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avkqn8 | why does the sound of a musical note differ with instruments? | For example, if you play an E on a guitar, it sounds like a guitar. If you play an E on a piano it sounds like a piano. But the notes are the same frequency. Why do they sound different? | Engineering | explainlikeimfive | {
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"In short, overtones / harmonics, which impact a given note’s timbre, which can be thought of as the individual hue of a sound. Most sounds you hear aren’t at all just one single frequency - many factors combine to affect a given instrument’s (or person’s, or animal’s) “voice”. The vibrating or oscillating elements give their own unique tones to the sound’s timbre, the geometry and resonance of the chamber contribute a shape, mathematically-related harmonics are generated, and our ear perceives a novel tone. Try playing with additive synthesis to hear this come alive for yourself :)"
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avlq48 | How do the air bags in vehicles accurately tell what speed to record when the air bag goes off? | Engineering | explainlikeimfive | {
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"The airbags have sensors that measure shock (acceleration, or change in velocity) very quickly. Your cars computer also knows the same reading because they're tied together. When the airbag deploys, an electrical signal is sent to the cars computer where the software can record the speed and other info, saving it to the built-in storage for analysis."
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avlv2u | The purpose of metering freeway on ramps at a given rate | Im not a civil or transportation engineer by any means, but the meters at freeway interchanges (twin cities, MN) seem pointless when the cadence allows enough time for merging cars to close their gaps while still on the ramps. Isn't metering suppose to keep vehicles spaced at the point of merge? What the point of having the meters if with a green light every other couple seconds?? | Engineering | explainlikeimfive | {
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"Those meters limit the flow of traffic to prevent even worse start-stop traffic. That because once you reach a certain capacity traffic gets waaaay worse really quickly with even the addition of a small number of cars. Those lights make sure we never reach that capacity. You mention the Twin Cities, back in like 2013(i think?) they actually did a study where they turned them all off for 8 weeks. High way capacity went down 9%, travel times went up 22%, speeds went down 9%, and accidents went up 26% when the lights were off. That means an hour commute gets almost 15 minutes longer without those lights. So...they do a lot.",
"I didnt phrase this question properly. I understand the general purpose of meters, but the DOT specifically states that the zipper merge is what keeps traffic flowing. When cars immediately bunch up again, right after green and before the freeway, the condition that the meters initially tried to prevent happened anyway. When cars are metered with a longer space in between each car, to more effectively encourage zipper merge, that is when meters prove their purpose. I was just at a meter today and it was a jam down the whole ramp regardelss of the meters alternating green lights every 3 seconds. It was just pointless to have those meters running."
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avlz80 | How is it possible to plug a single device or multiple devices into the same electric power outlet (for example using a surge protector) without a noticeable difference in power output? | Engineering | explainlikeimfive | {
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"It's only possible up to a point. I'm in the US so I'm going use 110v as an example. The voltage will be available to all the outlets on the circuit, but as you plug in more devices, the amount of current (in amperes) required increases. Eventually, you will overload the circuit and trip the breaker, or blow the fuse."
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avq14c | How does nuclear power compare to that of others (solar, wind, coal, etc.)? I've heard a lot of talk recently about how it's the safest and most efficient, but I know absolutely nothing. | Engineering | explainlikeimfive | {
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"Other than solar, which is done using something called a photovoltaic cell, or other solar heat collection methods, power ultimately is generated by mechanically turning a generator. This is typically done by either mechanically connecting a generator to turbine blades, as in a wind turbine, or by connecting it to a water turbine, in the case of a hydroelectric power station, or in the case of coal, oil, gas, and nuclear, by heating water to turn it into steam, and drive a steam turbine. The only difference between all of these steam turbine types basically is how the heat is generated to create the steam. That's it. Heat from burning coal, oil, natural gas, or the heat from a sustained nuclear reaction. The reason they say nuclear power is so efficient is because it creates such a **lot** of heat from a tiny amount of fuel. The fuel in to energy out ratio for nuclear energy is many *many* times greater than any other fuel/heat based power station.",
"It's not that nuclear is the most efficient per se, but that it provides the most power per unit mass (also known as energy density) as compared to any other power source. For coal, natural gas, oil, and nuclear this is measured in kilowatt hours per cubic meter, while for solar, wind, hydroelectric, and other renewable sources, it's measured in kilowatt hours per square meter. [This paper explains a bit about the difference, and how the conversion works.]( URL_1 ) & #x200B; Now, [let's talk a little bit about load profiles]( URL_2 ). & #x200B; Anywhere in the world is going to have peaks and dips in the electrical demand, based on human activity, time of day, time of year, temperature, and dozens of other factors. Not all power plants are made equally, and not all are best at meeting all load demands at all times. There are a few basic types of electrical loads that are on the grid at any given time, of which I'll touch on a couple briefly: * [Base load]( URL_0 ) is the minimum load that's always present on the grid - this is measured over a time span by a utility or regulatory body and is very reliable in terms of what the actual demand is over long periods of time. This can be represented by your home refrigerator and freezer that's always running, regardless of how many frozen meals you have squeezed in your freezer door. **Large power plants**, i.e. nuclear, coal, and large hydropower sites are best suited to meet this load demand. This is because these large plants are most economical when they're running constantly at a high load factor (meeting large loads), and they are slow to react to rapid changes or fluctuations in power because of several factors that are outside this scope (but which I'd be happy to talk about later). * [Peak demand load]( URL_3 ) is the load on the grid that occurs at a single point during a day- in winter it could be first thing in the morning as heaters are turned on, or in summer it could be in mid to late afternoon as air conditioning units are working their hardest based on outside temperature. This load has to be anticipated, and there are forecasting models that can help determine what the window is for when the peak will occur. Because it will be an instantaneous process, there need to be power sources online that can meet the peak when it hits. Smaller power plants, or what we call **peaker plants**, are often used to meet this demand. Gas turbines powered by natural gas or oil are often currently used to meet this demand, but they're horribly expensive per unit energy, have a lower capacity factor, and still have to be spun up and brought online beforehand (though this can be done in usually half an hour to an hour, as opposed to the days or multiple hours it will take to start up a nuclear or coal power plant). This is an application we're seeing more and more interest with regards to solar or wind, especially when paired with an energy storage system (i.e. batteries). Now, speaking of costs of power plants. Nuclear is horrifically expensive, for a number of reasons. Choosing a site for a plant has to be done very, very carefully, with regards to rights of way, access to a cooling medium (lake, river, coastal zone), seismic considerations, and distance from population centers, to name a few. In addition, very little of the land surrounding a site can be repurposed for other uses over the life of the plant. By contrast, solar can be installed in a variety of places, and the land can be devoted to other uses at the same time. Wind is much the same way- yes, individual wind turbines need a lot of space, but the land between them can be used for other purposes, currently such as farming or grazing. Construction costs for nuclear are also much, much higher, due to the very specialized nature of the work and materials required, the reporting criteria during the construction process, and the massive number of people needed to build a plant. In addition, operating costs are also higher due to the number of highly trained (and thus highly paid) operators needed to operate, administrate, and maintain a plant, and to periodically conduct refueling operations. **Finally, there's the question of fuel disposal**. This isn't nearly as big of a crisis as most everybody thinks it is, and [we've had the solution for what to do with spent fuel for quite a few years now]( URL_4 ). Unfortunately, the politics of the uninformed has driven a lot of the policy around reprocessing spent fuel and nuclear power in general, and it's been to the detriment of literally everybody. & #x200B; In conclusion, we need both nuclear and renewables, but for very different purposes and reasons. We need new nuclear plants to replace existing coal and oil-fired plants for base loading, especially as the population continues to grow. We need renewable sources to better respond to intermediate and peak loads, and to provide a greater diversity of load to help power all of our \"gadgets,\" especially as plug-in electric cars continue to gain more and more popularity. And just as urgently, we need more flexible power grids that can be adaptable and expandable to both. & #x200B; I hope this answers your question.",
"Nuclear power being the safest method of power generation is dependent on how you define safe. If we go by simply how many people have died by it then renewables like solar or wind are less likely to kill people, it can still happen (deaths from working at heights or deaths from machinery), nuclear power has defiantly got the risk of nuclear meltdown or radiation risks. However if we take safety to mean deaths per kilowatt of energy produced nuclear can start to be safer since one nuclear plant can produce a huge amount of energy when compared to renewables."
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avsueg | Why "righty-tighty, lefty-loosy" does not apply to twist-ties, like the ones on the bag covering a loaf of sliced bread, which are almost always wound backwards (turn clockwise to undo). | Engineering | explainlikeimfive | {
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"Nuts and Bolts need complimentary spirals to work properly, so the relevant industries and their manufacturers have all decided on a \"Righty Tighty\" standard. Twist Ties are glorified bits of string that tie to themselves. They don't need to match an industrial manufacturing standard to serve their core function. So twisting them \"Left or Right\" is simply a function of how the twisty tie machine programmer was feeling that day."
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avzsf2 | What causes the lines on back windshields to defrost/thaw faster than the front windshield? | Engineering | explainlikeimfive | {
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"The lines are a type of heater element baked into the glass whereas the front relies on warm defrost air.",
"The lines on the back get warm, and spread their heat through the back window. They do t get really hot, but hot enough to do the work. There aren’t such lines on the front windshields, so only the warmer air coming from the dash helps warm the front window. In some cars there are similar elements built into the front glass. Those still don’t warm the front as fast because they’re smaller by necessity (so you can’t see them) and because the front windows are larger and thicker than the back."
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aw234j | Whats "architecture" means in computer engineering? | Engineering | explainlikeimfive | {
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"To put it in true ELI5: You can make a quite literal parallel to the construction of a computer at the lowest level and a building. After the building is \"built\", other people will come in and \"fill the rooms\" - your operating system is interior design, applications are furniture, and the architecture is the building shell that holds everything up. The way this structure works is it creates a \"box\" - inside that box are a number of specific ways to calculate things and deal with memory. The Von Neumann model is probably the simplest way to start to understand this. It is quite literally a flow chart where a signal gets filtered to the right place. People who want to \"fill the space\" are given some ways and rules to interact with the box by the people who made the \"building.\" The way the inside of that box works can be different depending on its manufacture and sometimes you have different behaviors based on this. If you'd like any more specific details, let me know."
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awfvrg | Why do theme parks/water parks use height as a measurement for entry rather than a weight or age restriction? | Engineering | explainlikeimfive | {
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"Most rides depend on height to figure out if the safety harnesses will fit. It's also a lot easier to measure quickly than weight or age. Have you ever tried counting the rings on a 12yo boy?",
"try and get people to get on scales... noones gonna show up anymore",
"when i was a youngin i was like a half inch under the minimum height (12.7 mm for some) so the shoulder strap harness was loose but i sat hella up when dude checked it so he let me go. when the loopy thing went upside down (left, loopy, right, backwards loopy, done..kinda like that ship one) i left my seat just barely and the shoulder strap kept me \"at\" my seat. it was fuckin wild. i thought it was normal until my brother commented that that wasnt supposed to happen. *the safety harness is supposed to keep your butt on your seat.* i was too far away from mine. my weight wouldnt have mattered because gravity. and my age wouldnt have done jack shit.",
"You quick and obvious, can't be faked. Weighing people takes time and it is no better indication of age than height is. Age needs people to carry ID when they are dressed for leisure or they can just lie. A measure of physics size makes sure the for the seat, harness or whatever."
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awgewt | how does file encryption work? | Engineering | explainlikeimfive | {
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"Encryption takes place in \"realtime\". Basically veracrypt creates a virtual harddrive, which is the one you can use with the explorer. As soon as you write date to this virtual harddrive veracrypt encrypts this data on the fly and writes the encrypted data to the drive. You are not encrypting single files but a complete block device (hard disk). You would have been able to skip the whole encryption/formatting process of veracrypt making the initialization quicker. But that might lead to information about the disk which an attacker might be able to use against you. Simple file encryption works by using a normal disk and instead of writing the file to the unencrypted disk you would use a tool that encrypts the file and stores an encrypted file on the unencrypted disk."
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awmfzo | Why does connecting an electrical circuit without an appliance on it cause fires/explosions? | I was helping my unclere wire some light fixtures the other day and we had to take one out of the ceiling. We were on the verge of "capping" it, and I asked aloud if that meant twisting the two ends of the wires together and using one cap to seal them together, thus creating an uninterrupted circuit. He looked at me, laughed, and said "it goes **pow!"** Unfortunately, though he tried to explain *why,* we were in a bit of a hurry and I didn't really grasp his explanation. In my working model of electricity - which is obviously flawed - that shouldn't really do anything except waste a hell of a lot of your money by running power through a loop and back to where it's coming from, but that's clearly not the case. Why does it do that? [edit] Answered: Thank you all. The flaw was in me not understanding that flow without an appliance or something in the middle *doing* something and resisting the flow of electricity causes the wires to heat up. | Engineering | explainlikeimfive | {
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"The amount of current that flows is inversely proportional to the resistance. So if you drastically reduce the resistance, you drastically increase the current. Normally this will just trip your circuit breaker, since that's exactly what circuit breakers are for. Without one, it would heat up the wires so much it would start a fire.",
"That's what's called a short circuit. It causes a current so high that you'll melt something (or cause the circuit breaker to break the circuit). Effective current is equal to the voltage over the effective resistance (I=V/R). If you have an appliance between the two poles of the circuit, it provides an effective resistance. If you just connect the two poles, that resistance is minuscule, so current jumps up to more than the wire can handle.",
"Since a free wire connection means virtually no resistance and all connections in the house are in parallel, all the current that your house receives would flow through that wire which would cause it to overheat and melt, and would burn out it's cover and the house down with it"
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awos8j | How is it there are millions of combinations of the same type of key, such that two separate keys don’t open the same lock by coincidence? | Engineering | explainlikeimfive | {
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"Keys usually have 5 points that change, ranging from 0 to 9. So there are only really 100,000 different combinations, assuming the same type of key. It works, because any given person only has a 1 in 100,000 chance of having the same key as you.",
"They sometimes do. The key to my Sienna also works for my Tacoma (although it doesn't work the other way)."
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awqrmr | The natural gas to a stove travels via a pipe to my home from whatever plant. What prevents the flame from following this gas up the pipe and causing a massive explosion? | Engineering | explainlikeimfive | {
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"The flame needs oxygen to burn. There isn't enough oxygen in the pipe for it to keep burning.",
"Combustion requires both a fuel and and oxidizer. The gas flame in your home (stove, furnace) has port that provides air containing oxygen (oxidizer) to the natural gas (fuel). There is no, or very little, air in the pipe leading from the gas distribution center. Without air (oxidizer) combustion cannot occur in the gas line."
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awunka | Stick drivers, why is it that your car dies whenever you didn't press enough gas or release the clutch too early? | Engineering | explainlikeimfive | {
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"Because gas powered engines have very weak power output at low RPM. You have to apply gas and let the engine spin up for the engine to be generating enough power for you to be able to pull away, so if you pull the clutch too fast, it tries to pull more power out of the engine than it is generating, so the result is it stalls out. Slightly more technical: A normal engine running cycle involves the piston moving down, which pulls in air and fuel, the piston moving up, which compresses the air and fuel mix, the spark igniting it, the explosion of which moves the piston back down again, and is where the power is coming from, then finally the piston moves up again which ejects the exhaust gas out of the cylinder. This is called a four-stroke cycle, but of those four strokes only one of them actually generates power. There's a flywheel that keeps the engine turning during the parts of the cycle that aren't generating power, but if you try and make the engine do too much, it'll lose too much energy in those parts of the cycle that aren't generating power, and won't be able to keep itself going until the next power stroke. That's a stall.",
"The transmission has gears in it that connect the engine to the wheels. When a gear is engaged, the wheels will move at a ratio to the revolutions per minute (rpm) of the engine, determined by how low or high the gear is. When you press on the gas, it makes the engine spin faster, which in turn will make the wheels spin faster and the car will accelerate. If you are in a low gear, the wheels will move more slowly when the engine spins, but more torque will be available to accelerate the car. At higher gears, the wheels spin faster but less torque is available. This is not a problem because you are already moving and will need less energy for acceleration. The clutch disconnects the engine and wheels by disengaging the gear. When the clutch is engaged, the car's wheels can stop and the engine will continue to spin. This also happens when the car is in neutral. The clutch also helps sync up the gears, wheels and engine so changing gears is smooth. The clutch can also be used to switch to a lower gear for the purpose of slowing down the wheels of the car. This is called downshifting and is commonly used when turning the car. The reason a car can stall is that if the car is in gear and the wheels are moving too slowly, and there isn't enough gas to make the engine spin faster, the engine can't spin fast enough to keep going. When this happens, the engine will seize up and stall."
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awzffs | Why are some roads paved with asphalt and why are some roads paved with concrete? | Can some one explain the reasoning behind why some roads are laid with asphalt vs some being done with concrete? I know there is a difference in cost but are there any reasons besides that? | Engineering | explainlikeimfive | {
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"concrete is more durable, but it is also more expensive. asphalt costs less, but is less durable",
"Technically it's all Concrete, since Asphalt is a form of concrete. But, I get what you mean. Basicly concrete is more durable. While asphalt will have to be relaid fairly often on well-trafficed roads concrete is extremely durable to this kind of wear and tear, and it's also relatively cheap. This is especially true of roller compacted concrete, which is common for roads in some areas. The drawback of concrete is that it's really sensitive to temperature changes. It' expands and contracts a lot depending on heat, and it will therefor crack if the temperature gets too high (compared to normal). On top of that it does not handle frost heaves well at all (this is also true of asphalt concrete with a high ratio of gravel). As such roads in cold climates tend to use a fairly soft asphalt with low gravel ratio in order to handle ground-shifts better. It's more flexible, but it doesn't handle wear & tear that well. Overall, which material is used is based on \"How do we spend the least amount of money repaving this stuff based on this much traffic we expect and how hot & cold it gets during winter and summer?\". Lots of traffic and fairly stable weather that doesn't go below zero? Concrete. Lots of traffic, high temperature shifts in the ground but the ground won't freeze? Asphalt with lots of gravel in it. Low traffic, but extreme temperature changes and the ground will possibly freeze enough that frost heaves is a problem? Asphalt with lots of asphalt and not so much gravel in it.",
"Concrete can hold weight better than asphalt can so that's why more often than not highways are made of concrete while city/town streets are made with asphalt. Asphalt highways would need to be replaced fairly often with the constant semi travel"
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ax0fjo | Different color wires on electric motor. | Engineering | explainlikeimfive | {
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"There are three windings in the motor. Each is driven by alternating current, but offset in time, that offset is the difference in phase. To run this type of motor from a battery you need a motor controller to chop the DC from the battery up into those three AC sources. Basically, you have a magnet and a coil, if you just put DC on that coil, the magnet will align with that coil and stop. At that point you switch to a second coil to keep it moving."
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ax3ji8 | How do 2 factor authentication apps or RSA tokens work? | Engineering | explainlikeimfive | {
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"They have a clock, and a secret encryption key inside. They encrypt the time, using the key. You type the answer in, and the computer at the other end (which also has the key {remember that QR code you scanned}) does the same thing. If the answers are right, you're approved."
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axchfm | how does gas get delivered instantly to hundreds and thousands of homes, buildings, high rise condos, at the turn of a knob? | Engineering | explainlikeimfive | {
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"The same way it's done with water. With pipes. And as with water, it's kept under pressure so when you turn a knob, it opens a valve releasing some of the gas. And as with water, the diameter of the pipes can be pre-determined to restrict flow to manageable levels at the endpoints.",
"There are networks of natural gas pipes that run under ground like water pipes do. Those feed gas as needed to homes, etc. with meters monitoring the usage for billing.",
"The biggest thing to keep in mind is that the gas coming out of your stove is coming out of a tube directly connected to your stove. When you turn the knob, the gas isn't sent from the company, down the piping, up your tubes, and out of your stove top range. Think of natural gas like blood in your body. The gas company is the heart, and it pushes the gas around to the places it needs to go. However there's gas all throughout the system, just like blood. When you turn the knob you're opening an exit for the gas and it leaks out of the system, much like how when you cut your finger blood comes out because there's an exit. Since there's gas throughout the system, and blood throughout your body, the gas or blood coming out of the range top or cut in your finger isn't coming directly from the company or your heart. It's coming out of the system right next to where the exit opened up. It's one big pre-filled system, then pressurized. That way when you need gas, you just turn on the knob and the gas is waiting in the pipes in your house for you to need it. Then the company just keeps the pressure up so the system never loses gas pressure. The gas coming out of your range may have been in the pipes for hours or days after having left the company, though."
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axggmt | In baths/showers, why does the little knob you press down release water when you’re done, where is that water from? | Engineering | explainlikeimfive | {
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"It comes from the showerhead. The shower pipe is taller than the bathtub pipe, so when we block the bathtub pipe, water spews from the shower pipe. When we unblock the bath pipe, all the water that was on its way to the shower is pulled back down by gravity and out the bath pipe.",
"When you turn the water on and push the button, the water pressure holds a stop so the water can’t come out like it was a bath. Since the water can’t go out there, it instead fills the pipe going up to the shower head and comes out. When you turn the water off, the water pressure is gone and the stop opens again. The water running out is the water in the pipe between the bath and shower heads running out because of gravity."
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axict2 | What is the reasoning behind having different types and shapes of plugs in different countries, excluding the obvious different voltage answer? | Engineering | explainlikeimfive | {
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"text": [
"They all developed them independently. At this point any country switching would be costly and a massive pain in the butt, so no one wants to switch.",
"Different countries started getting electronics at different times periods. Most countries didn't like the plugs that others have made so each developed their own. Meanwhile, Hitler decided to throw a temper tantrum and the world never found time or importance to hold a meeting to standardize these plugs. Fast forward to now, no one really wants to change their whole system of plugs"
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axj03z | How does a V configuration of an engine make it better than a normal engine? | How is a V8 better than a normal engine with the same amount of cylinders? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It's mainly about saving space. 8 in a line is long and thin. Two rows of 4 is only about as long as a 4 cylinder engine but twice as wide.",
"It doesn't from a performance perspective. As everything has said it just makes it more compact. For example: You might fit a V8 engine in your sports car, but if you had to fit a straight 8 engine you would have to increase the size of the engine compartment dramatically, and then it would be more like a truck or bus than a sports car. The other advantage is reduced materials and weight. Having the cylinders closer together rather than all apart in a straight line means less material in the block, shorter crankshaft, etc. Huge weight savings and production cost savings.",
"It is shorter. What you call a normal engine is most likely a straight cylinder engine. In this configuration all the cylinders are placed in a line. However if you have eight cylinders all in a line the engine becomes very long and can be hard to fit. This may not be a problem in for example a bus where a long thin engine can be easy to fit under the floor. However in a normal car this is not so easy. So a straight engine usually only have at most four or five cylinders to fit in the engine bay. & #x200B; However a V configuration have two rows of cylinders. So a V-8 is the same length as a straight 4. This allows you to fit more cylinders into the same engine compartment. In addition the V configuration allows the cylinder banks to share intake manifold and cam shaft making it overall smaller. In for example a boxer engine where the cylinders oppose each other they need separate manifolds and cam shafts for each row of cylinders as they are too far apart. Another way to reduce the overall size of the engine is to have oval cylinders so they can be placed closer together or to stagger the cylinders from each other. The last option is what the W configuration does which can allow you to fit a W-16 in the same length as a straight 5 cylinder engine."
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axl1eb | What does DEF fluid do and why is it only for diesels? | Engineering | explainlikeimfive | {
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"text": [
"Diesel engines burn fuel at a much higher temperature and pressure than gasoline engines. The heat allows them to be more efficient, but it also increases the rate at which oxygen reacts with nitrogen in the air to form nitrogen oxide, one of the major pollutants in car exhaust. The big problem with nitrogen oxide is that you can't use a regular catalyst to remove it from the exhaust. And that's where the DEF comes in: It's a solution of water and urea, a combination that decomposes into highly reactive ammonia gas when you heat it up. They inject it into the hot exhaust before it goes through the cat, and inside the cat the ammonia reacts with the nitrous oxide into harmless water and nitrogen."
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axrk5z | How does the maximum capacity of Micro SD Cards grow more than 1000x, from a few MB to 512GB as of today? | Engineering | explainlikeimfive | {
"a_id": [
"ehvmrt3"
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"text": [
"It’s the basic concept of Moore’s Law. Constant improvements in integrated circuit manufacturing means they can make the circuits smaller and fit more in the same space. ICs are made using imaging technology. Basically, an IC is drawn on a transparent film. Light is projected through the film and through lenses to shrink the image and onto a silicon chip coated with a light-sensitive material. This transfers a very small version of the IC design onto the silicon chip. The constant improvements focus on being able to make that projected image smaller and smaller so that more memory circuits will fit on the same size chip."
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axs5ay | How come you have to set a thermostat to “heat” or “cool?” Why can’t you just set a temperature you want (72F, for example,) and it turns the ac or furnace on when appropriate? | This is referring to buildings, not cars. My work building is always terrible climate controlled. We might have a few sunny days, so corporate turns the AC on, and then we’ll have a cold snap,and it’ll be freezing in the store because the ac is still on. The same goes for the furnace. Why haven’t they developed some sort of automated system that would turn on the furnace or the AC if the temperature was colder/hotter than what the thermostat was set at? And if it’s not possible, why not? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"They do have them. In fact, almost all thermostats are designed to worth that way. There is usually a 4 to 5 degree \"deadband\" temperature difference between heat and cool set points. In other words, if you set the thermostat to call for heat at 69 degrees, it won't call for cooling until the temperature reaches 74 degrees and vice versa so the system isn't constantly fighting itself. It sounds like they aren't using the thermostat correctly where you work."
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axz1iu | How Do Touchscreens Work? | Engineering | explainlikeimfive | {
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"ehx0jws"
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"text": [
"In a nutshell. 2 different types of touch screens i'm familar with.. there is resistive which locate the touch by pressing on the screen (like the old mall kiosks and older ATM machines) causing it to deform the rubber-like top layer registering the layer touching the detection surface underneath. & #x200B; Then the now more common 'capacitive' touch screen found on newer devices. this is likely the more interesting one to you. So... the screen is covered in an electrically charged layer that, when your finger touches the screen, registers a voltage drop as your finger completes the circuit at the precise touch location the drop happened."
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ay5jf7 | While downhill, do cars consume more fuel while in neutral or while in gear with low revs? | Engineering | explainlikeimfive | {
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"text": [
"They consume more in neutral, as the engine has to be fed gas to keep running. When in gear, the engine is being driven by the wheels and requires no fuel.",
"Modern engines use no fuel while coasting in gear. It's called deceleration fuel cutoff and should be in any modern computer controlled engine. Press release from GM: URL_0",
"It will depend on the car, its age, and its programming. Most modern cars will cut fuel when coasting as the engine can be driven by the wheels. This can happen in manuals and automatics (bare with me here and I'll explain how an auto can drive the engine). The newer the car, the better it will control this. In a manual transmission, there is a physical/mechanical connection to the engine through the clutch. When you let off the gas, the power that was going from the engine to the transmission is reversed. The momentum of the car has enough force to spin the engine so fuel injection isnt neccessary. Since the momentum is being consumed by turning the engine, it slows the car faster than when its popped into neutral. This effect is called engine braking and is handy for saving fuel and brake pad wear. In automatics, there is a fluid coupling between the engine and transmission and this is where the confusion is coming from. The power from the engine is transferred to the transmission through an impeller pushing fluid go a turbine that drives the gears. Now there is also what they call a torque converter clutch which is sometimes locked and other times not. This torque converter clutch, when engaged, does create a mechanical connection to the engine which will distribute power both directions. Newer cars will use it during coasting so they can cut fuel and get those savings. Torque converter clutches have been around a long time, but they haven't always been used during coasting. There are also other strategies they can use to save fuel during coasting, but that's a whole other topic. Now if the trans is in neutral, then it has to keep spraying fuel to keep it running. It's best to just leave it in gear and not coast in neutral. Especially if it's an auto trans as they do like like going into gear from neutral while moving.",
"When a manual car is in neutral it will always consume some fuel to keep the motor running no matter the angle of the ground it's traveling on. While it is in gear however the downhill can help keep the engine alive allowing the car to keep running while not consuming any fuel."
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ay6k2q | EngineeringWhat is the glassy looking substance breaking off of a space shuttle/rocket when it is launching? | Engineering | explainlikeimfive | {
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"ehyloob"
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"text": [
"just ordinary ice. Space shuttles have to be kept incredibly cold because they usually use either solid or liquid oxygen as part of the fuel. This results in condensation forming on the outside of the rocket that due to the temperature quickly freezes. Once it launches it shakes free."
],
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ay7ejy | How do buildings collapse due to fire? While all the internal accessories may catch fire ultimately it leaves the walls and ceilings which are concrete so shouldn't at this point the fire stop? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The internal structure of buildings are made of steel. When you heat up metal it will tend to expand, and if you get it hot enough its possible for the structure to expand in such a way that shears the bolts off. This is of course assuming the building gets sufficiently hot enough, but it is absolutely possible for a fire to damage a buildings structure without directly igniting it.",
"Walls and ceilings aren't made out of concrete in most buildings. That would be way too heavy. They're made out of drywall and foam with beams every few feet."
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ay7kg5 | how do electricity and plumbing connect into rotating restaurants/hotel rooms/houses? | Wouldn’t pipes and wires get twisted? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"In most rotating restaurants, only the floor around the dining tables rotates. The ceiling mounted sprinklers, lighting, and centrally located kitchen and bathrooms do not rotate. So there is no need for power or water on the rotating part. As u/sergeantseven said, it is possible to send plumbing and electricity through rotary joints.",
"They have things called slip rings. Basically a giant ring sits on one side and a metal \"comb\" slides acrossed it. They have one for each wire. Plumbing is similar. The pipes have a part that can rotate without leaking water usually just a sealed \"donut\" like device. They require maintenance and do wear out over time."
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aybwuc | How do braces know in which direction to align the teeth? | How can braces pull a tooth forward and another one backwards, some other ones to left and right, while applying the exact same pressure from the front, where they are attached? | Engineering | explainlikeimfive | {
"a_id": [
"ehzl8yn",
"ehzwm7m"
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"text": [
"They don’t “know” which way to pull the tooth. They are put on by the ortho and pull the tooth in the direction the ortho sets it up to",
"The metal squares that are glued onto your teeth (“brackets”) are placed very precisely in the middle of each tooth. When your teeth are crooked, the centre of each tooth isn’t in perfect alignment. The wire of the braces slides through a little channel on these brackets. At first a pretty bendy wire is needed, as the brackets aren’t in a straight line. As the wire is tightened (which is actually the dentist swapping the wire for a more rigid wire, slowly increasing rigidity over time), the brackets are pulled into a line. This pulls the centre of each tooth into a line."
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aycsqe | How does rifling work? | Is the bullet slightly larger than the bore diameter, or is the bullet the same size as the bore diameter and it expands under the gas pressure to engage the rifling? I've been told both. Edit: been answered, also found results for "Swaging" and "Obturation" (Also "Driving band" Swaging Is when the bullet is larger than the bore diameter and Obturation is when It is roughly the same size but the gas expands the bullet to wedge itself into the rifling. & #x200B; Thank you for your responses. | Engineering | explainlikeimfive | {
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"The anser is that it depend on the bullet that is used and both have been used. & #x200B; The Minié ball that become common and famous in the Crimean and American Civil War had a skirt that expanded. It is called a hollow-base bullet. It was used in muzzle loading rifles and had the advantage that you did not need to force down the bulles while it engage the refiling like in previous muzzle loading rifles. & #x200B; Early breach loading rifles used hollow-base bullet. & #x200B; Today most (all?) rifles have bullets that have a higher diameter then the bore. If I am not mistaken the expanding skirt are not used on full metal jacket bullets. That bullets that has soft core of lead and a hard shell other of a harder material often copper alloy. They can be made with high precision and the material will engage the rifling. & #x200B; But all bullets are not full metal jacket bullets and lead bullets are common on revolvers so they can still use hollow bases that expand but all do not use that. Another example is air rifles that use hollow base but are often not rifled. & #x200B; To the answer is either depending on the ammunition. & #x200B; & #x200B; There have been other strange variant like hexagon bore and bullet it was very good but expensive. & #x200B; How the caliber of the bullet is compared to the bore diameter depend on where the bullet was designed. US ammunition are specified by the groove diameter ie the boree diameter + the depth of the grooves. So for example 9mm Parabellum have a bullet diameter of 9,03 mm so it engages the rifeling. & #x200B; The calibers do not necessary match the bullet diameter and the name can change a bit for various reason. .38 Special and .357 Magnum have the same bullet diameter. The change is to refuse the risk of someone trying to use the more powerful .357 Magnum on a .38 Special weapon that is likely to fail in a catastrophic way. The .357 magnum case is 1mm longer but you could if still accidentally use it in some cases. & #x200B; The US tanke cannon on Shermans in WWII was the 75mm and 76mm cannon hade a shell with the same diameter but the case size was significant differens and they would not fit the other cannon. So the name change is to reduce the confusion in logistic so a tank company with one caliber did not the ammunition they could not use. 75MM long of what the option would have been. & #x200B;",
"The bullet is ever so slightly larger than the bore diameter, such that when it's driven forward by the power of the cartridge, the soft metal engages the rifling, forcing the bullet to rotate. There's no meaningful expansion the bullet could undergo during the brief time it's in contact with the gas.",
"The bullet will be the size of the major diameter of the bore, so the valleys in the rifling. And it will compress into the the ridges allowing them to grasp the bullet and impart their spin into it."
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ayerrl | How a foldable phone screen is physically possible | Engineering | explainlikeimfive | {
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"ei07xft",
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"text": [
"If the screen can be made thin enough, it can bend without breaking. Even glass can [bend to a 5mm radius]( URL_0 ) if it is only 0.1mm thick. If you can deposit tiny LEDs on a plastic film, that can also be bent.",
"Imagine medieval armor. Imagine the difference between plate and chainmail. Plate of course being very hard and rigid, offering protection(screen). Chainmail, still offering protection(screen), but using many many links to make it flexible. So you still have the solid protection of plate, but with a almost folding aspect. That's done here on an incredibly small scale almost."
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ayjfyc | How do vehicles like gondolas and ski lifts that are attached to a single moving cable slow down significantly in the loading/unloading station? | I would think the cable would have to move at a constant speed throughout the whole length? I was specifically reading about the new gondola system at Disney World which will supposedly travel at 16mph but slow down to 1mph at the platforms. How can something attached to a single cable move that much slower in one area? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"High speed gondolas and chairlifts have special clamps where they attach to the cable. [Image]( URL_0 ) When the conveyance approaches the loading or unloading area, the clamp releases from the cable and the unit can slow to a safe speed. It is conveyed around an end pulley and reattaches once clear of the area.",
"The carriages for most of them that change speed like are detachable from the cables mid-transport, but do so with mechanical action, which greatly limits the chance it'll just detach randomly. This means they can have a fast moving cable for the majority of the transports, and slower moving cables for getting on & off - because the carriage detaches from the fast one and connects to the slow one."
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ayldhw | why does the temperature of the shower water change so much with a tiny push? | Engineering | explainlikeimfive | {
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"text": [
"Because the hot and cold water have roughly the same pressure, and come to the shower through similar pipes. But the knob that selects how much of the hot water and how much of the cold water to combine isn't actually a sensitive regulator that can finely control the flow of each type of water. It's more like a [circular hole]( URL_0 ) that opens to let more water through. A \"tiny push\" could rotate that from a small sliver to half that hole being open."
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ayq7x7 | Why is it that smartphone batteries are said to deteriorate if used while charging, but the same is not true for laptop batteries and laptops are encouraged to be plugged in most of the time? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"I have not heard this specific phrase often, but this mainly has to do with heat generation. Smartphones, as they are so small, develop quite some heat during charging ánd during use. Because of the compact formfactor the heat from using the phone will also enter the battery, unlike in laptops where this component is usually thermally quite well isolated. Modern batteries (lithium-ion) do not like heat a lot, and will deteriorate if heated often/long/much. & #x200B; A lot of phones even work on lower clockspeed while charging, and are therefore slower while charging, to prevent too much heat build-up.",
"Charging a lithium battery to maximum voltage damages the cells over time. Phone manufacturers try to squeeze every last bit of capacity out of the battery so charge it to the maximum safe voltage. Since laptops are often left plugged in all the time, to help slow down degradation of the cells they are typically charged to a slightly lower voltage. But leaving them plugged in all the time will still degrade the cells faster than storing the laptop at say 60%. Squeezing that 5-10% extra charge into a battery can cut its life 10 fold. However modern chemistries are much better than they used to be in this regard.",
"if the batteries use the same lithium technology they degrade the same way: by number of charge cycles, and amount of heat exposed to. the difference is that most laptops have their batteries on a separate circuit so they can be powered from the socket even when the battery is removed. this also means that the battery can stop charging when it's full, and only starts discharging when the cable is pulled the same is not true for phones. the battery is part of the main circuit, if you remove it the phone turns off even if it's plugged in. that means it has to charge and discharge at the same time",
"Because it’s bad advise, at least for lithium ion batteries. The charging circuit will keep the battery at 100% while plugged in which is not ideal but still better than constantly discharging and charging it. If you are not going to use a battery it’s best to store it cool and dry and at around 60% charge. Be aware that it will lose charge slowly over time which can be harmful when it reaches 0%. Some devices allow you to configure how far the charging controller is going to charge the battery. This also shows that there is some trade-off for the manufacturer to be made: Squeeze the last bit of capacity out of the battery or set a lower limit for improved life time. This is often done for electric cars, where they are advertised with a higher capacity than what is actually available."
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ayspjk | How are commuter trains able to operate backwards? | I see commuter trains where I live operate with the engine on the rear end of the train. How does that work in terms of not only the locomotive, but also how conductors and engineers operate it? Like, where do they go in the front? | Engineering | explainlikeimfive | {
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"These trains are designed to work equally well in forward or reverse. They push from the back or pull from the front. This makes it much easier to run the locomotive on a straight track without the need for huge turn around circles when they need to change direction.",
"Some trains are designed with a small operator's can in the side opposing the engine(s), and have engines designed to move the cars in either direction, eliminating the need to turn trains around.",
"The train \"engine\" doesnt actually have a transmission and gears to move the train. It's actually a diesel generator that generates a LOT of electrical power which is then used to power electric motors that power the wheels. It is very easy to reverse rotation on electric motors hence how they're able to go forward and \"backward\" Edit: to add to the second question. They can operate the engine remotely from the opposite end of the train.",
"The front/end of the train has a special passenger car that has a driver's cab in it, which allows the engineer to remotely control the locomotive from the other end of the train. Here's [an example]( URL_0 ) of the ones we have in Toronto. You'll notice the little window on the right side of the car (left from the photo's perspective). That's where the engineer sits. You'll also notice that this passenger car has a bell and horn on it, while the others don't. The [newer models]( URL_1 ) now have a full cab at the front, rather than the subway train style in the older ones. This system allows them to easily operate the train with a single locomotive. Otherwise there'd be too much downtime trying to connect another locomotive with cab to the other end of the train when it needs to reverse direction. For the locomotive itself, it doesn't really matter if it's pushing or pulling the train. Especially for light weight passenger trains. Diesel locomotives use electric motors for traction (powered by a diesel generator), so they can operate full speed in both directions."
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aysq9f | How do hand and leg wraps, like the ones used in boxing and MMA, actually work? | Engineering | explainlikeimfive | {
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"text": [
"I don’t know about leg wraps, but hand wraps are pretty important in boxing. You bind your hand tightly with the wraps, and it stops the bones in your hand shifting as you throw really hard punches. Using hand wraps, you can hit really hard things, really hard, and there is less chance of seriously breaking your hand. Especially if you put any gloves on on top of the wraps."
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ayuayd | What's the difference between the left and right side of earphones? | Engineering | explainlikeimfive | {
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"text": [
"There might be a physical difference. in some headphones they are mirror images of each other. In others they are interchangeable. but much sound is in stereo. This means that separate sounds are sent to each of the two earphones. If you are watching a show, this could make a real difference. A noise from left of screen will play on only the left headphone.",
"Left audio track vs right audio track; avenge seven-fold has a few songs (cant think of titles right) that shows how different the audio tracks can be. Also stereo sound is required for virtual surround sound aswell. Mono audio tracks are very rare these days",
"They play different sounds depending on what they what each ear to hear. Listen to Bohemian Rhapsody for a good example of this in action(different sections of the song will only be in one ear or the other). A lot of headphones will also be shaped differently depending on what ear they are supposed to go in. Take a look at these Apple headphones( URL_0 ). If you tried to put the right one in the left ear, it will be super uncomfortable and the actual speaker will be facing the wrong way.",
"A recording is typically in Mono or stereo. In Mon there maybe no difference as there is only one channel of information. this may not be the case in an audiophiles setup, but here you are modeling a sounds with a point source. A stereo recording uses two channels to present information, potentially recorded from a single point source that originally produced the sound. In this case, if youre recording a sound that came from one place in an open environment, it might sound right. If you record a whole stage full of people then you have a bunch of sources for the sound creating an image to your ear with complex timing based off the position of the sounds relatively to each other and relative to your ear. Do if you use two microphones or more, you are better able to capture the \"soundstage\" of a bunch of instrument, musicians, or sources. A stereo recoriding will have two channels, one left and right, that represent the recordings of two microphones or more. The two channels for playback attempt to mix a set of sounds to encode spatial information. Also, you might have certain instruments limited to certain channels, bounce the sound around from one to the other, use center channels or sub woofers, or use the 2 channels to encode other info."
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ayul0w | What is the difference between “four wheel drive” and “all wheel drive” in cars? Isn’t four wheels all the wheels? | Engineering | explainlikeimfive | {
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"They technically mean the same thing, though they've come to have different definitions. AWD typically refers to vehicles that power all four wheels at all times. 4WD typically refers to vehicles that switch between two and four wheels being powered.",
"4WD means all 4 wheels are putting out the same amount of power. AWD is a ratio, most of the motive force is applied to the front wheels, and less applied to the back wheels. [\"Basically, an all-wheel drive system can send a variable amount of torque to each axle, and the driver doesn't typically control this. A four-wheel drive system sends a fixed amount of power to each axle, and it can be switched on or off by the driver. So, how do they go about doing their jobs? Generally, an all-wheel drive system uses a center differential to distribute the engine's torque between the two axles, while four-wheel drive relies on a transfer case, which functions like a locked differential. \"]( URL_0 )",
"An All-Wheel Drive system is always active; all four wheels are always receiving power and pushing the car forward. A 4-wheel-drive system is not always active, and is either automatically engaged by the onboard computer or engaged manually. 4WD is not intended to be on all the time, AWD cannot be disengaged.",
"4-wheel drive has to be manually engaged and disengaged, and when it's engaged it drives all of the wheels all the time. All-wheel drive uses computers to detect slippage and send power to various wheels as needed. By default, the vehicle operates as front wheel drive or rear wheel drive, but when those wheels don't get adequate traction, then power it sent to the other set of wheels until traction is established."
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az3c6r | How does the transmission on a car work and why does it never work the same again when it’s replaced? | Engineering | explainlikeimfive | {
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"A replaced transmission should work better than the one you have replaced. The difference in feeling may be to do with the ECU learning being erased when the new transmission is installed. After a normal drive cycle it should \"re-learn\" how to shift depending on how you drive. For fast, aggressive driving it will learn snappy shifts and will hold gears longer, for slow paced city driving it will change up quicker to be more fuel efficient. & #x200B; The transmission uses fluid coupling and planetary gears to take \"drive\" created by the engine and send it to the differential. The trans uses different gear ratios to turn the drive from the engine into something useful. It multiples torque. There are probably a billion good youtube videos that will explain it in WAY more detail.",
"Automatic transmissions use a series of clutches and hydraulic pressure to engage gears of different sizes. Like a ten-speed bicycle, the ratio of teeth on the gears changes how many times the rear wheel turns for every time you pedal one rotation. Google for diagrams and exploded views. As for the second question, a properly rebuilt/replaced transmission should work exactly the same as the previous one, but tolerances in assembly can vary slightly. After a major car repair, people tend to be much more vigilant and conscious of drivability, and sometimes fixing one thing will make another problem more apparent. Perhaps a poor alignment it was masked by the transmission going out, or the fact that the transmission is being replaced is a good indicator that the car is aging and will need lots more repairs as parts wear out."
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az58l3 | What really happens to speakers when they get blown out, and why do they sometimes cut back on? | Engineering | explainlikeimfive | {
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"It depends on what broke; even in big speakers there's some really fine wire and thin metal as part of the speaker coil. If that shorts due to too much current, it's busted. But, overpowering a speaker can cause the coil to deform or move past its intended range, causing it to not move normally, it could move back into its original shape and position when the voltage is gone and it has time to cool down or magnetic resudial field dissipates. Also, it may not be the speaker, your amp or crossover could be cutting out due to exceeding tolerances."
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az5xbh | Why do liquid containers usually have an oval shape? | Engineering | explainlikeimfive | {
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"Rounded shapes are closer to a sphere which is the shape that encloses the largest volume in comparison to surface area of the shape. This means if you are trying to conserve material for the container it makes sense to trend toward a sphere. Another issue is that spheres distribute internal pressure more evenly. Think about a somewhat flexible container with flat walls and 90 degree corners. The walls will bulge and the corners open up to greater than 90 degrees. A rounded edge prevents that.",
"Including circles, ovals have a distinct advantage over polygonal shapes in the fact that there is no corners. This is especially important regarding thick fluids, like lotions, where a sharp corner can create a spot of blockage, which can end up congealing and blocking the spout. Smaller bottles will likely be completely circular, while bigger bottles will grow more oval to allow for an easier grip while maintaining the round shape."
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aze48b | How do you design locks that allow several different keys open the entry door to the same apartment complex, but also just the door leading to one of those apartments? | Engineering | explainlikeimfive | {
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"A modern lock have stacks of pins in them where each pin is split in two. Only if you insert the correct key will the pins will align with the cylinder and you can turn the lock. So called master key systems have some pins that is split in three. This means that there are two possible keys that match the lock as there are two different ways to align the split pins with the cylinder. This does weaken the system as now there are more places where a lockpicker can get the lock to open in. It is also possible to have intermediate keys in the system. So for example a cleaner might have a key that only opens some apartments but not all but the manager can open all of them. This is done by having multiple triple split pins in each lock. But of course this makes it even easier for a lockpicker.",
"Edit: don't listen to me I think the idea is the there are many rows of teeth on a key and in each lock. The outer lock only has tumblers for the first few teeth, so all the keys can match that, and the inner locks have more tumblers so the keys can individuate on teeth further down.",
"Explaining this takes a little time because you have to understand locks and how they work. There's terminology like \"Key Pin\" and \"Driver Pin\" and I can't remember which is which. But let's say the driver pin sits on top of the key pin. Where they meet is important because these are literally 2 different pins that the key itself pushes up. \"Sheer Line\" is what allows the lock to turn. So when the Driver pin is pushed up by the key and it rests right above the sheer line but the key pin rests right below the sheer line, the lock will turn. If not, it won't and what prevents it is the actual pin striking the body of the lock at the sheer line. [Here's a video]( URL_0 ) that not only addresses how this works, it also shows how a master key can be made using just 1 of the pins or all 5 pins in a lock. Keep in mind, some locks have 4 pins, some have 7 or 8 and these keys are LONG. :)"
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azelcv | How do computers get faster each year even though some processors have fewer cores and lower clock frequencies? | Engineering | explainlikeimfive | {
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"The processors have more, smaller, and more clever things inside them that allows them to do more work per clock cycle. Compare it to the gears on your bicycle, you can use a higher gear to cover more distance per turn of the pedals. If a CPU were an engine, clock frequency alone would only tell you how high it can rev. One of the least useful measurements in determining how good the engine is. The clock frequency used to be more relevant to the buyer back when processors only did one operation at a time, so a higher number always meant better. Now that number is only a small part of the picture."
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azepzm | How does your computer know the difference between USB-C accessories like headphones, storage etc? | Engineering | explainlikeimfive | {
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"This [answer]( URL_0 ) from a year back on a similar question explains how: > USB is more than just a connector, it's a whole set of protocols. One of the functions a USB device must support is the \"Get Descriptor\" request. The computer sends the Get Descriptor request through the USB, and the device must respond to it with a variety of information that identifies itself. The computer then looks up that information in a database and decides whether to treat the device as a keyboard, as speakers, or whatever.",
"The important part here is that USB devices all share the same protocol for communication. This protocol controls how information is sent between different people. Think of the post office. To send a package you need to put it in a box, declare the weight, acquire the proper postage and then add a proper address. The post office will then deliver the package to the address, who to receive it goes to their mail box, reads the address slip to make sure its the right house, and then opens the box. There are even rules to handle improper delivery, arbitrary sized packages, if you want the receiver to sign on pick up. That entire ceremony is the *protocol* for post office communication. it works because every post office follows the same protocol and are able to communicate and pass packages between each other the same way. USB has its own ceremony, and part of that ceremony is the setup phase. In the setup phase, the receiving device asks a bunch of previously defined questions to your headphones and your headphones has the answers to those questions ready just like you would with your package at the post office. The important question and usually the first question asked is GET_DESCRIPTOR. Which your head phones will then return an already written response with exactly the information you wanted. Specifically, it will include [codes defined by the USB protocol]( URL_0 ) about what class and subclass of device it is.",
"I guess what you are seeing is a USB connector attached directly to a peripheral, just as a pair of headphones, just like a regular old 3.5mm headphone jack is attached. What you are missing is that, likely inside the USB plug's plastic housing itself, is a chip, a CPU much like in a full-sized computer (shares many features, though much less powerful) that is talking the complex USB protocol to your computer, and then translating the sound data it's being sent into a signal your headphones can output. The cable you use to connect, say, your printer, keyboard or external hard drive to your computer does not have this chip in it - it doesn't need to, because it has that chip in the device itself, where it needs a load of circuitry anyway. Also, you can buy adaptors with a USB cable on one end, a headphone socket on the other. Either way, as other answers have explained, there's a chip that speaks the USB protocol, and when you plug a device into your computer, it queries the device, and the device tells the computer what it is. Sometimes a device is several thing (a phone can be a network connection, a storage device, etc) and you choose what mode to report. Some devices are several devices at the same time (a weird device can pretend to be both a weird device, and a storage device - when you plug it in, it offers to install the necessary drivers from the storage, to then let you use the weird device). Some devices do so nefariously - a USB key may be both storage, and a keyboard, and when you plug it in, it secretly types malicious commands, or secretly reads your keystrokes and sends them to a server to be analysed."
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azkyw4 | What does an audio file consist of? | For example, every photo we take with our cameras, are only consist of little pixels. So lets say, If I just open paint and put 1920x1080 amount of perfectly placed dots, it will be the same as the original 1920x1080 picture. Because that picture is ONLY consist of pixels, nothing more. What I'm saying is it's probably almost impossible to do, but TECHNICALLY it's legal and its working. & #x200B; But what about the voice recordings? Let's say I have recorded my sound for 10 seconds. But now I want re-create that sound with a program/software. What info do I need? I just want a TECHNICALLY working solution for imitating my voice. Hope I'm clear, sorry for the english. | Engineering | explainlikeimfive | {
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"Sound is pressure waves. A microphone detects the pressure changes and outputs electrical currents depending on how much the pressure changes. A sound card will detect the voltages that the microphone creates on the wire. It does this by periodically \"sample\" the signal and converts the voltage reading into a binary number. Compared to an image a sound file also consists of \"pixels\" or rather \"samples\". Because instead of an X and Y axis you have a time axis. And instead of colors for the pixels you have the pressure value in the sample, or potentially several values for stereo or surround sound. And just as an image have a resolution and a color depth an audio file also have a sample rate and different depths.",
"When you use an audio editor to zoom in on the recorded waveform, you will see that it’s a graph. That graph shows the actual back and forth movement of the microphone’s membrane as it was shaken by the air when you spoke. It’s the footprint of your voice. Sound is, after all, just something shaking back and forth, and sound recording is only a matter of mapping that motion as accurately as possible. In theory you could certainly draw that graph manually in the same way as you could recreate a photo pixel by pixel. I’m just not sure why you would."
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b029yc | Boeing 737 Max Anti-Stall System | Engineering | explainlikeimfive | {
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"For clarity; it's not yet known what happened, the anti-stall is just on the list of suspects. So, stall recovery in flights is not totally intuitive, particularly for novice pilots; in order to recover from a stall, you need lift, but for lift you need airspeed. Thus, the way to recover from a stall *is to nose into it*, deliberately diving to gain speed. The anti-stall system helps by applying extra control over the aircraft to get the plane's nose down if it detects a stall. Right now, it is suspected that something is causing the anti-stall system to kick in when it's not needed, forcing the plane's nose down and causing these incidents. It's also possible that the issue is related to 737 pilots not understanding the system on the 737 Max, as the anti-stall system is new on the 737 Max."
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b0d6vm | Why are some boats pointy on both ends, while other boats are pointy in the front and flat in the back? | Engineering | explainlikeimfive | {
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"The ideal high speed ship is infinitely long and infinitely skinny, this gives the least amount of drag but is impossible to build. The practical high speed ship is fairly long and fairly skinny at the water line, but this also makes it relatively unstable. A ship that is fairly wide relative to its length will be very stable; and make it a lot easier to put your stuff close to the water line which lets you carry more cargo with less of a risk of flipping over. Ships that have a flat stern often aren't concerned about absolute speed, there is often something else they had to worry about more than just going fast. It could be overall length like on a speed boat. It could be a need to load cargo in from some side and a big rear loading ramp was convenient. It could be that they're a big ass ferry only ever doing 6 knots so what do they care about high speed drag. Points on both ends help the boat go faster with the same horsepower, but not all boats care about speed.",
"A tapered stern allows the water to gently come back together to fill the hole the boat made as it passed. [The front and rear of the hull stay wet at the waterline]( URL_1 ) Square sterns are more efficient on faster craft, where the water cannot flow back together fast enough. The faster shape is squared off, [so the water can detach from the back of the boat and not drag on it.]( URL_0 )",
"Vessels move through the water more efficiently when they are streamlined (both ends pointy) because the flat stern (back end) creates a void as the boat moves which pulls it backwards a little. If you want to mount a motor on the back of your boat you're gonna need to make the stern straight so you can mount it in a way that is structurally sound. EDIT: There are many exceptions to this. First, they make trolling motors that you can strap onto the side of a canoe. This works because a trolling motor isn't very powerful and the shear forces this creates aren't enough to rip it apart. Second, many large ocean vessels have propellers that exit the ship from underneath. These ships don't need a flat stern and you'll notice that they tend to have more of a stub than a point in the back. This is a compromise between size and efficiency."
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b0eorp | How do multistage rockets work? And how do the rockets not just immediately fall apart upon launch? | Engineering | explainlikeimfive | {
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"A multistage rocket is, in ELI5 terms, a bunch of small rockets stacked up, instead of one big rocket. This is more efficient because as each rocket burns out it can be discarded, which means less weight for the next stage to push. They stay together on launch because they are firmly attached to each other, and because the forces of the launch actually are pushing them together, rather than apart. When a stage is discarded it is jettisoned with explosive charges that rather violently disconnect it from the rest of the rocket stack."
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b0euzv | Before computers were used, how did automatic elevators work? | By automatic, I mean by those that are able to automatically stop at floors to pick up passengers, and only pick up passengers if they are going the same direction (if not, they assign a different elevator car to pick up those passengers). | Engineering | explainlikeimfive | {
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"There are all sorts of logic circuits that can handle complicated processing that wouldn't be referred to as \"computers\". Computers are devices that can store data and then perform actions based on that data.",
"The first elevators were manually controlled. There were an elevator operator in the elevator car with the passengers throwing a leaver to control the speed of the elevator. But then the first unattended elevators used electromagnetical devices for its logic. This means relays that would do the logic and send the electricity in the right direction. There are still elevators in use with such systems. Computers are a rather new thing in the elevator business. There is often only a limited number of relays in a system. However each relay can do a lot of logic with mechanical devices in them. So a relay can have multiple positions, multiple signal wires, multiple contacts and physical barriers. And secondly a computer is built to do everything but an elevator only need simple logic. Even if you were to build the elevator control circuit out of single transistors you would not use many transistors, maybe twice as many as the number of relay you would need."
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b0f9pi | Why does the Boeing 737 MAX not have an automated system to pull up if it's on a collision course with the ground/sea? | Engineering | explainlikeimfive | {
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"It does have numerous automated systems. Unfortunately the recent crash *might have been* caused by one of these systems overriding everything else, trying to avoid an opposite accident involving climbing too fast (a stall)."
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b0hqcg | How can a car continue to function for 30/40/50 miles after its range to empty counter hits 0, is the range intentionally smaller than the actual capacity? | How can a car still travel for quite a distance after reaching empty/range hitting 0? | Engineering | explainlikeimfive | {
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"> is the range intentionally smaller than the actual capacity? Yes. It's designed to give you enough time to actually get to a gas station once it reaches \"empty\" or \"zero miles\" (or whatever your car uses).",
"I recall an old OLD ad in an old OLD magazine. I'd guess the mid 50's. It showed a typical nuclear family (Dad driving, Mom in the front, kids in the back seat) riding along in a convertible, all smiling and the caption said, \"They're running on empty.\" As /u/Seraph062 said, the ad touted the design which allowed cars to continue for (many) miles when the gauge said E. (This was before mileage indicators.)"
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b0hz8p | What do the transformers on the power lines actually do? | Engineering | explainlikeimfive | {
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"They convert high voltage power (suitable for transmission over distances) to higher-current, lower-voltage power (suitable for domestic use without frying your equipment).",
"The lower the voltage, the fatter the cable has to be to carry that power. For the best example of this, think about jumper cables for your car. So, that's fine if you are going ten feet, but what if you need to send electricity five miles or ten miles or 100 miles, what do you do then? That fat wire is expensive and heavy and hard to install. Well luckily someone long ago figured out that if you increase the voltage it will go farther and use a skinnier wire to do that. So normal household electrical voltage is 110 or 220, but to send electricity super long distances they change the voltage to over 50,000 volts. Otherwise the wire would be thick as your forearm. Well, when it gets where it's going, those transformers change it back to 220 so your house can use it."
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b0ogvq | What’s the difference between a big powerful engine that makes a car go fast, and a big powerful engine that makes a truck able to pull heavy things. What’s fundamentally different about them. | Engineering | explainlikeimfive | {
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"It all comes down to the power stroke. This is when the fuel is combusted, and hot, expanding gasses provide pressure, which is force, to push on a piston producing work. Force that goes around an axis is called torque. It get's its own fancy word. If you push a heavy box across the floor, that's force. If you turn a thumb screw, that's torque. Same thing. Work is force over time. The best illustration of this is if you want to push that box across the floor in half the time, you have to perform twice the work. Force doesn't have a speed associated with it, it's just an amount. Diesel trucks are designed to take advantage of diesel fuel, which burns really slowly. In the diesel engineering world, any Diesel engine that runs faster than about 1,300 RPM is considered a \"high speed\" engine. Remember that most diesels in the world power pumps, generators, trains, and cargo ships, they're gigantic, where you're whole body can fit inside the cylinder of some of these. You'll be hard pressed to find a Diesel engine that runs faster than ~5,000 RPM - maybe look at a Volkswagen GTI. Any faster, and you're dumping still burning, not yet combusted diesel fuel out the exhaust port, and that still burning, still getting hotter fireball is bad for that part of the engine, which wasn't designed to handle combustion. There are also engineering compromises in Diesel engines to handle the heat and force, and these parts and materials don't like moving fast without ripping itself to pieces. Anyway, since diesel burns slow as shit and hot as balls, these engines have very long strokes - combusting diesel produces a long power stroke, there is a long time you can capture energy from combustion and turn it into work. Gasoline burns really fast. Cosworth was building an F1 racing engine that ran at 22,000 RPM before the 2016(?) engine speed limit. It produces less force, but you can produce it more often. Remember what I said about work? Want to cut the time? Do more work. Acceleration favors work in the math of these equations, so gasoline is the champion of acceleration, hence racing engines. Also acceleration can be negative, not only can you speed up quickly, but you can slow down, quickly, too, because the combustion event can be so short, you can get a new charge of fuel and air in the cylinder sooner that produces the new greater or lesser force. We call this throttle response. In a diesel, you have to wait for that power stroke to finish, a lot longer, before a new charge goes into that cylinder. 2-stroke and rotary engines have even faster throttle response because there's less or no rotation that isn't producing power. So, can you race on a diesel? You sure can. There are all sorts of racing where torque is everything. Is it fast? Not really. Diesel can get you high speeds with gearing, and there's enough torque to turn those gears to get that vehicle up to top speed, eventually - you need torque, like int the Bugatti Veyron, to overcome wind and rolling resistance, but they'll never match the acceleration properties of gasoline. You can compensate with insane gearing, and lots, and lots of gears, but then you're talking a transmission that doesn't exist, that's too big, too heavy, and you spend too much time shifting, and time shifting is not time putting power to the road. Maybe one day there will be a CVT that can do it for a diesel racing application, but I don't believe the materials are there.",
"A couple of things the truck one will usually be a diesel and will normally be tuned to have a more broad power curve (peak power is over a large rpm range and usually at lower rpms) to prevent you from having to shift gear so much, a side effect of this is they should be slightly more fuel efficient. & #x200B; The far bigger difference however is not the engine but the gearbox. The gearbox can take the power of the engine and output a range of torque at the wheels. Truck gearboxes have lots of gears to ensure they are always outputting the optimal amount of torque. & #x200B; In theory if you had a gearbox with enough gears you could use a superbike engine to pull just as heavy a load as a big truck engine, it would just be incredibly noisy, use lots of fuel and you would constantly be changing gears due to the narrow power band (power peaks over a small range at a high rpm) of the bike engine.",
"Sticking strictly by your question I'd say it comes down to gearing. A truck with a big engine won't go very fast in 1st gear but will be able to pull very heavy things. A car with a big engine (Corvette for example) can go nearly 80 in 1st gear but you wouldn't want to haul a trailer with it.",
"In very general terms, for speed you want a lot of horsepower, whereas for towing/hauling torque output is more important. The various engines in your example will be designed with that in mind.",
"There are excellent answers like /u/mredding posted, but a bit more ELI5: Motors, like any other mechanical devices, are designed to do a task. You use the best design for the job you want to accomplish. A sledgehammer is fantastic for breaking up concrete slabs, but not an elegant device for putting picture hangers in your walls. A small gasoline engine (in general; there are exceptions) is designed to run very fast and be very responsive. A large diesel engine is designed to run at a much slower rate and be efficient. Trucking companies don't care about 0-60 mph (0-100 km/h) times. They want low fuel costs and long engine lives (lower rotation speed = less wear and tear on the engine per unit distance). A sports car owner wants something that goes FAST and does it RIGHT NOW, and if it only lasts for 200k miles, so what? Most people drive under 12k miles per year, so it's good for 15 years or more. A standard tractor-trailer rig can be driven 70 hours per week by one driver. Assuming an average speed of 50 mph (they go faster, but they have to fill up, take breaks, etc., and this is a *very* conservative estimate), they will cover 3500 miles per week, or 182k miles per year. Can you make one engine do the other's job? Yes, with gears. But it will be a lot harder to maintain a Corvette engine driving a semi, and a semi engine driving a Corvette will have godawful acceleration, and that is completely ignoring the weight and friction losses from all the gears.",
"Horsepower is how fast an engine can do work torque is how much work that engine can do.",
"The gear ratio in the transmission has a lot to do with it. (I have a 20 hp tractor that can pull my 300 hp truck backwards when it's trying to go forward.)"
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b0onsx | How do wells work? | How do people know where to dig? How does the water stay clean? | Engineering | explainlikeimfive | {
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"text": [
"There's always water underground. Everywhere on earth there's water underground. The only real question is, how far do you need to dig before getting there. So as far as where to dig, you can dig basically anywhere. But digging really deep is really expensive. So they have geologists who study the ground and the kind of rock in the ground to determine what place is best to dig. The water that's in the ground has filtered through rocks and soil. So it's basically clean already. Sometimes it needs some treatment but in terms of larger particles, it's mostly clean as it has filtered through hundreds of feet of rock and earth. And sometimes the water does not stay clean. Sometimes people suck up so much water that the well runs dry for a while. Sometimes there's so little rain in the area that the water level falls below where the well is dug and it \"runs dry\". Well, water is basically a constant battle to keep it safe, clean, and drinkable. Sometimes even that fails."
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b12tjp | How a plane with both engines which are completely destroyed can still fly and change direction on the sky? | # I've just watched Sully film, and I don't know why the plane with two engines broken can still move on the sky, and can even return back to the airport ? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Contrary to what Hollywood would show you, planes don't just fall out of the sky when their engines stop working. Instead, they turn into gliders, which can travel for long distances as long as they're okay with slowly descending towards the ground. If the plane was high up in the air, and traveling at cruising speed, it can fall gracefully for many many miles before it reaches the ground. Steering an aircraft is all about the air flowing over the flaps on the wings and tail of the aircraft. When the pilot steers, those flaps change their angle to move the aircraft, no engines needed.",
"It can still glide. Like a glider. Because it has wings."
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b1675v | How does a zip file compress data? Why don’t we make all files stored automatically compressed to save data? | Engineering | explainlikeimfive | {
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"eijntzy"
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"Storage is very cheap. Compressing data takes CPU resources, slowing down that cat video you are watching, and delaying access to files. Which you don't need to have because storage is very cheap.",
"Ooh! I was just about to write a zip compressor for a CS class, so it's very fresh in my mind. A very basic form of data compression is one that starts at the beginning of your data file and records any repetition. This works okay for things like ASCII text files and some images, but when your data is fairly random, it becomes less effective as you don't have bits that repeat as often. A slightly more advanced algorithm uses what are called [Huffman Trees]( URL_0 ), which record the number of times each character appears in the text/image etc (most notably also effective for ASCII text). It chooses encodings of very common letters (think vowels, for example) and makes them as small as possible. If 'e' is the most common character and takes up 32 bits, it can be given an encoding like '11' which is only two bits, effectively compressing it down to 1/16 of its original size. This happens for every character, and can often see about a 75% decrease in size from the original text file. As for your question, why isn't everything stored compressed; speed. It's certainly possible to make everything in your file system compressed, but it's a relatively slow process. In any data critical application, the space saved from compressing files will be made up for in time loss. However, sometimes ~~(as was the case in Gen 1 Pokémon safari zones~~ see below comments) it's necessary to take the performance hit for the amount of space it can save.",
"Zipping is like taking your tent down and packing it up. You can't use it that way. If you want to use it, you have to spend the time to unpack it and put it together.",
"One reason: a lot of the files that are large enough to care about compressing are photos, music, and videos. These are usually compressed already, using algorithms that are much more specific to the content (jpeg, mp3, and mpeg, for example). These algorithms compress much smaller than a generic compression like zip. Once compressed, further compression using another algorithm is unlikely to make the file smaller, and often makes it bigger. Another reason: it’s more work for the computer to compress and decompress the files every time they are accessed. It costs CPU cycles, and it’s hard to access just a small part of a large file."
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b1aym3 | How do vehicles detect how far you can go on your current amount of gas? Wouldn’t sensors not work due to the gas sloshing around? | Engineering | explainlikeimfive | {
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"eikrc51",
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"text": [
"Average gas mileage is built in. Cars estimate the remaining mileage based on how much gas is left. Yes, the gas sloshes around a bit, but while the car is in constant motion, the gas doesn’t move a lot. It moves around mostly when braking or accelerating.",
"There are baffles inside the gas tanks to keep it from sloshing around too much. Otherwise it's just an estimate really based on your current MPG. Start revving the engine or hit a strong headwind and that estimate will change.",
"my old van has plenty of petrol when driving downhill and hardly any when driving uphill, so yeah that problem used to be very really.",
"The inside of a gas tank is like a honeycomb so the gas doesn’t slosh around the way you might think. The rest is sensors and math to give you a decent estimate at current consumption rate.",
"I worked on this a few years ago but I can't remember the exact details. The sensor is similar to the magnet sensor on the coffee filter detecting low or no water. The sensor should indicate low level for 2 minutes before it qualifies. The 2 minute counter is either paused or reset during breaking, and accelerating as measured by a pedal sensors passed trough a filter. This is decided by both the ECU part provider, and the customer that knows the exact parameters of the tank and placement of the sensor. The low level decision doesn't guarantee the light turns on, that's done by another algorithm that also takes in consideration estimated power consumption, no idea how that part works, it's on a different computer in the network."
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b1edmr | How do scientists aboard the ISS ensure no water ingress on electrical equipment? | As the title suggests, I just watched this video [ URL_0 ]( URL_1 ) & #x200B; And I was curious as to what precautions were taken for the blobs of water that would break away and I can assume would hit the walls of the room they're in. I know they're only small blobs, but I've seen videos with Mr Hadfield and larger volumes of water (wet towels, how they wash etc.) and I wondered if they coat the walls with absorbent material or anything like that. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"They do try to seal up electrical components. Not only from water ingress but also dust. However it is not a much bigger issue on ISS then on Earth and a lot of the equipment they have is regular off the shelf components that you likely have at home. They do have a ventilation system that they have turned on quite high and most of the water droplets and dust tends to float towards the ventilation ducts. They can regulate the humidity quite accurately and will set it comfortably low to make the water evaporate quickly.",
"They actually re condense a lot of the moisture out of the air for drinking water. Anything that gets stuck dries pretty quickly because they keep the air dry for those purposes the only time you'll see water ingress being a problem is when the internal heating or ventilation systems fail. We saw this aboard Skylab, Mir, and Apollo 13 when they had the power down the command module usually there are little electric heaters everywhere to keep water from condensing on anything"
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b1g3er | why do bridges not form potholes but normal roads do? | Engineering | explainlikeimfive | {
"a_id": [
"eildfgv"
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"text": [
"Bridges lack what most roads have, a lively earth underneath them. Despite having many inches or sometimes even feet of packed gravel roadbed, the soil beneath undulates, heaving up in some places, and sinking away in other places. Additionally the gravel roadbed itself is susceptible to water displacement. Usually both are at work to do their best to screw up our roads. Bridges on the other hand usually have steel or concrete under the asphalt, thus are not subject to soil or displacement issues. And cement is perfectly capable of forming potholes. It's just a little less prone to than asphalt, because it must fracture first."
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b1pqm8 | how are rotary autocannons accurate when the barrelsnrotate? Wouldn't the trajectory be skewed? | Given the laws of inertia, if an autocannon is rotating it's barrelsnrotate firing, wouldn't the rounds be thrown tangentially as well as downrange? How is this accounted for? | Engineering | explainlikeimfive | {
"a_id": [
"einebnl"
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"text": [
"Let's see, if the gun fires 7200 rounds a minute that's 120 rounds a seconds which means a six barrel gun rotates 20 times a second, with an estimated 5cm radius of the barrel assembly gives you roughly 6.3m/s tangential velocity. Compared with the ~1000m/s exit velocity of the bullet this is almost negligible. That being said those guns tend to fire with the firing barrel on the down stroke so the tangential velocity is vertical which makes it easy to counter by mounting the gun slightly upwards when zeroing it. Aside from that these guns are meant to saturate an area with bullet in short bursts, not really aimed with a scope for high precision but they're accurate enough to hit within a 20m radius over 1000m distance in a burst."
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b1yq97 | How does ReCAPTCHA detect humans, when it is a robot? | How can a robot distinguish between a robot and a human, when a robot is running the detection system? Is it basically using our answers to learn which answers are right? If so, can't other programs do the same and bypass it? & #x200B; Or is it just an AI learning and not actually trying to detect robots? | Engineering | explainlikeimfive | {
"a_id": [
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"Google once said they actually analyze mouse movement as a major part of it. The pictures, and even simply clicking the box, are used to check if you’re actually using a mouse, and if you’re moving it in a natural manner: > Instead of depending upon the traditional distorted word test, Google's \"reCaptcha\" examines cues every user unwittingly provides: IP addresses and cookies provide evidence that the user is the same friendly human Google remembers from elsewhere on the Web. And Shet says even the tiny movements a user’s mouse makes as it hovers and approaches a checkbox can help reveal an automated bot. [Source (WIRED)]( URL_0 )",
"So, I don't know much about the picture-based ReCAPTCHA system, but I'd imagine it works much the same as the text-based system I'm familiar with. Anyway, this is what I understand about how it works: So, ReCAPTCHA was intended to serve two purposes. First, the prevention of bot access to websites, and second, assisting in the digitalization of scanned text. ReCAPTCHA would present the user with an image consisting of two words. The first is the control word; the computer had already figured out what it was, and would fabricate a new image with distortions that would make it difficult for other computers to read it. The second word was one that the computer *hadn't* yet figured out. So, the first word is really the only one that matters. If you get that right, you've proven that you're a person rather than a program. The second word, however, is an open-ended question. Your answer would be fed back to a computer to improve its text recognition capabilities. Some of these unknown words, once confirmed by multiple users, would be recycled as control words, since we already know that the computer would have difficulty interpreting it. Unfortunately, this system has...let's call it a loophole. Once people figured out that you could put anything you wanted for the second word, and the computer would accept it as valid, folks started bamboozling the system's creators. Instead of giving the standard answer for, say, [this captcha]( URL_0 ), you could type \"Suez BUTTSECKS,\" and the computer would accept it, because, hey, as far as the computer knows? It does indeed read \"Suez BUTTSECKS.\" I'd imagine that's part of the reason you don't see as many text-based ReCAPTCHAs anymore. Edit because I can't into spelling"
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b23al7 | What is a capacitor and an inductor on an intuitive level? | Engineering | explainlikeimfive | {
"a_id": [
"eipzcta",
"eiq0bp2",
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"text": [
"A capacitor is just two plates with an insulator between them. That's it. The plates are made in unusual ways, so that they can be really large and really close together, but that's the idea. When you push electrons onto one plate, the charge pushes electrons out of the other. If you disconnect it, the excess electrons on one plate, and lack of electrons on the other, is stored energy that can be used. And inductor is a coil. When you try to push current through it, it has to do work creating a magnetic and electric field. If you disconnect it, that magnetic field starts collapsing, 'trying' to push the current on. In this way, capacitors and inductors store energy. They can store that energy for hours, or nanoseconds, depending on how you use them.",
"If you think of a circuit as a system of pipes with water, a capacitor is like a stretchy membrane separating one end of the pipe from the other. Water can’t get through the membrane, but using pressure, you can push on the membrane, and the water on the other side will move too. In this analogy, water pressure is like voltage. An inductor is like a waterwheel. When the water first starts flowing, it takes energy to get the waterwheel to start spinning, so the waterwheel resists the flow. Over time, the waterwheel is spinning at the same speed as the water, so it doesn’t resist the flow at all. But when you stop applying the flow, the waterwheel will also resist the flow. It wants to keep spinning, so it keeps the water moving some, and slows down as it transfers its energy to the water.",
"A capacitor stores power and releases it steadily. We use them in high power microwave generators to limit surges. Always ground them out first or you could get a bad shock because they still store a charge after power is removed."
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b25asw | Why do empty hard drives feel the same as full hard drives | Engineering | explainlikeimfive | {
"a_id": [
"eiqaumu"
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"text": [
"The storage areas in hard drives are called the platters. The way in which data is written to these is magnetically. There's no ink or any extra material actually ADDED to the disk, it's just that the little areas on the disk are positively or negatively charged."
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b25rgw | Why don’t airlines make faster planes (more engines?) so flights are faster and there’s higher turnover? | Engineering | explainlikeimfive | {
"a_id": [
"eiqe2a2",
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"text": [
"They have to balance speed with fuel efficiency otherwise they wouldn't make a profit. That's why the Concord eventually went away, it was fast, but not efficient.",
"Airlines today today fly about 85% the speed of sound. As soon as you start to fly closer to the speed of sound and beyond, the air starts to behave very differently than before, namely, shock-waves start to form. Once this happens, the drag starts to increase dramatically. More drag means you need more thrust to overcome it, so you need to use more fuel, and fuel is very expensive. If you want to mitigate the increase of drag due to transonic and supersonic effects, you have to radically alter the design of your aircraft (compare the Concorde to the Boeing 737 to see what I mean). This means that you've now designed a plane that can fly reasonably efficiently at supersonic speeds, but is horribly inefficient at subsonic speeds. Since your plane has to fly subsonic to take-off, climb out to an altitude where it can fly supersonic, and land, the plane burns even more fuel. In addition to this, the plane cannot fly supersonic over land without creating harmful sonic booms on the ground below. This limits the number of routes that an airline can operate a supersonic aircraft at to oceanic flights only. More fuel = higher costs, which means a more expensive ticket. There's only so much people are willing to pay to get to their destination faster. For most people, 6 hours to cross the Atlantic is \"good enough\". This was demonstrated by the Concorde. Even in it's hay-day, it operated on razer thin profit margins. With rising costs of fuel, and more and more efficient subsonic airlines, it couldn't make it's operators money any more, and was retired."
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b29fqk | There are magnets in phone cases/holders, magnets in wallets that sit next to our phones; how do our phones stay unaffected when magnets wreck havoc on electronics? | Engineering | explainlikeimfive | {
"a_id": [
"eir5von",
"eir6ah0"
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"text": [
"Magnets do not wreak havoc on electronics. They can wreak havoc on magnetic storage such as hard disks, floppy disks, video tapes and audio cassettes. They can also affect antennas. The phone industry does not use magnetic storage, so they can use magnets for sensors, to know when a flip phone is closed and such. Careful - Laptops may use magnetic storage but are more and more going to nonmagnetic SSDs. So you are left with the effect on antennas. Magnets won't damage them but may interfere, so they design products that have magnets with the small sensor magnets far away from the antennas and any magnetic storage.",
"Magnets generally do not effect electronics, for two reasons: Firstly, they operate at high enough speeds that the slight impact magnetic fields have on wires and such can be corrected for. Far faster than a display needs to update, for example, electronic devices can use built in mechanisms, like check sums or parity bits, to determine if the data received is valid and unmodified. Any detected errors could then trigger a request to resend the data. Second, most concepts of magnets affecting electronics come from magnetic storage and old monitors. Magnets can modify the geometry of how data is stored on hard drive platters or tape, physically ruining the 1s and 0s that are stored. Modern electronics frequently use \"solid state\" storage, which uses silicon based transistors to build electronic, non-magnetic storage. This is frequently encountered as Solid State Harddrives and \"flash\" memory SD cards. Additionally, older monitors, called CRTs - Cathode Ray Tubes - used an electron gun steered by magnetic fields to illuminate a pigmented coating, which made up the red, green, and blue pixels we know and love. Introducing a magnet would prevent the computer from being able to correctly steer the electron beam, producing admittedly psychedelic effects in the display. In short, things like cell phones don't have magnetic media, and the inherent nature of the data is highly resistant to errors being introduced. Edit: elaborated points."
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b2b64n | How do ancient Roman fountains work? | What did they do to get the water to go up and out the top? | Engineering | explainlikeimfive | {
"a_id": [
"eirjdzw"
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"text": [
"They had aqueducts, raised artificial channels bringing in water to the city from high up in far away hills. If you keep the water high up, you can use lead pipes sealed with solder (\\*) that maintains the head pressure of the water to make it come out of a fountain still under pressure. \\* Plumbing and plumber come from the Latin for \"lead\""
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b2bifa | In the unfortunate event of the crash of a passenger Jet. How does the black box manage to remain intact? | Engineering | explainlikeimfive | {
"a_id": [
"eirmm2d"
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"text": [
"The black box is built much stronger then the airplane. Usually they use thick steel for its construction instead of thinner aluminium. They also fill it with foam and silicone instead of air. The black box is also much smaller so that it is less likely to be torn apart. And they place it in the tail of the airplane so that if the aircraft crashes the black box will be one of the last things to hit the ground. If you think about it a lot of things manages to remain intact during a crash. You often see entire wheel assemblies and sections of the cabin more or less intact after a crash. The black box is just built to have a much better chance of being intact then most other components. But it is not that unusual for the black box to be damaged or even completely destroyed. This is why a black box stores its data in a way that it can be put together in a laboratory afterwards so they can read out the data. This is why hard drives have not been used for black boxes as it is possible to shatter the drive plate which contains the data."
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b2dvbr | Why do some fishermen have poles with the holes (that the fishing line runs through) top versus bottom? | I could’ve googled this but since reddit seems to encourage these types of easily findable questions I figured I’d ask here instead. It’s an honest question | Engineering | explainlikeimfive | {
"a_id": [
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"eis35sn",
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"text": [
"The guides are on the same side as the reel. Some reels go on top (bait casting) some go on the bottom (spinning and fly reels)",
"The rods with the guides on the bottom as generally for spinning type reels and the rods with the guides on the top are generally for overhead/baitcasting type reels. the number, size and type of guides depends on the type of fishing and if it is designed for casting.",
"To add to the the other responses, typically a reel that goes on top has a larger line capacity, more room for stronger gearing and a different method of allowing the line to be pulled off under pressure (drag) which means that style is used for game fishing, where the fish may have several hundred metres of line attached. Until recently (last 20 years or so) spinning reels that hang under a rod weren't built strong enough to handle large drag pressures. Small bass style baitcasters can provide more accurate casting. As fish like to hang out in cover, accurate casts improve your chances of catching fish. Baitcaster reels rely on the bait weight to pull the line off a rotating drum so typically are difficult to cast light weights so spinning reels are great for casting lighter weights as only the line is pulled from a fixed spool when casting. Another consideration is that the torque applied through rod guides placed on top of the rod tends to want to twist the rod so that the guides are below, so a rod with guides on the bottom is more stable. About 15 years ago rods designed for baitcaster type reels started to come out that had a line path running from the top of the rod to the bottom to aid with that stability. Daiwa went one step further and produced rods where the line went inside the rod and out of the tip."
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b2fgay | Why are car brakes mounted in different positions? | Why are discbrake calipers mounted on differing positions on the brake rotors? | Engineering | explainlikeimfive | {
"a_id": [
"eiskrdp"
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"text": [
"The wheel on the left side of the car turns the opposite direction to the one on the right. Some parts are mirrored, but that's more expensive, because you need a \"left\" and \"right\" part. Where possible, the same part is used on both sides, which can make it \"backwards\" relative to the other side. Different car manufacturers have lots of other factors to consider, specific to their suspension design."
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b2lmi6 | Could planes benefit from having dimples like golf balls? | I watched the Vox video about golf ball dimples and cores and it made me wonder; could airplanes use the same dimple concept to increase stability? or do they already and i just never noticed? | Engineering | explainlikeimfive | {
"a_id": [
"eitfxan",
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"text": [
"No. Dimples help on golf balls because they help with base drag, that is drag created by the low pressure region behind the moving thing. However, the dimples increase drag from skin friction. Golf balls are not aerodynamic and thus have a lot of base drag, thus the dimples help. But airplanes are made very aerodynamic and have relatively more skin friction drag, so the benefit from dimpling the skin would be negated by the increased drag of skin friction.",
"It isn't necessarily there to increase stability but it does more importantly introduce energy into the boundary layer, resulting in less form drag so the ball flies farther. A sphere experiences a bunch of very different flow regimes depending on a characteristic 'Reynolds Number' which is mostly to do with its size, speed and the temperature of the air (which affects viscosity). For example, a sphere or cylinder sees Stokes flow at low speeds, then to a mostly laminar regime, then may start producing periodic eddies that start to shed and oscillate (karman vortex streets), then to fully turbulent flow, then something magic happens when the boundary layer becomes turbulent and the form drag drops right down. Then as compressibility becomes a factor the drag starts increasing massively. Then at supersonic awesome oblique shocks form, pressure waves bunch up and loads of energy is dissipated. Lots of university research projects have looked at various methods of dimpling aircraft. It's not the same as golf balls up there though because the Reynolds number and Mach number are both different, so the flow regime behaves VERY differently. Aircraft are probably better with very smooth surfaces partly because skin friction drag is also very important, and often dimples at those conditions could make drag worse, add mass and add cost. Also the fuselage is a structural pressure vessel and dimpling might result in needing more frames and stringers so again more mass. A result of weakening the pressure vessel like a dented drinks can. If an aircraft gets a dent or a scratch, the Aircraft Maintenance Manual instructs to blend out and restore the surface to a very smooth condition e.g. no more than a few thousands of an inch imperfection, maybe even requiring use of a filler."
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b36p2x | How do cars convert fuel to motion? | Engineering | explainlikeimfive | {
"a_id": [
"eixkg1g",
"eixkcxz"
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"text": [
"It burn the fuel with air. This creates a lot of hot expanding gasses. As the gasses expand they push on a piston. The piston is connected to a crankshaft and will turn this crankshaft around as it gets pushed by the gasses.",
"In short [fuel and air explode in the cylinder forcing the pistons down which turn the crankshaft]( URL_0 ), then the rotation of the crankshaft is translated to the wheels via gears and axles."
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b3h29f | Why do most public bathroom stall doors have cracks that people can see through and walls and the doors that don't go all the way to the ground? | Engineering | explainlikeimfive | {
"a_id": [
"eizlbxz",
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"text": [
"People suggest costs, which is probably at least part of the truth as producing something with huge tolerances is much cheaper (though we can generally afford toilet cubicles with privacy in most of Europe), but there's also the element of social control; ie. you're less likely to do something fucky if people can see you, thus reducing the risk of vandalism.",
"The partitions and doors are standardized and come pre fabricated, usually. So basically, unless you are careful with your measuring, drilling, and mounting ... there is going to be gaps. The less careful you are ... the bigger the gaps. Then have it installed by the lowest bidder, who is probably paying his guys less than minimum wage, and knows no one is going to call him on it."
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b3kknq | Why do showers screech sometimes? | Engineering | explainlikeimfive | {
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"text": [
"My shower had \"screeched\" for sometime before I got fed up and just had to fix it. After doing some research I found that adjusting the water pressure or cleaning the pipes/shower head was the best option (In case you were looking for a simple fix as well). As for the science, it is as follows: Sediment can build up in the plumbing causing the diameter of the pipes to shrink. This increases the water pressure and increases the friction created from the moving water. A result of the increased friction is the sound you hear. & #x200B; Hope this was what you were looking for :)"
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b3m4oo | Why is the vertical axis represented with a Y and the horizontal axis with an X and not other letters or symbols? Does it have any history or reason to be? | Engineering | explainlikeimfive | {
"a_id": [
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"ej0pvxm"
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"text": [
"From wikipedia: The axes may then be referred to as the X-axis and Y-axis. The choices of letters come from the original convention, which is to use the latter part of the alphabet to indicate unknown values. The first part of the alphabet was used to designate known values.",
"Descartes is credited for the introduction of x, y, and z in his La Géometrie. However In Cajori's History of mathematical notations, he notes that Descartes used the notation much earlier than the book was published"
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b3w3cx | What is the purpose of the mats/pads you see covering the grille on some diesel vehicles? | I see them all the time but my best guess is to maintain the engine blocks heat. | Engineering | explainlikeimfive | {
"a_id": [
"ej2kiz1"
],
"text": [
"It's because a cold diesel is noisy, inefficient and at road speeds the forced air that bypasses the radiator can extend the time necessary to achieve cabin heat and maximum possible efficiency. Think of it like a winter blanket without it your cold, grumpy and not really wanting to do anything. If you're dressed right that can change almost completely."
],
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b4j3ak | how does a clock work? How does the clock know when to tick on to the next second or next minute? | Engineering | explainlikeimfive | {
"a_id": [
"ej6zvt2",
"ej6y3m6"
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"text": [
"There's a difference between how clocks and watches do this but they operate on the same basic principle: to power the timepiece, you start by winding a gear which is designed to only unwind itself incredibly slowly. To regulate how fast it unwinds, and also to ensure an exactly controlled time measurement so the device never speeds up or slows down, they have an element referred to in general as an \"escapement\". On a clock, this escapement generally involves a gear and a pendulum. The pendulum works on the basis of gravity - it has a weight on the end which swings because gravity pulls it down, and gravity is pretty much a constant factor. Because gravity is a constant, if you raise the pendulum up to the same point and release it, it will always take the exact same time to swing back. Naturally the pendulum will slowly lose its kinetic energy and come to rest in the centre, so to keep it swinging the gear which the pendulum powers is designed to give the pendulum the most tiny of nudges at the end of its swing, thus setting it back to the exact same point it started off at and meaning it never loses power. On a mechanical watch, obviously you can't use a pendulum as there's neither room nor constant orientation for an item to swing in. Instead, the escapement is a coiled piece of metal called a balance wheel (plus of course the gear which it connects to). The gear part pushes the coil and effectively winds it up. Eventually it winds further than the gear has pushed it, at which point it uncoils itself, eventually catching the gear again (via some clever design), turning the gear and being reset all over again. In both cases, the escapement is designed so that the gear only turns once for each swing of the pendulum or spin of the balance wheel, and as said these should always take the exact same amount of time to move. If you work out exactly how long this time is, you can then design and set the rest of the gears in such a way that they turn the second hand/gear of the clock exactly once a second.",
"I'm not sure if it \"knows\".. It's the other way around.. I'm not an expert but i know clocks have gears that manufacturers adjust to rotate every one second, and a bigger gear to tick when the smallest gear rotates for 60 times and so on, imagine it like a gear with 60 pins \"I'm not sure if that exists but just for the sake of explanation\" that when this gear fully rotate it intrigues the minutes' gear"
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b4jum5 | Why do the numbers on phones have different tones when pressed? | Engineering | explainlikeimfive | {
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"ej75wqt",
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"text": [
"It's called tone dialing. Each number has it's own tone so the switching system can identify which number is being dialed. Rotary (and early touch pad) phones used pulse dialing where each button press sent a certain number of pulses and the switching system counted those to identify what was being dialed.",
"This is DTMF (Dual Tone Multi Frequency) signaling. Each row has a frequency and each column has a frequency. No frequency is a multiple of another. The button presses are identified by looking at the frequency content of the line signal. If there is energy at 770 Hz. and at 1477 Hz. then the \"6\" was pressed.",
"To add to what has already been said here about DTMF, the telephone network used to listen to the tones. Pressing a button literally did nothing but generate a tone that the network would listen for. If you could generate the same tone you could dial without pressing any buttons. This is where “phreaking” started. When a coin was deposited into a pay phone it would also generate a tone. You could pay for a call simply by generating the appropriate tones. Look up the phreaker, who went by the name Captain Crunch. He found that whistles given as a prize in the cereal could be used to generate tones to hack the phone system."
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b4k22r | What is that yellow foil around space probes and what is its function? | You know what I'm talking about. That yellow material that surrounds a probe and nearly covers the entire craft. Just what is it and what is it used for? | Engineering | explainlikeimfive | {
"a_id": [
"ej766r1"
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"text": [
"The gold and silver colored sheets you see are often a single layer of aluminized polyimide with the silver aluminum side facing in. The yellowish-gold color of the polyimide on the outside gives the satellite the appearance of being wrapped in gold. Multi-layer insulation is used on satellites primarily for thermal control and protects the delicate on-board instruments from the extreme temperatures of space. Depending on its orbit, a satellite can experience temperatures from below -200°F to well above 300°F, sometimes at the same time! Not to mention the high temperatures the onboard instruments can produce."
],
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19
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b4liom | Why is it always the carburetor? | For a good amount of lawnmower or go cart failures, the carburetor is broken. Why? | Engineering | explainlikeimfive | {
"a_id": [
"ej7geq3"
],
"text": [
"so the carburetor is seldomly broken. it does however have a lot valves prone to ckogging and as soon as the gas/air ratio is off, the engine doesn't start properly or doesn't reach optimal revelations. typically after a standing period, residue cloggs the main valve...tadaa engine won't turn over. the swimmer gets a hole, carburetor gets flooded...same result. there are a plethora of little things that bring that ratio of balance."
],
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3
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b4qdsy | how does a continuously variable automatic transmission work? | Is it more like an automatic or a stick shift | Engineering | explainlikeimfive | {
"a_id": [
"ej8h5wv"
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"text": [
"It isn't really like either, but it is automatic. [Here's a picture of a simplified CVT]( URL_0 ). Instead of gears they have two rotating spindles connected by a belt. Since the spindles don't have a constant diameter and the belt can move, adjusting where the belt sits on each spindle lets you change the input/output ratio. So instead of switching between distinct gears a CVT has a variable \"gearing\" that allows the controller to select whatever ratio it wants."
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b4r1t4 | Gear shifting on a bicycle, how do you do it properly? | So when I was really 5 years old and learning how to ride a bicycle with gears, by father told me to "never use the shifter on the left!". He was probably just trying to avoid a chainlink disaster, but now at 29 I am still hearing his voice in my head. How do you *actually* use the left gear shifter on a bike? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The left shifter usually controls 2 or 3 gears in the front, the right shifter controls 5 or more gears in the rear. For this discussion, let's pretend you have 3 in the front and 5 in the rear. Normally you'd leave it the middle gear in the front, and whatever gear in the rear you feel comfortable peddling. If you encounter a hill with front in the middle, and rear in the largest gear, but you still find peddling too hard. Perhaps you can switch into a lower gear. In this case you'd switch to the smallest gear in the front, and a gear in the rear that feels comfortable. Or in a slight down hill, perhaps you want to go faster, the largest gear in the front, and smallest in the rear will get you the greatest gear ratio for going faster. Generally it's advised not to be in the smallest in the front, smallest gear in the back or largest in the front and largest in the rear because that puts the chain at a diagonal. That risks putting additional strain on the chain."
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b4xc7p | Where does the water from a firehose reel come from? | I'm told that there will be a large water tank underneath any building that has a firehose reel and that the water will run out eventually but I'm not sure if it's right | Engineering | explainlikeimfive | {
"a_id": [
"ej9q188"
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"text": [
"In a commercial building there are three main possibilities: 1) it is attached to the underground water main, 2) there is a water tank on the roof for sprinklers/firefighting, or 3) there is a standpipe connection at the base of the building where fire fighters can connect it to either a hydrant or a pump truck."
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8
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b5hr0x | What makes the audible hum in electric boxes? | Engineering | explainlikeimfive | {
"a_id": [
"ejdjb15"
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"text": [
"The high current passing through the conductors causes them to vibrate. In large buildings they use metal plates as conductors rather than wires and they are taped together with plastic in between to absorb/dampen the vibrations."
],
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4
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b5i463 | How do cars in Cruise control slow down on hills? | They don’t engage the brakes, they don’t use magnets, honestly I have no idea! | Engineering | explainlikeimfive | {
"a_id": [
"ejdm61e",
"ejdm9e5"
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"text": [
"They use [engine braking]( URL_0 ). Airflow into the engine is restricted, creating a vaccuum that the pistons have to work against, slowing the car.",
"Engine braking! If you leave the transmission in gear, but feed no gas to the engine, the wheels have to force the engine to move, rather than the other way around. [Here's a video that explains how it works.]( URL_0 )"
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b5k653 | When you shut an engine off, why does the combustion process stop instantly? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"If it's a petrol/gasoline engine, then it's because there is no longer a spark being delivered to the cylinders where the fuel/air mix is burned. In these engines, compression is not enough to light the mixture, and once the ignition switch is off, the spark plugs no longer spark. (Different for diesel engines.)"
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b5khbi | How does a record player take a single groove on a record and turn it into separate left and right channels? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The groove is arranged like a V with a left and right wall. Each wall has a separate set of bumps and valleys on it, and the needle that rides in it has a sensor for the movement along each wall (something like a 45 degree angle). Left and right channels are encoded on the two walls of the groove."
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b5odkb | if all the ballast tanks are not working, how does a submarine surface? | Engineering | explainlikeimfive | {
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"text": [
"Some can inflate an “emergency balloon” that is loaded to a torpedo tube instead of an actual torpedo and use it’s lift force for an emergency surface",
"They have fins on the front and back called \"dive planes\". These work like little wings and can be tilted up and down to assist with diving and surfacing. If the ballast tanks are all completely full then the sub is probably screwed, but from a moderate depth the dive planes would be able to get them to the surface as long as they kept moving fast enough"
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b5xlic | How do vehicle brakes work? How can they withstand the immense physical stress throughout a car's lifespan? | Searched but couldn't find what I wanted to know. How do brakes in cars/trucks work? Every time I drive, I can't help but think about how much physical stress (whether it be friction or whatever) my brakes are taking, and wonder how long it will last before the ability to decelerate is compromised. I imagine the amount of abuse that brakes have to endure in order to stop a 2000+ lb car would be enormous. I've also heard that large vehicles (trucks, buses) have "opposite" brakes, but I don't fully understand what it means. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"> How do brakes work? There is a disk attached to the axles behind your wheels. You can actually see it [very often]( URL_0 ). When you press the brake pedal, it pushes fluid (see: [how hydraulics work]( URL_1 )) that cause your brakes to clamp down on that disk. The brake pads *squeeze* the disk, which causes a great deal of friction on it, which slows it down. Since it's attached to the axle, it slows the axle, which causes friction between the tires and the surface you're driving on, which slows down the car. That does cause a fair amount of heat, which is why your wheels have a lot of open space for air to get into and some sports cars and high performance cars have vents specifically to move air through that area. > How can they withstand the immense physical stress throughout a car's lifespan? They can't. They aren't supposed to. You are supposed to replace your brake pads regularly. In between the brake *calipers* - which are the things that are hydraulically linked to your pedal and cause the squeezing - and the disk, there are brake pads which are usually made out of graphite. The graphite is pretty strong - it can be squeezed pretty hard without cracking or breaking - but it doesn't take [*shear* force]( URL_2 ) very well. So as the disk continues to rotate as it's being squeezed, the graphite is ground off. This is a deliberate point of failure designed to allow the brake system to both *brake* while also *breaking* in a controlled way. As long as your pads are maintained, the pads will wear out without destroying the rotor and/or catastrophically failing when you are trying to not run into things. And brake pads are deliberately designed to be as cheap as possible (without compromising its function) and easy to replace. EDIT: brake squealing is also deliberate. It's a sign that your pads are worn and need to be replaced. If your brakes are squealing you should take your car in to get the pads checked. They might be dirty. They might also be worn. Worn brakes do not function as well and can damage your disks. > I've also heard that large vehicles (trucks, buses) have \"opposite\" brakes, but I don't fully understand what it means. IIRC, rather than squeezing the pads into the disks, with those vehicles the pads are stationary and the disks are expanded into the pads. This is done with compressed air rather than hydraulic fluid."
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b66sxt | Why are washers (flat steel rings) used before fixing nuts and bolts? | Engineering | explainlikeimfive | {
"a_id": [
"ejibeo1",
"eji9o8n"
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"text": [
"They are normally used to distribute the load of a threaded fastener, such as a bolt or nut. Other uses are as a spacer, spring (Belleville washer, wave washer), wear pad, preload indicating device, locking device, and to reduce vibration (rubber washer).",
"It increase the area that's bearing the force of the tension in the fastener. Stuff can only withstand so much pressure per unit area without bending/cracking. This makes the area bigger, so you can have more force without causing damage."
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b66xwy | How do moving prosthetics work? | If someone loses a limb/part of one such as an arm. What are they doing to control it? Like the elbow moves, the fingers grip individually. How are they controlling it to make these movements? | Engineering | explainlikeimfive | {
"a_id": [
"ejiuku5"
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"text": [
"The above poster is a little ahead of modern science. Someday they will tie directly into nerves, but currently electronic prostheses work differently. Every time you flex a muscle there are electrical currents generated in the muscle. You’ve probably seen an EKG trace for a heartbeat. What that’s actually showing is the electric current in your heart. Modern prosthetics have little EKG-like sensors that can detect when the amputee flexes a certain muscle. For arm prosthetics they place the sensors over what ever muscles the amputee has remaining and the amputee has to train on flexing those muscles to create the desired movements in the prosthetic. I use a pretty advanced prosthetic but it is totally controlled my two muscles in my forearm. It takes a lot of practice to get used to, but with good software you can do a lot."
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b678m3 | Network Routing | "Routing calculates good paths through a network for information to take. " & #x200B; But how? | Engineering | explainlikeimfive | {
"a_id": [
"ejidby4"
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"text": [
"There are a lot of different ways, but it basically boils down to this: Each router sends messages to its neighbors and then learns information about its neighbors, such as who they are and how long it takes to communicate with them. Through this, each router then can learn about the overall network and the times it takes to reach various areas. For example, Router A communicates with its neighbor, Router B, and knows that it takes 5 milliseconds on average to talk to it. Router B communicates with its neighbors A and C, and knows that it takes 5 milliseconds to talk to either of them. But, when A and B are talking to each other, B tells A what it knows about C and based on this information, A can deduce that it would take an average of 10 milliseconds to send a message to C through B. But let's say that C is also a neighbor of A and the direct connection between A and C only takes 7 milliseconds. Well A can tell the difference and it would know that it should send information destined for C directly to C, rather than through B."
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b67sut | I often see heavy machinery precariously placed on piles of dirt at construction sites .. who's job is it to make it safe? Do accidents happen frequently? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Engineer here. The person running the project gives guidance to the people using the machines (site superintendent). About 90% of the time everything is safe if the machine operators listen to the guy in charge. It is his responsibility for a safe work site, so if something were to happen, the blame falls on him."
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b6dlrf | Why does putting tape on windows help during a tornado? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Just in case your windows break, the tape will prevent it from shattering and all the little glass pieces flying everywhere. Easier to clean up and more safe",
"It doesn’t provide any protection for the windows, but does let you know where they are, and if they’re broken. It can prevent injury after the storm passes by helping people know it’s a window and not a hole. In some cases, it may help hold together cracked panes, but won’t prevent shattering.",
"One theory is that it helps keep the window intact by preventing too much warping and bending. Another theory is that if the window breaks, you are less likely to have airborne shards flying around. And some people do it just because they heard that is what you are supposed to do."
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b6t81b | How does the electrical grid, respond so quickly to power being turned on/off all the time all over the place, if they generate just enough power in real-time for the demand? | Engineering | explainlikeimfive | {
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"text": [
"although they can only provide enough to meet demand (at least until big battery banks become a thing), they are rarely running at 100%. e.g. you might have 2 generators each able to punch out 100MW, but if demand is only 160MW then each of them will be running at about 80% load. The remaining 40MW is known as \"spinning Reserve\" (at least where I am, sometimes called \"operating reserve\" elsewhere) and is immediately available to handle those transient load changes you might also have a 3rd 20MW generator (imaginatively termed \"non-spinning\" reserve) which is a quick start, but generally smaller capacity generator built to provide a boost to the online generators when the spinning reserve is about to be exceeded. you might even have a 4th (or more) 100MW generator on \"contingency\" reserve - these are generally slower to start up, and not very quick to respond to power spikes, and are more there for planned maintenance redundancy, or when the power plant \"knows\" it will have a long/medium length increase in demand (e.g. 5pm during summer when everyone gets home and turns on the airconditioning)",
"On the timescale of seconds, it's an automatic consequence of how generators work. On longer timeframes, the power stations are manually or computer-controlled. Every generator has a lot of weight spinning at high speed, so it stores a fair amount of kinetic energy. When there's no demand for power, the generator produces a voltage but no current flows through its coils. When you turn on a light switch, current starts to flow through the generator, creating a magnetic force that *slows down its spin*, changing energy from spinning kinetic energy to electrical. As users draw more and more electrical energy, the generator will spin slower and slower, until a person or computer at the power plant notices and \"steps on the gas\", adding fuel or steam to the turbine that powers the generator, bringing it back up to speed.",
"Voltage can vary within a range of +/- 5% (at least in the US). Some of that is due to the changing of the power grid load, as demand rises, voltage sags, until the control systems notice the sag and increase fuel to the generators. Pure resistive loads (like heaters or incandescent bulbs) will also eat less power during that time. The converse is also true, as demand drops, voltage rises, and the control systems cut fuel, and pure resistive loads will eat more power. Realistically, it needs a lot of load being added or shed at the same time before it causes big changes to the generators.",
"Many of the generators in the grid are \"synchronous\" generators, which are driven by some sort of engine. When multiple synchronous generators are connected to the same grid, then they become \"locked\" together - all turning at the same speed. In the US, this is 3600 rpm (60 Hz), but in other parts of the world this is 3000 rpm (50 Hz). Generators have the property that as you draw more power from them, they become stiffer to turn. So, there is a simple way of controlling them, called \"frequency control\". The speed is monitored, and if they are going too slow, then the engine is turned up; if they are going too fast, the engine is turned down. This is how the grid is controlled on a second-by-second and minute by minute basis. This is possible, because all the rotating synchronous generators spinning at high speed, have a lot of inertia. This means that when there is a sudden increase in power consumption, the frequency drops slowly over about 10-30 seconds. This gives plenty of time for the governors on the engines to detect the change in frequency and adjust the fuel supply. The grid manager will make sure that there are enough power plants running at partial power, and in automatic frequency control mode to handle any unexpected problems. However, for expected deviations, are more efficient plan can be used. Plants can be used as \"spinning reserve\". They can be running, but not at full power. However, the power plant and the grid manager can agree, that the grid manager can request additional power at short notice. For longer and planned deviations, the grid manager might tell plants that their power is not needed, and they can switch off for the night, or for the weekend. The job of the grid manager is to have enough plants available to provide spinning reserve, and frequency control; but not keep too many plants online and idling when it isn't needed. However, turning a plant off may mean it takes a long time to switch on again - it can take 4-6 hours to start up a coal plant, or 30-60 minutes to start up and warm up a large gas plant. Different power plants with different engine designs, might have different response speed, so they do different things. For example, hydro plants when in standby mode, can respond to a request for power in about 10 seconds. Other plants like gas, take a bit longer - maybe 2-3 minutes. So, in the event of a sudden spike in demand, the first thing that happens is a drop in frequency; and then over the first 5 seconds, automatic frequency control kicks in. Then after about 1 minute, the grid operator may ask their fast reserve plants to take over, so take the strain off the frequency control plants (so that they are ready to handle the next spike). Then the slower reserve plants can take over for the next couple of hours, until the spike has passed. If the spike is expected to last a longer time, or is very large, then there may be further levels of reserve. For example, diesel engines or fast starting gas turbine engines. Normally, these allow about 10-15 minutes to start up, warm up and synchronise with the grid; and these can run long enough to allow cheaper power plants to warm up and take over."
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b6yrgd | Why are roads made of asphalt instead of something more durable? | We get stupid amounts of pot holes every year and it makes driving in spring brutal and hazardous. I often wonder why they don't switch to say a metal substance or something so that they wouldn't have to keep filling potholes and repaving, which I'm sure costs the cities loads in the long run. Is it a money issue or a material issue or what? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"You can repair cracks and holes ,remove exactly how much you need to to do repairs under the road ,it is easy to make in small or larger amounts ie)tar,sand,gravel a bucket a torch and a shovel . Cheap in the grand plan compared to most other options . It is also flexible so with weather changes it gets less damage through movement .",
"The alternative you're looking for is Concrete. They do use it for roads and it's much more durable. It also cost twice as much.",
"Metal isn't feasible for many reasons, but the material that is feasible and is sometimes used is concrete. While more durable, it is much more costly. And given the nature of government budgets, it's often easier to do cheaper and more often than spend more less often -- as an issue of spreading out budget spend, as a means of creating jobs (especially in times of recession)."
],
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13,
10,
3
],
"text_urls": [
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b75k6g | How do planes fly for so long?? | I get the basics of planes flying, but marvel at how long they can stay up in the air steady. Wondering whether the engine should be too complex or how it can stay powered on continuously (including onboard flight and passenger electronics) for 5, 7, 12+ hours. | Engineering | explainlikeimfive | {
"a_id": [
"ejpekva",
"ejpej6l",
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"text": [
"The engine stays powered as long as there is gasoline in the tanks. And if you're unlucky like me, you'll have the plane run out of fuel mid flight. See: Gimli Glider.",
"The jet engines actually act as dynamos/alternators to power the computers/radar/etc... using the fuel to spin the turbines and compressors in the jet engines and also acting as a generator. There are alternative power sources, like the APU/EPU(Auxiliary/Emergency Power Unit).",
"It is amazing to me too. Two notable things about their efficiency: 1. Air is thinner at altitude, so airframes move through the air than less resistance than if they were flying through \"heavy air\" 2. Part of the jet engine design utilizes the ram air effect. So essentially the fact that the engine is slamming into so much air so fast actually makes it more efficient. IIRC most jets fly at just over half throttle at cruise (correct me if I'm wrong)."
],
"score": [
9,
3,
3
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"text_urls": [
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b7mx0i | why do car batteries lose their ability to be charged after sitting unused for a while? | Engineering | explainlikeimfive | {
"a_id": [
"ejsufth"
],
"text": [
"I believe it’s because of sulphation in the battery plates. Sulphur crystals form in some of the plates, and this damages/degrades the plates. The sulphation occurs as the battery discharges normally. When you leave a lead-acid battery to sit unused/uncharged it starts to slowly discharge and undergo this process. The damage/sulphation is proportional to the level of neglect, and even in normal use there will be a degree of this degradation with successive discharge/recharge cycles. If not maintained properly, after a period of time the battery will reach a point where the sulphation damage is so bad that the battery (at best) can only be partially recovered. Usually, by this point, it is simply unserviceable and a new one is required."
],
"score": [
21
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|
b7vekq | CVT transmissions? | What are they and how do they differ from other automatic transmissions? | Engineering | explainlikeimfive | {
"a_id": [
"ejug0d9"
],
"text": [
"A normal transmission has a set number of pairs of gears, with fixed ratios, for you (or an onboard computer) to pick from. A Continuously Variable Transmission (CVT) uses one of several techniques to continuously change the ratio, allowing more precise control over the ratio than a standard transmission could offer."
],
"score": [
6
],
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b80rbb | Why does asphalt on the highway sound different on different sections of road? | Engineering | explainlikeimfive | {
"a_id": [
"ejvajs8"
],
"text": [
"Higher air voids in the asphalt mix make it quieter to ride on as the air is not forced through the tire thread. This is a function of the different aggregate sizes and % of those sizes in the mix In contrast, concrete is pretty much solid and is very loud"
],
"score": [
10
],
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} | [
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