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f1qw76 | Household electricity is delivered at different voltages and frequency in different countries around the world. How did these multiple standards arise? Is one system better than others? | Engineering | explainlikeimfive | {
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"Somewhat haphazardly is the answer to how. It was really what was thought best at the time early on, and developing countries tended to use the system from their colonizers or whomever was hired to come in and advise on the electrical infrastructure. As to which is better, that is a subjective thing. Better at what and how? For example Europe uses a higher voltage than North America, but the original reason was to use smaller wires and so less copper. North America has lots of copper, so those countries saw no problem with thicker wires. Source: Electrical Trainee",
"The 50 and 60 Hz thing was just something that happened. Different power plants produced power at different frequencies, but as local grids were merged into larger grids, they all had to be brought to the same standard. For power transmission, more voltage is better, since it means you can transmit more power with less current - that is the amount of electrons flowing through a cable. More current means more power being lost to resistance before it even gets to the plug, and that lost power can heat the cable and potentially lead to an electrical fire. That is why you can safely draw twice as much power from a 220 or 230 V outlet compared to a 110 V outlet using equal cable diameter. However, higher voltage also means that cables and plugs have to be insulated better, since the higher voltage can jump a longer distance. Higher voltage plugs are usually built in a way that the contacts are recessed into the wall, like [this British]( URL_1 ) or [the German model]( URL_0 ). This is to prevent that the plug makes contact while there's still blank metal sticking out of the wall. Edit: It's worth noting that regardless of what kind of power you get at the wall, the power transmission itself happens at much higher voltage. There's also a great series on [YouTube]( URL_2 ) explaining how the grid works if you want to learn more.",
"Multiple standards arose because they were developed locally by many different companies each with there own standard. Initially, in the late 19th century, you hade AC and DC systems and different frequencies and voltages. The system was often per city and different cities could have different standards. In the 1910s- 1920s you started to have national standards but the government. Large counties that produce and export electrical equipment spread their standards. The most difference today is the plugs and not the voltage. You have 220-240V 50Hz and 127-100V 60HZ. For most stuff, the equipment work in one range and equipment that converts to lower voltage like computers the can hance the whole 100-240V range and both 50 and 60 Hz. & #x200B; The main difference between 110V and 220V is the current you need of the same power. Power is voltage\\* current so the current is halfe for the same power at 230V vs 110V. Higher current requires thicker wires so more metal is needed. Higher voltage requires better isolation. But the total result is that wire to transport the same power is cheaper at 220V. 110V might have lower electrocution risk but it is not a major difference. There is also another part and is a number of phases. In North America, you often have a single-phase 220V to a house that a transformer converted to 110V for low power stuff but you have the full 220V single phase for stuff like electrical stoves. In mainland Europe, it is common with 3 phase 400 V to houses. You have 230 V between each phase. Connect high power stuff to 3 phase 400 V require a lot of thinner wires then 1 phase 220V. This is very common where you use electrical heating for houses. In North America, 3 phase is used for industrial use but not households."
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"https://www.youtube.com/watch?v=v1BMWczn7JM&list=PLTZM4MrZKfW-ftqKGSbO-DwDiOGqNmq53"
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f1ulix | Why do wheels shake at specific speeds when a car’s alignment is off? | Why is there a sweet spot (50-60mph) where a vehicle will shake when the alignment is off? How does the shaking start around 50/55 and get better after going over 60? | Engineering | explainlikeimfive | {
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"It is caused by harmonics. The wheel actually shakes the whole time you're driving, but there is a certain frequency of vibration that causes harmonic resonance, and the fact that a vibration shows up much worse at certain speeds is a good indicator that you have harmonics playing into the vibration mix. What happens is that as the tire rotates with either a misalignment or damage to the tire or wheel itself, it vibrates. As the speed increases, so does the frequency of the vibration. There is a certain point at which that frequency will cause sympathetic vibrations in other parts of the car, and that's what you're feeling when it really shakes at a certain speed, and you get out of that harmonic range when the vibration stops at a higher speed."
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f1w6so | How do house builders avoid weather damage while the buildings are under construction? | Whenever I see unfinished houses in a downpour all I can think about is all the places water is seeping in to cause damage. How does the potential damage get mitigated by the time a roof and siding gets added? Does the wood really just dry out enough in the sun that it is not an issue? | Engineering | explainlikeimfive | {
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"Depends on what phase of construction they are in. In new construction, there is rarely any need to keep things dry during the framing phase. By the time you need to have things kept dry you'll generally see a house-wrap and windows installed as well as a roof (either the final roof, or an underlayment that will stay there for the long run, but is temporarily serving as a water barrier. The crudest rule is that if you're gonna put up insulation and sheetrock the house should be dry and be able to stay dry. Anything prior to that and you'd be ok with some moisture as long as it has a chance to dry out.",
"you build them let it dry out. Dupont Tyvek is special sheet that allows moisture to go one way but not the other."
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f23jiu | How is the structural integrity of very old buildings, bridges, etc. tested to ensure suitable use by people, cars, etc? | Engineering | explainlikeimfive | {
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"Civil engineer here. For old buildings, if they have the architectural plans then they can usually derive all the mathematical info they need and account for decayed members. If they don’t, they’ll try to generate one and usually schedule renovation. That’s mainly for old buildings like houses. Bridges can be tested for a variety of factors - they use a lot of deflection analysis, so like seeing how much a bridge will sag under a given load, or how much it’s cables (assuming suspension bridge) extend under that load. A lot of visual analysis occurs as well - cracks, rusty rebar, split timbers can all indicate the current state of the structure and can be accounted for in projections of how long it will last based on modeling. Other methods can also be used to look for wear *inside* a structure, like using electrical pulses or vibration feedback on concrete. Also, because building codes are so meticulous and regulated, a good inspector can actually refer to old building manuals and practically determine from those what kind of design life a structure was built for. It’s a fine-tuned skill and one of the aspects of civil engineering that is highly valued because of the experience it requires. My timber design professor was such a knowledgeable guy that he was brought in to inspect why a frame holding a very expensive painting fell, and it didn’t even take him long to figure it out. Honestly it’s pretty cool. Good question!",
"The most basic is looking for deterioration, looking for where corrosion has occurred, bricks fallen mortar cracked, and can get a general idea of the condition. Tension cables can be tested for how much tension they're under, and can have electrical current run through to check for corrosion.",
"On the back of this, are they periodically checked? A bridge in Nottingham has been declared unsafe as they found rust in the support s or something, I’d like to know how and why they found out.",
"I'm a Civil Engineer too from Brazil, let me just mention something. It's very usual here to have old buildings which you haven't got the structural plans to, and you can't guarantee the original builder followed the codes of the time (they don't even follow it now.) So one technique that's particularly interesting to test the strength of the concrete is that you can cut a cilinder out of a few columns (there are places in the column that you can do this safely) and test that cilinder's strength on a concrete press. This tells you how strong the concrete is, and you can close the hole with stronger concrete later. This is called destructive testing, and there are many non-destructive methods available, but this is a fairly straightforward as many labs would have a concrete press. Of course this doesn't cover the steel reinforcement, but as was already said that can be evaluated by other techniques.",
"\"Okay Joe bring one more elephant up here\" crash. \"Yup that bridge was only 4 elephants strong\"."
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f283op | How are structures able to be built such as oil rigs or bridges where the foundations are hundreds of meters deep in water? | Engineering | explainlikeimfive | {
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"There are devices called caissons that they construct where the pilings need to go. They are hollow boxes/cylinders that extend from the bed to the surface and the water is pumped out, and workers go down and install the foundation. They then remove the caisson. This is obviously not for water hundreds of meters deep, though I think they don't build foundations that deep. *edit*: further investigation shows that they can make concrete blocks that they bring down and simply rest on the sea floor. Probably other methods but I gotta get to work.",
"Simple. We make really long piles that are driven to the sea bed. Then the foundation is made on top of those. It sounds too simple to be true, but that how it is. But even the deepest bridge foundations aren't actually that deep. Some tens of meters, which is a lot when it comes to water. But oil rigs can also just float if the the water is really deep. As in deep enough that making foundations isn't practical. There are numerous ways to anchor and stabilise the rig a floating rig, which can be moved and reused.",
"Most drilling rigs are actually floating on the surface. They are meant to be moved around frequently from job to job drilling wells for production platforms. They have complex ballast systems that let water in and out to account for the weight of the rig to keep her afloat. & #x200B; Production platforms, depending on the location, are more likely to be fixed to the seafloor. They would typically be built adjacent to land somewhere in a drydock and then floated out to the field and dropped into place. & #x200B; [ URL_0 ]( URL_0 )",
"It’s really interesting. The will drive sheets of steel into the river/lake bed and make a water tight box around the area to be excavated. Massive pumps are used to keep ground water down. Then you’ve basically got an air pocket around the area you want to work. I’m not an engineer I’m just a labourer that works on these types of jobs. There is a lot more to it obviously but that’s the basics.",
"I was told that to build hydroelectric damns they would temporarily reroute the river, I assume they do it by dumping tons of material in the river to block it off and reroute it. They then build the damn in dry conditions and when it’s ready they destroy the initial barrage and let the river flow back to it’s original course, hitting the dam. Not your initial question but still related and interesting.",
"The tallest built in my area is the Troll platform, that's 472 meters. Way taller than empire state building and taller than Petronas tower. It was towed to sea and sunk and now produce gas with only the top above sea level. Imagine towing something way larger than empire state some 100s of miles to sea, it was an amazing view. They used concrete and built it from bottom and kept pouring the concrete. Katie Melua held a consert in one of the legs once."
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f2espo | How does the buzzsaw that can sense flesh sense flesh? Link in description | URL_0 I saw this today and I'm so confused. The resistance difference between a hot dog and wood feels like it should be within a rounding error. I'm curious about what kind of sensor would be used here. | Engineering | explainlikeimfive | {
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"The saw is running an electrical current through the blade as part of a safety system. Flesh, (including but not limited to hot dogs) conducts the current upon contact with the blade, which triggers a braking system. Any material that conducts electricity at a lower resistance than wood will trigger this system. (Once had a stray staple in a board cause the brake to engage, as the blade sensor detected a conductive material contact the circuit). Very expensive staple. Hope this answers your question. These tools are a great addition to a wood shop as most injuries happen on table saws.",
"> The resistance difference between a hot dog and wood feels like it should be within a rounding error. These saws are not detecting resistance. They are detecting electrical capacitance. They work the same way the touch screen on a cell phone works. There is an electric field sent through the sawblade. When something with a significant electrical capacitance (like a human hand, or a hot dog) comes in contact with the blade, the electric field is changed. Control circuitry within the saw detects the change and triggers the stopping mechanism.",
"Try using a piece of wood to type on your phone. Did it work? Same basic technology can be applied to a sawblade."
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f2kb18 | How can a scale be both sensitive enough to weigh light items, like dollar bills, accurately, yet also handle weighing heavy things, like rolls of coins? | Engineering | explainlikeimfive | {
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"I think that‘s the thing, you focus on very small things, where you need to be accurate on floating points, or you can measure heavy things. That‘s why you normally need to use a different weigh if it comes to very light things."
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f2l0c6 | What are the black rope-like things sometimes put on roads across lanes? Are they counters? How do they work? | Not sure if this is everywhere, but in the US occasionally these small ropes are affixed to the roads across the lanes. I guess they're used for traffic counting or something but I don't know how they'd work. Like how does it know how many axles you have? or what happens if two cars drive over the rope at the same time? Or what determines how long to leave it? | Engineering | explainlikeimfive | {
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"Yep. Those types are usually hollow rubber hoses sealed off at one end and attached to a pressure sensor at the other end. When a car drives over the hose it increases the pressure in the hose slightly triggering the counter to go up 1. If two cars go over at the same time it will probably count it as only one, but the frequency of that happening is low enough that they'll still get a good idea of how much traffic is going by."
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f2qccw | how do power plants ground sudden excess of power? | Let's say a whole neighbourhood or an industrial area got disconnected from the network. How would a power plant / network deal with the sudden excess power, and what's the biggest issue in handling it? Let's assume that no immediate storage like batteries is available, only things that need some time to start working. | Engineering | explainlikeimfive | {
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"In the very short term, all the moving parts in the generators act like a flywheel to store energy. If excess power is being generated, all the generators speed up slightly, and the grid frequency rises. Some power plants can be set up to monitor the frequency and automatically increase or decrease their output to compensate. You can see the changes in the UK's power grid frequency [here]( URL_0 ).",
"When there is a sudden excess of power the load on the generator suddenly drops. This makes them rotate faster. The excess energy is therefore used to spin up the turbines and generators instead of powering devices. The entire power grid will increase the frequency as a consequence which also increases the speed of all syncronous three phase motors in the grid which helps sink some of the excess power. There is then several mechanisms which gets triggered either automatically or by grid controllers to reduce the power generation and reduce the frequency of the grid back again. Typically they would close valves reducing the flow of steam or water to the turbines. It is also possible to disconnect solar panels and wind turbines or to power up high voltage transfer cables to other grids. Some places there is also pumps available to pump water to higher ground to be used later in hydroelectric power plants. Eventually they will get the frequency down and then actually bring the frequency lower then normal for a bit to compensate for the time the frequency were too high."
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f3lai8 | Why does bridge ice before road? | Engineering | explainlikeimfive | {
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"Bridges are elevated. Meaning cold wind blows not only over top of the road but also below the road, freezing the water more quickly."
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f3lvd6 | What caused houses to go from having crawl spaces underneath to being on a concrete slab, no space underneath? | Engineering | explainlikeimfive | {
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"Slab-on-grade is the cheapest, simply put. Most houses are built by larger real estate developers these days, rather than smaller home builders, and profits are the #1 concern.",
"slab houses are super cheap to build. They became very popular in post-war mid-century modern style houses like the ranch. Building during that time needed to be fast and inexpensive. It also had to become more efficient in the use of materials as the demand for post-war housing strained the supply of building materials. You still see basements in the In the North and North East but outside of freezing climates basements become and unnecessary expense."
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f3mujd | How are diamonds shaped and what happens to the bits of diamond that are cut off to shape them? | Engineering | explainlikeimfive | {
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"Diamonds are shaped by laser cutting and grinding. Broad strokes are done by lasers, and then grinding wheels are used to finish the diamonds. Removed material in the grinding process becomes diamond dust and is useful as an abrasive.",
"It's called cutting. It's more like grinding or sanding though. They use a wheel with tiny diamonds on it. As to what happens to the bits that are cut off, they're used for industrial purposes. like diamond cutting devices. They're used for cutting or polishing anything very hard."
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f3op42 | Why aren't sidewalks designed like roads? | Im not talking about asphalt vs concrete, im alluding to the flat nature of sidewalks. Why are they not slightly sloped to prevent massive puddles like roads. & #x200B; Why is it that pedestrian pathways has not seen much change/modernization? | Engineering | explainlikeimfive | {
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"Mostly because the benefits are outweighed by the cost. A few puddles on a sidewalk are not likely to cause fatal accidents. Roads are built with many layers usually rough aggregate, then finer aggregate, etc etc. This is expensive but is somewhat necessary to handle the loads and temperatures without deforming, collapsing or breaking down - ie being the cause of serious incidents. The cost of a road closure is also measured in productivity and economic activity lost. The cost of a sidewalk - well... not so much.",
"Currently researching the same topic for my design project. Walking paths have somewhat been changed and made to a near universal design. As a designer and some engineering I can say that flat walkways are the safest, the width allows people to walk in either direction, (with the exception of bike paths). It is better on your joints and is the best possible balance especially for elderly, there is no need for a slope because normally the sidewalk may puddle but the majority will fall over the curb into the gutter entering the drainage. I mean obviously not everywhere is the same but generally this is why sidewalk don’t need changing design wise",
"Roads are expensive, and are heavily engineered to account for things like drainage. Sidewalks are relatively cheap, and therefore are not engineered to deal with drainage, etc. Grading sidewalks to drain properly would make them more expensive to design and build. Additionally, sidewalks are much more susceptible to damage by tree roots and shifting of the ground, so even if they were designed properly in the first place they may not hold up over time."
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f3sclx | How do pool tables know when the ball that was potted is white so that it can return it instead of keeping it ? | Engineering | explainlikeimfive | {
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"There are three different ways a pool table knows to send your cue ball to the head of the table instead of the ball trap. Depending on the age and brand of the pool table cue balls are either magnetic, over-sized or weighted differently. Upon scratching all cue balls run along the same track as the numbered balls until they get to the cue ball separator. In the case of an over-sized cue ball, there is an attached ball shunt. The shunt is set to a height of just over 2.25 inches allowing the numbered balls to pass under. The over-sized (2.375 inch) cue ball cannot pass under the shunt, makes a hairpin turn and drops to a track leading to the head of the pool table. Newer coin-operated pool tables may use a magnetic cue ball. This cue ball is 2.25 inches, the same as the numbered balls. Magnetic cue balls either have a small metal cage embedded inside the ball or more recently are coated with a metal skin (Aramith type). Instead of a shunt forcing the ball to the cue ball return, a strong magnet is attached to the cue ball separation area and pulls the cue ball towards the track leading to the head of the pool table. Weighted cue balls are most commonly used in older Dynamo pool tables. These tables actually have three methods of distinguishing cue balls from numbered balls. They have a shunt for over-sized cue balls, a magnet for magnetic cue balls and a patented designed weighted cue ball return. Billiard balls weigh 6 ounces. The slightly heavier cue ball rolls through the separation interchange, activates a rocker dropping the cue ball into the hairpin turn leading to the head of the pool table URL_0"
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f41lzj | Why does the engine of this plane rumble? | [ URL_0 ]( URL_1 ) & #x200B; Even the window shakes... | Engineering | explainlikeimfive | {
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"Resonance frequency, basically the structure is receiving a little push in step with how the material normally flexes since each push is perfectly timed it is like pushing someone on a swing at the perfect time when the swing has reached its peak. URL_0"
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f46mtt | How does my voice travel over radio waves? | Engineering | explainlikeimfive | {
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"So basically when you speak you create some vibrations in the air around you. These vibrations affect a magnet inside a microphone, that then moves in sync with your voice. If that magnet is inside a coil, or a wire that's wrapped tightly around the magnet, then that creates a sort of unique electrical signal. That is transformed to radio waves and picked up by a receiver. The electric current is transformed to audio by the exact same process, just in reverse. The current is applied to the wire, the magnet vibrates, moving the air around it and that's the sound you hear. P.S. Sorry if my English isn't perfect, it's not my first language.",
"First, you speak into a microphone, and the air pressure of your voice is turned into a digital waveform. That waveform is then modulated onto a radio carrier -- that is, your voice wave and the radio wave are added together such that the radio wave now has a copy of your voice wave embedded in it. That radio+voice wave then gets broadcast via tower or satellite. At the other end, the receiving device picks up that radio+voice wave. Based on what frequency it's tuned to, that's the carrier frequency it tries to strip out, using the same procedure that was used to add the waves together in the first place. Once stripped, the receiver hears your voice."
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f49grx | when space shuttles blow up, someone has to explain it. How do they reverse engineer the debris to say that an engine valve was stuck? | Engineering | explainlikeimfive | {
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"The two space shuttles that blew up had their explanation from video and understanding of what was going on. The Challenger had a bad o-ring seal which was expected by some of the engineers in advance but they were overruled the flight took off anyway. They demonstrated later that an o-ring at a low temperature wouldn't be able to keep things sealed and that was consistent with what happened. With Columbia they could see where the problem started and then reviewing video they could see the damage that happened to the wing. Edit: corrected shuttle name",
"As u/SirHerald has explained, there is often video evidence as well as pre-event analysis by engineers saying \"this is a possibility.\" However, there are other methods used to determine root cause(s) in aerospace (and marine vehicles, etc.). Space vehicles and test aircraft are outfitted with \"telemetry,\" which transmits/records a number of different readings/conditions (a \"black box\" on production aircraft is a simplified form of this). If you know the performance characteristics, temperature, g-loading, speed, altitude, attitude (position relative to the wind and earth), system parameters (oil temperature, throttle setting, fluid pressures, etc.), control inputs by the crew, recordings of what the crew is saying, etc. you can see if one or more of them are out of order. Combine that with any physical evidence, and then you can understand that something was the cause of the incident or was the result of the incident. When you combine all of this, you can pinpoint the root cause(s).",
"When the cause of a failure is unknown you can also try something called a fault tree analysis. By ruling out all the faults on branches of the tree that can‘t have occured (by seeing if observational data is inconsistent with the fault) you should end up with very few probable causes left. That of course requires that all possible faults and their interactions have been thought of before. Sometimes new and unexpected failure modes can occur.",
"I used to do failure analysis for a living. Take all the broken parts that are available, figure out how it is supposed to work. Read alloy, polymeric and ceramic fracture surfaces to figues out which direction cracks propagated in. Trace the fracture back along the path to the origin. Figure out what event provided enough energy to start the crack at the origin.",
"Despite the geniuses commenting, after the Columbia disaster, I witnessed the military be deployed to stand guard at every bit of debris found by reconnaissance, as it lay on the ground (sometimes for days), across east Texas. The debris was recovered by specialists and combined at a warehouse. ALONG WITH video and telemetry the physical pieces were studied and placed to approximate the destructive event."
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f4nuw1 | Space Shuttle main engines “two strikes” | Bit of a specific one here but, I was looking at the Wikipedia article on the timeline of STS-51-L (Challenger disaster) today and I couldn’t figure out what one of the events meant. A point came during the vehicle breakup when the high pressure fuel turbopumps were approaching their redlines. This I understand. The next event seems to be the final communication from the number two engine: “Channel A votes shutdown, two strikes on channel B”. What the hell does this mean? | Engineering | explainlikeimfive | {
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"the shuttle had 2 computers, which were both running the same code. the idea was that the two computers would cast votes on important decisions, and that normally they'd agree, but if one of them had an error (a glitch really) then the voting outcomes would be different and the error could be caught and an overruling decision would be made by the astronaut. From what you've written, it looks like computer A wanted to shutdown the engine. Not sure about 2 strikes on channel B, maybe astronaut slang for saying that channel B agreed with A? Edit: Apparently the shuttle used a triple-redundant avionics computer, so there would be a majority vote on decisions ie: 2:1 against or for. Edit edit: But the main engine controller was dual redundant",
"Hi, retired Shuttle engineer here/manager of Atlantis OPF post Columbia. I coukd explain more about Columbia as I worked on the reconstruction committee, but will try to keep your question as EILI5 as possible. The space shuttle had several types of computers, and buses, all in control of different things, yet they could all over ride each other in the main scheme of things. The final data bits your referring to are broken bits, and not reliable. They are part of a \"redline\" shut down. As the ET broke up from aerodynamic forces after the top of the booster swung into it, it disrupted fuel flow to the engines. But they still had fuel in the system. We redid the shutdown codes after bad sensors caused an abort to orbit on 51-f. As the first tank ruptured, the engines began running rich for a few Microsoft seconds, so they tried to compensate, but couldn't. The vehicle at this point was breaking up, and the engines were pushing through the afternoon of the cargo Bay. Now is where your question comes in. The engines new something was wrong, and we're attempting not only to fix their fuel flow rate, but we're still gimbling trying to keep the shuttle on course, but by now their was no shuttle and full breakup had occurred. The 3 APUs (Auxiliary Power Units) were now destroyed or cut off, so any power or transmissions past this point are unreliable, and most likely static garble. But most likely, it was the engines signaling that they were getting ready to drop out from low fuel pressure."
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f543x6 | Why do dull razors cut you more when you’re shaving? | Engineering | explainlikeimfive | {
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"When something is sharper it cuts smoother and easier. Imagine trying to cut something and the blade is dull, it won’t cut very well or hardly at all. Same principle applies to a razor blade. It cuts hair easier when the blade is sharp, but won’t hardly cut when it’s dull. A dull razor pulls and tugs on the facial hair which causes it to cut the skin instead of the hair.",
"Dull blades have burs, little bits of metal twisted into itsy bitsy jagged little spikes like barbed wire pointing in the wrong directions. These burs develop after extended use, or from getting rusty if you wet shave and they oxidize. The little burs are what cuts and irritates your skin when the blade is dull. Properly sharpened blades don't have many burs, they are only sharp in the direction they are supposed to be. They cut the hairs that stick up in front of them, but not the skin which is parallel to them.",
"A dull razor will catch on hairs and pull on them, pulling the skin into a fold which can then get cut."
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f56onp | how do vacuum insulated bottles work? | The ones that keep your water warm or cold for hours and hours. | Engineering | explainlikeimfive | {
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"There are two pieces of metal. The inner container, and the outer container, they only come in contact with each other at the neck of the bottle. the void between them is a vacuum, that is to say the air has been pumped out of the void and a vacuum exists. Because there is now no air, the space between them can't transmit heat from one container to the other and thus cool or heat the liquid inside. So the vacuum acts as an insulator and keeps the beverage at the same temperature it was when it was poured in for a very long time. eventually, the minute connection between the two containers will cause the liquid to come to room temp what ever that may be.",
"Some types of heat (energy) like to transfer kinetically through collisions among atoms. If there are no atoms, like in a vacuum, then this kinetic transfer mechanism can’t happen. The better the vacuum and the completely it surrounds your beverage (i.e., no uninsulated caps or screws that go through the vacuum lining), the longer your drink stays hot/cold."
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f58cy6 | Why is it a practice to water newly laden concrete and not letting it dry out too much? Supposedly this makes it stronger but how? | Engineering | explainlikeimfive | {
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"Curing concrete creates heat. It's also evaporating the water out of itself. Watering the slab prolongs this process resulting in harder concrete."
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f5dkpo | How do internal combustion engines (ICE) get their characteristic sound, if it's only just a bunch of explosions? | I know how engines work, what makes them work etc. but this question has been on my mind for a while. How can a bunch of controlled explosions create the sound characteristic for a specific engine type? For example, a V6 engine sounds distinctly different than a V8 or I4, but how do they get their sound & why can't the sound be different, for example an I4 engine with the sound of a V12? | Engineering | explainlikeimfive | {
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"think of your exhaust the same as a brass musical instrument. When playing a trumpet or a tuba, the sound is generated the same, however, the output is totally different. an exhaust system is the same way. Its 'tuned' for performance and sound based on length of the expansion chamber, the diameter of the pipe, the baffles etc....",
"It's important to keep in mind that ICE engines do not (unless there is something severely wrong!) create explosions. Think of it as a controlled burn. As such, the sound you hear is a combination of sound waves interacting with each other as they leave the header and interfere. The number of cylinders, header design, and exhaust design all contribute to how this interference occurs. The firing order of an engine can also determine its sound. I.e. the v8 engines in german cars usually use cross plane crank shafts and have an even firing order allowing exhaust waves to flow smoothly one after another. Some american brands have uneven firing order and cause exhaust waves to collide and create either constructive or destructive interference. This results in the loud gurgling sound you hear from a classic v8. The valve lift, cam profile, etc. can all also have an impact on engine sound. The frequency harmonic differences between i4s, v8s, and v12s are due to the fact that as the engines increase cylinder count, there are (typically) more combustion cycles per rotation of the engine. So 3000rpm in an i4 engine has a lower harmonic than 3000rpm in a v12 (since there are 3 times the number of combustion cycles occuring per revolution).",
"Because the explosions are happening in very, very, very, extremely fast succession. The sound blurs together creating the sound. Why do different types of engine sound different? Because they operate slightly different and thus sound slightly different. You asking why a v6 doesn’t sound like an I4 or whatever is like asking why a piano doesn’t sound like a guitar. Because they’re different things.",
"1) If you think of a car engine and car exhaust as being akin to an instrument, then you can see that the tone, timbre, and harmonics of a car's engine noise will change depending on the precise geometry and materials of the exhaust side of the engine. 2) There's actually an interesting thing going on with respect to human perception which is fundamentally why you hear a continual \"buzzing\" tone from your car's exhaust despite the fact that combustion is actually a large number of discretized combustion events. In music theory, there's a thing called the \"inter-onset interval,\" which is basically the time between discrete notes, measured in milliseconds. The fastest reliable inter-onset interval is generally held to be around 100 ms, and something weird happens as you push beyond it to 50 ms; instead of hearing the discretized notes, you begin to perceive the notes as singular constant tone. This is because and inter-onset interval of 50 ms corresponds with a signal at 20 Hz, and *20 Hz is the lower limit of human hearing*. 20 Hz also corresponds with an engine operating at 1200 RPM, which is basically a high-idle engine speed. As a result, despite the fact that you're hearing individual combustion and exhaust events coming down the exhaust pipes, because these individual sounds are coming at you at such a high rate of speed and high frequency, your brain interprets them the same way it would a continual soundwave. This is also why engine sounds change pitch linearly with RPM; RPM converts linearly to exhaust event frequency, which corresponds directly to a \"tone\" coming from your cars exhaust.",
"There’s a lot of info here but I feel like no one is talking about how crankshaft geometry affects the sound."
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f5em5u | Why do speakers come with a “max volume” setting when it’s possible for the speaker to bust at that max setting? | Engineering | explainlikeimfive | {
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"It's not about the volume of the speakers it's about the power level of the audio receiver they're connected to. Most of the time they're made separately and the speakers are paired with a receiver that supplies more energy than required both to make sure it supplies steady power and in case the consumer wants to upgrade the system with more speakers down the line.",
"If we're talking powered speakers that you plug into an audio source there are two things that come to mind: Audio sources vary in volume level depending on the source material (file, cd, stream, etc) as well the actual power output from the hardware. It's entirely possible for the need to really turn the volume up. With that said, you don't want to run any device or machine at 100% for longevity purposes. It's up to the operator to practice restraint and not overwork the equipment.",
"The speaker doesn't know how much power it's going to get from the amplifier. So...that setting will be a different actual level based on what it's connected to as the source of power. the \"max\" is just a control mechanism for the owner of the speaker."
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f5scqp | Why can we not build a machine to go to the very bottom of the ocean but we can land on the moon? | Engineering | explainlikeimfive | {
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"Somewhat false premise as we have built deep-sea submarines that reached the bottom. This isn't done all that often because the high pressures present a more severe engineering challenge than the vacuum of space, and once you get down there it's hard to see much of anything in the black abyss. Like space, it has usually been easier to not pressurize a vessel for human use and just send a robot to do the snooping.",
"Because designing a machine to contain an atmosphere in a vacuum is less challenging than designing a machine to withstand the enormous pressures at the bottom of the ocean. The forces involved are far larger in the second case than in the first.",
"We can. They're called DSVs, or Deep Submersible Vehicles. The deepest part if the ocean is the Challenger Deep in the Marianas Trench in the Pacific. The first descent was in a vehicle called a bathyscaphe, the *Trieste* in 1960, to a depth of more than 10,900m.",
"It's easier to keep 1 atmosphere pressure in than it is to keep many atmospheric pressures out. This is basically it. At the bottom of the ocean you can get up to hundreds of times the normal atmospheric pressure (google says up to 300 times the pressure at sea level) , pressing in on a craft. In space you got 1 atmospheric pressure pushing out. Granted its against 0 resistance but still a fraction of what a sub faces at those depths.",
"The issue with going to the bottom of the ocean versus the moon is pressure. Breaking through Earths atmosphere is done through rocket force and with going underwater you reach a point where the water pressure is so great that it crushes most materials that would be considered to hold up to its strength.",
"There is a myth in Hollywood that if you shot a hole in the window of a plane that you would suck a human through it. Hell, you could shoot a hole in the space station and you probably wouldn't suck a human through it because the pressure difference is too low (Only one atmosphere) There is however at least one case of human being turned to liquid due to a pressure difference: [ URL_0 ]( URL_1 ) The pressure difference in this case was 9 atmosphere. Nine times that of space. Designing for this is much much more difficult. It's also far less showy.",
"Edit: appearently I gave out some wrong info, so please look at the replies for better info :) Since it's ELI5, imagine what happens when you stack a shit ton of foam on top of each other. It might not seem like much but at a point in height, the weight on the top becomes Soo much that the bottom of the foam can't hold it anymore. Same with water, imagine having like more than 11 km of water just on top of itself. You can go down because water is a liquid but the pressure that's building up will cursh you."
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f5xgvl | Why do sailors need to learn so many knots? | Engineering | explainlikeimfive | {
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"The same reason Chef's have so many different knives. Different knots are used for different things, some need to be untied quickly, etc.",
"You sort of don't need to. A bowline, 2 half hitches, a figure 8 and a rolling hitch are are you really need. The rest aren't used much (I can't ever imagine really needing a sheepshank for anything)"
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f60yvt | Why are so many large passenger planes equipped with wings that tilt slightly upwards? | Why not just have the wings flat? | Engineering | explainlikeimfive | {
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"The angle at which the wings angle up from flat, from the root (at the fuselage) to the tip, is called the dihedral. Dihedral makes the plane fly more stable - basically by having the center of lift higher up. edit: better grammar, more detailed explanation.",
"Stability. When a plane with tilted wings tilts the now more horizontal wing creates more lift than the other one and naturally brings the plane back to horizontal. Not all planes have this some fighter jets do have flat wings. But generally speaking upwards tilted wings improve stability."
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f6afi8 | Why can't wind turbine blades be recycled? | Engineering | explainlikeimfive | {
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"Because they are made from composite materials. That means they put layers of a a cloth like material made from glass fibers into a mold, and glue them together with epoxy resin. The reason you can't recycle that is that the process that hardens epoxy is an irreversible chemical reaction. So unlike regular plastic or metal, you can't just melt it down and reuse it.",
"They’re made of thermoset plastic, which from what I understand, means it’s more along the lines of a composite material, or two things that are put together and cooked in an oven.",
"Wind turbine blades CAN be recycled however it hasn't been cost-effective so far due to low number of blades to be recycled. What's more, the technology of fiber-glass blades recycling is still developed and improved since it's a relatively new problem for our world. In US there is a company that recycles blades - Global Fiberglass Solution. [ URL_0 ]( URL_0 )",
"It's because there does not exist a process with which to do it economically or environmentally. The blades are principally fiberglass, and newer, larger blades are carbon fiber. It's far cheaper to make these materials from new than it is to try to reclaim them, and no process exists to break these materials down. You can incinerate them, but they have almost no net positive caloric value, meaning you're effectively not producing energy by burning them, and now you have a pile of ash that is itself worthless and destined for the landfill. You've reduced the volume but not the mass."
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f6c8ef | How are we able to manufacture trillions of transistors in such a short time? | Basically this is my thought process. If you were to count 1 number every second, it would take you a looooooong time to get to 1 trillion. A quick Google search showed tens of thousands of years if not more. Even if you counted 10 or 100 numbers at once, it would still take a whiiiiile. So my question is: how can we manufacture so many transistors without it taking years and years? Like, if you could create 10 transistors AND put them into a microchip in 1 second (which seems like a lot to do even for a machine), it would still take years and years and years to create a single chip with this many transistors. Of course, obviously I'm missing something because not only can we apparently create a single chip like this but we create millions of chips, with billions of transistors on each, each year. The estimated number if transistors manufacturered is staggering! So what am I missing lol? I'm sure it's super simple...but it's been bugging me all day! Is it as simple as just having a machine that is prebuilt to make like thousands or millions of transistors in one swoop? But then how can SO many be arranged intricately on a chip in such a short time? Is it again just a bunch of prebuilt machines that do all this? Thanks! | Engineering | explainlikeimfive | {
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"> So my question is: how can we manufacture so many transistors without it taking years and years? The same way we can print newspapers with so many letters so fast: by printing whole blocks with many letters at once. For processors, the process is called [stencil-lithography]( URL_0 ). Basically light is shone through a stencil that blueprints a big part of the -or the whole- chip (with several millions transistors) and then focussed onto the silicon to etch the design. It might takes several exposures to make each transistors, but transistors are never processed individually. The optics that goes into this process are insanely complicated (for a variety of reasons, one being that most photons are too big to etch transistors a few nanometers in size), but at the core it's just a blueprint being printed using a stencil. I think [Extreme UV Lithography]( URL_1 ) is used for modern processors.",
"Yes, the process is automated. Yes, the process is highly parallel, masks used to expose wafers can for many CPUs worth of transistors in a single operation sequence. Most transistors aren't individual units.",
"Think about color photographs, how do we capture so many dots of color so quickly? By doing them all at once. So the design is all done, and a template is made, and that template is shone onto a substrate. Instead of encoding color, the light encodes depth information. The exact specifics depend a lot on the technology, but various depths of cut in various patterns will provide well defined results, acting like one type of transistor or another. Lets have a look though...you can see this: URL_0 Note that no part here is discrete until someone draws a colored box around it; we can separate them into a schematic, and they were, at some point, designed that way, but they have been optimized down into a single device. (edit: updated to link article directly instead of through another blog)"
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f6gz3i | How does a gumball machine dispense a correct number of gumballs? | Or any of the other old-school candy dispensers. What mechanism do they use to be able to consistently dispense a set number of candy/gumball pieces? Or is there an error rate and variability to the number of pieces they dispense each time? | Engineering | explainlikeimfive | {
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"Gumball machines have a little rotating mechanism in them (they vary but one type sort of looks like a radioactive symbol) that can hold one gumball at a time. It loads them, then when the person pays and twists the mechanism, the single gumball plops out"
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f6klat | When changing a car battery, why do you disconnect the negative first and then the positive, and vice versa when putting a new battery in? What will happen if you do it the opposite way? | Engineering | explainlikeimfive | {
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"The negative terminal is connected to the entire frame of the car, allowing you to use any metal point inside the car as a battery negative connection point. This means you could accidentally touch the positive battery terminal with a part of the car with your tools and cause a short circuit of epic proportions. Disconnect the negative terminal first to break this connection, and now the only way to make a short circuit is to touch both battery terminals together which is much less likely to be done accidentally. (There are a variety of reasons to make the entire car frame effectively the battery negative terminal, but that's a story for another day)",
"If you're cranking away with a wrench, you could accidentally bridge between the positive terminal and the frame. \\*boom lots of sparks!\\* If you disconnect the negative terminal first, you've isolated the frame from the battery."
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f79300 | How do thermal cameras work? | Engineering | explainlikeimfive | {
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"text": [
"Heat is actually mostly infrared light being transferred from one thing to another, because light is pretty much everywhere and a part of almost everything if you look close enough. Our eyes can only see specific \"colors\" of light (the rainbow), but there are a lot more colors we can't see, which special cameras can see. The pictures those cameras take are translated to colored light so we can \"see\" it too, like describing a scene in a movie to a blind person. You might have figured this, but Infrared is right after red light, and Ultraviolet is before violet. Naming things you can't see is hard. I tried to answer everything you might want to know, and include a fun (I'm a Quantum Physics nerd) fact. If I missed anything you don't understand just ask, or maybe someone smarter than me will answer them."
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f7b2kf | How are there millions of bike locks of the same model yet one key only unlocks one? | Engineering | explainlikeimfive | {
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"Each key unlocks many. It's just very unlikely that you'll find one besides yours that your key also unlocks.",
"It depends on how the lock mechanism is setup Say it has 5 tumblers with 7 pin lenghts there would be 7^5 combinations. There may be some mechanical limitations to the mechanism or methods that are used to make the lock harder to pick that reduce the number of practical combinations used (all the pins being the same or close in length would make the lock easier to pick) If there were 1 million locks like I described above and 10,000 key combinations each possible key would open 100 of the locks."
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f7w994 | why can’t an auto pilot land a plane ? | i heard that a pilots job can’t be replaced by a robot. Especially when the plane take off and land but I don’t know why. Please explain like I’m 5 and thank you in advance 🙏🏻 | Engineering | explainlikeimfive | {
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"Modern Auto pilot can in fact land a plane on it's own, but that accounts for less than 1% of all commercial landings. Pilot's generally prefer to use the autopilot to manage the flight and conduct the approach (turning towards the airstrip) and then conduct the takeoff and landing themselves. There's a number of reasons for this 1 - Pilot's like doing landings and like practicing their skills. If you don't practice you can't get good at it. 2 - Landing is the riskiest part of the flight and the autopilot can't account for everything, like weather, traffic, or sudden winds and turbulence. The pilot's have to monitor the aircraft when the autopilot is on and they find auto landing to be very stressful, so it's better for them to have control of the aircraft so they can react more quickly if there is a problem. 3 - Auto-landings aren't as comfortable for passengers and take longer to slow down than pilot controlled landings. 4 - The use of autoland is restricted by aircraft regulations and often can't even be used. Autoland requires very accurate sensors like GPS and ILS (Instrument Landing System) guidance which is supplied by beacons on the ground and is not always available. It's up to the Pilot to analyze this data on the instruments and use his intuition and experience to guide the plane in. Sometimes the best sensors are the 2x pilots 4x eyeballs, but tbf they can also get it wrong. The autopilot on the other hand is just a computer program, it performs its task as it's programmed and can't account for every situation. That's why there are still 2 pilots in the cockpit."
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f81ofe | How can satellite dishes receive high resolution media with little lag and no buffering time but this same technology can't be used to send internet to rural areas with massive lag and data restrictions? | Engineering | explainlikeimfive | {
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"It's the difference between broadcasting and internet type communication. With a broadcast a satellite is just beaming out a high power signal, and people are receiving it on the ground. There might be lag on it, how would you know? All you're seeing is the images and sound as they arrive. With Internet communication there has to be a two-way communication going on. That's where it becomes more difficult, because the lag between you sending the signal up, it getting down to where it's going, and the response coming back is far more noticeable.",
"Initial statement is wrong. TV dish antennas hav lag A LOT of lag. But audio/video is synced properly and shown as they arrive, so you dont perceive the lag. Where I live, I can hav the a match broadcast on radio and telecast on TV as LIVE but radio casting always has a few seconds lead. This is something you can try and see for yourself(if you can find one tho) As for satelite internet.... That can hav pretty OK speeds but at the cost of latency.... most add a minimum of 500ms(0.5s) of delay.... And thats *just a minimum*. One senior(from UNI) got to stay at the Arctic, tried using sat net or something similar for playing online multiplayer, most of the time servers timed out on connection request before he could join, on the other hand skype works o.k. [similar question was being asked by a fellow gamer on reddit, who had the chance of going to Antarctica for some work] ( URL_0 ) Edits: formatting, spelling, links, corrected info",
"In laymans terms: Lag is the time it takes for a signal to get from one end of the pipe to the other. So in the case of broadcast TV, or a large file download, lag doesn't matter - you can get the signal 2 minutes after its sent, but as long as you keep receiving a steady stream, you'll never know you're 2 minutes behind. But if you open a web browser and say \"show me URL_0 \", and it takes 2 minutes for that request to get to Microsoft, and 2 minutes for the reply to come back, then \"your internet is slow\". ... Even if it might be capable of downloading a whole episode of game of thrones in the next 2 minutes - it's the request/response delay that makes satellite internet suck. Now, there are other factors, like that the satellite delay is 1/3rd of a second - so if you pay a lot of money you can get 'fast' internet response if you have dedicated satellite time; and that TCP/IP just won't work with 2 minute round trip times (even if you are streaming a big file. ... And there are a few tricks that satellite providers use to hide the problem (which is why satellite voice calls don't suck any more, and satellite internet is much better than it was). But the crux of the issue is above, and it's caused by the time it takes light to travel 72,000km up to and back from a satellite in geostationary orbit.",
"The difference is between listening to someone with a bullhorn, and having a conversation. Satellite is like having a guy on a soapbox with a bullhorn. Nobody can effectively talk back, and there’s no way for anyone in the crowd to control what the soapbox guy says or when he says it. But they all get the same message at once, really quickly. The internet is like a cocktail party; all communication happens between two individual people at a time. Not only does it take a while for information to get across the room, there are a ton of unrelated side conversations happening, slowing things down. But it’s possible to talk back to someone, to request more information, or to request a different story altogether. tl:dr; the internet is more flexible than satellite, and flexibility costs you speed.",
"Satellite does lag you just can't notice it usually. I used to love in an apartment with paper thin walls and a super sports fan neighbor. He had cable I had satellite. If we were watching the same live sports program and there was a goal or awesome play or something I would hear him yelling about 5 seconds before the goal or whatever happened on my TV set. Curious about this I asked him what channel he was watching on, just to make sure this want there reason why, and we were watching the same broadcast. So there is some lag.",
"Satellite tv is basically one way transmission to everyone receiving the signal and you dont notice the lag. Satellite internet is two way where you notice the lag. Satellite internet is also extremely random, so the provider can't send the same signal to multiple houses to save bandwidth. Satellite tv (dish, etc) need a telephone line connection to the receiver so the box can be activated and your ppv movies can be purchased. That is very low bandwidth back to the provider, so any delay is not as noticeable and probably attributed to the tv/remote control lag. Satellite internet has the high bandwidth stuff come down the dish, but your low bandwidth google search text, mouse clicks, etc going thru a 56k modem connection to the provider. There is full satellite internet designed for very remote (in the jungle, on the mountain top) locations that does go thru the dish both ways, but it is extremely expensive to purchase the hardware and use (data fees). Iridium has satellite phones which can text, but last time I checked, it was $3us per minute for phone calls and $20 for 100 texts. No wifi hotspot or tethering available."
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f824zz | How is audio transmitted from a phone/computer to headphones? | Engineering | explainlikeimfive | {
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"Depends on the kind of headphones and how they're connected. The simplest is through the standard 6.3 and 3.5mm jacks [picture]( URL_1 ). These use an analog signal, which means it sends an electrical 'wave' along the wire similar to how AC current works. If you draw a graph of the voltage on the end of the wire over time [it looks like this]( URL_0 ). If you draw the graph of the air pressure of a sound wave over time, it looks exactly like that previous picture. So that electric signal goes into the headphones and into an electromagnet that pushes and pulls on the speaker cone translating the electrical wave into a sound wave. USB and Bluetooth headphones transfer the audio information as a digital signal. USB just sends it down the wire, Bluetooth sends it through a radio wave. Digital information is sent as a series of 1's and 0's which is represented in electricity by toggling between a higher and lower voltage like 0V and +5V [so it's graph looks like this]( URL_2 ). There's some other ways to encode the data digitally and I'm not an expert in USB specs, but the same basic principle applies regardless. Anyway, once the 1's and 0's make it to the headphones they run through a chip called a DAC, which translates 1's and 0's into the analog signal we talked about before."
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f87i10 | How do they supply hot tap water in whole country ? | I am currently in Russia and there is hot water supply in every building. I can see the pipes which contain the hot water but what is the source ? | Engineering | explainlikeimfive | {
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"I believe the term you're looking for is district heating (DH). It is used to supply a large amount of buildings with hot water by heating the water in combined heat and power (CHP) stations or thermal power stations. In some countries or especially in rural areas district heating isn't really used, but it's common in cold, densely populated areas where the need for heat is large. So the heat is usually generated by burning coal, biomass, natural gas or other fuels with different methods, and the released heat is captured to water and/or steam. If it's a CHP plant, part of the heat and energy is extracted as electricity in steam turbines. Most of the remaining heat is transferred to DH system in heat exchangers. DH system is basically just a huge system of insulated pipelines with some pumps to keep the water flowing. The pipeline is connected to buildings, where there is a separate heat exchanger that takes heat from the DH water to your domestic hot water, that you'd get from your tap. Domestic water is just clean, cold water coming from your local water supply, and the hot water is the same water but just heated. ELI5 explanation: power plants heat water in a water circulation system, and your house takes part of that heat.",
"The source is the local power station, as well as producing electricity the power station can use the exhaust heat to supply building heating and hot water to surrounding buildings, this only works in relatively densely populated areas.",
"In Iceland (where I live) we get all our hot water from the earth. It is pumped via insulated pipes and stored in insulted tanks near cities. We actually have a quite nice tanks like that here in Reykjavík. We built a restaurant and observation deck on it. Here is an image of it. Hot water for most of Reykjavík is stored in these tanks. Image: [Perlan (the pearl)]( URL_0 )",
"Each building has it's own water heater. Only cold water is supplied and it's heated inside the building and usually wamed and contained in an insulated tank until it's required."
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f89oqz | Why does electricity appear blue but sparks from electricity are yellow-ish Orange | Driving down the road yesterday they were repairing some electrical lines and I guess one of them sparked and it left a trail of blue sparks on the ground. But when I hook up a battery and short it with a wire sparks appear an orangish-yellow color. Anyone know why? | Engineering | explainlikeimfive | {
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"None of the answers so far have correctly mentioned the reason why electricity often appears blue. Electrical sparks are a result of ionizing the nitrogen in the air, which glows violet. It’s the same phenomenon that makes neon tubes glow. The yellow and orange sparks you see are little bits of hot metal flying off whatever the electricity is burning up.",
"The electricity itself isn't blue, per se. It's the ionization of Nitrogen in the air that makes it look that way. When you burn metals or create a spark, you aren't ionizing Nitrogen in the air, instead you are burning the material that caused the spark, which is going to burn a different color. That's about as ELI5 as I could get lol.",
"Sparks are, generally, not actually the electricity itself. Instead, they are small slivers of super-heated metal. The color is dependant on heat. Now, sometimes it is electricity jumping from the source to a grounded object. In these cases, it will primarily be a flash of white light, but may tint blue depending on atmospheric conditions. Edit: To clarify, the white and blue is the air super-heating, not electricity itself. You *might* see it go into the reds, but it is less likely.",
"blue = glowing nitrogen (high voltage through a stable gas makes it glow - this is how fluorescent lights and Neon signs work) orange = Burning oxygen & #x200B; Electrical arcs are blue, because they go through the air and make it glow, and since the air is mostly nitrogen, you get nitrogen blue. & #x200B; When you hook up a battery you should see both blue AND orange sparks, blue as you get close, and then orange after contact, because the orange sparks are from oxygen, a fuel source, and heat all meeting to create combustion together.",
"Electricity doesn't have a color. Light is made of tiny particles called photons, while electricity is made of electrons. When you \"see\" electricity, you are seeing a side effect of electricity, not the electricity itself. When electricity moves in outer space, where there is nothing for it to interact with, it is invisible! When you see sparks or lightning on earth, you are seeing ionized air created by electricity. Ionized oxygen and nitrogen glow a blueish color, and together oxygen and nitrogen make up about 99% of the atmosphere. If Earth's atmosphere was made of a different gas, sparks and lightning would be a different color! For instance a planet with an atmosphere made mostly of Neon would have bright red lightning! When you see red or yellow \"sparks\" caused by electricity (such as coming off an electric welder or the explosion of an electric transformer), you aren't seeing electricity, but tiny pieces of metal heated up to red or yellow hot. Electricity heated these pieces up and caused them to break off and fly away, but the electricity is invisible. You can see similar sparks come from non-electrical causes such as a flint/steel fire lighter, or metal being ground with abrasives. There is another type of electricity-to-light effect you see every day but might not notice: light bulbs! There are several types of electric lights. In none of them do you \"see\" electricity, only its side effects. 1. Old fashioned incandescent bulbs - these work by heating up a wire to be very very hot, so that it glows yellow white. There is a protective glass bulb around the wire filled with gas that prevents the wire from burning up. 2. Arc bulbs - these work almost like lightning! Electricity flows through a gas inside the bulb and ionizes the gas, creating light. Different gasses glow different colors. White fluorescent lamps are a special type of arc bulb. Another common type are the yellowish bulbs used in some street lamps, which are filled mostly with sodium gas, which glows yellow when ionized. 3. LED light bulbs are the newest type and are becoming more common. They use a special type of chip like in a computer that converts electrical energy to light energy. The electricity flows through the chip invisibly, the light is emitted by the chip due to complicated physics that are beyond ELI5.",
"Sparks are just hot pieces of things (usually metal), and they just happen to be glowing in that temperature range to produce red to white light. \"Electricity\" is that white/blue/sometimes purpleish color when it arcs because it's actually turning certain elements in the air into a plasma. The arc is so hot it's ripping electrons off the atoms, ionizing the gas, and the color light it gives off (called it's emission spectrum) is that bright blue color."
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f8a2dr | What's it mean when a house is settling? Can it settle too much? | Engineering | explainlikeimfive | {
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"Houses (all buildings) support a massive amount of weight. As time goes on, this weight starts to distribute better across the soft bits of the structure. Wood posts compress a little and the foundation sinks into the ground a bit. Settling is expected and planned for in the design. Interestingly, settling is so extreme in skyscrapers that it can misalign elevator shafts if not planned for. But, yes, too much settling is not good. It can cause the foundation to crack and all sorts of nasty stuff. If you look at the corners of older houses, you can find cracks in the plaster and drywall. This is caused by one wall settling lower than the others. Now, most places will settle, maybe shift a bit, and that is that. You might have to do some minor repair, or maybe raise the foundation (you'll see this around garages a lot). In bad cases, though, you get the Leaning Tower of Pisa, or the structure may become unstable and collapse."
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f8brgv | News reports say that the tools, metal shavings, etc. being found in Boeing 737 Max fuel tanks could lead to short circuits and fires. Are there wires in the fuel tanks? For what? | Engineering | explainlikeimfive | {
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"There are sensors in and around the fuel tanks, which are connected to wires. Jet fuel itself is too concentrated to burn, and the vapors have a relatively high flash point. However, some metal scraps rattling around inside the tank could damage a sensor or cause some sparks which would, in turn, introduce an ignition source into a flammable environment. Bad ju-ju for a metal tube a few miles in the air. They could also short out important sensors in and around the fuel tanks. The same goes for your car, though on a much smaller and less sensitive scale.",
"This was not just the 737 but also the 787 made in the Charleston, S.C. Boeing aircraft plant. It's like Boeing didn't realize airlines were not buying planes; the airlines were buying trust.",
"There are a number of fuel sensors, pumps, valves, etc. in the fuel tanks and fuel systems. These do require electricity to work. This does require wires to go into the fuel tanks to power these systems. Adding to this the fuel tanks in an airplane takes up most of the room in its wings. So sometimes the designers find no alternative route for the cables around the tanks and are forced to pull cables through the fuel tanks themselves."
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f8d3vo | How are submersibles different from submarines and why are submersibles not fully autonomous? | Engineering | explainlikeimfive | {
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"It's a definition problem If a vessel can submerge and operate autonomously it's a submarine If it can submerge but can't operate autonomously it's a submersible Autonomous in this case doesn't mean self driving, but instead by itself without assistance. A submarine will have air processing and food stores that allow it to operate for weeks or months without contact with another vessel. Most research submersibles are good for an afternoons adventure, maybe a day before they need to come up and refill their air tanks"
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f8fu35 | How do property surveyors figure out where to start? | I think I can figure out once they have a reference point, how they could super accurately measure everything from there. But often times property disputes seem to come down to a matter of inches. How does a surveyor know *this* spot is for sure correct and I can base the rest of the measurements on it? It seems like tiny errors over many plots of land could add up to being off by several feet. | Engineering | explainlikeimfive | {
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"In the UK at least there are numerous trig points set up throughout the country and surveyors will work back from one of those to create their own reference point within the site.",
"There’s a system with a small number of level-1 markers in a country and then many more level-2 markers based on those, and so on. By the time local land surveyors do their job they’re using level-4 or -5 markers which can be just plaques set in the curbs. They have access to a database giving the positions of the markers. Unless some gross error comes to light, these markers are considered accurate enough for property disputes."
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f8gkdg | How come stage lights make a noise when they are turned off? | Engineering | explainlikeimfive | {
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"They don't. That's just something they do in movies and TV shows for dramatic effect. & #x200B; What /u/ironhydroxide is talking about is the disconnect switch for the power taps. The lights themselves are not controlled by that switch. Instead most stage lights are either controlled by a professional dimmer system, or they have their own internal dimmers. That switch gets thrown well before the show starts and stays on until well after the show is over. It's true that older lighting systems used for small stages with low budgets might not of had dimming systems so the stage lights were either on or off, but even still they weren't typically controlled by relay systems. Source: I've worked in professional live events and theater for the last 25 years.",
"You're probably referring to the 'clunk' heard when large loads are turned on and off. This comes from a contactor. Essentially a large relay that makes it safer for a human to turn the switch on and off, because the switch itself is carrying only a few milliamps where the contactor can carry hundreds of amps (hundreds of thousands of milliamps)"
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f8hj9g | How do sewers in skyscrapers work? | Engineering | explainlikeimfive | {
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"36 year Master Plumber here. & #x200B; There are mandated offsets in the main stack pipes that slow down the flow from the upper floors. If not for these offsets the velocity of the waste would blow out the bottom fittings every time. Same for the roof drains.",
"\\ > And how do they make sure that a blockage on a bottom floor doesn't make the building flood with poop water? & #x200B; I do plumbing service in industrial and commercial buildings. Let me tell you that there is no way to make sure that a blockage on the bottom floor doesn't make the building flood. If, however unlikely, the bottom of a skyscraper drain stack got clogged you're looking at a shit tsunami through the lobby, with a pretty spectacular geyser coming out of a floor drain or mop sink. This does happen in condo or residential towers somewhat infrequently (mostly on bathroom sink stacks) if a stack get's clogged somewhere then whoever the lowest person above the clog will have everything draining into that stack from the units above them coming out of their plumbing fixture. Instead the solution is to make sure the stack never clogs. This is done through preventative maintenance, and inspections of the pipes. Though even without maintenance it would take A LOT to clog one of those up. & #x200B; I've only worked in buildings up to 55 floors, so engineers might design something different in taller ones, but typically it's just a straight drop from the roof to the lobby or basement for the drains.",
"How do they make the hot water so instantly hot, but at home i have to run it for 2 min before its hot?",
"Industrial maintenance here, highest building I worked in was 90m tall, shit pretty much falls straight down. How do they make sure it doesn't clog ? By hiring people like me and making sure it'll flood the parking before flooding the building. Note to you all, please stop throwing your tampons, news paper, lingerie, entire roll of paper and whatnot down the drain, thank you.",
"I assume you'd have a 'main stack' as in a bigger pipe that runs up the whole building, and then the smaller pipes that would branch out to toilets, showers, etc from there. So once the waste got to main stack then yes it would just fall all the way down. As for the other question, there are usually access points to reach pipes. So once a plumber determined the location of the clog they'd just fix it from the nearest available one.",
"As the more and more fixtures flow into the main stack, building code will require the stack diameter to increase to compensate for the extra gpm (gallons per minute) this reduces the chance of blockage.",
"Reading this while sitting - SITTING, careful spelling - on the 8th floor having some quiet time. Great question!",
"There seems to be a lot of BS here. Water/waste doesn’t fall down the middle of a pipe it runs down the sides of a pipe by a force I can’t remember the name of right now. It just continues to role down the edges and never comes close to “terminal velocity”."
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f8lj7v | Control system gain | I'm notoriously good at overcomplicating things; however, I want to explain a bit of technology that I'm passionate about to a co worker operating in a d9fferent disciple of engineering. This tech involves them to know about control system gain. How do I explain the concept well without using examples involving resistors or overshooting? | Engineering | explainlikeimfive | {
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"'Gain' in a control system is simply the ratio between output and input. In laymen's terms, it's the 'amplification' of the system. Or you can look at it with basic physical models. If I have a lever that's shorter on one side than the other, it forms a system where the distance moved by the shorter side has a 'gain' in distance on the longer side based on where the fulcrum is (the longer side moves further than the shorter side does).",
"If you're driving and you make a lane change slowly, that's going to take a few seconds but you will smoothly leave your current lane and smoothly arrive at your new lane. That's low gain. If you need to make a lane change quickly to avoid an accident, you'll jerk your steering wheel. It won't be smooth, and you'll probably end up wobbling around on the new line as you overdo it and have to correct, and perhaps overcorrect, but you'll change lanes faster. That's high gain. If you're really in a panic and slam your wheel to one side, you'll probably run off the road. That's a gain so high the system is unstable. Obviously there are simplifications here, \"gain\" can mean more than one thing (e.g. P, I, D gains in a PID controller), but you can use that kind of analogy to try to explain things."
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f93x9r | why do winter tires generally have a lower speed limit than summer tires? | (probably physics flair? Not sure) | Engineering | explainlikeimfive | {
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"Winter tires are optimized for traction in freezing and low temps. This means the rubber used is softer. Softer rubber does not go well at high speed...high speed equals high temperatures. High temps plus soft rubber equals tire failure. Edit..my spelling sucks today"
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f97aop | Why can't engineers remove the violent left/right movement and shakes of trains better? | If you ever try to stand and pee on a train, it is very noticeable how it shakes left and right between the rails. This seems like an inefficient waste of energy and a burden on the train's suspension and structure. It is also uncomfortable. The train in question is a relatively new Stadler Flirt, but the same issue is valid for all non-highspeed trains. The rails are, in part, quite old. But I figure their inaccuracies should still be possible to smooth out? So, question, why aren't train engineers improving the ride way more than they already do? | Engineering | explainlikeimfive | {
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"The technology exists, but it's too expensive so most manufacturers don't bother because rail companies won't buy it.",
"The simple fix is to stagger the rails instead of them being like ========= they should be like \"-\"- (where the quotes are offset rails) it makes trains far quieter and far less \"rocky\" from side to side, however, the increase in cost for laying track like that is higher than you would expect. The GO Train in Toronto is an example of how quiet and less \"rocky\" but I haven't seen it replicated anywhere else in north America (not that I've been on trains in every part of NA)."
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f99ria | Engine chokes. How do they work and when is it appropriate to use them? | Engineering | explainlikeimfive | {
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"During a cold start, particularly on smaller engines that use carburetors, the engine choke restricts the flow of air to create a richer fuel to air mixture to assist The warming up of the engine and carburetor flow until it reaches optimal performance. Running with a choke on during normal operation bogs down the engine, but during warm up It creates more favorable running conditions. Most often when starting my chainsaw or moped, run it with full choke for a few attempted starts until it coughs and sputters. Then change to half choke for the next few attempted starts. Usually it fires right up and you let it idle to warm up before turning the choke off. Turning the choke off too early usually results in a really rough idle."
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f9ayq5 | How can a CPU or monitor have more hertz than the 50 / 60 Hz that electricity offers? | Engineering | explainlikeimfive | {
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"The clocks and oscillators in monitors and computers are almost never derived from the line frequency. The systems have their own crystal based clocks that are separate from the main line frequency."
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f9cy50 | What's the difference between how a microscope and telescope are made? Why can one look far into space while the other can see things on a microscopic level? | Engineering | explainlikeimfive | {
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"The focal point. The microscope focuses to a point just past the lens barrel. The telescope is focused at infinity.",
"Microscopes are generally used to focus on really close things and magnify them a LOT. Because they have a small lens, they need a lot of light shining through/on to the object. Telescopes usually don't have as much magnification, but have much bigger lenses to catch more light, as (apart from one notable exception) starlight has spread out a lot by the time it gets here and so stars are pretty faint. Apart from this, the main difference is the focal point - really close vs infinity."
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f9esax | There are skyscrapers built in the 19th century. How were modern plumbing, electrical, air conditioning, and other wired systems later installed in these buildings? | Engineering | explainlikeimfive | {
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"Broadly the same way that they were added to any other housing, gradually and in available dead space. It tends to vary building by building and be somewhat 'evolutionary'. If you look at even relatively small multi-story buildings from the late 1800's you'll often find plumbing on the outside and things like chimneys repurposed as vertical pathways for utilities. There are a surprising number of gaps that can be used in most buildings (especially under floor..), not to mention that things like water and gas were often already a consideration so here is space to work with. Oh and we'd generally be talking about 'skyscrapers' that are vastly smaller than anything we'd see as one today, 10-15 storeys is a lot easier to manage than something three times that size!"
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f9lebr | Why is there traffic where an accident used to be even after the accident clears? And what makes it clear eventually? | Engineering | explainlikeimfive | {
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"The initial accident causes slowdown in traffic due to drivers taking precaution and driving slow. This in turn causes a ripple effect that causes cars even miles down the highway to slowdown. Once the accident clears it still takes time for traffic correct itself and speed up... and thus you get slow moving traffic even a long time after an accident has been cleared. But eventually traffic dissipates and cars move to regular speed."
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f9ws9q | Since trees grow so slow, and cutting down a tree is almost instant in comparison, how are we able to keep up with things such as paper products? | Engineering | explainlikeimfive | {
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"Decades ago various industries that rely on trees for materials like lumber recognized quickly and easily that although their businesses were sustainable it would require them to actually sustain them. Those industries thought ahead and began planting trees then for them to harvest now. Most industries that rely on wood use farmed trees that are planted following every harvest and left to grow for as long as it takes. If anything, they create the problem of *too many* trees, or at least too many of the same species in one area, creating a monoculture. The trees that are *not* being sustained are the forests that are clear cut to be used for something else, usually farmland. It's not the trees, it's the land that isn't being sustained.",
"Because trees can grow in parallel. Let's a tree grows ten inches per year, producing 10 pounds of wood. Let's also say we require 500 pounds of wood per year. We just need to make sure there are fifty trees growing at all times, and we'll meet our demand."
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f9yfsy | How do grenade launchers work? Why doesn’t an uncooked grenade just come out harmlessly when it is shot? | Engineering | explainlikeimfive | {
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"Grenade launcher grenades typically have some sort of arming fuse that enables the explosive to detonate after it has left the barrel of the launcher. From my understanding, the common 40mm grenade uses a fly-wheel which allows the spinning hull of the grenade to generate a certain number of rotations before the impact fuse is lined up to detonate the grenade.",
"A grenade launcher doesn't use an hand grenade, it's specialized greande with a propulsion charge. It's basically like a gun, you press the trigger which hit a percussion cap, this will ignite a propellant at the back of the grenade, just like with a bullet. But instead of pushing a bullet out of a long barrel, it propulse a large grenade out of small tube. This mean that the grenade is going at a relatively slow speed and its trajectory will do an arc to the target. Usually there is a system inside the grenade that arm it after it travelled a certain distance to make sure you don't kill yourself with it.",
"What type of launcher and grenade? Some set off a fuse after it’s fired similarly to a bullet. It goes off like a regular grenade. Some have trigger tips, so when it’s activated and then smashes into something it’s like pressing the boom button. Some are smart and can have the fuse be controlled to detonate at adjustable times or when impacting. These can be set to go off distance as well, so you could make it explode just as it enters a window to impact people taking cover. No more throwing the grenade back or jumping on it."
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f9z2cz | Why are there holes in elevator doors but only on the outside? | Engineering | explainlikeimfive | {
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"It is a keyhole so the elevator doors can be manually opened even if the elevator car isn't there. This is useful if you need to repair something or there is an emergency.",
"The doors on the outside only open and close, they don't go from floor to floor. The hole is for a maintenance key that opens them even if the car isn't there. This is used for maintenance, inspection, emergencies, .... The doors on the inside go up and down. This makes them vastly more complex to control safely. a mechanism that would allow a key inside to open both the inner door and the outer door would only work in the event that the elevator was at the right spot between floors, which is a pretty small fraction of the travel. Plus, only users are inside, and they wouldn't have the special key in case of an emergency. It's better to just give the key to the fire department.",
"It’s a key hole for a long probe type key. You poke the key in, sometimes turn it, and it moves all sorts of gubbins like a latch and a pawl. This releases the door lock, you slide the door open. You should see it all from the inside. Riding an elevator is brilliant (but do it with an engineer, don’t be an idiot). I used to ride the elevators on cruise ships when we inspected the shafts."
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fa39ig | How does your car know how much gas you have? | Engineering | explainlikeimfive | {
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"text": [
"There is a sensor in the gas tank. There are several types, but the simplest is a floating device (like a rubber ball) connected by a lever to an electronic component called a potentiometer (think volume buttons on old stereos). As the gas level goes down, the floater goes with it pulling the lever on the potentiometer. The varying electricity flowing through the potentiomenter is used to power the gauge on the dash, making it go from one side to the other as the tank empties."
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facgfm | even after having a huge R & D and workforce, why luxury car makers cannot make cars that are as reliable as Toyota corolla? | Engineering | explainlikeimfive | {
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"First off, Toyota’s R & D budget is huge. This is also reflected in the reliability of so many of their of products, such as their trucks and their luxury brand, Lexus. Second, simplicity and not pushing limits is often the key to reliability. Some luxury and performance cars push the limits of technology, and this will often come at a reliability cost. There are other examples of simple and super reliable cars out there. Classic Volvos are a good example.",
"Also, by the time a car has reached legendary reliability status (Honda Accord, Toyota Corolla), the cars that have proven reliability are no longer being made. IMO, the days of cheap Japanese cars being 100x better than the alternatives are over, and we're mid-reign of cheap Korean cars (Kia) paired with a warranty rather than reputation.",
"Reliability is not commercially beneficial to the car makers. There has been a shift, from selling a car at a huge profit that would last a long time...to selling a car at a lower profit that will require more maintenance and make more money from the servicing.",
"Creating new technologies comes at a cost. Typically you have luxury brands creating and applying new technologies in their cars. The bugs become known in real world applications. Overtime the economy lines can use or refine this technology cheaper."
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fact8r | Why are wind turbines only equipped with one turbine and set of propellers | Engineering | explainlikeimfive | {
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"It’s for wind reasons. The wind is stronger up high so the blades are at a height where they get more wind. If there was enough wind down low for a lower turbine to work well, they would simply make the turbine shorter. Making a turbine *taller* than it needs to be so you can put 2 sets of blades on it isn’t cost effective because the blades themselves (and gearbox, generator, etc) cost a lot and also the shaft gets more expensive the taller it is and the more weight it holds.",
"As you go up in height, the windspeed generally increases. A lower turbine wouldn't be as effective.",
"Because it's all about disc area A wind turbine with 20 meter blades catches 4x more wind than one with 10 meter blades. You really want the largest single wind turbine you can get so you get the most power out of the tower. Being higher gives an advantage which is why wind turbines are often built on hills, but the tower height determines the maximum blade length which determines the power you get from your pricy construction project If I build a 40 meter tower and my blades need 10 meters of ground clearance then I can have a 60 meter diameter fan! If you replace that with a smaller 30 meter diameter fan, that only leaves you space to add a 15 meter diameter fan. Your dual turbine configuration catches 5 units of wind while the single big one catches 8 with similar construction costs"
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faej5l | How does a car track mileage? How does it know how far you’re going? | Engineering | explainlikeimfive | {
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"Math. The car is aware of how many times the wheels rotate (as it is in control of how of many times the driveshaft turns based on gear and RPMs of the engine). Given that the wheels are a fixed diameter with a fixed circumference, it is simple math to translate how far the car travels for every rotation of the wheels.",
"Also if you change the size of your wheel, the mileage your car clocks won’t be the actual mileage travelled due to this calculation."
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fakam1 | The difference between 1 phase and 3 phase electricity, and how to easily tell what it is at my house? | Engineering | explainlikeimfive | {
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"It it’s at your house it’s single phase assuming your in America. 3 phase is reserved for industrial and commercial applications. But if you aren’t convinced take a look at your breaker panel, you will see a majority of your breakers are single pole breakers, or about 3/4” wide. You will have a handful of 2 pole breakers about 1.5” wide. And possibly one breaker at the top or bottom that is slightly larger than that. If you have three phase power you would have a second panel with breakers approximately 3 times as wide as the single breakers in your panel. Now onto the explanation of it. Single phase electricity operates at 60hz which means it reverses polarity 60 times per second. It’s operates in a sine wave back and forth at that 60hz. For residential single phase power one side of that sine wave reaches a 120 volt potential compared to earth ground, which is where the electricity what’s to go. Now if we take a second 120v sine wave and invert it from the first they both have the same 120v potential to ground. But to each other they would have a 240 volt difference. Because one sine wave peaks at the top side, simultaneously the other peaks on the low side. So if you look at your breaker panel, 2 feeder lines come into your main breaker, they then feed two separate buss bars that run the length of your panel. Alternating bars as you go down. A single breaker only grabs one buss, ie 120v for a plug-in. A double breaker grabs both buss bars, ie240v for an electric dryer. 3 phase electricity is created when you take that same original sine wave and rather than inverting it. You stagger it to be 120degrees after the initial do that for a third sine wave and you end up with three waves following each other creating a more stabilized voltage. With single phase your voltage potential goes from 240v and declines to a point where there is no voltage potential, and back up to 240. With 3 phase there is always a point where there is potential voltage from one sine wave to the other two because they are behind each other and not opposite each other.",
"AC is electricity with time-varying voltage. That is, the difference between the power supply line and ground goes from some positive value to some negative value, then back in a sinusoidal ( URL_0 ) pattern. Another way to visualize this is in terms of amps (current). Think of water sloshing back and forth in a trough. That's basically what the current is doing in an AC circuit. 'Phase' refers to a time offset. So if the time at which that sinusoid starts is earlier or later, it is 'phase shifted' from some reference sinusoid. For one phase power, there is only one sinusoid. For three phases, there are three sinusoids overlapping, each time shifted from one another 1/3rd of the wavelength (which is the same for each). When you set up a circuit this way, you create a situation where the total power at any moment in time is equal to the total power at any other moment in time (which is not the case for one phase power). It's also useful for motors since you need multiple out-of-phase magnets to create a motor and magnets can be created by time-varying voltages. At your house, it is very unlikely that you have three phase power - it's primarily for industry. However, if you do have three phase power, it would have 4 pins - one for each phase and one for the ground."
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faqbdo | Why aren't roads and highways made of the same stuff / using the same methods as airport runways? | Engineering | explainlikeimfive | {
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"Well, this is three separate questions 1.) Why are they not made of the same stuff: sometimes they are! But in general, runways are shorter than a whole road, so they can use more expensive materials. 2.) Why do runways not get a lot of potholes like regular roads do? Well, for one thing, runway traffic is a lot more intermittent than regular road traffic. Also, they can design runways specifically to bear the load distribution associated with planes. For cars, this is much more difficult because there are so many types of cars and trucks. 3.) Why don't I see the runway get repaved often? Well, first of all because of the reasons discussed above. But also because work crews are able to handle runway maintenance WAY easier and faster than regular road maintenance, due to the specialized teams and equipment on hand. Also, it is easier to completely close a runway for a brief repair than a road - road repairs often take longer than they should because workers are dealing with traffic related nonsense. Bonus: the stuff they use to patch potholes is almost literally garbage. It is hard to use and often quite ineffective. Source: am in my University's civil/environmental engineering program. Hope this helps!",
"Part of it is maintenance/preventative maintenance related. If you patch the cracks before the material under the pavement washes out, then the patch works. After it's become a big sinkhole, the ground underneath is all washed out, and the fix is much more complex/expensive. Part of it is money related as well. The city in general gets the cheapest contractors they can find to do road repairs. Airports try to run more like a business. They lose money when the runways are closed, so any kind of maintenance has a large time focus. So they'll sink more money into making sure the runways are quickly patched."
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fayahg | How do engineers create perspective-based allusions with art/sculptures? | Here is an example of what I'm referring to: [ URL_0 ]( URL_0 ) | Engineering | explainlikeimfive | {
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"That's actually pretty easy to do in any CAD software. If you draw a sketch in a plane, and then extrude it away from the plane you'll get a solid model of that shape. You then draw a sketch in another perpendicular plane and then extrude it away from the same perpendicular plane. That creates two three dimensional shapes that can be worked with. You find all the points where those shapes intersect, and if you look at it from the direction of your first sketch, that's what you'll see. If you look at it from the direction of your second sketch, that's what you'll see. The art comes from making those two sketches and the resulting geometry look cool from all angles.",
"Here's a simple thing that I created this morning in my CAD software, to demonstrate the concept. It's really simple, but the same theory holds for more complex work as well. URL_0",
"Artists, you mean. How do artists create that art. They create two 2D images and stretch them out accordingly by considering the piece in three dimensions, so that when you look at it from the one side you see one image and look at it from the other you see the other image. If you had a plan view from above the whole thing would look like a very bizarre, mangled thing."
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fb30pp | Since different countries have different voltages, is there a difference in charge times for devices? Or is it just for safety purposes? | Engineering | explainlikeimfive | {
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"No, there won't be a difference in charge times for any devices, and the reason is pretty simple. The charge voltages are determined by the batteries in use, not by the voltage available from the wall. This is true in most cases, until you get into extremely big batteries, like Tesla batteries or something like that. All the rules go out the window, then, just because the batteries are so big that they can take in more power than can be provided by household circuitry. Anyway, in most cases, like computers, phones, etc, the voltage that the device needs to charge is set by the battery chemistry and cell arrangement, and that is the same all over the world. The chargers are often able to work all over the world as well, with just a simple plug adapter. The regulators inside the chargers can take pretty much any standard voltage and reduce it to what is needed. Therefore the batteries all charge at the same time schedule all around the world, no matter the voltage in the outlet.",
"The rate at which a device charges is based on how fast it can *safely* charge the battery. Batteries hold a lot of energy and that energy can be released explosively if something goes wrong. The chemistry that charges batteries generates a lot of waste heat, which can degrade the battery if it's not controlled. If the battery degrades enough, it will fail and cause a short *inside* the battery, which generates its own heat. That heat, of course, degrades the battery, increasing the short, which degrades the battery, and so on. So regardless of the voltage coming out of the wall, the device can only accept so much without literally exploding. How much depends on the size of the battery and the battery type. And, regardless of the device, the AC current has to be [rectified]( URL_0 ) into DC to charge the battery. I can't think of any home appliances that will charge at anything even remotely approaching 110v, let alone 220v. That doesn't mean there aren't any, just that I can't think of them. A Tesla car charges at 240, apparently, but that also means it *won't* really charge at less than 240. Also also regardless of the voltage, current will charge the battery faster. Voltage is analogous to pressure, right? A battery is kind of like a spring being pushed back, and then the spring can be [slowly discharged]( URL_1 ). So, like a spring, in order to charge a battery you have to push harder on the battery \"spring\" than it is trying to push back. The higher the voltage inside the battery, the higher the voltage outside has to be to shove electrons to get them into the battery. But as established above, if you shove too hard the battery just explodes. You can increase the current instead. You're not changing how hard you shove the electrons, you're just shoving more of them at once. But, like higher voltage, too much current will blow up your battery."
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fbg5s1 | How do gas masks work?? | Engineering | explainlikeimfive | {
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"They have a filter in them that catches large particles (usually the dangerous stuff) while letting oxygen and CO2 in and out. It's also important that they sit tightly on your face and form a seal - if any old air can get in, then it's not doing its job."
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fbgr8f | How does the water temperature change in a sink and shower? | Also, why does flushing a toilet make the water hotter? | Engineering | explainlikeimfive | {
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"The plumbing connects with a hot water heater, which preprepares an amount of hot water for your sink and shower. But there is also a cold water pipe, which bypasses the water heater. If the plumbing is done wrong, and the water diverts from the toilet intake to the shower, then flushing the toilet kills the cold water running into the shower, leaving you with only hot water flowing. As for the temperature of the water, it is regulated by mixing the hot water from the heater with cold water from outside the heater. The more you open the hot, the hotter it gets, because there is more hot water than cold."
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fbkw30 | Why can't aircraft carriers just have longer runways? | I've seen the Pearl Harbor movie where they make a big deal of taking weight off the planes because the ship's runway is just too short. Why can't they just be longer? Or was just that because they lacked the time during ww2? It seems like the problem still exists today and i just don't get how a massive ship would be affected by a longer runway. Maybe make it telescoping like a firetruck's ladder so it can be retracted during bad weather. What's the limiting factor here? | Engineering | explainlikeimfive | {
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"Carriers are already absolutely massive, and expensive. Anything mechanical (like a telescoping mechanism) is more expensive (to build AND to maintain) and subject to breaking, especially at sea. WW2 planes also had a lower power to weight ratio than modern jets just because of technological and metallurgical advancements.",
"The aircraft carrier would have to be *a lot* longer to support most planes loaded with max payload, which is why we use catapult launches today. A Nimitz class aircraft carrier is just(?) 332 meters long, this seems like a good distance until you learn that the **minimum** takeoff distance for a fighter like the F18 (not even the super variant) is around 500 meters and that's the minimum distance when not heavily loaded. You'd have to make your aircraft carrier at least 50% longer to support unassisted takeoffs of heavier aircraft. This makes it significantly more expensive to build and operate, often slower and less maneuverable to boot. Modern aircraft carriers all have either catapults to assist takeoff or a ski jump at the end up the runway to loft the plane up and give it a bit more time to pick up speed before it impacts the water.",
"Pitch. The longer the runway the more the beginning and end of the runway move vertically up and down",
"Aircraft carriers have hooks that help slow the planes down when they land. A aircraft carrier big enough to have a full runway for a plane to land without extra help would have to be absolutely massive. It would be more reasonable to call such a craft an island rather than a ship.",
"Fighter planes need about 3000 ft. of runway. If a carrier wanted to put in full runways, they would both a take off and landing runway—so you can launch and recover at the same time. They aren't exactly placed to end to end (there is a bit of overlap) so the combined runways would be about 5000 ft. long, or about 1500 metres. The longest ship ever built was 458 metres. This means a full runaway carrier would need to be three times larger than longest ship ever built. That is a huge ship. A ship that largest would never be able to fit into any harbour or dry-dock. You wouldn't even be able to build a ship that size with any current location. Also, a ship that size would require a lot more power to move properly. Instead of using more power to move the ship, they use a minimal amount of power to launch and land planes from a shorter runway."
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fbncwx | How do they design rooms with particular acoustics? | Engineering | explainlikeimfive | {
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"I'm planning to do grad school for this in a few years, but the info I've been able to gather is that it's a lot of trig. Because, y'know, waves.",
"If this is a concern at the design phase, there is software that could simulate acoustic behaviour. In the past, I imagine this was done with passed-down knowledge that was the result of trial and error, built over time to become trade knowledge. If a room has already been built, the acoustic profile can be modified by using specific materials to absorb (much more often than reflect) (certain) sounds, in specific parts of the room. If the room is going to be used for a concert or performance and have speakers, etc., one of the first things the audio engineer will do once the equipment is set up is to play some pink noise (kinda like white noise but more useful) and walk through the space with a frequency analyzer to figure out which frequencies are naturally amplified or reduced by the physics of the room, and this will be used to set up an initial EQ for the sound profile that will be tweaked as instruments etc. start making noise."
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fbnxt3 | Why do crossbows seem to be able to penetrate modern ballistic body armor so well? | Engineering | explainlikeimfive | {
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"Ballistic body armor is made of woven fabric layers. It’s designed to stop ball ammunition, that deforms upon impact. Crossbow bolts are pointed. Stabbing weapons (crossbows included) aren’t the intent of the armor. It doesn’t do well with ice picks or certain knives, either.",
"It's because of the material of the arrow vs a bullet. A bullet have more energy than an arrow, but the tip of the arrow is usually made a steel, while a bullet is made of lead with a copper layer on the outside. At lead the usually bullet that people shoot. The bullet proof vest is designed to deform the bullet and redistribue the force over a large area. But an arrow is made of a stronger metal that won't deform, but instead will pierce the boby armour. At least that's what you get if you look at a body armour designed to stop a large pistol caliber. Here a video of a level IIIa body armour. [ URL_0 ]( URL_0 ) That said, there is stronger body armour able to stop a rifle round or even an armor piercing round. I doubt that a crossbow would be able to stop those, but I would depend on the strenght of the crossbow and the distance of the shoot."
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fbygf6 | When they say a car has a 1.5l or 2l engine what does it really mean? | Engineering | explainlikeimfive | {
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"text": [
"That's the approximate volume that the cylinders in your engine take up. If you have four cylinders, and each one holds .5L of air, you have a 2L engine."
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fcacwy | How do electronics without internal fan maintain safe temperatures? | Engineering | explainlikeimfive | {
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"Two main ways: First if they don’t use that much power or dont move much they simply don’t get that hot. Second natural heat loss to the surrounding air happens with or without airflow, and increases with differing temperatures. This is a factor of the materials used and their surface area, some devices add heat sinks to increase surface area to help heat loss. Airflow from fans helps make sure that the different temperatures mentioned above stay about the same, because it moves the heated air away and puts new colder air in contact with the hot thing."
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fcksom | How is soil effected when buildings/sidewalks/houses (etc) are built on top of it? | Curious to know. Currently studying soil science and want to know all about soils. Feel free to comment some facts you know on the subject as well. | Engineering | explainlikeimfive | {
"a_id": [
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"In most cases, it compacts. As you'd expect. A properly engineered building will conduct a soil survey of the area (or at the very least, look it up from a table in a book of standards, the NDS is used for the United States in particular) and dertermine its various qualities like how much load it can take before squeezing out, how much it is expected to settle over long durations, and how moisture affects it. That last bit is something most don't think about... different kinds of soil react to water in different ways. Some kinds of soil just repel water, others let is soak through without trouble. But some absorb water like a sponge, causing it to swell and exert pressure on the structure from below. This swelling action can be enough to crack foundations or topple structures if not accounted for."
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fd8zyu | How do cars work! | Engineering | explainlikeimfive | {
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"Tough question, do you mean how does an internal combustion engine work?, or how a differential works? Or how automatic transmission works? But the most basic answer is, we spray gasoline into a cylinder compress the air/gas mixture light it on fire (because it is compressed it is more explosive) that explosion pushes the cylinder away, that spins the drive shaft. A transmission/clutch allows a constant spinning drive to slow, speed up, disconnect (not spin) the wheels allowing the car to stop at stop signs, or go up hills. There are a lot of electronic components, charged by the car battery 12v, and that is recharged by an alternator (basically a generator turning rotational energy into ac power. The rear differential allows the inside wheel (during a turn) to spin slower than the outside wheel, some good videos about how this works online. The suspension/struts keep the wheels on the ground when the car bumps up off the road."
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fdfier | What is the difference between anti-tank guns and self-propelled artillery? | Why can't I just aim the artillery down or the anti-tank up? Why do they have to be different guns? | Engineering | explainlikeimfive | {
"a_id": [
"fjh2f65"
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"These terms are not mutually exclusive. An anti-tank gun is a form of artillery designed to destroy tanks. Self-propelled artillery is an artillery piece that is combined with some sort of vehicle mechanism that allows it to move on its own. You can certainly have both, most notably Tank Destroyers."
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fe4bqf | why touching both ends of a battery with your fingers doesn’t complete the circuit and discharge the battery through your body. | Engineering | explainlikeimfive | {
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"Your skin is a [terrible conductor]( URL_0 ). Technically you complete the circuit but resistance is too great (and voltage or a battery is too small) for any significant current to flow through. For a 9V battery you'd get about 9/100000 = 0.1mA. But you can always zap your tongue instead. :-)",
"It does, but your skin has a resistance between 1 kOhm and 1000 kOhms so that 1.5V battery only produces a current of 0.001-1.5 mA which is lower than you can feel for the most part (you'd feel the 1.5 mA but not much below) If you want a more extreme example of this consider licking a 9V battery. Your tongue has very low resistance, between 100 and 1000 ohms so you get 9-90 mA flowing through your tongue which is more than enough to feel. You've mixed up \"current doesn't flow through your body\" with \"perceptible current doesn't flow through your body\"",
"Current needs 2 things to flow, voltage and conductivity. Now the average battery voltage just isn't high enough to overcome the resistance that your skin exhibits. There will be a small amount of current, but it's not enough to cause any trouble. That's basically what Ohms law tells you btw. U=RI or in the context of your question I=U/R where I is conductivity, U is voltage and R is resistance.",
"The voltage of a regular battery is too low to complete a circuit across skin... Even the rectangular 9V battery is too low. Dry skin has a pretty high resistance. Not sure what the actual voltage threshold is, but at 64 volts, I've been shocked (working on locomotives). Although I don't recommend it, you can put a 9V battery on your tongue to complete the circuit. When you do complete the circuit, the energy is dissipated (usually as heat).. so that 64 volts I conducted across my hand left a small burn mark."
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fee6re | Do fridges work harder with more items to cool? | If there are more items in the fridge does each one cause the fridge to have a higher uptime when maintaining colder temperatures? (Username not related) | Engineering | explainlikeimfive | {
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"Actually, if the fridge is full of objects, it is easier to keep it cool, because they can take in a lot of energy while barely raising the temperature. But if you put a lot of warm stuff in the fridge, it does take longer to remove all the heat in them.",
"It takes more energy to cool more items, but once they reach the temperature of the fridge, it they take roughly the same energy as air to keep cool.",
"Others are discussing the way a fridge must cool down any things you put into it, but there's also another scenario: long after all the things you've put into the fridge are cool, what does the fridge have to do? If you open the fridge door to take out a can of beer for example, a lot of the cold air in the fridge escapes and is replaced by room temperature air. That air will have to be cooled down by the fridge. But the things that were in the fridge will barely notice a change in temperature (unless the air is really hot). Technically, if the things you store in the fridge are not crowded to the point of limiting normal air flow inside the compartment, the more things you have in there the less air will require cooling after the door is briefly opened."
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feki94 | Why do some mirrors make you look different than others? | Engineering | explainlikeimfive | {
"a_id": [
"fjolswp"
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"text": [
"Because the surface of the mirror isn't flat. For example, if you look at your reflection in a drinking glass, you will see a distorted reflection. Same for funhouse mirrors."
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5
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fexn3g | how are gymnastics bars so flexible without breaking or cracking under all that weight? | Engineering | explainlikeimfive | {
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"text": [
"Gymnastic bars are made out of fiberglass and given a wooden coating. Fiberglass is, by design, an incredibly flexible material. And that as well a sproper trianing allows them to bend without breaking when used by gymnasts. But by no means are they invinsible, they can break it's just rare. Like with pole vault shafts"
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ff0pzm | Why do both Diesel and Petrol pumps have the same shape nozzle? | Engineering | explainlikeimfive | {
"a_id": [
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"fju0bsu"
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"text": [
"Because most people aren’t total imbeciles, quite simply. Of those who put gas in their car, a good deal of them can both read and comprehend the writing on the pumps",
"Diesel pumps won’t fit in something that takes gasoline for the most part and they are obviously marked as well.",
"Diesel pumps nozzle are bigger than gasoline nozzle so, you won't be able to fit it an a gazoline car. Obviously, you could still pump gazoline in a diesel car.",
"It’s more cost effective to make things the same shape/parts so that you don’t have to buy twice as many replacement goods. Luckily diesel is generally always in obnoxious green color and separated from the other nozzle"
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ffgcog | How long does the aerobic/anaerobic digestion process used by sewage treatment plants and organic waste recycling programs take to cycle through? | I've been reading on how organic waste from sewage and food waste is broken down into biogas and/or fertilizer. But there is very little mention as to how long it takes. How long does it take for one of those massive digestion tanks at sewage treatment plants to completely cycle through? How long does it take sewage between arriving at the plant and being fully processed? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The key phrase you're missing is 'retention time's. It's usually a continuous process from my understanding, so there's always stuff flowing in and out of a tank. The retention time is the average amount of time that a specific volume of water would spend in the tank. Discussion [here]( URL_0 ) for a discussion on retention time in a theoretical plant.",
"Three things. Retention (detention) time is the time it takes a volume of wastewater, let's say a liter. Depending on the flow rate and type of treatment system typically retention time is about 10 hours for a conventional activated sludge plant. The microbes doing all the work breaking down the pollutants typically have a residence time of 5-10 days within the activated sludge process. This is the aerobic portion of treatment. Solids removed during primary and secondary treatment have a retention of 25-30 days. This is the anaerobic process. With advanced treatment systems these times are longer. Source: 32 years in water and wastewater treatment."
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ffljcq | Why a battery is short circuited when connecting the terminals without anything between but not when they are connected with an LED and resistor in between. | Is there a certain amount of resistance that is required in order for a battery not to be short circuited? How do I find out what that resistance is? & #x200B; If I connect a battery to an LED without a resistor, will the battery still possibly be short circuited? & #x200B; Why does it matter that there is something using the electricity in between the positive and negative terminals of the battery? Does the current have to be slowed in order not to short circuit? If so, by how much? Also, would there be a way of making a battery that isn't negatively affected by a short circuit? And does short circuiting use the battery's power more quickly than if it were in a non-shorted circuit? & #x200B; Edit, bonus question: A NOT gate can be created with a switch that bypasses the output (LED for example) by creating a short circuiting, but is a NOT gate normally created by a switch that is naturally in the closed position and only in the open position when pressed? I think that would make sense. & #x200B; Thanks! | Engineering | explainlikeimfive | {
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"Batteries have a discharge rate they are rater for. Usually 1C which means it takes 1 hour to discharge. If you short it all the energy will flow as fast as the chemistry allows which results in the energy being dumped as heat inside the battery. A load has a resistance which limits how much energy can flow. If a battery has a capacity of x amp hours, to discharge it at maximum power you need to draw x amps. A=V/R so R=V/A. A 2 amp hour 12V battery would need a 6 ohm resistor. Note that car batteries are build for surges so they have high C rating but can only be discharged a bit or they degrade. A semiconductor like LEDs dont have a set resistance so you need a resistor to limit it unless the battery voltage exactly matches the LED voltage(3V for blue/white). It will burn at higher voltages and not conduct at lower. To make a NOT for a LED you use a second transistor to bypass the transistor in series with the LED. This way you only waste the power needed to turn on a transistor. But more efficient systems exist."
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ffr6h5 | How did they turn the big gun turrets on a battleship? Are tanks turrets turned the same way? | Engineering | explainlikeimfive | {
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"Basically at around deck height the turret narrows a little before continuing down into the ship. This lip sits on rollers that hold the full weight of the turret. Above deck the turrets are in their turrety shape but from the deck down the turrets are perfectly round. To rotate the turret there is usually one large gear ring across the entire diameter that engages with one or more motors that rotate it. I think some older tanks have a backup hand crank to do this as well Interestingly gravity is usually the only thing that keeps the entire turret in place, sometimes a sinking ship will roll over and the turrets will fall out completely",
"Along the ring of the hole for the turret, you have ring gear that if fixed to the ship/tank. You put a gear on the current that engage the teeth and rotate it to turn the turret. Who you rotate the gear depending on the design. I know for certain that on tanks you initially had hand ranks and they still have them today as a backup. To increase speed, you use electrical or hydraulic motors depending on the model, this starts even before WWII. There were a few early tanks with small current with not gears you just grab handles and turn with your body. How it was powered on a battleship is another question. I would guess that you have manual system for backup and the motorized system can run on steam, hydraulics or electricity perhaps even a small internal combustion engine as a backup. Here you can see the ring grear on a IOWA class battleship. [ URL_0 ]( URL_0 )"
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ffsmf8 | How do the A/C and heat work in a car? | Engineering | explainlikeimfive | {
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"text": [
"Similar to how they work in your home. The cars heater takes engine heat that is usually vented through the radiator and uses some of it to make the inside of the car more comfortable - that's also why it takes a little while for the heater to start working if you just started the engine. In your home a gas or electrical furnace generates the heat, but in a car there's already plenty of waste heat so no \"furnace\" is needed. The airco is basically a pump that compresses a liquid (a compressor) - as the liquid is squeezed together it heats up. The heat is vented to the outside air. The liquid is then sent through a heat exchanger where it is allowed to expand again, as it does so it cools and takes heat from the air sent along the heat exchanger. The cool air is blown into the cars interior. Home aircons use an electric pump (that humming noisy thing outside when the thing turns on), but often a car airconditioner just uses the car engine itself to run the pump. Which is also why the airco won't work if the engine isn't on."
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ffufnz | why flat bed tow trucks use beds with a little bit of an arch to them - instead of being truly flat. | Engineering | explainlikeimfive | {
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"The built-in arch compensates for the sagging due to heavy loads on the bed. So when the load is applied, the bed of the truck wants to be flat, instead of sagging down. This is more important for large trucks than it is for pickup trucks, say, because of the length of the bed.",
"Couple concepts needed to understand this. First, metal breaks when the stress gets too high. Loading a truck trailer puts stress on it, you can almost think of \"load\" and \"stress\" being nearly the same idea. Second, stress goes in more than one direction. There is compression (squeezing) and tension (stretching). When you load a truck trailer and it sags, the top surface of it is being compressed and the bottom surface of it is being stretched. So when the truck trailer is manufactured, it can be made with a stress already in it. I'm really going to simplify here: they put an upward load on the beams of the trailer as it is being made, and when it \"solidifies\" (i.e. the welds or the casting or whatever), the metal is stuck with that stress in it. The top surface is stretched and the bottom surface is compressed and it is bowed upwards. And this is the opposite of what a load on the trailer will do. So say you add a load to the trailer slowly - the trailer is pushed down and that upward bow is less and less - and the built-in stress in the metal is actually counteracting the stress of the load, so the overall stress is DECREASING. At some point the trailer is flat. You can continue to add weight and the trailer will bow downwards. At some point you reach whatever the safe limit is and you must stop. But the whole point is to allow a trailer to carry more weight than it normally could without the pre-stress. edit: Thanks for the gold!",
"Ah, a topic I can answer. URL_0 This is what I am currently driving- well, I'm in the dock but you get the point. We have upwards of 100,000 pounds (45,000 kg) of steel/aluminum on our flatbeds. The arch is to provide weight support so the deck doesn't bow under all that weight.",
"It's built-in so the weight will still keep the arch pointing up, it's not made to go flat or point down under design loads. If it's overloaded the bow won't come back up. It's one visual cue that the trailer's not ok. Source: Father worked at trailer factory."
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fg18jq | How are wooden baseball bats so durable? | In the MLB there are 250lb+ men who hit the ball with exit velocities over 100mph and yet the bat doesn't shatter into pieces. I know sometimes the bats do crack, but most of the time they are fine. How? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Hitting the ball with the grain of the wood the correct way. Like how a stack of papers won't bend along the edge, but will bend easily across the sheet.",
"According to this source, a pro baseball player goes through 120 bats per season on average. There's only 162 games in a season, so the average bat doesn't last more than two games. That might be due more to optimal performance than durability, but in either case we can conclude that a bat becomes structurally imperfect very quickly in a pro setting. URL_0"
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fgff4q | How do magnified mirrors work? And why do they seem blurry if you look into them from a distance? | Engineering | explainlikeimfive | {
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"text": [
"A lens is a piece of glass that bends light so that the rays converge to a single point. If you bend a mirror it will make all the beams converge in the same pint, so it’s the same as a lens, only instead of passing light through, it reflects it, so both the observer and the object are on the same side, or in this case both are your face Just like a magnifying glass you need to be in the right place for everything to be in focus",
"A normal mirror is flat, reflecting light at the same angle thus the reflected image is in the same proportions. However, if you curve the mirror, light reflecting off it will bounce off in different directions depending on the part of the mirror light hits. For example, you can buy a mirror to help apply makeup that is concave. This takes light coming in and focuses it to a smaller point. If your eye is at the focal point, you'll see everything magnified. But if you back up beyond the focal point, the light inverts and becomes blurry. Some diagrams may help. Found some simple ones here: URL_0"
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fh40f7 | How come normal roads are so susceptible to potholes, but you barely see any on motorways? | Engineering | explainlikeimfive | {
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"text": [
"Pavement design engineer here. Pavement has designed based on the expected traffic it’ll handle- specifically, the number of *large, heavy trucks* it’ll handle. Passenger cars and light trucks barely damage the pavement. It’s the huge semis that have the loads that damage the roadways. So motorways are designed to withstand those loads and thus are thicker and build with more layers (the subgrade, or soil under the pavement, is often improved/stabilized as well.) Roadways don’t carry that kind of truck traffic so they’re less thick and less stabilized. Along with truck traffic, there are a few other things that cause potholes- -bad drainage (common on urban low volume roads) - freeze/thaw cycles (cause the pavement to expand and shrink, causing cracking.) - cracking that isn’t maintained/sealed (again common in urban low volume roads because no one wants to wait for construction during rush hour.) So you have a few things going on. The motorways are thicker with better materials, have better drainage, and are maintained more often. More money is spent on them. The cracks are sealed promptly and maintained. Large cracks are patched. And bad pavement is milled off and replaced on a cycle. (And, typically, motorways are controlled by an entity that has a larger budget, too.) Edit: spelling",
"Roads less travelled typically aren't as thick as major roadways. Often they are built differently too, using weaker (and cheaper) stuff to make it. Major roads are recovered more often, before they can become a pothole parade."
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fh8asn | How do counterweight systems, like old style lifts, work? | I know there's a weight on both ends. But how does the system control which goes up or down? | Engineering | explainlikeimfive | {
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"text": [
"The counterweight weighs close to the same as the lift when empty. There is a motor that pulls on either the lift or the weight. Since they balance the motor only needs to lift the weight of the stuff inside the lift, and not the whole weight of the lift and the stuff inside (plus some extra friction in the system because of the extra weight on the bearings). That way you can use a much smaller motor and less energy when moving the lift than you would need for a non counterweight system."
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fhujls | How does a wheel and axle make work easier? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Wheels reduce friction but an axle and wheel works like a lever and fulcrum: either you can apply a great amount of force over a short distance and receive a great amount of distance or you can apply a small amount of force over a great distance and receive a great amount of force. Think of a lever as a wheel and a fulcrum as an axle. Basically, it uses the mechanical advantage of distance to reduce the amount of force needed to move things. Edit: maybe think of it like an axle, a fulcrum, a pulley, and a wedge all allow you to divide or spread out force over a distance and that allows you to apply more force over time (and the reverse is true as well: you can increase force applied at a smaller distance/time and have it be dispersed over a greater distance/amount of time, depending on where your fulcrum is and where you apply force)."
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fhykg0 | In what way does the mpg or kmpl number of a car depend on its speed? Is the advertised number based on average speed or a specific speed (say, 60 km/h)? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The advertised number is based on a specific test condition The EPA has two profiles, one for city and one for highway, that involve speeding up, coasting for a bit, slowing down, speeding up, etc over the test. The city test is about 20 minutes long and the highway one is 12.5 minutes long. The rated fuel economy is only true for those specific test profiles which is why people generally see different real world numbers You can see the test profiles here URL_0"
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fi1goc | why don’t you have any signal in elevators? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"RF energy is absorbed by the metal box that makes up the elevator. Thus signals between you and the cell tower or even local router can't easily get out nor in."
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fifz1p | What will happen to the sewer system if enough people can only use paper towels, napkins, etc to flush? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"In places where the sewer system can’t handle tp people put a little trash can by the toilet. You throw your paper away and don’t flush it. This is pretty common in small towns in less developed countries. I’ve also visited countries in Asia where there’s a bucket and a little measuring cup sort of thing that hangs on the side that you use to to wash yourself. There are many paths to cleanliness.",
"Toilet paper (if you haven't noticed yet) is extremely weak when wet. While paper towels retain their structural integrity when wet. Meaning that paper towels will still be a solid mass of fibers in sewage systems. Much like fiber I'm your own digestive tract, those fibers cling to solid particles and grow into larger solid masses. Thus if enough people use them it creates large heavy blockages which are known as \"fatbergs\" It's actually a huge problem in many large cities and the main culprit is supposedly flushable wipes (which actually aren't flushable at all)."
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filsmm | How do experienced organizations like the military effectively ration food to provide sustenance, avoid waste, and avoid running out? | Engineering | explainlikeimfive | {
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"It actually becomes rather easy when you're dealing with larger numbers of people. While one person's appetite and diet varies day to day, those changes even out with massive numbers of people. So while you may be really hungry today, it's unlikely that 1,000 people are all going to be really hungry today as compared with yesterday, unless they all ran a marathon or something. So you keep track of the history of things. Say you run a cafeteria for a school. You plan out your meals to provide a balanced diet; people are getting roughly the right ratios of carbs, fats, proteins, etc. You expect, say, 10 percent fewer diners on friday, because more students just leave after morning classes to start their weekend early. Maybe spaghetti day is super popular, so you have fewer diners bringing their own food and you serve 10% more people that day. If you find that you're using, on average, 20 cans of corn per week, you order 20 cans per week. Just as with a family, it's a matter of learning from the past and keeping track of what works, what doesn't, and when to expect variations.",
"The military is probably one of the worst examples you could use. At least in reference to the United States military, they have a horrible habit of fraudulently spending so that they can ensure they have the same budget every year. They claim to consume everything that they purchase, but a lot of that consumption is throwing away the products. generally speaking, once an organization hits a certain size, their waste is inevitable due to the size of the infrastructure. You can do two of the three things. You can provide sustenance and avoid running out by having an excess. You can provide sustenance, avoid waste, but potentially run out. You can avoid waste and running out, but odds are that someone will be lacking in sustenance."
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fis7zq | How dependent is “the grid” on people? | Engineering | explainlikeimfive | {
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"It depends on where you live and what systems your municipal providers have invested in. Most stuff would probably work fine, *for a while*. The problems arise when something breaks, no one fixes it promptly and little problems cascade throughout the system, becoming big problems. For example, a clogged strainer at a water pumping station is no big deal on a routine day. A controller re-routes supply, other stations ramp up flow and a crew is dispatched to clean the strainer, bringing that station back up to capacity. If however the controller doesn’t re-route supply or there is an electrical fault at another pump station, then cities can end up with low or no water pressure. That is a big sanitation problem."
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fj12lm | Why do tin cans have those extra creases/lines? Why aren't they smooth like an aluminum beverage container? | Engineering | explainlikeimfive | {
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"Any time you see a corrugation, it's usually entirely for one reason - if it was a flat sheet, it would bend. By corrugating it, you are preventing that bend from occurring, as it's difficult to bend a corrugation. Don't forget that drinks cans are pressurised, so can't bend. Tins aren't, they are just sealed.",
"Structural strength - Less likely to dent. Aluminum has different structural properties, and I believe those beverage containers have a smaller diameter, so are stronger.",
"The \"ribs\"or corrugations on these cans are there to strengthen the side walls and lid. This helps them resist denting. The cans are filled with food, then flash cooked with steam, the lid is then quickly assembled and then crimped with a special machine which produces a mechanical seal, while the food is still near boiling. The cans are then cooled in a cold water bath for several minutes. The hot steam in the top unfilled space excludes air and causes a partial vacuum to develop inside the can as it is cooled. This fact is actually important as the design of the joint of the lid is such that the force of the vacuum inside clenches the lid against the sides, improving the tightness of the seal. However, the partial vacuum make the can prone to buckling or denting. This doesn't usually affect the seal or the quality of the food but is unsightly. The Corrugated ribs where added to improve denting resistance. 2) On the other hand, aluminum drink cans don't usually have such ribs because they're usually *pressurized*, unlike food cans. The positive internal pressure is very effective in resisting denting and crushing. Even if you manage to temporarily dent them, the internal pressure causes the dent to spring back out as soon as the force is removed. Final note: Despite the colloquial name, modern food cans are usually zinc plated *steel*, and usually have an additional coating of paint or lacquer on the inside to prevent corrosion from food acids. Modern cans contain no actual tin. Food vessels made of tin or tin alloys such as pewter have been made by skilled artisans since at least the iron age. Early attempts at hermetically sealed food were made with glass bottles and either cork stoppers or tin lids. But these were easily broken. Inventors switched to using cans formed of tin sheets, and employed skilled plumbers to fabricate them by hand. As thin steel sheets became widely available, canners switched to steel that was coated in tin because it was much cheaper, stronger, and lighter in weight. The unfilled lidless cans along with the lids were then dipped in a bath of molten tin or tin-based solder. Hence the term \"tinned cans.\" The tin coating served to protect against rusting and also filled ocassional gaps in the bottom joint. Finally, the lids were sealed on the cans by flowing more tin solder around the head joint, a process also sometimes known as \"tinning.\" In the Late 1800 a process was invented to seal the lids by mechanically crimping the joint instead of soldering. This saved a great deal of labor. The public had long used the term tins or tin-cans by this time despite the switch to steel construction. However zinc is much cheaper than tin and offers similar corrosion protection, so using zinc plating or an alloy of zinc and aluminum became industry standard in the 1990's and the use of tin has gone out of favor in most cases."
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fj8mug | Why pilots used to say "when in doubt, land long" ? | It comes from a book I'm reading , quoting some astronauts talks transcriptions , they often refers to a specific terminology used by pilots. E.g. "break, break" or "no sweat" | Engineering | explainlikeimfive | {
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"Basically, landing long you're going faster and landing further down the runway than ideal. Landing short you're slow and landing closer to the beginning of the runway. When landing long you have more airspeed and altitude and more options. If there's wind shear it's less likely to drop your airspeed below stall speed. If everything isn't right you can accelerate, climb and try again. If you're landing short, you're slow, maybe on the edge of stalling, you have less chance to go around. Wind shear might cut your airspeed even lower. If you do stall, you crash and die(Maybe literally) It's oversimplifying, but airspeed and altitude are your friends."
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fjninn | Why does RPM spike when you turn? | I parked my car yesterday and was straightening the tires when I saw my RPM go up from about 700 to 1000. Why does it do this? | Engineering | explainlikeimfive | {
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"If you were stopped and you noticed this, it’s because most vehicles have power steering now. Power steering takes power from the running engine to operate the steering pump. When you turn the wheels, you operate the pump, increasing engine rpm. Try putting it in park and turning your wheels, the same should happen. Also in park try turning the a/c off and on. The a/c pump also runs off engine power and will effect the rpm."
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fk61pt | How to work the gears on my 10 speed bike? No judgment please. | My brain never could wrap around how and when to change gears on a 10 speed bike, so I’m limited on bicycle riding. I can drive a manual car, so if you need to use that as an example, feel free. Please help me understand so I can ride bikes with my little ones. | Engineering | explainlikeimfive | {
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"The bike is just like the car in this regard. You (the bike's motor) have a limited amount of force you can apply to the pedals (torque) and a limited maximum pedaling speed (red line). If you set the gear low, you can travel slowly up a hill, where the load is larger, but you hit your pedaling red line when you go downhill. If you set the gear high, you can go faster, but it's hard to start moving because you don't have enough torque. Sadly, the range of optimum power output for a human is smaller than a V6, so your bike needs more gears than your car even though it doesn't go as fast.",
"When I was learning, I tried to find a large paved empty space (like a deserted parking lot) so I could focus more on the feel of the bike and less on traffic. Enjoy!",
"I didn't see this mentioned, I hope it's not to obvious. You should only shift while you're actively pedaling. It will take some practice, but you'll need to remember to downshift to a comfy starting gear *before* you stop. If you're only riding with your kids, you'll only really need two gear positions: starting from a dead stop and cruising. Once you find a good gear for starting from, usually shifting the front sprocket (left shifter) up a gear will provide a comfortable cruising resistance at a kid friendly speed.",
"Assuming you actually have a bike with 10 gear configurations (most modern multispeed bikes have more, with 16, 18, 21, 24, and 27 being common): * Your left-hand shifter switches between the 2 gears on the front chainring. Ignore it for now. * Your right-hand shifter switches between the 5 gears on the rear chainring. This is the one you will use mostly. * You want to keep your legs pedaling at a steady rate, usually around 60 strokes per minute. When it gets too hard to do this (mashing), downshift using the right shifter. When you have to pedal extra fast to get any resistance (spinning), upshift. Ideally, you should be feeling a small but firm resistance you can maintain indefinitely. * Back to the left shifter. I think of the big front chainring as a cruising mode and the little one as climbing mode (or into the wind mode or I'm really tired mode). I stay in cruising mode most of the time, downshift as things get harder, and switch to climbing mode when I run out of gears. Similarly, when I am in climbing mode, I upshift until I run out of gears, then switch back into cruising mode. * Note that cruising mode and climbing mode usually have some overlap. Your lowest cruising mode gear will be lower than your highest climbing mode gear, so you might need to upshift or downshift a few times when changing modes."
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fkosq2 | Current in a wire flows opposite to the direction of flow of electrons, what exactly is current then, if there is nothing actually flowing? | I know that flow of electrons is not current, it is opposite to the direction of flow of electrons, is it just a convention? why such a convention was chosen if it is one. . Please correct me if you think i have very wrong assumptions. | Engineering | explainlikeimfive | {
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"* Back when Benjamin Franklin studied electricity, he discovered that current flowed but wasn't sure which way was positive and which way was negative.... * So he guessed. * Later they found out he had it backwards. * But they had used his conventions for so long that they kept it. * So \"current\" and flowing electrons are the same thing just the signs make it seem otherwise.",
"It is a convention that was chosen at random, because it was known that there were two \"kinds\" of electricity that canceled each other out. This was before electrons were known about. However, that doesn't make it \"wrong.\" *Usually* what is physically happening when we talk about current is flowing electrons, however that is not necessarily true. Current is the net flow of charge, not the flow of electrons. **Current is (flow of positive charges) - (flow of negative charges)**. In a normal copper electrical wire, it's only electrons that are moving, and they are negative. But in a battery, both positive and negative ions are moving, in opposite directions. In a semiconductor, positive \"holes\" and negative electrons both move. In the solar wind, electrons and protons both move. etc.",
"Because Benjamin franklin just guessed which way it went and nobody was bothered to change it when they found out he was wrong.",
"It's a flow of \"holes\". Imagine a traffic jam where you all shuffle forward a bit when there's a space, that space seems to ripple backwards as the cars come to fill the gap. Same with holes - electrons come to fill a hole, so the hole appears to flow in the other direction.",
"At least in german education you are usually taught about the concepts of technical and physical current flow. Technical current flow is form positive to negative where as the real phyiscal current flow is the movement of electrons from negative to positive."
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fkvkb9 | How does a single thread run on multiple cores? | REDIS is single threaded. So what does it mean when I deploy it to machines with 2 or more cores? How does the single thread utilize these multiple cores? | Engineering | explainlikeimfive | {
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"It doesn't. That's the point - each thread only runs on a single CPU core. If REDIS doesn't support multiple threads or multiple processes, it will only use 1 core. Other things can use the other core though. The OS itself, scheduled jobs, remote access, logging, whatever else can use the other core without impacting REDIS.",
"In order to process multiple threads the OS runs the thread in turns, each one gets to run on an available core for a few milliseconds so over time all threads can progress. If a thread has no CPU affinity it can happen that on the next turn it runs on a different core, so the thread technically runs on multiple cores, but only on one core at a time. To make it clear this means that at most it's processed as fast as a single core allows. Because of this, when running a heavy thread on a dual core CPU the task manager may display both cores having a load around 50% giving the impression the thread runs on both cores simultaneously but this really means it runs on each one about 50% of the time."
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fkxxdt | - Why Does A 4 Cylinder Motorcycle Engine Sound Different To A 4 Cylinder Car Engine? | Engineering | explainlikeimfive | {
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"Sound suppression is a huge part of it as well. Cars have massively more exhaust hanging on them, and the engine is tucked away. Motorcycles have quite short exhausts and aren't particularly well known for running intentionally quiet. The exposed engine also let's you hear all the gear whine and clakety clack of various parts. If you bogged a bike down with all that, the differences would be much less obvious, and more like why a boxer sounds different than an I4, all else being equal.",
"The engine note will have a lot to do with whether the cylinders are in an I4 or V4 configuration, the angle of the V, the firing order, and how the cylinders are collected in the exhaust manifold. All this will have a great effect on when an exhaust pulse is released into the exhaust system and how it travels down and exits to where you hear the note. Additionally, cars are far more likely to have a flat-four configuration, which is relatively rare in motorcycles. The flat-four has pistons horizontally opposed to one another and they fire simultaneously to cancel out primary harmonics (engine vibration). This is going to generate a note that is going to be very rare in the motorcycle world. Flat-four or boxer engines are very popular with Porsche, Volkswagen, and Subaru. 2-stroke engines are far more popular in motorbikes than cars, and they, too, have an undeniably unique sound. Not only does it change how often an exhaust pulse is released, but the valving may also be different, shaping the kind of noise the exhaust is going to generate as it whooshes through those internals. The configuration of the valves in the engine will tune the sound of the exhaust like a trumpet. 4-stroke engines are typically cross-flowed, where the intake comes through one set of valves on one side, and out a set of valves on the opposite side. 2-stroke engines may be valved or valveless, and their configuration is exceptionally important because you want the exhaust to exit completely and help pull in a fresh charge. This is called scavenging. There is additional scavenging in the exhaust manifold. A tuned manifold is designed around the firing order so that the pulses go down the exhaust pipe in regularly spaced pulses, each pulse using its inertial to help pull the exhaust out the exhausting cylinder behind it. This increases engine efficiency, also changes the sound. A tuned header will make sure all the pipes are the same length before they're joined at the collector - since the collector is at the back of the engine, the closest cylinder has the shortest distance to travel, and ends up getting a loopy pipe! Or you can forego the whole thing and just combine everything wherever is convenient for the engine packaging, either on the bike or in the car's engine bay. Cars additionally scavenge within the exhaust system with a crossover pipe. If you have a V configured engine, then the two banks will have their own individual headers, and they can be combined in an H, X, or Y configuration. As you can imagine, this has an effect on the exhaust note. By comparison some bikes, especially dirt bikes, use expansion chambers to promote scavenging. Another aspect is engine speed. Motorcycle engines are tiny by automotive standards. They're low torque and high horsepower because they have a huge power to weight ratio, and unlike a car engine, you can buy a production street bike with a redline at 21,000 rpm. A piston engine! The damn thing has to move in one direction, stop, move in the opposite direction, and stop again, before repeating the cycle! Up to 350 times a second! And you're leaning over that critical mass with it resting between your legs should that decide to go south... By comparison, F1 cars are currently limited by regulation to 15,000 rpm. Cosworth built an F1 engine for Ferrari that went up to 22,000 rpm but its existence incited the initial engine speed limit before the 2016 season. You have to appreciate that these engines only work in these \"cars\" because they're actually lighter than some street bikes. A couple companies have actually tried putting F1 engines in street legal cars, but with all the weight incurred in meeting street legal regulations and safety, they just weren't powerful enough to get the car moving from a standstill, the cars were too heavy. Digressing, most street cars have a rev limit of about 8,000 rpm before they're likely to self-destruct because they're literally so massive. Finally, there is the muffler. Its job is to absorb and cancel out the pulses so that the noise level is reduced. These things can be tuned through their geometry and materials. Some mufflers use sound deadening materials like fiberglass - it's like your car is screaming into a pillow. Your whole engine system is a glorified musical instrument. The ultimate tin whistle."
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fl7wai | I've heard building mechas is really difficult but there is no problem in building small humanoid robots (Boston Dynamics). So can't we just upscale them and make mechas this way? | Engineering | explainlikeimfive | {
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"Square-Cube law is a bitch. If you take a human, and increase them in volume so that length width and height are all 2x bigger, they will be 8 times the volume, but the area of their footprint will only be 4 times as big. The surface area of an object scales squared, while the volume scales by its cube. This means that the weight per square inch of foot will increase significantly. There are other similar reasons why things don't just scale up, but most come back to square cube law in some form.",
"Well, like others said there is the square-cube law, but that's not the only reason. \\- Small humanoid robots are not easy to build. They are expensive and usually great at only a limited amount of things. For example, most of boston dynamics robots are good at moving on legs. They have great equilibrium, can move in different terrain, etc. But they can't relly lift much than small object, they have limited dexterity, etc. \\- Almost if not all humanoid robots are just demonstrator, test, prototype. They exist to improve our know how and show to public/investor for companies to get more investment. Upscaling them to make mecha is just upscaling cost, with little demonstration that it would bring them more money. \\- Mecha are not a good idea. People like them because they are cool looking and that's why we see them in fictional stories, but in real life even if they would be cheaper, barely anybody would pay for them. They are simply almost always a better machine to do the job.",
"Boston Dynamics’ robots are not easy to build. Nor are they easy to power. Nor are they inexpensive.",
"The big problem is what is often called the \"square-cubed-law\". It's called that because some properties of an object increase with the area (square), whereas others increase with its volume (cubed). In other words: If you make something twice as big, it's less than twice as strong. For example, ants are strong enough to lift objects that look ridiculously large in relation to their body size, even though they have tiny legs. But if you scale an ant up to the size of an elephant, its legs would just collapse under its own weight - which is why elephants have legs like tree trunks. For engineering, this means that making things bigger is often difficult. A hobbyist can make a scale model of a passenger airliner using nothing but styrofoam, whereas Boeing has to use strong materials like aluminum and carbon composite for the real thing. And likewise, a boston dynamics robot scaled up into a mecha sized war robot would probably crumble under its own weight.",
"\"Just upscaling\" doesn't work because of the [square-cube law]( URL_0 ) - if you take a working robot design and double its scale you're moving 8 times more material with motors that are only 4 times stronger. Eventually your materials fail because of the weight on them, or the motors are unable to move the robot.",
"In addition to the Square-Cube law, you also have limits on materials. As you have much higher weights, the torques becomes much higher, the ground pressure spikes a lot more, the heat dispersion becomes more problematic and so on. Also the reason as of why you want to have such a colossus needs to be answered. The rule of cool does not apply to economic realities. Bigger is not always better :/",
"It is a mistake to think we have \"no problem\" building those kinds of robots. Boston Dynamics makes cool stuff, but they have been at it a while and there is a reason we are don't see their robots running around everywhere. They have a very limited battery life, and right now, they are so expensive you are better off with a traditional robot or even just hiring a guy to follow you around and do stuff. Even if we had the technology for mecha (we don't) they question would be, the question would be, what is a more effective military option, one mecha or six fighter jets and twenty tanks?",
"A lot of people have covered the square cube law, that's a significant engineering barrier. However theres also the issue of practicality. The first significant problem with a large biped robot as a weapons platform is that it can fall over. How much damage would the top part of it receive if a 50ft tall robot just like tripped? Never mind the insane difficulty of just designing something that size that can be mobile. If you can just mount missiles and cannons on tanks, artillery, warships and planes why bother with a hugely complicated giant walking robot? Pacific Rim looked cool, but if we got attacked by actual Kaiju the solution would be to just blast them with missiles launched from literal miles away. It would probably only take one. They make bunker buster missiles that can penetrate multiple layers of steel reinforced concrete THEN explode. Nothing organic could hope to withstand that."
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