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a5u75x | Why do streetlamps give off yellow light and not white | I've noticed that most streetlamps emit a yellow light instead of a white one. Is this because of the lamps age? There are a few that are white but they are all pretty new. | Engineering | explainlikeimfive | {
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"Street lamps were sodium vapor lamps for decades, white LED street lamps have only started getting installed in the last decade Low pressure sodium lamps are extremely yellow as they only emit one wavelength, this results in everything looking either yellow (if it reflects it) or black (if it absorbs it) High pressure sodium lamps are white and let you see colors a lot better but they're still very distinctively yellow These lamps have very high efficiency compared to incandescents and basically match LEDs, and have a very long service life. Their only downside is the yellow which is why in most places they're only being swapped for LEDs when they fail rather than proactively",
"The yellow lights are cheap and robust. This is very important when you have thousands of lights out in all weather. However more recently LED light have proven that it is cheaper and can be even more robust. And LED light also come in a wider range of colors which helps traffic safety. So a lot of street light are being upgraded to the new types. But this takes a long time as the old lights are quite robust and there is usually no reason to upgrade unless the light is broken."
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a5uku0 | Why do some cars have a wider or small turning circle? | I would have thought that having a smaller turning circle is better than a wider one. Why then do some cars have a wider turning circle than others? | Engineering | explainlikeimfive | {
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"In general a smaller turning circle is better as it gives you more maneuverability, but it comes with trade offs. The turning circle is related to the wheelbase of the car(distance between front and rear wheels) with a smaller wheelbase giving a tighter turning circle but a pickup truck with the wheelbase of a smart car would run into an assortment of other issues with max loading, stability, and max slope it can tackle While a smaller turning circle is nice, it's really a second or third level priority for a vehicle design as it must first achieve it's primary goals"
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a5w3u9 | What's a blow off valve and why is it being used mostly in Track cars? | Engineering | explainlikeimfive | {
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"Blow a lot of air out of your mouth and while doing that cover your mouth. The air has nowhere to go right? That’s what a blow off valve is for. When your turbo is producing boost and you let off the throttle all of that air runs into your closed throttle valve. The BOV allows that air to escape so you don’t get a backup of air into the turbo. That backup of air can damage the turbo and it can also slow it down which makes it much more laggy when you get back on the throttle."
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a61syn | What does it mean to blow a fuse and what's the process that happens when a fuse is blown? | Engineering | explainlikeimfive | {
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"A fuse is an electrical component that protects a circuit against too much power going through. It's usually a glass tube with a thin wire passing through it, and when too much current goes through that wire, it melts. Once this happens, the power can't reach the circuit, and so it stops working, and the fuse is 'blown'. Quite a few devices that I've seen with fuses have it so they are very easy to replace by hand, so you would simply unscrew the blown fuse and insert a fresh one and everything should be back to normal. In most modern homes, they instead use a Circuit Breaker, which flicks a switch when the current is too much. To rectify this issue, you can just flip the which back."
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a65vid | Why are we using kg/cm² as a measuring unit for pressure when it implies mass per unit area not force per unit area? | Engineering | explainlikeimfive | {
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"Where are you seeing that unit used for pressure? The SI unit for pressure is the pascal, which is N/m^2 as you'd expect."
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a68yg4 | Why are "economy cars" always front wheel drive? | I have noticed that all of the economy cars, like civics and priuses and basically 90% of cars are front wheel drive for "gas mileage" & #x200B; How does the location of the powertrain impact gas mileage/is there really a big noticeable difference on paper? | Engineering | explainlikeimfive | {
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"If you want to drive the rear wheels with a front engine you need a drive shaft running the length of the car to the rear differential. This means it's way easier if you have the engine feeding straight into the transmission which feeds straight out to the drive shaft, but this results in a car with higher ground clearance and a longer front end which isn't desirable A transverse engine which runs the width of the car and feeds into a transaxle transmission is very compact and easily powers the front wheels resulting in a small, low car with a stubby nose. A smaller car us a lighter car, and a lighter car is more fuel efficient",
"1) Front wheel drive means a lighter car since you need fewer heavy parts to transfer the drivetrain to the real wheels. 2) It's simpler to build and design, which allows for less expensive or better value cars, which is the type of car you are looking at when you're looking at good gas mileage.",
"With a front wheel drive you can point the engine such that it directly drives one of the front wheels. & #x200B; With a rear drive car with a front mounted engine you can get a rotating shaft that points towards the back of the car but you then have to convert it to a shaft that points at one of the wheels and you lose some power due to friction that takes place in that converter. This is another reason why electric cars can be so efficient, some are designed to have the motors inside the wheel so there is no loss of power trying to get the motion of the engine into one of the wheels."
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a69dcc | Why is it that a hairdryer can get hot in a matter of seconds, but a car’s air conditioner/heat can take several minutes to heat up? | Engineering | explainlikeimfive | {
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"Hair dryer is pretty much just an electric element that gets hot as soon as its energized (turned on). Air conditioner is a series of mechanical components that work together to take heat from one space and absorb it into a refrigerant (liquid/gas inside the unit) by manipulating the pressure of the refrigerant by a process of compressing and expanding to expel that heat to another physical location. Therefore its a bit more of a process then just turned on a switch.",
"A blow dryer draws an incredible amount of electricity from your outlet though thin tungsten wires that makes heat. Your car uses the coolant that cools the engine to heat the compartment. Your car can not provide the amperage needed to heat the wires of a heating element without adding a whole new electrical system. Which would be expensive and heavy",
"The hair dryer uses electricity from the wall to heat wires that air is blown past to make the hot air. A car on the other hand uses heat from the engine coolant to heat air, but the engine is a big chunk of metal. It takes a while to heat up and transfer to the coolant.",
"The entire purpose of a hair dryer is to get hot, so it does that pretty well. A car's purpose is for transportation. The heater is just a very nice side effect. Also consider the materials involved, and the quantity. Your car engine is over a thousand pounds of metal. If you're interested in using the heater, it's probably cold outside, so that's over a thousand pounds of very cold metal. As mentioned previously, heating is just a side effect, so all of that metal needs to warm up first before the heat will pass to you. The hairdryer, by comparison, is a tiny little scrap of metal, in a plastic shell. Heating that up is much much easier than heating up an engine block."
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a6ap9l | How do basic Christmas lights work with 110v USA AC power without any extra electronics? | ***EDIT: This post has been answered by: /u/earlma1 ___ I just accident broke one of the ends of my generic basic Christmas lights. Literally just wires connecting all of these lights together. How are these rated for 110v?? How do they not get too hot? Also, why haven't they ran a second wire from each bulb to the next so that you don't have to replace a bulb for the rest of the line to light up?? | Engineering | explainlikeimfive | {
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"The amperage draw on the lights isn't that high which is the important factor. Voltage is just the driving force or the potential from one point to another.",
"On most sets, it’s a bunch of serially connected lights, so if one blows, they all turn off. There are better lights that are able to handle the loss of bulbs. With the advent of LED, it’s also much less of a problem. As for the power, they are small bulbs that don’t draw much. With some, there are resistance elements, usually in the plug."
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a6b1re | Why do water pipes sound like they're going to explode when turned back on after a couple hours of being completely shut off? | Engineering | explainlikeimfive | {
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"It's usually the hot water pipe, and what you're hearing is thermal expansion at work. The pipes are held in the walls or under the subfloor with clamps, and as the pipes expand from the newly hot water rushing into them and slip in those clamps they make noise."
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a6dhv7 | Which lubrication to use when? | I'm confused. There's regular oil, silicone oil, WD-40, petroleum jelly and graphite powder. I have zero idea how to decide which one to use for what application. | Engineering | explainlikeimfive | {
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"Depends on the item and context. Also, no such thing as \"regular\" oil - Different lubricants have specific features and uses, and equipment has unique needs for lubrication - viscosity, additives, corrosion inhibitors, that sort of thing. Car oil - in your car engine to lubricate and cool bearings. look up the correct grade (usually an SAE number like 5w-30, where the w indicates the winter grade) to match with the engine manufacturers specs. Not for sex. Silicone oil - specifically for use with silicone items, usually sex toys. Don't use with anything not silicone. Don't use any other lubricant on silicone items either. Possibly for sex. WD-40 - heaps of uses! The wd stands for water displacer, so it's good to use as a light corrosion inhibitor, but will need frequent reapplication. Don't use it to lube bike chains as it can damage the bearings. Not for sex. Petroleum jelly - heaps of uses, it's also known as white Vaseline. I use it on seals in hydraulic and fuel systems. Not for sex. Graphite powder - a dry lube for small intricate machinery like locks, or in high heat areas where a conventional lubricant would dry out. Can also be found mixed in liquid, and is then called \"colloidal graphite lubricant\" as the liquid is just there to help apply it faster and more evenly. Not for sex.",
"When you hit a problem where you need lubricant Google what you need. I can tell you the WD40 is a penetrating releasing lubricant, meaning it's good at getting stuck things unstuck. Graphite power is a dry lubricant meaning it's going for things like locks where you really don't want to get it gunked up with dust and crap that will otherwise stick to a wet lubricant. The others, I'm less sure about."
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a6h2f1 | why are anti material rifles better at destroying military equipment rather then anti personal? And what part of it makes it that way? | Engineering | explainlikeimfive | {
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"Anti material rifles are good at destroying equipment because they use very powerful ammunition. The .50BMG cartridge used in most American anti material rifles has more than 6 times the energy of the 7.62x51mm cartridge used in marksmen's rifles. A large high energy bullet is good at punching into engine blocks and other tough targets, and can even hold a sizable amount of explosive inside the projectile, but both the bullet and the rifle that fires it are extremely heavy and bulky. A 50 caliber rifle can definitely be effective as an anti personnel weapon, but a much lighter weapon will kill someone just as dead, will have much less recoil and can allow a soldier to carry much more ammunition. Another factor is than most .50 caliber ammunition isn't intended to be used to used in super accurate long range roles, so anti material rifles often end up being less accurate than real \"sniper rifles\" simply because their ammo can't be trusted to give consistent accuracy.",
"As other's have touched on, anti-material rifles fire significantly larger cartridges(bullet + powder) than normal anti-personnel rifles do, even if numerically the bullets seem to be similar in size. A .308 Winchester round is 51mm long with a 12 gram bullet, but a .338 Lapua is 93mm long with a 19 gram bullet that leaves the muzzle with about 60% more energy Another factor that makes these rifles better against equipment than normal ones that you have ammunition options. Different bullets are suited for different jobs. Sometimes punching holes in something will take it out but sometimes you need to kill it with fire The standard 7.62x51mm round used in large NATO rifles primarily comes in variants of \"Ball\" rounds which are mostly lead and occasionally have a steel core to go through thin armor, there are some armor piercing rounds with tungsten cores and tracers but that's about as exotic as it gets. The 12.7x99mm round(.50 BMG or 50 cal) has a ludicrous amount of ammo options. You can get a Ball round, an armor piercing round, an incendiary round, an explosive round, or if you really want to bust something up you can use a [high explosive incendiary armor piercing round(HEIAP)]( URL_0 ) which will punch through armor while exploding and lighting fluids on fire. This round is understandably significantly better at taking out planes, cars, and anything full of fuel than just an armor piercing round."
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a6mtfl | Most mountain roads have runaway truck ramps. How do the truck drivers stay in control of the truck long enough to get to the ramp? | Engineering | explainlikeimfive | {
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"\"Runaway truck\" means you don't have the braking power to stop safely, not that you have no steering (or NO brakes, for that matter)",
"Inexperienced truckers will sometimes ride the brakes coming down a mountain rather than engine braking or just letting it go. Which causes the brakes to overheat and possibly fail. When the brakes fail they're still in control of the steering of the vehicle, they just cant slow down. They may not even be going that fast when they realize their brakes have failed. The ramps either have gravel pits providing greater friction to slow down the truck or veer off to go up the mountain using gravity to slow down."
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a6pxwo | Why do vehicle doors latch without “shutting all the way” if you don’t shut them hard enough? | Engineering | explainlikeimfive | {
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"They use a 2 stage latching mechanism to avoid doors opening during an accident. From a [previous post]( URL_0 ): [[–]ARAMCHEK_ 148 points 5 years ago The idea is to ensure that the door will not easily come open on it's own. The catch/latch is referred to as a \"Bear Claw\". When it wraps around the \"striker\", which is the stud or u-shaped piece, it engages the claw to grip tightly around it holding the door in place. The claw is spring loaded so that it always wants to be in the open position, that's why there is very little force required to pull the door handle. Now the back side of the claw actually has teeth on it like a gear and there is a piece of metal that buts up against these teeth that is released when you pull the handle and returns when the handle is released. So because the claw will spring open quite easily when the handle is pulled they will put extra teeth on the back side of the claw so that if it manages to slip, then the door will not come all the way open. But because that claw has rotated it is no longer tightly gripped around the striker so you will be able to move the door a bit. Some Bear Claw Latches will even have two sets of claws in order to insure maximum safety, and others may even have multiple sets of teeth so that the gear would have to slip twice before you fall out of your vehicle. [–]Thunder_bird 61 points 5 years ago Good explanation. It's a safety device. Back in the 1950's and '60's, lots of R & D went into designing simple -yet-safe door latched. The double locking latch we have today has been proven over decades to have demonstrable life-saving benefits. Mostly it acts like a second latch to hold the doors closed in severe accidents, when door latches are under great stress"
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a6uccm | why trains nowadays have multiple engines in front. | I've seen trains that have up to 5 engine cars at the front. Are they doing anything? | Engineering | explainlikeimfive | {
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"Because those trains are too heavy to be pulled with one loco. Sometimes, one locomotive is also put in the middle or back of train because the weight pulled would break the couplers. Sometimes, extra locomotive is added when train is going through steep terrain or during snow or rain, when wheels can slip more easily. Sometimes, rail company just wants to transfer locomotive between two different stations, so they hook it up to some train that goes that direction.",
"*TL:DR: There are weight/height/width/length/economic limits that prevent us from using super powerful locomotives on long/heavy trains, so we have to use the combined pulling power of multiple, less powerful locomotives.* Railway tracks are only rated to carry a certain amount of weight at any given point. If you try to put a massive engine into a single locomotive, the amount of weight that the locomotive puts on the tracks at each axle becomes too much. So, we have locomotives that cram in as much power as is cost-effective to do so, while maintaining good weight distribution over the axles, and reasonable running/maintenance costs. Larger engines also add other complications, such as volume requirements (trains need to fit into a certain height and width as dictated by the lines they run on, and are also limited in length based on the curves on the line). Bigger, more powerful engines can also cause greater stresses on the chassis and components of the locomotive, increasing the weight even further by requiring a stronger chassis to support the engine, and in turn increasing running and maintenance costs. Given these limitations, if the train being pulled is too heavy for one locomotive, you just add another locomotive (and these extra locomotives are controlled via the front locomotive either using cables or using wireless/radio communications). Some railways also include extra locomotives for trains that will be running high grades (hills), where the spare locomotive(s) will remain unpowered for most of the run, but will be turned on to provide extra power for the hilly portions. [ URL_2 ]( URL_1 ) One curiosity in locomotive design (among many) is the [DDA40X]( URL_0 ) which was built with 2 engines inside it."
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a73z4n | What are hash tables and how do they work ? | Engineering | explainlikeimfive | {
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"You have a lot of things that you want to store, but you want to be able to find them really really quickly without having to look through all of them. You assign them all a unique name and then you perform some math on the characters of that name. The actual math isn’t important, but it needs to be the same math every time for every name. The math returns a number between 0 and 100 (the hash). You store all of the things in boxes numbered 0 through 100 according to the result of the math. Next time you want to find an item, you perform the math on its name and get it from its box. Some items will have the same hash and that’s okay. The idea is not for them to be unique. The idea is for them to be evenly distributed across all of the possible values. So given 1000 items, a good hash algorithm (the math) should divide them pretty evenly so that each box has around 10 items in it. This way, you only need to look through ten things rather than 1000 to find what you want. You can expand this concept to any scale that you want.",
"Some good answers so far. I just wanted to point out an obvious and easy example of a hash is if an office puts your records folder in a box marked with the first letter of your name. Its not the most efficient hash, but it is one.",
"A hash is a transformation of a number of any arbitrary value to a number of a fixed, finite range of values. For example, you may hash an integer of any value into a range between 0 and 340,282,366,920,938,463,463,37. That's not just some strange number, that's the largest integer that can fit inside 128 bits. An example hash would be modulus math. If the domain is from 0-9, then we're basically dividing any input by 10 and taking the remainder. So 7 - > 7, and 14 - > 4, etc. And of course, all your data, all your input, everything on a computer is essentially one big number, so we can hash names, addresses, player profiles, emails, ANYTHING. A curiosity is that the transformation doesn't necessarily map a value within that range to the same value within that range. In other words, 7, once it goes through the mathematical transform, may not map to 7 in the destination range. This is important to understand, because hashing isn't just about trying to cram a number of any value into the result range - hashes have other properties to consider, typically distribution is a big one. Hashing is used for all sorts of purposes in computers. One use is cryptography. Your passwords are never transmitted in plain-text, but as a hash. The server you're logging into doesn't know your plain-text password, it compares the hash you submit to one it has on file. There are clever techniques to keep some secrets private so no eavesdropper can resubmit the same hash or generate a new one. Another use is as a check to give confidence data was transmitted intact or is authentic. Distribution is important to your interest. A good hash is going to evenly distribute it's inputs across the output domain. So knowing something about the nature of your inputs may decide what sort of hash is used to maximize this distribution. A hash table is a data structure, where the data is itself hashed to determine where in the data structure it gets stored. This may be across memory, a file, or nodes in a network. The nice thing about this data structure is that hashes of this nature are supposed to be fast to calculate (some are intentionally slow, ie for crypto) and it acts as an address, so the computer knows exactly where to find the data - some data structures require marching across tables and redirections to finally find where the data is, and then you have to go and get the data."
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a77g2r | Why do trains use steel wheels on steel tracks instead of another material, like rubber, for more traction? | Engineering | explainlikeimfive | {
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"You don’t want more traction. The less friction between the wheel and the rail, the less energy it takes to keep the train moving. 🚂",
"The Montreal and Paris metro systems both feature rubber tires. Reading Wikipedia it says it’s because of grades and tighter turns that steel wheels. Vancouver’s skytrain has steel wheels with steerable axels and linear induction motors to get over these exact issues. Honestly it looks like very few metro systems use rubber tires aside from those two specific call outs."
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a7at1o | Op-Amps in relation to Audiophile equipment | Engineering | explainlikeimfive | {
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"An [op-amp]( URL_0 ) is ideally a type of amplifier with infinite gain and infinite input impedance, it also has differential inputs. In practice this means it can be connected to anything without loading the circuit (connecting it to your microphone doesn't affect the microphones performance). Negative feedback can be added to give it a defined gain as well (this is not audio feedback). The typical goal of an op-amp in a circuit is therefore to get a perfectly linear gain (no distortion of any type), it doesn't impact the input and gets the desired gain through all levels of input power (doesn't generate it's own noise into your audio, and the performance isn't frequency dependent). A typical op-amp does have mostly flat performance through 1MHz, far far above anything that matter in audio equipment. With that in mind, \"swamping the op-amp\" mean the feedback was adjusted to get a gain that was too high, this causes the large input signal to drive the outputs past the power supply voltages (where it's clipped, because it doesn't have power to reach that). It shouldn't really be an issue in a properly designed board, but I suppose it happens. Usually with audio equipment you just care about low noise, so picking op-amps with low noise is important. For the rest of your questions: > What will an Op-Amp do in reference to sound quality and recording or sampling of music? Low noise is the big thing you probably care about, you don't want noise in your audio, low quality op-amps can introduce noise, this is especially important when you're recording from an unpowered microphone, typically it feeds into an op-amp with the gain configured high, op-amp noise can result in audible noise in the recording. You also care about flat frequency response, but op-amps are usually really good at that in the audio range. > •Do certain Op-Amps have 'special effects' such as does one Op-Amp crunch sounds better than another, or does one Op-Amp have an 'atmosphere' it gives sounds that another may not? > •What interesting* abilities does Op-amps offer in reference to tweaking of imported sounds? A good op-amp should have no \"effects\", it's goal is to amplify, and nothing else. If it does something else, then it's a lousy op-amp."
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a7dq1r | How does shower water go from cold to hot and vice versa just by the twist of a knob? | Engineering | explainlikeimfive | {
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"Imagine two pipes that are connected to a single spigot. The left one is hot, the right one is cold (for argument's sake) When the two pipes look something like this: \\ V / | | | Then the hot and cold mix together more-or-less equally and you get warm water. If the spigot looks like this: \\ V / | \\ | then it closes off the cold water, and is letting only hot water in. Similarly, if it's like this: \\ V / | / | Then you get cold water out. Finally if it goes all the way sideways: \\__V__/ | | Then it is off. Note: I have never managed to get ASCII to work on Reddit so I hope this turns out looking alright. EDIT: Forgot to finish my explanation: Your shower knob controls the orientation of that middle bit; due to limitations in ASCII I can only get a few angles, but basically you can get any percentage of hot to cold that you're able to dial in on the dial.",
"Your bathroom has a cold water pipe, and a second pipe that brings hot water from your water heater. The faucet blends these two to make whatever in-between temperature you want. Turning the knob changes the proportion of cold and hot water going into the blend.",
"The shower tap has two input pipes, hot and cold. When you turn the tap you adjust the flow between the two, varying the mix of temperatures. An electric shower is basically a heating element in a can. The element heats the can and the water flows over it - the hotter the can, the hotter the water."
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a7fvfw | What factors go into the programming of timing and priority of a stoplight intersection, and how do citizens successfully request them to be reprogrammed if they aren't a good match for current traffic patterns? | Engineering | explainlikeimfive | {
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"Lots of pieces here, I’ll highlight the ones used in my region. Signal timing: Generally the goal of signal timing is to allow the greatest number of vehicle through a given intersection over a given timeframe without a 0 for any path. That can’t be simplified to, major roads with high volume get longer times, smaller roads get shorter times. You then have to factor in the ‘wait line’ for any turns that are signaled. (E.g. Left turn arrows) if the lane is 10 cars long, you ideally want to ‘clear the lane’ at each cycle. To gather this Dept of Transportation (DOT) will deploy traffic counters, gather GPS data, and query the signal’s own sensors which can be presence for turn lanes, pedestrian requests, and emergency vehicle interruptions. Then you have to perform this for the ‘system’ under review. Usually they look at a few miles or multiple crossings. Once they have all that the goal is then optimize for the system, not just the one intersection. As for the ‘who’ it depends on who is responsible for the roads in question. The answers can be (US): City, County, State, Federal. Generally, the larger of the two will take ownership of an intersection with they cross, but that can be super regional in the laws and budgets. If you want to make a change, the owning entity will either have an engineering department or a Department of Transportation; this is where you would log the request. It’s also always good to ping your local representatives (more people is more influence) and have them advocate for a review. All in all, it’s generally lost in the process to spend money on roads for repairs, new, revamp, or demand management."
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a7h9rz | How can the Parker Solar Probe travel so close to the sun and not just burn up? How is it able to send back pictures and data with all of the radiation? | Engineering | explainlikeimfive | {
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"It's standing in its own shadow! The probe brings along an umbrella which it hides behind. (How's that for ELI5?) From the NASA website ( URL_0 ): At Parker Solar Probe’s closest approach to the Sun, temperatures on the heat shield will reach nearly 2,500 degrees Fahrenheit, but the spacecraft and its instruments will be kept at a relatively comfortable temperature of about 85 degrees Fahrenheit."
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a7ipmp | Why do some engines produce more torque or pure rpm than other even if it's smaller or less pistons. | Like a single cylinder engine can be stronger or higher cc's than a 2 cylinder engine (motorcycles) | Engineering | explainlikeimfive | {
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"Smaller is *easier* to have a higher RPM red line on, because the reciprocating mass inside is much less, meaning the bearings aren't compensating for so much weight moving around in there. CCs (aka liters, also sometimes measured as cubic inches) is just how much air volume the engine as a whole can move. A humongous single-cylinder engine might have 10 liters of displacement, because that's how much of a difference there is in volume between the top and bottom of the piston stroke. Engine volume affects performance but isn't really an indicator of performance; for example my 256 c.i. engine produces nearly twice the horsepower, and more torque than, an old 318 c.i. Dodge V8, purely by having more advanced tech to harness the power put out by fuel combustion. A lot of factors go into torque, from bore and stroke to how much of the energy can be truly harnessed and turned into rotating motion through things like cylinder head shape and fuel injection and whatever else. Horsepower is just an equation factoring torque and the RPM that torque is being made at."
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a7o4jr | Why don’t planes have/use wings to fly like birds do? | Engineering | explainlikeimfive | {
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"It's not nearly as practical. Many early plane designs attempted to do this but it is extremely difficult to produce enough lift in this manner to elevate an airplane. It also results in a really really really bumpy ride. Birds specifically evolved to be extremely lightweight. Their bones are largely hollow. While we might have tried mimicing the flight behavior of birds, it's not practical when you need some sort of heavy engine and fuel to run the engine which is driving your airplane because you then need to lift that weight. A few ridiculous early designs: URL_0"
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a7yp5k | How are skyscrapers able to bend and sway without breaking? | For clarification, I read about how they stay steady- but haven't found how something on a concrete foundation can move without cracking and crumbling apart. | Engineering | explainlikeimfive | {
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"The question has already been answered quite well, but I wanted to add a concept that is often taught in engineering classes, and probably also to machinists: \"Everything is a spring.\" Almost every solid material known to mankind has, to some extent, the same property that makes a stereotypical spring do what it does. The property is called elasticity, and it describes the amount which the material can stretch or bend in response to a force and still return to its original, unchanged state. It's most obvious with something like a rubber band or a Slinky, where you can push or pull very gently and the object can move a huge amount without damage, but it still applies to things like glass, concrete, and ceramic. For these materials, you have to push much harder and you might not be able to see the movement by eye, but they're still measurably changing as you push on them. Now, if you use those same materials in something the size of a building or a bridge, then all the small movements can add up to something easier to see. The Tacoma Narrows Bridge collapse is an extreme example of this, both of the principle that things can always flex, and as a really good demonstration of why it's taught to engineers. [You can see]( URL_0 ) how much the steel and concrete are able to move without immediately crumbling to dust. Now, spoiler alert, in this case the bridge did collapse. But it had been flexing and moving like that every time the wind picked up for 6+ months before the day it failed. The bridge had been open to the public for four months, and prior to the public opening the workers building the bridge had already been experiencing the movement."
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a852a5 | Why do buses have so much pneumatic noise? What is all that air doing? | Engineering | explainlikeimfive | {
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"The air brake system is required to brake heavy vehicles. The air lines travel all over the bus between the engine compartment and the wheels. When the driver presses the brake pedal, the air compresses and applies the brakes. When the brakes are released, the air must be released somewhere but can't be put back into the system. The air is instead released back out of the bus so that it can drive off. That happens every time the brake pedal is pressed and released which, in the city, is a lot.",
"It’s the valves releasing excess pressure on the air brakes. They have to constantly repressurize and balance to the correct pressure levels to work properly.",
"Most heavy vehicles have *pneumatic* brakes. The engine has an air compressor that runs right of the engine power (kind of like a generator would) that is there to feed the braking system with air pressure. There is one system that requires a constantly applied air pressure to lift the parking brakes. And there are several (typically at least two of them) systems that apply the brakes when the brake pedal is pressed. Pneumatic brakes are simply a lot more reliable and easier to maintain than the hydraulic brakes on a car, when you take into consideration the size of the vehicle and the ability to attach trailers and such. I know, buses usually don't have trailers. But buses are as heavy as trucks, so they use the same components and inherit a lot of the technical solutions from trucks. Anyway. Once you have added the compressor system to the vehicle for the sake of the brakes, you can as well start using it for other things as well. - the wheel suspension system is a set of air cushions - The drivers comfort seat is often pneumatic (though, in reality it often has its very own compressor) - the doors are opened and closed with air pistons - ramps that makes the bus accessible are often pneumatic - any behaviour where the bus leans to a side to make the floor level with the ramp at the bus stop is often achieved by temporarily controlling the air suspension system As a result you get a lot of pneumatic noise. - when the doors open. - when the doors close. - when the driver lifts his foot of the brake pedal. - when the driver sets the parking brake. - when lots of people get on and off and the suspension adapts to the shift in weight. And, oh. The signal horn is often pneumatic too. (which is why it literally looks like a trumpet. Because it kind of is. But when that's used, there are other obvious noises that hides this fact."
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a85x9n | How does a generator spin at the same RPM, but can produce varying amounts of power? | For example on a steam turbine that rotates a generator @ 1500rpm. How can it produce 2MW then 15MW without spinning faster? | Engineering | explainlikeimfive | {
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"Imagine pushing a toy car at 1 mile an hour. Pretty easy, right? Doesn't take a lot of energy. Now try dragging a tank through the mud at 1 mile an hour. Takes a lot more force, and uses a lot more energy. Energy, and the physics concept of \"work\", boil down to making something move by pushing on it. Both parts of that statement -- movement *and* pushing -- are equally important: you get more energy when you push harder *or* when that push makes something move farther. These two equal factors apply to electrical energy too, where \"amount of push\" is roughly the same as voltage, and \"amount of movement\" is roughly the same as current. When more current flows through a generator, it produces more power at the same voltage. As the current increases, **the generator becomes physically harder to turn**: the turbine must push harder to achieve the same rotation rate, so more energy is transferred from turbine to generator. You can see this effect for yourself with a simple DC motor from a toy. This can act as a generator too. When its terminals aren't connected to anything, it's easy to turn, but when you connect a wire across the terminals so current can flow and electrical energy can be generated, it gets harder to turn, and the extra energy you provide goes into electrical energy which winds up heating up the wires."
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a86d5e | why do revolvers have a different style handle compared to semi-automatic pistols like a Glock? | Engineering | explainlikeimfive | {
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"The bullets in a revolver are in a rotating cylinder behind the barrel. In a semi-automatic pistol, the bullets are in the handle. The shape of the bullets puts a geometry constraint on the handle."
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a86v40 | Sometimes letters in electronic signs flicker on and off. Why is it that they can flash in such regular intervals, or even flash at all for that matter? | I’m mainly curious why it happens when lights aren’t supposed to, (like the “T” in “Target” flashing) but any sort of explanation is appreciated. | Engineering | explainlikeimfive | {
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"A certain failure mode of some types of light like [fluorescents]( URL_1 ) is when there's not enough material left in the electrodes at the end of the tubes. This is called emissive material, and it...it basically makes the environment within the tube suitable for a gas arc to strike. So the light can start, but when it warms up, the current requirement becomes higher than the ballast ('power supply') of the lamp can deliver, so the light goes out. It cools again, can fire up, and is fine until it warms up, and then goes out again. The develops to the point where the light never strikes up, it just flashes and flickers without properly firing, and eventually you might just get a glow from the electrodes at the ends of the tube, but nothing else. Other light types like arc lights, mercury vapour lights, and so on, like [these]( URL_0 ), they can stop working in a similar way, because there's a gap an arc strikes across and eventually the electrodes wear so the gap is too wide for the power supply to be able to keep the arc going, once the light warms up (takes more power once it's hot). So you end up with the light cycling. With that type it tends to be a slower thing, on for maybe a minute, off for a few minutes, back on for a minute, like that."
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a88eic | How are mountain peaks' heights measured using multiple satellites (GPS)? And before GPS? | Assuming I know basic trigonometry. | Engineering | explainlikeimfive | {
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"Before GPS, you would use a sextant or similar angle-measuring device to measure the angle the mountain peak is above horizontal. Then you would walk a fixed distance away, and repeat to obtain a second angle above horizontal. Using some basic trigonometry, you would be able to get a somewhat accurate estimate of the mountain’s height. This method doesn’t account for curvature of the earth, but it’s good enough to estimate the height of a mountain and your distance to it. The math for those interested: Assuming the height of mountain is h, and the distance from your original position is x, and you walked 1000m closer, while the angle changed from 15 to 30 degrees, you can set up the following equations and solve them tan(15) = h/x tan(30) = h/(x+1000)"
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a897jm | Why jet engines on planes don’t have a grill on them to prevent things like birds getting sucked in. | Engineering | explainlikeimfive | {
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"Birds would be sucked in anyway and diced bird isn't significantly less destructive to jet engines than what makes it in right now. You'd be adding cost and sacrificing efficiency for no real gain. Oh yeah and it's one more place for ice to form from where icicles might destroy engines, so that's bad.",
"You would just end up with either a bird stuck in the grill until it does get sucked though, or the grill would break and end up in the engine. It would be one more failure point for ice related issues, and it would make the maintainers life harder as it would mean having to remove the grill before doing an engine crawl after flights.",
"You need a really strong grill to withstand a hit from a 15 pound goose at a couple hundred miles per hour. A strong grill is a heavy grill which will also restrict airflow and hurt engine efficiency which will cost millions of pounds of fuel per year. If the bird breaks the grill and sends metal into the engine then you've made things worse. Planes are designed to be as light as possible, it's really hard to give a plane enough armor to matter if you want it to still have good performance. A grill would always hurt performance but only maybe help with a bird strike but occasionally also make it wayyy worse. We've gotten good enough at avoiding birds with airliners that the math doesn't indicate that a grill would add more value than it takes away",
"The MiG 29 Fulcrum has these doors on the jet inlets that close during taxi and takeoff. They open up when the aircraft leaves the ground. This is possible because there are inlets on the top of the wing where the jet cowling meets up with the wing, to allow air to feed the actual jet and thus generate thrust. The purpose of this system is that many Russian combat aircraft are designed to operate from improvised airfields, roads, fields, etc.",
"Here’s the real issue. Should this grill do its job and stop a bird from going into the engine mid flight, you now have a dead bird carcass disrupting air flow into the engine which is very likely to cause a flameout or a compressor stall. In an emergency situation in flight, having an I damaged engine unable to produce thrust is about as useless as a damaged engine. To add on the efficiency part, you don’t want to disrupt the air going into the engine as much as possible. Anything below optimal air flow will incur a performance penalty and make the engine run hotter, which decreases engine life in the long run. The potential for icing greatly increases and ice buildup on a grill surface can seriously decrease air flow causing your engine to either flameout or suffer a compressor stall at higher power settings. The amount of bleed air needed to run a “grill anti-ice” system would also incur a significant performance penalty since you now have a greater demand for engine anti-ice. It also will definitely add weight which further compounds the performance issues.",
"Some helicopters do have grilles over their turbo shaft engine intakes. The [CH-53]( URL_0 ) is one. Jets fly too fast for a grill to work.",
"The A-37 attack jet had screens that rotated up into position over the intakes on the ground to prevent the ingestion of debris. The jet was small and the intakes were only a few inches off the ground, so FOD was a real danger. However, the screens were only for ground use and had to be retracted at takeoff. [A-37's taxiing]( URL_0 ) As an aside, the engines were so low to the ground that we couldn't stop for more that a few seconds when taxiing on asphalt. After that the jet blast would dig divots into the pavement. Source: former A-37 pilot.",
"A little late to the party, but short answer - you don’t need one. On most commercial jet engines, ~85% of the air that comes through the front of the engine doesn’t actually go into the turbine. This is called a high bypass engine. The centrifugal forces are stronger on dense solids/liquids than less dense air. This forces unwanted particles to the outside where it harmlessly bypasses the turbine and is blown out the back. Military engines, on the other hand, send nearly all the air through the turbine. This is why most of the answers here about grills/shields are relating to military jet engines. Source - I’m an engineer for a jet engine manufacturer.",
"Oh yes let's try to clog the jet engines air intake with birds piling up on the grill. \"Johnson get up there and scrape that Christmas goose off my grill.\"",
"Something that hasn't been said yet - shockwaves. Many jet aircraft will fly near or past the speed of sound (mach 1). When the air around an object is at the speed of sound, shockwaves are formed to allow the air to properly move around the object. These shockwaves will cause a spike in pressure. Carefully tuned, this can be beneficial for the engine as high pressure air in the inlet means more air mass, and better propulsion. However, too many shocks at the wrong places can cause increased drag (pressure pushes aircraft backwards). This can also cause unwanted vibration in the engine/nacelle/wing, damaging the structure. Grills could also cause unpredictable shock formation which can cause a whole slew of performance and structural issues for no real gain as seen with the posters below.",
"Grill - > reduced airflow + added weight - > lower airflow - > reduced peformance in engines - > more fuel to compensate - > added cost on your ticket. There, ELI5.",
"Jet engines dont push the plane forward, they suck the air past the plane, so there is a massive amount of pull into the engine. The grating would therefore have to be extremely heavy so that the middle of it would withstand that force, which means weight which is the enemy of all aerospace engineers. Also they wouldn't help much, because a bird being sucked into an engine at 500mph is going to break any grate short of a thick fence, and at that point youll just be cutring the bird into bits to hit the engine further in, and again, weight. Not to mention, the aerodynamics people get mad when you put something in the way of the air. They do some kind of magic, not sure what, but it ain't natural. I could explain more, but I think that's a good start. Source: I am a jet engine engineer"
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a8bke6 | How is the Boring Tunnel supposed to make traffic better? | It's a small tunnel the size of one car, so only one-way traffic is possible. Also, I'm not sure about this, but you might need to take a car elevator to get to the tunnel? I don't really get the point of this project. Yeah, it's a tunnel and that's cool, but what's the new idea behind it that makes it such a big sensation? | Engineering | explainlikeimfive | {
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"The small tunnel was a proof of concept. They're making plans for much larger and fully automated tunnel systems but you've got to start small. They're trying to figure out how to make tunnel boring cheaper and it's faster and easier to do that by digging a bunch of skinny tunnels than spending 6 years and $20B digging a Chunnel then trying something else on another Chunnel",
"You’re [not the only one to wonder this]( URL_0 ). Ultimately, it’s Elon Musk getting to test his concept of an alternative people mover. The first tunnel is the demonstration mile, with no other real practical purpose. It cost around $10million, which is substantially lower than drilling major tunnels. But it allowed the Boring Company to develop the skills and technology for bigger projects — as they now plan to custom build their own boring machine, which an order of magnitude more efficient than the commercial one they have been using.",
"It’s not, it’s so rich people can avoid to sit in traffic and get whisked away underground. You and I get left in the 20th century."
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a8gsxi | How are birds not a major problem at airports? | Engineering | explainlikeimfive | {
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"They are! That's why airports go to extreme lengths to keep birds away. Airports use many techniques to keep the area clear of birds, such as: * Eliminating bird habitats. Birds usually come to the airport area due to the availability of food sources. Denial of food to birds by eliminating the sources (like landfills, garbage, crops, dumps etc) will reduce the chance of birdstirke by eliminating the source. It also helps to keep the airport and surrounding areas unattractive to birds (for example, by eliminating water stagnation, vegetation cover etc) as it prevents the birds from nesting there. * Scaring them away. A number of airports use a number of bird repellents like pyrotechnics, cannons (mostly just prior to aircraft approach to prevent bird habituation), chemical repellents etc. In some cases, specially trained animals (like falcons, dogs etc) have been used to scare away the birds or they are trapped. * Killing the birds in the area, though this drastic step is usually not implemented except in the most extreme cases. In general, the nesting sites of birds are destroyed to prevent them from staying permanently near the airport.",
"They \\*are\\* a major problem for planes, which is why large airports have dedicated safety crews to scare them off, amongst their other duties of clearing other debris off runways and taxiways (stray plastic bags, etc).",
"Pearson airport has such a big problem with Canada geese that they use a bald eagle to scare them away. The eagle is named Air Force One.",
"At the other end of the scale, things tend to get a bit improvisational with regard to getting rid of birds. Way back when, I spent a week on a gliding course based at a small, grass aerodrome perched on top of a flat-topped hill (UK Welsh border area) and the first job every morning, before any launches, was to drive round the perimeter of the airfield a few times in the world's most decrepit Land Rover, blasting Tina Turner through jerry-rigged loudspeakers. Seemed to work. Sidebar: it was also to get rid of sheep. Loads of sheep farms in the area, and sheep have a tendency to wander. It turns out that if a sheep thinks it's about to be pounced on by an aerial predator, it jumps - and a panicked sheep can *really* jump. The near-silent *swoosh* of a landing glider, coupled with a sudden shadow, can panic a sheep, and if you think a bird can do damage, imagine what a sheep hitting your much more fragile glider can do - especially when you're a few feet from touchdown and a hundred pounds of woolly idiot has just decided to say \"hi\"..."
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a8hegq | why are all pairs of double A batteries inserted in opposite directions in electronic devices? | Engineering | explainlikeimfive | {
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"Money. Many electronic devices require batteries to be connected in series (positive terminal of one cell connected to the negative of the next, and so on). Using aternating directions allows the connector between batteries to be reduced to a simple short metal strip rather than a wire or a long metal strip.",
"A single battery cell produces 1.5 Volts (9V batteries have 6 inside). By connecting them positive-to-negative (in series), you get 3 Volts. Many small electric and electronic devices are designed for 3V. Connecting them positive-to-positive (in parallel) is still only 1.5V, but 2x the battery capacity.",
"Batteries are connect in series (positive to negative) in devices. To simplify the design one of the sides of the battery compartment is a flat strip of metal that bridges the poles of the battery. If you designed the device with the batteries lined up side by side you would need to run a wire or strip of metal to the other side of the compartment. It's just less practical to do it that way.",
"1) they aren't always, and 2) it makes it easier to run them in series. Allow me to elaborate: if you look real closely at the battery holder, you'll notice that at one end the + terminal if one battery is connected directly to the - terminal of the other. Then you only need one + and one - connection on the circuit board itself, plus a tiny bit of conductive metal to bridge the two batteries. As for why you'd run batteries in series (as opposed to parallel), this let's you double up on voltage. Many electronic circuits use 3 volts. Handily, AAA and AA batteries are 1.5 volts each, which is why remotes, etc use two such batteries, in series and hence backwards from each other."
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a8rfvy | How do deep sea submersibles take compressed air down to depth without it affecting their overall buoyancy? | From my understanding, any submersible will flood certain tanks with water in order to cause them to sink. When ascending, they pump air back into those tanks to increase that buoyancy. Why does that air not seem to factor into overall buoyancy until it is in those tanks? | Engineering | explainlikeimfive | {
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"Buoyancy is about density. Compressed air is more dense than air at atmospheric pressure, and is thus less buoyant. So moving the air from a tank in which it is compressed, to a tank where it is not compressed increases overall buoyancy of the vessel.",
"The air itself isn’t what makes the submersible buoyant. An object is buoyant if the amount of water it displaces is greater than it’s weight. So with that in mind, let’s say a submarine is buoyant if it’s ballast tanks are empty - that is, filled with air. When we open those ballast tanks, and fill them with heavy water, the sub suddenly weighs more than the amount of water it displaces, and sinks. The compressed breathable air within the actual submarine is pretty negotiable when you consider how much the entire vessel weighs. Also, the compressed air is carefully monitored and figured into the actual design of the sub. EDIT: also, ballast air isn’t taken from the breathable air within the sub. There specialized high pressure air flasks that store air for ballast use."
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a8xh6q | Why Are Some Motorcycles So Loud? | I’m wondering if any motorcycle riders or enthusiasts can help solve a mystery for my friends and me. Today we were sitting at a nice little cafe on the Main Street of a small touristy town. The sun was out, people were happy in the lead up to Christmas, the birds were chirping and everything was fantastic (including our food and sangrias). Then a REALLY loud motorcycle came down the main drag. The rider appeared to go extra slow (no traffic in front of him), and then in front of each crowded patio he revved the motor so that his bike made as much sound as possible. Our conversation paused when this happened in front of the restaurant we were in, and looking around there were quite a few pretty annoyed people, a baby started crying at the table behind us, generally everyone around didn’t like it. The rider slowed and looked right at us, and revved it a few more times, then continued on down the block doing it in front of each populated establishment. We could hear him several blocks away still. My question is: why do some motorcycle riders seem to want to emit a lot of noise while riding in densely populated areas? Anyway, just been wondering this for a long time and thought maybe Reddit would have the answer. By the way, about 5-6 more motorcycle riders came and did the same thing within the hour and a half we were there eating lunch. By the third one we stopped trying to talk over it or looking at the rider and just stared at one another until the bike passed, then resumed our conversation. Edit: original post edited to remove any form of speculation per the rules of this sub | Engineering | explainlikeimfive | {
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"I ride a fairly quiet BMW, this might help non-riders understand a bit of the revving. & #x200B; Motorcycles have standard transmissions that require you to feather the clutch and throttle while at slow speeds to maintain speed and balance. It sounds like you're revving the engine just to make noise but that's not how I ride. & #x200B; Motorcycles are also not seen very well so some like to be loud so they get noticed and not pulled out in front of.",
"I ride, have a couple bikes. One is a 1700cc Kawasaki Vaquero with custom pipes. Pretty sure not as loud as what you experienced but they have a nice low rumble when rolling on the throttle. I am very, very self conscious and aware when rolling up to a traffic light especially if the car next to me has their window down. When the light turns green, I wait until that car pulls ahead and I ease into the gas as well. some people are just assholes, you apparently ran in to a flock of them.",
"Certain people really want that kind of attention, positive or negative. For some of those people, riding a flashy, obnoxiously loud motorcycle is a way to get that attention. Trust me, people that actually enjoy riding motorcycles hate them just as much as you do, if not more. It gives all riders a bad reputation.",
"Some people are assholes, at least that fits the scenario you described. You'll probably find that the guy revving his engine in front of busy places has an incredibly small penis and thinks making all that noise will compensate.",
"It's been said that loud pipes save lives. I don't really agree with this notion, but if even one person was spared from getting run over or off the road by a inattentive driver, then I guess it is not a false statement. I ride all the time and honestly when I take out my baffle, I have to wear ear plugs. When I am on long rides my ear drums get sore.",
"To all you motorcycle AND car people who have obnoxiously loud exhaust, I hate you. I literally wish for your death when I hear that shit. Fuck you. Nobody gives a shit about your 20k dollar car or motorcycle. You have failed at life when you resort to this type of shit. Seriously, hook up a garden hose to your exhaust and place the other end in your mouth. Now rev that motherfucker until I can hear it in Florida."
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a8y39d | why are so many German roofs built very steep so snow falls off, then with little fences so snow doesn't fall off? | Engineering | explainlikeimfive | {
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"The steep roofs are less prone to collapse under the weight of snow, compared to flatter ones. So they are effectively safer/ cheaper to build in places with heavy snowfall. However, due to the high angle, the snow or ice can slide off in large pieces and be dangerous, so the \"fences\" act to prevent/ reduce that. Melting snow and smaller bits can still run off which is why a fence type structure is preferred to a solid barrier. Edit: contrary to the insistence of some, there is no support for the idea that snow is deliberately held on top of roofs in order to provide insulation in Germany. The main/ sole reason is to prevent dangerous falls. URL_0",
"Not in Germany, but in the US those little fences are so big chunks of snow/ice don't fall and hurt people. I would guess they serve much the same purpose in Germany. You see them alot on metel roofs as they have more of a tendancy to have the snow slide off in large chunks. Steep roofs are also common as it allows more useable living space.",
"Can you give an example of what you're referring to? I haven't seen any little fences like you're describing. Maybe a link to a picture or something?",
"We have the same in Norway, and the point of theese \"little fences\", or snow catches, as we call them, is to stop the big pieces of snow and ice from sliding down the roof and hit people below the roof",
"One of the reasons for the tall and very steep roofs is temperature control in the basement. Traditional German houses, e.g. Bavarians, habe long tall houses with tall roofs that are parallel to the equator, so that one side is colder (north side) and the other warmer (south side). Their basements have holes all the way to the surface on each of those sides. Warm air lifts up and cold air falls down creating a continuous air stream in the basement and keeps a relatively cool temperature. This also keeps the basement dry and safe from mold. Simple ideas like that were important because Germans have had strict laws regarding food and beer and how it should be stored for centuries when electricity wasn't an option.",
"The fence prevents giant slides of all the snow on the roof at once, which can be dangerous. It still permits bits of snow to roll off.",
"A steep roof prevents snow buildup - when snow falls it will not be able to build up to any great depth before sliding down the roof. The downside to steep roof pitches is that that provide the least amount of practical living space needing a house to be very tall in comparison to its width - so steep pitches (45°+) are mostly found in areas like the Alps and Scandinavia with regular and heavy snowfall, lesser pitches (30-45°) in areas of less serious snow (the UK and the lower altitudes of countries like France and Germany), while flat roofed properties (great for providing the most floor space possible) are more typical for warmer areas like the Mediterranean which don't typically experience snow. The small fences you see are to catch the snow - this does go partly against the idea of using a steep pitch to shed snowfall, but allows for the snow removal to be intentional and controlled. Snow (and particularly ice) will slide down the roof and catch on the fences, and can then be more easily removed from ground level - on a shallow pitched roof this would require access to a much larger roof area which can be problematic. Without a guard, when you get a sudden thaw you would end up with more unpredictable dumps of snow which can be risky for people entering and exiting (especially those that slam a door when leaving and potentially cause the snow to slide).",
"Northeastern Japan has the same style of roof. I guess it is universal wherever you have heavy snow. On the same topic, a friend of mine is a residential architect in Montana and she says her clients from LA simply cannot understand that a large 2nd or 3rd story outdoor deck will simply snap right off the side of a building if enough snow falls.",
"The steeper the pitch the less snow can build up on it. A small amount of snow building up on your roof is a good thing because snow is good insulation but a large amount is a bad thing because of the strain the weight puts on the building. So you pitch the roof according to the amount of snowfall you expect in those conditions and how wet you expect the snow to be with the objective of ensuring that in snowy weather a small amount of snow is going to stick to the roof but not too much.",
"Looking at them I would expect that the steepness is there to have fresh snow slough off when its snowing and blowing around. While it's still fluffy having little avalanches off the roof isn't a big deal, it's soft and billowy(relatively speaking). But after a few days when what's left up there has been thawing and freezing and compacting into ice sheets you don't want them to slide off on the first warm day and kill someone. So there's a ledge. I assume it also acts as a little gutter to direct the runoff to the ends so you don't end up with a roofline of enormous icicles building up.",
"Professional roofer here,not German tho but Norwegian.. close enough. Steep angle roofs have many advantages over less angled roofs.. in general they more easily keep the water out since it doesn't lose much speed when hitting the roof.. they for the same reasons tend to last longer. Water is the big enemy of a roof. Even if it doesn't go all the way through, having water soaking the roof itself will shorten it's lifespan. So I'm guessing now, the shape is traditional but back in the day it was practical. Snow can weigh a lot but that's an easy problem to fix.. more material or thicker material. Loads of other countries with more snow have less slope as a traditional norm so I doubt it has anything to do with that.",
"Roofs are steep so you can have extra floor(s) for low cost. For same floor area they are cheaper to build and heat (less walls and roof). Also flat roofs accumulate snow and you need to build the much stronger roof because wet snow can be extremely heavy.",
"I am in no way an expert on this but I assume the reason to keep the snow on the roof is because it provides isolation. The roofs may be this steep as a result of that because it could be better to hold the weight of the snow. (Again, no expert... Could be completely wrong)"
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a8y9lp | Why do squirty ketchup bottles get explosive diarrhea when they're nearly empty? | Engineering | explainlikeimfive | {
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"Because the air in the bottle has nothing (ketchup) to slow it down so it pushes out faster than if it were a full bottle, and takes small little remnants of the rest of the ketchup with it.",
"Because they're not almost empty. They're almost full of air instead of ketchup. You know when you have gas? The sound it makes? Yeah."
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a8ysnq | You know the arrow on the car signaling your next turn? Where does the sound come from and how does it make it? | Engineering | explainlikeimfive | {
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"Originally it came from a solenoid switch, a switch activated by an electromagnet. The current would make a magnetic field to close the circuit and light the signal, creating a clicking noise behind the dashboard. These days the sound is expected as feedback that the signal is activated and it is produced by a speaker or in some cases a solenoid switch that isn't connected to anything."
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a91qg7 | Why do middle-eastern houses normally have flat roofs while other countries upside down V shaped? | Engineering | explainlikeimfive | {
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"Middle eastern homes don’t have to deal with the snowfall. The flat roof also helps with collecting rain water. In places that get snow they have V shapes so the snow slides off and doesn’t build up on the roof and cause it to collapse. Thirdly is material. A lot of middle eastern homes are made of brick, with timber being in short supply. It’s much easier to make a framed home out of wood than brick.",
"The V shape helps deal with heavy rain and snow, something most parts of the Middle East don’t have to worry about",
"Snow and rain, countries with little to no rain and no snow can use a flat roof which is easier to build, an inverted v roof is for support so snow doesn't collapse it and rain falls off easily",
"In countries that have snow you have peaked (v shaped) roofs so that the snow does not collect deep enough to collapse the roof. That is not necessary in countries that do not get snow, though you do still have to have proper drainage so that you do not get leaks. But that too is not much of a problem in most of the Middle East due to low annual rainfall numbers. Additionally historically people would sleep on their roofs at night to be cooler and having a flat roof made that easier."
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a92aio | Telemetry | I saw an example as tagging wild animals to track their behaviors. But, I don't feel I am really understanding what Telemetry is. | Engineering | explainlikeimfive | {
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"Telemetry comes from the Greek word \"tele\" meaning \"far off\" or \"at a distance\" and the Greek word \"metron\" meaning \"to measure\". Telemetry is the act of measuring at a distance. We usually use it these days to talk about data being captured from one device and exported to some other location for storage and analysis. In the case of wild animal tracking, telemetry is the time/location data being generated and transmitted from their tracking devices to some central database that cross references it against maps and other related data."
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a9498t | - If I'm absolutely new, which would be the best (and maybe even the easiest) computer language to learn? | Engineering | explainlikeimfive | {
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"Python is pretty and makes some things easier and quicker but I found myself having to do some extra work getting myself started. You'll need to install some things and do some research. It might be a bigger leap jumping to other languages from python because python uses blank spaces as part of the programing language. So if you have a function (which is a sectioned off list of instructions) for example and its nested in some other code our nested code is tabbed in where other programming languages often section off code using wigglers {say hello}. Its visually more organized and ecourages good habbits, less forgiving of errors. You can use it to make robots instructions, games, blender 3d software, chat programs. I use geany to write python in. .py scripts need an interpreter. C++ can make all kinds of things. Its a strong language. More of a climb. Have more access \"under the hood\" but it can take more to get a simpler idea out but you can work in more detail. I. Remember dev c++ being good. Creates more traditional programs Javascript, html, css - for websites. Html and css are more for displaying information in a browser and javascript enables more display options and calculations. Runs from a .html file commonly and needs a browser usually",
"Go with python. It's the simplest and most widely used language. After python or if you want something else, go with java.",
"Pick the tool for the job. Different languages lend themselves to different applications and platforms. If you just want to learn to code for the sake of it, Python is a good starting point. The reason Python is a good choice is that it's relatively simple to get started with but still allows you to explore more advanced programming topics when you're ready. It has a broad feature set that is (conceptually) transferable to other languages and it has a wide range of common libraries for a wide range of topics (games programming, AI, scientific computing etc.) JavaScript is pervasive these days in more than just websites. It's become a very powerful language largely due to the ecosystem surrounding it but I couldn't recommend it as a first language. Its design is... esoteric, so you are better off having a good grasp of programming concepts from another language first, which will help you to write rational JS later.",
"I'm the opposite, I learned basic in the seventies but I don't know which language to learn now, I was considering python.",
"Python is one of the easier, yet versatile languages. JavaScript has some quirks, but is useful if you want to make websites. But my best advice is to look around at your peers; is there anybody programming who might help you when you have some questions or need help. That would be more helpful for you, if you choose a language where there is an immediate resource you can use.",
"Python is the easiest to learn, the compiler (program that creates a program using your code) handles a lot of the routine issues like data types automatically. C is a pain to code in, but often the first language taught in universities because it’s the closest to actual hardware code. Java/C++ are the next most “fundamental” language, it requires you to understand every object / function / variable or your program will fail constantly. It needs more discipline and work to use, but sets you up to learn other languages easier. JavaScript is esoteric, I don’t recommend it as a first language.",
"I'd say, start with a strongly typed procedural language. It doesn't have to be current (for me, I started with something in the Pascal language family), you are simply looking for something to teach you good habits around declarations, type safety and structured programming. From there, I'd jump into C. It's an ancient language, but the C language family (ie C++, objective C, C#, java, javascript and so on) pretty much still runs the world, and honestly, once you understand procedural programming, C is much easier to learn than anything else in this family. Plus, there's a surprising amount of places where C is still the best (sometimes only) option. Embedded systems for example. Once you've got C down, learn an object oriented version of C. I'd suggest java as the best object oriented language in the C family for a learner, but you might choose C++, C# or objective C depending on what platforms you ultimately want to develop for. Once you have these down, you should have good skills, good habits and a familiarity with the major different programming philosophies (procedural vs OO). At this point, you should pick a language you like. Python is very popular, as is java."
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a97s73 | How do planes not hydroplane when landing on a wet runway? | Engineering | explainlikeimfive | {
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"Ooh! Ooh! I know this one! Hydroplaning and sliding are two different things that people often confuse. Hydroplaning occurs when the tire is spun by a drive force so quickly that the rpm exceeds the force of friction and lifts the vehicle out of the standing water on the surface and glides across the top of the water. When a plane lands on a wet runway it CAN slide if brakes are applied too much too soon, (though at landing speeds most jets and turboprops use thrust reversers or change the angle of their propellers to slow their speed) but cannot hydroplane because nothing is mechanically spinning the wheels other than contact with the surface, so the tires cannot spin faster than the speed needed to create the hydroplaning effect.",
"The runways are engineered to prevent it from happening. The pavement is made of a porous material that absorbs a lot of water, the runway itself is cambered to discourage puddling, and it is grooved to help channel water to the edges."
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a9bx7s | How does an image or video get put onto a screen with so many pixels? Whats the hardware involved. | This question isnt about how the actual screen works (which is all I seem to get) this asking how does the computer go from a bitmap (I think its called), or a recieved image over the internet or a youtube video thats obviously in binary to an actual image that you can see thats made up of hundreds of thousands to millions of tiny pixels? Is there a chip in a phone or a laptop with just as many connections going from it to each pixel? | Engineering | explainlikeimfive | {
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"No. There aren't 1920×1080 connections from the processor to the screen. There's the CPU (central processing unit) that interprets the information from the internet and decodes it into a bitmap. The bitmap is then passed into a GPU (graphics processing unit) either one by one bit (serial) or in chunks of bytes (parallel, several bits passed at once). The GPU then makes the specialized work of storing, mixing and transforming the bitmaps. When the image is ready to be displayed, it is then sent to the screen, again either by serial or parallel connection but it doesn't address each individual pixel. The job of sending each color to each pixel is destributed through dedicated chips on the screen. How this is done depends on the design of the screen. For example, one chip can control a whole line of the screen or a tiny subset of 8×8 pixels. These chips work like the train track selectors: they know the order of the bits which they are receiving and then select the correct pixel, allowing the bits to flow down the right track until the correct pixel. This is done hundreds of times per second, in a parallel way, so fast, that we can't see it without super slow motion cameras. In modern screens, this can't even be seen trough slow motion because the dedicated chip only tells the line or subset of pixels to display the new colors when every pixel already received its bits - when everyone is ready, it signals the group of pixels to display the color stored in the tiny temporary memory of each pixel."
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a9chsa | How come we can leave devices charging overnight without them heating up or burning? | Engineering | explainlikeimfive | {
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"Modern devices and their batteries have circuitry and programming that detect their charge levels and do not exceed safe levels.",
"If an electronics device was unregulated by the electronics, you just put a 3 Volt battery backwards over a 9V supply to recharge, it would heat up too far, vent, then explode or burst into flames. But supplies and even some plugs are more clever than that. They read what is on charge, for example the batteries I use in my vape. They’re rated to 3.7V. So the charger reads them, they’re at 3.5, empty as hell. It’ll push current “backwards” through them quite quickly, and they’ll warm up a little. As they warm up, and charge up, the voltage changes across the terminals. Quite quickly. That’s why you can 80% charge a battery in about 50% of the charge time. When the battery gets to about 4.0V, it will realise it’s not got far to go, and start to charge it the rest of the way more slowly. Safely. When the batteries get to 4.2V, the “maximum” they should be charged to, it shuts the charger off and stops pushing it in. Ages ago, when everything was different and all mobile phones needed their own chargers, the voltages required were all a bit different. And using the wrong charger will brick your phone. So you’d have different size plugs so you couldn’t do it accidentally. Due to USB and internal management of battery charging within devices, things are more universal. But you should still be careful of the maximum charge speed a battery can safely take. Hope that helps."
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a9dqo2 | Why are the keyboard keys arranged as we currently see it? | Was asking this because I heard from a friend that there are Filipino linguists making a study on how to rearrange the keyboard based on the Filipino language. I just want to know how how the currect keyboard keys arrangement came to be. Thank you for your answers! | Engineering | explainlikeimfive | {
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"It was to prevent the letters (the parts that move and strike the paper) from jamming on a typewriter. So the keys were moved to separate the letters most commonly used to together. People just got used to it so we kept it for computers. However, the QWERTY and AZERTY keyboards are not the only ones that exist. There are many other less popular ones, such as the DVORAK keyboard.",
"The QWERTY keyboard was created for a machine called the Sholes and Glidden Type-Writer (it was not the first typewriter but it was the first to be called a typewriter and was the first successful typewriter). It was manufactured by the Remington company and a follow-up, The Remington No. 2 , is like the Model T of typewriters, the machine that became a huge hit and made typewriters so popular. The layout waa designed over many years as the inventors played with the layout, number of rows, arrangement of letters, etc. Their primary concern was mechanical - jamming of the hammers as noted by others but also the fact that the way this typewriter worked made it impossible to see what you were in typing (the typing line was inside the machine and blocked from view) which made it hard for typists to know there had been a jam until several lines later when the badly typed lines came into view. To avoid jams they placed common English letter pairs far apart (s, t and c are placed away from h to avoid jamming on sh, th, ch for example.) Beyond this the layout doesn't take into account a lot of other aspects of efficient typing so other keyboards have been invented that claim to make typing easier. For instance, in English, something like 60-70% of typing is done with the left hand on QWERTY. This has two problems: alternating hands between letters makes for better rhythm, but many words are typed using only the left hand. Secondly, most people are right handed but do most typing with their weak hand, which is less efficient. Also, even very early on, technical improvements in the hammers and typing mechanisms made jamming less of a concern. So alternate keyboards hace existed forever. The popularity of the Remington No. 2 and the efficiency of a standardized layout is why QWERTY is so universal today . And all the claims of the other keyboards don't matter much because people can be very good typists on any layout they are comfortable with. What the Filipino project is basically trying to do is create a layout in the principles of the Dvorak keyboard (which allows most typing to be done on one row, with the left hand typing vowels and common punctuation and the right typing common consonants with the least used letters on the bottom row which is most difficult to reach). It's designed for English, so a Filipino version would place the most commonly used letters in the specific language on the home row and be designed to maximize alternate left- and right-hand typing."
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a9eaug | A car guy friend said my small 2013 Chevy Spark (89hp) was "designed" to be revved up often. How do they design that? | Engineering | explainlikeimfive | {
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"Smaller engines have less inertia and the piston travels less linear distance. Because the engine speed is pretty much determined by how fast the piston travels linearly (= rubs, wears and tears) inside the cylinder, the rotationnal speed can be higher is the displacement is shorter. As explained, power comes from either torque or rotationnel speed, and torque is pretty much fixed by design (displacement & stuff) Higher end engines can achieve greater speed with lighter alloys (less inertia in the piston) and tighter manufacturing specs, at the cost of being potentially less reliable (lighter alloy might not be as durable, tighter specs might wear faster)"
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a9f3ud | Why are airplane seatbelts different from those found in cars? | Engineering | explainlikeimfive | {
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"Airplane seat belts are only there so your body stays in its chair to be identified by seat number.",
"They're designed for different purposes mostly. Car belt is mostly to direct against horizontal forces, head-on particularly but also side impact. Airplane ones mostly need to hold people down in their seats against vertical forces, turbulence, bumpy landings etc. There are also design differences. Cars mostly have a convenient strong pillar to anchor a shoulder belt. Aircraft seat positions differ depending on the layout the buyer wants, they are not fixed relative to any anchoring points in the fuselage, even if that were possible.",
"Becuas the seatbelt is mostly for taking off and landing and turbulence . Not so much for in the event of a crash."
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a9j50g | why do spinning lights sometimes look like they are spinning the opposite directions than they are actually spinning? Like a light-up top for example. | Engineering | explainlikeimfive | {
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"It's to do with the max \"framerate\" of your eyes. The soonest you register the newest frame is by the time it is perceptively behind the expected rotation. So it visually looks like it is rotating the other way."
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a9jcgj | how do carborateurs work? | Engineering | explainlikeimfive | {
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"For an engine to operate you need 3 ingredients: 1. Air 2. Fuel/gasoline 3. A way to ignite those two items, usually done by a spark plug (a small amount of electricity passed between a small gap) So how do we get these 3 ingredients into the engine? The first two are taken care of with what's called the carbeurator. A carbeurator (carb) for short is a device used to mix air and fuel into a proper amount to go into the engine/cylinder to be ignited. It does this by allowing air to enter a large section and pass through a smaller section (called a venturi). The smaller section speeds up the air and allows a suction from the float chamber (area a pool of fuel is held). The faster the air moves, the more suction, the more fuel is sucked into the venturi. This fuel and air combination then gets sent to the engine/cylinder and is ignited from out small amount of electricity called the spark plug. This then burns and gives us energy to use."
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a9jsre | How do touch lamps work? Recently went home for the holiday and my nephew had one. One of those touch anywhere and it turns on lamp? How does that happen? | Engineering | explainlikeimfive | {
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"Touch lamps will send a very low current through the metal parts of the lamp. Your skin can hold an electrical charge. We say that it has capacitance. The circuitry in the lamp can detect the change in capacitance when you touch the lamp. It interprets this change in capacitance as an instruction to turn on. You'll notice that it doesn't work if you touched the lamp with a piece of dry cloth but probably would with a wet one.",
"What's fun is touching and holding the lamp, and then when someone touches you (like giving you a five with the other hand), the lamp switch activates. The lamp can detect a change in capacitance in you if you're holding onto it.",
"There are a number of ways. One simple way is to simply use the outer case as an antenna. Have you ever touched the input pin of an amplifier? Your body picks up lots of electric noise, and when you touch the contact, you feed all that noise into the amplifier, which amplifies it and feeds it to the speakers as a loud buzz. It is easy to build a circuit that uses such a burst of noise to turn on a switch."
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a9kkl1 | channel 3/4 and VCRs | Engineering | explainlikeimfive | {
"a_id": [
"eck7qbv",
"eck869p"
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"text": [
"Most older TVs didn't have video signal inputs like today. To send something to the TV, it had to be a modulated RF signal, just like an over-the-air broadcast. Due to channel frequency spacing, most cities could only have a broadcaster on channel 3 *or* 4, but not both. So one of those channels was usually available for the VCR to 'broadcast' on.",
"That is only the case if you connect the VCR via coaxial cable, the same input used for an antenna. Basically no one does that now, as better quality ways exist, like composite and component video. The reason is that when VCRs were first invented, the antenna was the only input on the TV. Composite and other inputs common nowadays didn't exist yet, as there was no reason for them. So they had to send the VCR's signal like a broadcast TV signal, which meant they had to choose channels. And basically nowhere had TV stations broadcasting on both channels 3 and 4, so just an option to choose between those is sufficient to allow everyone to choose an unused channel for their VCR to use."
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a9n0jy | How do drywall anchors work? | Engineering | explainlikeimfive | {
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"text": [
"Different anchors work a bit differently. However the main concept is that when you put the fastener inn the anchor will expand so that it does not fit through the hole in the drywall any more. Some drywall anchors will expand as you put the fastener inn and some will first expand as you tighten the fastener in the anchor."
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a9nnn4 | why are car keys use different mechanisms (Sliding Pins?) then our normal house keys? What are the advantages/disadvantages? | Engineering | explainlikeimfive | {
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"text": [
"Keys can only be inserted one way into pin locks. Wafer locks, for example, allows insertion two ways. That means less fiddling about trying to insert the key into a keyhole that can be hard to see and is sometimes obscured by the steering wheel.",
"Dang, why \"do\" car keys use different mechanisms would of course be correct",
"There are many types of mechanisms for household locks as well. The traditional pin style is simply the most common. All operate on the same principle however that the valleys in the keys move something that allows the plug to spin. The choice of style is usually dependent on factors such as durability, level of security, and cost to produce."
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a9omp7 | How do spark plugs in an engine know exactly when to fire? | Engineering | explainlikeimfive | {
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"text": [
"There are a few answers to this as there are multiple types of ignition systems. I’ll try to explain as simply as I can. Electronic ignition systems use a myriad of sensors to determine down to the millisecond when to allow the coil pack to release the charge. This is based on engine load, elevation, oxygen content of air intake, throttle position etc etc. computer say go, coil pack fires and spark plug sparks. Combustion ensues. Cap and rotor systems work a little simpler. There is a coil, this supplies a high powered charge to the rotor and cap system. The rotor is turned by a shaft that also controls the valve train. It spins and is driven by the timing chain. As the rotor spins in the cap it passes by contacts that are connected to the individual spark plug wires. The current then passes on to the plug and blammo we have ignition. There is an even older system that is obsolete now with a cap and points but who uses those any more.",
"With a 4 stroke engine the crankshaft goes around twice, once to pull in air/fuel and ignite it, and once to push out the exhaust. That's about as basic as I can make an otto cycle. Early electronic ignitions had wasted spark. The spark wasn't drunk, it just sparked on every rotation since there was only a sensor on the crankshaft. The wasted spark is the one that fires while the exhaust is being pushed out. It would also fire multiple cylinders at the same time. Since there is no oxygen left, nothing happens. Once ignition systems got more advanced we started adding a sensor to one of the camshafts. Since they only go around at half the speed of the crankshaft, the ignition system can tell if it should fire on that rotation or not. For the engine to know the exact moment to fire the plugs, it will use multiple tables depending on sensor inputs. With modern engine test beds, we can tune an engine's entire running range with extreme accuracy. I even had a chance at my last assignment to use a high speed camera that views combustion through a tiny glass window in the cylinder head. It's really cool to see how minor changes change the way fuel explodes."
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a9qfj3 | How do rockets keep going in a straight line during takeoff and landing (SpaceX)? What prevents them from going sideways? | Engineering | explainlikeimfive | {
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"text": [
"A couple of things: & #x200B; 1) The rocket is built such that it is balanced right. The axis of thrust is straight up and down along the body of the rocket. Play Kerbal Space Program sometime and see what happens if you don't balance the center of gravity along with the axis of thrust. 2) The engines themselves can pivot/gimbal on their mounts. This is what is used to steer the rocket as it makes its ascent. In the case of Spacex's Falcon first stage, there's also gas jet thrusters and fins that are used to rotate and control the rocket stage to put it in landing orientation.",
"Falcon 9 has three sources of control authority: Thrust vectoring of main engines. Cold gas thrusters(RCS) Grid fins (while landing) The main engines control the ship kinda like you would balance a broom on your fingertip, it's called an inverted pendulum. If you want the rocket to go to the left, you move the bottom of the rocket to the right. on the way up anyway. Landing is more complicated, but you can think of it like launching, just in reverse. Here's a good video of that: URL_0 Though the rocket only goes straight up at the very start, after a few seconds it starts turning towards its desired orbital plane(usually mostly east), because most of the velocity you need to gain is sideways. You only go up at all because you have to get out of the atmosphere."
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a9sy1y | Why do some of the newer types of headlights seem to "jiggle" when viewed from your rearview mirror at night, but look perfectly fine when viewed from the side mirrors? | Is this an effect of the headlights? Or the tint on the rearview mirror? Or some weird lighting illusion from the newer types of bulbs? | Engineering | explainlikeimfive | {
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"ecmgqoq"
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"text": [
"I wonder if some of the headlight manufacturers use PWM to control their brightness. Basically PWM pulses the power to the LED at a faster or slower rate to make them appear brighter or dimmer. This can be used to produce a daytime-running-light, normal brightness, and high-beam with the same set of LED’s. If used, this pulsing could produce the flicker you are describing."
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a9w9x7 | Cost effectiveness & usefulness of an deep trench vs a wall | Might need an Engineer for this one. So much talk about this border wall for the US that it got me thinking about the pros & cons of a trench vs a wall with regards to security. If the US dug a 50ft deep(or deeper?) by 30 ft wide (or wider?) trench across the border, reinforcement being optional, would that be more cost effective and faster than using building materials to make a wall? Would yearly maintenance be about the same or less? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"A wall would be cheaper. Digging a trench like that would be expensive and time consuming. The amount of excavators required to remove that much dirt would be incredible. The wall could at least be manufactured all over the country and shipped to the border for installation allowing much greater coverage in terms of meters per day. Digging a trench of significant size to be meaningful would still require engineering support to maintain the integrity of the wall and potentially require every excavator in the US/Mexico and still take a long time to build."
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a9wygj | Why do air conditioners vent out heat? How do they work? | Engineering | explainlikeimfive | {
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"text": [
"Air conditioners use refrigeration to chill indoor air, taking advantage of a remarkable physical law: When a liquid converts to a gas (in a process called phase conversion), it absorbs heat. Air conditioners exploit this feature of phase conversion by forcing special chemical compounds to evaporate and condense over and over again in a closed system of coils. The compounds involved are refrigerants that have properties enabling them to change at relatively low temperatures. Air conditioners also contain fans that move warm interior air over these cold, refrigerant-filled coils. In fact, central air conditioners have a whole system of ducts designed to funnel air to and from these serpentine, air-chilling coils."
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a9xf6r | why do spanners make a tink sound when dropped on the ground and other tools dont ? | Engineering | explainlikeimfive | {
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"text": [
"A wrench is a solid piece of metal, which can vibrate through itself freely without being dampened by any wood or fiberglass, or secondary piece of metal (as pliers). Is it really the *only* such solid metal tool that will tink? Probably not. But many other tools have fiberglass or multiple parts."
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a9zbvq | Why do ceiling fans have odd numbered blades? Normally I only see them with 3 or 5 blades. | Engineering | explainlikeimfive | {
"a_id": [
"ecnnfxp",
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"text": [
"it’s to do with preventing resonance and increasing air flow. but you can get fans with 2, 4 and even 6 blades. it doesn’t really matter.",
"I looked this up and it just says 5 blade fans are quieter less efficient and 3 blade fans are better but louder. You probably can get 4 blade fans I just don't know where."
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aa02nc | How do refrigerators work? | Engineering | explainlikeimfive | {
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"text": [
"You pass a compressed fluid through an expansion valve. Fluids get colder when they expand. Also, the expansion will cause some evaporation inside the tube. Evaporation absorbs heat which will cause the tube to get even colder. That's the cooling part. To get it to run all the time, you need to complete the cycle. The tube leads to the back end of the fridge where there is a pump/compressor where the fluid re-condenses and releases heat (the tubes on the back of a fridge are warm!). Then the fluid is ready to passed through the expansion valve again."
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aa3y0c | Alloys forged from weak metals becoming stronger | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The individual metals have a very regular atom structure: a metal roster. This in itself is not all that strong, and contains a lot of holes. Alloys have a mixed roster, with smaller and larger atoms together. While still a roster, it is more dense and the gaps between the atoms are smaller. The irregular structure also makes it harder for deformations to propagate through the roster. **Small analogy:** If you build a regular row of same-sized dominoes, one disruption makes the entire row collapse, whether they are small or big dominoes. If you alternate small dominoes with larger ones, a disruption in a single small domino is not strong enough to push over its neighbour big domino. Also a big domino may only push its neighbour small domino aside without pushing over other big dominoes."
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aa4z48 | Airbags! How do they work? | How can they differentiate between fender benders and going over big bumps? I’m wondering more about older cars that didn’t have as many sensors. | Engineering | explainlikeimfive | {
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"text": [
"There were a variety of ways airbags, in older cars, were tripped. The most used method in the 70s (when they were first introduced by big companies) used a ball, tube and tiny computer. The ball would roll around in the tube, and only a rapid deceleration would trip it, meaning a crash or extremely sudden stop. All the airbags in the car were connected to the computer, which was connected to the ball in the tube. Once activated all the airbags would be tripped. In newer models, an electronic sensor is used, which detects the impact at the front and sides of the car. Here’s a video if you are still confused: URL_0"
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aa7kkh | How is gravity calculated for distant planets and moons? | How do we know the gravity for saturn is 107% of earths gravity, or how did we calculate the escape velocity for moon for the Apollo 11 mission. | Engineering | explainlikeimfive | {
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"text": [
"Gravity is the same everywhere, there's the old Newton formula to calculate the gravitational force that depends on the masses of the two objects and the distance (radius) between their centers. There is also a formula for calculating orbital velocity based on the mass of the planet. So if you know the orbital period of a moon, and the distance, you can calculate the gravity of the planet.",
"There are many ways we determine the characteristics of objects in space, depending on what it is. One simple method for smaller objects like asteroids is to estimate their density by using spectometry to identify what they are made of, estimate their size visually, and solve for mass. But the best way is if you can measure the gravitational effect they induce on other objects. For the moon it is extremely precise, because its gravity effects things here on Earth. We know exactly how far away it is, so it is just a matter of measuring the Moons gravitational force here on Earth, and using the inverse square law to solve for the gravitational force on the surface. For Saturn, you just have to measure the velocity of the moons orbiting it and the radius of their orbit. With that you can solve for the force of gravity at that altitude, with which you can again use the inverse square law to solve for force at the \"surface\" (although it doesn't have a surface, because it is just gas, so the figure you read is the force at an arbitrary point in the atmosphere they decided to call the surface)",
"Its actually really easy to figure out the gravity of a planet you can see with a moon orbiting it, you really only need two equations and we'll work backwards and solve for Saturn's mass and gravity using just Saturn's radius, Titan's orbital radius, and Titan's orbital period which are all easy to determine with a big telescope. Titan orbits Saturn at a mean distance of 1.222 mkm which means it's orbit covers a distance of 7.678 mkm in just 15.945 days giving it an average speed of 5.57 km/s(wiki agrees with this number so we haven't messed up yet!) Now for the math! We know that tangential acceleration is equal to v^(2)/r and since Titan isn't flying away that'll equal Saturn's gravity at that distance. (5.57km/s)^(2)/(1.222mkm)= 0.025349 m/s^(2). We also know that gravity falls off with the square of the distance so g1/g2= r2^(2)/r1^2 therefore (g_saturn)/(0.025349 m/s^(2))=(1.222mkm)^(2)/(radius of Saturn)^(2)=(1.222 mkm)^(2)/(60,268 km)^(2). Rearrange to solve for g_saturn and you get 10.42 m/s^2 This less than precise math got us an answer of 10.42 m/s^2 when the truer answer is 10.44 m/s^2. Never needed to use the equation for Universal Gravitation, just needed some measurements of an orbiting body, knowing tangential acceleration, and knowing that gravity falls off with the square of distance(this is the most obscure bit) to figure out the gravity(and potentially the mass and density) of a planet that we can't physically measure We've made very accurate math models of space which lets us determine a lot about celestial objects with just some measurements of distance and time."
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aabwqm | Why are are cars’ 0-60 mph times faster than 5-60 (“rolling start”) times? | My infantile brain tells me that if a car is moving at start, it has a “head start” on accelerating to a given velocity. But Car & Driver tells me I’m wrong. What am I not factoring in? | Engineering | explainlikeimfive | {
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"Its counter-intuitive but you should remember that during a 0-60 time test they aren't pressing the accelerator and revving up when its time to go, they're instead pre-revving the engine to peak power then releasing the clutch so they start moving with full power going to the wheels When you're at 5 mph you're generally in a low gear at near idle RPM, so when you want to get up to 60 MPH you have to floor it and wait while the engine revs up into the peak power range, then you're in a similiar situation to the 0-60 test for the next few gears but you lost a good fraction of a second revving the engine up from 1500 RPM to the 4000-6000 RPM that it needs for full power.",
"For best 0-60 times, a skilled driver typically revs the engine all the way up before releasing the brake and/or clutch."
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aacy7g | - Why do big trucks have one or two pairs of wheels that they don’t use? | With big trucks (8-ish pairs of wheels) it’s common to have a few pairs of wheels “floating” above the ground and not being used. Why do they do that? | Engineering | explainlikeimfive | {
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"It's so they can disperse their load over more axels if there load is to heavy. It floats because it is impractical with lighter or no loads.",
"They are axles that can be dropped down to compensate for extra load. But they need to be lifted for empty driving or for cornering. Generally operated from the cab of the tractor.",
"As my father, who had driven and or worked around trucks for 30 years explains it, it's to meet legal requirements. Ostensibly, the weight of the load is dispersed across all the wheels, and these trucks are designed to work with the two sets of wheels in the back, and two sets at the end of the trailer. But the law says for a given tonnage, there must be so many axles on the ground - presuming the truck manufacturers and logistics companies were going to do the right thing. Nope. Extra wheels means extra cost. So these floating wheels are only employed to meet the legal requirement they typically don't even bear any significant weight. Of course, there are special purpose trucks and trailers that do put weight on more wheels for really heavy loads.",
"They don’t need the tires when it’s not carrying anything. Just gives a little more support when it’s really weighted down",
"If you have two axles that does not steer you will get a lot of sideways force on the rubber when you corner. The further between these axles the more force. This will result in more wear on the tires, harder to corner, longer turning radius and more wear on the ground. So a lot of trucks with lots of axles can lift some of their axles in the air when not needed. This reduces wear on the equipment and makes the truck more nimble.",
"They're called a \"tag axle\" if it's just wheels, \"drop axle\" or \"lift axle\" if it has power or steering. They're mounted on hydraulics or airbags which allow them to be lowered to the ground as needed. The additional wheels increase carrying capacity if needed for a heavy load. When not needed, they're lifted. This increases gas mileage, makes it easier to make tight turns, and puts less wear and tear on the truck. [It's all controlled from the cab, drivers can lift or drop at will.]( URL_0 )"
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aaeioo | Why do so many warships and container ships have a large bulge at the bow below the waterline? | Engineering | explainlikeimfive | {
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"text": [
"If you're referring to [this]( URL_0 ) its called a [Bulbous Bow]( URL_1 ) and is there to reduce the drag on the ship and therefore improve its top speed and fuel efficiency. Normally the bow will create a set of waves as it pushes through the water, but adding the bulge in front creates a second set of waves. If you space the two correctly then the waves will cancel out at the boats cruising speed and significantly reduce the drag on the hull. This is generally only useful for ships that spend most of their time cruising at a specific speed which means its great for cargo ships and warship which will make month long cruises across the Pacific but less useful for a little ferry that cruises back and forth across a little river.",
"The bulge modifies the way the water flows around the bottom of the vessel, creating less drag. This increasing speed, fuel efficiency, range, and overall stability of the vessel."
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aah264 | What is, if any, the relationship between transistor size, power consumption and cost? | A pattern that I've noticed: Midway through the generations of consoles or processors, the companies responsible release a product that is smaller/has smaller transistors, integrates more components into a less units, cost and power usage goes down yet maintains a similar performance to the previous unit. Is there a direct relationship between making it smaller after next-gen technology arrives time and making it more cost-efficient? | Engineering | explainlikeimfive | {
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"Before we hit the current wall* of performance, processors generations would alternate between performance and energy efficiency. For example, a dynacorp 3-series processor would be a LOT more powerful (e.g. 20-50%) than it's predecessor. A year or two later, they'd release a 4-series processor which had performance slightly better than the 3-series, but used less power or put out less heat. Until very recently every time chip makers figured out how to produce smaller transistors, they'd negate the power savings (and then some) by cramming even more transistors onto the same chip. \\* recently, (the last several years) there's been very little that can fully utilize existing processors, so the emphasis has shifted to power efficiency and size rather than power. The big push is to get desktop-grade performance to an efficiency level and size that works in mobile devices.",
"In general, smaller transistors use less power. When you shrink the transistor by 70% in each direction then you only need 70% the voltage to turn it on and it takes up half the area. The lower voltage means less power/heat each time the transistor turns on or off. The smaller transistors means you can fit the same chip into a smaller die which means you get more chips per wafer and have lower fallout. Game consoles are generally running with processors built on older technologies that Intel and AMD already worked all the kinks out of so they can move to a smaller process with far less uncertainty(and engineering effort) than Intel can so those cost savings are a bit more immediate for Microsoft and Sony."
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aaitph | How a battery is able to charge wirelessly | Engineering | explainlikeimfive | {
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"text": [
"To simplify things, let's think of electricity as movement, say, waves. Waves carry a certain energy, which is why a boat will rock if the sea is wavy. Now, imagine our boat. Imagine you have on the boat a bathtub full of water. What will happen to the water in the bathtub, if the boat is rocking about on a wavy sea? If you said the water in the bathtub will be bouncing around, you guessed it right! But how? The bathtub isn't touching the sea! Easy: the movement of the waves goes through the boat, and shakes everything, including the water in the tub. The same thing with the wireless charger - it creates a sea of electric waves that rock about everything in a small area around the charger, but only the battery contains material that can become wavey (like the water in the tub), so these electric waves only manifest in the battery as charge, and not in the plastic around it (the boat).",
"[How does it work?]( URL_0 ) > Wireless charging works by transferring energy from the charger to a receiver in the back of the phone via electromagnetic induction. The charger uses an induction coil to create an alternating electromagnetic field, which the receiver coil in the phone converts back into electricity to be fed into the battery."
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aanblv | Why can’t normal airplanes go to space? | I saw that our atmosphere is ~300 miles in depth. Normal airplanes can fly much farther than that so why can’t they just fly straight up for 300 miles at a slower speed than a space rocket? Or why not a supersonic jet? There’s something I’m not thinking about. Edit: Thanks for all the info everyone! I knew ELI5 would know the answer! | Engineering | explainlikeimfive | {
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"Consider, why can't a swimmer swim into the sky? Because there is no water in the sky, and the water is what supports the swimmer. Airplanes \"swim\" through the air. The air is what supports them. So they can't fly somewhere without air.",
"Their engines rely on the oxygen in the air to let them burn fuel and their wings require air to generate lift. As they get higher and higher the air gets thinner and thinner which means their engines generate less thrust and their wings generate less lift until they reach a point where they can't make it any higher. Around 100km up a plane would have to be traveling at orbital velocities(thousands of meters per second) in order for their wings to generate enough lift to keep them airborne, but since most planes can't get much above 300 m/s they can't get close to that high. We've made some rocket planes that can go up that high, but that's because they carry the oxygen their engine needs with them so the thin air poses less of an issue.",
"The way jet engines works has been explained, but you also asked why they can't just go straight up. Let's imagine a rocket that goes straight up into space and runs out of fuel. Once it's there, what happens to it? Gravity from Earth still effects it, in fact, it's still very strong at a mere 300 miles up. So it just falls back down to Earth. How do things stay in space without crashing back down to Earth, or in other words, stay in orbit? We not only need to go up, we also needs to go sideways to orbit the Earth. When an object is in orbit it is still effected by gravity. In fact, without gravity it would not be possible to orbit anything. Our rocket needs to go fast enough that as it falls it keeps missing the Earth. If you do this at the correct altitude and velocity you'll orbit the Earth instead of crashing into it. Orbiting is a lot harder than it sounds, it's also counter intuitive. You're in orbit in your rocket, and just a few kilometers ahead of you is a space station you want to dock at. You're going at the same velocity as it, so to catch up you turn your engines on...and now you're going away from it!? But you're pointing right at the space station, why are you going away from it? Simple, by increasing your velocity in the direction you are traveling you go into a higher orbit, and as you go higher in your orbit it will take longer to orbit the Earth. To catch up to the space station you actually need to point away from it and turn your engines on to lower your orbit. You'll orbit the Earth faster than the space station. You'll then need to pass it up before going back up so you can meet it. If you want to find out more about orbital mechanics there's a game called Kerbal Space Program that will teach you everything you want to know.",
"Saying that the atmosphere is 300 miles deep is very misleading. Two third of the atmosphere is bellow the summit of Mount Everest. The higher you get the less atmosphere there is. It is a matter of definition where the atmosphere ends and empty space begin. It just gets thinner and thinner the higher you get. Aircrafts need atmosphere to fly and if they go too high the atmosphere becomes too thin and they will no longer be able to generate thrust from their engines and lift from their wings. Different aircraft can climb to different altitudes. The experimental X-15 were able to go over 100km but were unable to stay up there for more then a few minutes. Similar with the current SpaceShip Two aircraft. The SR-71 and Mig-21 aircrafts were reportidly able to sustain flight at 25km by flying several times faster then the speed of sound and using specially designed engines built with exotic materials.",
"As you go higher in the atmosphere the air gets thinner. Even at the orbital altitude of the International Space Station there’s enough atmosphere that the station has to be boosted up several kilometers every once in a while due to drag. If you can fly straight ahead for 300km at an altitude of 10km, which is where most planes fly you can sustain flight and counteract gravity with only 25% of the atmosphere at ground level. If you want to double your altitude from 10km your plane would have to be **4 times** more efficient, when most planes are barley able to stay in the air at 10km. To reach space you would need a plane that can sustain flight with **100 times** more efficiency than an airliner, and on top of that it would need to be 70 times better at producing thrust (as atmospheric oxygen makes up roughly 70% of your burning fuel’s mass) in addition to generating the required lift to counteract gravity 100 times better. Simply put for an airliner to make it to what we recognize as the boundary of space it would have to be **7000 times** better at flying than it is at normal cruising altitude per unit of mass. Which based on current airliner designs and performance envelopes would mean it would have to have a range at normal cruising altitude of about 80 million kilometers without refueling. This is way beyond what can be done."
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aav1k3 | Why do cars have gears? | Hey. Was just wondering, why do cars have gears? Why not just simply accelare and brake? Please, keep in mind Im no engineer. Thanks in advance! | Engineering | explainlikeimfive | {
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"The gearbox translates the speed of the engine (rpm), into the speed of the wheels (mph). As you rev the engine higher, the wheels will spin faster, but once you reached the highest rpm of the engine (known as the redline), the wheels cant spin any faster because the engine can't go any faster. Because an engine has a lot of torque and power, you can translate the relatively slow rotation speed of the engine into faster and faster wheel speeds! This is why you change up through gears when you're going faster and faster; it keeps the engine at a manageable speed whilst keeping the wheels turning at the right rate for the road speed! Hope this helped, gearbox and engine mechanics are fascinating rabbit holes to go down! Edit: Format... Mobile reddit sucks for paragraphing!"
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ab11it | If nuclear submarine fuel lasts 20+ years, why can't we use this technology to power cities? | Engineering | explainlikeimfive | {
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"We do. A nuclear sub contains a nuclear power plant which is more or less a very small version of the same types of nuclear power which we do use to power cities. However, even over 20 years, the amount of energy needed to power a sub is quite small compared to the amount of energy needed to power a city, as such, the nuclear material of a power plant generally lasts only about an year and a half before needing to be refueled, and of course there is way more of it, producing way more power.",
"Nuclear plants do exist, but keep in mind cities are much larger than a single submarine. There are lots of costs and risks associated with nuclear power, and some people aren’t comfortable with it enough to gain widespread adoption. It’s an extremely efficient fuel source, but the word “nuclear” scares a lot of people.",
"We do use nuclear power plants to power cities. However, they have experienced some popularity issues due to a few high profile incidents like Fukashima and Chernobyl.",
"I think there is one huge thing overlooked so far. We don't send the folks down on nuclear powered subs because there is a shortage of housing on base. We do it because they have an extremely important mission, and we are willing to piss away vast amounts of money to accomplish that mission, and compact nuclear reactors are the only feasible way to do so. In addition to the money, they are also willing to take risks that we would not take in the civilian world. As already said, we do have nuclear power plants that power cities using fission chain reactions, same as submarine reactors do. But I don't know if I would call a gigantic fixed land-based power plant the same \"this technology\" as a compact portable reactor is. A sizeable fraction of the crew of a sub works in the power plant. What fraction of your city works down at the power plant?"
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ab1ags | how was the ISS assembled? And how are repairs and maintenance performed in the event of a collision with space debris? | Engineering | explainlikeimfive | {
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"The ISS was assembled by flying it to space in pieces and assembling it later with robot arms. The solar Panels were just unfolded like a piece of paper by motors. Repairs are done by performing a spacewalk if necessary. Some maintenance can be done from the inside. In some cases the damage to parts is accounted for in beforehand so you only need maintenance very rarely."
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ab1hcx | how do really big dams get built? | As in, how do they deal with the water if the dam hasn't been built yet | Engineering | explainlikeimfive | {
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"They divert the river to go around the construction site. The most common way to do that is they build diversion channels around the side of the normal riverbed and then dump dirt into the river to build what's called a cofferdam. This temporary earth dam will hold back the water and force it to go through the diversion channels. Now that the construction site is dry they can build the permanent dam a little ways downriver. When that dam is complete they remove the cofferdam and plug up the diversion channels.",
"They divert the water somewhere upstream into artificial channels to go around the dam site.",
"OP, [this engineering series]( URL_0 ) helped me to understand stuff like how dams are built when I was in elementary school. Even as an adult I highly recommend it. Pro tip: there are additional episodes about other things such as domes, skyscrapers and bridges. Edit: Skip to 16:39 for the answer to OP’s question."
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ab1zsu | Why are bolt-action rifles still manufactured/bought when semi-automatic rifles exist? | Engineering | explainlikeimfive | {
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"Bolt action rifles are inherently more accurate, easier and cheaper to manufacture, far more reliable, and may be subject to fewer regulations or restrictions based on local law.",
"Bolt action is simpler and, with fewer things moving around, can be more accurate. They also tend to feed ammunition a little more reliably meaning a wider variety can be used. Mechanical simplicity can mean lower cost and greater durability.",
"I work in manufacturing and in firearms industry. And have done some competitive shooting. The more basic/simple the design the cheaper it is to make. So dollar for dollar you can make a more accurate long range rifle as a bolt action. Reducing variables reduce failure/wear points. I have very accurate semi auto rifles that will beat most bolt action guns without question, but are way more costly. Generally if you are hunting you're not planning on many shots, just one good one, so a bolt action is going to work well for you. This is very generally and you'll find many gun guys could go on for hours about many more points to consider. However your main question is why do they exist, it's because they fit the intended use the best. I build derringers, 2 shot break neck pistols that fit in your palm. Little to no functional difference to how they were made over 150 years ago. How else can you buy a brand new easy to conceal firearm for 100usd? They're not accurate and terribly slow to reload, however having something easily at hand that let's an intruder/thug/rappist/etc... know you have means and are ready to fight back is why many people still buy these guns.",
"Easier to clean, get less dirty, hand re-loaded ammunition shells can be tighter tolerances (since you are using your hand to pull out the rounds versus using gas/blowback reactions). If you use a form-fitted round (previously fired and expanded to \\*perfectly\\* fit your chamber, it's pretty tightly in there, and a semi-automatic will sometimes not have the force to eject the form-fitted brass casing after firing.",
"Bolt action rifles are more accurate and more reliable than semi-autos. They have less moving parts to break and have less variation in between shots to make them more accurate. They are very popular with hunters and sport shooters for these reasons. They also tend to be much cheaper than semi-autos; guns are very expensive so price can dictate what people buy. The reason why I like bolt actions is they are very fun to shoot. Manually cycling the gun after every shot makes shooting more involved and fun. Same reason why many people still drive manual transition cars, being more involved with the function is more fun sometimes.",
"Accuracy, the lock up is much tighter . This is why you see so many long range bolt action rifles",
"/r/guns has a good explanation that I cant seem to find but basically the tolerances are tighter on a bolt action rifle than a semi auto rifle. From personal experience shooting my ar and bolt gun I can say some of it is mental. With my ar I know I can take a follow up shot quickly and without taking my face off the rifle or moving my hands so I tend to not focus on the fundamentals as much and speed up shots.",
"I'm not a gun scientist but I do know the mechanism is more robust yet simple and reliable and less prone to jamming and tend to be higher power than semi automatic. Semis use the force of the previous round to load to chamber the next round and as such there's always a small chance of a jam. Bolt actions are loaded manually so there's less chance of a jam. Moreover, it requires more skill and dexterity to reload a bolt action, and I believe you get more power since some of the kinetic energy isn't being redirected to be used to chambet the next round. It's sort of like how people drive manual transmission even though automatic transmission exists, or how some men use straight razors when gilettes or electric razors exist.",
"One important factor that I haven't seen mentioned in a top comment is safety. I have, for years, taught children and youth how to shoot. Most often with pellet rifles, but also with rimfire and centerfire firearms. In early lessons, I want to know, with *absolute certainty*, that they have exactly one round to fire, and with a bolt- or breach-action I can see immediately how many rounds they have. I hear their single shot, I can see that the action is open and empty, we're good. Have I ever let a child shoot something with more than 1 round? Sure, SKSs are pinned for 5 rounds in Canada, and if a youth is well versed with firearm safety, I'm certainly capable of counting to 5. .22s? Sure, we might plink away at targets, but again, safety and training first. In the past decade I've yet to have a near-miss greater than a child accidentally pointing the barrel of an open breachfire pellet rifle at me. Adults on the other hand are bad listeners and don't always realize how serious it is to point a gun at somebody, even if it's apparently unloaded. I have the scar from a hole in my left hand as proof of that.",
"I'll go ahead and add \"pure fun\" to the list of valid explanations here. Racking a bolt and firing in one smooth motion is satisfying as all fuck.",
"Bolt action rifles are much less complex than semi automatics for starters because they have much fewer moving parts. They can be broken down and cleaned much easier than a semi and are much less prone to breaking as there isn’t anything to break. Additionally, with a bolt action rifle you don’t experience jamming like you can/will on a semiautomatic. This can be from the shell failing to eject properly or a new round not cycling correctly etc. Thirdly, on a bolt action, when you fire all the recoil goes straight back into your shoulder. On a semi auto, there is recoil from the firing of the round, from the bolt hitting the buffer, and from the bolt cycling forward again which can lead to your next shot being inaccurate. But the main reason is the simplicity and reliability of a bolt action compared to a semi auto.",
"Weight is also a factor. More parts=more weight, when youre hunting do you want an extra pound to carry?",
"Bolt actions are around cause they are going to be lighter than a semi automatic rifle do to you are cycling the action. And significantly cheaper to make accurate.",
"Simple design, and a different shooting experience. I enjoy semi-auto but I also enjoy Bolt actions. Further Bolt action is far far better to teach someone how to handle and fire a weapon as it forces thought between every shot. I am currently teaching my children about guns and as such I bought a bolt action .22LR. I don't want someone learning how to shoot a gun to be able to accidentally squeeze off multiple shots.",
"I don't understand people replying \"less moving parts means it's more accurate,\" how? I'm not saying that it's wrong, but how does that actually work out? Accurate to longer distances, sure, because you're not spending any propelling gasses to cycle the action, but at intermediate ranges, I simply don't see how less moving parts is better. Especially because on rifles like the AR-15, or AK-47, where bolts are returned home by a spring, the said spring absorbs some of the recoil, allowing for more accuracy by the shooter. Someone please explain."
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ab3rqo | Why do some wheelchairs have the top of the rear wheels angled toward the user and not parallel to the chair? | Engineering | explainlikeimfive | {
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"This is a way to increase the footprint of the base of the chair. It will increase the stability of the chair and increase the ability to turn sharply. It also decreases the amount of the wheel on the ground and reduces the drag of the wheel.",
"In sports most wheelchairs are like that. It prevents fingers or hands from being crushed when the wheels come together in sports like wheelchair basketball because the bottom of the wheel is always gonna come into contact with the other wheelchair first."
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ab9wzk | Why are PCs so much better than Macs for gaming? | Engineering | explainlikeimfive | {
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"It's a big chick-and-the-egg situation: nobody develops high profile games for OSX as few play games there, and nobody makes hardware running OSX that is powerful for running games. Apple doesn't include powerful graphics processors on their laptops because that's not their target market.",
"For a long time, Apple used completely proprietary hardware. This meant you'd have to re-develop half the game all over again if you wanted to release it of Mac. The market share of Macs is far smaller than PCs, so game developers release for the more popular platform first, as it nets them more money. Nowadays Apple uses the same hardware as PCs, but the OS is still different, so a fair amount of redevelopment still is required, and the market share argument still applies. Think of it this way: anything that requires interfacing with hardware must go through the OS, and each OS is entirely different. That means you have to redevelop the entire engine for each OS, and depending on how you've architected your code, you may also need to redevelop major portions of the game as well."
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abca43 | How are big firework shows (NYE, Independence Day, etc) implemented? Obviously, there are no trial runs before the big show, so how do they know how it will look like, and guarantee that everything is in place and will work as intended? | Happy new year everyone! | Engineering | explainlikeimfive | {
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"The expense of a massive, nationally-televised fireworks display buys a lot of professional experience, reliable technology, and redundancy. Just like surgeons don't \"practice\" surgery on a patient before they cut them open, but they don't need to. They've done it so many times that they're prepared for any eventuality. Any highly-skilled professional brings the same skillset to their job. Also, in many cases, you won't know if something did go wrong. Let's say that eight fireworks pop instead of ten for a given frame. Well, that's okay, because you won't likely miss the other two. It's like if a politican skips a line in a speech, you probably wouldn't know unless they react to their own mistake. The devices are also pretty reliable, provided they're dry and high-quality. Experts know how they work down to the grain. Finally, unit tests help. By ensuring that each charge fires as expected in isolated shots (probably in isolated areas, too) these guys make sure everything will go according to plan.",
"Shows are scripted. This requires knowledge of all the types of fireworks being used and the effects they create. Shows can be tailored to music as well using these scripts. Launchers are staged with all the fireworks loaded (this takes hours in advance). Fuses are wired with igniters and wired to firing boxes or possibly electronic firing systems. Connections between the firing controls and the fireworks are tested for continuity before the show starts. When the show starts, the launching can be done by computer, or by manually pushing buttons, or using wands to complete circuits. In the manual version someone can be standing by with the script and a stopwatch and working with another person to launch one or more sets in time with the script. Source - I helped do the 2007 New York Marathon Fireworks display.",
"They test individual components separately; the confetti, the rockets, the crystal ball, etc. They may do this repeatedly. For instance, there's the... Magnellan telescope. If it breaks, they can't fix it, and it already costs some 30 billion dollars. they test it. Repeatedly.",
"My hometown used to host the pyrotechnic guild of America’s convention so... hooray free fireworks! What wasn’t so good was the guys being out on a barge firing fireworks off until 4am because no one supposedly could get a hold of them to tell them to stop :) And on errors, one year, the fireworks all got set off at once. Some timing error obv. For ten minutes, it was like WWI artillery barrages. And then... silence. :)"
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7ugcdg | The ultra cool treehouses people build to actually live in- do they require constant upkeep? Because the trees are always growing wouldn’t you have to constantly be adjusting the house? I want one bad but not sure I have the know how to keep it up. | Engineering | explainlikeimfive | {
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"I'm sure some of those treehouses fall into disrepair for that very reason, but if done professionally, they can be accounted for. Not all tree's grow indefinitely, there is a maturation point where the available resources equilibrate that halts further 'growth'. Knowing which tree to build on is researchable. There are also building techniques that allow certain places to expand, walls secured in non-competing places can displace in a single direction--similar to how bridges are given enough freedom of movement to avoid collapse without hindering the structural integrity."
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7uk406 | - why do large trucks, busses etc. have larger steering wheels than smaller vehicles? | Engineering | explainlikeimfive | {
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"When there's more weight resting on the wheels, they are harder to turn. Having a larger steering wheel makes that easier to overcome. Even though pretty much all vehicles now have power steering, you still need to be able to steer the vehicle in case of a failure, so they still have large wheels in spite of this.",
"Leverage. The longer the lever, the more force you can apply. Steering wheel is applying force to turn the steering column. Bigger wheel =more force. You need that force if power steering fails or is not exist on the bus. A consumer driven vehicle has 2000-3000 lbs downwards force on the front wheels. A truck or bus has maybe 5000-10000lbs on the front wheels"
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7utrbi | How much energy can wind power stations produce? | I have found some facts, it can make about 600 KW. How to understand these numbers. Is it KW/hour or per year... ? How many people are able to use energy from 1 wind power station? | Engineering | explainlikeimfive | {
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"Kilowatts is a measure of power (that is, energy over time), so it's already time-based. If it can produce 600 kW, that means it can produce 600 kilojoules per second. The \"average\" home (the kind where they say \"this is enough to power X homes\") uses 1 kW, so a 600 kW power station could power around 600 homes."
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7uuah2 | How are goods efficiently taken out of ISO containers at ports and put into semi-trucks? | I hear a lot about how ISO containers have revolutionized international transportation of goods, allowing goods to stay in one container for many legs of journey. Why do semi-trucks in the USA use their own containers instead of hauling ISO containers? It seems really inefficient to have to unload hundreds of boxes from an ISO container into the back of a semi truck for every ISO container reaching the US. How are goods cheaply taken out of ISO containers at the ports to be packed into the back of a semi-truck? | Engineering | explainlikeimfive | {
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"ISO containers are also known as \"intermodal containers\". Intermodal containers are *designed* to be moved from ships to trucks and trains - that's literally what the name means. They're not unloaded at the ports onto trucks.",
"The ISO containers are not unpacked at the ports. They are sent by rail or semi with a chassis trailer to the purchasers warehouse. The purchaser then unloads the container at their warehouse and adds the contents to their inventory. This inventory is then dispersed to the local retail outlet or other warehouses by the typical semi you see on the street.",
"They aren't unloaded in the ports... the shipping containers fit onto a flat frame connected to the semi tractor, turning it into a semi trailer. [LIKE THIS]( URL_0 ). They are then driven to warehouses or distribution centers away from the port for unloading and warehousing or distribution."
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7v15fs | Why are cars seldom offered with diesel-hybrid powertrains? | Engineering | explainlikeimfive | {
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"There's a few reasons at play here. I think first and foremost is the fact that both diesel motors and electric motors both give lots of bottom end torque, as opposed to a petrol engine that gives top end torque. Normally with a petrol hyrbid you will have the electric motor dealing with the low end power, then the petrol engine kicks. With a diesel hybrid you would end up with lots of bottom end torque, but nothing at the top end. There's also the problem that diesel engines are usually more expensive to manufacture. Now bolt a few thousand pound elecric motor onto it and you're making a much more expensive car. The fuel savings will have to be much greater to now account for the increase in purchase price. Petrol cars also have the benefit of having much lower emissions to begin with, which can be made even lower with the addition of an electric motor. A diesel engine with an electric motor may only be brought down to the emission levels of a very good petrol engine. There are a few diesel hybrids I know of offered here in the UK. Mercedes offer a Bluetec hybrid, and Citroen offer their e-HDI engines which are a diesel hybrid which I know is used on the DS5, maybe others as well."
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7v1acv | How does a truck emergency break work? How can it stop so fast? | I was watching [this video] ( URL_0 ) and I was wondering, how in the hell the truck goes from full speed to 0 so fast? | Engineering | explainlikeimfive | {
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"If you're talking about large trucks or buses, they use an air brake system. The \"Emergency Brake\" is also the parking brake on most of the large vehicles you see with air brakes as opposed to hydraulic ones. Air brake systems have both an active and passive system- the regular braking system used in normal operation and the \"spring brake\". The system works by building up air in a tank fed by an air compressor (there's other parts but those are the basic elements) and when it has a full load of compressed air (90-150 psi in most buses, not sure about large trucks) you can press the foot brake, which uses some of that compressed air to send power to the brakes at the wheels, thereby slowing the vehicle. The spring brakes are the opposite- they're *always* pushing, using- you guessed it- big springs. When the system charges with air and the parking brake is released, the air pressure in the system overcomes the springs and holds them back, allowing normal operation. When you pull the parking/emergency brake, it removes air from the lines and the spring brakes clamp on. If you have an air leak, the system is also designed that if pressure drops too low, the emergency/parking brake will snap on automatically (usually around 40 psi in a bus), thereby forcing the vehicle to stop. The parking/emergency brakes are very powerful but won't stop a bus in a four-wheel slide. It's more of a very hard braking action. Same thing when you press the foot brake hard enough- you can put a *lot* of pressure to the brakes. However, this is not a good idea to do often- the brakes heat up fast and if they get too hot you'll lose braking power. Drivers of air-brake equipped vehicles require special training and certification in order to operate them under US law. Edit: The action shown in the video is due to several factors: * Well-adjusted braking systems. * An alert and very well-trained driver. * Probable lighter load than normal. * Optimal road conditions for a rapid stop.",
"Trucks use a different braking system than cars. Most use an air system that releases pressure on the breaks when the pedal is depressed. The release in pressure allows strong springs to push pads or shoes against a drum or caliber creating mass friction and slowing or stoping the wheel from spinning. Each wheel, including the trailer, have brakes which helps reduce speed. Heavy loads also help to stop rather than light loads, by creating more force to help the tire grab the ground below. The more tires, the more stopping friction there is.",
"The following is true in some but not all cases. For example if the road has something on it like ice, water, oil that forms a thin layer between the tires and road. It is much easier to drive my 5000 pound bus on ice than my toyota. However in the case of a solid nondeformable smooth surface extra mass linearly scales with force of friction and thus cancels out the mass that linearly scales in the inertial term. The equation is [F^(friction)=μ⋅N]( URL_3 ) where F^(friction), is the force of friction exerted by each surface on the other. It is parallel to the surface, in a direction opposite to the net applied force. μ, is the coefficient of friction, which is an empirical property of the contacting materials, N, is the normal force exerted by each surface on the other, directed perpendicular (normal) to the surface. N = mg In this equation, N refers to the normal force, m refers to the object's mass, and g refers to the acceleration of gravity. For an object sitting on a flat surface. The force required to stop the truck on a flat surface is F^(stop) = m⋅a m is mass and a is the acceleration. Because we want to stop as quickly as possible we want to maximise a, but F^(stop) must be ≤ F^(friction). So we can say that they are equal at the best possible stopping distance. so we combine them to get μ⋅(m⋅g)=m⋅a, dividing both sides by m and rearranging we get a = μ⋅g notice that the mass of the truck canceled out perfectly. When you are dealing with a decline the Normal force is equal to [N =mg⋅cos( θ )]( URL_1 ) The force to stop while going down hill is higher because gravity is pulling you down hill so you must counter that acceleration with even more force in the opposite direction. here is a neat little video that explains the trig needed to calculate the [Inclined plane force components]( URL_0 ). F^(gravity) = m⋅g ⋅ sin(θ) So we combine this to get F^(stop) = (ma)+(m⋅g ⋅ sin(θ)) once again we set F^(stop) to = F^(friction) and get μ⋅(mg⋅cos( θ )) = (ma)+(m⋅g ⋅ sin(θ)) or simply a= (μ⋅(mg⋅cos( θ )) - (m⋅g ⋅ sin(θ)))/m once more magicly the mass variable cancels out. I made this [google sheet]( URL_2 ) with all the math and a few graphs and such. Please keep in mind that this all assumes the braking system was properly designed and maintained so it can absorb the kinetic energy required to perform a perfect static braking maneuver. Namely applying the maximum breaking force without slipping, on perfectly clean smooth dry concrete. Perfect trucks driven by perfect drivers, on perfect roads don't exist. TLDR - the mass of a truck does not affect braking time or distance under ideal conditions.",
"Even though I read the title I still thought this was /r/watchpeopledie material until it was over.",
"This truck did not have such brakes, it was simply the driver's reaction time that saved that kid"
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"http://thecraftycanvas.com/library/files/2013/02/free-body-force-diagram-block-on-frictionless-incline.png",
"https://docs.google.com/spreadsheets/d/10jnT_xdBlavyKafyjlcL832WeF0W2o98UK-Uua0dI6w/edit?usp=sharing",
"https://www.wikiwand.com/en/Friction"
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7v7uc7 | How are signals transmitted into a rotating thing. Like helicopter or tire | Engineering | explainlikeimfive | {
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"OK, so this is the rotor head of a UH-60 helicopter. I can tell you for a fact that wires you see in the pic are for the de-iceing system for the blades and droop stop system. These don't transmit any radio but push electricity to heater mats under the surface of the blade. this is done via a rotator stator with a brush system. The brushes drag across a plate to transmit the power. The system is disassembled and rebuilt every 960 flight hour(used to be 720 hr) to correct wear and erosion of the material. 17 years Army Aviation, 14 working on Blackhawks specific, last 4 doing phases (480 and 960 hour inspections)",
"Tire communication is wireless. Inthe picture I would assume with a slip ring. This is also the case in cars with buttons in the steering wheel. Basically you have the same as a 3.5 mm cable for your headphone in the phone. You can spin the plug and still listen to your music. Edit: some people pointed out that in cars steering wheels indeed clocks prings are also commonly used.",
"The answer is \"all of the above\". Some systems, especially those needing to transmit a lot of power, will use slip rings, which are carbon brushes contacting copper rings. Some systems will use induction. VCRs used that to get the video signal off the spinning drum with the video heads in it. Many types of motors and generators work that way too, of course. For the pressure sensors in tires, they are battery powered and send the information via a radio transmission. That's for the \"direct TPMS\". The indirect TPMS systems do not have any sensors inside the tires anyway.",
"Hey I know that thing all to well. That's specifically the rotor head and swashplate / pcr set from a Sikorsky H-60 helicopter. The only mechanical effect transmitted through the wires is the lockpin puller assembly condition and the drive motors for fold/spread operation. You can see all harnesses emerge through the beanie on top. Along with the puller status / spread/fold condition there is a separate harness to drive a heater mechanism for blade de-ice in cold weather conditions. There's only one blade heated at a time, cyclically typically. All of this info is transmitted down the bellcrank shaft at different frequencies to a computer. Not every harness you see in here is electrical. There are 4 hydraulic lines in the photo as well that serve to prevent blade hunting which is the forward and aft motion of the blade as it cuts through the air. That is also managed just below the top beanie plate, above the bell crank and is, for the most part an non-managed system - as in it manages itself. Then again, all collective pitch and cyclic motion is transmitted mechanically through the bridge (not pictured) which manipulates the blades directly through the swashplate (the bottom circle object) and the 4 pitch control rods that provide angle of attack control to the blades. Ah helicopters, they're scary. Especially when the spinny bit gets separated from the non- spinny bit. Just keep in mind, these things have a single hand tightened nut holding the spinny and non-spinny bits together.",
"[This might help.]( URL_0 ) I used to wonder the same thing, but in a simpler example: how do they make front brakes for BMX bikes that allow the handlebars to be spun around without tangling up the brake cable? Of course, that's not exactly how it works for electrical cables, but same principle: two rings allow cables to run along spinning things.",
"Tpms systems (tire pressure monitoring systems) use a battery powered sensor inside the wheel of the tire to send the information wirelessly to a receiver in the vehicle. Also some vehicles will use the wheel speed sensors (abs) to sense a change in the diameter of the tire (one going flat), then trigger the warning light."
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7vbll9 | Can smartphone companies make a better phone than what they release? Do they really make the best phone they can make or do they not give it their all so they have something new to release the year after? | Engineering | explainlikeimfive | {
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"In any project or manufacturing situation, you can always make a \"better\" product. However, it will likely cost more, and/or take longer to make. Your goal is not to make a \"better\" product, its to make a product that is the right quality, right goodness, right price, and right time for release."
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7vf6te | How does traction control and ABS help you when driving in the snow? | I'm not entirely sure of the difference between the two and how they work. | Engineering | explainlikeimfive | {
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"ABS releases and reapplies the brakes rapidly to prevent/minimize skidding (tires work better if not skidding, so it makes you stop shorter). Traction control usually does two things. It cuts the throttle when acceleration causes skidding (again, tires work better when not sliding, so it improves performance). It will also typically independently apply brakes to prevent spinning (if your front tires are sliding you can't steer, if you're sliding sideways the brakes and gas are both unable to point the car forwards). Traction control will typically apply brakes on one side or on opposite corners to steer the car while letting off the gas, typically keeping the car pointing when you're steering, even without if you're going so fast that the back starts to fishtail away from you.",
"Traction control controls how much force is applied to each individual wheel, helping keep stable in curves (where wheels have different speeds) and wherever one or more wheels are off the ground. ABS servers simply to \"vibrate\" the breaks, breaking and letting go of them about 10 times a second to prevent the wheel from locking (which essentially turns it into a ski) Edit: numbers"
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7vgi58 | How does a phone's (specifically an IPhone) cooling system work? Since it's a smaller computer, is it essentially the same? | Engineering | explainlikeimfive | {
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"Phones are designed to utilize passive cooling only. That being, they do not generate enough heat through standard operation to require a fan. This is due to the size, power, and space required for fans and various failure points introduced by them - and also any CPU that generated enough heat to require active cooling would not be usable as a mobile device as it would drain the battery very quickly. Since you mentioned the iPhone in particular, the most powerful iPhone's (iPhone X) CPU is the A11, I can't find exact specs on this but the power usage of the CPU is likely in the 5-10 watt range. For comparison, processors in laptops are usually in the 25-45W range (on the low end, these may not need active cooling to cool) and desktop processors tend to range anywhere from 65W to 85W+.",
"not quite, there are no fans in a phone (any phone to my knowledge), they have to use passive cooling. some have a heatpipe to distribute the heat around a little bit. ultimately the heat just dissipates through the case."
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7vl1ue | Do foundations in the ground weaken overtime in buildings? | Hi, Just wondering do the various types of foundations used in constructing a house/skyscraper (e.g. pile foundation), weaken over time as there must be presence of e.g. water or other chemicals within the ground that may react with the concrete foundations? | Engineering | explainlikeimfive | {
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"It really depends on the kind of foundation. There's an entire field of engineering dedicated to answering this sort of question, called Geotechnical Science. Skyscrapers usually stand on a foundation that rests on steel piles. Piles are giant tubes that are literally hammered into the ground until they hit bedrock. Then they hammer them down some more until the bottom of the pipe gets gnarled up so you can't pull it out. The pipe itself is made with a thick layer of rust on the outside. Normally rust is bad, but it turns out of you cover a steel thing in rust, it's the ultimate anti-rust paint. Water and stuff underground can't rust your steel if you rust it first."
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7vormv | Why do some old or tall buildings have black stains on the exterior near the top? | When I went to Brazil, I saw many apartment blocks like this. I doubt it's mould because it looked nothing like mould and I've never had a clear answer about it. Edit: Added Imgur link of what I mean URL_0 | Engineering | explainlikeimfive | {
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"Where I'm from it happens to a lot of older buildings made of Limestone. It's acid from rain slowly reacting with the Calcite in the Limestone. Here's a site that explains it: URL_0 If it's the same building materials there, then that would explain it. If not, then I have no idea.",
"I live in brazil and grew up in a small, old town that looks exactly like the one in your picture. My own house was pretty similar to those in the background. So the thing is: that’s dirt. Nothing more than that. Dirt from years, sometimes even decades, because no one would actually bother cleaning/washing that high of a building. Too much of a trouble. That’s why newly builded/painted buildings don’t have it. Part of that dirt is a dark greenish kind of algae that grows in wet spots - we call it limo. That’s the reason why the dirt concentrates under those embossed decorations: after raining, those are the spots that won’t receive direct sunlight and thus will remain wet, allowing the limo to grow up in the humid, fresh environment.",
"Tar washing from the waterproofing on the roof onto the sides during rain?",
"Any coal power plants in your area? Could be from that.",
"Others have mentioned pollution both from the air and the building materials which is true. It is often also from moisture, which is causing mold growth. Since the tops of buildings often have decorative overhangs that will get wet, but not dry out fast enough because of shadows. In addition the sun provides UV which will kill the bateria that causes the mold, so again if its shady the sun cannot 'bleach' it.",
"The bot has removed my comment from your post however I provided you with the simplest, clearest answer. I will expand upon my comment in the hope that you might be able to see this. URL_0 I believe what you are referring to is \"patina\", when small chemical reactions occur on the exterior surface of a material that's exposed to air, rain or pollution. Essentially meaning the material is weathering. This effect is especially evident with metals and stone-based materials. URL_1 \"As concrete is porous, moisture can penetrate slightly into the surface causing tiny chemical changes and crystallizations, creating evidence of age and weathering, and further hardening its surface.\" This patina is usually visible on older stone buildings or even more recent post-modernist buildings such as those of the Brutalist movement. See below: URL_2",
"Maybe you should include a picture that actually shows what you're talking about. The buildings in the picture you link to are too far away to tell, and the one in the foreground is a pristine white."
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"https://paloform.com/paloform/the-beauty-of-age-concrete-and-patina/",
"https://media.architecturaldigest.com/photos/56aac8d75cd8c4e42b99e298/4:3/w_768/brutalist-architecture-masterpieces01.jpg"
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7vxnlq | What are the benefits of having 9,10, or even 11 gears in an automatic transmission? | Engineering | explainlikeimfive | {
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"Internal combustion engines don't provide power equally throughout their RPM range; there are certain RPM values that produce optimal torque. By having more gears, you can be in your optimal power band through more of the typical speeds. Similarly, lower RPMs means lower gas consumption, so rather than revving up to 3-4k RPMs you can go between 800 and 1200 and then shift into a slightly higher gear that puts you back at 800. Trucks (semi, not pickups) have had huge gearboxes with a dozen gears in various combinations for a while, but most commuters don't want to deal with that level of shifting for everyday driving, so before automatics were a thing, they had the 3-speed and 4-speed and 5-speeds as pretty standard for a passenger vehicle, but then automatics became a thing, and got better, and now we can fit 11 gears in them so we do, because gearing advantage is worth it and the costs are low enough now that it doesn't drastically spike the price of the car."
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7w01yp | How can the thermometer on a car give the temperature without being affected by wind from driving? | Engineering | explainlikeimfive | {
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"Wind chill is specific to humans and animals trying to maintain body temperature. It doesn't actually mean the temperature is lower, only that you feel as cold as if the temperature were that low in still air. This is because moving air carries heat away more effectively than still air. So thermometers are not affected by wind chill. In fact there's an opposing effect that very fast vehicles (we're talking Concordes and SR71s here) whereby moving very quickly through air causes you to heat up. Cars aren't fast enough for this to be a noticeable effect. In fact moving air helps car temperatures be more accurate. A car sitting in the hot sun will show a temperature that's substantially higher than the surrounding air temperature but, once you start driving along for a few minutes, the moving air will make the car thermometer accurate again.",
"wind doesnt effect temperature, its only a factor for us humans because we sweat, and evaporating water has a cooling effect and wind accelerates evaporation, but theres no water on the temp sensor of a car, so not an issue."
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7w1dua | Why is E85 85% ethanol? | What makes that ratio so special? Why not a 50/50 ethanol blend? In fact, why don't they just sell pure ethanol and remove the reliance on petroleum all together? | Engineering | explainlikeimfive | {
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"text": [
"E85 has between 51 and 83% ethanol, by law (in the U.S.). Outside of the US it has 85%, and you can get 100% ethanol in some places too, mostly in warm areas. You have to mix it because it won't ignite in cold weather without some gasoline - the exact mix of ethanol and gas is often changed depending on where you are (the weather!).",
"> What makes that ratio so special? It is about as much as every passenger vehicles can take without damaging the engine. > In fact, why don't they just sell pure ethanol and remove the reliance on petroleum all together? In the winter you wouldn't be able to start your car. There are no passenger vehicles designed to take 100% ethanol and the utility of a fuel consumers can't use is pretty low."
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7w9sh1 | How did ancient civilizations manage to construct big constructions like for example Parthenon and Temple of Artemis? | Engineering | explainlikeimfive | {
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"text": [
"Those civilizations were actually greatly advanced in mathematics. We still use the same basic methodology today that was used back then in a variety of structures such as domes and arches. Scaffolding was used then and is still used now. That’s the great thing about math. It works and it will always work. We can just improve on it."
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7wd906 | How does the power grid differentiate what customer is using what suppliers power, when it's all going through the same transmission lines? | Engineering | explainlikeimfive | {
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"It does not. All of the producers submit power to the same grid, and all of the customers get power form the same grid. Even in countries where the power production market is a free market, the distribution grid is managed by a single company as it is considered a natural monopoly. Every producer sells power to the grid at a certain price, then the grid sells that power to the customers. The thing is that in the case of little private customers, instead of buying from the grid they have a contract with an wholesale company that buys power from the grid and ensures the power supply for its customers.",
"Think of it as a bucket. Several companies fills the bucket, several customers empty it. However, one company owns the bucket, and they know exactly how much each company puts in and each customer takes out. So, they can see that you have taken 1 liter, and charge you for that, and they can see that ElectroCorp has put in 500 liters, and pay them for that. That way, it all works out in the end.",
"I assume you’re asking because your local power company is selling people on paying more to ensure their power comes from ‘green’ sources? As others have said, it’s just about fulfillment. You pay for green power and they make green power. It’s mushed up in the middle, but it’s there. These programs usually directly fund the production of green power, too. I work for a power company and we’re about to rollout, for lack of a better term, a community garden solar farm. People are making the investment to produce more clean energy where they live."
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7wezru | What are the devices spraying liquid at the launch pad on rocket launches? | Engineering | explainlikeimfive | {
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"text": [
"[Sound supression]( URL_0 ). The noise of the rocket engines is so loud that it could physically damage the delicate parts of the spacecraft if it's allowed to reflect off the pad. So they fill the air with water droplets to scatter and absorb a good fraction of it.",
"That's just water, and the sprayers are just valves fed by a water tower. It's a very simple system; open the valves, water sprays. Believe it or not, it's a \"Sound Suppression System\". A rocket launch is very loud, incomprehensibly loud. It's so loud the sound can actually damage the rocket, and that's especially true when it's close enough to reflect off of the launch pad. Spraying tons of water (literally, NASA uses ~2.5 million pounds of water, per launch) below the engines effectively absorbs a whole lot of the sonic energy. NASA claims they cut the sound pressure in half, and that's a significant difference!",
"In some launches you can see the same looking sprays but they're spraying sparks, what are those for?"
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7whpmy | What is the fin-shaped object mid way up the proposed BFR Rocket design? Is it a form of fin or does it serve another purpose? | Engineering | explainlikeimfive | {
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"text": [
"That's the second stage delta wing with split-flap. It's used for pitch and roll control of the second stage, like a directional spoiler. Probably also an awesome camera mounting location."
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7wky9m | How exactly does an iron lung work? | Engineering | explainlikeimfive | {
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"text": [
"An iron lung is essentially a chamber that is sealed around your body that changes the pressure. To get you to inhale air, the chamber reduces the pressure around your chest, which causes it to expand. This expansion creates a partial vacuum in your lungs and air travels the natural way down your trachea into your lungs. To get you to exhale, it increases the pressure around your chest, generating positive pressure in your lungs, forcing air out through your trachea. Generally iron lungs are being replace with ventilators use either a endotracheal tube through the mouth to the lungs or a tracheostomy (hole in the neck directly into the trachea). These work by creating positive pressure to force air into your lungs and neutral or negative pressure to empty your lungs of air. Iron lungs are just too bulky and generally impractical. Ventilators have a lot more flexibility in terms of settings. You can adjust oxygen concentration, inspiration volume, inspiration pressure, expiration pressure and other factors. You can't use your arms for very much inside an iron lung, while a ventilator gives the patient more mobility and autonomy."
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7wmfdj | what is the difference between a $10 HDMI cord and a $150 gold plated HDMI cord? How are some high speed and some 'ultra high speed'? | Engineering | explainlikeimfive | {
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"text": [
"No difference what’s so ever. HDMI is digital. 1s and 0s no in betweens. One of the biggest cons going is expensive HDMI cables.",
"So, the term \"high speed\" or \"ultra high speed\" is pretty meaningless. That said, different cable construction can handle different switching frequencies(baud rate) resulting in different specs on what they can do in terms of resolution and frame rate. The most common speeds are: 4.95Gbps allows for 1080i(not p) at 60fps. 10.2Gbps allows for 4k at 24fps. I *believe* these also do 1080p at 60fps. 18Gbps allows for 4k at 60 fps. So basically, ignore the words, pick the cheapest cable that has the numbers that will work for what you need in both baud rate and length.",
"No difference. When I worked in Best Buy, we could get stuff like that at cost, and cables generally had the most extreme markup. That $80 Monster HDMI cable? $3.00 at cost."
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7wn93c | How do rocket engines work? | Engineering | explainlikeimfive | {
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"text": [
"The principle is really simple; the difficulty is in scaling things up to allow for pumps that pump an enormous amount of fuel per second and nozzles that can withstand immense temperature and pressures. All you need for a rocket is some fuel to burn and create a really hot, high speed flow. For a liquid rocket engine this usually means mixing a fuel (often kerosene (RP-1) or hydrogen) with an oxidizer (generally liquid oxygen). This is ignited and sent through a nozzle that directs the resulting exhaust away from you. With a solid fuel rocket you have some solid that burns at a known rate (typically as a function of pressure). You shape the fuel inside the booster such that the burn rate is what you want, then direct that exhaust through a nozzle. This all works because \"for every action there is an equal and opposite reaction.\" When the rocket accelerates exhaust down at a high speed it gets pushed up. This allows the rocket to fly in or out of the atmosphere since it doesn't need something to push off of--it's pushing off of its own fuel.",
"Imagine you shove one of your buddies. They go one way and you go the other, right? This is more formally referred to as \"Every action has an opposite and equal reaction.\" If we controlled for other factors (you are both in free fall, both weigh the same amount, etc.) then you would both move apart at exactly the same speed. A rocket then propels itself by throwing stuff out the back really fast, the faster the better because the faster it is thrown the less stuff is needed. To do this they burn fuels which causes them to expand, which are then directed out a nozzle so they only go one direction and the rocket goes the other. The fuels have their own oxidizer mixed in or it is supplied directly by the rocket out of liquid oxygen tanks. The rocket is in essence pushing off its own exhaust."
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|
7wrux8 | why train rail tracks have rocks between them | What purpose do they serve? | Engineering | explainlikeimfive | {
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"They don't just have rocks between them, they have rocks **under** them. The rails sit on thick wooden blocks called \"ties\". The ties are set into gravel which allows water to drain while supporting the enormous weight of the train without shifting. They spread out the weight so the rest of the ground can support it.",
"A part of the answer is missing here. The rocks have also a very precise size (or at least a range of size) that allows them to stop vibrations generated by the train and prevent the rail to resonate/oscillate which could have disastrous consequences. Of course stoping vibrations have an impact on the rocks that get smaller and smaller with years of use. I use to work for French railroad company and just replacing ballast on the network was already a tremendous amount of work for the company."
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