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cvjp8h | How do multiple light switches work? | I know about circuits and a single switch. But the multiple light switches really confuse me. They don't have a set position for off and on. They essentially reverse the state of the light bulb. So how do they work? | Engineering | explainlikeimfive | {
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"In this case, you can think of electricity like a train on a train track. Pretend you have two tracks, side by side (a North one and a South one, for example). A train is traveling on the north track, headed for the depot. On the journey, there are some switches which can alter the trains path. If the switches are off, the train keeps travelling on the north track, but if they're on, the train is redirected onto the south track. In essence, the switch makes the train \"switch\" tracks. If you flip the first switch, the train moves onto the south track. It's gonna miss the depot. However, if you flip another one further down the path, the train goes back to the north track and is on route to the depot. As long as the switches are flipped on or off to cancel each other out, there's nothing to worry about. In the analogy, the train is the electric current, and the depot is the bulb. Switches redirect the electricity, but as long as they cancel out, then the light stays on.",
"/u/jammin-john is exactly right. For the visual learners, though, [here's a good wiring diagram]( URL_1 ) for circuits with two SPDT switches. Using DPDT switches, you can have [three or more switches]( URL_0 ) serving the same circuit, any one of which can reverse the state of the light."
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cvkhrt | When building a bridge over a large body of water, how do they get the pillars so deep into the water and how is the foundation secured? | Engineering | explainlikeimfive | {
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"[check it out]( URL_1 ) [this photo is a good visual]( URL_0 ) Basically they make a little enclosed area and then suck out all the water from that area, essentially putting a dry hole in the middle of the water, then in that hole they build the bridge support.",
"These days, there are a few techniques. But the most common is it drive steel pipes into the river or ocean bed, then use an auger - a big soil drill - and pumps to extract the soil from inside the pipe. Don't worry about the water. They extract soil below the bottom of the pipe, too, so that there is a void underneath the base of the pipe. Then they drop steel reinforcing into the pipe, and fill the pipe with heavy concrete. The concrete is heavier than the water is, so it stays at the bottom and the water is pushed out of the top. You then end up with a concrete pile - the steel rusts away, but it's only there to help form the concrete pile - sitting on a concrete plug that is down beneath the river bed. The finished construction looks like an upside-down mushroom, deep down in the soil. Each one of those piles can support a lot of weight, and as there aren't expensive to put in, they put down a lot. Then a headstock is cast on top of them, and the bridge (or other construction) built on the headstock.",
"There are numerous techniques. One common one that is often used in waters that are sufficiently shallow is cofferdams. Basically they pick where they want to build and erect a temporary dam around the place and pump out the water creating a sort of island below the sea level for them to work on."
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cvp03e | New SpaceX and Amazon's Project Kuiper, low earth orbit satellite internet. | How much latency are we actually talking about here? I know that c is only 66% or so through glass due to refraction but is the remaining 33% that significant a drop? When factoring in the distance to these in orbit and then back again, what exactly are the savings? If there were any to be had, I would have expected the high frequency traders that have oceans of money to do this. I heard they already paid for an undersea cable to shave off only 4ms fo round trip. | Engineering | explainlikeimfive | {
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"As I understand it, the idea of space-internet revolves more around availability than speed. It's not going to replace fiber optics any time soon, but you can't run a fiber optic into an RV trailer in the desert without spending a lot of money. Even then, just because it won't be faster than fiber optics does not mean it will be slow."
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cvqyfg | why are paddling pools blue etc instead of black to absorb the heat and keep warm? | Surely it would be better to have a black/heat absobant base than blue/white which seems to be the standard so that the water keeps warm.. | Engineering | explainlikeimfive | {
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"Blue reminds people of the seas and oceans (or rather shallow water near the beach). Black would be creepy to many people (b/c it looks like deep water). Absorbing heat can make the water too hot, and most pools are sold in areas with a lot of sun, and people want their pools to stay cool. Lighter color makes it easier to see dirt, so you know when the pool is clean.",
"Blue pools are A) familiar and B) remind people of \"clear blue waters\". That being said, my parents new a guy who had a black bottomed pool. It was the coolest thing about his house.",
"Who wants to swim in a hot pool in the dead of summer? Who wants to swim in a dark pool?"
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cvwsqz | How does a car horn work and where is the sound output for it? | Engineering | explainlikeimfive | {
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"The relay is a break basically. The electrical current is always running to it. The relay when engaged by the interrupt signal by the horn being honked co.pletes this Circuit by connecting the relay. It's the same as how your computer keyboard works basically"
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cw0niz | How do large open stadiums/arenas use air conditioning effectively? | Engineering | explainlikeimfive | {
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"they only use the a/c in the enclosed areas and/or they have barriers such as those hanging things you walk through or some high powered air blower, which effectively creates a barrier, etc, or they just have enough high powered fans so that air is constantly moving and it doesn't get hotter than ambient.",
"Chase Field in Phoenix is a great example of a huge air conditioner. It uses chilled water, which is actually frozen by the chillers overnight when power is in much less demand, and then uses that to cool the stadium and 30 or so other buildings in downtown Phoenix. I don't know exact numbers, but it has the cooling power of the air conditioners in approximately 2500 2000 square foot homes. When it is 110º outside, the air conditioner can keep the stadium at approximately 78º inside. Some areas are obviously hotter than others, but the whole thing is comfortable, and the whole thing is air conditioned. University of Phoenix stadium, in Glendale, AZ, is another great example of a huge air conditioned building. Again, using a water chiller system, they can cool the entire stadium to comfortable levels. This system is 8,000 tons of air conditioning, which is about 2300 homes worth. The bills are enormous, with the air conditioning portion alone costing between $500,000 and $600,000 per month in the summer months."
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cw8agu | What are models of the earth's magnetic field used for? | I know models of the earth's magnetic field are useful, and I know that they are typically generated on like an annual basis or slightly less frequently. If someone was able to develop accurate models of the earth's magnetic fields which were accurate on a day-to-day basis, what would those be useful for? | Engineering | explainlikeimfive | {
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"The Earth's magnetic field is unstable. The North and South magnetic poles drift around and change strength (which affects compasses). On a day-to-day basis, tracking this wouldn't provide much information (that I'm aware of). However, geological evidence suggests that we're overdue for a magnetic reversal, and during this process, the magnetic field will weaken significantly, making it much harder for the field to protect us from solar radiation. It's not so bad for organic life, but it puts our astronauts and satellites at great risk.",
"I used to work in the oilfield drilling and placing wells. My subsurface instrumentation relied in part on the earths magnetic field to detect which way the well was being steered. We had models that would take the gps coordinates and the date as inputs. I don’t think it was detailed enough to matter say to day but it would change week to week",
"Satellite ADACS engineer here As another poster has said, LEO Sats can use magnetorquers to detumble any tip off rates and gain pointing control right after launch. Some of my past work has been writing the control laws that do this detumbling process. More importantly, we couldn't afford a star tracker for our program. Instead, we can use fancy math and knowing the location of the sat around the Earth, the direction of the sun(measured and absolute), and the magnetic field(measured and inferred from location), then we can determine where we are pointing in absolute space which you can imagine is super useful for satellites that need to point their solar panels at the Sun, or point at a specific point on the Earth. Due to the recent movement of the poles, I actually had to update our IGRF model coefficients on the flight software for our satellite.",
"Another thing not mentioned yet is that some satellites use [magnetorquers]( URL_0 ) to orient themselves. Having a map of the Earth's magnetic field helps with that."
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cwbj6b | Why does converting from AC power to DC power (for example, in an adaptor) create noticeable heat? | Engineering | explainlikeimfive | {
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"[This article]( URL_0 ) explains the typical converter circuitry and how it works. The heat comes from the fact that you always have resistance in the materials used; some heat is generated in the transformer, both in the wires (electricity flow) and in the transformer core metal (magnetic \"flow\"), and if you scroll down, the main capacitor(s) that \"level out\" the voltage have spikes of high current flowing through periodically. And current through wires generates heat (electrons \"flow\" around the metal atoms like a river through pebbles, and the \"resistance\" of the atoms to this flow generates heat)."
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cwf9hc | When you flush a toilet from the top of 100 story building, how does it reach the ground? Does it just fall straight down? | Engineering | explainlikeimfive | {
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"DARN IT! I was all ready to go to bed. Now I have to stay up to see if this gets answered."
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cwj5ui | Why don’t structure fires create a chain reaction of gas line explosions the lead back all the way back to the source? | Edit: sounds like the consensus is lack of oxygen in the pipe network and one way valves. Thanks folks! | Engineering | explainlikeimfive | {
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"You can't have an explosion without oxygen. Gas pipes are full solely of gas, and they're also really quite tough. You have oxygen at the end of the pipe, so you might get a fire at the end, but the oxygen won't burrow down into the pipe because the hot gasses (CO2 and water) that are bursting out of the end of the pipe don't let anything else come back the other way. As a result, gas pipes tend to just keep a small flame at the end of them during a fire, rather than having the fire chase down the entire pipe.",
"Gas pipes has [flame arresters]( URL_0 ). They work by cooling down the flame so much that it goes out.",
"Firefighter here. Among the other very good answers others have provided about the natural gas industry safety practices. It should also be noted that one of the very first things we do is cut utilities to the structure involved in the incident. The Incident Commander determines if they want us to stretch hose to fight the fire. (You all would be shocked what we can do with a water extinguisher only.) At the same time he orders the stretch he will order a unit to find and disconnect all power and gas utilities. To avoid fueling the fire and eliminate the electrocution risk to the hose team. Because it's just not possible to operate a hose line without getting wet. [This is a tool every member of my department carries in their PPE.]( URL_0 ) You can see it includes a handy gas-valve wrench slot to accurately shut off standard gas-safety valves. The link includes a video to show you how we shut off a gas valve.",
"The gas has to be mixed with oxygen to be flammable. The gas in the pipe is of too high concentration to burn. Gas has to be with in certain flammable limits or concentrations to burn. Also most residential gas service has an over flow check valve that will \"trip\" or engage if too much gas begins to flow to the home.",
"Same reason using a lighter doesn't make the lighter explode. What's in the container isn't in a combustible state."
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cwl17u | why do pens stop writing when they clearly still have ink? | Engineering | explainlikeimfive | {
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"Because the tip dries out. Assuming you mean ballpoints pens (which are the most popular kind), the top has a tiny ball which rolls along the writing surface. If the ink on the tip dries out it can cause the ball to stick, so it doesn't roll anymore."
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cwumaq | Why are CPUs/Processors so small? Couldn't we double our processing power / GPU by increasing the size of the chips? | I wouldn't mind twice the CPU/GPU size for a gaming PC | Engineering | explainlikeimfive | {
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"You can improve processing power by increasing the size of the chip, but there are some issues, and you won't necessarily get twice the processing for twice the size. The biggest issue is cost. Cost of a chip increases faster than the size (due to the higher chances of a defect). So a chip 2x the size costs more than 2x the $$$. Another issue is the I/O bottleneck. Processing speed can be limited by how fast information can be delivered to or sent from the processor. So to double the amount of processing power, you might need to increase the I/O speed or number of signals, both of which are going to have cost impacts and possibly impact the size of the package. If you're going to double the size of the chip to get more processing, you're probably going to add more cores (and cache memory). That means that what you are working on must be able to be split between multiple cores efficiently. Sometimes this is true, sometimes it isn't. Hot hot hot! Microprocessors get hot, and increasing the size of the chip increases the amount of heat you have to be able to dissipate. So the thermal solution used is going to have to be more capable, which usually means bigger and more expensive. Of course, along with the heat comes the power delivered. The power supply needs to be able to provide the required power, and the motherboard needs to be able to deliver it without causing noise or ground bounce issues. All of these things are problems that can be overcome. All you need is money.",
"A simplified answer: The cost of a chip scales faster than the increase in area. A chip twice as big costs more than twice as much.",
"Would a bigger running track be faster or slower to complete? You could fit more runners but that only helps in some ways. This is sort of how server processes work. Also if there is anything wrong with that bigger track you cant repair it and have to repaint the entire track."
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cwyuam | What is piezo-electricity and what are its uses ?? | Engineering | explainlikeimfive | {
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"Piezoelectricity is an effect found in some solid materials that causes a charge to build up when it's under stress (an applied force). This relationship makes possible to use electricity to cause deformation of the material, known as the *converse piezoelectric effect*. This basically means you can create movement just by applying an electric field, which is very useful in the manufacturing industry. On of the key uses is in 3D printing, specially the drop-on-demand binder and material jetting processes. These work by selectively forcing small droplets of material in place and moving over the surface. Using a piezoelectric actuator means that an electric current can be used to accurately and rapidly deposit these droplets. It also means that a thermal actuator doesn't need to be used, avoid problems with thermal cycling and burning of the material.",
"Piezoelectricity is basically when electricity and materials bending go together. Either bending the material produces electricity, or applying electricity to the material causes it to bend. I'm using \"bending\" in the loosest sense possible here — anything that applies that sort of force on the material, even if it doesn't visibly (or permanently) bend. /u/Penguin__Farts did a good job of covering some uses for the electricity - > bending case, so I'll cover the bending - > electricity case instead. One use for this is lighters in gas stoves — pushing the button forces a hammer to strike a piezoelectric hammer, and that produces enough electricity to generate the spark that lights the gas. It's also useful for building sensors. For example, piezo pickups are used for classical (Spanish) guitars, which use nylon strings so the magnet-based pickups found in electric guitars wouldn't work. Also, at least some digital drums use piezo-based systems to sense striking the drums. Also — I don't fully understand this one, but apparently quartz clocks use *both* directions at once to produce the steady timing necessary for a clock."
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cx5vvr | Why are the nozzles on squirt mustard bottles shaped the way they are, but other condiments all have the same short cylinder cap? | Engineering | explainlikeimfive | {
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"Oh I know this one. Finally I can contribute. Mustard was originally engineered with a tapered top because it used a Twist top cap that allowed you to open it by turning it. By making the nozzle more like a funnel you increase the surface area between the closed nozzle and the open nozzle. Old natural gas valves sometimes work this way as well. By increasing the surface area you create a better seal. This is necessary because when you take mustard out of the refrigerator the cold air trapped inside the bottle tries to expand and if you had a normal nozzle on the Barrel shaped container it would eventually pop open forcefully. Now imagine mustard is trapped at the top between the cap and the air pocket. Mustard volcano! The funnel shaped nozzle allows you to easily open the bottle, dispense the mustard, and close the bottle, while keeping the mustard inside. Modern inverted containers don't have this problem because generally the weight of the bottle was enough to keep them closed and modern plastics give a bit more, so they often have the same caps as other condiments. Edit: wow, who knew my first major comment on Reddit would be about a mustard bottle. I'm trying to get to all the questions as quickly as I can, I just got done with work and checked my inbox and holy cow. Also thanks for the silver Anonymous stranger!",
"Do they? Don't condiments all have a variety of openings?",
"Can you clarify? I know old mustard and ketchup and other condiments would have cone shaped nozzles but all the modern ones for inverted bottles are the same as well. What discrepancy are you talking about?",
"Mustard is mostly for squiggling on, either on a hot dog or on bread, ketchup is for splooshing, generally. The nozzle design corresponds to the main use of the condiment. Look at mayo... mostly jars to use a knife to spread onto stuff. If they make a squeeze bottle it's usually long and flat to cover lots of surface area.",
"It's because the first successful brand with a squeeze bottle used the funnel cap. So everyone after that copied it. The cap is now synonymous with mustard, so if you use a different shape, the consumer reacts negatively (it can't be good, it uses a ketchup cap!). That's also why few other condiments use it (that mayo may taste like mustard!). It's somewhat amazing how much we taste with our eyes.",
"It's not any particular rule that they do. Any differences has more to to with which particular brands are common in your area, and whatever designs they prefer.",
"This is probably a regional thing. I just searched for mustard bottles and found a variety of caps. Some are funnel shaped, some are not. I’ve also seen funnel shaped caps on tomato sauce, ketchup and bbq sauce bottles. Which brands are you thinking of?"
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cxcyvf | Why are motorcycles so much louder than cars? | Engineering | explainlikeimfive | {
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"I'd say it was more down to the exhaust. The engine being uncovered makes a little difference, but on a car, you have the catalytic converter which dampens noise, there's a silencer and also a back box. On a motorbike, there's a silencer and that's it. It's exhaust is also shorter making less distance to attempt to silence the noise"
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cxhgvb | Vertical takeoffs for jets | Engineering | explainlikeimfive | {
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"The jet's exhaust nozzles can be rotated to point down to force the jet up. On the AV-8 Harrier there are 4 nozzles that can rotate and some bleed air from the engines is routed out the wing tips for extra control. The F-35B uses a combination of the single exhaust nozzle rotating down and an auxiliary lift fan behind the cockpit that opens up and is driven by the engine."
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cxhjg6 | Why are car tires filled with air? Why not making them entirely out of rubber or fill them with something that isn't gas to make them puncture proof? | Engineering | explainlikeimfive | {
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"1) A thick rubber block would be *much* more heavier than pressurized air, which would require more energy to turn, which would mean burning more gas to do the same thing a car with a regular air tire can do. 2) The air in a tire allows the tire to easily bend / conform to things in the road. If you had a solid block of something rolling down the road that was not that flexible, it would probably wear and deform faster. 3) It would be a lot more expensive.",
"Tires themselves are an important part of the suspension, the air inside absorbs all the small shocks and bumps and vibrations from minor road surface imperfections before that ever gets to the springs. The air also rapidly returns to its original shape, pushing the flat spot from the road contact back into round before it has completed a rotation. A lot of the early attempts at non-pneumatic tires suffered from excessive wear and vibration even on perfect roads because the solid material alone doesn't fully rebound quick enough. Then there's more complicated handling and fuel mileage concerns due to the increased rolling resistance and unsprung mass of a solid wheel. I actually worked in the tire industry for a while and the non-pneumatic tire was jokingly referred to as \"nuclear fusion\" - you see studies and news articles but it's still perpetually ten years away.",
"The air in the tire has a ton of advantages: 1) It's cheap (always a bonus) 2) Air is light. In vehicle design there is the concept of [\"Unsprung Mass\"]( URL_0 ) which is the weight of the vehicle that is not carried by the suspension (I.e. the axle, wheels, brakes) you want to reduce that mass as much as possible since you get better traction. 3) The tire while inflated acts as a shock absorber and contributes quite a bit to your overall suspension. (It helps reduce the effect of the unsprung mass too) 4) The \"Hardness of your tires has a huge impact on your fuel economy and your comfort. Tires that are too hard give a rough ride, tires that are too soft reduce your fuel efficiency. Rubber changes hardness a lot of with temperature (that's the reason you have winter tires and Summer tires it's not the tread as much as the hardness of the rubber). 5) Rubber degrades over time (it loses it's elasticity). This is the case in all tires, but air doesn't degrade over time (and you can just add more). So overall you get better life with less rubber. 6) **Air works**. There are concept designs of alternatives to air but nothing really takes off because Air is simply very good to fill that role. When you don't need complicated engineering to solve a problem it's best to avoid spending the time and money on the problem. & #x200B; & #x200B; > **puncture proof?** Unless you have my luck and lose 2 tires with 6 flats in 2 weeks, tires are pretty resilient to punctures. Also with air, failures are often slow (leaks are often slow leaks that take a few days to reduce your pressure) and in those failures you can just add more air to get you to a shop. If it was solid rubber, a failure would be more catastrophic and you would have no easy fix aside from replacing it.",
"Some tires aren't, but air has a number of advantages. Like it can compress, so you don't feel every bump in the road transmitted through the tire into your seat. It's lighter, so your tire is (at least relatively) light as well, increasing your fuel efficiency (and I assume, making changing them a bit less of a pain). They also wear better, as a pure rubber tire has trouble dissipating heat buildup. And of course, air is pretty cheap. This isn't meant to be an exhaustive list, but basically filling them with gas does present a number of benefits and not doing so doesn't make a clear winner."
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cxlxix | Why are some mirrors closer than others? | I have a handheld mirror that i use for makeup and my eyebrows etc, one side is more zoomed in than the other. How is that possible? It it a different type of mirror, or is it the shape (like it bulges out more and therefore is more zoomed) | Engineering | explainlikeimfive | {
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"It's the shape. A makeup mirror is typically concave, so the light coming in from different angles around a focal point reflects back straight. This makes objects in the focal range appear larger but slightly more dim than a flat mirror would be. In contrast, a convex mirror would be like those that help you see around blind corners or the side-view mirror of a car. Things look further away, but you get a larger viewing angle to see if something is there."
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cxn4q9 | with socket sets being both metric and imperial , why are both kinds using imperial drive? IE: 1/4" 3/8" | Engineering | explainlikeimfive | {
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"In the US, imperial drive is still used because the machine turning the socket is still likely to be imperial. It's just the socket that's metric, not everything else."
],
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3
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cxod96 | Why are bricks stacked the way they are rather than just one directly on top of the other? | Engineering | explainlikeimfive | {
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"text": [
"By staggering them the weak grout seams are minimized in the vertical direction, making the wall somewhat stronger.",
"Have you ever seen that experiment where they put two phone books together with one page overlapping the page of the other, so they interlock? And then you can't pull the interlocking phone books apart from eachother? That's why, the pattern they're in interlocks all the bricks together, forming a much stronger wall than if they were stacked on top of eachother",
"In-between the bricks is structural weakness, because the filler isn't as strong as the bricks. The way they are stacked now minimizes that weakness by making all of the structure being held up by brick, if it was just one on top of the other you would have giant lines of weakness.",
"Stability. If you knocked out one brick in a stack, all those above it have no support. Not the case with the way they build"
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cxqypa | Why are all aircraft generally white in colour? | Engineering | explainlikeimfive | {
"a_id": [
"eymwcjc",
"eymvw0t"
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"text": [
"Cost: Airplanes are already expensive enough to build as it is, let alone paint costs. Weight: Paint adds anywhere from 600-1200lbs of weight to the plane, which decreases fuel efficiency and therefore increases operating costs. Heat: White reflects sunlight away from the plane better than colours would, which keeps cooling costs down. Resale value: Plain white planes are more likely to sell than coloured ones, should they want to sell the plane. Damage inspection: its easier to see cracks and damage on a white background compared to a coloured background. Safety: It's easier to spot a bright white plane if you're on a search and rescue mission to find a crashed plane. And I'm sure there are plenty of other reasons, but you get the gist.",
"White reflects the sun and heat away better than black, so that the inside of that metal can in the sky doesn’t bake everyone alive or use too much energy trying to cool everyone off. Maybe a more technical answer but that’s the way I understand it. PS I wouldn’t be surprised if the dyes are expensive and an aircraft is huge so $$$"
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cxtxoc | What’s so hard about making computer chips that companies like intel have a monopoly over it? | Engineering | explainlikeimfive | {
"a_id": [
"eyne9vv",
"eynedpz",
"eyney9s"
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"text": [
"You need to be able to cut billions of transistors out of the silicon wafer with a length of 7 nanometers, and you have to be able to mass produce this. There is a steep steep steep startup cost. An example of trying to fight intel’s monopoly, rumors speculate that Apple will be making their own chips in the next couple years. They already make their own mobile CPU’s and some other proprietary chips.",
"There are 3 aspects 1. Physical Aspect 2. Design Aspect 3. Mass production aspect 1. Chips are made from silicon and there is something called silicon lottery, your i5 and i7 have same source silicon but some silicon turns out to be of low quality and that is used to make it and high quality are used to make i7. 2. Designing a CPU is not easy task take a look at the documentation for one of the Intel processors it's thousands of pages. AMD had to spend so much time and resources to design Ryzen CPUs to compete with Intel 3. As I the 1st aspect making a chip is hard and mass producing is even harder. Intel is not the only company that makes chips but it is one of the few that mass produces it",
"If you mean to replicate a similar product rather than outright stealing their IP. Nothing too much. Probably a couple of dozen PhDs and a few hundred core design staff. About ten thousand engineers in various disciplines, several years of focused effort and maybe 5 billion dollars in development costs should get you there. If you don't use a commercial foundry, you probably need about 10 billion dollars to build the infrastructure. (and a few more thousand employees) Of course, if you intend to sell it then probably add marketing and money to get software developers interested in your product. Oh yeah, probably also need some incentive for hardware manufacturers (like PC companies) interested in incorporating it into their design. Roughly speaking a few more years and a few more billion dollars. Not forgetting, that you might want to get ahead of the R & D curve, so consider a research department that looks at technology 5-10 years out - nano materials, adv chemistry/physics, etc etc. Shouldn't be much more than a few hundred million a year. Round numbers - employ 20K (highly paid) people, start with 200 billion dollars in the bank and be prepared to wait a long time. Other than that, a piece of cake."
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cxxae5 | How do the glasses work that let people see color for the first time in their life? | Engineering | explainlikeimfive | {
"a_id": [
"eyo352x"
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"text": [
"They work on people that have overactive rods/cones in their eyes, they basically filter the wavelength of light that you're seeing too much of. Typically red/green color blindness. They don't work with people that are lacking the ability to see the colors."
],
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5
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cy2jp7 | How do rotating restaurants on buildings get power? | A coworker and I were talking about this the other day. How is it that the rotating restaurants have power? I understood that the center is stationary, so that's where the power for the unit would start. It would have to be connected to the rotating part somehow. You cant use wires, because eventually they would become twisted/tangled/broken. | Engineering | explainlikeimfive | {
"a_id": [
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"eyp9vyf",
"eyp9ib2",
"eyprp5e"
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"text": [
"The same way trams roll down the tracks metal contact plates within the spinning part transfers the electricity without wires",
"Rotary couplers are a standard industrial gizmo. You run the power to the coupler and brushes transfer it to the rotating part.",
"The whole restaurant doesn't rotate, only the outer seating area. In the middle is a core with the motor underneath that spins the rest of it that is stationary that the power would be located in. Imagine trying to be in a busy kitchen while the room was spinning. That is a safety hazard.",
"First, the one near me simply has a ring-shaped floor for the dining tables and chairs and everything else is fixed, so there's no need for any rotating power outlets. Second, it's easy to make a special [rotating transformer]( URL_0 ) for AC electricity. You have the primary winding fixed and the secondary winding rotates. There's no physical contact between the coils themselves so this arrangement can be much more reliable and long-lasting than mechanisms with sliding contacts. Transformer efficiencies can easily exceed 98%. Note that I suspect that very few or no rotating restaurants actually use such a system."
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cy3wjn | How is the NASA helicopter going to be able to gain enough lift for sustained flight in the Martian atmosphere? | Engineering | explainlikeimfive | {
"a_id": [
"eypj0of",
"eypjeol"
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"text": [
"Answer: the atmosphere on Mars is thinner so it has less \"air\" to move downwards to create thrust. However, the gravity on Mars is also only about 38% of what it is on earth. So the thurst to weight ratio is still great enough to provide flight capabilities.",
"A normal helicopter rotor spins at between 250 and 600 rpm. The rotors on the mars helicopter will be spinning at about 2000 rpm. Because of this, it will be able to generate enough lift despite the thin atmosphere. The helicopter is also extremely light and gravity is lower on Mars, which makes it easier to generate sufficient lift."
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cy4hva | Why are tires black in color? Why not green or blue? | Engineering | explainlikeimfive | {
"a_id": [
"eypnoek",
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"text": [
"Carbon black is added to the rubber in tires to add durability. It’s possible to make tires in lots of colors, but they lack some of the durable features such as heat dissipation that tires with carbon black have.",
"Carbon black absorbs UV rays and turns them into heat. UV is very damaging for rubber and plastics so the carbon black slows down the rate at which the rubber decays from sun damage. It's also why plastic pipes for drip irrigation are often black.",
"White wall tires fell out of style, Billy Joel taught me that. Kids bikes are different colors so it's not that they can't be different colors.",
"Tires are constantly on the ground 24/7. They roll around in everything. If they sold blue tires they would end up being black by the end of the first day you put them on your car.",
"No one really even special orders colored tires. I figure its because there's simply no demand"
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cy77yr | Why do instruments sounds different to the human ear? Obviously the materials they’re made of affect the sound somehow, but aren’t sounds just a function of amplitude (volume) and frequency (pitch)? Why do the air molecules bouncing from a piano sound different than those of a cello or flute? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Like other people have said, one single note is rarely ever a single note, its a combination of many notes that, when put together, produce what you perceive to be a \"single sound\". It's like how your computer screen is made up of red, green, and blue pixels but put all of that together in a certain ratio and you get what you perceive to be a \"single\" colour.",
"Yes, its about amplitude and frequency, but NOT about just ONE amplitude and frequency, its about the combination of other harmonics that a string or whatever produces. If you analysed the sound (or timber) of a note for different instruments, you would see that its composed of the actual pitch (lets say 100hz) that has the highest amplitude AND higher harmonics, which are frequencies like: 200hz, 400hz, 800hz...and so on. These other freqs usually have quite weaker amplitudes than the main pitch and usually they get weaker the further they are from the main one. Plus there are also frequencies that are not in perfect ratio to the pitch, but the amplitudes of those are the lowest, but they're still there. Anyways, its the combinations of amp ratios of all the other frequencies to the amp of the main pitch that makes the distinct timber or sound of the instrument, or in other words: Tl;dr: its about the freq spectrum profile, not just about the main/the strongest pitch with the biggest amplitude.",
"This is a phenomenon called [timbre]( URL_0 ). In short, a single note played on an instrument isn't a single frequency, but a whole family of lesser tones accompanying a primary tone. These \"overtones\" are determined by the material and shape of the instrument.",
"Any real world sound is made up from *a shitload of frequencies*. Even if a flute and a piano are playing the same note, they're just sharing the same *fundamental frequency*. There's a bunch of other harmonics (multiples of the fundamental) in different strengths and quantities that are responsible for the specific timbre of the sound. One way of exploring & understanding these is by looking at how synthesizers create sound. [Here's a really cool interactive website]( URL_0 ) that covers the basics of creating sounds that might help you understand the differences."
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cyfjax | how do car alarms know if a window is broken, and why do they go off of the car is shaken? | Engineering | explainlikeimfive | {
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"text": [
"To detect breaking glass, car alarms use either a microphone or a pressure sensor. Breaking glass has a distinctive frequency that can be detected by the microphone. And opening a window (or door) will cause a brief, small (but detectable) change in air pressure. Some car alarms actually use the vehicle's speaker system as the pressure sensors. [Source]( URL_0 ) If a car is shaken (or lifted by a tow truck) it can activate the alarm's tilt sensor, which is a mercury switch. A mercury switch is nothing more than a vial of mercury with two electrical contacts. The mercury is always touching one contact but it only touches the second contact - thus completing the circuit - if the vial is tilted. Or shaken.",
"Some cars have interior motion detectors Also - some cars have tilt sensors which will trigger an alarm"
],
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|
cyin8l | Why fans (computet ones for sure) tend to have odd number of blades? | Engineering | explainlikeimfive | {
"a_id": [
"eys7fud"
],
"text": [
"It's not just PC fans, look at most fans. It's not a hard set rule or anything, but they will tend to have odd numbers of blades. It has to do with harmonics, even numbers of veins tend to induce vibration/ noise. Having an odd number of veins is an simple and cheap way to eliminate that- nobody wants a loud fan"
],
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cyl4z1 | why does the falcon rocket seem to explode blue plasma mid flight while other types of rockets do not? | Engineering | explainlikeimfive | {
"a_id": [
"eytbmvc"
],
"text": [
"It doesn't You saw the video with the glowing curves that came off the side of the rocket didn't you? That's the exhaust from the cold gas thrusters on the rocket, it uses those to turn itself The launch took place at just the right time of day that it was dark enough on the ground but bright enough in the sky that you could see the light reflecting off the exhaust of these thrusters. You'll only get this effect for launches around sunrise and sunset, you won't get this reflection during the day(ground is too bright) or at night (it's dark up there too) so it's fairly rare. It's similar to the plume that has been seen after two launches from Vandenberg URL_0"
],
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|
cyu7ly | I have a kitchen machine that has a "reluctance motor", and this is a commonly listed selling point. How does a reluctance motor work, and why is this a benefit over other motors? | Engineering | explainlikeimfive | {
"a_id": [
"eyui36d"
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"text": [
"In an electric motor you have two basic parts; the stator, and the rotor. The stator is a magnetic ring that has a bunch of wires around it. When you add power to these wires, they create a magnetic field. A rotor is the part that does the spinning, and it is in the middle of the ring. In a typical induction motor, this rotor also has electricity flowing through it created (induced) by the magnetic field of the stator, to create another magnetic field, and as it rotates, the N and S poles of each of the components attract each other, and then the current switches direction as the rotor turns since the current being induced changes direction. This changes the polarity of the magnetic fields so they repel each other so that the rotor doesn't just stick to one of the windings. This is the basis of electric motors. A reluctance motor is pretty much the same, except the rotor is just a piece of magnetic steel without current flowing through it. The windings around the stator basically create a field that would cause the rotor to rotate, and they keep changing up the polarity to keep that rotor rotating. This ends up being cheaper because it's just a simple piece of steel added to the center of the motor, and it's more energy efficient as there are a lot of energy losses in inducing a current into the rotor. Basically instead of using a magnet to spin another magnet, you're using a magnet to spin a magnetic piece of metal, which is more efficient."
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cz0i0j | What does affine mean? | Hello all, Hope you are having a great day. I hear affine, affine transformation, affine function, etc a lot in the computer vision related papers and tutorials. What does it mean? what is its use? and what is the opposite of affine? also what does " every linear transformation is affine, but not every affine transformation is linear. " mean? this is very confusing! Thank you very much in advance | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Imagine you have a series of values x={1,2,3}. We can apply a transformation/function to each of those values to get a new set, which we can call y. An affine transformation is any transformation of the form y=a\\*x + b. For example, if we applied the transformation y=2x - 1, y={1,3,5}. Our original set of points, if plotted with equal spacing, were all in a line, and a nice property of affine transformations is that they can guarantee that our new set of points is also in a line. However, they are in a *different* line. The new line has a higher slope and a lower intercept. Affine transformations are closely related to linear transformations, but a little more general due to the \"+b\" part. Essentially, a pure linear transformation can't change the intercept of the line, but an affine transformation can. People often use the term \"linear\" loosely to refer to a function with both linear terms and constants (and in other contexts they can be called \"linear equations\"). However, when you're talking about transforming a vector of points, \"affine\" is technically more appropriate."
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cz1ql3 | - Why do showers go from the temperature you set it at to like volcanic levels of scalding heat water then back to normal | Like i was taking a shower then i turned off the water to put soap and stuff but when i turned it on again and got dealt fire damage by the water , then it hit me that this has happened to me every time i took a shower regardless of which shower it is and where it is located. I only know that it is something to do with the heater cause i have never experienced this when i forget to turn on the heater , so i would really like to know why thus actually happens | Engineering | explainlikeimfive | {
"a_id": [
"eyvkcy4"
],
"text": [
"Your hot water pipe meets your faucet at a higher pressure than the cold water. When you turn it off there’s hot water that isn’t mixed with cold water in the line and it takes a few seconds for the mixture to get correct again. We see this all the time on older showers in older buildings."
],
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cz6rt2 | - The technology behind instant foam handsoaps | This has boggled my mind since I was a child. Please shed some light on this...I know it can't be that complicated. | Engineering | explainlikeimfive | {
"a_id": [
"eywd3dh"
],
"text": [
"It's most likely simple aeration. Basically there would be a little mess piece that the soap gets pushed through(think of blowing bubbles but smaller) and this makes the soap foam up because it's made of a bunch of tiny bubbles. This is how I imagine it would be done."
],
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czmstf | What are features of the WC-130 as opposed to other planes that makes them better suited to fly directly through hurricanes? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It's not that it's better suited to fly though hurricanes, it,s just that it can sample the air and collect different data about weather. A C-130 could go through hurricanes juts like a WC-130, but without the sensors it would be useless.",
"C-130 are propeller planes that fly relatively slow compared to jet turbine planes. The plane also has redundant engines and can stay in the air when 2 of them fail(1 per wing). The slowness also increases data gathering and tighter turns in comparison to jet turbine planes."
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cznhoj | How do astronauts wash their clothes and shower in the ISS where the water supply is very limited? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The water is recycled, even urine is recycled. [there’s a shower unit on the space station that they use, though there’s a suction device to remove the water after use. ]( URL_0 ) There still isn’t a way to wash clothes in space. Instead astronauts incinerate them during reentry into earths atmosphere.",
"All that water is collected, condensed, purified, and reused, even breath, sweat, and urine. The Russian side of the ISS doesn't like to reuse their urine, so the US side will go over and collect it and purify it out into potable water every once in a while if water supplies start to run short. The water supply isn't \"limited\" in this sense because every drop is recycled multiple times.",
"They don't, being in space can get rather stinky after a few weeks in space, though the general environment is relatively clean human bodies aren't."
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czoj98 | Why do vehicles NOT have a heating element windshield defrost feature like the rear window? | Engineering | explainlikeimfive | {
"a_id": [
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],
"text": [
"Because it's a Ford patent. And yes, you can buy an european Ford with heated windshield. I highly recommend it!",
"Some do. My Ford Focus has a windshield that can defrost. The heating elements are super thin and are vertical. They aren’t straight lines but they are squiggly. (Can’t find a picture on google though) You can see them if you focus on them, but normally when you’re driving you’re looking further ahead and you don’t even notice them. After a quick Google search I found out that Ford used to own the patent in heated windshields but that it expired and that there are more cars now that use windshields that can defrost."
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czs85t | An "open nuetral" electrical house problem. | My coax cables are melting, and I'm trying to work with my cable company, power company, and possibly and electrician. Everything on the internet points to and "open neutral" and I can't quite get together what it means? Shout out to all the electricians and power guys making sure our houses don't burn down and our TVs don't explode, by the way. Update: Power company and an electrician came out. It wasn't an open neutral. It was a messed up ground somewhere in my house though. (I think. The pros fixed it lol.) Thank you all for your concern though! Still don't know jack about electricity. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"I had a problem with an occupancy light switch in my house. I replaced a couple thinking they were going bad but eventually I found an outlet that had a neutral wire that was sort of twisted together and no wire nut. It was making an intermittent connection and causing the problem. The other guy is right-find any outlets, etc that are on the same circuit and open them up. Check all the neutrals.",
"An open neutral occurs when the white wire, which is the return path for the electricity, disconnects from your house, usually between the power pole and where the power comes into your house. This is a serious problem, and you should turn off your main breaker if you haven't already. & #x200B; The power comes into your house via two \"legs\", or two halves of a circuit. Assuming you're in North America, you'll have 240V when you put both those halves together. That's good for things like electric ovens and dryers. Most of your devices only expect electricity from one leg, 120V. The neutral divides those legs. When the neutral goes away, weird stuff can happen. Your TV that was on one leg, and a light bulb that was on the other leg suddenly look like they're connected together, you get an imbalance of voltage between them, and your TV is bound to fry.",
"So, as others said, I think this refers to a situation where the neutral wire in your outlet is disconnected. The neutral wire is supposed to be the bigger of the two slots. Normally current flows between the hot wire and the neutral wire. If the connection to the neutral wire is \"open\" (not connected), that's dangerous because current might flow from the hot wire to ground by another path, possibly starting a fire or shocking somebody. This is why some appliances have a ground connection in addition to the hot and neutral: if current from the hot wire isn't making it back to the neutral wire, the ground wire (connected to the metal frame of the appliance) gives it an easy path back to ground. So, I'm guessing that this is happening with a device that uses a two-prong plug, not a three prong plug (since a three prong plug should keep this from happening). If it's a three prong plug, then that could mean that the ground connection on that outlet is also not connected correctly. To be clear, this is a dangerous situation. This is the type of electrical problem that DEFINITELY HAS THE POTENTIAL TO KILL SOMEONE. You should stop using that outlet immediately, and you should be suspicious of other outlets in your house. Get an outlet tester (they're cheap) and go check all the outlets in your house. The problem you're having is quite likely due to either very old wiring that wasn't maintained well, or badly done amateur electrical work. Either of those things could mean there are other lurking problems in your house's electrical system. Edit: A problem like this could affect all the outlets on the circuit. You should flip the breaker for the circuit containing the affected outlet. Bear in mind, if devices plugged into the affected outlet (or, potentially, other outlets on the circuit) have a 'hot' chassis, you wouldn't necessarily notice even if you touched them. You wouldn't notice unless you touched them AND you were touching something with a path to ground, which could be a cable, a wet floor, another appliance, or a pipe. This is a very bad scenario, because unlike the shocks you might get from sticking a finger in a lightbulb socket, THIS situation would result in electrical current flowing between two different parts of your body, quite probably crossing your chest. Bottom line, you need to get an electrician in there. But until you do, you should keep that entire circuit without power. As electrical faults go, this is one of the most dangerous ones you could possibly encounter in your home. URL_0"
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czx7d8 | is it that Google can't or wont't optimize the RAM usage on Chrome? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"It's a combination of the two, really. Chrome *could* be redesigned to use significantly less RAM than it does...but to do so would be to turn away from one of the things it was designed to do: namely, treat each tab as an entirely separate little sandbox in memory. That's expensive, and there's only so much you can do while preserving that design paradigm.",
"I believe they do... Just quite aggressively. The theory is that RAM is no good to anyone if it is doing nothing so they put as much of it to work as possible. (As you may have guessed from this eli5 answer, this isn't my area of expertise!)",
"They are optimizing. Problem is that their definition of \"optimal\" is to use up as much freely available system RAM as possible to make Chrome feel as snappy as possible, diminishing returns be damned."
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|
czywi1 | Can the global internet storage ever be capped? | Engineering | explainlikeimfive | {
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"ez42cnr"
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"text": [
"It doesn't really work that way. The Internet really is just a whole bunch of computers connected by switches and routers owned by all sorts of people/corporations. The big companies just have bigger, faster, and way more expensive hardware. As long as they can keep buying hard drives and servers to put them into and network switches to connect them with, they can keep adding more storage. Heck I have around 30 TB of storage in my office at home. All the internet sees is servers that response to queries. So, as long as the earth has the resources to make hard drives and the electricity to run them, I don't think we'll see a limit in our lifetimes. Even then I imagine elon musk will build a datacenter on Mars or something."
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9
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|
d012q1 | Why do the fuel meters in cars only work if the car is turned on? | I thought it was a mechanical/analog measurement. Or is it only the indicator itself that needs to be turned on? | Engineering | explainlikeimfive | {
"a_id": [
"ez4svoa"
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"text": [
"It's an analog measurement at the tank, but the gauge isn't wired to that any more. The input goes to the car's computer, and the computer drives the gauges. When the computer is off, the gauges are off."
],
"score": [
5
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d09e8v | How do microSD cards hold so much data when they are in fact very small? | Engineering | explainlikeimfive | {
"a_id": [
"ez7zpeg",
"ez8rmui"
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"text": [
"In a word: Micro-manufacturing. Data has no inherent physical size; it's simply ones and zeroes. The smaller you can make those ones and zeroes, the more dense you can encode data into a given medium. Imagine writing your name. Now imagine writing your name again, half that size. And again, half *that* size. And so on and so forth. Eventually you'll reach a point where you can probably *imagine* writing your name smaller, but can't actually write any smaller, because your hand or the pen are too big. Micro-manufacturing solves those issues. Specialized machines are able to \"write really, *really* small\", and allow us to fit more data in less physical space.",
"They pack very small transistors on them which hold a good amount of data. So in theory, it doesn’t matter if they’re small in size."
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41,
3
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|
d0bggt | What does flux do when used in soldering/welding/forging etc..? | Engineering | explainlikeimfive | {
"a_id": [
"ez8gwuc"
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"text": [
"Oxygen is an impurity in metal. Flux works to remove oxidized metal and prevent new oxidation from occurring, resulting in a more pure, stronger joint."
],
"score": [
7
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|
d0cbt0 | How do shotgun spells split into pellets? | Engineering | explainlikeimfive | {
"a_id": [
"ez8lg1y"
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"text": [
"The shotgun cartridge (the bullet in laymans terms) contains a small plastic liner called a wad; the pellets (called shot) are contained within the liner. When you pull the trigger the gun powder in the cartridge causes the wad to travel down the barrel, as the wad exits the end of the barrel (called the muzzle) air resistance causes the wad to peel away from the shot allowing them to spread and travel forward."
],
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6
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|
d0m7wp | Why do major tunnels have buildings at the entrance? What is inside? | Like this: URL_0 | Engineering | explainlikeimfive | {
"a_id": [
"ezaizk2"
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"text": [
"They house all the equipment needed to operate the tunnels systems. Ventilation, monitoring systems, etc. They often have offices in them for the people that support the tunnel. It's much more complicated than just a hole in the mountain."
],
"score": [
20
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d0pv02 | How do Helicopters fly? | Engineering | explainlikeimfive | {
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"ezbls07",
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"text": [
"Think of the rotor blades as kind of a bigass propeller. They push air down to hold the helicopter up. Now...If you were to look at a cross-section of the rotor blades, they have the same shape as an airplane wing (steeper curve on top, relatively flat on bottom). It's literally a spinning wing. Now, there are three sets of primary flight controls on a helicopter: the collective, the cyclic, and the torque pedals. The collective is what makes the helo go up or down. Changing its position alters the angle of the rotor blades everywhere at once. To ascend, the leading edge of each blade tilts up, making it take a bigger bite out of the air and force more air downward, which drives the helicopter up. Down is the reverse. This angle, by the way, is called the \"angle of attack.\" The cyclic controls forward/reverse/left/right motion (you can move it in a circle). It does this by changing the angle of attack of each blade individually as it approaches a certain position. To go forward, the angle of attack increases as the blade approaches the rear-most position and reverses as it approaches the front-most position. This forces the tail up and the nose down, tilting the rotor blades relative to the ground. Remember how I said you could think of the rotor blades as a bigass propeller? Well, now your propeller is kind of tilted forward, so your helicopter is gonna move forward. Reverse things so that the blades tilt down at the rear and up at the front, and your helo goes backward. Make it tilt down at the right side and up at the left, and you move sideways to the right. Reverse that, and you go left Now, as for turning the nose left or right: Those bigass blades are spinning. To spin them, the engine pushes against a shaft. Well...Newton's Third Law says the shaft pushes back against the engine--and since the engine is bolted to the airframe, it wants to spin thw airframe in the opposite direction from the rotors--if the rotor turns to the right, the airframe wants to go left. We call this counter-torque. Notice how most helicopters have a small propeller mounted on the side of the tail? We call this a tail rotor, and it's there to cancel out that counter-torque. Now, we can actually take advantage of that counter-torque to turn the airframe in the same direction it naturally wants to turn, but if we want to turn the opposite direction, we have to overcome that tendency. That being the case, the tail rotor is designed so that the pilot can change its angle of attack just like on the main rotor--except that he or she doesn't need full directional control; the pilot only needs to be able to balance out the counter-torque for straight-line flying, and adjust it to turn left or right. This is done with foot pedals. Helicopters are very complicated machines--even moreso than a comparable fixed-wing airplane. A friend of mine who is an aircraft mechanic has a t-shirt that says the following: Helicopter (noun): a million moving parts rotating around an oil leak just waiting for metal fatigue to set in. It's amazing to me that we can even teach a human being to fly one at all, let alone the aerobatics some of them are capable of.",
"The main rotor spins really fast and pushes air down (which pushes the helicopter up). To move forward the rotor tilts a little (can tilt forward, back, left and right) which changes the direction the air is being pushed. Also the angle of the blade can be changed which changes the amount of air that is being moved."
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d0togf | How do bus routes and time schedule got planned and designed by the government in big cities? | I believe there should be an algorithm or using statistics of some kinds to plan the route for the buses as well as determining the frequencies of the buses. | Engineering | explainlikeimfive | {
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"ezd8pw1"
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"text": [
"The CTA here in Chicago realllllllly needs to ask themselves that question. Their schedules are so unpredictable and bizarre. It’s almost like they said “fuck it, this is a busy neighborhood, let’s just throw out 4 buses an hour and hopefully all goes well!”"
],
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4
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d0zw85 | How do fire vents help prevent/reduce fire damage in buildings? | My old freshman dorm had fire vents which connected 3 floors of rooms. They were extremely unpopular because they were designed in such a way as to amplify noise from the rooms connected to them. Someone on the 3rd-floor could hear someone sneeze on the 1st-floor directly below them. Do these vents actually help prevent serious fires, and if so how? | Engineering | explainlikeimfive | {
"a_id": [
"ezfrl5e"
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"text": [
"Ventilation serves two purposes in firefighting. Firstly, fires cannot survive without oxygen. One of the first things to do in a fire is shut down the ventilation so that no more oxygen enters the area. This starves the fire. Secondly, smoke can be as dangerous as fire. Smoke is un-burnt fuel, which means that even though you might extinguish a fire, the smoke has the potential to re-ignite. When the fire is extinguished, the ventilation system removes the smoke from the heat so to eliminate that risk. Also, smoke on its own is dangerous the humans, so removing it also prevents respiratory damage."
],
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5
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d1246m | Why do some trucks have wheels that don’t touch the ground? | Engineering | explainlikeimfive | {
"a_id": [
"ezg7bvm",
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"ezg901x",
"ezh4pyx"
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"text": [
"The additional axle (wheels) are there to give more support for heavier loads. Unless the truck is loaded to the point where it needs them, the wheels are suspended off the ground.",
"I think you are referring to dump trucks and semis? If so... Trucks are required to be under certain weight limits. How much weight is on a wheel is also a restriction. The extra wheels are usually only used if they are really loaded down. When they lower them and the wheels start to help support the weight of the truck and load, it helps them meet certain weight limits. For a very simple example, consider a truck with 6 wheels, 4 are in use all the time. Normally, the truck can only carry 1000lbs, as each wheel is only allowed to carry 250lbs. One day you want to carry 1200lbs. With four wheels you are over your weight limits ( @ 300lbs each). Now drop that extra axle and use all 6. Now we are running 200lbs on each wheel. You are legal again. Just as an fyi, a lot of the weight restrictions cone from the damage trucks do to roadways and also bridge design. To design bridges you will make assumptions on loads the bridge could carry. If normal trucks are 50,000 lbs, and now some one comes through with a convoy of 100,000lb trucks.... Ooops? Also, heavy trucks beat up asphalt pretty hard. A commonly started figure is that one truck does as much damage to the road as 10,000 cars. Also, according to SSTI, \" a four-axle, single-unit truck weighing 60,000 pounds causes six times as much pavement damage as a comparable truck weighing 40,000 pounds.\"",
"When the truck is empty the stopping distance is shorter. They can pull up an axle and save fuel and expensive tyre wear.",
"These other guys put way too much thought into it. They are simply like that to lower wear and tear if the weight limit does not exceed the axle weight limit. For example, my companies trailers have the two standard axles on the back. My states tandem axle limit is 34,000 lbs (17,000 per). If the weight in the trailer is less than that, a pneumatic valve fills small air bags that lift the axle into the air. Saves hubs, suspension, and tires. The fuel saving is negligible because they are not powered axles. When they get loaded beyond that threshold, they lower back down."
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d13y38 | With the speed of charging becoming a major point of contention for electric vehicles, why can you not simply add multiple charging ports to a Tesla to increase charge speed? | To my understanding, charging a battery is essentially just refreshing the electrons stored within a battery. There's a lot of talk about Tesla's "supercharger" which charges Tesla vehicles much faster. I'm just wondering why you can't have like 4 or 5 ports in the vehicle to charge simultaneously? Is there a restriction of electron flow into the battery? Why are EV companies just upping the voltage instead of trying to figure out something different, because I DO know there is a restriction for the bandwith of voltage a wire is able to carry. Just seems very imprudent. Also, couldn't you just bundle 5 cords together and.. quintuple the charging speed? | Engineering | explainlikeimfive | {
"a_id": [
"ezgw0li",
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"text": [
"The problem isn’t the amount of current you can push through a big pin, the problem is reversing the chemical reaction that produces power without overheating the battery. If you overheat the battery, it starts to run away and then your Tesla burns down. Also, a Supercharger is ten modules iirc of the same type a Tesla carries one or two of built-in. So they sorta do exactly what you’re suggesting.",
"Most of the restriction on charging speed is on the battery side, not the supply side. Charging requires a reversal of a chemical reaction in the battery, which produces heat and can destroy the battery and cause explosions or fires. More cords would mean more power in, sure, but that's what the batteries can't handle, at this time."
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d19jpy | Why do flurecent lights flicker when they are turned on? | Engineering | explainlikeimfive | {
"a_id": [
"ezj9s9j",
"ezjbrtt"
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"text": [
"Certain electric lights, such as fluorescent and sodium vapor, rely on an electric current flowing through a gas to emit light (UV in the case of fluorescent). That current can take a few tries to really be sustained as the elements heat up, so it flickers and dies a few times as it’s starting from a cold start.",
"A fluorescent light contains a gas. When electricity is applied the elections collide with those of the gas which causes an emission of light. When the light isn't used for a while the gas cools and becomes a liquid on the side of the tube. Once the tube gets warm enough all of the liquid is a gas again but it takes a little while. So the light appears to flicker in the mean time."
],
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d1qkx9 | how ballistics work, and how they can trace a bullet back to a particular gun? | Engineering | explainlikeimfive | {
"a_id": [
"ezp6vyt",
"ezp86jx"
],
"text": [
"When a bullet is fired, it travels down the barrel. Almost all modern firearms (except most shotguns) have what's called \"rifling\" in the barrel. These are grooves that are in a spiral shape. They force the bullet to spin. As the bullet travels down the barrel, it's scraping the sides, getting spun by the rifling. This creates grooves in the bullet itself. Microscopic imperfections cause these grooves to be unique to a specific firearm. If you recover a gun, you can test fire it and compare the round you fired to the round you found. Alternatively, you can do the same thing with casings. Imperfections in the firing pin and chamber are unique to a specific firearm.",
"So you are asking about forensic ballistics, the science of matching projectile to weapon, versus ballistics in general, which is the study of the behavior of projectiles. So first thing to understand is that unlike what TV shows, this is in no way exact. Like “science may be too strong a word” not exact. Second, matching a bullet to a gun requires comparison. Basically they must have a bullet they know was fired from a given weapon to compare to the one they think was fired from that weapon. Two bullets from two unknown guns could be judged similar enough to be fired from the same weapon but that doesn’t tell you what weapon that was. Why this whole field is problematic: Guns are a mass produced item and their barrels are no exception. Forensic ballistics can tell the difference between two different make/models but when actually tested by a third party, the success rate of most practitioners was barely better than guessing."
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d1zns6 | Why are solar panels glossy and reflective, wouldn't it be more effective if more light went through the glass? | Engineering | explainlikeimfive | {
"a_id": [
"ezs3k43",
"ezrlyvu"
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"text": [
"Anti-reflective coatings, such as are used on optics on glasses, cameras, etc., aren't going to survive long in the weather and they're very expensive, so the gain wouldn't be worth it. Using the matt surface to reduce reflections, as is done on glass picture frames, would be a dust magnet and be hard to clean and it doesn't so much reduce reflections as scatter/diffuse them so that they're not as apparent. Panels generally have three surfaces: both sides of the glass cover and the front of the cells. All of these can reflect light away. Mostly the reason for not treating them is that cells are so cheap that just adding more cells is a more economical way of making up for losses. It's rare for people to be constrained by space. Even paying more for higher-efficiency cells will be cheaper than adding coatings. Maybe they do this in space where it's worth plenty of money to maximise power/weight and they only have one one surface (no glass cover).",
"The angle that the light is being reflective is a fairly large one so that light wouldn't normally contribute much to generation of electricity light entering vertically goes straight through."
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7,
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|
d1zu0v | If you have a trombone in 1st position you can change notes with your mouth, those notes you can switch to are B flat F and D. My question is how does the same amount of tubing produce three different notes. | Engineering | explainlikeimfive | {
"a_id": [
"ezrn9h3"
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"text": [
"They are called overtones. Basically there is a base frequency that a length of tubing will produce when you buzz your lips at the end of it. The higher notes are integer multiples of the base frequency (base x 2, base x 3, that sort of thing). Providing a higher tension in the embouchure (the muscles in and around your lips) will cause your lips to vibrate at these higher frequencies. Typically this only applies to brass instruments because they are just specialized tubing, but it is possible to produce overtones with certain woodwind instruments as well. I was learning that some years ago when I still played saxophone."
],
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3
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|
d2e8hb | How is it possible to fit a billion transistors in a CPU chip? | Engineering | explainlikeimfive | {
"a_id": [
"ezuc5k9"
],
"text": [
"The problem your mind is having is that the idea of a billion is large, and the cpu size is small. So it's confusing you. But a billion is big, in a different way than the cpu is small. Let me explain. A billion is a large number 1,000,000,000 to be exact. But the question is a billion what. A billion people. That's half of China. A billion ants. That's one tree trunk. Both still much larger than a cpu. But the difference in size between a tree trunk and half of China, is still no different in number. The number almost doesn't matter. Size does. So what's this got to do with anything. Well, the transistors are tiny. And I mean tiny. You couldn't see them. You couldn't really see them with a microscope. They are so small that you could lose it on your finger, and even with a csi team, never find it. So while there may be a billion of them. They are so small, it doesn't matter."
],
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3
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d2ev1d | Engineering question - Compass | Engineering | explainlikeimfive | {
"a_id": [
"ezufqrw"
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"text": [
"In a surveyor's compass, the markings are on the compass, and the rotating needle is an indicator that points at one of the markings. In a prismatic compass the markings rotate on a round card and a special prism contains the indicator. By looking through the prism you can see the markings rotate under the indicator."
],
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4
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|
d2ukh3 | Why does cap of every bottle or tube opens anticlockwise and closes clockwise. Was it decided initially. | Why does The caps of bottles like soda bottle or cold drinks opens up rotating anti clockwise and closes clockwise. Same is with any tube like toothpaste or any ointment. | Engineering | explainlikeimfive | {
"a_id": [
"ezwwex8"
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"text": [
"It goes back to why are all screws and lids tighten clockwise? Your bicep muscle. The arm motion to tighten a screw or a lid is called supination. The arm motion counter clockwise is pronation. the muscles that do that are smaller and not as powerful. Your arm will tire less from screwing in 10 screws than unscrewing those same screws, in general. So in general, anything where you want to exert more force to tighten, its clockwise. Of course this applies to a right handed person. Everything is opposite for a left handed person."
],
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24
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d2za1e | How do they build oil rigs, in the water ? | What are the process How do they dig through the ocean Just a little bit of everything | Engineering | explainlikeimfive | {
"a_id": [
"ezxouku",
"ezxrxqm"
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"text": [
"In shallow waters they construct the structure in parts, float them out and start dropping them and assembling them. In deeper water they use some sort of floating platform that's anchored down or has a series of rotating propellers that keep it in place.",
"Oil rigs have legs that look like bell-bottom pants. The rig is built close to shore or even up a river. The bell shape legs are later pressurized with air to raise the rig higher in order to be towed out to sea. Once in deep water and near its destination the bells are filled with water and lowered to it's desired height from sea level. The legs never touch the bottom but are anchored to the seabed preventing the oil rig from floating away. There are some really big rigs that have sections shipped out on barges and assembled onto the oil rig platform."
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10,
6
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d39125 | How does the keurig/coffee maker make that amount of cold water so boiling hot in such a quick time? | Engineering | explainlikeimfive | {
"a_id": [
"f00hv55"
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"text": [
"For one, it uses a *lot* of power. Another trick they do is heat water while it's being drawn up through a thin tube. It's a lot easier to heat the water in the section of the tube right before it hits the coffee grounds than simultaneously heating all the water contained in the machine."
],
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7
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|
d3j2d5 | why do douchey cars make that loud popping noise when they downshift? | Engineering | explainlikeimfive | {
"a_id": [
"f03482w"
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"text": [
"The popping sound is likely unused fuel igniting in the exhaust. The “fooosh” noise is from the turbo releasing unneeded pressure. Why would you put a rear wing on a front wheel drive car?"
],
"score": [
5
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|
d3vo33 | why do mac trucks have Spinning death spikes on their front wheels? | Engineering | explainlikeimfive | {
"a_id": [
"f05gfc9"
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"text": [
"It is decorative, some truckers like them because it makes ignorant people pay more attention to keeping their distance. For some reason people think that spinning spikes over the wheel bolts are somehow worse than the spinning wheel bolts themselves. The spikes are plastic."
],
"score": [
7
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|
d3z5h3 | How are manmade lakes made and how do they function? | Do they ever run out of water? Does it start with an original body of water? I am so confused to this idea of making a lake. Is it a colloquial term and not actually man made? | Engineering | explainlikeimfive | {
"a_id": [
"f06206j",
"f064e3n",
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"text": [
"You find a valley with a stream/converging creeks running through it. Erect a dam across the mouth of said valley. Wait... And now you made a lake.",
"> **\"Do they ever run out of water?\"** I can't find any examples of a 100% dried up man-made lake at the moment, but it's definitely possible for these artificial lakes to slowly shrink and dry up due to local climate changes, global warming, bad droughts, engineering human error, and over-diversion for irrigation. A good example would be the man-made [*'Salton Sea'*]( URL_1 ) lake in California > **\"Does it start with an original body of water?\"** Yes. Normally, land is excavated / barriers in the form of dykes are erected / building a dam in a valley. A river is then diverted to the lake-to-be. It will then fill up to a point where either a) the flow slows down and the water level stabilizes, or b) it fills in too much and water is let out through [*'spillways'*]( URL_0 ) > **\"Is it a colloquial term and not actually man-made?\"** If the conditions that led to it were made by humans, and not natures, than yes. Also, Man-made lakes are also called *'reservoirs'*",
"Some lakes result from gravel extraction for making concrete. As that gravel was produced by a river eroding rock as it snakes across the land, gravel extraction usually takes place adjacent to a river. When dredged out the pit left behind fills with water by underground percolation as the water table is at the level of the water in the river. Often these lakes are converted for leisure use. Fishing, sailing, water skiing and so on."
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"https://en.wikipedia.org/wiki/Spillway",
"https://allthatsinteresting.com/salton-sea-history"
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d40rpl | How are insulated water bottles made? and how do they work? | How are they made? How can the bottles retain heat or cold temperature? How do they work? Edit: those stainless cups are included in the topic as well. I'm quite curious about how each part of the cup/bottle is important and how they help with the functionality of the "product." | Engineering | explainlikeimfive | {
"a_id": [
"f06h0io"
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"text": [
"The have vacuum between walls to prevent heat coming in or out and are shiny to reflect heat back"
],
"score": [
3
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d4gfui | runaway Diesel engine | What causes Diesel engines to “runaway” and if one does, is there a way to stop it? | Engineering | explainlikeimfive | {
"a_id": [
"f0bfg83",
"f0cy17p"
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"text": [
"This all started with the the older 2 stroke diesel engines. When they were started they started at full throttle and immediately dropped to idle. Unless a little shaft about the size of a hot dog broke. Then the engine stayed at full throttle and \" ran away\" . These engines came equipped with a emergency shut down. Which consisted of a spring loaded flap to cover the air intake. Modern diesels do no have this issue. A \" run away\" now refers to when a turbo oil seal goes out and puts oil into the air intake. Causing the engine to run on oil. It will continue to run until it's out of oil. No way to really stop it once it starts. Unless you can put something, !like a clipboard over the intake.",
"Diesel engines don't have a throttle. They always take in a full charge of air, and control the power by adjusting the input of fuel. If something goes wrong with the amount of fuel, then the engine can just keep accelerating. The system for injecting the right amount of fuel can be complex and break, and end up just squirting in lots of fuel. Or something flammable can come from another source, such as a leak of oil from the turbo seal. Either way, without a simple throttle to close, the engine just keeps running. And that's normally the way to stop it - find some way to make a throttle, to block off the air intake. Or you can blow CO₂ from a fire extinguisher into the intake, so the engine doesn't get enough oxygen to run."
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d4jjaj | Why are waterproof phones rated for time periods submerged etc... (ie, 5m for 30 mintues). Doesnt waterproof mean water does not get in? Why is there a time limit. | Engineering | explainlikeimfive | {
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"Water pressure will force its way through most joined materials eventually it is only a matter of time before the \"weak points\" are overcome.",
"I wonder how long the device has to be taken out of the water to restart the, let's say, 5 minutes it can be submerged.",
"The depth rating that they list isn't actually a promise to you, the consumer. If you read your manual/warranty it'll say never submerge it, ever. Your warranty won't cover fluid damage at all. What it actually is, is a disclaimer. \"We tested the phone at x depth for y minutes and it survived, *therefore if you have water infiltration you must have done something worse*.\" This lets them get out of their [extended service contract]( URL_0 ) if you admit you submerged it on purpose. > (d) to repair damage caused by reckless, abusive, willful or intentional conduct, or any use of the Covered Equipment in a manner not normal or intended by Apple;"
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d4l16v | How to planes slow down so rapidly on landing? | Engineering | explainlikeimfive | {
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"At landing a plane is more like 140 knots (160ish miles) per hour. At high altitude a plane does 400 mph, but it slows down over its descent because 400 mph is beyond its speed tolerance at low altitudes. Thicker air means 400mph is way more stress than it can take, but when the air is thin 400 mph doesn't feel so fast to the plane's structure. On landing, brakes usually do most of the work. The panels that raise up from the wing tops have a small drag effect, but their true purpose is to make the wings stop producing lift so that the weight of the plane settles on the wheels. At 140 knots on landing the plane is still on the edge of wanting to fly, so for the brakes to be effective we have the get the weight off the wings and onto the wheels. Engines in reverse is a thing, but it's not used at low speeds (something like 80 knots?) because it has a tendency to kick up anything on the ground in front of the engine which would be at risk of getting sucked into the engine. Edit: this does vary a bit by plane. I have flown (in a simulator) a large plane that doesn't have those top-of-wing panels (sometimes called Spoilers) so it focused more on reverse thrust to stop.",
"As far as turbine engines go most commercial aircraft have thrust reversers. They are flaps that act as part of the turbine cover near the back that when activated move to the rear nozzle and deflect the trust somewhat forward. This video will give you a better idea. URL_0"
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d4uoni | how does an automatic transmission know when to shift? | Engineering | explainlikeimfive | {
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"The computer typically monitors speed, throttle, and brake inputs. If the throttle is suddenly pressed all the way down, the computer knows to drop into the lowest possible gear for a certain speed. If the car detects braking, then it assumes you're coming to a halt, and will likely try and sit in the highest gear it can without stalling. In addition, this system can be used or fooled by a driver who has a lot of experience in a certain car. For instance, if I floor it up to 30, then briefly let off the pedal before flooring it again, my car will go into second gear. Meanwhile, if I floored it normally, it would wait until about 50mph to change gears. Alternatively, if I suddenly floor it after braking, the car will have to change gears suddenly which will result in a kicking feeling for passengers and extra wear on the transmission."
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d4v84c | Why are the spinning wheels on a bank vault door so big? Why couldn't a smaller wheel work, or a knob, or a handle? | Engineering | explainlikeimfive | {
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"Same reason old cars without power steering used big ass steering wheels, like they said, leverage"
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d4w3s8 | How do those huge rotating generators that are present in power grid stations provide momentum to smooth the spikes and ripples in electricity? | Some one told me its through electrical inertia. I am not aware of that specific term :p Will be grateful for your reply. Thanks | Engineering | explainlikeimfive | {
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"In alternating current (AC) power generation there is a need to keep things steady: the frequency of the AC, and the voltage. The frequency is supposed to stay rock solid at 60 Hz in the US and 50 Hz in most other countries. Voltage is of course constantly fluctuating, but there is a way to measure it properly and come up with a numerical value in volts. For the purposes of this discussion, let's talk about a load designed for 240 volts. In a smaller generator, like the ones that fit into the back of a car or truck, their circuitry is often limited to adjusting the steadiness of the voltage. The thing which settles the frequency is a mechanical device called the governor. Because of the size of the engine and limitations of the mechanical linkages, the governor on a small generator isn't very good at keeping a steady frequency when loads change. However, as we scale up from a 4 kW generator to a 20 kW or 100 kW generator, mechanical governors are more able to smooth out frequency when loads change. This is due to the size and mass of the rotating machine. So we would say that the mechanical inertia of the 100 kW generator would be much greater. Load changes on a large generator will still change the frequency of the output AC, but much less. Hypothetically, let's say that a 4 kW generator switches from 60.5 Hz to 58 Hz during the brief time frame in which a load is added and then the engine accelerates back to around 60.0 Hz. Perhaps the 100 kW generator goes from 60.2 down to 59.6 when it takes up a load, and then goes to 60.0 after loading. Did you notice that on both generators that I said that they were higher than 60 Hz during their no-load operation? Well, that's important. Because virtually all generators start above the target frequency when idling or under no load. But as load increases, something called a frequency regulator will lower the output frequency to the target. In a mechanical governor, this is just how they work. An engine targeted at 3000 rpm will lag a little at full load or when driven beyond its rated capacity. It might only produce 2800 rpm at full load and 3200 rpm at no load. And it may fluctuate constantly. The smaller the engine and mechanical (rotating) inertia, the less stable it is. There is also voltage regulation happening in a generator's electrical system. This tries to keep the (electrical) excitement of the rotor in a certain range, but again, it is not always constant or steady. So when loads change, a voltage regulator inside a generator \"bucks\" or \"boosts\" the generator's output voltage to keep your 240 VAC loads working properly. When you scale up to a large generator for power production, such as the water turbine inside a dam, a stationary jet turbine, or a superheated steam turbine from a coal or nuclear plant, you will be dealing with a different set of rules. First, these large systems are interconnected in parallel, meaning that if any one generator broke down, it would automatically be severed from the rest of the grid (electrically) and the surviving generators would now immediately pick up the load which had been taken by the failed generator. As long as there is spare electrical capacity in the grid, then the grid continues to run. Nuclear plants don't normally ramp up, so this extra capacity is normally taken by coal, gas, or hydro power plants. Those 3 types of plants will do this: they will imperceptibly slow down, just like the 4 kW generator, when loaded. However, this will be hard to detect at your home without a counting oscilloscope that costs $20,000! All that happens at that moment is that more water, more steam, or more gas turbine fuel is sent through the machines, and the grid keeps pumping out AC to homes and businesses in the area. At your home, your voltage and frequency may drop down a little bit, but the difference will usually be negligible. Imagine that a turbine at a nearby dam just broke down. One near me has a few generators rated at 45 MW. That's 45,000 kW, or about 12,000 times more powerful than the generator in my garage. If it had been operating at 30 MW during the heat of the day, and the dam had 3 more units on the site operating at 30 MW, then there is enough reserve capacity in the power station to take up the load. But it would be likely that other plants in distant parts of the state would ramp up as the voltage and frequency on the grid began to drop. The gas plant 200 miles away may have a better response time than the water valves keeping the water turbine spinning. A BROWN OUT would happen if the grid lacked extra capacity, and you would see a voltage drop at your home... perhaps the 240 VAC you expected would be 190 VAC, and lights would dim and motors would slow down. Most power companies nowadays I think forgo a brownout and just kick off loads from the grid. That forces a blackout to certain distant customers while keeping the core of the grid running at the correct voltage and frequency within very small tolerances (\\~0.5% for voltage, \\~0.05% for frequency). Rolling blackouts happen when different neighborhoods get blacked out in series throughout the day. There are some really exotic ways to allow some extra electrical load buffering that aren't mechanical and aren't being done at the generator. Grid things. It's so advanced that I don't know that I can explain it easily. It uses electrical components that you can think of as a battery to keep some of these momentary blips from reaching customers. You can even actually use a battery system to backup an AC power grid. This is done routinely onboard almost every military submarine in the world, because lead acid batteries are very reliable. Batteries are also a source of backup power in most computer datacenters. One last thing. \"Power grid stations\" is a bit of a vague way of saying \"electrical power generating stations\" I believe. Please don't be under the impression that electrical substations with their transformers have a lot to do with smoothing out AC power fluctuations. This would likely only be the case for one of those exotic types of electrical buffers that I mentioned briefly. Substations just convert and transmit power and do very little more than basic filtering."
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d4z7j6 | How do popups/redirects keep you from using the back button and why do browser developers still allow it to happen? | feels like for the better part of two decades the back button has become more of a suggestion. yes; i pirate. yes; i understand adblocker helps on some devices. | Engineering | explainlikeimfive | {
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"If you hold down the back button (at least on Chrome) a small history pops up, and you can select the page you were on before you clicked the link",
"Simply pressing the back button moves you back one step in your current browsing history. The redirects of these ads utilize multiple steps, meaning the one step back just takes you to the previous redirect and it just ends up coming back to the same site at the end. Browser developers don’t fix it because it’s exploiting the way the back button works on every other site. You’d be breaking the entire functionality of the back button just to try and fix this one thing that’s at worst a minor annoyance for most people"
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d509t6 | Why are diesel engines so much shakier than conventional petrol engines? | E: Post solved, thanks for all your informative replies! | Engineering | explainlikeimfive | {
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"Depends on the vehicle you mean. But one significant difference is that they run at lower RPM which makes each of the engine strokes more noticable. If you mean engines of big vehicles like trucks or tractors, then it's also that they have huge engines compared to that of a car.",
"The combustion inside of Diesel engines is self-induced due to higher compression, so it's hotter and faster and the whole cylinder filling combusts at once. In a petrol, the spark plug ignites the fuel-air-mixture at the top and the combustion wave then \"slowly\" travels through the filling. That difference makes Diesel engines rattle more.",
"Diesel engines run at a lower RPM and with much higher compression. This can lead to the engine shaking a bit more. They also do not compress the fuel like gasoline/petrol engines do, they compress the air and then inject the diesel fuel into the compressed cylinder. This means that very high powered fuel injectors are needed, which can make quite a bit of noise."
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d50aoy | why do musicians wear in ear monitors how do they work? | Engineering | explainlikeimfive | {
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"What you hear in the audience comes from strategically placed speakers. The musicians can't hear it that way because of where they're standing. So, the ear monitors play what you're hearing so they know when to come in with their part.",
"They wear them to hear the music easier, if your in a loud theatre/arena/stadium you won’t be able to hear the music clearly. It helps you stay on beat, keep in tune, they relay the music which is why sometimes the musicians will take them out if it’s out of sync. As to how they specifically work beyond that, idk.",
"The stage sound can be divided to three sources; band/backline, monitors and PA. PA is just for the audience, does not care about the performers need very much. Band and backline are the actual instruments used, drums, guitar amps, piano, violin etc. A lot of those are not strong enough to be heard even in a small club, not to mention a large arena. So they need to be captured with a microphone. Monitors are needed so that the musician can hear what they are playing. A singer can't hear themselves, the noise levels are too loud. But here we have a problem: a microphone captures any sound that enter their effective range. It does not differentiate between the PA used for the audience, the monitors on stage or the actual sound source. And since the signal from the microphone is amplified and feed back on the stage or house (house is where the audience is). This can create a condition where the sound from the speakers enter the mic, gets amplified and then comes back out from the speakers, is being picked up again, amplified and so on. This is a feedback loop, the every familiar loud whine or whistle that is used wrongly in Hollywood as a sign of bad public performer (sorry to ruin yet another cliche...). There are ways to solve this. The microphones used are directional (cardioid polar pattern). It picks sounds that come from the front louder and quieter sounds that come from the back of the mic, away from it. This is first fix, second is the placement of the monitors. They need to be a set distance from the mic and come from a direction where the mic is the least sensitive. Since audience wants to see the stars, we have to use wedges on the floor. They angle their speakers to point towards the musician. Getting too close to them will create feedback. This limits movement on stage a LOT. The easy solution is to use in-ear mics. Not all like them, they can make the sound to be too dry, you miss some of the connection to the audience and can be too much inside your own headspace. But they also allow better monitoring sound and also prevent hearing damage if correctly used. They are also very personal things, you don't like to put just any plug in your ear. Not to mention, they are wireless with all the problems that come from \"magic wires\".",
"It kind of depends. Mostly the earphones play what the audience hear But they can also play a metronome to stay on beat, or sometimes both"
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d50e14 | How does a theremin work? | About five minutes ago I stumbled upon this video: [ URL_0 ]( URL_0 ) This musical instrument is so different from all the other more frequently seen ones. I tried looking some things up, but it's so unique most of the explanations take some considerable background knowledge. Hopefully I can find an answer here! | Engineering | explainlikeimfive | {
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"The [wiki article]( URL_1 ) explains it in more detail, but it basically works using the same principle as [touch screens]( URL_0 ): [capacitance]( URL_2 ). Your body can accumulate (static electricity) charges and affect / respond to an electric field. The field acts differently if your body is there vs. just air."
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d52xw6 | How do researchers know a submarine, and external components, will withstand the pressure at a given ocean depth before initial use? | Engineering | explainlikeimfive | {
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"It's actually pretty standard engineering. Different materials have different strengths, depending on their composition, temperature, age, whether they've been irradiated, and other factors. We know those factors, so we can calculate how deep a component can go (and therefore how much pressure it will be exposed to) before it yields. Interestingly, submarines do compress noticeably when they go deeper; the scene in \"Down Periscope\" with the sagging line is a bit exaggerated, especially for such a small boat, but that trick does work. Source; qualified submariner that helped build a submarine.",
"they can create same pressure in a test chamber. They know which materials and designs could survive pressure in the past (or rather how much pressure they can survive before breaking). and they can use this info to make math model predicting how much pressure a new part can survive. and they make all the parts to survive twice the pressure they actually expect. So is there is a small mistake in the math, or small defect in manufacturing, they got enough of a safety cusion to survive it. Finally, they keep an eye on their sub as they go down. If there is too much creaking or other signs of trouble, they stop and go back up."
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d59vic | When are the right times to use a capacitor and when to use an inductor | Engineering | explainlikeimfive | {
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"You use a capacitor for almost every single case you need a reactive component. They're cheaper and smaller. You use a cap until you can't. Inductors are useful for chokes (reduce EMI on cables/connectors), passive filter networks (which are fairly dated but common in audio gear), and on power supplies with high current demands. The failure mode of an inductor is also less catastrophic than a cap. Inductors will melt internally and then short, caps will pop and leak over the circuit board and act as an open circuit or in really bad cases they can go boom. Iirc some people use them in conjunction with hall effect sensors for protection circuitry but idk how common that is."
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d5byl9 | Why do high speed trains have blunt noses instead of pointed ones? | Looking at pictures of high speed trains, it seems that most of them, and all the new ones, have rounded noses, some of which, like the new ICE-4, have [very blunted ones]( URL_1 ), even more so than the [previous generation ICE]( URL_0 ). It seems that noses that end in a sharp point are almost never used. Why is this? Shouldn't sharp edges perpendicular to the airflow be able to slice through the air and therefore create the least drag? I would have thought that an optimal nose shape for a high speed train would be one similar to that of a fighter jet, with a pointed nose. | Engineering | explainlikeimfive | {
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"This has a lot to do with the way trains enter and exit tunnels. The shape is biomimicry from birds that dive into water and don't create or create a very minimal splash. This concept was extrapolated to high speed trains to reduce the sonic sounds that would be emitted from exiting tunnels.",
"You need a bluntish nose to fit the coupler. Two train segments coupled together experience *far* less total drag than 2 more pointy separate train segments. Also I'm guessing pointy noses only really start paying major dividends at transsonic speeds, just going off the fact that they were used for Concorde aircraft but basically none of Boeing or Airbus's subsonic jets, though again that could be simply a matter of the blunt design fitting into terminals more neatly.",
"> I would have thought that an optimal nose shape for a high speed train would be one similar to that of a fighter jet, with a pointed nose. Trains have a significantly higher length-to-width ratio than any other vehicle, which means drag affects them differently than it does a car or a plane. Also, even the fastest trains in the world are still nearly an order of magnitude slower than the fastest jets, so their requirements are different."
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d5hzwt | How do Homes with grass roofs not rot | I see photos from Northern Europe of homes with grass roofs. As awesome as it is, How does the retainage of moisture not rot the material beneath? | Engineering | explainlikeimfive | {
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"There's a waterproof barrier underneath, either layers of plastic/rubber sheets or concrete. Which is more suitable depends on the climate and how likely you are to get repeated freeze/thaw cycles. Concrete is more durable, but susceptible to damage from freezing moisture in cold climates.",
"OP, are you talking about a thatch roof or a modern green roof? Please share a link with a picture of what your are referring to for clarity.",
"The wooden structure below turf in traditional kammi (gammé) eventually rots and the beams must be replaced from time to time. The climate is quite dry, however, so they can keep for decades. Most Northern Europe wooden structures are similar, the wooden structures are meant to be replaced."
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d5olbj | How do sea mines/depth charges function and cause damage, compared to 'regular' explosives? | Engineering | explainlikeimfive | {
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"They're two different things. But they cause damage in the same way. A **mine** has a \"contact fuse\". If something rams one of the points on its outside with enough force, that point slides into and detonates the explosive in the middle, and it goes off with a huge boom. Bang, dead ship. A **depth charge** has a \"compression fuse\". If you cause it to sink into the water, as it goes down, the water pressure increases. When it reaches a certain level of pressure that is detected using a \"hydrostatic piston\" (think thermometer that gives off an alarm at a certain temperature, but with water pressure instead), the charge detonates. Okay, so that's how they work. Well, how do they damage submarines? They're really effective because water is a whole lot more dense than air is. Have you ever been really close to a firecracker or firework when it went off? You could feel it happen, right? Well that's caused by air being pushed super-fast away from the explosion, and that \"shock wave\" forces a wave of expanding air to hit you. Unless you're way too close, you'll feel that shockwave as a slap, or maybe a punch. But water is WAY more dense than air. Wave your hand through air and it's easy. Wave your hand through water, and it's a lot harder. And the same is true for the wave that shockwaves cause. Shockwaves in water are a LOT harder. They create a lot more impact than shockwaves do in air. So when an explosion-caused shockwave hits a submarine, it's really potentially damaging because that wave causes so much water to instantly slam into that sub that it might crush it or cause some of the welds to break open... and bang, dead sub.",
"Mines and depth charges are just conventional explosives underwater, which is where their targets are. They cause damage in mostly the same ways, by causing shockwaves that tear apart their targets. One major difference though is that while air is easily compressed water is not, and it carries this shock from the explosive very well. Do this near the metal side of a ship and it can easily blast its plates apart.",
"They function the same way, but how they cause damage has some differences, although there's some overlap. Different explosives also work different ways, but from the context of your question, we're talking about explosives that produce a detonation as opposed to a deflageration or decomposition. The the primary difference between explosions in air and water is how shock front acts.. Explosives that detonate produce a shockwave, which is a supersonic area of high pressure that moves outwards from the source. This wave is incredibly destructive. Now air is easily compressible, but water is not compressible. This means that shockwaves from underwater detonations don't dissipate nearly as well as ones in air, which makes underwater detonations propagate faster and over greater distances. In air you also get some damage from shrapnel and heat, which isn't really the case underwater."
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d5wqkj | Would it be possible to divert the Nile to irrigate the Sahara? | Engineering | explainlikeimfive | {
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"Yes. But then the rest of lower Egypt would have to go without the Nile which would make it a desert."
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d5xv3j | Car engine capacity, horsepower, fuel consumption for dummies | Hi, In a process of buying a new car and here is something I simply cannot understand so I was hoping that someone will be able to ELI5 this to me. My current car has 1.6 petrol engine, with 126 HP and it's fuel consupmtion is very high. But some new cars I'm looking at have 1.2 or even 1.0 engine (turbocharged) and they also have 126 or even more HP. I guess that with these, my fuel economy would be better, but am I right about that? Will 1.0 engine be able to drive when fully loaded or when I have to go uphill? | Engineering | explainlikeimfive | {
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"New cars make power more efficiently. So they won’t require as big of a motor, or as much gas to get the job done. As long as you don’t exceed your load capacity you’ll get up those hills just fine.",
"The displacement of your engine is relatively unimportant. Your concern should be more fuel-efficiency, and maybe horsepower. Modern engines can squeeze the same horsepower out of a third of the displacement, all while being *more* efficient. To find efficiency, just google the gas mileage. In terms of horsepower, unless you're driving up a mountain with a trunk full of sandbags, you should be fine - unless you want a little bit more acceleration, but the only real benefit of that is the feel of it. The time when I've personally found horsepower most relevant is when passing on the highway. In a 200hp car, I can speed up quickly and pass. Meanwhile, in a 120hp car, a similar maneuver will take twice as long or more, and the engine will be stressed more.",
"Okay there is a significant difference between classical naturally aspirated engines and modern turbocharged engines. The so called downsizing. The 126HP of the 1.0 turbo engine is only there for a very small band on the rev counter. Usually right at the end of it. If you use all those max HP, you also need a lot of fuel. But due to the lower capacity (correct term is displacement), the engine is more fuel efficient if driven slowly. The fuel consumption is very dependant on your drive style. The 126HP of your 1.6 naturally aspirated engine does not require you to rev as high, the torque comes earlier and more linear with the rev. If you use all those max HP, you might even get better fuel efficiency because the engine does not rev as high. But due to the higher capacity, the engine has a worse *minimal* fuel consumption no matter how civilized you drive. So basically, the fuel consumption is not very dependant on your drive style. Of course, modern engines have more features to reduce fuel consumption like more efficient gearboxes, better fuel injection systems, turning off cylinders on low load etc. So if you drive very civilized and usually without much load, and mostly on flat roads, the modern turbo engine will give you good efficiency. In that case, you will most likely never use more than 50HP anyways. But as soon as you acutally demand the theoretical power from the engine, it will feel more sluggish, nervous and inefficient compared to an engine with the same HP but more capacity. Ok, theory aside, a 1.6 is not a big engine. It's generally speaking still a small engine. It should not have high fuel consumption (whatever you call high) to begin with, unless you drive like a maniac, or there is some technical issue with it. There's websites where people write down their real fuel consumptions for any car and engine there is, you can check what your current car does on average, and what the cars you are looking at do on average. Don't trust the numbers the car makers tell you! Those are not realistic."
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d5yu8w | Why do semi trucks and large vehicles emphasize they make wide right turns and not left turns? | Engineering | explainlikeimfive | {
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"When they turn right at an intersection the turn is much sharper and they cross into the left lane. In left turns they have a whole intersection to turn across and so they don't cut lanes.",
"Left turns are naturally wide on most roadways since you're crossing several lanes. Their turning radius is roughly the same in both directions, they will make wide lefts on one-way roads.",
"In addition to what was previously mentioned , in the US we drive on the right most side of the road. I would assume the sign says “Wide Left Turns” in countries where they drive on the left side of the road.",
"Short answer: Because there are lots of idiot drivers out there. Longer answer: When a large vehicle is making a right turn, they will often have to swing to the left prior to turning in order to complete the turn safely. Because of this, there can be enough space to the right of the turning vehicle that another vehicle could conceivably believe they have enough space to pass on the right (almost never a smart move). However, because the larger vehicle is turning right, another vehicle trying to pass on the right would T-bone the turning vehicle. So the sign is basically saying, \"Don't be an idiot, and please watch for my turn signals.\" Left turns are pretty much always wide turns, because they typically require crossing at least one other traffic lane."
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d6az39 | How does electricity actually move something? | Engineering | explainlikeimfive | {
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"When electricity flows through a coil, it forms a magnet. When a magnet is placed near a coil, and the electricity keeps changing direction, the magnet is therefore spun. This is a very simple motor."
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d6d3jx | How does a company get a very specific, specialized tool or machine made? Particularly if they are the only entity in the world that needs one? | Engineering | explainlikeimfive | {
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"Where I work, we do this on the monthly. We require a tool, equipment or fixture to do a specific job, we write a specification with rough dimensions, material(s) and purpose and then 3D design something which will work in that application. Then machine it. I'll use our most recent as an example. We needed a large spanner for a fixture we designed, but the overall diameter of the spanner end couldn't be more than 10mm larger than the actual bolt (38mm) as it wouldn't fit within the gap. We drafted a basic spanner but with a thin walled head and sent it to our machinist who produced the part for us. 2 hours later we had a tool suitable for the application.",
"You find a fabricator that can do the one-off work you need, or several vendors if necessary. There are a lot of shops that do limited production stuff."
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d6daoa | How does a blood pressure monitor actually measure blood pressure? | The one that wraps around the arm and squeezes it. How is that actually measuring the blood pressure? | Engineering | explainlikeimfive | {
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"It squeezes your arm until blood can’t pulsate into your arm. It starts to let go until blood starts to move. That’s the top number. It keeps on letting go until there isn’t enough squeeze left in the cuff to detect the pulsating blood. That’s the bottom number.",
"Blood pressure is normally measured manually by clinicians since is largely more accurate. When the pressure in the cuff reaches your systolic blood pressure, the top number, your heat beat in your arm can no longer be heard using a stethoscope. When the pressure comes off, certain noises, called Korotkoff sounds, can be heard. This is the sound of the heart forcing blood through the restriction caused by the cuff and represents the diastolic or lower number. The pressures at which the sounds stop and begin again represent your blood pressure. The computer detects sounds as vibrations which it turns into electrical signals and produces a digital read out of your blood pressure.",
"To add to the other response. The cuff applys pressure to your arm which pinches off your blood vessels, the heart then beats and when the blood can't get through the preasure in the cuff is greater than the pressure in your blood vessels, and when the technician hears the heart beat again the cuff has a lower pressure than your heart is producing."
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d6lwxx | Watched a movie about WW1 recently and wonder how the guns on the German airplanes didn't hit their own propellers and damaged them. | Engineering | explainlikeimfive | {
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"Originally, they just put a metal plate on the back of the propeller and let bullets bounce off. Later there was a gear that synchronized the firing with the propellor so the bullets couldn't hit.",
"There is a cam on the prop shaft that activates an interruptor that stops the gun from firing when the prop is in the way. Or some are simply fired by the action of the engine. Plenty of YouTube videos demonstrating this. URL_0",
"It's a synchronizer tied to the propeller. When the trigger it pressed **AND** the propeller is in the right place, the gun fires. The pilot can hold the trigger down, and the gun fires every time the prop won't be in the way, up to the speed of the machine gum mechanism."
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d6q917 | -how does a submarine (or whale for that matter) displace hundreds of tons of water which also has incredible pressure on it seemingly effortlessly? | Engineering | explainlikeimfive | {
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"Whales move their tails, or when required the whole body in a wave like motion. Moving the head up will cause water to fill that gap, then they push down, and the water is forced backwards. This raises their body, which then causes water to rush into the gap, so they press down and the water is propelled backwards. This, according to Newton pushes them forward in the \"equal and opposite reaction\". Subs do it by being the right shape, and using nuclear or very powerful diesel engines to spin a propeller. They basically work the same as old planes did.",
"It's not effortlessly. Submarines have a nuclear reactor onboard to produce the power required. Also, the Ocean is an open container. While there is pressure, there is no restriction to fluid movement."
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d6znbc | What is the difference between centrifugal and positive-displacement supercharger? | Engineering | explainlikeimfive | {
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"text": [
"A supercharger is just a pump. A centrifugal pump uses the inertia of air in order to move it. Basically, it spins and uses the high speed of the now-spinning air to send it flying out in the direction it is supposed to go. Positive displacement pumps use a physical object to directly push air where it is supposed to go."
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d70rid | Why do manual transmission cars turn off if you come to a complete stop while in gear? | Engineering | explainlikeimfive | {
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"TL;DR version: The rotational speed of your tires is locked to the rotational speed of the engine, so if one is at zero RPM, the other has to be at zero RPM, unless you disengage the lock (clutch) between the two. The major differences between automatic and manual transmission cars is the device that connects the engine to the transmission, and how they work: Manual Trans, Clutch: two solid discs are pressed together, connecting the output of the engine to the input shaft of the transmission and creating a solid lock between the two at a 1:1 ratio; i.e., for every 1 turn of the engine, you get 1 turn of the transmission input shaft. The clutch is disengaged by depressing the clutch pedal to, separating the two discs so the engine turns freely irrespective of the transmission. Auto Trans, Torque Converter: an impeller driven by the engine output turns inside a fluid filled casing, when the fluid pressure is sufficiently high enough, a turbine connected to the transmission input turns with respect to the impeller from the engine, giving you the same 1:1 ratio as a manual transmission at full pressure, or 1:x ratio where x is dependent on the fluid pressure inside the casing. So why does a manual transmission car stall? Every engine has a stall speed, or an RPM where the engine no longer produces enough power to overcoming the pumping loss of turning the engine. The stall speed varies from car to car, but most have a stall speed between 300-750 RPM, for the sake of this example, we'll say 500 rpm. As a manual car slows down, with the clutch engaged (pedal full up), the clutch is locking the engine RPM and wheel RPM together at a ratio determined by the what gear the transmission is in. As you come to a stop, your wheel speed is low enough that the engine RPM approaches the magic 500 RPM, you'll feel the car buck and the engine will run VERY roughly, you feel the engine start to stall. The engine isn't just fighting its own pumping losses, it's fighting the resistance of your wheels and entire drivetrain while trying to turn. Once the car slows below that point where the wheels are causing the engine to turn slower than 500 RPM, the engine stalls and ceases to produce power completely. To prevent this, you have two options; 1 - depress the clutch, breaking the lock between the engine and transmission input, you can stay \"in gear\" because the engine is no longer connected to the transmission input, or 2 - (recommended) depress the clutch, shift to neutral, and release the clutch, this keeps the engine output and transmission input locked together, but in neutral, the transmission input isn't connected to the transmission output/drivetrain/wheels, so the engine is allowed to turn freely. This is the recommended option as it reduces wear and tear on the clutch throw-out bearing, which is the device that separates the clutch plates when the clutch pedal is depressed. If you are quick, you can prevent a stall, when the engine chokes out, by quickly and fully depressing the clutch and giving it some gas at the same time, if done before all rotational energy in the engine is lost, you can get the engine running over stall speed again. So what happens in an automatic under the same conditions? As the car slows down, the wheel RPM brings the engine RPM close to its stall speed, just like a manual. However, the automatic transmission begins to reduce the fluid pressure inside the torque converter, which allows the impeller (engine output) to spin at a different rate than the turbine (transmission input), all the way to a minimum pressure point where the engine can continue idling even when the wheels are stopped because there is minimal resistance in the torque converter. Most automatics will begin to reduce that pressure at 1000 rpm and continue to drop the pressure to until there is a 1:0 ratio between input and output at engine idle speed, which is typically 100-200 RPM over stall speed. I've oversimplified how autos works slightly to make the explanation a bit easier to digest. Automatics vary wildly in how they regulate torque converter pressure, lock up, and shifting, but it's mostly irrelevant to understanding the question at hand. URL_0"
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d7g3mi | how does a stirling engine works? | Engineering | explainlikeimfive | {
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"Hot stuff wants to take up more space than cold stuff. If you put something that changes volume a lot based on temperature, like a gas, and put it into a container and don't give it anywhere to go and then heat it up, it will push on that container to try to take up more space. If you make that container able to expand - with, say, a piston - it will push on it and force it to expand. If you then cool that gas off, it will contract. Again, with nowhere to go and not able to pull in additional gas to fill the empty space, the gas will just take up less space. The pressure outside of the container will be greater than the pressure inside, so the [hotter] outside air will push on the outside of the container and squeeze it. The air outside is *always* pushing on the piston, it's just that the hot gas inside is pushing harder, until it cools down and then isn't pushing harder. And heat will go from where it is to where it is not. So what you do is add a heat source (like a flame) on one side of a chamber with a piston in it, and a small opening next to the flame. As the piston moves back, it sucks hot air into the chamber, and then closes the hole so that air can't get in or out. The hot air is now taking up all of the space it can inside of the chamber, with the piston all the way back and the chamber as big as possible. The hot air heats up the walls of the chamber, which in turn heat up the air around the outside of the chamber. This is helped along by heat sink fins that increase the surface area so more outside air comes into contact with the hot metal of the chamber. The air inside the piston is now less hot than it was. As a result, it wants to contract and take up less space inside the chamber, and does. Since the chamber is closed, no new air can fill that empty space. Instead, the air outside of the engine is pushing harder and so it pushes the piston back inward, squeezing the space inside the chamber, and squeezing the air inside. Squeezing *would* heat the air back up, but instead the hole opens up and the warmish air is pushed out of the chamber. The piston is attached to a flywheel which holds onto the momentum of the piston and keeps it moving. So the piston starts pulling back out again, which sucks in more hot air from right above the flame. The hole closes again, and the whole cycle repeats until a force is applied to stop it or the flame stops. More efficient stirling engines don't just get rid of the warmish air, but move air around through multiple chambers, sometimes with multiple pistons that extract as much of the heat from the air as possible."
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d7vdlr | Why particle accelerators exist, and what exactly do we benefit from them? | Engineering | explainlikeimfive | {
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"The stuff we see all around us is generally the most stable stuff that can exist. Any really exotic particles decay very quickly so they don't last long enough to exist anywhere that we can find them. But a lot of those particles can teach us a lot about how the universe works. The universe is defined by how particles interact, so if we can find some really strange ones and see what they do, it'll tell us more about how the laws of the universe work. So how do we find them? Well, you shove a metric ass-load of energy into some ordinary particles to energize them into those really unstable particles. *All* particles are made out of energy. The universe is made out of *fields* that exist everywhere at normal background levels of energy. If you put a bunch of energy into one spot in that field, it starts interacting with other fields in certain ways. So, for example, if you put a bunch of energy into the electromagnetic field, you get a photon! If you put a bunch of energy into the electron field, you get an electron! And that little packet of electron energy interacts with the electromagnetic field so that it can trade energy into it to make a photon, or photons can be absorbed into the electron field to do stuff to electrons. Some particles don't seem to exist in normal interactions because the energy needed to make them don't normally happen. Like the Higgs field, which exists everywhere but Higgs particles do not. There's just not enough energy gathered up in one spot in the Higgs field to make a Higgs particle. When enough energy *does* end up in the Higgs field to make a particle, that particle very very very quickly falls apart and the energy ends up in other fields. But we want to study the Higgs field! And the best way to do that is to look at Higgs particles! (The Higgs field is involved in giving particles mass.) What we have to do is make our own Higgs particles by introducing a ton of energy into the Higgs field. What's the best way to shove an ass of energy into a field? Make some particles go *really* fast and then smash them into each other! If they smash into each other hard enough, the energy sort of bleeds over into other fields and if there's enough, it'll form new exotic particles that we can measure and study for the fractions of a second that they exist in the detector.",
"> Why particle accelerators exist Because humans make them. To accelerate particles. Because otherwise where would we get the really fast particles we want on demand? > what exactly do we benefit from them? There are bunches of different applications. Radiotherapy is one major use, where accelerators are used to make the radioisotopes used to do things like help kill cancerous tumors. Another use is ion implantation where ions on one element are accelerated to be embedded into other solid targets, changing their physical, chemical, or electrical properties. This can be important in things like semiconductors, or things like toughening steel or producing stronger metal surfaces on something like an artificial joint that must withstand a lot of wear. And then of course there is the research applications. This can be directly practical stuff like material sciences where organizations are researching different materials to make various products better, or it can be the highly theoretical high energy physics where we are gaining a greater understanding of our universe. Such knowledge may not be immediately, directly applicable but a greater understanding of how everything works has been a huge benefit to humanity so far."
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d7wizp | how we are supposedly wasting water if we leave the tap running if all water is just re-treated and put back into the water system? | Engineering | explainlikeimfive | {
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"A bunch of energy went into making that water good to drink, and then some more energy went into moving it to your tap. If all it does is go back to the water system then that energy was for nothing. Saying \"you're wasting water\" is a shorthand way of saying \"you didn't honour the effort put into bringing that water up to drinkable quality\".",
"You are wasting treated water that will go out with wastewater to be treated again. So all that clean water going into the sewer will take a lot of energy to be made drinkable again.",
"* the more water you waste, the more of it that has to be treated, the higher the cost * the water is put back into the system *for someone else downstream to use*...it is no longer available to be used by your community, and if water starts to run short, it costs more * using more water does not make it rain more, which is where your water ultimately comes from",
"Depending on the area, where you get your water from might not be where you put it after you're done with it. For example, if you get your water from an aquifer and then it winds up in a river (or even just on the ground), it might not make it's way back into the aquifer. Certain sources of water can take a long time to replenish so if the source you're drawing from isn't where you put it when you've used it you can actually drain the system.",
"Most places treat water and then let it into a river or the ocean. Very few places put it back into the water supply.",
"I am no environmental alarmist and often question prophecies of doom, so don't misunderstand my reasons for replying, but it seems like you think the water is being treated and then sent back down the same pipes. It isn't. In most cases, waste water is treated, but only so that it can be \"returned to the water cycle,\" or in other words, poured back in to a river or ocean. In some areas, various institutions utilize water reclamation, but that water is used for things like watering the grass in city parks or agriculture; it doesn't return to your tap. Your tap water is still coming from rivers, or aqueducts, or pumped out of the ground. So with that said, generally your watershed will only collect so much fresh water per year, and your dams will only hold so much as a buffer, and the aquifer only replenishes so quickly. It is definitely physically possible to run low on fresh water reserves. The reasons people go nuts over the situation are: 1. Biologists, ecologists, and the like are notoriously bad at economics. They ignore the fact that humans are pretty good at innovating, hence why all the population bomb projections to date have failed miserably. 2. Governments make it difficult to innovate, so certain areas can develop long-term problems. 3. Alarmism sells."
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d80zi8 | if solar panels convert solar energy that would otherwise be lost as heat into electricity, will mass usage cool the earth? | Engineering | explainlikeimfive | {
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"All energy consumed by humans ends up as either light or heat. This happens because energy cannot be created or destroyed, but heat energy once it is very spread out is rather useless. This means that any solar energy we collect and use, whether it opens doors or runs computers, will dissipate as heat and light. That's more or less exactly the same thing that happens to sunlight, but with an extra step in the middle where we use that energy to do things before we let it go.",
"No - because all the energy that the solar panels convert into electric energy would then be converted into heat when it is used. Lights, for instance, convert much of the input energy into waste heat, and the energy that is made into light becomes heat once it is absorbed by surfaces or atmosphere. The light that escapes into space is completely negligable. Same with all other appliances. The exceptions, like the electrical energy that reduces aluminium oxides into aluminium, are also negligible on a global scale. Large scale solar will actually warm the earth - slightly - because solar cells, in most cases, reflect slightly less solar energy than the land surfaces they might cover."
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d83jjb | In a PN junction diode, how do the holes migrate from P to N? Don't the holes in the P type just get filled by the free electrons from the P type? | Engineering | explainlikeimfive | {
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"Holes is a logical concept unlike electrons. An atom is neutral so \"absence of electrons\" is termed as holes. When we say holes moves from P to N, we actually say that electrons move from N to P where earlier there were holes in P(lack of electrons) and now there is no lack of electrons so no holes whereas in N there was no lack of electrons but now there is as electrons have moves from N to P so now there are holes in N, so we say that holes moved from P to N Imagine there are 2 buckets one has a ball and there other does not. The bucket that does not have a ball is a hole. If we move the ball from one bucket to another the ball moved from one bucket to another and the hope also moved from second bucket to first."
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d87vwg | how Stephen Hawking’s chair worked? | Engineering | explainlikeimfive | {
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"text": [
"He has a sensor on his cheek, one of the few muscles he still has control of. The computer shows a list of possible words like intellitext prediction and slowly highlights each one in turn. When he wants that word, he twitches his cheek. He can only select a few words a minute. All the live speeches are recorded ahead of time and just played back."
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d8bqnk | Why do people put resistors for LED lights, when they can function when connected directly to a power source? | Engineering | explainlikeimfive | {
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"A LED has a forward voltage, if your power source is below that voltage, you get very little current, and the light doesn't turn on. If you're above that voltage the LED doesn't limit the current, and burns out instantly. If you're very close to that voltage, you might get away with relying on the resistance of your wires and traces, but that's a rather extreme cost cutting measure, and if you're running on something like a battery with variable voltage, doesn't give good results. A \"white\" LED might have a voltage drop of 3 volts. If your power source is 5 volts, then there is a 2 volt drop across your resistor, if you don't have a resistor, that 2 volt drop is effectively short circuited. Maybe your power source can limit the current to a safe number, maybe it can't. Adding a resistor to the LED lets you control that current, a 20 ohm resistor would drop the current to say 100mA. There are more efficient ways to drive LEDs, but you always need to control current somehow, so you'll still have a very low value resistor in series with the LEDs, so your driver knows how much current is flowing through them.",
"If the flow of current is like the flow of water, then an LED is like a super efficient watermill that has very little friction. This mill will spin so fast that it will destroy itself very quickly, so you have to add some brakes to slow it down (the resistor). It will run fine for a while even if you don't add brakes but it will wear itself down quickly. Another thing is that LEDs suffer from \"thermal runaway\": when they start to heat up, they start to draw more current, and this causes them to heat up even more, drawing even more current... and soon they will be drawing way too much current, overheating, and burning out. A resistor doesn't have this issue, so it will keep the current in check even when the LED or the resistor start to heat up. In other words, yes, an LED can work fine connected straight to a power source of the correct voltage, but even then they eventually become unstable and draw too much current, and a resistor can take care of this problem.",
"A resistor reduces the total energy flowing through the device, limiting the brightness and preventing burnout.",
"You can connect an LED directly if the voltage of your circuit matches the forward voltage of the LED. For you average red LED, connect less than 1.6v and it won't light up and no current will pass. < 1.8v it'll light up and pass a small amount of current ( < 5mA). Put if you connect more than 2.2 volts, the current will be a lot and burn out the LED. So if your circuit is around 1.7v, you can connect directly. If more than that you need to use a resistor to bring the voltage down, but then you are wasting energy with the resistor. If you have a micro controller in your circuit, you can connect led directly but then flash it really fast and to a human it'll look like it's on, but it won't pass much current and burn out.",
"First -can you provide a reference - or how you have come to believe your statement \" **they can function when connected directly to a power source** \" -- this is not accurate - if (a big if) the source is only capable of specific voltage ad current ( below the spec of the LED) will this work.. LEDs are not linear - for example, doubling the applied voltage results in much more than doubling the current through the LED. So small changes in the applied voltage can lead to failure of the LED. ( if the LED is rated for 1.1V and 200mA - it will probably die if 1.2 or 1.3V is applied to it) The addition of the Current limiting resistor - ensures that only the amount of current that the LED can handle WILL flow through the LED - and are usually used when the source voltage is significantly higher then the LEDs rated voltage. There are LED driver circuits - specifically made to drive LEDs in their normal operating region, these typically do not need resistors, they are more complex, cost more, but yield much higher efficiency."
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d8cob6 | Why do car doors have those “checkpoints” when you open them that causes the door to swing back if you don’t get it just right? | Engineering | explainlikeimfive | {
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"There is a spring-loaded wheel with notches at specific points. It is good at holding the door steady with no effort by you, but the side effect is that it pushes the door *away from* spots between the steady spots.",
"Haha, you inadvertently guessed the correct name for that part. It's actually called the door check. All it is designed to do is hold the door open at a certain point to resist the door from swinging open or closed. Some are a lot stronger than others, and they all wear out over time.",
"My dad drove a ‘74 el Camino. Those doors were heavy as hell and had no stopper. Hitting the doors was really common. What you’re seeing is a “fix” to that."
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d8ehvn | How does Ground work in low voltage / DC electronics? | From the first introductions I had to electricity as a child, I thought that I understood what a complete circuit was. I actually took classes about high voltage electrical work, residential and commercial AC current applications. I've also done a lot of my own mod and repair work on home electronics and I've installed a few car stereos over the years. But for the life of me, I can't understand why ground is used as the return for almost all low voltage circuits. Obviously, you want Hot (-) to be insulated and controlled, but ground (+ ...?) is usually just hooked up to any large bits of conductive material. This is obviously a protective measure but if ground can just be the body of a car, or an RF shield, how does that allow the circuit to be complete without causing excessive resistance? | Engineering | explainlikeimfive | {
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"The term \"ground\" isn't the complete name, it's is called \"a common ground\". What they mean with it is that for everything in the electrical appliance, that is considered the 0 volts. Why is a common definition of 0 volts necessary? Some appliances use only 0V and +5V. Some use -12V, 0 and +12V. To calculate the various parts of it, you will work with sinusoids[sp?] and offsets. To make life easiest, they picked -12V and +12V instead of 0V and +24V: You don't need to take any offset into account in your calculations (after all, 12 x sin(x) fluctuates between -12 and +12 and it is the same sinusoid as 12 * sin(x) + 12 fluctuates between 0 and 24). So, why do you sometimes need a common ground outside the appliance? Because you are receiving electrical input from other sources. The easiest example was the computer and the printer: If you didn't connect the common ground outside the appliance and the plugs were inserted wrongly in the wallsocket / powerboard, you could get an electric shock if you touched the metal of the printer cable connector (yes, grandpa speaks, this was way before USB and plastic cables): If you had a voltage seeking screwdriver with a light in it, it would light up if you touched the connector. Turning the power plug and suddenly it all worked fine without shocks or lighted up screwdrivers. A less obvious example was your bike with a dynamo for the light (yes, grandpa again): The dynamo is connected to cable which goes to your light, the rotation of the dynamo generates the electricity but why only one cable? Because the frame of the bike is the common ground: You only need one cable from the dynamo (less things to break) and the return path is the frame of the bike. Same with cars, same with radio (where the common ground is actually the earth)."
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d8f7im | Why does the power go out for a few minutes and come back on a couple times before a much longer outage? | Engineering | explainlikeimfive | {
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"A lot of power outages happen because a branch falls and hits the power lines and short circuits it. It's enough to trip the fault protection circuits and turn off the power lines, but all that power through a branch is usually enough to burn it to pieces and it stops being a problem. So they're programmed to put power back on a few times to see if it's just a branch that needs a little more juice to burn off or if it's a problem that will actually need people to go fix."
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d8ftn8 | how are the lights on a Ferris wheel powered without the wires twisted? | Engineering | explainlikeimfive | {
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"They use a [slip ring connector]( URL_0 ) or similar rotating electrical connection to feed power form the stationary generator to the rotating wheel's electrical circuits.",
"Imagine a record player, but turned on it’s side. The stylus arm has a carbon brush instead of a needle and the “record” is the hub of the Ferris wheel. Electricity is transmitted down the arm (which is attached to one of the supporting legs) through the carbon brush to where it touches a thin metal strip on the hub. That strip of metal is insulated to prevent electricity from charging the entire structure, and has the wiring for the lighting attached to it. It’s an easy way to transfer electricity from stationary to rotating objects. The alternator in a car operates on much the same principle."
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d8oovb | Where does the electricity being produced by power plants go when the power goes out or when there's too much being produced? | Power plants produce power, and they create enough electricity to meet the demand of the consumers, but when the power goes out, where is all that electricity going? | Engineering | explainlikeimfive | {
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"The power plants automatically start creating less electricity. The current power grid has almost zero energy storage. All power must be used as soon as it is created. The only significant energy storage is in the inertia of the spinning generators themselves. If demand increases or decreases, the generators start to slow down or speed up, and someone at the power plant (or an automated system) has to adjust the \"gas pedal\", burning more or less fuel to keep the generators spinning at constant speed. There are a few locations where energy can be stored, especially \"pumped hydroelectric storage\" facilities that consume electricity to pump water up a hill, and then release it downhill to create electricity when needed. But these contribute just a tiny fraction of a percent to the power grid. This issue of storage is a big problem for the switch to future renewable energy, since wind and solar vary unpredictability, and can't be easily ramped up to meet demand. As a result, people are thinking seriously about the \"grid energy storage\" systems /u/Red_AtNight describes, including gigantic batteries or bigger pumped energy storage systems. But that's for the near future. Right now, with today's power grid, you can't bank electricity.",
"To tag onto the already good answers here, if a section of the grid goes down, the voltage on the remainder of the grid might go up slightly until the power plants adjust their output. We're talking a few volts at most.",
"When the power goes out its usually due to the grid (which is one big electrical circuit) being broken in some way. Thus no energy flows at all. Most power plants have a system that slows or stops energy production when this happens. Similarly, the plant's equipment that senses a power outage can sense how much the grid is using. Electric companies also closely monitor how much power is used and have several equations to estimate power usage on a given day. They produce according to the estimate, then adjust according to the live demand they measure. In some cases, some electric utilities will store the excess power (which is really inefficient) in either batteries or capacitors until it is needed.",
"If a major power outage occurs, all power plants have procedures to start idling their plant. In steam powered plants (Mostly coal, oil, gas and nuclear), they redirect excess steam to their cooling towers and begin turning down steam production. They have to keep enough on standby to prepare for when the power demand comes back. Most other power plants can idle rather easily. Gas turbines just lower fuel flow. I don't believe solar voltaic or wind plants need to do anything. Electricity is only generated when there is demand. A power plant can't create more electricity than there is demand for. There has to be something on the other end of the wire. What can happen is at steam power plants, that they create too much steam. And as I mentioned above, they send that steam to cooling towers, as they can't use it and it's dangerous to have too much steam pressure."
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Subsets and Splits