so important: A copper cable equals a digital dirt road, tv cables equal a normal road and fiber optic cables equal digital highways. With the amount of digital traffic today we'd need highways everywhere. Still a lot of countries are still running on dirt roads (copper cables), whereas South Korea invested in a network of highways (fiber optic cables). Edit: Added some adjectives to make the explanation clearer."
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g02ov8 | How can prosthetic limbs move? Are there wires somehow connected to nerves? | I don’t understand how someone with an amputated arm, can receive a prosthetic arm/hand, and be able to move their fingers. | Engineering | explainlikeimfive | {
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"Well the remaining muscles near the wound still are partly functional and can be controlled with proper training. Sensors, a few of them would be placed around the residual limbs and when these are engaged can send electrical through the receivers in the limbs which are mapped to different functions of the prosthetic. That's why training is required and its difficult. Muscle send signals. Sensors read signals. Prosthetic help you masturbate."
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g03wqs | Why are constructors still using crushed stones alongside new railroad tracks instead of concrete?" | Engineering | explainlikeimfive | {
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"Higher surface energy can absorb way more than things with lower surface energy without suffering catastrophic failure. Try hitting the sand in the beach with a hammer. It's very tough. It is very malleable. You can't cause it to \"fail\". Now take the sand, and turn it into glass. Hit it with a hammer, and you'll see that it can shatter. It is harder, sure, but it isn't tougher. It is brittle. It fails immediately. The purpose is to maintain integrity of the surface. Bunch of smaller rocks can maintain a surface exposed to constant vibrations much more cheaply and effectively than one large solid piece.",
"Short answer: Ballast (crushed stone) is cheaper to install. Longer answer: Ballast is cheaper to install, but more expensive to maintain (depending on the lifetime of the railway, condition of the subsoil etc) than slab track (concrete). However, as trains become faster more slab track is being used as it's more stable and there's no risk of bits of ballast being made airborne by high speed trains passing over concrete slab. Slab is also commonly used in stations and tunnels where even a small amount of track movement would be unacceptable.",
"Concrete is brittle in comparison and the weight and vibration would lead to cracks. It would be very costly to repair and you would have to repair very frequently.",
"Concrete can’t absorb water into the ground like the ballast you commonly see on tracks. They’re also better at distributing the weight of the tracks and the trains that travel along them.",
"This may not be the only reason, but using gravel is much cheaper than pavement and requires far less maintenance."
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g0b3g6 | how do ships in bottles work? | Engineering | explainlikeimfive | {
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"They build the ship outside the bottle, with the masts able to fold down, and then they put it in and extend the masts. [Video]( URL_0 )."
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g0ns9w | Watts vs VA | Why is power draw measured in WATTS ( which is volts multiplied by amperage ) but power production or power sources are measured in VA ( volt amps ). Are they not identical? What’s the reason for the difference. | Engineering | explainlikeimfive | {
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"For a purely resistive load, like a light bulb or heater, volts times amps equals watts. But many loads are not purely resistive; they can also be capacitive or inductive. By far the most common of the two is inductive: most motors, for example, are inductive loads. These loads consume power but \"return\" some of it without using it. So there's a thing called a \"power triangle\" that shows the relationship between the \"real\" power (measured in watts; this is the actual amount of power consumed), the \"reactive\" power (measure in volt amps reactive; this is the power that gets \"returned\"), and the \"apparent\" power (measured in volt amps: for a purely resistive load, this will match the real power).",
"I will try my first ELI5 answer. Take your little red wagon, some string, and your little brother and go to the bottom of a small hill. Sit your brother on the wagon and tie one end of the string the string to the handle. Now, grab the string a short distance from the wagon and slowly walk up the hill, pulling the wagon behind you. Be careful not to jerk or pull too hard. The strength the string needs to be, so it does not break while you are steadily dragging the wagon, is the Watts. This is slightly like a resistive load like you'd find with a light bulb or a heating element (as others have mentioned) Now go back to the bottom of the hill. Position the wagon and your little brother in the same place but this time walk back up the hill with the other end of the string. Pull the wagon up the hill hand over hand. Each pull brings your brother a bit closer and the wagon may even coast a little bit before your next pull. This is like an inductive load like in an electric motor or the alternating current in an AC circuit (which 'tugs' 60 times a second). Unlike when you slowly pulled the wagon up with you, in this case you are tugging repeatedly on the string over and over to get the wagon up the hill. This means the string sometimes needs to be a little bit stronger in order to not break when you pull each time. This is like the Volt-Amps. The amount of effort it takes to get you, your wagon, and your brother to the top of the hill is about the same in both cases. This is why, in electrical systems, wiring and equipment that needs to handle AC current or feed power to motors, etc, are rated in VA because at certain points in time, they need to handle more. VA is always larger than W in these cases. Situations where there is a steady load VA = W as there is no ‘tugging’. Edit.. Apologies, I kinda broke rule 4 I think."
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g0qqyn | Why do electrical cords sometimes have one prong that is slightly bigger and why do they both have holes through them? | This is the type of plug I'm referring to: [ URL_0 ]( URL_0 ) | Engineering | explainlikeimfive | {
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"Polarity! While for many applications (especially an incandescent light bulb) it doesnt matter which prong power goes in / comes out, sometimes it does. Especially electric motors, and having them all push/ pull in the same \"direction\" is more efficient for the electrical grid as a whole. The holes have a couple of uses: 1st they allow for locking out/tamper proofing, along the line of a plastic tag with instructions like \"you must do x,y,and z before plugging in. 2nd, they align with bumps in the socket that help keep the plug snugly secured and prevent accidental removal."
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g19via | How do tank tracks operate with one engine? | In order for tanks to turn while moving forward, they have to run the outside treads faster than the inside, but how is that done with a single engine powering both? Does an M1 Abrams accomplish this the same way as the M4 Sherman did? | Engineering | explainlikeimfive | {
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"Going roughly from oldest to newest: Probably the simplest steering system is known as \"clutch breaking\". To turn you simply disconnect one of the tracks from the engine (with a clutch). For sharper turns you would apply a brake to the disconnected track. This has the disadvantage that it slows the tank down if you're moving forward, and requires you to move in order to turn. For lighter tanks you could use a differential in place of the clutch and just use a brake to control the tank, but this requires dumping A LOT of energy into the brakes as tank mass goes up. There was also an early approach to allowing both tracks to be powered in a turn (which would enable things like turning in place) was to split the power as it came out of the engine. Either with dual shafts, or with dual transmissions connected to a single shafts. This was not done too much as it adds a bunch of mechanical complexity (tank transmissions are kinda a PITA to make, and prone to failure). Probably the fanciest approach is to use a controlled differential. You have two 'inputs' into your differential, one is power from the engine, the 2nd sets how fast one track runs with respect to the other. These systems come in a range of complexity from fairly 'dumb' (where you basically only have a 'fast' or 'slow' setting for each track) to more complex \"double differential\" systems where the \"speed\" of the differential is variable more or less at will. The M4 used the \"controlled differential\" approach. Most modern tanks use some variant of the \"double differential\" system.",
"There is a gearbox that takes the output of the engine and turns two drive shafts, one for each track. To pivot the tank, one track goes forward and the other backward. There are clutches and other controls tied to these tracks, it's a very simple user interface (like a motorbike) but a much more complex actual drivetrain."
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g1dq06 | why is paddle shifting still considered automatic transmission? | Why is a semi-automatic, paddle shift still not the same as manual gear switching and is not as good as a manual for drifting, etc. Thanks! | Engineering | explainlikeimfive | {
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"A quick answer: Clutch A manual gear box has a clutch that can be disengaged at any point in time removing power from the power train. The clutch can also be partially engaged via a pedal much the same as the gas pedal to give variable amount of power, known sometimes as “bite”. The clutch is essentially to large plates typically the size of dinner plates. They exist between the engine and drive train. The clutch when disengages allows the engine to run whilst disengagement of the drive train so a gear change can be made. Clutch plates are typically very durable and are designed to grip. [This is a great demo]( URL_0 )",
"Paddle shifters don't have a mechanical link between the controls (the paddles) and the transmission. With a manual transmission, you actually move gears around when you move the shifting lever.",
"You can't \"dump the clutch\" with a paddle gearbox. This is where you redline the engine with the clutch disengaged and then very rapidly lift the clutch pedal - the massive surge of power to the wheels when you do this allows you to break traction and spin the wheels."
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g1eb2j | Why do concept cars always get watered down for production? | When a car manufacturer puts out a concept car, the stylings are always quite aggressive and eye catching. But once that model goes into production, it almost always becomes something that kinda looked like at once point might have been a concept car. | Engineering | explainlikeimfive | {
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"text": [
"Production cost. That’s typically the driving factor behind most changes. A concept car can look as good as you want because you only need to make one - and they tend to be bespoke made by the manufacturer without using mass production techniques. Once the go ahead comes through to build the concept properly as a mass production vehicle things will be changed to make it easier to build the car on a large scale. Everything needs to be cost effective. So if dies (for making the panels) can be made simpler, and thus easier to maintain, then that happens. Same for interiors - luxury products cost more, even when bought in bulk, and although a customer may be willing to pay more for them, the extra cost on the manufacturer to train staff, make better production equipment, etc. may not balance out. Source: worked in automotive manufacturing for various companies for the past 20 years. I can go into more detail if you wish.",
"A lot of the styling choices on concept cars are not compatible with modern safety standards. Aggressive looks usually includes lots of sharp corners and lines which have to be smoothed out to be safe to crash. But this ruins the look. There is also quite often issues with the height of safety structures that needs to be changed. And car designers rarely make sure to leave room for components where the components needs to be. There kind of always tends to be too little room for a full size fuel tank, a frame that can actually support the weight of the vehicle, places to run the exhaust, wiring loom and other lines, crumple zones, air condition, battery, etc. This is all things that you may not notice is missing on a concept car but you would certainly notice it is missing when you are looking at it in the dealership.",
"The manufacturability of a concept car isn't very good. It's one thing to make 2-5 copies of a show car, and it's a completely different thing to produce tooling that can stamp out 10K copies of that shape. Plus, you don't have to crash-test the concept cars, or meet all the highway safety laws."
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g1k8xk | why are hexagon nuts so much more widely used than square nuts? | it just seems like square nuts would be superior, simpler shape, thus easier to create, sharper corners, thus easier to grip, and the sharp corners make it so it takes more for it to wear down. | Engineering | explainlikeimfive | {
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"text": [
"Square may be a simpler shape, but consider this: to reach the next flat side, you have to turn a square nut through ninety degrees. A hexagonal nut, you only have to turn sixty degrees. The greater number of flat sides means it's easier to get your tool in to work on it. You have a point that square nuts take more time to wear down, but hexagons don't give up that much in terms of longevity."
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g1wha7 | difference WiFi booster extender vs repeater | Look to get proper WiFi signal in all rooms of my house. Large home. What to look into? | Engineering | explainlikeimfive | {
"a_id": [
"fni1sxz",
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"text": [
"The best option is an extender, which uses a wired connection. If you can run an Ethernet cable between two rooms, or if you could use a Powerline adapter, then you'll essentially have two (or more) Wifi access points that are both equally fast and powerful. If you want absolute maximum speeds, have your house wired for Ethernet and put an extender in every room. The next best option is to get a \"mesh\" system like Google Wifi, Orbi, Eero, or Deco. They create a fast point-to-point wireless communication between all of the nodes throughout your home on a totally independent wireless channel (not over Wifi) and they all work together to blanket your home in Wifi. These devices are more expensive but they're super simple to set up, they require no extra wiring, and they work great. The worst option is to get a repeater. What that does is connect to your main Wifi access point, and then broadcast a new Wifi access point from another room. When a device talks to the repeater, it has to receive that message and then send it over to your main Wifi access point over Wifi. This is better than nothing, but it actually increases the total amount of interference because that extra communication is all happening over Wifi. It tends to give you higher latency and slower bandwidth overall. Note that any Wifi router can be configured to act as an extender or a repeater. If you have a spare, you can repurpose it. The term \"booster\" is generic, it refers to any of these.",
"A repeater has to send your data packets over WiFi to talk to your router. An extender sends your data packets to the router through an etherenet cable, which has lower latency (time taken to get data from A to B) and a higher bandwidth (amount of data you can squeeze through a connection per second)"
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g1x0px | Why do car tires need to be filled with air? Why can’t tires be made of solid rubber? | Car tires seem to be mostly rubber anyways and the hazard of getting a nail in them or having them slashed are both negative. There hasn’t really been any noticeable fundamental innovation in car wheels in a long time. What is the benefit of having an air filled wheel? | Engineering | explainlikeimfive | {
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"text": [
"A solid rubber tire would be super heavy and expensive, and not absorb impacts nearly as well. Heavy tires are going to suffer more on bumps and put more stress on some components of the car, as well as reducing efficiency and such. Beyond that, air pressure in tires can be adjusted depending on weight distribution to maintain ideal traction.",
"Makes the ride a lot softer. Forklift tires are solid rubber and you feel EVERYTHING. Really hurts after a long day. Also the weight of a solid rubber tire will take a lot more power to move putting more unnecessary strain on the vehicle. There actually are a couple airless options out there, but none DOT approved and only made for small recreational vehicles like ATV's. Also pretty exspensive.",
"The air in the tires cushions the ride. The tires feel like they’re inflated really solid, but there is a considerable ‘give’ in tires as you drive. Solid rubber tires would be much less forgiving for impact, and they’d have a _lot_ less traction. There is a much larger contact patch provided between air-filled tires and the road. Solid tires would be a lot more likely to skid around, because the contact patch would be a much-smaller circle (since there wouldn’t really be a flattened spot in a solid tire like there is in an air-filled tire where the tire met the road). Also — every pound you don’t have to drag around with the vehicle helps with fuel consumption — there’d be a lot of weight carried in the solid area of the tire that would normally be filled with air.",
"This [article]( URL_0 ) mentions some worthy alternatives to air tires, I guess ultimately this is what you are looking for. They all are in the process of research and testing, but it shows tires don't need to be filled with air",
"Cost and functionality. Solid rubber tires would be way, way more expensive to manufacture (and hence, purchase) than hollow ones. Having air in the tires also helps them do their job better. They’ll flex and cushion to absorb the impacts of the road better and help avoid more damage to your suspension and other delicate parts of your car.",
"Rubber actually has a lot less \"give\" than compressed air. I suppose you could have a solid tire but you'd end up with an extremely rough ride, which would also add significant wear and tear on your vehicle. That flexibility also allows tires to flex around objects, such as a rock or a curb, which ends up increasing traction. If the road surface wasn't flat enough, you'd end up with a situation where only the edge of the tire contacts the road."
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g1x6su | How do traffic light sensors work? | I’ve heard everything from headlights to car weight, how do they actually know your car is there? | Engineering | explainlikeimfive | {
"a_id": [
"fni4p8e",
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"text": [
"Magnetic coil under the pavement. Change in induction makes the detector know you’re there. And also why motorcycles sometimes and definitely bicycles have a hard time activating it. Edit: look for cut marks on the pavement, usually rectangular but also oblique, to catch more metal",
"As /u/TheRegen said, it's an induction loop under the pavement. A current flows through the loop and that makes it generate a magnetic field. When a large body of metal moves into the magnetic field, it changes it. That will result in a change in the current flow through the inductor, which allows a circuit to detect it."
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g228c9 | why do all cars have the same distinct engine sound when driving backwards? | Engineering | explainlikeimfive | {
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"fnjd6dp"
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"text": [
"Almost all cars use a straight-cut gear for reverse, and the sound you hear is the sound of a straight-cut gear. Go look for in-car video of race cars and you will hear that whine, because straight cut gears are noisy, but they are more efficient than the helical gears that all road cars use. Straight-cut gears are also cheaper to make, which is why car makers use them for reverse.",
"All cars manufactured since a long time ago use helical gears for their forward gears. Helical gears are cut in a spiral pattern, so that each pair of teeth gradually engage and disengage, which makes the gear much quieter and more durable. However because helical gear teeth are angled, this makes the gears push their shafts along their axis, which is hard on the transmission if a lot of horsepower is involved. The reverse gear is a straight-cut spur gear because it is cheaper to manufacture. Racecars use straight-cut spur gears because they are stronger and more efficient, but are incredibly noisy."
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g28m65 | How the columns of a bridge are built under the water? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"They lower a huge metal box into the water, then pump out the water inside the box. They build the pillar inside the now empty box, then let the water back in afterwards. There's much nuance to it, but that's the general idea.",
"They build a cofferdam and pump the water out so they can work in a dry place to excavate and build concrete forms. Then they pour the footings and build the supports. Eventually they remove the forms, and the cofferdam leaving the finished support under water. Check out this wiki link with some good pictures. URL_0",
"One of the ways is to sink a hollow enclosure to the bedrock that sticks above water, then drain the water from inside. Then they work inside the hollow space to bury the column in the bedrock, fill the space back up with water, and then remove the enclosure, leaving behind a grounded column."
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g2doho | How do they bend wood for things like canoes? | Do they cut it out in that shape? Or do they make it flexible somehow? | Engineering | explainlikeimfive | {
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"text": [
"Wood has a certain amount of natural flex. For more substantial curves, the general practice is to steam or boil the wood and then bend it to shape and clamp, glue, screw, or otherwise restrain it; when it cools and dries, it retains its new shape.",
"In order to steam wood to make it bendable, you build a sealed box, place your pieces in it and attach a steam generating kettle or clothes steaming device. [This device sold by Lee Vally Tools]( URL_0 ) is designed specifically for this purpose. Canadian Northwest Coast natives are known for [their beautiful ceremonial boxes]( URL_1 ) which you might be interested in.",
"The thinner an object is, the more you can bend it without breaking it. So if you have very thin sheets of wood, they can easily be pressed into a curved shape. If you then glue several of these curved sheets together, the glue will ensure that they keep their shape. That is how most wooden boats are made today, since this material is much more durable and water tight compared to traditional wooden planking. For traditional boats, they bent the planks into the desired shape using heat and water.",
"You can think of wood like thick paper. Paper is normally pretty rigid and firm, but get it wet and it folds in on itself. People in factories can do that with wood using steam to make the wood bendy. Then they can use molds to form the bendy wood into boat shapes."
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g2ebfh | Because planes have been grounded and haven’t flown for weeks,are there potential mechanical/safety issues once travel restrictions are lifted? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It is not uncommon for an airplane or a pilot to be grounded for periods for various reasons. So there are precedures on how to inspect and certify them before they can fly passengers again. The problems is that these procedures are intended for when a single aircraft needs to be brought back into action. The issue is that there are not enough mechanics and pilots to check all the airplanes if air travel were to suddenly open up again. So airliners are doing what they can to keep as many of their airplanes in the air as economically possible. This includes flying empty flights and flying cargo flights with passenger aircrafts. As for your car it is not designed for short trips around the neighborhood and might actually take damage from it. The engine needs to get up to temperature in order to fully burn the fuel and needs to be at temperature for some time to clean any sot or foulings that were deposited when it was running cold. In addition your battery will not charge enough to replace the lost charge due to cranking it so you will slowly lose battery charge. The main advantage you get from running your car is that you know it works so that you can fix any issues before you really need the car but on the other hand you will get more problems the more you run your car.",
"I work at an airport which has a bunch of 737s grounded and parked for the time being (check my submitted posts for a pic). The company that owns them is using this opportunity to run all the scheduled maintenance checks , so we have mechanics in every week looking at them."
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g2gnry | Why does double bagging groceries work? Isn't the second bag carrying not only the load of the groceries but also the load of the bag? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The load is the first bag is negligible. Think of it like toilet paper - 1 ply is pretty weak, but 2 ply is stronger. A thicker bag will be sturdier than a thin one, everything else being equal.",
"Both sets of bag handles are pulling down on you, which means the weight is distributed between each bag more or less evenly.",
"I would use nylon rope that could only lift 500lbs to lift 2,000lbs. How? I wrapped it around a few times. The weight would be distributed through each wrap. Meaning that each wrap was lifting less than 500lbs. But combined they lifted the 2000lbs. Also, this was with a forklift. I'm not claiming that I lifted 2,000lbs by hand."
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g2lbgs | why do builders and carpenters use those extra big square pencils instead of the regular pencils the rest of the population uses? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"They don't roll off your work space, the thicker lead is stronger and easier to see on dimensional lumber and you look cooler sharpening it with a knife than you would spinning a round pencil in a sharpener",
"The larger squareish ones: 1. don't roll! 2. can be easily sharpened with an exacto or other hand-held knife common on the jobsite. You tend to chop a ticonderoga in half when you do that. 3. little easier in gloves. Also...i suspect they are better marketing materials given how big you can print on the side....and pretty much everyone gets these for free at the lumber yard.",
"The wood they are writing on isn't as smooth as the paper you write on with a normal pencil. The thicker and stronger lead wears better.",
"Squares don't roll and their size makes them less likely to fit into small cracks. Their worksite might have numerous places that a normal pencil would roll away and fall into some crack somewhere. Especially if working on the upper framework of whatever you're building, you don't want your pencil to get away from you when you're up high.",
"A regular pencil runs out of graphite sooner. It makes a finer line, but that detail is not so important to rough work. A dependable long lasting carpenter's pencil is the way to go. I sometimes use a metal scribe or even a nail as a Neanderthal."
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g2mxdv | Why do masks have pleats? | Engineering | explainlikeimfive | {
"a_id": [
"fnmcrij"
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"text": [
"Pleats allow the mask to conform to the curvature of your face better so it doesn't bunch up. Pleats also allow the same sized mask to have a larger surface area so it will take longer for the mask to get saturated."
],
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g2pop2 | How do the darts from tranquilizer guns work? | And why does it take times for the guns to work on animals? | Engineering | explainlikeimfive | {
"a_id": [
"fnmu0gl"
],
"text": [
"I would suggest looking at [this video]( URL_0 ) that shows exactly how it works and show high-speed video of it hitting a target. It is a syringe that is compressed by gas pressure at the end, It ejects liquid trou the side of the needle and not the end like a normal syringe. You put a small piece of a tube around the needle that blocks the hole and it is pushed back when it hit the target. It takes to have an effect. Just look at some video on youtube of when it is done on an animal and you can see that it takes time to have an effect. It can take a few minutes."
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Subsets and Splits