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is5j4z | What really is electricity? How does it work? What is Amp, Voltage, Resistance and all that and what is the difference between a 110v and a 220v outlet? | Engineering | explainlikeimfive | {
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"So you can think of electricity as flow of a liquid through a pipe. Amps are the actual flow rate, how much electricity is moving. Volts are the pressure of the fluid, higher pressure, higher power. Resistance is more like the viscosity of the fluid, it literally is a measure of how much resistance to flow your fluid has. There are a whole bunch of other things that factor in where the metaphor breaks down, but that's a decent analogy of the basics. As for the difference between 110V and 220V, the difference is in the power that can be sent through devices. The power equation is this (Power)=(Current, measured in Amps)*(Voltage), and wiring doesn't want to handle higher currents, as that makes them heat up faster, so current must stay the same. The only option then, is to increase the Voltage, so when you need high power devices, like appliances, electric car chargers, etc. you can use the higher power, but slightly more dangerous 220V circuit.",
"Imagine you have two water tanks which are connected by a pipe. In this analogy water represents electrons, the pipe represents a wire, and the tanks represent two differently charged metal objects. If there is more water in one tank than in the other, water will flow through the pipe to equalize the water levels. This is similar to how electrons will flow from a negatively charged pole to a positive one in order to equalize the charge level. If you then put a propeller in the middle of that pipe you can use the moving water to power it, just like you can use electricity flowing through a wire to power an electric motor. Voltage is equivalent to the pressure difference both tanks. The bigger the pressure difference, the harder the water will try to flow from one tank to the other, and the more load you can put on the propeller before it slows down the water flow. Resistance is equivalent to how hard it is for the water to flow through the pipe. If you make the pipe smaller or put lots of obstacles into it ( < = > worse conductivity) less water will flow through it, and the propeller turn slower. Amperage is equivalent to how fast the water is moving through the pipe. In practice the speed is determined by how much pressure difference (=Voltage) there is, and how hard it is for the water to move through the pipe (=Resistance). This is how we get the formula I=U/R. Note that all of this so far was describing direct current. For alternating current rather than continuously moving in one direction the water is pushed back and forth inside the pipe. However, apart from that the same principles apply."
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is8gyt | What is the point of a Water Tower? | Engineering | explainlikeimfive | {
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"The water is pumped up and stored in the tower. The water is then gravity fed to the town. This is cheaper than having a thousand and one pumps needed to pump the water directly to the taps.",
"Water pressure. By storing the water high in the water tower the water doesn’t need pumps to be delivered when you open your faucet, it just flows by gravity."
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is90c0 | Why do we only use huge wind turbines to harness wind power? | Seems like having thousands of smaller turbines attached to peoples homes and businesses (especially skyscrapers) across the country would generate a significant amount of power collectively. | Engineering | explainlikeimfive | {
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"It's a cost/benefit ratio question: larger turbines generate more electricity per unit area they take up and per unit cost. When trying to harness wind speeds high enough and consistent enough for solid generation, a higher hub height is better. There are smaller turbine models that exist and can be used on buildings, but they're usually neither as efficient nor as cost effective.",
"No, not at all. Firstly, near the ground at homes has terrible winds. Obstacles on the ground block wind, so putting them higher up in unobstructed fields or seas gives them a lot of access to faster and uninterrupted winds. Secondly, small turbines could cover the same effective area as a large one, but at a much higher material and labour expense. It would take more material for the blades, more generators, more power electronics, and more wiring for power production. Installation would take way longer. Large turbines take less material, and gain from economies of scale by producing large.",
"Larger wind turbines are just better Winds are stronger higher up so higher towers have access to better winds Larger wind turbines also capture wayyyy more wind. A 100 meter diameter wind turbine requires a tower twice as tall as a 50 meter one and blades twice as tall but captures 4x the wind. Massive offshore wind turbines can capture up to 12 MW on a single tower, the largest onshore one is only about 5 MW Big turbines are just more cost effective than small ones"
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isbnop | How do computers count time? | I know if a processor has a speed of 1Hz It makes one cycle each second. So to know an interval of time you just count the cycles passed. But what about modern systems that change their speed between ranges of GHz in mere miliseconds. Also How does a computer know How fast itself is running without comparing It with an external time source? Does It just have a fixed speed osciloscope that It compares to the CPU osciloscope? | Engineering | explainlikeimfive | {
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"You've assumed that the cpu measures time based on its own clock. This is not the case. For determinations of time, there is a separate oscillator on the motherboard whose only job is to count seconds. The cpu can query this number to determine the time. The cpu clock is generated by a completely separate oscillator and has nothing to do with timekeeping.",
"What are you asking? Are you asking how a computers clock works? Or are you asking how a computer knows how fast it is? Those are two completely different questions, without much overlap. I don't know about the second, but the first is something called \"Unix Time\" which is just a continuous integer number of seconds since Jan 1 1970, which counts up and up, one second per second. A computer clock can check the current Unix Time, do a bit of math, and come up with the time to the precise second.",
"~~The sine wave of the input power is consistent for example in North America its always 60hz. So that can be used as a tick.~~ Computers also have a crystal clock circuit on the motherboard, which is the same type of chip used in a digital watch. When power is applied the crystal resonates at a set frequency. X number of ticks equals a second. The crystal clock is powered by a watch battery when the main power is cut, so the clock is always running. EDIT: I think what you are trying to ask, is how does a computer know how fast it's own CPU is running? The CPU uses it's clock cycles to determine the speed at which it's cores operate. Because the gates have to fire in sequence to work, the clock is used to coordinate everything. When the CPU is operating the clock speed is a known factor, and this can be passed from the CPU to the operating system using a built-in instruction."
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isdd5n | Why do new cars ignition restart at every stop? | Engineering | explainlikeimfive | {
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"It saves gas in city traffic where you are constantly stopping and going. They figured that you spend more gas idle when stopped then if the engine were to turn off and restart."
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istsyw | What happens under the hood when a car is in normal mode vs eco mode vs sport mode? | Engineering | explainlikeimfive | {
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"The automatic transmission shifts at different RPMs. Shifting to the next gear sooner will save fuel because the engine doesn’t rev up as much, but you’ll accelerate more slowly. Shifting later allows the engine to rev up to the red line which will maximize acceleration and burn more gas.",
"It depends on the car. Some adjust things like engine timing, fuel injection, suspension stiffness, throttle response, shift mapping, etc. Some just make the dashboard lights turn colors. Green means eco, red means FAST."
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it463i | - I was wondering if someone built a car from scratch, can that person drive it legally? (I know there must be a lot of different rules for different countries) | Engineering | explainlikeimfive | {
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"It would have to be inspected by a government official first and given a roadworthy certificate to certify that it is safe and operational, but otherwise yes.",
"Legislation is indeed different. You wil almost always have to get the vehicle inspected. Exactly what this inspection includes varies but is more thurough then a regular anual inspection as they have to evaluate the design and the assembly of all components rather then just the components that wear down over time. In many ways it resembles the certification for a new vehicle design but is more light weight. It does not include a crash test or detailed engineering reviews and you can often get away with designs that would fail on a production model. Some legislation does have a more simplified process for existing car designs. This is most common when people buy vehicles as parts kits and assemble it themselves according to the instructions. In this case there have been a review of the design already and maybe even crash tests so the inspection only makes sure you actually put it together right. Similar inspections may apply if you are substantially altering the design of a vehicle or if you are rebuilding a salvaged vehicle. But exactly what these inspections involves and how much it costs varies a lot between different legislation."
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it5rg9 | How does electricity 'knows' the shortest travel path? | Engineering | explainlikeimfive | {
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"It does not. Electricity follows the path of least resistance, not the shortest path. But if you replace the question with \"How does electricity 'knows' the lowest resistance path?\" The answer is still it does not know. Electricity will travel in all possible paths at the same time, it is just that the amount in each path depends on the resistance. Take a bucket with water and connect a couple of plastic tubes. Put something that slows down the flow in some like cloth, a twig etc. Leave one tube without any blockage. This is like electricity with a different path with different resistance. Water will follow each path but the amount depends if there is anything in it that blocks the flow. If you have the bucket close to the ground and the pipes almost horizontal the flow it lower then the bucket up in the air and the pipes vertically. This is because the gravitational potential difference is lower. For electricity, you have an electric potential difference that works the same way and changes the flow rate. The electric potential difference is known as the voltage. The explanation is that each molecule is pulled down by gravity and move when the molecules that were in front of it have moved. So in a tube with a blockage, there is less space for the molecules and they will bump into stuff that slows them down. You can do the same with a larger object like balls and it is quite clear what happens. Electricity is the same and how may elections that can pass through a crosssection of a wire depend on the rate the one in front can move away. The rate the electrons move in the wire is slower than the water. 1-ampere trough a wire that has a diameter of 2 mm will move at 23 μm/s = 0.000023m/s. So electricity follow all possible path the amount in each path depends on the resistance, higher resistance = lower flow.",
"It doesn't, it just chooses the path of least resistance, which is usually the shortest path if the current is going through is all one material. As for how it does this, imagine you're stuck in a large bush and the only way out is to push through it. You can't see where it's easiest to do that, so you just push everything and find the easiest part. Then you move forward, until the path gets too hard to push through, then you repeat. Electricity basically does this, only at incredible speed."
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it63ld | Why does a cell phone use up more battery on 4G than on Wi-Fi? | Engineering | explainlikeimfive | {
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"4G base stations are located much far from your phone than your WiFi router, so it's more power required to reliably transfer data. WiFi transmitter uses up to 100 mW of power, and GSM can go up to 2W.",
"When communicating with a WiFi source the receiver is usually at most a few meters away from the phone, when it comes to 4G in some cases the tower can be a few kilometers away, your phone however still needs to communicate with the tower which requires much more power for the tower to still be able to receive the phones signals, this is also why your battery drains faster if your connection to the tower is weak (your phone needs to put in more energy into the signals for the tower to be able to receive them)."
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it71p0 | Why do most of the shopping carts have one defective wheel? | Engineering | explainlikeimfive | {
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"Three wheels form a plane, always flat. A fourth wheel is not defective, just not necessarily resting on the floor, so it wobbles.",
"Mostly confirmation bias. Since there's a lot of shopping carts and they are constantly in use, chances are high that some of them will have one or more wheels broken. If no wheels are broken, you usually don't pay attention to this fact, it's just a normal shopping trip. If one wheel is broken, you notice it and register it as a \"ha, one more for the defective carts list\". Having two or more wheels broken is more rare, and such carts usually draw too much attention and are sent for repairs. Personally, I never had a systemic experience with defective wheels on shopping carts.",
"My question is more along the lines of why do I always get the loudest cart that insists on turning by itself for my first choice? Then I have to push it like it's not an issue for me because I'm an adult and not a picky child but secretly I'm envious of all other cart users and I'm most likely lifting the cart slightly so that wheel stays off the ground."
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itd108 | How does putting a vehicle in the first gear when going downhill act as a brake, and why does this not cause the gearbox to burn out like a brake? | Engineering | explainlikeimfive | {
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"The gearbox transfers the energy between the wheels and the engine. It does not use any of the energy so it does not become hot. But when you put your car in a lower gear the engine have to go much faster to match the speed of the wheels. And the faster the engine rotates the more air it have to compress with its pistons and this requires energy. Normally it would add some fuel to get a combustion that gives it energy to spin but if you let off the throttle and the engine is spun by the wheels the fuel flow is cut off completely. So the engine is using power from the wheels to compress air. This does make a lot of sound and heat. But unlike the brakes the engine is very good at getting rid of heat. Firstly it is much bigger so it takes a lot of time for it to heat up. Secondly it is able to push a lot of hot gas out the exhaust which takes away a lot of the heat from the engine. And thirdly the engine have a water cooling loop connected to a big radiator with a fan that is able to keep the engine cooled down. Meanwhile the brakes on the car is just four small disks, they have no where near as much cooling as the engine. This is why there are signs posted at the top of steep hills telling you to put the car in a lower gear and not use your brakes all the way down.",
"Have you ever taken a vacuum cleaner and pressed your hand against the end of the hose, and noticed how the vacuum cleaner instantly starts to work really hard? Gasoline engines (and some diesel engines) have a throttle valve which regulates how much air can enter the engine. When the engine is spinning but the throttle valve is closed, each time a piston goes down on its intake stroke the engine is desperately trying to suck air past the closed throttle, just like a big vacuum cleaner with your hand pressed over the end of the hose. This takes lots of work, and it's called \"pumping loss\". When you're going down a hill and the throttle valve is closed, the energy to spin the engine and overcome pumping loss comes from the wheels. This creates the braking effect you're familiar with. The gearbox doesn't burn out because it isn't providing the braking forces, it's just transmitting them between the engine and the wheels. Note that many older diesel engines don't have a throttle plate, and don't produce significant pumping losses. This is normally a benefit and is one reason why diesels get better gas mileage than gasoline engines, but it also means they need other methods to produce an engine braking effect. On large trucks this is usually done via a Jacobs brake, which is an efficient but very loud method of creating an engine braking force. Newer passenger diesels often have a throttle plate for emissions reasons now, and can provide vacuum-based engine braking (but also get worse gas mileage than their predecessors)."
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ithfdv | Why do cheap cars look cheap? Isn't it a matter of design? Can't they make a cheap car that looks like a ferrari or any good car? | Engineering | explainlikeimfive | {
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"The flip side to cheapness is that you have to sell a lot of the car. In order to do this, you babe to appeal to a lot of people. Which means features like good storage, economy, passenger room, etc. In addition, you have to use simple construction techniques to keep the cost of parts low. All these things add up to a basic vehicle. The design has to accommodate all these things, which limits the styling somewhat. Supercars are only intended to go fast and not much else, so most of their interior space is given over to the engine, cooling systems, and suspension. But with a family car, you want a lot of interior space, which means less for the engine and other systems, as well as a blocky, inflated design.",
"If you sell a range of products, with an introductory or basic level at one end and the super-deluxe premium ultra at the other, you want your potential customers to be able to tell at a glance which one is which If all the products you see look the same, it will be a lot more difficult to convince people to buy the higher-end models. People like expensive things to *look* expensive, and unfortunately the only way to accomplish that is if cheap things look cheap."
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itlwux | What’s the purpose of a bed frame? | Engineering | explainlikeimfive | {
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"It raises the bed off the floor on thin legs. That prevents heat loss the the floor, makes it harder for pests to gain access to bedding, and makes it easier to get in and out of bed.",
"You mean the thing that holds the mattress up high off the ground? That's what I call a bed frame, and it seems pretty self explanatory to me so maybe you're talking about something else. But, if we are talking about the same thing, then yeah...to lift the mattress up higher where we can get on and off easily plus it can contribute to some general design creativity for the room.",
"Making the mattress a height that’s easier to get into, provide air circulation to keep mattress fresher. Also warmer than sitting on cool ground/floor.",
"Well..that’s what the bed is - the platform where you put your mattress on. Or do you have something else in mind? Like a four poster? Those posts are typically for decoration."
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itm1v3 | why are guns still so loud? Why hasn't gun technology improved in tandem with noise cancellation technology? | Engineering | explainlikeimfive | {
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"The shockwave of the expanding explosion is loud by its very nature of being a shockwave. Plus, many bullets travel faster than the speed of sound, creating a sonic boom. You can cut down on sound, but this also cuts down on performance and outcome. You have a choice: Effective bullet or quiet. You can’t have both.",
"Because the expanding gas pushing the bullet down the barrel bursts out the end of the barrel too and, lacking the confinement of the barrel, promptly expands the air at the end of the gun resulting in a very loud bang. There **is** technology that reduces this significantly. Called “suppressors”, often incorrectly called “silencers”. These attach to the end of the barrel and provide a chamber for the gas to expand into, with baffles that slow the progression of gas and absorb energy. These aren’t difficult to make and can have a large effect on sound levels, but are **highly** regulated in a lot of places.",
"Noise cancellation can't help with this. To actually *cancel* a noise as it occurs you need to create a second noise whose sound wave is exactly opposite to the first. But you can't do this if you don't know what the first sound wave will be like. Yes, you'll know it's a loud \"BANG\" type of noise, but that's not specific enough. You need to know exactly how and when the air pressure is going to go up and down. Even if you did know this, note that the anti-sound has to be as loud as the target sound (even if the result is, ideally, silence). And you're not just canceling the sound for one person wearing headphones - you're trying to make the gun silent for everyone in earshot. So that would mean playing a sound of over 140 dB coming from the same location as the gunshot sound. What speaker are you going to mount on your gun that's capable of creating a sound that loud? So you're left with passive rather than active noise control, i.e. materials and structures that dampen or muffle the noise by breaking up the sound wave. But that's not easy either. Again, you're dealing with a powerful pressure wave. A small piece of equipment isn't going to stop that in its tracks. Hence why existing suppressors only manage to shave something like 20 dB off the gunshot noise, which thus remains very loud (and so the barely-audible \"plop\" you sometimes hear in TV and movies is a laughable bit of fiction).",
"The noise from a gun is two sources. The boom from the exploding power and the *crack* of the bullet’s sonic boom. The quietest gun is a gun with a suppressor and using “subsonic” ammo. It’s a much smaller powder charge to begin with, so less boom and no *crack*."
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itxh72 | Why are the car interior lights like in the trunk of Yaris, made of rough to touch plastic? | Engineering | explainlikeimfive | {
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"Lenses with a matte finish (rough and bumpy) are intended to help direct the light into a larger and more diffuse pattern to illuminate a larger area. Without it the light would be more like a spotlight shining directly on whats underneath it.",
"If the roughnes is a regular pattern thn it is most likely being used for its optical effects. Basically it is a lense or many lenses probably acting to spread out the light.",
"That's called a Fresnel lens. It's a way to get a big lens in a small space, say if you wanted to spread light from a tiny bulb all over a trunk's interior."
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iu21ot | How do electric prosthetics work? I mean how are people able to control the fingers and the wrist? | Engineering | explainlikeimfive | {
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"Ok so older prosthetics have hidden physical switches/buttons that were activated by pushing on it in a certain way with whatever muscle remained (so if you lost an arm, a muscle in your shoulder activated it. Newer prosthetics use electrodes/computers to track the muscles movements, instead of having physical switches, and then translate that information into the motor moving in a certain way. New New prosthetics will actually time sensors into the nerves themselves. And track the signals running in them. (So if you lost an arm, they would tie sensors into the nerve that is what is left of what used to run into your arm, sense your brain will still send “arm” signals down that nerve.)"
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iug8hm | Why toilets have tanks ? | It seems to me that pluging the toilets directly to the water system would enable us to use pressure (and maybe get cleaner toilets, or reduce water) but instead there is this tank system where only gravity moves the water and I fail to see any benefit to this more complex and possibly less effective way of doing... So why the tank for toilets ? | Engineering | explainlikeimfive | {
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"A tank actually provides more pressure, which is necessary to actually make the siphon work to flush the toilet. You're dumping a gallon or so of water in a few seconds. Many home supplies simply don't have enough pressure to do that. Tankless toilets are a thing though, often in public restrooms. Homes with low pressure mains water can have one, but you need a pump to get the pressure up.",
"Rare are the cases where water pressure is good enough for this, and having a \"wall\" of water falling over the toilet's solids is still more effective at actually pushing than spraying it with the water system pressure. Have you tried hosing something on the floor? If somewhat heavy or stuck to the floor you would need not only a good pressure, but also to point the water flow directly. Imagine having to have that pressure in about half of the toilet. It's harder to do and usually much less efficient. Also, there is the bonus of not having to keep the toilet unflushed if you notice you are out of water. If directly connected, you could unawarely run out of water and have to let the toilet stay on that state..."
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iugpj4 | - why some cars sound like they are starting when they are already running | Lately I've noticed that some cars just as they start to move away from traffic lights on the green signal they make very much the same noise as when you start engine. However when looking at them all seems to be already running. What is causing this? | Engineering | explainlikeimfive | {
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"Auto start-stop. The car turns itself off when stopped to save gas. And then when the driver takes their foot off the brake it very quickly restarts itself.",
"So many cars now have this eco friendly option built into it. It temporarily stops the engine when you come to a stop. The idea behind this is an idle engine creates a lot of exhaust and starting the engine up creates less than letting it run. Frankly i find it to be a pain in the ass but its a thing."
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iup1xa | Why do single-use bags have short handles and most reusable bags have long handles? | I know that the long one as are for hanging over your shoulder, but I dont get why? Of course there are reusable bags with short handles too, but in my experience, 99% are the shoulder ones. I hate them, I just want to hold my bag the way the I hold a regular paper or plastic bag without it dragging on the ground. | Engineering | explainlikeimfive | {
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"Single use bags are made of thin stuff, which would probably stretch and break if made into long handles. If your handles are too long why not shorten them? Sewing, fabric glue or just tie a loop. Don’t get mad, get shorty."
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iupbva | Why won't planes on ground take off or move although the engines are running | I always wanted to know why planes - be it propelled engines or jet engines - won't move a single bit on the airfield, although the engines are spinning almost as fast as in air. Are the brakes and friction so strong? | Engineering | explainlikeimfive | {
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"The brakes have to be stronger then the engine. Remember that they have to be able to stop the airplane on the same runway that it took off from. So they have designed the aircraft with brakes that are more powerful then the engines. In addition all but the smaller propeller aircraft have a variable pitch propeller. So instead of changing the speed of the engine to control the speed they pitch the propeller so it is flat against the wind or angled. This can result in them running the engine at full speed but with the propeller not pushing any air and therefore not generating any thrust.",
"The engines are running, but at low power and are not generating thrust. It's a lot like when your car engine is running, but not enough to move the car. When the throttle is opened, the thrust increases and the plane begins to move.",
"Depends on the plane. At least with large jet airliners, there are three easy ways to prevent motion. First, there are brakes. The engines honestly don't push that hard compared to the weight, and as such the brakes can stop its motion. Second, the engines are not at full throttle. The spinning of the blades is fast, but not full speed until they're ready to go, at which point you can hear them audibly speed up. Third, many of these craft have thrust deflectors that can partially reverse the engine exhaust. This can even allow the planes to back up."
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iurlxz | Will all buildings collapse eventually? | Like skyscrapers? Will they eventually collapse or will human engineering last forever? Do buildings need maintenance to their foundation? I hear of parts of buildings being replaced but what about the actual raw structure? | Engineering | explainlikeimfive | {
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"text": [
"Buildings have a design life to them. Without intervention then yes, they will all fall down. It’s a problem we are experiencing currently in the United States. A lot of the buildings we built during the industrial revolution are reaching their service life and we are not sure what to do with them. It’s expensive to tear buildings down, so most are retrofitted and repurposed.",
"You would have to define \"eventually\" to have any type of serious discussion about this topic, but yes, everything eventually decays in some way. Beaches are a great example of what decay and wear over time can create. With buildings specifically, one huge factor is steel reinforced concrete. Using ferrous-metal reinforcing bars and grids for concrete construction was a major engineering advancement which created the world of cement we now depend on everyday. The problem is that iron will eventually be exposed to air and/or water and oxidize (rust). The reinforcement will then expand and weaken the cement until it cracks. This allows even more moisture exposure and accelerates the process. The Roman Colosseum for example is built with a seawater-form of otherwise unreinforced concrete. It has taken a couple of ~~centuries~~ *millennia* and a long period of neglect to reach it's current form. If this structure had been built with modern ferrous-metal reinforced concrete it likely would not be there today. Therefore, the ultimate answer to your question is yes, all buildings will decay into rubble and eventually dust. The details of how, when and why that happens is always specific. Remember that \"buildings\" are a very recent addition to the planet."
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iuxtul | How are oil rigs built | Engineering | explainlikeimfive | {
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"text": [
"The old ones were built into the sea floor. But as oil fields started being discovered under deeper and deeper water, it got to be too much and most modern rigs float. I actually recommend going over to YouTube for this. I watched a really good video about it."
],
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9
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iv7i1m | Why do the Space X reusable rockets use engines to land instead of a parachute? | I would think that a parachute would be lighter and use less fuel. | Engineering | explainlikeimfive | {
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"text": [
"They would land way too hard, and have no way of landing upright. Instead, they'd land at a speed that would cause massive damage to the rockets or completely destroy them, and even if they somehow came in at a non-damaging speed, they'd land at a random angle which would greatly increase the risk of damage. And as the rockets are meant to be reusable, splashing down at sea like you'd see with a lot of older manned vehicles isn't feasible. You'd need to fish the rockets out of the ocean and even then, they'd be ruined from contact with loads of corrosive seawater."
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ivj1fr | Why is it since so many electronics and applications require batteries in pairs, there isn't simply one larger equivalent? | Engineering | explainlikeimfive | {
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"Once something becomes a standard, it's usually very disruptive and often not worth it to change from that standard. Even if they aren't very common, there are still some devices that only use one battery. I have a flashlight that uses three. Some devices put the batteries end on end, others have them side by side. And for devices with the batteries side by side, some might have them right next to each other and some might have a little bit of space. There's very little benefit to making a larger equivalent because there'd have to be at a minimum two configurations for the end on end and side by side devices, and they'd be incompatible with devices that use an odd number of batteries so you'd still have to make the singles. And economies of scale means that it's more efficient to make a lot of the same thing rather than a smaller number of different things.",
"AAA and AA batteries both output 1.5 volts. If two are linked together in series, that increases to 3 volts which some applications need. Two AAA batteries are not worth a single AA battery in that sense.",
"An 18650 battery would produce 3.7v which would be enough to replace two 1.5v AA or AAA batteries in series. However 18650 batteries are large in comparison so not suitable and not exactly user friendly as they can easily be installed backwards",
"[There are type of batteries]( URL_0 ) which does serve the role of delivering 3 volt from one battery instead of 2x1.5 volt batteries. My guess is, that the problem is those (camera type) batteries are not as easy to purchase in every supermarket as the more well known sizes. So the people designing battery driven devices often decide to go for the 2x1.5 volt set up to make it more convenient for the customer."
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ivq8i6 | How does a vehicle's thermostat work? | Edit: I should clarify that by thermostat I am referring to the climate control thermostat that adjusts cabin temperature. I suppose knowing how the engine thermostat works is also a great question. Thank you. | Engineering | explainlikeimfive | {
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"Think of the air moving system in your car as a loop. At the front of the car, there are three incoming air tubes. The first is hot air heated by excess heat from your engine, the second is outside air, the third is cooled air from the condenser. Now all three of these \"roads\" meet the air systems loop at the same point. At that point this looks like three \"roads\" on a street combining into one \"road\" in the opposite direction. When you are turning your thermostat hotter or colder you are moving a plastic covering that uncovers the area of one \"roads\" worth of air. As you move from cold to warm to hot, that opening goes from fully open to the condensed air, to partially over both condensed air and outside air, to over outside air, etc. until it is fully over engine heated air."
],
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ivqa2n | Why does it make a difference which way I wear a face mask? (i.e. blue or white side out) | Engineering | explainlikeimfive | {
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"Blue (or colored) side iz waterproof, white is absorbent, therefore you want to wear the white side inside. We also use this in emergency medicine to see blood droplets on the inside better, also the absorbent side can be checked for bacterial cultures.",
"Colored side out. Some masks are white on both sides, so you'll have to see to which face the straps are glued to, that is the face that should be inward. This is also the case for colored masks.",
"Blue side out to protect you better from droplets spraying at you, white side in to catch your droplets better so they don’t leak out and infect other people. Btw, around other people, esp mask refusers, wear glasses too. Eyes are mucus membranes like the mouth and covid-19 can enter your body there.",
"From these comments I've... I've been wearing my masks wrong the entire time, and no one fucking told me I mean, I've fucking been to Doctors' offices, and not a single one wanted to fucking tell me \" hey your masks is wrong btw, flip it around\"",
"In general, the coloured side is waterproof and designed to block droplets from bypassing the mask, the white side is designed to be more comfortable for you and absorbent to an extent. However, if you're wearing the mask like this right now, *don't* fip it over. The white side is already covered with dust, germs and droplets, you're better off just leaving it the wrong way round till you're home."
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ivryvt | Why does 10k volts in a taser only stun but 220 volts in a wall socket can kill you on the spot? | Engineering | explainlikeimfive | {
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"text": [
"Because volts are just part of the equation that tells you how much juice comes out of the wires. A taser is high voltage but low amps. Its akin to being hit with a BB gun thats been pumped a few dozen times. It hurts like hell, but the amount of stuff coming out isn't enough to cause serious damage. A 220v socket is like being hit by a falling boulder. It's moving much slower, but the amperage is so much higher that it doesn't matter.",
"Tasers **do** kill people. They are “less lethal” not “non lethal”. You will not have to look hard to find examples of people dying due to taser use. The 220V in your wall *can* kill you. It is dangerous. Don’t mess with it. But it won’t always kill you. Most of the time it won’t. You can get zapped by a faulty wire and be just fine, your arm/hand/whatever will just feel weird for a bit. It can kill you if the path crosses your heart, or if you put an open palm on a charged object because it can cause your grip reflex to activate and hold your hand on it until someone rescues you or you die. The premise isn’t entirely accurate, but on to your question: Tasers don’t actually deliver 10,000’s V to you. They have that in the mechanism to generate the shock, but by the time it reaches you it’ll be closer to 1200V, still high but a lot less than the five figure numbers. The electronics are set up to keep the current low, so the delivered power is also low, much lower than your wall socket. The pulses are also momentary - apply 1200V to someone constantly and they’re gonna die, quickly. Apply it instantaneously and the amount of power delivered is tiny. The way a taser works is that the moment it starts to shock it cuts off and charges up the next shock - it’s an instantaneous exposure to electricity. So the net power delivered to you is very small. 220 in micro shocks from the wall socket would be similar if you controlled the duration the same way, but is not, the current is constant until you break contact so can very seriously harm you."
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ivv742 | How are roads/streets/lanes naming decided? When we refer to a court or crescent, we know what type of road it is. What is the deciding factor for the designation or a road vs street? | Engineering | explainlikeimfive | {
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"In the US, there are no laws at the federal or state level. Most cities do not have laws except that the city planning department can deny a request. So, generally, whoever builds the road can name it. Whether it is named with street, road, avenue, court, or whatever, is based on whichever sounds best to the person doing the naming. Also, in response to another comment, most dead end streets and courts are not designed that way. The city plans usually list them as streets that have not been completed or are temporarily blocked. The legal requirements for creating them is very cumbersome, so they normally make plans to make them a normal road at some point in the future but never actually do. Source - I was a developer and planning commissioner. I created several subdivisions and helped write a city's general plan.",
"[This video]( URL_0 ) shows how streets, boulevards, avenues, etc are different! It’s an interesting watch and I hope it answers your question a bit",
"I'm not an expert, but IIRC: In general there are no rules, except for large cities, that often have avenues in one direction and streets in the other, and alleys that are dead ends or one way without parking. Each road needs a name for the fire department and postal service. Private roads can be named whatever you want, provided the local government okay's it. \\[Welcome to crank street off of puddle lane!\\] There are many historical naming conventions, that cities tend to follow, but there really isn't much holding them to it.",
"In UK it appears councils can set their own preferred naming convention in their planning regs. For example kings Lynn.. URL_0 It appears though that just about any variation can apply to any roadway.",
"In Transport Planning terms the difference between a 'Road' and a 'Street' largely signifies how we think of the main purpose of the place. A Road is something we pass along - it signifies a route where the main purpose of the road is.aa a highway for movement. A street is somewhere we also spend time where the movement function is a secondary function - or at least that there are clearly two main uses. In the UK we talk about 'High Streets' as the main Street in a town with retail and other place functions. In the US this is 'Main Street' But the principal extends to local streets where traffic flow isn't the first though of what is the most important thing going on. This definition is layered ontop of a lot of semantic and debatable historic points and different perspectives. It's most definitely not a black and white difference.",
"A road doesn't have to be any particular thing, it just goes between two places. A street is a public road that has buildings on both sides."
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iw4xhl | Why do we label transistors with Gate/Source/Drain instead of something less confusing like Switch/In/Out? | Yes, gate/source/drain make sense when you think about how electrons are moving through the transistor. But those words have almost no relation to how the transistor is used in a circuit. This certainly made it a lot more confusing for me when I was trying to learn circuitry. | Engineering | explainlikeimfive | {
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"text": [
"Well, \"gate\" is pretty descriptive, particularly when you get used to it. It acts as a gate for the current flow. \"Switch\" would be a bit of a misnomer in many circumstances, since a transistor is NOT a switch. It's intrinsically an analog device; an amplifier. \"Switch\" also has a specific meaning to electrical engineers, and that ain't it. Source and drain are less descriptive. Most people get used to them pretty quickly, though. I don't remember them causing me any confusion when learning. I'm not sure why you say they have almost no relation to how a transistor is used, though. And in a decent schematic, it's clear that there isn't much current flow through the gate, since the line denoting it doesn't touch anything else. So it's obvious that the current flow path is through the other two terminals.",
"The names are decided due to the working principle of a transistor. The gate simply gates(controls) the charge carrier flow. The source is the source of charge carrier and drain is the drain of charge carriers. Depending upon the charge carrier(electron/hole) the current direction might vary. While it would seem to be less confusing with names like \"in\" and \"out\" it would be extremely confusing in silicon level when the transistor is being manufactured."
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iw6yja | how do the toy cars that you pull back then they zoom off work? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The wheels are connected to a spring-like material that can mind up. URL_0 Instead of springing in and out, the springing motion is rotational."
],
"score": [
3
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iwf1s5 | Why are disposable razors only good for one use while something like a safety razor can be reused for multiple shaves? | I can’t decide whether it’s a difference in steel quality that causes disposables to dull quicker, or if it’s related to microbe buildup on the blade and avoidance of folliculitis (in which case, wouldn’t you want to dispose or sterilize both after each use?). Or maybe it’s just a marketing strategy to sell more disposables? | Engineering | explainlikeimfive | {
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"text": [
"You CAN re-use it. They tend to be cheaper and poorer quality and thus wear out faster, but it's the handle that's disposable, not the blade necessarily.",
"You can strop a cartridge razor, and then it’s good for many shaves. However, there’s a limit to how clean you can get it, and thus how many times you can re-use it.",
"Disposable razors are quite often difficult to clean, so they clog up with bristles. Have a look; sometimes there’s no “vents” behind the blade so they’re useless after one shave. Safety razors can be cleaned more easily and don’t clog.",
"the angle and thickness and quality all play a role. disposable razors are consumer trash made as cheaply as possible to force consumption. the ads that say the shave is closer are almost always, \"we got people familiar with disposable razors and gave them safety razors and they couldn't get a close shave\" it's all advertising.",
"Your question has been answered several times.... Look at the prices of these disposable razors, and of the cartridges. They are CRAZY expensive. Yes, they often can be used more than once, although I know some guys with heavy beards (i.e., thick hair shafts) who can only get one effective use... after that the steel edge is just too uneven. For my safety razor: I can get 100-count for about $8 - $10. Each blade lasts me two weeks without stroping; longer if I do. The balance and shape of the razor head are fantastic. Combine that with my beard prep of choice (*Taylor of Old Bond Street* -- seems expensive to purchase, but a 5.3oz container can last 12-15 months for about $17) and my badger hair shaving brush... no stubble; no rash; no bumps; no folliculitis; just smooth skin! I haven't bought a disposable razor in over a decade.",
"“Disposable” doesn’t mean “one-time use”. It refers to the fact that when they go dull, they’re meant to be thrown out rather than swapping out a cartridge. Also: if you don’t care about the little lubricating strip, you can buy medical grade disposable razors that are virtually identical to the Gillette blue basic ones on Amazon, 100 for like $14.00. They work just fine."
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iwk6gf | How can train engines pull so much weight? | Engineering | explainlikeimfive | {
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"text": [
"I addition to everything else that people have said, railways are very flat. So trains never have to go up big hills. For freight, railways should always have a grade of less than 1.5%. For comparison, federally funded highways in the USA are supposed to stay under 6-7%, but there are many roads that are in the 10-15% range. So trucks need a lot more hp / ton, since they need to deal with hills.",
"Ultra low rolling resistance The power required to pulled a weight at a given speed is determined by the forces pushing back on it. The air resistance of a train is pretty constant regardless of the length as the frontal area doesn't change much, but the rolling resistance scales with the weight of the train. Steel wheels on steel rails don't change shape very much so there is very little friction stealing energy from the train even though it is very heavy with lots and lots of cars. The engine only needs to have enough power to overcome this very limited rolling resistance. Getting the train started at a decent speed requires high torque which is done by electric motors, but once its up and running the overall power consumption of a train is very low. A train can move a ton of cargo around 500 miles on a single gallon of fuel while a truck is in the 100-200 ton-miles/gallon range"
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iwojck | How do they get water into water towers on top of buildings? | Engineering | explainlikeimfive | {
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"text": [
"Same way they get water Into water towers that are on the ground, pumps. They simply pump the water up",
"They pump the water into the holding tank. The water is raised so that gravity can lower it if needed later.",
"Rooftop water towers are usually fed by the city water system. After the water comes into the building, it enters a pump, usually in the basement, that pumps the water to the roof. Then the water is feed back down into the apartments in the building using gravity.",
"They use pumps to bring the water to the larger, common tank, which then provides the water pressure for those in the buildings. The alternative would be that those below the city supply would have water pressure from the gravity-fed supply, and those above world each need pumps."
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iwtrpk | Why were red LEDs so much easier to make than LEDs of any other color? | Like the first ones were red, and all the early ones were red as well. Was there any thing that made red easier? | Engineering | explainlikeimfive | {
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"text": [
"LEDs work by using a semiconductor to control the flow of electrons. The electrons give off light of a specific wavelength (colour) when they cross the band gap (lose energy) in the semiconductor. We had to find semiconductors that had a specific band gap that corresponded to the wavelength of light we wanted to produce that colour. The first widely used semiconductor was gallium arsenide phosphide, which gave off red light. Aluminum gallium indium phosphide, as well as GaAsP can be used for red, orange or yellow LEDs. The first blue LED was made with gallium nitride, but now uses a mix of GaN and indium gallium nitride. InGaN and GaAsP can both be used for green, as can gallium phosphide. InGaN is much harder to produce than GaAsP, and a Nobel Prize was awarded for finding a way to make it more easily.",
"Different colours use different elements; red, amber and green use elements that are reasonably easy to source and manufacture. Cheap ways to make blue weren’t discovered until this century, which also means no white."
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iwy0os | Why is it easier to peddle a bike uphill in a low gear when the weight is the same as a high gear which is much harder? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Our muscles find it easier to push/pull a lighting force many times, than it's is to push/pull a heavier force fewer times. For example, it's easier to lift a 10lb dumbbell 10 times instead of a 50lb dumbbell twice, enough though you technically put the same amount of energy into the dumbbell. When you're bike is in lower gear, you peddle a lot more to get your rear bike wheel to rotate once. You need some amount of energy to get uphill, but if you spread out that energy over a longer distance (as in, the distance you peddles/feet need to rotate) than you need less force (from your muscles) to get the bike moving uphill.",
"Same concept why pushing a door open close to the hinges is harder than at the handle. It's about how the same force is translated"
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iwyh1w | What is inertia? | Polar moment of inertia, area moment of inertia etc. All the inertia stuff. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"\"Inertia\" and \"moment of inertia\" are really different things. Inertia is the resistance an object has to changing its speed or direction. Moment of inertia is a physical quantity which is used instead of the mass when calculating kinetic energy and momentum for a rotating object. Really not sure I can simplify it any more than that, unfortunately."
],
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5
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ix1jdz | Why do some cars have 1 exhaust pipe at the end and other cars have 2? Is one functionally better than the other? | Engineering | explainlikeimfive | {
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"text": [
"Having two exhaust pipes will often allow you to have bigger exhaust which may result in a tiny bit of improved performance and reduced sound as the engine does not have to push exhast through a tiny pipe. However in most cases it is purely an estetic choice. Two exhaust pipes look better then one.",
"So the size of an exhaust pipe at its narrowest point determines the max rate exhaust can go through it. If that rate is smaller than how much your engine can output exhaust, it will choke the engine and decrease power. Bigger engines/more powerful vehicles require larger exhaust systems to be able to send through all of the exhaust. 1 method is to have a pipe with a larger diameter. You often see this on pickup trucks--one large pipe. The other method is to have multiple pipes because it might fit more neatly on the bottom of a car to have 2 (or even 4 sometimes) thin pipes instead of one thick one. So a car with 1 may be older/less powerful and not need any more than 1 thin pipe to handle the exhaust. Sports cars and trucks and such will have bigger and/or more numerous exhaust pipes because their engines output exhaust faster and need that."
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ixs3yn | how can four wheelers e practically submerged in water without flooding the engine but cars can get a little water in their engine and it shut the whole car down? | Engineering | explainlikeimfive | {
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"text": [
"They have snorkels. Engines are sealed units save for intake and exhaust. If the intake sucks in water it will destroy the engine since water doesn't compress. If you have a snorkel the engine can suck fresh air from above the waterline. The exhaust has enough backpressure to escape from the exhaust pipe even while submerged.",
"The four wheeler engine would also have big problems if water got inside it. The difference is that the vehicle designed to go off road also has care taken to position the air intake far away from the ground and protected from splashes. Some vehicles will even use a snorkel to keep the intake above the rest of the vehicle."
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ixzwoj | How does plastic get its characteristic "rough" texture? | ELI5: How does plastic get its characteristic "rough" texture? If anyone here has ever sat on a cheap all plastic chair, or looked closely at basically any injection-molded plastic object, you've probably noticed the texture. Sometimes a simple texture like less spikey sandpaper, and sometimes a complex semi non-repeating pattern of lines, like the pattern under bark eaten by worms. I have no idea what its called, and if anyone here even just knows the name I would be super grateful as that would allow me to just look it up myself. What I'm wondering is how it gets this texture. As I understand it, the molds are machined, and it seems to me that it would take tons of effort to machine these patterns. Is the pattern even made on the mold? I've been off reddit for a while now, so hopefully this post is okay. Thank you! | Engineering | explainlikeimfive | {
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"OMG my moment has come. & #x200B; You're actually talking about a couple different textures that result from different things we do to finish plastics (get them ready for everyday use). It usually starts with molding. Molten plastic gets squirted into a mold that shapes it into a useful thing, like a desk seat. Most of the surfaces are patterned with a slightly bumpy smooth surface that is designed for two main reasons: It helps the plastic release from the mold and it prevents the plastic from showing too much wear and tear as it's used. & #x200B; But more processing is needed. These molds are usually two pieces that come together, like the two halves of a waffle iron. This can cause little bits of molten plastic to bleed out the edges where the molds meet. These fringes are cut/sanded off with a rotating tool, and that cutting leaves behind a \"worm-eaten\" texture that you've noticed. Those marks could be buffed or polished away, but desk chairs are usually too cheap for that to be economical."
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iy20mn | Why can't we go back to the moon using a duplicate of the old equipment? Why do we have to spend billions developing new tech? | Engineering | explainlikeimfive | {
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"The old equipment is gone. It was inefficient, unsafe, and didn't have to contend with things like all the space debris and satellites that orbit the Earth now. We have much better technology now, good enough to allow astronauts to spend more time on the Moon. So we'll get more bang for our tax-payer buck. Also, NASA research very often benefits humankind in areas outside of space travel. So allowing them to develop new tech is usually a good investment in the future here on Earth.",
"Technically speaking we don't. However, technology has improved, and off the shelf parts that were used in the 60s are no longer available. We can make Pretty much everything lighter, more reliable, and better than we did before. Just to put into perspective how far we've come, the computer that landed us on these moon in the 60s was 32kg, and had ~45 kilobytes of storage, and ran at ~2MHz. The average phone today is less than 3% of the weight, has 250,000 times the storage (assuming 16GB storage), and runs 1500x faster (assuming processor speed of 3GHz). We may not *need* to redesign, but the flight computer example alone should indicate why it's a good idea.",
"The major expense in \"designing\" a new rocket isn't in actually designing the rocket. That's easy to do. Its building the equipment that you need to build the rocket. You can't just go out into the jungle in Ghana, hand some dude step by step instructions on how to build a rocket engine, and expect that you're going to get anything built. Building a rocket engine requires a lot of machinery and without that machinery you can't even begin to get started on it. On a basic level you need things like lathes, presses, cranes, and all of the other stuff that you need to work with metal and plastic. That stuff is *mostly* generic int that you can just buy it off the market. But even the generic stuff is expensive and some of this equipment will need to be custom made, which is even more expensive. Imagine, for example, that you need a really big crane. But nobody else needs cranes that big so nobody else can build cranes that big. Now you need to build all of the equipment to build the really big crane and then throw all of that equipment out when you're done because you're the only person that needed a crane that big so once the crane is built, the equipment becomes useless. With a huge rocket there is going to be a lot of equipment like that and its all really expensive to build. Then you're going to need things that have been specifically made for this particular project, such as molds and dies. Every single piece on the rocket needs its own mold or die, so you're going to end up needing millions of them and all of this has to be custom built. Then once you've got all of this shit made you need somewhere to put it, so you're going to have to go out and build at least 1 new factory, probably more. Then you're going to need a way to transport this shit from the factory(ies) to the assembly station to the launchpad. Again, the equipment needed to transport this all needs to be custom built. And as before, if there's no factory that can build a rocket carrier then you need to build *another* factory for that and all of the equipment in that factory. So why can't we just use all of this stuff from the Apollo Program? The answer is that this equipment isn't just immensely expensive to build, its also expensive to maintain. When they shut down the Apollo Program they made the decision that they were never going to use that equipment again so they sold it for scrap to avoid having to pay for maintenance on otherwise worthless equipment. Deciding to rebuild a Saturn 5 rocket wouldn't save any money because you still need to rebuild all of the equipment needed to build the rocket, and that's the main source of the \"design\" costs that you see quoted to build a new rocket. On the other hand, there have been 60 years of advances in material science since they started working on the Apollo program. Those advances allow you to use better, cheaper materials and the cost savings from that more than offset whatever minimal amount you save from not having to duplicate some of the old engineering work on the rocket itself.",
"Technically we can. But we will achieve nothing by doing so. The goal now is not just to go to the moon, plant a flag, take a few rocks and return. If we want to do new experiments or to build a base we need to send much more equipment than was sent on previous missions. And to do that we need much more efficient rocket, we can't just make it bigger.",
"Apollo astronauts took risks that wouldn’t be acceptable today. Some essential systems had no backup at all, due in part to the tight weight limits they were operating under. One example is the ascent system used to leave the moon. If that had failed to ignite for any reason there was no backup and the astronauts would have been stranded on the moon with no chance of rescue. While space exploration will always be a risky endeavour, it’s unthinkable that we’d send out a mission now with no contingency for such a major system failure. Hence we need to find a new way to do it.",
"There aren't \"duplicates\" sitting around in some warehouse, in the first place. It would probably be possible to recreate it with a lot of effort and billions of dollars of effort, but why would anyone do that? Sending a manned mission to the moon is not much of a challenge (in a general sense) today. Existing technology would do the job fairly easily (unlike the situation in the 1960s). The issue is that there is no particular reason to land 2 persons on the moon for a day or so (which is what the Apollo missions did). The moon might seem \"small\" relative to earth but the surface area is about 15 million square miles - of which a short termed manned mission could explore a vanishingly small portion of. Remote controlled landers and orbital scanners are far more useful. The question is not \"why can't we?\" but rather \"why should we?\"",
"We can't use the old tech for a few reasons. 1) a lot of blueprints don't work anymore. Also, even if we had all the plans, we couldn't use them. NASA used the plans for the Saturn Rocket engines essentially as guidelines. They would tinker with each finished engine to the point where each one is a 1 of 1 kind of thing. 2) the materials used are now illegal or too hazardous to use. 3) we don't have the technical know how or means to build components. There are great videos on YouTube about the guidance computers and how painstakingly they were hand built by extremely skilled workers. We don't have the same production infrastructure as we had then. Edit: see my update below. Tl,dr: the blueprints weren't the final product. Problems would come up. Technicians and engineers would come up with fixes for these engines, so each individual engine was essentially custom. No one kept the notes of the fixes or changes in the design.",
"Biggest reason is that those designs were inefficient and not very safe. The kind of designs Apollo missions used, now NASA will be sued for putting humans inside such dangerous spacecrafts."
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iyb2ck | - Transistors and their connection to logic gates. | Engineering | explainlikeimfive | {
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"A logic gate is a theoretical construct that takes two (usually) binary inputs and outputs one binary output. So, for example, an AND gate outputs yes/TRUE/1/yay!/whatever when both inputs are yes/TRUE/1/yay!/whatever and no/FALSE/0/nope!/whatever otherwise. You use logic gates to do binary arithmetic and logic operations, which are fundamental to modern computing. \\*A\\* way to implement a logic gate in hardware is with an electric switch. In that case, the binary states are \"high voltage\" and \"no voltage\" or, less commonly, \"current\" and \"no current\", or \"open\" and \"closed\" if you talk about the switch circuit itself. You can do this with any switch...a common household light switch, a relay, a vacuum tube, or...a transistor. A transistor, in the logic gate context, is just a very small, very fast, electronically controlled electric switch. The first big jump in computing came when we went to electrically switched switches, rather than mechanically switched switches (from relays to vacuum tubes) because now there's no moving parts and you can go a \\*lot\\* faster. Then we got another big jump with transistors because they can be manufactured from semiconductors and produced in incredibly small and integrated packages in one shot, rather than wiring up a bunch of individual components. This brought the cost per switch so low that \"everybody\" could carry a few billion transistors around in the their pocket for cheap.",
"Logic gates are an abstraction. They represent the idea of taking binary inputs and giving binary outputs. Transistors are electronic components that are used to implement logic gates in physical hardware. Imagine you have a pipe with two valves built in, and you need both valves open to let water through, you've got yourself a hydraulic AND gate. If you have the pipe split in two and rejoin again, with both sides of the split getting a valve, you've got a hydraulic OR gate. To complete the analogy, say instead of turning the valves by hand you invent a valve controlled by water pressure. If you have both a valve that turns on when it's actuated, as well as one that turns the water off when it's actuated, that's actually a pretty good analogy for how certain types of transistor work. Now you can feed the output of one gate into the input of the next, and you're away building a hydraulic computer."
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iyexpu | For how long can a submarine stay submerged underwater before it needs to get new oxygen? | Engineering | explainlikeimfive | {
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"If it’s a nuclear submarine, it generates its own oxygen through the electrolysis of water. Nuclear subs are more limited by the amount of food that can be kept on board since they generate their own oxygen and fresh water. Eventually the nuclear reactor needs a refuel, but that’s every few years.",
"It depends on the submarine. I believe modern nuclear subs are able to produce their own oxygen and fresh water, and are only limited by their food supplies, so they could go out and remain submerged for months.",
"Diesel submarines have a limitation of a few days because they are relying only on electrical batteries when under water, and the batteries only charge when the diesel engines are running, and you can't really run combustion engines under water because there's nowhere to vent the exhaust out to. Nuclear submarines can technically stay underwater for as long as the air purification system stays working. The main limitation there is the amount of food that they have for the crew (obviously once the food runs out you run into other issues).",
"It depends on the submarines and the rigging. Back in the days, for example during WWII, submarines did not have any way to replenish the atmosphere. So they could only dive for a few hours at a time before the air in the submarine would get high in carbon dioxide and low in oxygen. But as missions were changing and technology became better submarines would bring carbon dioxide filters and pressurized oxygen to extend their dive time. How long depends on how much supplies they bring which can depend on the mission. If they bring too much supplies they might not be able to fit as much other equipment. This is true even today. Even more advanced equipment allows us to extract oxygen from seawater using electricity and also to use electricity to filter carbon dioxide to be vented into the ocean. In theory this would allow submarines with this equipment to stay under water forever but in practice it is limited by their food, spare parts and other supplies. And if it is a diesel electric submarine it is limited by the battery charge which is not a factor on nuclear submarines. But in all cases how long a submarine can stay under water depends heavily on what they bring with them and this can vary a lot between different missions as the different missions have very different requirements."
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iygfnk | why do memories(SRAM/DRAM) need continuous refreshing to store a bit of information? | Engineering | explainlikeimfive | {
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"I believe only DRAM (the more common type) needs to be refreshed. DRAM uses a capacitor to store information because it's smaller and cheaper. However, a capacitor is inherently temporary and will drain over time. Because the capacitor drains, the bit will eventually be lost. So the capacitor needs to be recharged every so often to prevent it from draining. Edit: fixed mistake.",
"SRAM does not need any refreshing. It is called static ram for a reason. It doo not need constant power to keep the information. You store the data in transistors connected in a circle, most common is two inverters in a circle. DRAM needs refreshing because it stores data as electric charge in a capacitor and they do leak some and will get discharged over time. Today when it is SDRAM that is common they have automatic refresh so you just need to signal auto-refresh often enough and it takes care of the refreshing itself. Older DRAM you needed external logic for part of the refreshing procedure.",
"The issue is that the charge placed into the tiny capacitors that store the bits will slowly leak off (I say \"slowly\", it is refeshed about every 64 milliseconds). The insulation of the capacitors isn't perfect and charge cannot be stored forever on its own. There is a tradeoff between long storage times without access to power, and rapid access with frequent changes not wearing it out."
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iyhhjk | Why can't countries that want to build Nukes build Nukes? Especially since several countries built them, some 75+ years ago | Engineering | explainlikeimfive | {
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"They can and do (see Israel, India, Pakistan, NK, South Africa, etc.), except for signatories to the non-proliferation treaty (if they feel compelled to take the treaty obligations seriously). Of course it's expensive and difficult to do so, but the technology is not beyond the reach of most nations. For most though, it's not in their economic interest to build nukes, but it does make sense for them to seem to want to. Diplomacy involves carrots and sticks. Shelving a nuclear program might yield some diplomatic and economic carrots, or provide latitude in other unseemly areas. Throw in sabotage by other countries (see [stuxnet]( URL_0 ) for example) and it's a tough climb to get to nuclear capabilities even with adequate know how, funding and political will.",
"There are two answers to this. \\- They don't have the technology to do so. Not every country is technologically advanced as the US, UK, Russia, etc. Some countries have been trying for a long time to perfect the technology to do it, but unsuccessfully. \\- It's not to the benefit of the globe that there are more nuclear powers. There are only 9 countries in the world that have Nuclear weapons, as far as we know. Imagine what would happen if more countries did? If some of the countries in the middle east had them. We could end up in a nuclear war. It's bad enough that North Korea and some other countries have them. So the United Nations and some of its member countries have worked hard to make it so other countries don't develop them, sometimes turning to violence. The world doesn't want more nuclear countries. We recognize the potential for much violence if that happens. So we keep it from happening.",
"To add, it is also a geopolitical issue. Building nueclear weapons is highly threatening to your neighbors and violates a number of intentional treaties. There is a good chance you will end up isolated and sanctioned like North Koera and Iran. Or worse, just invaded during development, like Iraq or Libia. Most countries find that developing an alliance with a nuclear power gives sufficient protection without the massive international blow back. There is a reason the push in Ukrain to defend itself from Russia is to join NATO, not build a nuclear arsenal. It's sort of a isolated basket case country that wants them to begin with.",
"They can, given some time and money. Actually the hardest part is refining nuclear material sufficiently for use in weapons. After that building a functional (if not optimal) bomb is pretty easy. But you can't go buy any of the equipment off the shelf, you have to do it all in your own. And usually people quickly figure out you are trying and do everything they can to stop you.",
"You need weapons grade fuel, which you can't buy on Amazon. The few countries that can supply it are very carefully monitored. You can also build a reactor to generate fuel, but the materials needed to do that are also specialized and carefully monitored.",
"Something I haven't seen people here touch on is the payload delivery system. Building a nuke is hard, but feasible for many nations. What is more difficult is making a system that can deliver it to your potential target, otherwise what good is it? 75 years ago, they were dropped from big planes, but today? Those planes would be missile fodder and wouldn't get close. Modern ICBMs are much harder to build. A reliable missile system is just as hard as building the explodey part itself.",
"Can is a difficult word. If by \"can\" you mean has the physical capability, most countries have that. If they had the desire and the all-clear from the rest of the world, they absolutely could do it. If by can you mean \"would be allowed to\", then the reason they can't is that the international community and the current nuclear powers don't want it to happen. All of that is, of course, is a moot point because not many countries truly want nuclear weapons. It only makes them less safe. Once you let that nuclear genie out of the bottle, you paint a target on yourself. If you get into a war with another nuclear power, you risk far greater destruction than a conventional war could cause."
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iyhofx | What causes the tic-tac noise inside remote controls and other small electronic devices? The noise that is generally very annoying but doesn't seem to have caused anything to stop working? | Engineering | explainlikeimfive | {
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"A small piece of plastic from the shell or a small piece of the board has broken off and is bouncing around. If the remote has screws connecting the two halves of the shell you may be able to remove the bits by unscrewing the shell and separating it.",
"I was always the kid who took shit apart to try and \"fix\" it. Can confirm that 99 times out of 100, its a piece of broken plastic screw post. They can be pretty thin sometimes and a drop from a decent height can break off a side of one pretty quickly. Even now if I get a device that starts rattling, I pop out one of the screws and open the plastic shell enough for it to fall out."
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iyni23 | What makes some rooms have good acoustics? | Engineering | explainlikeimfive | {
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"Usually large rooms with reflective surfaces give a good reverb sound, also different angles(non parallel walls and ceilings/floors) help to diffuse sound to avoid weird ringing and flutter echo. Depends on what you are going for, you can make a smaller room sound bigger or a bigger room sound more “dead”"
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iywev4 | Why aren’t OBD sensors a standard part of you cars electronics offerings | Engineering | explainlikeimfive | {
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"More information isn't always good, the vast majority of users are not technically inclined Most cars have a method to read out the OBD codes without a reader. Old Dodges would print them out on the odometer if you did a little trick with the key. Users who are capable of fixing issues are generally capable of getting the codes, users who are incapable of getting the codes are likely going to just go to a mechanic Its more useful for most people to have a \"please service soon\" light and an \"oh crap, service now!\" light, any more granularity leads to confusion. Is it okay to drive with a misfire on cylinder 6? You have 5 others O2 sensor 3 error? Well clearly there are two spares that are working! The average driver just needs to know they should visit a mechanic",
"The dealer and the manufacturer both benefit when you associate the light turning on with “I need to go to the dealership” If they helped you understand when the light means low air pressure versus “your engine is about to explode” then fewer people would have the urgency to go spend money at the dealership.",
"Many people are talking about the legacy of why we still have a Check Engine and require an ODBII port to access it. However it shouldn't always have to be this way. In the past automotive computers were very expensive for functionality (think about it as cost per feature) so things were distilled down to the single most basic descriptor to reduce costs. Now computing and displays are so cheap that its possible to replace diagnostic codes with clear descriptors or at the least expose the data logged (yes all modern cars log data, just depends on volume and fidelity) for the customer. [ URL_0 ]( URL_0 ) Right now there are laws being passed in various states to require manufacturers to allow customers simplified access to this data so they can effect repairs themselves. Otherwise we may end up in a world like just happened with Tesla:Telsa had a network outtage. [ URL_1 ]( URL_1 ) This caused many features to misbehave and some owners couldn't access their cars (They had been dependent on network features). Imagine that Tesla for whatever reason doesn't want to support the older cars. They could lock owners out of features or the cars themselves. John Deere is already doing this with their tractors. Requiring escalating costs to patch or update their farm equipment for much more than a third party could provide. This isn't about warranties, this is about locking customers to have to pay the Original Equipment Manufacturer in order to keep their vehicles functional. So the simple answer is: \"It was originally done that way because it helped keep costs low. But continues to be this way because it is part of their business plan.\"",
"Far fewer issues than people think are engineers having some sinister plot to make things as difficult as possible for the end user. Anyone who would be inclined to resolve the issue themselves has an OBD reader or can easily get one, anyone who isn't won't benefit from seeing the code given that the code only says what's wrong, not why it's wrong. So there's no point increasing the electronic complexity of an already electronically complex vehicle, which adds more cost (for you as well as company) and more failure points.",
"It's a \"barrier to entry\". The average person isn't tech savvy. Even if they were told what the error was, they wouldn't know what it means, or how to fix it. P0455? WTF is that? \\*googles it\\* Evaporative Emission Control System Leak Detected? My car is leaking!? Meanwhile, someone who knows would just wonder \"did I tighten the gas cap?\"",
"There's not some sinister reason. Many vehicles have more information displayed on the dash these days. \"Check electronic throttle system\" popped up on our company truck the other day. But at any rate you can get the codes read by an auto parts store for free, but a faulty o2 sensor could be a bad sensor or a problem in the exhaust system, the engine computer doesn't know if the sensors are giving accurate info and something's wrong with how the engine is working vs if the sensors are bad most of the time. If you don't have the mechanical ability and curiosity to read the codes and look them up, you shouldn't be doing your own work on your vehicle anyway.",
"Instead of your car lighting the check engine light, let's say it displayed this in the information display: P0100 OBD-II: Mass or Volume Air Flow \"A\" Circuit What would you do? I know what to do, but then again I have an OBD reader and understand the codes. Most people wouldn't understand it and would just take it to the repair shop. So why not just display a light for those people? It's cheaper and generally less alarming than some random code.",
"The important thing is that the computer is not telling you what is wrong - it's telling you what the computer saw that was unexpected. An O2 sensor code may or may not mean you need an O2 sensor. If it's the \"heater circuit open\" code then you need to check the circuit from the computer to the o2 sensor, the o2 sensor heater circuit itself, and verify the computer can command enough amperage to run the circuit. & #x200B; So the OBD codes are not intended for end users - they are intended for techs who will use it as a troubleshooting guide, not a diagnosis. For those who understand that, and are willing to do the correct troubleshooting, we can pay $25 for an Actron scanner to read the codes (or \\~$1k+ for an Autel/Bosch/SnapOn scanner with live data and bidirectional testing features...)",
"The average person has little understanding of what the codes mean. The average person who knows a little knows much less than they think they do. In your example a code for a faulty 02 sensor could be one of several things with a bad sensor only being one of those things. Say someone's car thows a code for a bad 02 sensor. They pay a mechanic to replace the sensor. That doesn't fix the issue, now they think they are getting screwed when in reality the sensor was fine and the issue was elsewhere but they refused to pay for a diagnostic because their car told them they had a faulty o2 sensor.",
"One very prominent reason would be that there's a lot of people who assume they know about cars when they most definitely don't. Telling them specifically \"Hey, the O2 sensor is defecating on the duvet, swap it. The bolt is 10mm hex, and you'll need a 2\" extension to get in past the recirc system on the left side.\" is a recipe for them to be monkeying around under the hood like an idiot, doing damage to various random parts, and when their junk still doesn't run right they'd be either going to social media to trash the brand, or they'd sue the manufacturer for \"misleading them\" in some way. Generally speaking...the OBD system as-is serves as a good gatekeeper; if somebody is too stupid to get that right, odds are good they're probably not people who would be well-served to be told what parts are faulty. I know of at least a dozen people who need an idiot light to tell them something is amiss, but who think they could competently replace pretty much any part on the entire car. Those people are really not people you want to give concrete answers to because they will interpret those answers in the stupidest possible way imaginable. Additionally, dealerships do make quite a bit of side money from people bringing cars in due to a CEL. It's lucrative and until it isn't, it will (and probably should) exist. Too many people think because they used to watch Engine Masters and Roadkill on youtube that they can swap any part and make any car run. These are the people who would pull the oil pan to replace the oil pump (because the screen clogged, pump's still 100% fine), halfass put the pan bolts in, drive as far as the engine would go starved of oil until it seized, and then blame the manufacturer on social media for the failure. That, in itself, is a considerable liability for the manufacturer. Not to mention if it throws a rod and there's a bit of oil left to coat the rear tires, odds are good the goof doesn't know how to drive out of a wreck so it'd end up being a class-action lawsuit John Doe 1-10000 style. From a manufacturer standpoint, the fewer monkeys you have eating bananas over the mechanisms, the better. You simply cannot give the population that kind of power. If they knew anything they wouldn't need a CEL to tell them there was a problem in the first place. A parts replacer needs only to be given a general direction and a diag readout would play right into their hands. Better if there's a few steps involved to weed out the least suitable right off the hop. (BTW, the IAC valve in my truck needs a good cleaning. I'm noticing a little bit of errata especially when I raise the load; if I'm at a red light and switch on AC, she goes from creamy to mildly chunky for about ten seconds until it equalizes. My CEL hasn't yet come on, but it will if I don't intervene. There is a chasm of difference between a parts replacer and a competent mechanic. One, you really want working on your car, the other you'd do well to forbid even looking at your car. Lots of parts replacers think they're mechanics. They're not. A parts replacer would swap the valve when all it needs is a good spray and scrub.)",
"You can get a decent code reader for like 20 bucks! I got a code reader and if anything pops up I just Google the vehicle model and the code. I got all the information I'll ever need on where to get started repairing my vehicle!",
"Most people don't know jack about cars, and I'd venture to say even more people lack the ability to accurately diagnose the root cause of the problem. Take your example of \"faulty O2 sensor\". Car throws a p0131 code, first result on google says: * Failed Oxygen sensor * Damage or unplugged wiring * Open or short * Improperly reading coolant temp sensor * Failed heater circuit for oxygen sensor * Most commonly the sensor has simply failed due to age and wear The average person would say, \"replace the O2 sensor, easy peasy\". The code may imply that the O2 sensor has failed but really what it means is that the sensor is reporting a lean condition that may be caused by other things such as a vacuum leak, clogged injector, exhaust leak, etc.. On top of this when an O2 sensor reads lean and throws this code its also increasing the injector pulsewidth and adding more fuel to try to compensate for a perceived lean condition. This translates into higher hydrocarbon and carbon monoxide emissions and potentially can damage the catalytic converter long term (not good). Then there's the cost factor, Ford sold almost 2.5 million cars last year. If it cost $2/vehicle (Idk how much it would cost to implement, just a random number), then they've shaved $5 million off their net profit. Shareholders wouldn't be happy, Ford execs wouldn't be happy, and if they started raising car prices to offset then the consumer wouldn't be happy. Basically, it comes down to is for most people seeing a bunch of numbers and sensor data on the dash would be the same thing as seeing a glowing yellow light. Some people would try to DIY a repair and end up negatively reviewing the vehicle because they don't posses the knowledge. It would end up negatively impacting emissions and it would lower their net profit by implementing it",
"OBD2 readers are super cheap. If you think you are skilled enough to fix the issue, just buy a reader",
"Ford Service Manager: \"Notice how our service area is larger than our sales area? That's because we make more of our money on the repairs and service after the sale.\"",
"Because it doesn't know with 100% certainty you have a bad O2 sensor. Error codes are a path to the problem area. Diagnosis is still required in many cases. I can't even count the number of \"It has a bad O2 sensor\" customers I have had that had a small hole in the exhaust creating false downstream readings.",
"I think because it’s not as simple as that. How can a car’s computer tell the difference between a bad O2 sensor and a break in the wiring? The codes are meant for the diagnostician to use, not the driver.",
"The check engine light has a name! Malfunction Indicator Light (MIL) it’s an easy thing to let the 5 year old operator know there js a malfunction that requires attention from adults. Now, smart 5 year olds may buy a ELM327 dongle with an app on their phone to read these malfunction fault codes. This may focus the diagnostic search, or just plainly send the technician chasing ghosts. See the youtube channel of [DiagnoseDan]( URL_0 ) if you’d want a taste of what the codes can and can’t tell.",
"Someone has probably said this but.... & #x200B; Its like when people go to Autozone or something and get codes read. The dude/chick behind the counter pulls your codes. You have an 02 sensor code. They're going to try to sell you an 02 sensor. Most have no technical training or knowledge, they are retail employees. & #x200B; The average person, if there instrument cluster told them what was wrong they would either ignore it like they do the check engine light or be taken on a wild goose chase because they don't even have the basic understanding of how the systems work or how they are troubleshot. & #x200B; Now you could have a leaking exhaust gasket introducing unmetered fresh air into the system causing an 02 sensor stuck lean code. That may be the only code in there. In peoples minds they just want to replace whatever the code says there is an issue with. The code says 02 sensor, so ill just replace it. & #x200B; Its a common misconception that Computers/Readers just tell you what's wrong. Automotive systems are extremely smart but it is a very rare case (dont get me wrong, with experience there are certain things that you can be sure of, IE 02 Heater Circuits) that a code will say \"this bad, replace it\". & #x200B; There are just way too many variables to have a definitive answer on what actually is wrong and it takes someone who knows how it functions and what could lead to incorrect readings etc in certain systems to truly troubleshoot it. & #x200B; Easiest for the general public, orange light comes on you should be ok but get it looked at. Orange light comes on and flashes, shut it off before failure or deep damage occurs, have it looked at. Easy logic for the public to follow without wasting time and money hanging parts that may not fix it."
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iz0wb0 | How does burst fire work for firearms? | I understand semi-automatic and automatic fire, but I am not sure how the mechanics work for burst fire. How does the firearm know to only let 3 rounds out? | Engineering | explainlikeimfive | {
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"In most cases there is a rotating cam inside the fire control group that engages with the trigger each time it's pulled. When the trigger is held down, the FCG allows full auto fire for three rounds until the cam disengages the trigger. When the trigger is reset, the cam resets with it."
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iz9kcb | How does a piece of rubber around your teeth protect (mouth guard) them in sports? | I'm looking at this from the perspective that if I punched someone on their teeth with one on, it would still knock a tooth loose no? | Engineering | explainlikeimfive | {
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"Hello! Your friendly internet dental hygienist here! Think of a sports guard like insulation. It’s going to support and stabilize your teeth as well as absorbs any blunt force trauma to your mouth. If the trauma is severe enough, damage can still be sustained to the teeth, but the damage will be lessened with a sports guard than with none. Also, a sports guard does more than protect teeth, it can also save your tongue and cheek from being bitten or cut during trauma."
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izffs4 | why we don’t use ocean or salt water in toilets instead of freshwater | Engineering | explainlikeimfive | {
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"A) salt is a bitch. Let us know when you come up with this awesome salt resistant coating B) most places aren't anywhere near the sea.",
"You are right that salt water isn't good for pipes. While you could make pipes that are more resistant to the effects of salt water, you would need to make two sets of pipes to each home or business, one with salt water and one with freshwater. The hassle and expense of having twice as many pipes isn't seen as worth the savings of not having to use freshwater in toilets.",
"Two reasons 1. Water treatment relies on bacteria, some of which dont like saltwater. We would need separate treatment plants with different technology. 2. We'd need twice the pipes. Additionally, most places dont really have a problem with water supply (with there obviously being some prominent exceptions). USUALLY, the big issue around water is treatment. Issues are not caused by supplying water, but by dealing with the waste.",
"We could. But then you'd need an extra water pipe system that has to be seperate. Likely not worth the investment as the most expensive part of water is cleaning it after it was used, and not extracting it (in most places) Unless you plan to throw the wastewater back into the ocean untreated."
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izhdyr | Why are most gas stove knobs like off > high > med > low, rather than the less counterintuitive off > low > med > high? | Engineering | explainlikeimfive | {
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"A gas stove might have problems lighting in low setting. It is also better to turn in off from a high setting as a hotter flame produces less sot. So the manufacturer designs the knob with the off and high settings right next to each other. This way you need to go through high in order to switch between low and off.",
"Because turning the knob simultaneously opens the gas and fires the ignitor. With full gas pressure you will have a more reliable and consistent ignition on the first try. If you try to do it on the low setting sometimes the flame doesn’t light evenly around the burner and you end up with a half-lit burner. Worst case scenario this can result in unburnt gas leaking out."
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izhzwf | Why do they use rebar in concrete? | So, I know they use rebar in concrete to enhance the strength and I’m fine with that, but why are they using something that will degrade in 10-20 years and that during that degradation destroyed the concrete from the inside? Why can’t they use something like epoxy resin and fiberglass? Or is there simply nothing with the strength that compares to enhancing with rebar? Note, the Empire State Building was built without rebar and will be standing long after many buildings crumble in NYC. | Engineering | explainlikeimfive | {
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"Concrete is very good in pressure but weak in tension, so the rebars take it. If it's done correctly the steel doesn't degrade at all.",
"Construction rebar is epoxy-coated to prevent corrosion, and the caustic environment of concrete is enough to prevent corrosion from taking place. It's a preferred addition to concrete structures because its physical properties are substantially similar to concrete itself, so you don't have to worry about structural failure caused by the two materials behaving differently as temperatures change.",
"Steel has a good strength to weight ratio, a fairly high Young’s modulus (how stiff it is), good thermal compatibility with concrete (it expands/contracts at approximately the same rate as concrete) and is economic and concrete grips to it fairly well. Provided it is kept dry it won’t corrode even over decades, even when wetted it is resistant to corrosion due to the alkaline concrete that slows corrosion, and in hostile environments with lots of salts you can fairly economically coat it with galvanizing or epoxy to slow/stop rust. If steel/rebar in your building is getting wet you have leaks and more immediate problems to worry about than a decades long rusting process. When it fails it fails in a ductile manner. It stretches and deforms before it breaks, so everyone can see something is wrong and get out. Empire State Building: This is a steel framed building. If corrosion were an issue the steel beams and columns would be having major problems. When you see it was built “without rebar” this refers to the floor slab construction where they use a (now) archaic system where instead of concrete and rebar they used cinder and draped wires. The wires are still steel. They don’t rust because they’re kept dry. The Empire State Building’s durability is no different than any other maintained steel framed building. Fiberglass: This tends to be brittle. If it fails it snaps... you can use it, but it’s often supplemental. Carbon Fiber in an epoxy resin: This is used to strengthen concrete beams, columns and slabs. It’s normally supplemental to rebar, because the methods to adhere to slabs aren’t reliable in fires, and the way the systems work it’s more flexible so if you were t only use it you would see large deflections. Other fibers: Theres a method using “micro fibers” - millions of little strands each about an inch long that get mixed into the slab. This is commonly used in slabs at the ground level that get cast on the ground level where there isn’t a basement and the slab can rest on the ground. Due to having nothing that can corrode these slabs tend to be durable."
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izn5ui | Other than Color, Are all Electrical wires the same? | Engineering | explainlikeimfive | {
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"Yep. The metal is not different. Not to say their are not different metals to build a wire out of. But your car for example: the wires leading the each terminal is the same metal.",
"Pretty much. If it's within one housing (say your phone's charging cable) they're all pretty much gonna be the same, but for more complex devices some wires are going to be thicker than others, and some will use different shielding depending on how much power is going through it"
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izq4st | Why are motorcycle so loud? Do they have to be that loud because of how they’re built or is it just for show? | Engineering | explainlikeimfive | {
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"A lot of it is just for show, although many people argue that \"loud pipes save lives\" meaning it alerts people in cars and trucks to the fact that there is a motorcycle nearby. There are many Japanese and German motorcycle manufacturers who make extremely powerful bikes that are very quiet. Personally I ride a KLR650 which has a throaty thumping sound (single cylinder - they call them thumpers), but it's not really noticeable from more than maybe 100 feet away.",
"Harley = loud on purpose. Engine is even built to be louder at the expense of efficiency and power. Others aren’t as loud",
"Both. Some people put louder exhaust pipes on their motorcycle on purpose. They believe it’s cool or they believe the extra volume will help alert drivers of their presence so they don’t accidentally run them over. But design also plays a role. Motorcycles are designed to be lightweight whereas the average car is designed for comfort. Cars are much heavier, so if you add a really nice muffler on it, it doesn’t have a profound impact on the overall weight of the car. A motorcycle might sacrifice sound dampening in order to reduce mass. Also a car’s engine is surrounded by the body of the car, dampening the sound further. Motorcycle engines are more exposed. Lastly, motorcycle engines rev faster than typical car engines.",
"It can be either, but my experience with “loud for a purpose” exhaust was the first time I split lanes on the freeway (legal where I live). I was cautious and terrified and my bike is very quiet. Another rider came up behind so I let him pass and he had on a loud (when revving high) aftermarket exhaust. When cars would be tight around the lines, he would rev a little bit and you’d see them split like Moses parting the red sea. It made his splitting lanes 100x safer than it was for me.",
"Aight so I didn’t see an actual explanation scrolling through the first bunch of reply’s... The sounds you hear from an engine is caused by very fast air leaving the engine. When it hits the (relatively) slow air outside of the engine, you get a collision and a shock wave, which is what you hear as a “loud engine”. Most engines have mufflers, which is a part attached to the exhaust of an engine which forces the air through a tortured path (think of a maze, but for air) that slows down the escaping air, making the shock wave smaller and “quieting” the engine. This has the side effect of creating back pressure, which pushes back on the air escaping from the motor. Some engines (cars, motorcycles, etc) have straight pipes, which just means there’s no muffler or resonator or catalytic converter or anything else. This is done for different reasons. On cars and motorcycles set up for racing, you want to reduce that back pressure as much as possible. But you do that along with adjusting the intake and changing timing, spark, etc to optimize how much power you get out of the engine. On the other hand, some people throw straight pipes on their motorcycle with no other changes, which simultaneously makes the engine incredibly loud, an emissions nightmare, and makes it run like crap. There is no good reason to do this, don’t do this.",
"A stock road motorcycle is sold with a muffler that contains 'packing' which is a fill of multi layered fiberglass that keeps the noise to 96 decibels, an AMA mandated level. To obtain that 'loud pipes' sound, the buyer of the cycle must remove the stock packing or buy an aftermarket pipe for the motorcycle.",
"A lot of it is rider preference. The bikes aren't that loud from the factory, but the rider installs their own exhaust pipes to make it loud because they like it personally. Bikes in general are also louder because there is a lot less travel in the exhaust system. A cars exhaust system can be 3-4 times longer, so thats more space that can be spent quieting the sound vs a motorbike",
"ELI5 version: stock exhausts on bikes are usually quiet. Aftermarket exhausts make the bike go faster because it helps it breathe. Which also mutes the sound a lot less, making it louder! A lot of riders like how they sound. Usually motorcycles run better and faster (results may vary) when you don't restrict the exhaust. Stock exhausts are usually fairly restricted to meet environment and decibel levels for the city. Less restriction means that more sound leaves the exhaust and reaches your ear. A lot of these performance exhausts come with baffles that limit the sound, but people take them out because it \"sounds\" cooler. They're also illegal in most states because you have to be around 90db or so. A lot of straight pipes and performance exhausts will be 100-120. I'm a rider and am looking to upgrade my exhaust, but am super conscious about how loud it'll be, because an overly loud exhaust is sooo obnoxious.",
"It's just for show. Many people claim \"loud pipes save lives\" but statistics show the opposite - modified bikes are more likely to be involved in an accident, and those accidents are more likely to be fatal.",
"Depending on the bike you can gain about 5-6 HP just by swapping the exhaust with an aftermarket one, the muffler creates back pressure that reduces power. Most of the time who swaps pipes also replace the airbox, which can give another +10 HP. These are huge gains for a bike. It is also relatively cheap and an easy DIY.",
"The larger the sound the smaller the resonance chamber. You see, the shorter the resonance chamber the less time the sound has to be muffled. That's why they're so loud. There are plenty of bikes that have long resonance chambers though. It really depends on the man buying the bike. Some men enjoy long chambers, others prefer a short chamber.",
"No vehicle is allowed to emit more than 80 Decibels, according to Federal Law. Motorcycles included. Loud pipes DO NOT save lives, and these aftermarket mods are not US legal. I do admit, they aren't often enforced, but... Also, putting the more effective muffler on the motorcycle does add weight, which is not loved by the rider. I have lived next to bikers, they had the audacity to complain about my Marshall. Was a short conversation. Rock N' Roll wins again. (No, they did not want my amps pointed at their house full blast at 6:30am). Chased another guy who \"engine-braked\" past my house regularly into a gas station, the confrontation was quite amicable. He had a super-modded bike, I had a newborn. Bikes are cool, but no, they don't have to be so loud",
"From a motorcycle drivers perspective. It's half and half. You have an open air engineer with a very short distance from the engine to the exhaust exit. This adds sound right away. There are usually resonators and mufflers added to make the air take longer to travel out and quiet it down, but it adds a lot of weight, and it's usually only to one side of the bike. There are many aftermarket exhausts that keep the muffler, but get rid if the resonator. They add a bit of sound without adding too much (I like these). Just like cars you can get rid of the muffler and resonator all together and you just get all engine noise. Depending on the engineer these can be mildly loud or extremely loud. Almost all bikes are made with quiet exhausts to pass standards in various markets.",
"Harley's are loud because that's what their buyers want. Sport bikes are loud because removing the noise costs energy, which costs speed. Same as race cars. Tuned opened pipes are fast.",
"I'm a motorcyclist, but I've only rode Japanese bikes. I find excessive exhaust noise to be obnoxious, and don't buy the \"so they'll hear me\" excuse. I asked someone familiar with Harley Davidson bikes about the excessive exhaust noise, and he told me that the bikes come off the assembly line functioning with relatively quiet exhaust. Then the first thing a new Harley buyer does is put loud pipes on the bike. So the bikes need not be loud, it's just childish owners.",
"Free flowing exhausts generate more power, but also more noise. It's the same in cars, I'd suggest the cost of car parts vs the relative cheapness of motorcycles and their parts, along with the recreational nature of the vehicle leads to more people installing loud pipes on bikes. Some do it for show, aka just for the noise and the \"look at me\" factor, but I personally don't think a $500-1000 can is worth the 3% horsepower gain, the additional emissions, the noise pollution for others, or the increased risk of hearing damage. A whole system is cool, and you can get a decent gain, but my bike is already stupid fast, it's just unnecessary to me RE: the above factors. I owned a Harley once where a guy put straight pipes on it, not only was it stupid loud, it made the bike run like shit... it's a meme basically, \"the Harley tax\". Seems like every fuckboi with a CBR puts a can on their bike too, cuz fuck the polar bears and the neighbors, I'm a rebel bruh!"
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izy144 | Why do municipal buses in the US have flat noses while school buses have normal hoods? | I saw a school bus today with a 'cab over' design. It made me realize that I almost never see that design for school buses even though it is almost universal in other types of buses. Anyone know what the reasoning is behind that? | Engineering | explainlikeimfive | {
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"School busses are a bit smaller than city busses and city busses require a flatter lower floor so people can walk around; putting a driveshaft all the way from the front of the bus to the back would mean either raising the floor way up or putting a hump in the middle, so they put the engine in the back. School busses don't really have that requirement, so it's okay for them to take a more simple approach and use what is essentially a flatbed truck with a shed on top.",
"The engine is in the back of most municipal busses. The engine of most school busses is in the front.",
"A big reason is capacity. A type D bus (Flat nose transit style) can carry more passengers than a type C bus (Typical nosed school bus style). For example school bus builder Thomas builds both type C and type D buses. Besides proving that some school systems do use flat nose buses, otherwise why build and sell them, the type D bus carries 90 as opposed to the type C at 81. So then, why don't schools redo their routes to take advantage of the larger buses? Route time. Dropping off 90 kids at 90 houses in a rural area would take forever. So you break up students into more, but shorter routes, and purchase the cheaper type C buses. For commuter transit systems, which tend to exist in more urban areas, overall capacity tends to be more important, so you see type D buses used more often.",
"The engine being in front of the driver has significant advantages for maintenance. Since school systems often keep their buses for decades, ease of maintenance is critically important. Also, since the engine-in-front versions are simply a bus body dropped on a traditional Class 6 truck chassis, the cost to purchase is lower."
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izy36a | What is it about a .50 caliber round that makes it so much more destructive than smaller stuff? | What is it about the size and speed and whatever else about this round makes it so much different than others? Is there a projectile size and speed that sees some type of jump in ballistic properties? Everything from popular culture to reliable reports talk about the "fiddy cal" with reverence and fear. I used to shoot pistols and rifles a lot; .22s, 9mm, 7.62x39, and the like. I know that the composition of the round matters a lot in terms of damage, penetration, and destruction. But once we get above a typical rifle round (.30-06 and other hunting rounds) and into .50 territory we start to hear about "anti-materiel" capability and body-exploding impacts. What characteristics of a firearm projectile flips it from "high-power" to "anti-materiel"? | Engineering | explainlikeimfive | {
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"When people talk about \".50 cal\" typically they mean .50 BMG. Which has the characteristics you describe because it is larger than calibers like 30-06 in every dimension. The case is significantly longer and features a significant increase in cartridge case diameter and thus volume. This volume is filled with a significantly heavier powder charge and uses a much 'hotter' gunpowder than many regular size cartridges. Finally it propels a gigantic bullet. Where a 30-06 bullet may be 200 grains in weight (1 grain is approximately 1/7000 of a pound) a .50 BMG uses bullets in the 600-750 grain weight range and pushes it at similar or higher velocities (depending on charge). Energy is a function of mass and velocity, so having a higher mass and equal or higher velocity means that it will have much greater kinetic energy. This is where the 'body exploding' characteristics come from. There are smaller, weaker 50 caliber cartridges which behave more like the 308 winchester or the 30-06 you mentioned. Some examples are .50 action express (notably from the desert eagle), .50GI, 50 beowulf and .500 nitro express.",
"The bullet and the cartridge are just sooo much larger so they hit that much harder. They're also large enough that specialty rounds have been made You reference a 7.62x39, that fires an 8 gram bullet at 730 m/s A .30-06 round comes in somewhere between 8 grams going 1000 m/s and 14 grams going 750 m/s. In WW2 there were tons of variants like the M2 armor piercing round that had a copper jacket over a steel core to help it punch through armor, or Incendiary M1 rounds with the blue tip that are full of material that ignites on impact. .50 cal is where a lot of the fancy rounds live though. Your basic .50 cal round has a 50 gram bullet moving at 900 m/s. While the bullet is only moving about 20% faster than the AK's round, it weighs 6x as much. The large capacity in the .50 round gave them plenty of room to make armor piercing rounds with steel cores, or incendiary rounds with flammable material, or tracer rounds with phosphorous in the back, or Armor Piercing Incendiary-Tracer rounds (API-T) with a steel core, flammable material *and* a glowing base. They even had enough volume in the bullet to make high explosive rounds with tungsten penetrators inside. [Wikipedia has a helpful comparison image]( URL_0 ) to show the size of the .50 vs the 7.62x39 (dark greenish one fourth from the left), and the tiny .22LR round all the way at the right"
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j0211a | why should we compile a program if we have kernel apis? | Well, talking about windows programming why should I compile my program for more cpu architectures if we have the same kernel api? Thanks Maybe it's a dumb question but it's tricking my brain | Engineering | explainlikeimfive | {
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"Because when you compile your program, it gets converted from your high level programming language into low level instructions which are CPU Family specific. The Intel x86 family use one instruction set, but the x64 processor family have a different instruction set. There is backward compatibility but there are also new instructions which you will only take advantage of if your program is compiled for the newer x64 instruction set. In addition, there are high level APIs in Windows which are only available for 64bit applications, and don't have backward compatible 32bit versions."
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j04m91 | Why are 'competitive/Paralympics' wheelchair's wheels slanted? | So I was watching [this]( URL_0 ) video of two (apmutees) people playing badminton on wheelchairs and noticed that the wheel were slanted and I can't understand why they do that...so smart people of reddit please tell me | Engineering | explainlikeimfive | {
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"The slanted wheels help stability and stop the wheelchair tipping over during am impact (in the case of wheel chair rugby) or allow you to turn quicker (in the case of racquet sports, without risk of tipping over).",
"It creates a wider base, which allows them to change direction and maintain balance easier. If you look at pro tennis and badminton players, they will intentionally put their legs wider than their shoulders and keep their legs bent. It allows them to quickly move themselves around the court, as their center of gravity is already low, meaning they can go strait to pushing their body around, instead of “dropping” from a standing position. It also allows for faster turning and better handling of the chair in general, compared to regular wheelchairs.",
"It helps give them a wider more spread out base, basically the different size and angle and placement of the tires also harder turns. It also lets them do things like lean way back for a 3 point fade-away without the chair tipping. Think of the Paralympic wheelchairs as the sports edition."
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j08j8c | How is this light made? URL_0 | Engineering | explainlikeimfive | {
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"If you go to their [product page]( URL_0 ), and click on \"Specifications\", you see this little bit of info: > Universal Power Supply, 24v output So that's how. This light uses 24V, which is still considered safe to touch. 24V is about the highest you can go before you start worrying about danger. Also it's probably DC which is a bit safer than AC. If I were you, I wouldn't put metal things on the shelf."
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j09xbu | Why do cyclists wear small and flimsy helmets when sometimes they can ride as fast as a motorcycle? | Engineering | explainlikeimfive | {
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"Bicycles don't normally reach the kinds of speeds motorcycles do. You aren't going to go 65 mph regularly on a bicycle for example. Another factor is that motorcycles are much heavier. If a motorcycle crashes the rider will be tumbling alongside a 300-400 pound object. In a bicycle crash the bike likely isn't even a tenth of that weight."
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j0fool | why car batteries don't die when we're driving/fully started, but die when we leave a light on for a few hours | Title, why can we drive for hours and hours on end, with headlights, radio, a/c, etc. (besides stopping for gas, bathroom breaks) But when we leave a light on for as much as an hour, the car battery will pretty much die instantly. | Engineering | explainlikeimfive | {
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"Your cars battery, for the most part is used to start the engine. Then your car runs off of the alternator, which also charges the battery. So. While your driving your not actually actively using your battery. When your car sits and is not running the alternator is not in use. So your battery is what keeps things going, and since the alternator isn't on to charge it up, it's being depleted continuously which leads to the battery dieing. As for how long it takes to deplete the battery, that's dependant on the batteries capacity as well as it's age and how well the battery had been taken care of",
"When the motor is running the car battery is being constantly charged by the alternator which is run by a fan belt.",
"The battery is used to start the car. Once the car is started, the alternator takes over powering the electrical components. When the engine is turned off, the battery is the only thing capable of powering those components so that’s why a battery will die if you leave your lights or radio on while the engine is off.",
"Your cars engine recharges the battery when the engine is running. A battery can store only so much power. Many batteries (like in your phone) use relatively little power at one time, because your phone doesn't have moving parts (except maybe a vibration function). A car battery needs to deliver a huge burst of power all at once- enough to turn your car engine over until the engine fires up and then uses fuel to continue running. The battery can power your engine itself if you wanted ... for about 30 seconds. Then it would be flat. Once the motor starts, the energy comes from the petrol burning. That energy then partly flows back into the battery to recharge it, ready for next time. This uses something called an alternator If your alternator fails, the battery will eventually go flat and you won't be able to start your car."
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j0ncsb | What do nanometers (nm) refer to when talking about microprocessors? Why is smaller better? | I often hear about a new, smaller microprocessor that is, for example 5nm instead of 7nm. | Engineering | explainlikeimfive | {
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"Basically this is the size of the \"switches\" inside the processor. The more of these you have the more calculations you can do and the faster you can get things done. Smaller switches means more processing in the same amount of space.",
"When talking about nm when it comes to microprocessors, it can mean two things. The most common one that likely everyone has heard is in reference to the fabrication process name. For example TSMC's 7nm, in the context of the first 7nm CPU in the world. That meaning is nothing, it is just a marketing term. 20 to 30 years ago, the process name had meaning behind it, related to the second meaning I'm talking about. It used to relate to the physical size or distance of something on the actual CPU. Smaller is better because it allows less distance to move elections between components. This means it can be faster and more energy efficient. Smaller also means you can fit more in the same amount of space.",
"A microprocessor (or any other chip) consists of millions of electronic elements (such as transistors) that are extremely tiny. These elements are created by a special and very expensive machine on a surface called a wafer. Multiple chips are created on a single wafer as the chips are tiny and the wafers are about as large as a small pizza. The nm is a measure for the accuracy at which the circuits can be created by the machine. A nm is about 150 000 times smaller than the width of a hair. Developing machines that can manage this accuracy is extremely hard and it is also common to have some amount of produced chips on a wafer that are bad. The percentage of good chips on a wafer is called the yield. But the benefit of smaller nm sizes is that the created circuits are smaller, allowing more chips on one wafer which reduces cost. Also, having smaller circuits means that they can be more power efficient when they run and this can allow a chip to run at faster speeds. When manufacturers start producing with a lower nm technology, the yield is often low. But for microprocessors many \"bad\" chips can be salvaged by disabling some functions or memory and selling them as lower specced processors."
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j0ob09 | What do the brush type things on the side of escalators do | So on most escaltors on the side near your feet there are these brush looking things that stretch along the escalator and ive never known what purpose they actually serve. | Engineering | explainlikeimfive | {
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"They are there to alert you through friction against your pants or legs that you are close to the edge. That way you can avoid getting pieces of clothing stuck in the crack between the side and the moving part. They also keep the shoe laces away from this crack. They most certainly are NOT to clean your shoes. In fact it is a terrible idea to try to clean shoes with it, because you need to take your shoes, laces and pants close to the edge and that defeats the whole purpose of those brushes. EDIT: Howly caw! I am floored with all the positivity this comment has received. Thanks everyone. I am amused that of all the thoughtful comments I write on reddit, this one received so much traction. I am glad that all those who were using the brushes to clean their shoes now can do so with the knowledge of the risks.",
"Three things. 1) To keep things like laces and trouser cuffs away from the gap at the edge of the moving steps where they might get trapped and pulled in. 2) To reduce the amount of dust and debris that makes its way into the mechanism. Some still gets through, though. 2) To help ground static charges that build up in the escalator during operation.",
"Ok but for real, if they are to keep people away from the dangerous parts of the escalator, why did they invent them as something extremely fun to touch and jam your shoes into?",
"They're to discourage you from standing too close to the sides where you or a piece of clothing could potentially get caught in the escalator.",
"The brushes are a warning! Stay far away if you can. You don’t want to get something stuck between the edge or cracks in an elevator, like your shoe laces or long hair or some clothing.",
"My work recently had to have them replaced on the travelator; it's the flat escalator. The escalator company said it's to help reduce static shock.",
"It's for scraping the meat off after you get stuck in escalator and you go around through all the gears and a full rotation of the belt.",
"They're there to make sure shit doesn't go where shit doesn't belong. Think of those little \"brushes\" as your friendly \"anti final destination\" helpers.",
"It's to stop litter and rubbish collecting under the escalators and causing a fire. (please check King's Cross fire for reference)",
"I didn't understand a damn thing in this thread until two minutes in. Kept reading 'calculators'...",
"They have several uses, but the biggest is to let static charge run away from the machine instead of building up and either shocking someone or damaging the electrics of the machine. An escalator is basically a giant Van De Graaff generator.",
"When I was 12, I got my shoelace stuck in an escalator. I noticed it was stuck only about 3 or 4 stairs from the top. So I yanked my leg a few times and the shoelace finally snapped literally on the last step, only inches before the step started descending into the grates. I was with friends and mentioned it to them right after it happened, and pretty much the mood was \"ha that's interesting.\" Nobody really cared, including me. I didn't think much of it at the time, and wasn't freaked out or anything. But as I've grown older, I'll think back on it sometimes and wonder what would have happened if I didn't notice and break the string myself. Would the escalator have just ripped the shoelace for me? Or did I come with inches of a gruesome injury or maybe death?"
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j0ukjf | Why do some stairs have that little hangover at the edge of every stair? | Doesn't that little hangover over the stairs risk you tripping when going up? | Engineering | explainlikeimfive | {
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"That part of the tread (the horizontal part that you step on) that overhangs the riser (the vertical part between treads) is called the *nosing*, and generally it's there to provide a little more space on the tread for your foot without having to increase the stairway's *run* (the overall horizontal distance travelled). It's helpful for ascending and descending the stairs, as long as the nosing isn't too long. If it's too long then yes, you do risk tripping on it. Accessibility guidelines and laws like the *Americans with Disabilities Act* (ADA) will specify a limit on the length of the overhang. ADA for example requires that nosings can't overhang by more than 1½\"."
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j0vhq4 | Why do lollipop sticks have a whole on the side of them ? | Engineering | explainlikeimfive | {
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"text": [
"It gives something for the candy to attach to more solidly. A slick plastic stick may cause issues for candy to grip, so they add the hole to ensure a good connection between the two.",
"you have 2 of them the one that goes thru the length of the stick is a safety precaution against choking in the odd event it gets ingested. the one in the side of it inside the actual candy is for the molding process so it gets a \"hook\" to grip on while cooling off, without this you might have issues with the candy sticking to it during manufacture."
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j13u7g | How do prosthetic arms/hands work where they actually have fingers/wrist that move? | Engineering | explainlikeimfive | {
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"There’s probably more than one way but the ones I’m aware of read impulses from muscles in the forearm and translate that to finger movement. Basically you train it to work by performing a certain action and pairing that with the new movement; eg you flex/twitch a forearm muscle, it reads the electrical impulse from that and learns how distinguish it from other impulses in your forearm, then when that impulse happens the finger tightens or whatever There are fancier versions now that tap more directly into the nervous system and some that even have fake skin and can give some sense of tactile feedback but I can’t speak to how those work (although I’d imagine it’s basically a much more precise interpretation of the nervous system output along with experimentation of giving the nervous system input)",
"Let's say you think about curling your finger and the finger curls. No finger, no curling. But if you try to curl you finger and theres nothing there, the nerves responsible still fire like they've been trained to.The nerves that control certain motions you can no longer do are detached from the stump's nerve bundle and attached to nearby muscles. These newly reattached nerves still cause the muscle they're placed on to twitch, which can be picked up by an electrode implanted nearby. The electrodes can then communicate with a prosthetic, so you place a prosthetic hand that's wired to curl that same finger when it registers the electrode picking up a muscle twitch. Your thought (curl the finger) is then carried out by the prosthetic. The advantage to this is its intuitive, that action's pathway is already mapped and the same nerve gets the right response so the learning period is shorter than if you had to train an entirely new pathway. The electrodes can be energized by the prosthetic itself using the same technology as a wireless phone charging pad. The two communicate using bluetooth. I'm not sure about the process behind receiving tactile feedback from a prosthetic, but I'd imagine it's a similar process in reverse."
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j14tfl | Why do downshifts after certain revs lockup the tires? | I know that downshifting during a corner will lockup the tires if you don't rev match. I know that downshifting when going out of the speed of the gear your shifting to, will lock the tires. It makes sense that the tires would lock, more so in the second one because the drivetrain can't go that fast in the gear you're in, so the tires lock until you're in that range. But with turning, I can't figure it out. You're not outside of the gear range, just lower revs. But why does lugging the engine by making it rev harder lockup the tires? I'm kind of embarrassed asking this, as I knew the answer before, but I just kinda forgot after driving an auto for a while | Engineering | explainlikeimfive | {
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"Shift into too low a gear, the motion of the tires is slowed to rev up the engine, you’re engine braking. Normally not a problem, the tires have lots of traction and can handle this. You even do it on purpose going downhill. But tires have a finite amount of traction, not just forward and backwards, but side to side, and it all adds up together. So you’re taking a tight corner, tires are near their limit sideways, and you suddenly engine brake them, they may lose traction. Normally they won’t stop, maybe your differential isn’t applying power since it has no traction, or it’s your car’s electronic controls. This is also why 911s are famous for fishing out the tail in corners when you let off the gas."
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j150dd | Why are Bulk Tankers different shapes? | Bulk fuel tankers are generally oval on the sides and flat at each end. LP gas, natural gas, and ethanol tankers are more round on the sides, and at each end. Grain haulers are a different kind of round, and difficult to describe. Asphalt tankers are round on the sides, and flat on the ends. Milk tanks are generally similar to fuel tanks. Why all the differences? | Engineering | explainlikeimfive | {
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j1hbe2 | Why do houses have gutters? They are nothing but a leaf storage semi tube. Surely there's a significant reason to them. Wouldnt rain just run off of the roof with it being shaped like a Pyramid. Yes im dumb. | Edit*** From the help I've realised why. Thanks folks. | Engineering | explainlikeimfive | {
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"So rain doesn't fall directly into your foundation, which will eventually erode over time. You want to make sure water is diverted away.",
"Roofs catch a lot of water. Without gutters, a line of water would stream onto the ground, on the building, and onto people entering and leaving through doors, and splash everywhere a make a mess. It also would carve ruts into the dirt beneath the roof.",
"Gutters direct water away from the building. Without them, or if the gutters are packed with leaves, the water can run down along the side of the building and damage either the building itself or the foundation that the building sits on. With proper gutters, they will direct the water away from the building so it doesn't have a chance to cause that damage.",
"Without gutters, rainwater runs down the roof and waterfalls off the edge. Over time, that rainwater splashing down from the roof would erode around the base of the house. Gutters funnel the water down to the ground softly, and often away from the foundation, so it doesn't erode and cause damage."
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j1mfnt | How can a speaker create all of the sounds in a song (for example guitar notes, drums, and vocals) simultaneously? | Engineering | explainlikeimfive | {
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"text": [
"It's just one sound. One really squiggly wave, which was originally a whole bunch of different waves added together, which our brains have learned to dissect back down into individual separate sounds which we associate with different sources."
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j1p0li | How does hot water work in apartment buildings that don’t have hot water heaters? | Engineering | explainlikeimfive | {
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"There’s typically a boiler in the basement that serves all the apartments. Some cities have hot water as a service, too, but they’re rare. I think Reykjavik is one",
"In Brazil, in apartment buildings that don't have a common heater, it is usual to have either electric heated showerheads, electric passthrough tankless heaters, or gas passthrough tankless heaters in the apartments."
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j1s6v2 | The Rusty Bolt Effect | I read the wikipedia article but I still can't wrap my mind around it. URL_0 | Engineering | explainlikeimfive | {
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"Basically, the design of radio hardware (antennas, connectors, cables, etc.) assumes that you have nice metal that behaves “properly” in an electrical sense...it’s a good clean pure low resistance. If you have parts of the metal that aren’t in good condition, like a rusty bolt or a corroded connection or something else that screws with the conductivity or resistance, you can get interference in the radio signal. A very rough analogy is a water pipe. A good pipe is nice and smooth and the same diameter all along. Water flows nice and smooth and steady. Rusty bolt effect is like putting cracks and joints and rough spots (and possibly rusty bolts!) inside the pipe...the flow isn’t as smooth. You’ll get turbulence. If you’re a musician, a tube instrument like a trombone or flute is a better analogy, since that’s also a resonator like a radio antenna. Even a tiny pinhole in the instrument body can cause squeaks and octave jumps and other interference with the main signal."
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j1ua1q | If suddenly everyone in a city turned off all electrical appliances at the same time would the power station suddenly overload due to a surge in excess electricity production? | Engineering | explainlikeimfive | {
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"I'm a control engineer in energy production. It would depend how fast people turned off everything. Our system of stabilization assumes people don't turn their stuff off all at the same time. Generators would start to spin faster, and they'd close a steam valve to reduce power. But if it happened too fast they'd go into emergency stop instead, activating a bypass to direct steam away from the turbine. And cutting their connection to the energy grid. This wouldn't destroy anything (propably), but restarting would take days or weeks, because only very few powerplants are able to start without first taking electricity from outside for 8 hours to run a pump that moves water through the boiler until it's hot enough to start the turbines. Edith: Just read you mean a single city. In a large grid like Europe or the US that would only make a smallish dent, the current of the cities powerplants would just be redirected and an operator would decide wich powerplants should be throttled to compensate.",
"The generators and turbines would surge, i.e. start to spin faster as much of the load on them disappeared. I don't think it would break anything, though. As soon as sensors noticed the drop in load, the station would \"throttle back\" - if it's coal or gas it would reduce fuel injection, if it's a hydro plant it can actually stop generating power and even take some of the excess for itself, to pump water back up above the dam. In a nuclear plant they'd lower the control rods and damp down the reaction to get rid of the energy surplus. If the surge was really severe, they could even vent steam from the turbine loop, and let the steam pressure crash; that would allow the turbines to coast down."
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j1xn7a | What makes keys so unique? How is it that a key cannot open a few other doors even if it goes all the way through the keyhole? | Engineering | explainlikeimfive | {
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"text": [
"The key presses in pins to a certain degree to make the lock open. The key is cut to the shape that presses the right amount of pins with the right amount of pressure."
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j1y52t | How long could an aircraft that had the capacity to refuel continually mid-flight, fly before having to land? | Engineering | explainlikeimfive | {
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"With fuel not the limiting factor, human limitations and those of the engine are what you have to consider. Beyond basic human needs like food and sleep for the pilot, many engine components (especially in piston aircraft) are only good for a few thousand hours before needing to be replaced. A good example is the world record setting flight of the Cessna-172 *Hacienda* which flew continuously for 64 days. By the end, the engine was barely able to produce enough power to climb the plane because of how worn out the components were.",
"It depends on the aircraft. Maybe the aircraft most famous for in flight refueling was the SR-71 Blackbird. They routinely refuelled multiple times during the flight to reach half way across the globe and back again at several times the speed of sound. However their limitation was that they could not refuel the igniter for the afterburner. So they could only slow down to refuel and then speed up again a few times before they were forced to land. In addition to this the crew had no food and limited water. However the world record was set back in 1958/'59 using a Cessna 172. They refuelled from a truck driving under neath them and not from another airplane. And they had modified the airplane to be able to change the oil while running and were bringing both food, water and oil in addition to fuel from the supply truck. Eventually after 64 days in the air the engine had worn out and had to be overhauled to be safe to fly. And since they had no way of overhauling or changing the engine in the air they had to land."
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j2ke7m | How does data travel through internet? | Engineering | explainlikeimfive | {
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"They work the same way as a radio. You use a current to create radio waves, and have a receiver that can detect those radio waves. By rapidly altering how fast or how loud those waves are you can encode information in them, similar to how you can use a flashlight to transmit morse code by turning the flashlight on and off in succession. By using those radio waves to encode information you can transmit videos, photos, music, text, what have you. Other people who know how you're encoding that data in radio waves can then pick up those radio waves and decode it back in to data you can enjoy."
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j2kr56 | Why the light flickers after it has been unplugged (or turned off) | Image: [ URL_0 ]( URL_0 ) I think it has something to do with capacitors, but maybe I am wrong. Edit: The light is an LED light | Engineering | explainlikeimfive | {
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"There basically three kinds of light bulbs that work in slightly different ways. Old fashioned light bulbs designs, called incandescent or halogen, push a lot of electricity through a teeny-tiny wire. This makes the wire get very hot and makes it glow, like a candle or fire glows. This wastes a lot of electricity in heat, but they are cheap and easy to make. Fluorescent bulbs work filling a glass tube with a special gas and two metal caps on either end but no wire connects the plates. The electricity jumps from one plate to the other using the gas as the \"wire\" and the gas absorbs some of the electricity's \"energy\" . The gas releases the energy in the form of light that we cannot see. The inside of the glass tube is painted with a special white paint that absorbs the invisible-gas-light and the paint then gives off light in a color that we can see. So it's kind of a two step process. The LED bulb in the video works in two steps like fluorescent bulbs, only instead of metal plates and glass there is a special type of computer chip inside the base of the light bulb. The computer chip receives electricity and produces light in a very, very specific color. Some LEDs are blue, or red, or green, but a very PURE red or blue or green. That doesn't make a good light bulb unless you're in a submarine, helicopter, or on drugs. So they coat the inside of the bulb with the special white paint which absorbs the red, or blue, or green light and it gives off nice white light. What's probably happening in the video is when the electricity turns off, the last bits of electricity go through the computer chip and the white paint inside the bulb is giving off it's last bits of white light energy in pulses after the lamp is unplugged."
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j2lhct | How do tunnels not collapse | So recently me and my friends have been going I drainage tunnels (for fun we aren't doing anything malicious, we just want to try something new and adventurous) and we're going I'm tomorrow and I'm a bit nervous (as always) cause I'm afraid that the tunnel will collapse, it hasn't and my friends say it won't but I need a second opinion. (also I'm not worried about the water rising because of rain, we do check the weather beforehand) | Engineering | explainlikeimfive | {
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"If there’s a lot of weight bearing down on the tunnel the roof will usually be arched. This gives the structure much more strength because the arch must be compressed to break instead of just snapped in half - most building materials have very high compressive strength but aren’t so strong if you try to bend them. If there’s not much weight, then a slab of something sturdy like reinforced concrete will hold the weight easily."
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j2sodl | Why do wind turbines only have three blades and not more? | Engineering | explainlikeimfive | {
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"With an even number of blades, a fan or propellor structure will have points of its rotation (i.e. where the blades are vertical or horizontal) where it has unstable moments of inertia, and at those points it will put twisting motions on the whole assembly and you'll get a wobble. [A little like this gem of a t-handle screw driver on the space station.]( URL_1 ) Same thing, a two bladed turbine blade would want to flip like this and impart a wobble, leading to damage. Why it wobbles like this comes down to whats called the Intermediate Axis theorem regarding moments of inertia of an asymmetric top around its 3 principle axes of rotation. Without a lot of math, its hard to explain, but [this video does a good job.]( URL_0 ) In our turbine blade, the big masses in that guy's disk would be the masses of the blades themselves, but a minor acceleration in the motion of the turbine fan when the blades were say horizontal would start the runaway acceleration of those small masses, leading to the whole thing wobbling until it tore itself apart. And the destabilizing force to upset that two blade system could be a simple as how far the turbine nacelle is swaying in the wind that is turning the blades. _Thats cool and all but I didn't ask odd vs even, I asked why not like 5 or 7 blades?_ You avoid the whole problem by having odd number blades, and anything beyond 3 is just unnecessarily complex to manufacture - then you get into aerodynamic problems of \"too many blades\" etc. There also needs to be sufficient mount space for the root of each blade to the turbine hub, more blades means bigger hub which means bigger nacelle which means stronger tower etc. etc. Or, you make narrower blade roots, but that necessarily limits their size while maintaining their structural characteristics. Smaller blades deliver less torque to the turbine hub > generator and you get less power in the same wind conditions.",
"With more blades each blade arrives in the disturbed air from the preceding blade sooner. This means that the blades are less efficient, so as you add blades you get diminishing returns in terms of total energy produced. Three blades hits a sweet spot of extracting lots of energy per tower, without making lots of extra, inefficient blades."
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ko936d | Electricity | So, I've been trying to expand my horizons recently, learn more about everyday things. One thing I'm struggling to get right is electricity. I thought I had it cracked with Voltage being pressure, Amps being the sheer amount of electricity and watts being... Something.. But now I learn there's resistance, ohms and other crazy terms. Can anyone help with a literal ELI5? | Engineering | explainlikeimfive | {
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"Ok, but take it as an ELI3:) Electricity is the motion of electric charges. The physics ends here. Your other doubts regard the definitions of our measurements of electricity. Resistance is measured in Ohms. Power in Watts. Intensity in Amps. Voltage in Volts. I try to give you kind of \"real life example\". Think at the Niagara Falls. Electric charges are water. Voltage is \"how high are the falls\". It tells us how badly the water (or for the electricity the electric charges) wants to go down. Amps is how much water goes down per second. Ohms are how narrow are the falls: even if the falls are very high, if they are narrow not much water will go down. There is a formula: Voltage=Ohms*Amps Watts tell us how \"powerful\" are the falls are. Take it as a definition: Watts = Amps * Voltage . Basically it counts both how much water goes down and how badly it wants to go down. Watts are basically what you pay for in your bills. You are charged for how much energy you consume. Energy=Watts*time. Edit: if you want a more complex and correct explanation tell me. But I could not explain better without mentioning more complex physics and math.",
"You may try to see electricity as a rope in a tight tube. Pulling the rope is voltage. Movement of the rope is current. Resistance to the movement of the the rope is namely resistance. More resistance - more ohms. You can even feel the heat produced in the tube. The amount of this heat is a measure of work, produced by the moving rope."
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kokliw | How can fireworks be used to spell messages and draw pictures in the air, if they seem out of control? | Engineering | explainlikeimfive | {
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"They're not out of control. The physics of explosions is very well understood, and a firework is just a series of well-designed bombs that go off with careful timing. The fuses in fireworks burn for a specific amount of time, which is calculated to get each part of the firework to its place in the sky before it goes off. By carefully arranging the individual bombs/shells inside the outer firework shell, the placement and orientation of each can be controlled.",
"They aren’t really out of control is the thing. Fireworks (like the ones Disney uses, for example) are bundles of charges made to go off in specific patterns, colors, timing, etc. They’re engineered to do that"
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kp00be | How circuit breakers work? What makes them trip? | Engineering | explainlikeimfive | {
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"There is a spring and a coil. When too much current runs through it the coil creates a magnetic field stronger than the spring and pulls the switch into Off position. It's basically a Relay with a clearly defined activation current",
"It uses magnetism usually to trip it. Current running through a wire creates a magnetic field, the amount of magnetic field is proportional to the current. We can put a magnet at the end of a switch, think of it like a typical light switch, and a coil hovering above that. If the magnetic field becomes big enough (if the current is large enough), it will apply a strong enough force on the magnet to switch the switch off. You can calibrate the coil and other parameters to make the trip point be whatever you want."
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kp2qjj | How is it that a glass fridge shelf can support so much weight in the middle of the shelf (including some flexing) without breaking at the edges where it is sitting? | Engineering | explainlikeimfive | {
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"Glass is very strong. One of the strongest materials in tension as opposed to compression. Fiberglass is used to build all kinds of things that need strength where weight is not much of an issue. It is also brittle so I suspect you are confusing brittle with weak. Concrete which people think of as strong is weak in tension but very strong in compression."
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kpiczp | Why aren't we making plant based fuel from eucalyptus trees instead of Fossil fuels? | Engineering | explainlikeimfive | {
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"There are only so many eucalyptus trees that are the right types to produce biofuel and it takes a ton of work to transport them and then convert them into usable fuel (and only certain kinds of fuel at that). They can't grow back quickly as well, so once you cut down an area you have to replant it and then wait years for it to regrow. So the cost is going to be very high, even if it's better for the environment. Fossil fuels are a lot more convenient. It takes a lot of money to set up an oil well, sure, but then you're going to get tons and tons and tons of oil out of it with very little work, and that oil can be processed into many different fuels using refineries that we already have built and invested in. And oil companies aren't going to replace all that without a really really strong business reason. Fossil fuels are going to run out at some point, but for now they're still cheaper and more flexible than most biofuels.",
"Up until around the late 1700s the majority of our fuel was from sources such as trees. People would chop the wood and convert it into charcoal for uses such as smithing or simply burn the wood for heat or energy. The problem was the shear amount of trees we required and we were chopping down trees far faster than they grew. So we started turning to coal. It was at least as energy demse as charcoal if not more and it didnt require waiting decades for a forest to grow and could be used instantly (rather than months to dry before being cut and charred). We coundnt grow enough wood for our energy uses in the 1700s what makes us think we could do it now?",
"Eucalyptus are especially bad because the wood is so hard. Cannot be easily cut or split after it is dry. And high ash residue too."
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kppue9 | how do solar panels turn solar energy to power? | Engineering | explainlikeimfive | {
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"When a photon hits a silicon atom in the solar panel, if the photon has enough energy it will knock one of the electrons off the atom. This forceful ejection of the electron creates voltage. The number of electrons knocked out by photons makes up the current. The rest of the solar cell is basically transporting that electron to a load, then bringing an electron back to the panel to complete the circuit."
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kprdem | How do sewers even work | Seriously? Where does all the poop go? Especially in rural areas? Does the poop have to be pumped and relocated? Does it just sit in the ground? I've never understood how sewers could possibly work | Engineering | explainlikeimfive | {
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"First they have to separate out the liquid waste and the solid waste. I believe this is done using settling ponds, which just lets solid waste fall to the bottom. Kind of like panning for gold only disgusting. The heavy stuff falls to the bottom, the stuff that's lighter than water will float to the top. So basically they use density to separate solids from oils and fats and liquids. The solids become sludge, and that can be treated further before going into a landfill but I think different countries deal with it in different ways. pretty sure they're able to farm with it in China although I'm not sure if that's still a practice. It would be really cool if we could farm with it safely. Eventually, after solids are removed, the liquid waste gets treated, which means using enzymes and bacteria and other chemicals to convert it into grey water. Then it can be used for irrigation or pumped back into rivers. I used to work at a water utility and do education for kids. We would have field trips of kids come and we would show them this very basic process. But, it wasn't a treatment plant, it was just a fresh water utility so we didn't have to show them like settling ponds or anything. We have a few of them in my county and they smell terrible. Like....driving through a field of farts.",
"> Does the poop have to be pumped and relocated? Yes. I live in a hilley suburb, and there a couple \"poop pump houses\" around town that pump the waste up the hill towards the treatment plant."
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kqd42n | Do the newer cars waste battery when they automatically turn off at stop lights? | My new car turns itself off to save gas (I’m assuming..?) at stop lights and I was wondering if it has any negative effect over time on the battery or starter? | Engineering | explainlikeimfive | {
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"A lead-acid battery (the type used in most ICE cars) is designed for shallow discharge - you use a little, and put it back right away. They last well when you treat them that way. The car has an alternator, which charges the battery from the engine when it is running. Battery starts car, car recharges battery, rinse and repeat. The thing that kills your battery is deep-discharging it - running it right down. The new car doesn't do that - it replaces the energy necessary to start your car right away. So no, you aren't killing your battery.",
"Yes and No The autostop feature is a gimmick to save you a tiny amount of fuel at the stop light. While starting your car frequently can cause unnecessary wear on the starter, cars with this feature are designed with this in mind so the starters are heavier duty to compensate. Starting your car also drains your battery, but the battery is constantly charged by the alternator while you are driving so it doesn't really matter."
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kqfi8s | What does premium gasoline actually do? | In the United States at least there are 3 grades of unleaded gasoline at most pumps. Does it really matter what grade of gas you use? Can I use the lowest grade one week and the next week get premium if I can afford it? Does it help with milage or does it keep your engine clean? What is the difference? | Engineering | explainlikeimfive | {
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"Use the gasoline recommended by the manufacturer. If you do not have a special high-performance car you would use the lowest grade. There is no advantage to use a higher grade. You need to design the engine to have higher compression for it to be useful and then lower grad will work badly in the engine. The octane rating of the fuel is about how much you can compress it before is spontaneously detonate. So use the lowest grade the manufacturer recommend because it leaves more money in your pocket.",
"Follow up question. When would you ever use mid grade? Most cars use regular, some higher performance engines use premium. Is mid grade just a money maker for the oil companies from the people who think higher octane gas cleaned their engine or gets their non high performance engine better mpg?",
"The quality of fuel has nothing to do with the energy contained in the fuel (it's all essentially the same), but on your engine's ability to extract that energy without unwanted and possibly destructive side effects. Higher-performance engines need fuel that can put up with higher compression ratios. In terms of what you should use; use whatever fuel your manufacturer recommends. If the car is getting older and knocking more often, consider moving up to the next highest grade of fuel. In addition, if you throw an aftermarket turbocharger on, you'll probably also have to move up a grade or two.",
"There is no such thing as premium gasoline. That is a marketing word. What we have is gasoline with different octane (or RON) ratings. The octane your engine needs is mostly based on engine compression among other things. If your vehicle is rated for 87 octane you will gain nothing by putting in a higher octane gasoline. If your car is rated for 93 octane but you use a lower octane it can cause pinging or knock. Modern vehicles have a sensor that detects this and the engines computer will adjust the timing of the engine which results in less power output. In the United States all gasoline has fuel additives to clean out your fuel system and engine of gunk and deposits. It is [federally mandated.]( URL_0 ) There is a list of [top tier fuel brands]( URL_1 ) that are supposed to do a better job of ensuring a higher quality of gasoline to begin with, proper mix of fuel additives and better fuel storage techniques. Personally I recommend Shell or Texaco.",
"Premium gas denotes higher octane rating. The higher the octane - the higher compression (how much pressure it can take) it can handle. Engines work by mixing gas and air, and igniting the mixture. The resulting explosion (fire) pushes a piston which then turns a crank... let's just say moves the car. **Allegory** \\- Imagine two springs: one is soft and one is stiff. The softer spring you can push down and release and it might jump off the ground a few inches. The stiffer spring will be harder to push down but once you release, would probably jump off the ground quite a bit higher. The principle is the same for engines: lower octane gas can't be compressed as hard and thus don't create as much power. Higher octane gas can be compressed harder and the resultant explosion (release) is more powerful. Higher octane gas can be compressed more and the resulting explosion produces more power (aka horsepower). **Advanced explainer:** to take advantage of higher octane gas you generally need to do something called \"Forced induction\". Forced induction is a fancy way of saying \"force more air\" into the cylinder (where gas and air mixes). Because the higher octane gas can be compressed more, it also needs more air in order to fuel the bigger explosion. The only way to get that much air and quickly enough into the cylinder is through forced induction (turbo/supercharger).",
"The grades of gas have a rating called an octane rating. In very VERY simple terms, this means how hard it is to make that specific gas combust. Higher octane rating means the harder (and subsequently, more controllable) it is to combust. Premium gas (high octane gas) is harder to combust, which is good when you need gasoline to combust at a very specific moment (like for sports cars). Lower tier gas is cheaper but is easier to combust, which is fine if your car is a simple commute to work vehicle. Ive seen it thrown around from time to time that lower tier (than the manufacturer recommends) gas, since it can combust earlier than needed (due to its lower octane rating), could damage a car's engine due to combusting too early. I cant confirm that, but its food for thought. Speaking SOLELY from my case, Its generally not a good idea to run a vehicle with a grade of gas lower than the manufacturer recommends. My vehicle (2003 dodge ram 1500) will die after running with lower than premium grade gas after about ten minutes. Hope this helps!",
"Higher octane gas can withstand more compression in the cylinder than lower octane gas. The higher the compression ratio, the higher octane you need to avoid premature combustion of the fuel/air mixture, also known as spark knocking. A compression ratio is the measure of how much air is squeezed to the top of your cylinder during the Squeeze stroke of a 4 stroke engine: Suck, Squeeze, Bang, Blow. The ratio is measured by comparing the amount of air in an unpressurized cylinder, 1, to the amount of air in a pressurized cylinder, usually 8-12. Engines designed during the days of leaded gas require the highest octane at the pumps nowadays because the tetraethyl lead in the gas greatly improved the gasoline's stability, allowing for engines to run compression as high 16:1. As an aside, adding a turbo or supercharger to your engine, or building something like a [Mini-me]( URL_0 ) increases compression and can sometimes require premium gas, racing fuel with an octane rating of 100+, or an octane booster additive to avoid spark knocking. Aside from being required in higher compression engines, premium fuel usual contains lots of additives like detergents to clean carbon build up in your engine, oxygenates to allow cleaner burning, antioxidants to add stability to the fuel, and anti-knock additives, previously including lead compounds. Racing fuel companies tend to treat their blend recipe like Coke and their secret formula, and for good reason. Different blends offer different performance, and racing blends run above $40 a gallon. It even smells different than normal gas. To expand upon octane ratings, a common misconception is that higher octane gas, the premium stuff, will increase performance. To an extent this is true, due to additives in the gas, but not due to octane. Octane is a measurement of how much compression the fuel can take before it ignites, and compression is generally a determining factor on how much power an engine makes. Higher octane gas does not affect compression, and therefore does not affect power output. Putting jet fuel in a Miata doesn't change the fact that it's still a 1.8L Miata. On the coal rolling side of things, diesel has a cetane rating that tells you how fast the fuel combusts, rather than how much compression it can take. Compression in a diesel engine can average from 14:1 to 23:1; the heat from the extremely compressed air ignites the diesel and produces the Bang, rather than a spark from a sparkplug. Higher cetane ratings mean the diesel combusts faster; a higher cetane is better for faster diesel engines, like those in road cars. Huge shoutout to [Donut Media]( URL_1 ), they make learning about cars and the ins and outs of engine much more entertaining than your dad yelling at you about your flashlight position. Would highly recommend to anyone that wants to learn something new or just want something entertaining to watch.",
"\"What grade of boomliquid is required for my rollmachine?\" What a strange planet. One of the fundamental basics of engines is that you want the air/fuel mixture to burn in a controlled manner, not explode. When the air/fuel mixture does explode, this is called knock, and can destroy engines pretty quickly. Gasoline is rated according to its resistance to knock. This varies from engine to engine, as well as factors such as how hard the engine is working, how hot it is, how hot the air/fuel mixture is before ignition, and others. The general rule is to use the grade of gasoline recommended by the manufacturer, although there are some exceptions to this. My wife's Chevy Cruze has a turbocharged engine, and I have found that it seems to be a lot happier on premium fuel. I could probably get by with super, but since our other car is a VW GTI tuned for about 290hp, I'm used to spending the extra money on gas anyway. For most cars that are tuned for regular, using premium is just a waste of money. It won't clean your engine - gasoline already contains detergents that do that. It won't necessarily improve your fuel economy - engines that run on premium tend to be more efficient, but they have to be tuned for it, so if your car is tuned for 87 octane, 91 or 93 won't help you at all."
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kql0uv | why does electricity make noise? | Like when my headphones charge I can hear it. My laptop charger has a small silencer or it. An older toaster we have makes noise just when it is plugged it, not even running. What causes the noise? What determines how loud it is, and what engineering solutions do we have to muffle it? | Engineering | explainlikeimfive | {
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"Electricity on its own will not produce noise. But electrical current will induce a magnetic field. Alternating current 50Hz or 60Hz will alternate this induced field 50 or 60 times per second. This alternating magnetic field can cause the conductors or anything magnetic to vibrate creating noise. Often called the 60Hz hum. You also get many higher overtones like 120hz, 180hz, etc. Stopping it depends on the device and the current. Sometimes it is too expensive. Sometimes it is as simple as twisting the wires together. There are other ways to get noise from electricity, but this is the simplest and most basic. Noise is just vibration and can have many causes",
"Electricity flowing through wires and components creates a magnetic field. This field causes the components to vibrate. Not enough to see, but enough to cause very minor disturbances in the air, which we hear as sound. It gets louder the more electricity is used, since that creates a stronger magnetic field which causes components to vibrate more. I don't know how they insulate it to reduce the sound though.",
"Hoping this post gets the idea of ELI5. (Engineer here, sorry) The noise you hear is coming from an internal source an is amplified by the housing. The noise source is in most cases a voltage/power transformer. The main goal of developing e.g. toasters or phone chargers is to make them cheap. So the developers choose cheap transformers and thin plastic housings. The most audible noise is radiated by “wobbly“ (most likely to oscillate when excited) surfaces, such as thin plastic or metal sheets. TLDR: thin plastic surfaces amplify internal sound sources. Now what to do? You can increase the stiffness of the housing by using thicker plates or different materials. Or you fight the Sound source, which is in most cases a lot more difficult and expensive. Ooor you create an exact opposite of the disturbing noise and add it up to reduce it (so called active noise cancellation). This is super expensive and works only in special use cases."
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kqle7j | How come carburetored vehicles have a hard time starting in the cold, where fuel injected ones start right up? | Engineering | explainlikeimfive | {
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"Carburators evaporate gasoline, because liquid gas is hard to ignite. When it's cold, that doesn't work as well. Fuel injectors vaporize gas by spraying it at very high pressure. That's a less temperature sensitive process. Moreover, the computer that controls fuel injection can do all sorts of temperature driven things that a mechanical carb can't do.",
"At cold temperatures, the air is denser meaning more oxygen in a given space. Because the engine now sucks in more air, the air/fuel ratio is off so it’s harder to start. To counter this, a carb has a choke to choke the air and bring the air/fuel ratio closer to how it should be. Injection is computer controlled so the computer just injects more fuel when the temperature is low."
],
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3,
3
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kr17ni | How come water doesn't enter large vessels at the propeller shaft? | Water can enter through even the smallest cracks, but how do you avoid water entering ships at the propeller shafts. I mean...seals in general, must fit tight, but here you still have to allow for movement. How do they do it? | Engineering | explainlikeimfive | {
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"text": [
"They use a “Garloc” seal. It’s a lubricated seal that encircles a polished part of the shaft. The inner lip of the seal has a spring providing constant tension and the seal material is very hard and long-wearing. Some are even made of a graphite impregnated material to improve lubricious and wear properties. They are also packed on either side, often with a wax/grease impregnated fibrous material.",
"A lip seal of some sort. They usually sport a sort of \"cup\" where the pressure of something trying to get in or out actually makes them seal tighter. The same way a crankshaft doesn't leak oil out of your car. Imagine the wiper blade on a car, except formed into a donut shape, at its absolute most basic form. Google for lip seal or radial shaft seal for pics and more info.",
"Seals. The pressure isn't very high, so a thin film of pressurized grease pushes the water back. Sometimes there are problems, even with [gazillion dollar destroyers]( URL_0 )."
],
"score": [
13,
7,
3
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"https://news.usni.org/2017/04/05/navy-found-fix-uss-zumwalt-engineering-problem"
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kr378k | How do servos and stepper motors work, and what is the difference between the two? | Engineering | explainlikeimfive | {
"a_id": [
"gi7btai"
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"text": [
"A servo motor is a motor with some sort of feedback device attached to it. There are couple of common feedback devices such as tachometers, encoders, and resolvesrs which work on different principles but all serve the same purpose. They give the machine some way of determining the motor's position. You can tell a servo to move 3 rotations, and it will do it because it has some means of actually measuring those rotations. A stepper motor is usually open loop. This means there isn't any feedback device and it can potentially lose track of where it is. Steppers are built so that they can essentially \"index\" some number of degrees. You send a pulse of power, and it activates the winding, pulling the shaft to it's next position. Send a bunch of pulses immediately after each other and it rotates like a normal motor. Again, there's no feedback so it becomes possible to stall a stepper motor, and your system won't realize that the motor isn't where it's supposed to be. This is called losing steps."
],
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4
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kr5fay | How did bombers in WWII survive being shot at with bullets and flak? | I see pictures and hear stories of aircraft struggling back to base with hundreds of bullet holes or missing engines/parts of wings or shrapnel inside the wings. How did they stay in the air after all that anti air fire and why are modern aircraft weaker than them (Iran shot down one easily)? | Engineering | explainlikeimfive | {
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"text": [
"Well, Iran shot down a plane with a surface to air missile. Which is 1000s of times more powerful than bullets and flak. (and im probably still off by a few orders of magnitude) Bullet, unless they hit something super important just punch holes in stuff. A missile explodes and destroys the craft. & #x200B; Fun fact, there's a lot of survivorship bias here. *A lot* of bombers *did* get shot down, and the ones that survived were the ones where important parts didn't get hit. You really never saw a craft that hit the cockpit (which kills the pilot) or hit the engines return. & #x200B; [Here is a great video about that by Eddie Woo.]( URL_0 )",
"I mean, over 12 thousand bombers were shot down during WWII, so I'd be hesitant to act like they were somehow resistant to anti-aircraft fire. Some aircraft were hit less critically, and were able to limp home. But, like I said, 12,000+ were destroyed and hundreds of thousands of people were killed, so...",
"WWII bombers making it back to base after massive damage are like the epitome of survivorship bias You hear about the epic tales of the planes that took significant damage but got lucky with it missing the critical systems. What you don't hear about are the ones that took a lucky single hit and went down. There's a lot of redundancy in a plane, particularly a large one, and losing 40% of the wing area to 20mm AP rounds is bad but not plummet from the sky bad, but a single machine gun hit to the tail control linkage can be plummet from the sky bad because you can no longer control the plane despite the small hole in it. Modern planes can still take pretty significant damage and make it back to base. There's a case of an Israeli F15 that landed with a single wing after a training accident. But bear in mind that the weapons modern planes go up against are far superior to WWII AA Guns and AA Artillery and are often high speed missiles or radar targeted high velocity gun batteries. Late war Anti-Aircraft weaponry was absolutely devastating in the Pacific Theater with radar guided 5\" guns able to pick off planes from quite a distance away.",
"Bullets and flak can tear a plane up, but the plane can still be aerodynamic enough to fly to safety as long as its fuel lines or vital systems aren't taking direct damage. These days there are missiles with a lot more explosive power than bullets that are guaranteed to do more damage to planes if they land a direct hit.",
"Bombers are hard to shoot down because they're designed to be. Their wings give them more lift than they need, so they can still fly with holes in their wings. Their engines give them more power than they need, so they can still fly with a destroyed engine. And so on. The tradeoff is that they're big, heavy, slow, and consume a lot of fuel. Modern commercial airliners like the one Iran shot down aren't built for durability. They're built to use the least amount of fuel possible (to keep ticket prices low), so redundancies like having extra engine power would just be a waste. There are modern aircraft that are just as hard or harder to shoot down than WWII bombers: things like attack helicopters or the A-10 Warthog are armored and extremely durable. But you'd never want to take a passenger flight in one of them."
],
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krax3v | Why do some outlets have a reset button? | What does it do? Why is it needed? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"They are called GFCIs( Ground Fault Circuit Interrupter) . It measures the electrical current leaving the outlet, and compares it to the current coming back. If the is a disparity is more than 1/10 of an amp or so, it turns the outlet off. The test button tests this function, and the reset button resets it after it trips. They are usually located in wet locations, bathrooms, kitchens, or outside, etc. If the current is not returning to the outlet, it is “leaking” out somewhere to ground and is a danger to people.",
"This video is pretty good at explaining what they are, why they exist, and how they work: URL_0",
"Those are GFI (Ground fault inhibitor) outlets. Essentially they have a circuit breaker right there in the outlet. It's to protect you from electrocution. Usually they're required when the outlet is near water like in bathrooms and kitchens. The breaker in the outlet can respond quicker than the main breakers back at the electrical panel in the basement and thus reduce the chance you'll die! The reset button is to reconnect the circuit breaker if it has tripped."
],
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19,
3,
3
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krpsti | How does a car's steering not go off course when there's a change in suspension height? | I've been looking at how the steering in cars work and they all come down to pushing or pulling on the wheel to change their angle. But when the wheels go up or down due to bumps, shouldn't the distance between the wheel and the steering push rod change, causing the wheel to turn without the driver's input? | Engineering | explainlikeimfive | {
"a_id": [
"gib7cjb"
],
"text": [
"There are ball joints on the inner and outer tie rods. These allow for some movement. Also, what you are describing can happen. If you hit a pot hole hard enough it can cause the steering angle to change. That’s why when I hit a bump I hold on to the steering wheel more tightly. There is a limit to the amount of movement the ball joints can handle."
],
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ksb61u | Why is glossy plastic always scratched when looked at under direct light? | Engineering | explainlikeimfive | {
"a_id": [
"gifrrir"
],
"text": [
"The gloss comes from the surface finish of the material. So, an opaque plastic has microscopic mountains and valleys that obscure light reflecting off of it, resulting in what we see as the opaque material. The glossy plastic also has microscopic mountains and valleys, however they are far less significant - think of them as hills and ditches instead. Because the hills and ditches are much smaller in magnitude than the mountains and valleys, the surface finish of the material appears glossy because it is closer to being completely flat on the surface, reflecting light more uniformly - resulting in a glossy appearance. Creating a scratch on one of these materials creates what you could think of as a deep valley. This deep valley is easy to spot among hills and ditches (glossy finish) but among mountains and other valleys (opaque finish), it is just another valley and is far less noticeable. As a senior undergraduate taking manufacturing engineering classes, that is the best way I can express my understanding of the subject."
],
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ksnu75 | why are the engines of a plane in the middle and not on either end? | Engineering | explainlikeimfive | {
"a_id": [
"gih2f3o"
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"text": [
"They can be. Single-propeller aircraft generally have their propeller right at the front ([example]( URL_0 )). Some jet aircraft (particularly military ones?) tend to have their engines right at the back ([example]( URL_1 )). That said, there are a couple of reasons why having the engines in the middle is generally a good idea, particularly on larger craft. Engines tend to be heavy. Having them near the middle helps keep the plane balanced (too far forward and the plane will constantly be tilting down, too far back and it will constantly be tilting up). Secondly, it minimises unwanted turning effects from the engines. If the engines are angled slightly and are in the middle, the turning effect (to spin the plane) will be pretty small. If the engines are at either end, the turning effect will be much larger (think about a see-saw, and trying to turn it by pushing on one end rather than the middle). For normal aircraft, having the engines in the middle helps keep it stable (a slight change in the direction of thrust from the engines won't make the aircraft start spinning out of control). I suspect (purely speculation) part of the reason military craft have engines at the back (aside from not having room to put them in the middle) is that they can use the extra turning effect for manoeuvring."
],
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5
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"text_urls": [
[
"https://en.wikipedia.org/wiki/File:375th_Fighter_Squadron_North_American_P-51D-5-NA_Mustang_44-13926_(cropped\\).jpg",
"https://en.wikipedia.org/wiki/File:BlueAngelsFA18.jpg"
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|
ksu8lw | how does a bugle produce a range of notes with no keys? | a piano has lots of keys and one key = one note or on a guitar, the length of the string determines the note when you press down on the frets. i understand those. but i don't understand how an instrument like a bugle or a trumpet can produce so many notes with so few options to manipulate. i don't know a lot about music. i learned some of the basics back in elementary school and learned some more when i became a dancer but that knowledge is really of music theory rather than instruments. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"> the length of the string determines the note when you press down on the frets. i understand those awesome! In wind instruments, it is the length of the \"tube\" that determine the pitch. When trumpet have their button pressed, they are adding length / creating shortcut for the tube to change their length. check this out: URL_0",
"So, you know that the length of the instrument corresponds with a note, but there is more than one note that fits the same length of tube. Think of notes in terms of soundwaves. Each note has a wavelength that determines the pitch of the note. If you measure the length of the tube you can fit different wavelengths or notes in the tube. Take the number 50, and think of all the numbers that fit. 1, 2, 5, 10, 25, 50. You get 6 notes out of that one tube. Now wrap some other tubes around it with some valves and now you have a selection of tube lengths to play with.",
"If that boggles your mind, remember the humble didgeridoo. You wouldn't think a long hollow log would have much of a range. From what im reading below they operate the same as bugles, just a tube you use to amplify the sound you make with your mouth."
],
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ksufay | what's keeping us from having powered armor or at least the power loader from Aliens? | Engineering | explainlikeimfive | {
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"text": [
"Nothing. We do have it. It's called an \"exoskeleton suit\". [Powered exoskeleton - Wikipedia]( URL_0 ) There are also unpowered ones that augment ergonomics so we're functionally stronger even if the suit itself isn't adding power.",
"The power loader from Aliens is pretty much just a human shaped forklift. The forklift works fine and is far simpler. Wheeled vehicles are simpler and cheaper to build and repair, and easier to operate than walking vehicles. Power Loaders and other mech suits are way cooler, but apparently that's not a metric utility vehicle manufacturers design by.",
"If you mean ubiquitously, forklifts, backhoes, and cranes do a far more efficient job while being much easier to maintain and being far safer than sticking a squishy human being into a cage surrounded by several lines of thousands of psi of hydraulic fluid.",
"Power. We have all the tech required, hydraulics usually provide the best strength but are slow. Electric motors are as fast as you need them to be, but consume lots of power. Regardless, it's pretty much battery tech (or any other power storage ) that's holding us back. We can make a suit that makes you stronger, but you have to be plugged in, or carry heavy batteries and only run a short time",
"nothing really. our current hydraulic machines more than enough can do what a powerloader does. hacksmith on youtube is building one out of a bobcat",
"Building a power loader is much harder than it looks. Hacksmith Industries on youtube have been building one for some time now. In order for it to be able to lift the same load as in the movie it has to be built much heavier. URL_0"
],
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ktaz06 | How do AM/FM radio stations gauge how many people are listening at any given time? | Engineering | explainlikeimfive | {
"a_id": [
"gikwfm5"
],
"text": [
"Surveys of random people, mostly among people who live in the major population centers. [Wikipedia]( URL_0 )"
],
"score": [
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"text_urls": [
[
"https://en.wikipedia.org/wiki/Nielsen_Audio"
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Subsets and Splits