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bhxtca | Why are the clips on all car seat belts different to clips on all airlines? | Push the red button vs. Lift the flap | Engineering | explainlikeimfive | {
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"While the red button is easier to push, there is less room for mechanical error with the lift the flap method, which means less maintenance."
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bhz37k | Why it takes so much time to build Sagrada Família? | Engineering | explainlikeimfive | {
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"It’s considered never ending both because architects had to recreate the plans for parts of it (original plans got set on fire is my understanding); and because it’s built entirely by donations to the church. Not the capital-C organization church, but the individual cathedral.",
"Work was halted for many years (mostly due to money) and went backwards due to wartime damage. Then for a long time they were going slow because they weren't totally in agreement about what Gaudi's vision was (some plans were lost, others never completed) and so they wanted to put off key decisions until a consensus was reached about what it should look like. Now it's basically about money. Carving stone takes time, but if they hired more stonemasons they could carve more stones and get it done quicker. But that would mean having to build more workshops, so doing it more slowly is cheaper."
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biicn0 | Why don’t automatic cars stall at traffic lights? | I understand they use a clutch, but how come the power is instant and there is no lag/it’s smooth to accelerate? | Engineering | explainlikeimfive | {
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"They don't use a clutch. Instead they use a fluid coupling called a torque converter which works kind of like one turbine spinning another with transmission fluid, or think of one fan blowing another fan to make it spin. The torque converter is designed to allow the input and output shafts to spin at different speeds, including one being stopped completely. When power is applied the u get smooth acceleration because the fluid absorbs a lot of it.",
"A automatic transmission uses what is called a torque converter. It's basically two opposing fan blades. One fan blade is connected to the engine the other is connected to the transmission. The torque converter is filled with oil. When the engine is turning it spins its fan. The fan sprays the oil against the fan connected to the transmission and spins the second fan and drives the vehicle. When you are stopped the engine is not spinning its fan fast enough to turn to second fan connected to the transmission to overcome the brakes of the vehicle. The fan connected to the transmission is stopped or stalled. Once the brakes are released the fan on the transmission can usually turn. Unless you are on an incline or in a hole. Then you would accelerate the engine which turns the fan on the engine faster which in turn applies more fluid force to the fan on the transmission. The state of the torque converter is accelerating now. The engine fan is turning the transmission fan, but the engine fan is turning quick with the transmission fan is accelerating to the speed of the engine fan. Which give the vehicle a smooth acceleration. A good visual of this would be if you took two house fans and pointed them at eachother. Turn one fan on and it will blow air into the second fan making it turn. You could hold the second fan with your hand. When you let it go it will start to spin.",
"People here are correct in that traditional autos don’t use clutches, but nowadays a lot of cars are transitioning to using electro-hydraulically-actuated clutches which are more efficient than torque converters and basically are a computer controlled clutch.",
"An automatic doesn’t use a mechanical clutch. It uses a torque converter, which is hydraulic. It’s calibrated to transfer power above a certain rpm. So at idle, it allows the engine to spin without transferring the power to the wheels. In a manual, the clutch doesn’t care how fast the engine is spinning, if the pedal isn’t pushed, it’s transferring power to the wheels. And if you stop the wheels, you stop the engine. I’m a mechanic, not an engineer, so I’m sure someone can explain it much better than that, but that’s a start."
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biofuu | How do modern vehicle speedometers work? Tire rotations per minute? | Engineering | explainlikeimfive | {
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"Yep, tire rotation. Knowing the diameter of the tire and multiplying that by pi gives you the distance traveled per rotation. That means that if you do anything to increase the diameter of your wheels, you need to also get your odometer adjusted, or else you will actually be driving faster than your car thinks you are going.",
"It's already been answered, but most vehicles now have a VSS (vehicle speed sensor) that measures pulses on the transmission, and does math of the tire size to figure out speed. Your wheels might also have speed sensors to ensure ABS and traction control work, but these are not used to determine vehicle speed.",
"How much error is introduced by tire wear? New tire vs old worn tire...",
"I just answered this in a different question. But in short, yes: URL_0"
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biw2lc | Why does software go down/crash so often? | Engineering | explainlikeimfive | {
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"Did you miss the planes crashing recently? How many cars get major recalls? Software is not immune to mistakes, but it's compounded by a combination of users that use it poorly and hardware not created by the software developers. As a programmer, I can't make your hard drive not suck. I also can't make you keep enough free space, or run other software that conflicts with mine.",
"You guessed it, the problem is that the standards are so low. People have a new idea for something software should do, and expect to see that released to the general public, in full use, in just a few months. Most engineering projects go through a much longer design and quality-control process, and some even require formal approval, which if granted incorrectly can cost someone their career."
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biwaoq | How were we able to build the tallest building in the world in 5 years, but there are those that think 5 years is too short a time to make a new roof for Notre Dame in Paris? | Engineering | explainlikeimfive | {
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"For the cathedral, they wouldn't just be building a new roof, it will be a restoration process which takes time. It is also a cultural heritage site which means it's important to history and protected by many rules and laws. Any plan to rebuild should be reviewed and approved by the pertinent authorities and the people of France. The Burj Khalifa on the other hand was a completely new building who's construction was controlled by fewer people who could more or less build it however they wanted because they had less rules/laws to adhere to.",
"Restoring a historical building is very difficult. You have to be very careful to be sure you don't damage anything, and if you're doing a faithful restoration you need to source both supplies and workmen that may no longer be commonly available. Companies that can knock out a skyscraper are a dime a dozen, but there's only a handful of people in the world who can design and build a wooden cathedral roof.",
"That five years is just to build it. Planning, design, bids, sourcing materials, etc took significantly longer. That's also not taking into account the fact Notre Dame is a historical building, and those are always a massive bureaucratic nightmare",
"Architect here. Historical restoration is difficult for several reasons. I'll list a few below. These are just examples BTW. 1. Same or similar materials have to be used. You can't use cement mortar if the building originally used lime mortar. You can't use steel truss if the original used wooden truss. 2. Even the type of wood and stone has to be original. If they used cedar, you can't use teak. If they used marble from South Italy, you can't use marble from Greece. 3. We do not have structural drawings from the original construction. If, say, the Burj suffered fire damage.... We have the structural drawings, the architectural drawings and all other HVAC, MEP, Fire drawings. We can safely modify, repair and build on top of it. We have the math and physics sorted. We don't have that for old buildings. The plans of Notre Dame are actually more of measure drawings and don't really give you structural details. 4. The finesse in carvings, paintings, stone inlay etc has to be done by hand, by highly skilled workers, for authenticity. That takes time and money. Lots of it. They even have to match the pigments, the brush strokes and the styles of art. 5. They still have to incorporate modern lighting, fire safety rules and follow construction bylaws. 6. The architects and historians working on this are some of the best in the world. They are not easily available. They also take time to do things very perfect. 7: They have to follow the historical plans to utmost perfection, and details are not always available. So they must also research, that takes time.",
"They could knock together a roof and have it on in a matter of a few weeks, but they're trying to restore the roof back to how it was, and that involves building techniques and materials which are very rare today. In addition, restoration of a building which was damaged includes a lot of work to ensure that you don't accidentally damage something else in the process.",
"You could argue that Notre Dame took 183 years to build, and accurately restoring it means understanding how it was built originally, then learning the forgotten techniques, then building it using the original methods, but slower taking care to make the same decisions and discarding your mistakes that didn't match the original mistakes. Plus, this is a repair, so the whole thing also starts with cleanup. By that logic you would expect replacing the roof to take much longer than how long it took to build the original roof. And since that may have been decades given the original timescale, 5 years sounds way too fast. I think everyone agrees they could slap a steel roof on in under a month, but that's not what they are putting in, the planning of the roof may very well take years. And the design will dictate the effort required. It's one thing if you want to stop off at home depot and grab a couple engineered beams like everyone else. It's a whole nother thing if you need to start an expedition to find 20 trees that match your specs, and then negotiate with whatever owners you happen to find to buy it.",
"As others have pointed out, there's a difference between building something fresh and restoring something. When restoring something, there's a spectrum between \"Original state\" and \"Appearing original\". In the former, you've made things exactly as they were originally built, including using the original methods (which you might have to pay researchers a lot of money for several years just to rediscover). Appearing original basically involves building the thing you want, then covering it in a facade that looks original but is usually fake to some degree. For important historical buildings and such, it is usually considered far better to restore to original state than to just appear that way. Furthermore, the skills involved for restoring things are a rare thing. It is not uncommon for large projects to have a lag-time before you start of 5-10 years while you pay for some workers to become master stonemasons and such that are actually skilled in the particular methods (that you might have had to pay researchers to rediscover). And that has to happen before even the first stone is laid in the restoration process.",
"Reno trades person here, it's not just a new roof. Smoke and fire damage has probably completely destroyed lots of other stuff. Smoke damage can change the composition and look of concrete and mortar, so think of the countless statues and pieces of other masonry art that now need to be cleaned or remade. Smoke and fire damaged buildings are often just torn down and rebuilt from the ground up because restoring things damaged in a fire is often too slow, costly and also structurally unsafe. It's probably more than just a new roof the cathedral needs. New construction is quick and straight forward. When I rip open a home several decades or more old though, that's a completely different can of worms because you never know what you'll find.",
"The Burj Khalifa was probably not actually fully completed in that time period. The overall structure may have met that deadline and some floors could still be just the skeleton waiting for an occupant to purchase and finish to their specification. I'm not actually sure about that but it's common in structures waiting for commercial occupants. They also don't have what any normal city would allow for utility setup. Everyday multiple trucks show up to get the buildings sewage pumped in and hauled away. Not many locations would tolerate having a setup like this. It would be like saying Detroit solved their water problem already by trucking in bottled water.",
"The foundation on my house is sinking. it's an inch or two lower on one side than the other. I had a guy out to look at it, they wanted to drill 22 holes around the perimeter of my house, hit bedrock, pump them full of concrete, then prop my house up on them. It'll cost $75k and take a month or more. The guy hung around for a while and we discussed it further, and the subject came up, what would it cost to drill the 22 piers and fill 'em with concrete if there wasn't a house there. Guy says $5k and they'd be done in a day. Apparently shit costs more and takes longer when you have to move a whole fucking house to do it.",
"It's not because of the time to construct but the process of having it **designed, consulted, redesigned, bidded, and finally constructed**. *Architecture is a public process.* A significant building will mean lengthy public consultations and various opinions having to be weighed, measured, and accounted for.",
"Restoring something to be identical to what it once was as compared to building something new all willy-nilly takes a lot more time.",
"Imagine playing Jenga. You're building your tower up for a new game. You need to be careful laying the bricks, so they don't topple, but all in all its fairly simple. Now imagine looking at a Jenga tower in a game that has been going on for a while. Lots of bricks missing. The owner has even customised some bricks. And you are tasked restoring it to the initial setup while maintaining the owners customization. Oh and by the way, he lost some bricks.",
"Some of those long timbers were cut from huge primeval trees that no longer exist. It might take 400 years to grow trees tall enough to provide the replacements. ;-)",
"We're talking about a 13th century masterpiece, made with carved stones, stained glass, etc. Sort of things have to be done by people, it takes time, it's an art. Not a brand new skycraper made with concrete and metal",
"We could build an exact replica in a year, quick simple and painless, but to restor and rebuild while keeping it as original as possible takes a lot of time and planning. You are making custom pieces to fit into groves that have been warped over time, without damaging the existing structure.",
"Quality hand craft, vs modern machine construction. If you’re holding to a historic remodel you’d want to do everything identical to how it was done when built. Hand tools and all. It’s easy to plop up a new sky scraper using modern tech that has a cheap glass shell, and would probably topple over if an earthquake hit. Not sure if that skyscraper would last more than a few hundred years.",
"Well, we could excavate an olympic swimming pool in a day with an excavator, but it takes an archeologist months to excavate even a tiny site. It's one thing to build from scratch, it's another to rebuild a damaged structure while retaining as much of the original structure as possible, while building it with the same material and methods as the original (although with modern equipment, no need to use a hand drill when you have an electric). In my opinion, they should make it different. Build a glass roof, like a \"ghost\" of the original roof. But, that won't happen."
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biwpx8 | Why do oil companies build pipelines that go all the way across a country(s) rather than building a refinery next to where the crude is kept? | Engineering | explainlikeimfive | {
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"Oil is sent to markets where it makes the most money. Chicago is a major hub, for example, because it distributes to the NE of America. The Gulf is another, as it's a major global distribution spot. One main reason is the main demand for the product is rarely where the oil is in the ground. Another is that the product is commingled. When you extract natural gas from the ground, you also extract a lot of natural gas liquids. Those are used for very different things, and separating them at source woild mean you now need to distribute to multiple locations. Also, keep in mind that \"oil companies\" is very broad. Companies tend to be more specialized. Some are transportation companies (e.g. Pipelines). Others are upstream, which is pulling the product out of the ground. Midstream is processing the product. Downstream is distribution to end user. The process and economics of all of these are very complex, and beyond the scope of most companies."
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bj4psx | How will we take down the mega-skyscrapers like Sears or Taipei 101 or Burj Khalifa when their time comes? | Engineering | explainlikeimfive | {
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"If it ever came to that point, they would gut the building to it's base concrete and steel, and then dismantle it floor by floor. They probably wouldn't ever do that though, more than likely the buildings will be renovated. It might not seem like a lot, but it's pretty easy (in the grand scheme of things) to completely change a building without tearing it down. For example, the company I work for does a lot of work on old buildings in DC, they'll (they being the owners of the building, my company just provides steel) go in and remove the old stone facade, infill openings in the concrete, or cut new ones for new elevators or stairs, and then they'll put up a new shiny glass curtainwall and you'd never know it was the same building.",
"What about the demolition tactics where upon detonation buildings fall in on themselves?"
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bjead6 | why does banging electronic devices such as calculators against the table revive dead batteries temporarily? | Engineering | explainlikeimfive | {
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"It maybe the contacts touching the battery are loose or dirty rather than dead battery. Shaking it could make better connection",
"My analysis based on car batteries. When car batteries starts to wear down white stuff accumulate on the terminals which causes contact problems so you need to clean. It could also be the same to our little remote calculator battery. Little corrosion aka rust causes batteries to loose contact thus hitting makes batteries wriggle a little causing a few minutes of working time.",
"A battery works like this: during normal operation a reaction inside the battery removes electrons from one pole making this pole lacking electrons compared to the other. When the battery is connected to a circuit, these electrons will flow thru the circuit and end on the other pole. As the process repeats, the chemical reaction inside the battery creates a thin undesired oxide film around the poles that ends insulating these poles from the chemicals, stopping the process. At this point, the battery is dead, because the poles are insulated from the chemicals inside the battery (electrolyte) and the chemical process cannot continue. A rechargeable battery can be brought to life because the charger will force a reversed flow of electrons inside the battery and remove the insulation from the poles. Nope, the charger is not \"pumping\" electrons inside the battery, just removing the insulation from the poles, making them able to react with the electrolyte and making the battery work again. Even a rechargeable battery will be dead after a few cycles because a little bit of corrosion happens on the electrodes during normal operation and this corrosion will accumulate and ruin the electrodes themselves with time. I guess banging the batteries in a hard surface will physically remove part of the oxide film from the poles, making the electrodes able to get contact with the electrolyte again, reviving the battery for a while."
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bjfrzn | How engineers can be sure that the hard shell of airbags won't hit someone during a crash? | Engineering | explainlikeimfive | {
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"They're scored on the inside to allow them to tear predictably. Kinda like how some grenades have similar cuts to get even distribution ( looking at you takata).",
"The airbag shell isn't just hurled into the car cabin when the airbag goes off. They split open to release the bag but the pieces remain attached to the mounting brackets. So they don't hit people in a crash because they are behind an expanded air bag.",
"People do still end up with black eyes or broken noses from air bag deployment- but it’s generally seen as preferable to actual loss of life.",
"The whole point of airbags isn’t to provide a nice soft surface— it’s to provide a place that is vastly preferable to the steering wheel or other hard(er) surfaces within the car. The whole purpose is mitigation of injury, not entire prevention of injury. Usually by the time the airbag goes off, injury is probable. Making that injury something that isn’t severe is the point. As said already, the airbag covers are scored so they split open and the airbag operates through the hole."
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bjjs49 | Why does natural gas despite having a higher RON value, performs worse than petrol when used in a car engine? | Engineering | explainlikeimfive | {
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"The RON represent the level of compression of the fuel, but natural gas is a gas and not a liquid like gasoline/petrol. & #x200B; So even if natural gas have an higher energy/mass than gasoline (about 15% more), it also have a terrible energy density or energy/volume (about 0.1% of gasoline). & #x200B; So ya you can compress natural gas more than you compress gasoline, but you gonna have a LOT less natural gas in your cylinder than you could with gasoline. This mean you will have a lot less energy available with natural gas. The reason is that on a car the volume is really important, you can't have super large cylinders to use more natural gas. In a power plant, it's the other way around. You can make your combustion chamber larger and the difference in mass that you need to transport, become a more important factor and in that case Natural gas is more efficient."
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bjq1uh | How are major tunnels made under water? | I'm really stuck on understanding how tunnels can be made under water. And also... Under mountains for that sake. I'm stunned thinking about it | Engineering | explainlikeimfive | {
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"Sometimes they use giant boring machines that work like a mole, digging the tunnel out, and sometimes they will pre-build the tunnel in sections, sink it, then connect it together / cover it.",
"Underwater tunnels, to my understanding, there's a trench dug first, then the tunnel is dropped in in segments, and connected together through underwater welders and other such forms and then sealed. The water then gets pumped out and it all gets cleaned up. Mountains it's basically a giant drill that gets driven through the mountain making a tunnel then people build the walls and what not to keep it from caving in. That or it's built, placed, and then earth gets moved on top of the tunnel but that's generally not done for an actual mountain.",
"We build the tunnel above water and then sink it. We build tunnels through mountains by using special equipment and explosives in a controlled way, making sure to support the mountain above and around us so it doesn’t collapse on us midway through.",
"Not about tunnels specifically, but last week the Practical Engineering channel on YouTube posted a video called [How are Underwater Structures Built?]( URL_0 ), which is related and pretty interesting.",
"There’s lots of different types of tunnels. The only one I have experience with is HDD (horizontal directional drilling) for underground pipelines. These are commonly used to go under water bodies. As for larger tunnels such as through a mountain for driving they use TBMs (tunnel boring machines). These are truly amazing in my opinion and are obviously freaking huge. It would have been so fun to engineer this. HDD: URL_1 TBM: URL_0"
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bjrqyh | How are sea links/sea bridges built? | I've always wondered how they could built bridges across seas. Are piers built to go all the way to the bottom on the ocean floor regardless of how deep the water is? | Engineering | explainlikeimfive | {
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"Bridges are typically built at the closest meeting of two bodies of land and with the most shallow floor. Planners and engineers will try to find the sweet spot. So no, they do not just pick a random location no matter the deepness; They choose carefully. We can only build so deep underwater. Caisson's and cofferdams are common methods for working underwater, but those are very limited in how deep they can go."
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bkckh4 | Why do builders use wood to frame houses? | Wood seems susceptible to lots of types of damage: water, termites, weather changes, etc. Why do builders frame houses with wood and not something stronger like steel? | Engineering | explainlikeimfive | {
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"Renewable resource. Much cheaper than metal and way easier to manufacture and goes through less change during manufacturing. Wood is unbelievably strong too. Much stronger than you think.",
"In a word cost. A steel framed house would cost 2 to 3 times what a wood framed house would cost. And that is just for the studs. You would also have to use Metal Clad wire, instead of romex, for all of the electrical. Again this is considerably more expensive.",
"Wood is easy to work with. It's cheap, strong,and flexible. It's also easily available. To build structure for a wall or framing for a door, you need lots of nails and screws, wood is solid and easy to cut in to, so it's easy to trim it to the proper size if you're building framing for a door.",
"As has been stated below. Wood has lots of benefits over steel for small scale construction. It's properties of insulation are also a huge part of it, especially in places with extreme temperatures. & #x200B; Most house design also requires snow and wind load calculations, and the elastic properties of wood are great for giving houses and small buildings a little \"wiggle room\" during powerful weather events. & #x200B; Source: Civil Engineer",
"I'm a steel fabricator. And I can tell you that steel like weather less than wood does. Welds especially. Cold and warm weather is especially nasty for it. It would rust, rust would damage it and the frame and the building. Believe it or not, but even a steel reinforced concrete isn't \"eternal\". With weather cold/warm cycles it will slowly break down, and once it starts to rust the steel starts to expand cracking the concrete. Also steel isn't really \"Stronger than wood\". We'll it is and isn't. Depends totally how and what you do with it. Steel has different properties to wood. But I work with steel, and we use lots of wood to shape steel with. To prop it, to bend it, wedge it, force it in to shape. But the kind of wooden elements you build houses with, are actually better than steel in many mechanical aspects. And this isn't considering that the tooling and methods required to shape it. I dare you to try to cut a 2 by 4 of wood with a handsaw, then to saw a similar steel bar with a handsaw. But it isn't like we don't use steel and aluminium frames in buildings. Weight bearing structures are sometimes made of steel, if the situation calls for it. The bottom frame could be made from steel beams if the terrain is hard. But where steel and aluminium shines is in retrofits. Let's say you want to remove a whole bearing wall, you can easily replace it with steel frame, or more commonly with aluminium (if the budget allows for it). But we are currently replacing the use of steel and concrete in buildings with things like CLT (Cross Laminated Timber), Which has many superior mechanical qualities for building when compared to concrete, steel, and aluminium, often rivaling both materials. It is a fascinating thing, CLT."
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bkjjz0 | How do watches know how to advance exactly one second? | Engineering | explainlikeimfive | {
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"All mechanical watches and clocks use something called an escapement. The escapement is driven by force from a coiled spring or a suspended weight, transmitted through the timepiece's gear train. Each swing of the pendulum or balance wheel releases a tooth of the escapement's escape wheel gear, allowing the clock's gear train to advance or \"escape\" by a fixed amount. (Source: the internet) That fixed amount is one second. The gears are designed precisely to do this.",
"The basic concept are oscilattors, or put simple, pendulums, a string with a weigth on its end. How quick and in what interval it swings depends on factors like the length of the string and how far you hold it out from its initial position, the displacement; try it out yourself with some rope and vary its length. This can be adjusted to be exactly one second, then put some gears at its base which move everytime a cycle ends and you have a basic watch. This behaviour is managable with any kind of oscilator like a spring. So you calculate what properties it needs to have to swing in an 1 second interval and you got your watch set."
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bkk7kb | Why can't cities like NYC and Boston create landfill to build on like they did in the past? | Much of Boston is built on reclaimed land, as well as much of Lower Manhattan. The WTC is basically built on a giant bathtub that keeps the Hudson out. Why isn't that as common today? | Engineering | explainlikeimfive | {
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"Not to be snarky, but why would they want to? That waterfront area is now incredibly valuable, the people/companies owning the land there want to keep it the way it is to maximize their value. And filling in the bay/harbor is expensive- why not build in other directions that might be cheaper? Finally, skyscrapers need solid foundations- part of the reason Manhattan is so built up is that the bedrock that supports the skyscrapers is close to the surface level, making it easier to build tall structures. Filling in the harbor would add to the depth that pilings would need to be driven (you’d need to go through the landfill, then through the mud below it to hit bedrock). I’m not sure what you mean about the “tub” at the WTC- I believe that construction cleared the land down to the bedrock and then built retaining walls to keep the surrounding soil/structures from collapsing in, along with any potential water seepage. But the structure sits on solid rock, it’s not floating.",
"I reckon the biggest problem is cost. Second you have individual problems like the Hudson that is actually a river with a watershed, that water needs to keep flowing. Netherlands has a lot of reclaimed land, but the initial cost is very high and it requires expertise as well as maintenance. Once the land prices are above the price per square unit of reclaimed land it'll start to become feasible.",
"While I cannot speak to the east coast of the US, there is a huge reason why it went out of style on the west coast of the United States. Earthquakes. During the big 1912 earthquake, San Francisco realized what a terrible idea filling in wetlands/bays to create more building space is. When you take a bowl of water and add sand to it, you eventually get enough sand to have some of it above water, but if you shake it the sand compacts and the water comes to the surface. This is what happened (more or less) in 1912, but the ground brought parts of building with it. I’ve over simplified a lot about liquefaction (effect described above), so I’m sure somebody with a degree in geology can fill in the gaps (or correct some inaccuracies) to paint a better picture of this. Edit: add a d to ad to make it add",
"Plenty of places still do this, like Lagos, Hong Kong, and Dubai. San Francisco’s airport is on fill. Some parks in New York aren’t on fill, but are built on structures to create more land. Houston has a lot of excess mud from dredging the ship channel, but it’s mostly used to create storm barriers and wetlands. Mostly it’s super expensive to do. With sea-level rise forecasted, it becomes even more risky. There are more cost-effective, safer ways to find land to build on.",
"In places like Hong Kong, such projects are still progressing, and the country has \"reclaimed\" upwards of 40 square miles, most notably to build a new airport to replace the old Kai Tak runways where you'd be close enough to see laundry being hung out from apartments at the same height as your landing 747. Here's a recent article about a new runway and roadway they're planning: URL_0",
"If you're interested in this you should read about the polders in the Netherlands and the ever-escalating efforts the Dutch have to keep the North Sea out.",
"Environmental engineer from Boston here. In the United States doing something like that today is against most if not all environmental protection policy for the shore/ocean. I don't even know how one would try to work with the dep/epa to allow for the filling of shorefront. (Also I dont manage large projects so I may be naieve here). Currently, disturbing ANY soil in Boston costs a TON of money because the old fill contains PAHs and metals (contamination), which is a big deal in Massachusetts. . Probably not much of a concern in China though.",
"I grew up in NY right next to the East river. There was a proposal to create an entertainment district in the river (because of the natural shape of Manhattan it was a good spot) that was fought down until it was rejected. Current residents don't want decades of construction and to loose their water views. The arguements usually cited environmental protection reasons rather than their personal preferences. No one cared about the fish in the East River until this project was proposed and then suddenly a lot of people 'cared' about those fish a lot.",
"NY kind of is planning on doing it again, but not to use for buildings. It'll be to protect Manhattan from rising water.",
"Copenhagen is building a huge new metro line and they are using all the sand that has been extracted from the underground to build a huge artificial island near Nordhavn. Check it out, it’s quite impressive.",
"A giant bathtub that keeps the Hudson out ?",
"Not sure about Boston, but this has taken place slowly throughout history in NYC, and has already happened deliberately. The area called Battery Park City was built on created land.",
"Also, garbage now is a lot different than garbage in the past. Look at spectacle island. It's mostly ceramics and glass. Stuff that doesn't leak toxins to the degree that current garbage does. (There's likely to be lead based paint in some of that garbage but still) Now we have things like computers, batteries, plastic, and many other things that have heavy metals and acid in them. Those eventually leak into the environment in landfills and after all the effort to clean up Boston harbor that would be tragic. I think it's worth using said trash for other purposes and up cycling it but we just have to make sure that it doesn't kill anything."
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bkqab0 | How do the cameras on rockets that are right behind the thrusters not melted down from insane heat? | Engineering | explainlikeimfive | {
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"CuriousDroid on YouTube does a great video on this topic as a whole. Short answer: Hide the camera and point it at a mirror made of quartz that sees all of the heat. Long answer: URL_0"
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bkyvp3 | What is the difference between 4WD, AWD and 4x4 | Engineering | explainlikeimfive | {
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"4WD is Four wheel drive.. same as 4x4... It means you can select which mode you want in vehicle, usually reserved for trucks and Jeeps.. either have all four wheels powered or just two. AWD is all wheel drive, meaning the vehicle always has al four wheels engaged and you cant turn it off...usually reserved for cars and SUVs"
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bl0emv | Why are there certain portions of the highway that sound really high pitched when you drive over them, then other portions that are normal sounding. | I know, strange title. Do, on the highway the road is made up of different “slabs” some of these slabs sound like any other local road, practically silent. Other slabs are high-pitched and often lighter colored when you drive over them. Why and how are there these variations on highway roads? | Engineering | explainlikeimfive | {
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"Asphalt and Concrete. The later one is usually high pitched due to its“porosity”, being more abrasive. Edit: grammar.",
"In addition to the other explanations, as well as being cheaper and harder wearing than asphalt, concrete also retains similar grip levels as it wears (unlike asphalt, which becomes smoother and less grippy as it wears). Furthermore, as it is harder wearing and can be laid in thick slabs, it does not suffer from grooves appearing along the lines where most wheels travel, as can happen to asphalt (which is laid in layers that can become compressed). The A45 (now the A14) through Bury St Edmunds in Suffolk was one of the first stretches of road in the UK to be laid with concrete, as an experiment to test its suitability for roadbuilding. Due to the fact that it snaked through the town on a route which included curves which were considered extreme for a road with a 70mph limit, it was thought to be a good test of the surface's grip-retention abilities. It was duly surfaced with concrete through the whole town, but objections from residents about noise meant that the whole stretch had to be bordered with high fences, trees and other barriers. This negated any cost advantage concrete may have had, and in the UK it was subsequently only used stretches in areas with low population density that required low maintenance and high grip levels. Most of the stretch through Bury St Edmunds has since been resurfaced with asphalt as part of a rolling program of upgrades. There are still stretches of concrete motorway elsewhere, with one very noticeable example being on the M25 south of London. This section shows another problem with concrete roads, namely that the joins between slabs decay long before the road surface. The result is the jarring \"thumpa-thumpa-thumpa-thumpa\" noise commented on by others here, as the car's axles hit the joins at different times.",
"In addition to the other reasons given, there often grooves cut into the concrete to improve traction and to help shed water. If the grooves are cross-wise to your direction of travel, there will be a high-pitched whine as the wheels roll over them. There are some highways where the spacing of the grooves are variable so your wheels [play a tune]( URL_1 ) as you drive over them. [Example]( URL_0 )"
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bl0tb9 | Why do formula 1 cars look the way they do? | F1 cars are known as the "ultimate racing cars". i wonder why, the further up on the racing leagues you go, cars don't look anything like traditional cars at all, and especially why they all look the same at that. i understand the details of aerodynamic wings etc are changed over the years, but why are all of the cars looking mostly alike? do the rules state that F1 cars have to look exactly like that? if so, why? when/where did this design originate? if i build a car that is faster than an F1 car, but looks like a dump truck, could i race in an F1 tournament? | Engineering | explainlikeimfive | {
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"F1 cars are super light as they are as bare bones as possible, they are largely shaped the way they are to provide optimal downforce/weight ratio allowing for more grip and stability. Fun fact, for certain turns F1 cars need to go faster (thereby increasing downforce) rather than slower to avoid crashing from lack of grip."
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bl5ng2 | why are tires not a solid piece of rubber, and are instead hollow, and filled with air? | Engineering | explainlikeimfive | {
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"Solid rubber tires are used in large and heavy industrial applications (think of those absolutely enormous dump trucks), where the weight of the vehicle would pop an inflatable tire. Smaller vehicles like cars, trucks, and buses use inflatable tires because they provide more cushion."
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bl6vvt | Why does an electric kettle heat up water so much quicker than a stove does? | Engineering | explainlikeimfive | {
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"Electric kettles have more efficient heating methods. One of which is an immersion heating element (an electrified wire inside a metal tube immersed in water). This ensures that almost all of the heat produced is transferred directly to the water. Conversely, if you put your hand (safely) above a kettle on a gas stove you will feel the residual convection heat that is going around the kettle and being wasted."
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bl7141 | Why is it that when they run an old steam locomotive for show, they always have a running diesel in the makeup? | I was watching some of the shakedown runs on YouTube of Union Pacific's "Big Boy" #4014, the freshly-restored example of the largest locomotive ever made. I noticed that, like virtually all other classic steam locos that are run on main lines for nostalgic purposes, there was a running diesel a couple of cars behind it. I am curious why they do this - is it in case the steamer breaks down, to keep the load on it as low as possible, or some other reason I haven't thought of? | Engineering | explainlikeimfive | {
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"Passenger cars require electricity. The older steam locomotives dont have generators, but the newer ones do. The diesel locomovite is needed to supply electricity to the cars. Source: I used to be an Amtrak Carman",
"Generally, steam engines are very reliable and rarely \"break down.\" There are several reasons for running a diesel behind a steam engine. One is for tractive power. Another is dynamic breaking. Probably the two biggest reasons, however are (1) the steamer will require less water if a diesel is pulling part of the load. Railroads no longer have water towers every 20 - 30 miles, so it's not very convenient if they run out of water. And (2) the insurance carriers often require it for safety reasons.",
"If they run it on a track that is in use, I think they need to always have a backup available. There is a video somewhere on YouTube that shows a steam locomotive on a tourist-type excursion, and it blew a drive cylinder due to the oiler failing. I think they said it took them 8 hours to get it towed back to the shop for repairs. If that had been on a working track can you imagine what a logistical nightmare that would have been for the freight trains stacked up and waiting to get past? So I'm sure they err on the side of caution every time."
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blgmds | What is a sewer system doing wrong when methane gas builds up? | You see these videos all over reddit of kids and adults dropping matches or something on fire into a manhole, only for it to result in an eye-popping explosion of methane gas. It makes sense that a sewer could have methane gas from organic waste decomposing, but my question is what is done to prevent that and why is it so often not apparently prevented? So that is to say, that *should* be done to prevent methane buildup in a sewer system and why isn't that done reliably? | Engineering | explainlikeimfive | {
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"Improper ventilation can cause the buildup of sewer gases. I believe that stagnate water in the sewers also contributes a lot to the build up of sewer gases. This is usually caused by blockages such as when too many people are illegally dumping oils and solid items down the drain."
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bliwmf | How does my record player know the vinyl is finished so that the arm lifts up and goes back to the rest and stops it spinning? | Engineering | explainlikeimfive | {
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"Because it get close to the center and at a certain angle a connection closes to start that action.",
"The arm is always moving toward the center as the record spins. When the arm reaches a spot a specific distance from the center it stops and raises. It is the same location for all records.",
"The position from the center spindle tells the record player aka turntable aka Victrola when the record is over. The sound on a record is carried on a single* spiral groove which runs from the outer edge towards the inside. The space between successive turns of the groove (aka pitch) increases after the last track so the tonearm moves rapidly to the inside and triggers the mechanism *except for side 2 of “Matching Tie and Handkerchief ”",
"Record needles move from the outside in on the spiral groove. The distance it has to move is standardized. Once it moves to the innermost point, it trips a circuit that causes the arm to retract. It's basically like a little off switch that's only hit when the arm is in the position it would be at the very end."
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blkkk3 | How do traffic lights work? | Back in the day when i was younger i thought there was some employee hiding in a nearby building overseeing and controlling the lights in his hideout. Now i know that’s of-course not the case but how do they work exactly? | Engineering | explainlikeimfive | {
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"So... Inductive loops, video and microwaves can all be used to\"sense\". Signal timings are based on the speed of the corridor, the amountof traffic on each street and turning in different directions, and sometimes on nearby signals of they are coordinated. Basically, the sensors tell the computer what is going on, as well as other field gathered data, and the computer runs through some if-then statements created by an engineer to try and make thetimings as efficient as possible."
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blqpk6 | What happens when a tap is off? Does the water just wait, and how does keeping it there, constantly pressurised, not cause problems? | Engineering | explainlikeimfive | {
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"There isn't a huge amount of pressure there, and it's passive. It's like when you have a water-tank with a tap at the bottom. The water doesn't know a tap is there, until it's opened.",
"The amount of pressure in the pipes is not enough to damage iron, copper, PVC, etc pipes. If it were, water would shoot out at extremely high and dangerous speeds when you did open faucets.",
"To expand on the topic, if the pipes ARE drained, say to repair a leak, when you turn the main back on and open the taps you will get a lot of sputtering as the air is forced out of the pipes and they fill back with water. This would be quite inconvenient if it happened every time you used the tap. Also, in cases like a winter vacation home that's not being used for long periods of time, water MUST be drained from the pipes. When the home is not heated, the pipes can get cold enough for water to freeze. Freezing water expands, bursting the pipes. When it gets warm again, big problems.",
"In most places in the US water pressure comes from gravity! That's why the water is stored in those tall towers rather than on the ground. The towers are placed at a certain height to produce a certain amount if pressure. That amount of pressure is not high enough to bust the plumbing in your house. Think of it like a water cooler with a spout at the bottom (like the Gatorade coolers you see used for sports). When the spout is opened gravity pulls the water out. When it closes the water just sits there. Water treatment plants use big pumps to put water into those towers as it is used up. Because of that the pressure always stays the same. When you close your tap the water stays under pressure just like in the cooler.",
"Related question: If you pour tap water directly into a glass and drink that, it can taste kind of stale and warm. If you wait a couple of seconds after turning on the faucet and drink that water, it's fresher and colder. How come? Is the water that's been waiting in the pipes actually stagnant? Should people not be drinking that water in certain cases?",
"It's my understanding that the water supply coming in to your house has a limiter valve, so the PSI in the lines can never get above a certain amount.",
"Yes it's like if you try to blow out your breath with your mouth closed. The pressure doesn't hurt you. Same with water pipes, the pressure is very, *very* small compared to the strength of the pipes.",
"Guy who worked in water here. Eli5 bit... Imagine a tiny town. One house with one tap, a water tower, and a well all connected to one pipe. The well kicks on and fills, draws water from the ground. With the tap closed it fills the water tower to the pumps max pressure or until it’s told to shut off. Say 150’ tall tower. Now that tower being full supplies pressure via gravity into the pipe going to the house. When the house tap is opened water drains out of the tower. When it’s closed it sits there with the pressure caused by gravity. When the tower gets too low the well kicks back on and fills the tower. More in depth The pressure of water works equally in all directions In the system for the sake of this discussion. So if we add more houses, more towers, and more pipes and even more wells... it all still works the same. The issue then becomes having the volume to sustain the pressure. In most systems pressure is developed by gravity ie; elevated storage tanks. Be it water towers, stand pipes, or storage tanks on hills. Some systems they have variable pumps where using gravity to provide pressure is prohibitive. For every 2.3? (I forget the exact number now) feet of elevation you get 1 psi at the tap. This works out to about 60-65psi. When the wells run pressure from the well acts equally in all directions and the tower fills if no taps are opened. When use is low the tower supplies the pressure. In systems with no towers a variable pump is used. It bleeds off once a set pressure is met so it doesn’t “dead head” building pressure until a pipe bursts.",
"Rarely there are problems, called leaks, but plumbing is a well engineered technology.",
"Inside the tap there is a mechanism called a tap gland that works like a valve, you turn it/tighten it to open/close the flow of water. The water waits at the gland until it's opened.",
"Yes, it waits. Think of it like the water cooler at work with the little lever you pull for the water to come out. It's like that, but a bit more pressure. Now imagine that water jug being a big water tower that you see on the side of the highway, connected to your tap.",
"Water is pumped to the top of the tower. And it just waits for you to turn on the tap. This is the same as if you filled up a funnel with a tube and held it above your head put closed the exit tube. Its just waiting there for you to open the tube, gravity does most of the work."
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blqr5d | How do engineers make things vibrate! | Like the vibration function in controllers.. phones.. etc, what is the science/engineering behind this? | Engineering | explainlikeimfive | {
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"It's incredibly simple. They use a small electric motor, with a small weight offset/uncentered on the shaft. When the motor is powered, it wobbles, vibrating the phone.",
"Lets take a wheel, then add a lump of material to one side. Spin the wheel and it will make the object its attached to rock side to side Scale this down and thats how you have vibration in controllers and phones. Slow rotations for low vibrations, high rotations for high vibrations. Hope this is ELI5 enough"
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blxw3b | Why is retrocompatibility so hard to achieve on modern consoles when a significantly different and rather cheap system like the Wii was able to do it ? | Engineering | explainlikeimfive | {
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"Because compatiblity through emulation is difficult and almost always inexact. For true compatiblity you want the same hardware. The Wii was backwards compatible with the GameCube because the Wii was just a faster GameCube with more RAM so it was easy to just reduce the clockspeed to run older games. Other consoles reuse the chips from older consoles for other purposes so that they can fall back on them for compatiblility. Both the PS2 and the Nintendo DS used the outdated CPU of their predecessor (PS1 and Gameboy Advance) as their sound chip. Finally some consoles just stuffed the previous console inside them - the Gameboy Advance (as well as the SP model but not the Micro model) included the Z80 like processor from the Gameboy and only used it to play Gameboy games. The launch version of the PS3 also included a full 'Emotion Engine' PS2 CPU though it was dropped from later models."
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bm0ac6 | Why is the talking in some TV shows/movies quiet then the music at the Same level of volume as loud as a jumbo jet taking off? | Engineering | explainlikeimfive | {
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"Audio is optimized for a multi-channel theater-quality audio system. When it's squished down to a single channel coming out crap TV speakers, a lot gets lost in translation."
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bm3c2c | How do machinery such as diggers transfer power to the tracks or wheels when the top half spins? | I often wandered this and couldn't find any answers. Am I correct in thinking that the hydraulic pumps are located on the top half of the machinery? If yes, how do you get the fluid to the tracks or wheels? *Edit*: just to prevent confusion, I'm aware you can't use ordinary hoses as they will begin to kink and snap if you rotate the digger too much | Engineering | explainlikeimfive | {
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"Caterpillar trained mechanic here. Modern era excavators do have hydraulically powered tracks, along with all the other moving parts. The engine is only there to provide power to the hydraulic pumps. There is a component called a rotary manifold that allows the hydraulic fluid to flow through multiple separate galleries while being able to rotate indefinitely via its two separate halves. URL_0"
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bmj47k | when people say the pyramids are built aligned to true north, it sounds very impressive, but what does it actually mean? | Engineering | explainlikeimfive | {
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"Magnetic north is where your compasses will point to. It is the magnetic field caused by the iron in the earth’s core swirling around and can drift slightly over time. True north is the determined by the direction the earth actually rotates. The Egyptians somehow worked out the rotation of the earth on its axis, and aligned the pyramids to that direction.",
"That the pyramids are aligned to the sun. Recent experiments with the indican circle method (putting a stick in the ground and tracing the shadow throughout the day) have produced similar alignment results. URL_0 p.24-28",
"It means they are aligned by the stars. Not by magnetic north. \"True\" directions are based on the sky. Magnetic are based on the poles."
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bms56u | Why does deleting memory that has already been deleted result in a segmentation fault? | Dereferencing a freed pointer in c++ |||| |:-|:-|:-| |||| | Engineering | explainlikeimfive | {
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"Segmentation faults occur when you try to access memory that either you don't have permission to access or isn't there. Trying to de-reference a null pointer or a pointer outside your memory for example because you are not allowed to access memory address 0 for the former and you can't de-reference a pointer that isn't there in the latter. You're trying to delete something that isn't there because it's already deleted.",
"Generally, when you allocate memory from a heap, you get back a pointer. That pointer is also part of a record kept by the memory manager that also stores who owns it, permissions, and how big it is so that when you free it or your process is killed, the memory can be marked as available for other allocations or defragmentation of free space. When you free that memory, the record is erased and your pointer is zeroed out. If you try to use a null pointer you get one type of fault, a null reference fault. If you try to use a saved pointer from before you freed it, the memory security hardware catches it and you get a protection fault. Specific to x86 platforms, your pointer address is associated with a region of memory called a segment, which in protected mode refers to a record called a segment descriptor in a table maintained by the kernel. When the kernel frees that segment, its segment descriptor is cleared. When the hardware can't find a segment descriptor it throws a segmentation fault. The kernel then burns your app to the ground. If it's the kernel itself, you bluescreen.",
"The routines that allocate and free memory maintain data structures so they can keep track of which memory is in use and which is available. If you free the same piece of memory more than once then that data structure can easily become corrupted with unpredictable consequences. Exactly what happens will depend on the implementation of the memory \"heap\". It's possible for the allocate and free code to do some checks at runtime to guard against errors of this kind but that slows down programs and can't be perfect anyway. For example, if you free a pointer, are later allocated that same pointer for a different purpose, but then erroneously free the initial allocation a second time, there's no way for the free routine to detect that error. Sometimes people use testing versions of free and allocate to check for coding errors. The code runs more slowly but they can quickly find and, hopefully, diagnose issues. That way the program will generally stop with an error as soon as something like a double free happens, as opposed to randomly crashing sometime later, or even not crashing but producing incorrect results. The problem is that the thing you pass to the free routine is just a pointer to the first memory location in the space allocated. To free it up, the software needs to know how much memory was allocated, and how to add that space back to the pool of unused memory. This is handled by hidden data structures."
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bmxzfh | What determines how much fuel you car uses? I've seen people say higher gears mean less consumption, but surely if you are going faster, you're using more fuel? | Engineering | explainlikeimfive | {
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"Look at the RPMs when you're driving sometime and compare that to the speed. When you're accellerating, you might be pushing 3-5000RPM but only going 0-15MPH. If you're in 5th gear and cruising, you might be pushing 2200RPM but traveling 70MPH. If you've ridden a bike, it's a pretty similar deal as with car gears. It's easier to get moving at a lower gear but takes comparatively more effort to get up to speed than it does to maintain a higher speed. If you got stuck in first gear, you'd just spin around and around without doing much. If you went into the highest gear, you'd be able to maintain a much higher speed for the amount of effort you're putting in versus a lower gear.",
"To understand why faster doesn't always mean more fuel spent you need to understand physics and forces, but in this case they are relatively simple. Have you ever walked around tile or hardwood floors with socks on? Or maybe walked on a frozen patch of ice? Basically, everything, even things that look very smooth to us, are bumpy. They have jagged edges that produce some friction, and that helps things stop and sit still on surfaces. If you notice when you walk on slippery surfaces, you can avoid slipping if you walk more slowly. Or, if you've ever pushed a heavy book on a dining room table or countertop, you may even feel the book \"get lighter\" after it started moving. \"Static\" friction is greater than \"kinetic\" friction. Static means still, and kinetic means motion, generally speaking. So when the book is at rest on that table, those bumpy surfaces interlock like jagged teeth. Once you got it moving, it was slightly raised above those bumps, and could move more easily because of its momentum. A car is much bigger than a book, which means as it moves it carries more momentum. You can think of momentum as how difficult it would be to stand in front of something big that is moving and trying to stop it. The friction points are really along the axles of the car, in this case we aren't as concerned about the wheel's contact to the ground. As the car's engine spins the axle, the car gets moving. Lower gears provide higher torque, which just means they are \"strong\" with rotating things but are slow, like a lumbering giant. As the car starts moving, that initial static friction is overcome, and the car needs less torque to keep moving, since it now has momentum. A higher gear will allow the car's engine to spin the axle faster, thus increasing speed and, with it, even more momentum, which again requires even less torque. As the car gets going faster, however, the air resistance eventually becomes significant. This means the engine must work harder and harder for each incremental increase in speed. At some point the engine just cannot go faster. (Race cars, super cars, and even the fastest vehicles in the world have limitations on the size of the engine and how much wind resistance it gets.) Before that maximum speed, however, there is a sweet spot. The sweet spot is where the air resistance is low (air is very light) and the car has gained good momentum over the initial static friction forces. Here, the car's engine actually works better than if it were going slower, because the friction and air resistance forces are lowest. It can operate at a high gear, so it can spin the axle with less effort and not at such a fast rotation that it has to work really hard. It's like a jogger's marathon pace, faster than a walk but much slower than a sprint. Of course running is different because we aren't really overcoming friction to gain any momentum, so we can always go more efficiently by going slower. The mechanics of walking are different from spinning wheels. I really hope this helps, I would love to try to answer more questions if you have them."
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bmytpy | When a video is taken in a windy place, why does the wind sound so much louder in the video than in reality? | Engineering | explainlikeimfive | {
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"Because sensitive microphone membranes are much more sensitive to being disturbed by wind that is the human hear. Search for \"dead cat\" to discover how professionals try to minimise the issue.",
"Because the wind is much closer to the microphone - as in, it's *literally inside of it* \\- than any other sound.",
"It has to do in part with the stiffness of the housing of the microphone. Most mics have a stiff housing to protect them from being dropped and allow things to be attached to them. Human ears are much softer and so done resonate at the same frequencies as the stiff housing. Windscreens are soft coverings that can added to mics to reduce wind noise."
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bn4l87 | How does traffic happen on highways? | I get how an accident could clog up a lane or two or construction could cause some blockups as 4 lanes just got turned down into 2, but then how does this run into the issues of being in a standstill for 20-30 minutes? | Engineering | explainlikeimfive | {
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"A single car changing lanes at the wrong time or breaking too hard could cause a traffic jam as the cars behind also need to brake and it causes a chain reaction. [Here's a great GIF]( URL_0 ) explaining how it happens. If you want to learn more about it, take a look at [this video]( URL_1 ) by CGP Grey on Youtube.",
"There’s a study from Japan where a group of drivers drive were told to drive a specific speed on a circular track without passing anyone. The researchers found out that when the number of cars on the track go beyond a certain value, the drivers can’t reach their target speed without bumping into the car in front of them. This leads to what you’ve experienced — one driver slows down, which makes the driver behind them slow down, and so on and so on. The slowdown is a chain reaction, as described above. As such, not all drivers slow down simultaneously, and there’s a small “bunch” of cars that are in the process of slowing down at any one instant. Now here’s the fun bit: that “bunch” moves backwards as the slowdown chain reaction progresses. And the apparent speed of that “bunch” can be calculated in simpler experiments based on number of cars and target speed. So, when a lane is blocked by an accident or construction or whatever, the cars squeeze into the remaining lanes, the number of cars on those lanes increase above the critical number, and waves of slowdowns progress backwards. Pretty neat, unless you’re in the middle of it!"
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bn52zh | double clutching | Engineering | explainlikeimfive | {
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"Disclaimer:I do have a class A CDL but by no means a professional driver. After you are about to up shift say around 2000 rpms, you'll clutch to go to neutral, let your rpms drop to about 1500 then clutch again to kick it to the next gear. This all happens in less than 2 seconds."
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bn5kpj | Why is the engine sound of a F1 car so high pitched? | Engineering | explainlikeimfive | {
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"The pitch relates to the RPM (revolutions per minute) of the engine. Current F1 cars rev to about 12500 rpm. A modern muscle car can rev to 6000-7000 rpm. In the formula 1 V12 era, engines would rev to about 18000 rpm. Here’s an example URL_0"
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bnb0xs | why are electrical bikes so heavy compared to normal bikes? | I know of course that you have to count the motor and battery, but even then e-bikes often have a very heavy frame and wide tires which makes it very difficult to ride with if the battery is dead. Why not put a motor and battery on a light weight bike? Wouldn’t that also improve the speed? | Engineering | explainlikeimfive | {
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"Motors and batteries are fairly heavy, but comfort of the user is also a frequent design goal with many ebikes. Wide tires provide a much smoother ride as lower tire pressures can be used. Especially so for rentals, which often use a one-size-fite-most step thru frame (which are inherently heavier than a diamond frame).",
"You can, like the Bianchi Aria e-Road but it's a lot of money: URL_0 The battery and motor add a lot of cost, so they usually cheap out on the actual bike and give a cheap, heavy frame. Also, since eBike max speed is limited by law, there isn't much point trying to maximize bike design for speed. It would help with range, but most eBikes have more range than people need.",
"Partly because the frame has to be strong enough to support the components of the battery and motor. But I would estimate mostly because the things that it takes to make a bike lighter, better materials and more precise manufacturing add cost. Electric bikes are already more expensive because of the battery and motor. The companies estimate that if they also made them more more expensive to be light they would sell less."
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bnba2g | Why should you test GFCI outlets and breakers once a month? How can they fail in an unsafe way? Is there a reason they don't fail safe? | Engineering | explainlikeimfive | {
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"If you electrocute yourself, the GFCI is supposed to turn the power off. If it's failed, then it won't turn the power off and you may die. They cannot really be designed to fail safe, because you want them to move the switch to the off position when they detect you electrocuting yourself, and there's always the possibility that e.g. the moving parts have got jammed or stuck somehow. Because it is a safety system, with a high risk of death, the manufacturers recommend monthly testing. Depending on what you are doing, and how likely you think an electrocution is, you may decide that testing them more or less often is reasonable. It's your life, you can choose the safety level you want. If other people are involved, please ensure the GFCIs get tested regularly. Since you live in the US, if someone gets killed because a GFCI failed, you know they'll sue you for not testing it."
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bneooo | How is the temperature measured and how can the temperature be so accurately predicted for future days? Is there some huge ass thermometer in every city? | Engineering | explainlikeimfive | {
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"Far more complicated. In the US, we have the national weather service, which monitors and predicts the weather. Instead of one big thermometer, they have hundreds or thousands of weather stations scattered all across the country, and work with tons of other private groups like colleges or laboratories to gather data like temperature, cloud cover, barometric pressure, humidity, etc... They've been collecting and studying this data since the country was founded, and now know what patterns to look for so they can predict future temps and weather based on the patterns they see. Mix in data from weather radars and satellites, and you can get a decently accurate picture of what the weather is like anywhere in the country by looking at it as a whole."
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bnlnnb | How does glass get recycled? | Engineering | explainlikeimfive | {
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"If the glass vessel is hard to produce (ie expensive) then it may be cleaned and re-used directly. For everyday things like beer bottles the glass is cleaned, crushed into small bits, and fed back into the glass production line along with other scraps from earlier production runs. It's called 'cullet'. Minor variations (like different color, composition) are corrected for once the glass batch is fully melted.",
"There are 2 main ways 1. Things like bottles get cleaned and reused 2. The glass gets melted down are re-formed in to something new",
"In addition to melting and being made into new glass containers, crushed glass can be used as aggregate in asphalt roads replacing granite stone. Crushed glass can also be used as a ground cover in planters replacing organic mulch, but the glass must be given additional polishing steps to remove all sharp edges.",
"Infact lead can be recycled from lead gladd TV screens and it's about 20% lead by weight. At the capital of Alberta they turn that melt lead glass TV's for recycle",
"Glass is one of those materials that doesn't really need any special processing to recycle. In many cases it's really as simple as: - clean it - crush it - melt it down - boom, \"new\" glass.",
"Something I've always wondered is how beneficial recycling really is. Like, after the creation of a billion recycling bins, the creation of and emissions from recycling trucks that have to pick up and transport all the recycling, the creation of and emissions from facilities that sort and break down the recycling, is the footprint as reduced as we are led to believe it is? Or is the main goal about reducing litter and cutting down on the amount of space that's taken up in landfills? I remember hearing about how reusable bags basically don't make much practical difference since you would need to reuse each one a large amount of times to make it worth the large carbon footprint it takes to produce them compared to plastic and paper bags but so many people forget their reusable bags at home and end up just buying more and more while they're out. Not to be overly negative or anything, I'd just like to know how accurate the information I've heard is. Since the theatre around saving the planet tends to be more important to people than actually saving it (like plastic straws being vilified just because they aren't recycled the way they're meant to be and electric cars that still need to get electricity from giant power plants that aren't necessarily green), I'm always a little suspicious of the actual effects of the average person doing their part since it's quickly out of their hands and in the hands of corporations that are ultimately responsible for all the damage in the first place."
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bnm4vt | Why do all soda companies have the same size and shape of can/bottle? | Wouldn’t companies have variance between products? Or is there some sort of standard that causes all of these cans and bottles to be manufactured the exact same way? There are some other examples of this but soda is just the first that comes to mind. | Engineering | explainlikeimfive | {
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"While it is true that a different company takes care of the packaging, this doesn't stop them from requesting different sizes and shapes. Or even building their own packaging facilities. However most soda companies would try to stick to the standard. That's party because they don't want to lose potential sale from things like vending machines. Or stores that can't be bothered to handle logistics on storing and handling a specific container shape, while every other brand is easier because they're similar.",
"But there are different kinds of soda bottles? Like for example the 0,5l bottles for Fanta, Coca-Cola and Sprite are all [shaped differently]( URL_0 ). Or maybe I'm misunderstanding your question.",
"vending machines. Storage. That's it. Cooler shelves and vending machines are designed to take a specific can/bottle size. At least here in the US.",
"The soda companies only really make the drink that goes inside the bottle. A different company creates and sells them the packaging for their drinks.",
"They don't all have the same size and shape. For example you can see a list of available shapes/sizes for cans from one beverage packaging manufactuer [here]( URL_0 ), no less than 25 different varieties of size/shape available.",
"It's in Pepsi and Coca-Cola's best interests that they are both able to bottle their drinks anywhere on the planet and that they bottles will both fit into common sized shelves and fridges, and will pack evenly into common sized trucks and pallets. They are kind of in on it together."
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bntidn | When your car displays the RPM's on your dashboard, what part does the actual rotation that the car gets this measurement from? | Searched the sub and didnt seem to find this question. Apologies if I didnt look hard enough, though. Also, apologies if theres a better sub for this. Is it the drive/crank shaft? The transmission? The axel(s)? | Engineering | explainlikeimfive | {
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"This can come from several sources but usually a crank angle or cam position sensor. The crankshaft and camshaft are mechanically connected at a fixed ratio. The position of the crankshaft is important for this like spark timing and fuel injection timing. Basically the sensor tells the computer where each piston is and that information also provides the data for the tachometer."
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bnu63k | The air conditioning in a car works the same basic way as a fridge. Why does a fridge need to be left to stand for a few hours if disturbed, whereas the aircon in a car copes with continual disturbance? | Engineering | explainlikeimfive | {
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"Because when you move a fridge you generally tip it on its side , if your car is on its side you have bigger problems that the air con",
"There is oil in the refrigerant that stays in the compressor to lubricate it. If the fridge is on it's side, usually for a while (hrs while moving). The oil can run into the lines and out of the compressor (which is at the bottom) and the compressor will fail if restarted before waiting. The same could happen to a car, but it would have to be on that much of an angle for an extended period of time to allow this without the car not functioning for various other reasons.",
"A fridge is designed to use very little power so it has little mechanisms and uses gravity to help circulate some of it's liquids. A car air conditioner has all the power of the engine to use and it uses it to pump all the liquids where they need to go. No gravity needed."
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bo1xix | Why there is no international standard for electric plugs? | Engineering | explainlikeimfive | {
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"Nobody wants to spend a shitton of money to retrofit every plug and appliance in a country. There would be absolutely no gain except for tourists not having to buy a $10 adapter.",
"Like a lot of things, designs have evolved in different ways for different criteria and become so widespread in their own area that nobody wants to change. For instance the British type has a high safety design, all sockets have an earth receptacle, whether used or not ( * ). The power receptacles are shuttered so nothing can be pushed in, and if they are half pulled out the metal of the pins is not accessible before the circuit is broken. Plugs all have their own fuses ( * ). The price for that is a rather bulky plug that makes storage of some items difficult. Other countries designs have different plus and minus points. ^* - excepting two-pin shaver sockets with isolating transformers.",
"... As a side note all Brits over a certain age know how to wire a plug as until 1992 it wasn't a legal requirement to sell electrical items with plugs attached. Appliances were mostly sold with a raw wire and you bought a plug as well and took it home to wire it yourself.",
"When they first got invented by America in the 1900s, they weren’t exactly flawless, so when the technology got to other countries made their own adjustments and tweaks",
"In the early days of electricity, it was used mainly for lighting. Appliance sockets came later, and in the early 20th century, most major countries had *several* different incompatible types put out by different manufacturers. As time went on these condensed down, but for a combination of reasons, ranging from national pride to different priorities about size and cost and safety to real differences in voltage and phase, many countries kept their own standards. And it's not a matter of the rest of the world refusing to follow American standards: the first patents for electrical plugs are actually [British]( URL_0 )! But they're nothing like the plugs used today... And even within a country, there's no universal standard. In addition to the most common American plug, the US uses [dozens of other plug types]( URL_1 ) for higher-power appliances. Even for a given voltage, amperage and phase, there are usually two different kinds."
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bo3mvo | Why rivets are still used when we now have advanced welding techniques and hex-bolts? | My garbage disposal failed this weekend when the rivet holding one of the metal teeth broke. I was surprised to see that rivets are still sued and learned they are actually still used in many applications. I began to wonder, why is this part not welded/solid cast if it was meant to be non-replaceable, and why was it not bolted/screwed if it were? Why are rivets still used in many application? | Engineering | explainlikeimfive | {
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"Rivets are very strong in general. Maybe not the cheapo ones they use in a waste disposal but overall. Modern airplanes fuselages are held together (mostly) with rivets. Look at any bridge dating back to the Industrial revolution, if they use steel they’ll be held together with rivets (that have lasted centuries).",
"Rivets are cheap. Very cheap. A lot cheaper than threaded bolts. Welding needs a qualified welder. Any pleb can use a rivet gun",
"Rivets can be the fastener of choice when done properly. Large aircraft have been riveted together since before WWI. There are extremely high guidelines and tolerances for airframe repair."
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bogxco | If a primarily coal powered city has a large uptake of home solar, say 1MW out of 4MW average usage prior to solar, how much does the generation actually go down by after accounting for cloud cover and generator wind up time? Is it 25% less or significantly less? | Edit: Thank you for all the responses. For clarification, I don't mean the efficiency of solar panels on a house, I mean it more for a closed grid system that is not interconnected to another city and does not have battery backup, how much "spare" power generated and wasted, effectively cancelling out multiple MW of home solar production. This has been answered in a lot of different ways | Engineering | explainlikeimfive | {
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"This can get a little complex so I'll try to keep it as ELI5 as possible. First, I do work for a utility that has a diverse fuels portfolio and is a discussion commonly had even at the lower levels of the company. Solar is great but it has one large Achilles heel, the sun. Immediately it has a 50% capacity factor, meaning how long it can produce power for the day, week, month, year. Add in some clouds, thunder storms, dust, or snow and it reduces the capacity factor further. Elevation and temperature play a large role in solar production as well. The west coast, Nevada and Utah specifically are great for solar due to their elevation in the mountains, usually clear skies and cooler temperatures at elevation. This makes the process much more efficient. Take into account battery storage. You need to cool the batteries and inverters. In the south for example, higher temperatures means more parasitic load to run the air conditioner, this reducing the amount of watts available to the grid. Oddly enough, solar rarely provides the power required to the grid at peak load. Think about human activities, elevated load demand in the morning (people waking up) and much more in the evening( running air conditioner, cooking, tv, lights, so on) this is when the sun is going down and solar generation is very low immediately putting load on battery storage. Now the problem with traditional power generation is it relies on steam. Fuel source does not matter, gas, oil, coal, nuclear all take time to warm up components, especially the turbine and build up enough steam pressure to roll that turbine. Combustion turbines (think giant jet engine) can be dispatched rather quickly, however a coal plant will be a steam electric station. Ample time for cycle clean up, warm up and other operational processes can take up to 24 hours depending on time offline, outage activities, and size of unit. So, to answer your question, it depends, but typical dispatching will be slide load at the peak 10am-2pm to meet demand and renewable capacity then run wide open from 2pm to midnight and slowly lower load in the early hours of the morning and start the cycle all over again. The grid operator usually keeps a slight surplus of MWs on the the line and will adjust for small load variations. Capacitors are also used to provide quick adjustments to line voltage while a traditional steam electric system ramps up. Hope that stayed ELI5 and answered... something. Edit: paragraphed since it was on mobile Edit2: thanks for the gold!",
"when it's a subreddit of explain like i am 5, and you don't even understand the question :(",
"The typical capacity factor globally for solar is consistently about 20-23% believe it or not. Varies a bit per each region, but it’s surprisingly consistent. Hot and sunny areas actually have lower panel efficiency due to higher temperatures affecting the semiconductors. Meaning, 1MW of solar produces 1MW x 8760hrs/yr x 22% = 1927 MWh. Coal steam capacity factor is about 80-90%, so 31,536 MWh for a 4MW plant.",
"This entire thread is one giant ad for renewed interest, investment, and research in nuclear energy.",
"Based on your initial question and follow up questions I think you’re asking about how much traditional (coal) generation changes when solar generation increases or decreases momentarily. In the utility world we call power usage by our customers “load”. In fact, generation is primarily driven by load, so if you add more customers on the lines they will increase the load and as such the utility must increase generation to carry the load. So if the city has a 4MW load and all 4MW are being generated by coal, the coal plants will be outputting that power solely. If the city adds 1MW of solar generation, in the ideal sense the utility generators will “back off” to 3MW of output and the remainder of the 1MW load will be sourced by the solar generation. Realistically due to daylight and weather, and other considerations, solar is only about 20-30% efficient depending on where you are in the world. So over the course of a year that 1MW solar generation may actually only average 250 kW on any given day. This is because solar generation output is affected by momentary issues like clouds or extended ones like darkness, storms, and weather. This inconsistency can be mitigated by installing batteries that are charged by the solar generation and a controller that enables the batteries intelligently when the output of the solar generation is not efficient, like when a cloud passes over. Same goes for night-time usage - with a big enough battery you could potentially ride through the night and increase that solar efficiency. Unfortunately battery tech is not quite there yet, but we are making strides. Ultimately in a modern solar generation system there should be some type of supporting battery technology paired so that when clouds and weather affect the generation the load does not see big swings of generation. Imagine if a cloud were to cover the solar field and reduce the output quickly from 250kW to 50kW. That’s 200kW of load that just lost generation, and the generators would have to increase output to make up for it. Generally, generators cannot respond quickly to momentary changes like that and without controlled batteries for “ride through” on solar issues, the power quality of the system would be lowered. Source: EE at a large utility that is currently in the process of installing solar generation.",
"Your question could be asked clearer. If you are saying your solar has a max output of 1 MW at peak sun, then the coal station wouldn't alter its output much. Depending on your grid, you would likely just sell the excess power to another municipality or dump it. If you mean that your combined solar has a constant output of 1 MW due to an installed capacity of lets say 4 MW and some sweet battery storage, than the coal station can scale down its generation since the solar load is reliable, and you'd save that 1 MW of coal power. How much that buys you in reduced emissions sort of depends. It could be as simple as the coal station shutting off a generator it no longer needs, or it could be running a generator at lower load. Running a generator at less than 100% load will use less fossil fuel, but the EFFICIENCY you are getting out of the fuel will also be lower as the generators are designed for peak efficiency at 100%, not lower.",
"This video does a pretty good job of explaining the problems with solar and I think answers your question also. URL_0",
"I can't even understand the question... And you want a dumbed down answer? 🤔",
"Base-load power stations are sticky, but many coal plants are ending their natural end-of-life anyway. Solar generation means that simple natural gas peaking plants, which produce power only when it's needed and not available from other sources, can be used instead of large, inflexible coal plants. This means cleaner power is used, and only the power that will be consumed is produced using fossil fuels.",
"There are a lot of other factors. This city is part of a much larger interconnection, with thousands more MW’s of load and hundreds of other generators. If the coal plant is producing 4MW to serve 4MW of local load and suddenly 1MW of solar comes online, *in theory*, the coal plant would ramp down to 3MW, because of 0MW of scheduled flows in/out of the area. If it doesn’t, they’re going to export 1MW to other areas, effectively giving it away for free. A region will have an Area Control Error, “ACE”, that calculates a MW value based on scheduled tie line flows, frequency bias, area load, area generation, etc. When everything works as planned, ACE is maintained at 0. If an area under-generates and imports more power than scheduled, ACE is negative, while a positive ACE means the area is exporting. If the area wasn’t part of any interconnection, then the coal plant would absolutely have to adjust its output as solar generation output changes; for a system to maintain a frequency of 60 Hz, load and generation must be balanced. Otherwise, 4MW coal + 1MW solar = 5MW energy serving 4MW load, frequency would be through the roof, the coal unit would trip offline from over-frequency relaying (to prevent damage to the steam turbine), suddenly resulting in 1MW serving 4MW load, which ends in a blackout. Source: I work for a large electric utility as a Transmission System Operator"
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bp46yn | What do/did sail boats do when the wind is blowing the wrong way? | Engineering | explainlikeimfive | {
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"They zigzag in the general direction. They cannot head straight into the wind as they would be blown backward. So, they use the rudder (flappy part in the water) to steer the hull (the ‘boat’ part) to the left or right of the direction the wind is coming from. This gives some pushback against the wind. Next, they rig the sails to catch the wind at an angle, so the wind will push back but also to the side. This sideways push combined with the left or right hull steering allows the boat to slowly move in the direction of the wind. After traveling so far in that direction, they zag to the other side so they don’t get too far off course from where they want to go."
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bpa5yi | Why are modern printers still so prone to errors? Why can the same color be so different on the same page? | Engineering | explainlikeimfive | {
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"Because the « color mix » is not the same. A printer use Yellow-Blue-Pink and a monitor use Red-Blue-Green. The Printed image colors comes from reflected light and the Monitor ones from emited light.",
"Printers are sold extremely below their production cost because if they were sold to make a profit no one would buy new printers. Instead printer companies make their printers cheap and defective so that you have to constantly fix it or purchase a new one. Printer companies make a profit through selling extremely overpriced and printer specific ink cartridges. This is why some printers will not work if even only one ink is empty so they you have to go purchase a new set of ink cartridges. Its an annoying market for consumers."
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bpc8ar | Why does the touchscreen of my phone not work if my fingers or display are wet, e.g. from rain? | Engineering | explainlikeimfive | {
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"Most modern touch screens use electrical sensors to detect where your finger is touching the screen. Water, a better conductor than skin, throws off that process. Some old touch screens relied on detecting places on the screen where physical pressure was applied by sending where light was being disrupted, and hence water would have no affect on them. At least that's how I remember it."
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bped6c | With the recent news of the possibility of launching 11,943 satellites into low earth orbit for the Starlink Plan, how do the satellites not crash into others already in space as well as the recently launched ones? | Engineering | explainlikeimfive | {
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"Every time you put something in space it follows a carefully calculated and variable-scrubbed path. Barring extreme malfunction there's almost nothing that could move it around once it's in space. Plus space is massive so everything is far apart"
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bpioo0 | How do road line painters get the markings exactly where they need to be? They always seem to be perfectly in the middle no matter how complex or uneven the road edges are. | Engineering | explainlikeimfive | {
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"Before the striping paint or thermoplastic is applied, a crew going out and layouts of the location for all the striping. This is called cattracking. It is small marks in white or black paint that serve as a guide for the painting machines. It will have the start and stop locations of each line and the alignment. For curves they will use a length of rope to match the curve, then cattrack along the rope. Once that is approved the the local agency, they either install it with a small hand cart that the operator starts and stops by hand ( URL_0 )or for large road way jobs, they use a truck ( URL_1 ). Most of the catracking marking are then covered by the road paint or thermoplastic. You can sometimes see remnants where there are skip lines.",
"Used to do striping for a few years. There a multiple ways companies end up painting the road. Depending if the job is a new layout or existing, we may simply trace over the lines already in place or measure out new placements with measuring tapes and chalk lines. Depending on your location, oil based paints may be banned and water based may be the only option. Some larger companies also use some kind of thermal material. I've seen people use paint rollers, hydraulic pump machines, and industrial vehicles with sprayers on the back. You could imagine that the rollers may be used on small private lots while the pump machines could handle that to large lots. Typically you will find the industrial vehicles handling government jobs or major road ways",
"First I have a clarifying question. If the road edges are complex or uneven, how do you define “perfectly in the middle”? Wouldn’t it be more reasonable to say the line defines the middle, and that’s why it’s always in the middle?",
"I was on a job where there were people painting new lines on a road. The company that was painting them had a crew go ahead and set some markings to tell the second crew where they should go. From there, the second crew came in on a machine that had several kinds of paint and a few sprayers. One side had a long arm that extended out to the edge of the road and would drop a burst of spray or a continuous spray depending on whether a solid or a broken line was needed. The paint itself smells really really salty. Anyway, they spray in one direction then flip around and do the other side",
"Measuring tape and chalk string. Your average parking stall width is anywhere between 8 to 9 feet. The length or depth of the stall is on average 18 feet. The line itself is typically a 4\" line. The engineer plans will tell you exactly how everything should look and measure. Sometimes plans are wrong and you need to improvise. More often than not, you're just restriping an existing layout."
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bpm47p | why are fans wired to go from off to high, then medium, then low, and not the other way around? | Engineering | explainlikeimfive | {
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"It has to do with the amount of power being supplied to the fan. From the \"Off\" position, a fan's going to need a certain amount of power in order to overcome inertia and get its bearings spinning. By switching from Off to High, you give it a lot of juice so that it can get going. If you tried to go from Off to Low, it might not get enough power to spin."
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bpm77q | how do car horns project so well? | I don’t see any speakers on the car, so how does it work? | Engineering | explainlikeimfive | {
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"So usually cars have two horns in the front of the car, a high pitch and a low pitch. So a standard electric car horn does have a diaphragm just like a speaker. Inside there’s basically a plunger connected to the center of the diaphragm and on the other side of the plunger is an electromagnet. When you hit the horn button. The electromagnet forces the plunger to bounce off of it so fast the diaphragm produces a frequency, a loud one. The combination of the high and low frequency together makes the sound travel farther and through more surfaces."
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bpnwid | why do engineers build roads in mountains in a curved fashion? why not in a linear way through the mountains? | Engineering | explainlikeimfive | {
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"Your question doesn’t elaborate well enough. I’m a civil engineer. If you’re asking about tunnels then the short answer is money. It’s much easier and more cost effective to build 5 extra miles around something, than dig and support through it. If you’re asking why we don’t go straight up a mountain, then other negative impacts are at play: -Foundational structures are much less stable and reliable at steep inclines. -People drive old cars that are not powerful. Vehicles that fail going up steep slopes certainly cause more than one death, especially on a mountain side with sheer dropoffs. Not to mention everyone else they kill on the way down. Why not propose a safer gradually slope where vehicles can fail and idle without detriment? -Traffic would increase because in traffic engineering (and the real world) everyone sucks at driving. Driving up high distances would make every slightly uneasy person drive slower. So the time to get over the mountain would increase. May as well introduce a gradual slope for a longer distance (15 mph vs. 60 mph). This greatly increases the flow of traffic. I could go on and on and will if you want me to.",
"It's easier for vehicles to climb a gradual incline which follows a curve rather than climbing a steady and steep incline(straight incline). Also if any vehicle breaks down, it won't come straight back. It'll come and stop at the curve."
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bpop9s | Why has no one ever created a water bottle with an air inlet valve at the bottom? | Like a small hole that would make emptying the contents out of said bottle a lot easier and a lot less chaotic? Is it because it was infeasible, or nobody ever thought of it? | Engineering | explainlikeimfive | {
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"This would probably work, the issue is cost, water bottles cost pennies to make, adding this kind of complexity would sky rocket the cost. Would you pay 4 times as much for this bottle?",
"It would certainly limit the amount of water you could put in the bottle. when you remove the cap the pressure of the water would force it to flow out of the bottom hole, whilst air freely replaced it via the cap, until it was at a lower pressure than the surface tension of the water. As surface tension differs depending on heat too you might find the water leaked more as the day progressed."
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bpv7er | What are the purpose of 4WD and 2WD in vehicles? As well as each having their own Hi and Low buttons? | I've bought my first truck and it came with these buttons on the dashboard. But i do not know what they're meant for. Please ELI5 | Engineering | explainlikeimfive | {
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"2WD stands for Two-Wheel Drive, either Front or Rear, depending on your car. Most likely, FWD. In Two-Wheel Drive mode, the power of your engine will be sent to a single axle, and split among both wheels on that axle. This is the most common way you'll use your car. The unpowered wheels will roll passively, like the front wheel on a bicycle. In 4WD (Four-Wheel Drive) mode, the engine can deliver power to all four wheels simultaneously, if it detects a loss of traction. Hi and Lo modes refer to the gear ratio being used: Lo provides much more torque at low speeds, which is useful for navigating hazardous situations, such as snow and terrain."
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bqdn86 | What are gearbox ratios? | I often see ratios for the specs of gearboxes like 4:1, 7:1, 30:1. What does this mean? | Engineering | explainlikeimfive | {
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"It's the ratio between the number of teeth on the input gear to the number of teeth on the output gear. For a ratio of 4:1 (4), the output gear will complete 4 revolutions for each revolution of the input gear. For ratios where the input gear has more teeth than the output, speed will increase at the cost of torque. If the input gear has less, torque will increase at the expense of speed."
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bqfols | Color-blindness glasses filter out colors, but wouldn't that make the problem worse? | For example, glasses for red-green color-blindness filter out yellow, so it's like a blue filter, but wouldn't that only worsen the problem, for red, yellow, and green are not visible at all? | Engineering | explainlikeimfive | {
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"Normally, people's eyes have three color receptors, for red, green, and blue light. However, there's some overlap. Orange light, for example, will excite both the red and the green receptors a little bit. For some people, *red* light will excite both the red and green receptors, which is a problem because then it seems really similar to when orange light is received, since both receptors respond similarly. The glasses take out a section of light that's most overlapped. This means that a chunk of the red and a chunk of the green light is simply filtered out, but *some* of the red light (the \"redder\" light) remains, and *some* of the green light (the \"bluer\" green light) remains. As such, when someone wearing the glasses sees a red balloon, they'll only see the reddest light coming from that balloon. So it will appear definitely red. Whereas when they see an orange balloon, it will no longer make the red receptors respond since the reddest light from the orange balloon will have been filtered out, allowing the green receptor to respond a little bit to it, and the red receptor to respond a little bit to it (due to the orange balloon still having *some* red light that gets through on the reddest side of the spectrum) and so the orange balloon can be seen as distinct from the red balloon. Meanwhile, blue balloons look blue, since they never had as much red or green light reflecting from them to begin with."
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bqg2eu | What’s the difference between gel, rollerball, and ballpoint pens? | What is the difference between the mechanism of each pen? | Engineering | explainlikeimfive | {
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"Ball Points use oil based inks which are stickiest. Roller balls come in 2 types: Gel Rollerball - medium stickiness. Water based Rollerball - least sticky. Mechanically they have the same design at the tip, varied for the viscosity of the ink base (oil, gel, or water). Edit: Some water based roller balls are so “runny” they have a section between the reservoir and the tip which slows the ink flow to stop it from spilling out. This section uses capillary action and vanes similar to modern fountain pens."
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bqhxk2 | Whatever happened to those weird noises affecting nearby speakers when we received a call on a cell phone back in the days, as illustrated in the link? | URL_0 I was appreciating the nice little attention to that detail in gta4, but it got me wondering how come it's gone nowadays. | Engineering | explainlikeimfive | {
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"Only 00's bois will remember, or however kids are talking these days.",
"The cell phone transmits quite a bit of RF energy when it is talking to the tower. That energy can leak into the amplifiers in a stereo system and disturb their operation, creating the sound you hear. I don't know exactly what happened, but I would guess they fixed this issue by: - shielding the stereo amplifiers better (metal box) - adding RF filters to the amplifier inputs - making opamps with better RF rejection (basically built-in filters) Something like the above. I would also hazard a guess that there are probably a lot of stereos floating around where this still isn't fixed.",
"This is pretty tough to ELI5, but I’mma take a shot: Back when cell phones first went digital, there were two competing “languages” for the cell phones and towers to use. CDMA and GSM. When wireless things talk to each other digitally, usually only one can talk at a time, otherwise the other stuff gets confused as it can be hard to tell what parts of what it is hearing is from one thing versus another. CDMA uses a system where the wireless radios in the devices are pretty much always on. GSM used a system called TDMA which meant each device gets so much time to send a signal, then other devices get turns. In GSM when it isn’t talking it turns off the transmitter on its radio. It then turns it back on when it talks. Have you ever played with a really old amplifier, like one from the 70’s or so? When you turn them on they can make a pop noise as the power is applied to the speakers. The GSM radio is making a pop noise every time it turns on. The actual digital signal of the cell phone is so high pitched, that even if your speakers could play it, you wouldn’t hear it. But those pops are timed just right so that they add together to make some awful sounds to our ears. (Non-ELI5, the frequency band of the radio switching is in audible frequencies). While those pops can be picked up in just about any electronics, on their own they are not strong enough to move a speaker, at least not enough to be heard by humans. However, when they get picked up by the electronics that are then amplified, you hear them over the speakers. This is even more likely to happen if there are microphones around, as microphones put out such a low level of power they get amplified twice. Once to a level that regular electronics can work with them (called Line level, usually done by a pre-amp), then again to be enough to move speakers. Why don’t we hear it anymore? When GSM moved to 3G, it went to a “language” called UTMS. UTMS uses a new version of CDMA, which wasn’t compatible with the old version of CDMA, called WCDMA. CDMA providers still used regular CDMA for 3G. When all the providers started going to LTE, it was decided to use WCDMA for LTE. There are other signals and things on cell phones that can cause noises in audio systems, but the very distinctive and memorable one was the GSM noise. Note below: US GSM providers: AT & T, T-Mobile (and all the companies that got bought up by them so that we really only have 4 providers today) US CDMA providers: Verizon, Sprint (and all the companies that got bought up by them so that we really only have 4 providers today) So if you were in an area with no AT & T or T-Mobile coverage you might not have ran across this.",
"Yea I remember dating my first gf and I'd leave my phone by the speaker so I could tell when she was about to text me. Good old days",
"The band of the radio spectrum in use might have changed as we switched from GPRS / 2G to 3G and onwards. Higher frequencies being needed to transmit more packets of information at a faster rate."
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br7c93 | Why do home LED lightbulbs have so much heat on heatsink yet devices like iPhone that use LED lighting seem to have very little | Engineering | explainlikeimfive | {
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"Because a LED bulb with a heat sink will emit many time more light then the screen of a iPhone. A low power LED bulb do not need a heat sink. Just try to illuminate a wall in a dark room with the screen and compare that to a light bulb. There might be a difference in efficiency and the phone product less heat for the same amount of light and that is because how you it is constructed so you can run a LEDs on mains voltage versus the battery in a cellphone. A LED bulb often is made as cheap as possible but the cellphone charger and voltage converter in the phone is more advances, expensive and efficent. But the main difference it still the amount of light they emit."
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bra3t8 | Why do car seatbelts have one strap whereas airplane pilot seatbelts have two straps? | Engineering | explainlikeimfive | {
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"Car seat belts are optimized to reduce injuries in case of a crash. Pilot seats are made to keep the pilot in his position at any cost, even in a falling and wildly spinning plane.",
"Pilot harnesses are actually a 5-point harness; there's a strap that comes up between the legs, with a 4-part buckle assembly, and then a lap belt (L and R straps) and two shoulder straps (L and R) go into that. You find this same sort of harness in the seats of high-speed race cars. The use-case is the same: keep the person/people in control of the vehicle firmly in place despite the extreme forces exerted on them trying to pull them out of their seats in some extreme conditions that either may (pilot) or will (racecar driver) occur in normal operation.",
"Comes down to how you are most likely to die. You are very likely to survive the plane crash. You are less likely to survive the ensuing fire, and will probably die of smoke inhalation. A complicated seatbelt is the last thing you need as your skin melts and your lungs fill with carbon monoxide. With car seatbelts, they are designed to keep your head from smashing through the steering wheel and into the dashboard. That kind of thing is pretty fatal most of the time. Cars usually don't catch fire and explode after a crash. Which is why seatbelts in cars are designed to save you from the collision most likely to kill you (the one with the dashboard).",
"It's a cost/function formula. Let's start with planes: There are three types (oversimplifying) of seat belts. Planes don't crash very often, so the seat belts aren't about saving your life in the event of a crash. They do, however, experience turbulence, shaking the plane pretty badly. If you look at a passenger seat, it's just a single strap to keep you from flying out of your seat when the plane drops. It's the cheapest option, but as effective as it needs to be. The stewardesses get two straps to hold the upright while rear facing. This lets them have a good idea of what is going on in the plane, even in an emergency. Then, move to the pilots, and they have a 5 point harness. As the plane drops or shakes, they need to be upright, in place and able to control the plane. Now, as we move to a car, you'll notice a two strap system in most passenger vehicles. Cars are more likely to crash than a plane, and passengers are more likely to survive. These three point systems hold you in place to prevent whiplash and other spine injuries. However, since most of the time you're not in an accident, they are flexible enough to let you comfortably move around. In the case of a crash, the driver mostly needs to be able to hit the breaks and remain in their seat, so a 5 point harness is overkill. A simpler belt will be more likely to be used, and doesn't loose much over a 5 point, plus is cheaper and fits more people. We've actually seen a move from a single strap seatbelt for cars, to the two belt system in the front seat, to a two belt system in 2 of the three rear seats as well, to now almost all cars have a two belt system in all three seats. This is because cars are generally traveling faster, and are safer and are more expensive. You're more likely to survive the impact, and it will have more force, so there is an added benefit to a more secure strap - with cars costing more, you're less likely to notice the extra cost. Further proof: race car drivers use the 5 point harness. They are going faster, subjected to stronger forces, and need to have control of their car in much more extreme scenarios. Plus, the cars are built for them, so the straps don't need to be as easily adjustable. They aren't reaching in the back for a soda, or adjusting the radio - so comfort isn't as important."
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bragnp | why is there a tower with a burning flame at the top of it in every petrol plant ? | Engineering | explainlikeimfive | {
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"Usually when oil is extracted, there comes with it a crapload of water and natural gas. The fluids go into a vessel called a separator which, you guessed it, separates the oil, water and gas. The water is taken aside and usually pumped back into the ground or purified and used for other purposes. The oil heads to a fractional distillation column. The gas that is left behind is usually not pure enough to make it worth purifying, compressing and storing/selling. So what do you do with all this flammable-but-not-pure natural gas? In some plants they use it to feed the boilers that power the plant itself or provide other functions. But sometimes they cant do this or the amount of gas produced is just so high that the boilers cant use it all. In those cases, the most economical thing to do is to just burn it. As pointed out before, the carbon dioxide has a lower impact on the environment than the methane otherwise would.",
"I remember being told those are natural gasses that cant be captured. And because just releasing them is very harmful ( heavy geen house effects ), they burn it instead ( slightly less green house effect ). See [Door to hell]( URL_0 )",
"URL_0 These are used for a number of things, from burning off 'waste' gases to converting methane to CO2 thus significantly reducing environmental impact. The purpose and frequency of use are dependant on the process(es) they're associated with, so the ones you're looking at could have any number of purposes. Most likely, it's to burn off excess natural gas or relieve pressure from another part of the process. Source: Environmental stack tester in U.S.",
"Besides the common burning excess natural gas others point out, they also serve a more general safety purpose. Many if not most of the processes in a refinery or chemical plant deal with gases as inputs, intermediate or final products. Just like with natural gas (as everyone else mentioned) if those products are released it is much safer to combust them than to allow them to be released in their uncombusted form. So, many of the flares you see are kind of like pilot lights on your water heater or other natural gas appliances. They stay lit so that when there is an upset in the plant the products can be shunted to the flare stack and burned (automatically) before they are released. If you have to ask yourself if you have ever seen a plant burning off excess product during a process upset, you haven’t. If the plant or process is big enough, the roar can be heard for miles and they can light up the night as bright as day for just as far."
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braryn | How do our toilet pipes that lead to sewers remain unclogged for years on end? | Engineering | explainlikeimfive | {
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"Because most the stuff that you put down your toilet is a semi-solid or break down very easily under flowing water. that is why you're not supposed to put sani wipes or feminine products down the loo because they do not actually break down like paper or poo. in the same regard, you should not pour grease down your drains either, cuz it solidifies in the cool pipe & begins to clog and build up on the walls"
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brexk1 | How are really tall buildings able to withstand high winds? | I live in Chicago and get super anxious when it's Windy out ( I know that its called windy for another reason but it was also WINDY recently). How is it that these tall buildings don't fall over, how safe should I feel? The swaying also bugs me out when I'm inside them. | Engineering | explainlikeimfive | {
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"Most skyscrapers are built with a series of counterweights in them to help from swaying too much. The buildings are also to designed to sway in the wind. It actually makes them safer. Imagine a stick that has been dried out. It’s very rigid, but it can be snapped easily. Then take a stick freshly cut from a tree. It can bend quite a bit before it actually breaks. That pliability works the same in the buildings. Then think about the tall buildings in places like San Francisco and Miami. These buildings can take beatings from massive earthquakes and hurricanes and still stand strong. Windy City wind doesn’t compare to hurricane force winds. So you shouldn’t be concerned at all.",
"Steel frames. They're strong. Tall Buildings are engineered to withstand a certain limit of windspeeds. Then engineering principles say to apply an amount of over engineering as safety factor, typically 1.5x or 2x But should we ever get the much speculated tornado that hits the Loop, no amount of over engineering will be enough. Something is gonna come down",
"They are usually built so that the swaying is damped by the building. For very large ones there's a pendulum or a similar device that absorbs the swimming. It's the opposite of how you play with a swing (the playground toy) and try to go faster - instead you try to stop yourself from swinging as much as possible (without skidding your feet on the ground, because buildings don't have that option.) The shape us also made so that the resonance frequency (the frequency at which the swaying is most impactful) is different from typical swaying in a building. Resonance is also well understood by the swing-example, it's the rhythm your parents/friends/siblings get into when shoving you to go faster."
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brnh9s | Why are the majority of space rockets made in white instead of other colors? | Engineering | explainlikeimfive | {
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"I'm not sure for rockets, but I know planes are white mostly for two reasons : white paint is cheaper and it's easier to spot technical defects on a white surface.",
"The ISS is shielded with metallic surfaces for maximum reflectivity, and white thermal blanket.[\\[7\\]]( URL_0 ) 📷 ISS WITH THERMAL BLANKET COVERING This blanket, or ‘beta cloth’ is composed of woven silica fibres, and has been used since the Apollo era. Its resistance to micrometeorites would protect against paint flakes like the one that chipped the cupola. However, when NASA Engineer Robert Frost was asked in 2013 which aspects of the ISS would be changed if it were redesigned today, he suggested that the trusses might have improved thermal stability, and would probably be coated in thermally resistant paint. & #x200B; here is an interesting read with a little info on the topic. & #x200B; [ URL_1 ]( URL_1 )"
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brqhlh | How do home users use virtual machines | I understand that in a work environment, different types of servers doing specific tasks can be each a VM. | Engineering | explainlikeimfive | {
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"The same way everyone else does. Software testing, running legacy programs that no longer work on modern OS's, encapsulation to help prevent programs from interfering with others, running virtual desktops for thin/zero clients, honeypots to catch hackers, etc. The only difference is that VM's at home are much less common than in the work place; And that VM's at work typically run on dedicated servers, usually through the OS called ESXi. Where as a home user will probably just run it on a normal desktop PC.",
"\\ > How do home users use virtual machines & #x200B; That's a really open question. They can use them just as an operations team can - install a hypervisor on a computer and go to town. & #x200B; How can they use them practically? Well that's a different story. Frankly, there is limited utility in complete virtualization. You typically don't need whole instances of operating systems when what you're really looking for is containerization and some semblance of isolation. As that is typically the use case, Linux and Docker is the winning combo. & #x200B; What would you containerize? Every god damn thing. Every network facing service can run in its own instance, contain only those components of the environment which it needs, map only parts of the disk it needs, expose only the ports it needs, etc. & #x200B; What do I run on my home server? I run internal and external web servers, a mail server, file share, drop box, media server, disk backup for my laptops, and git repos. The host OS monitors the containers and can restart them if a failure is detected.",
"A \"virtual machine\" is just a program that a person can set up to create sort of an operating system with an operating system. Like starting up a digital computer within Windows with its own digital operating system to run its own programs. Windows 10 has a built in feature to create a virtual machine, called Hyper-V, or you can download third party programs to set one up. From there a person can install an operating system to the VM. It uses computer resources (so you have to factor in that the base operating system, like Windows, will use memory and processor power and then the VM operating system will use memory and processor power; it also needs hard drive space to load the data to). People use it on home computers to test out new operating systems (no risk, no necessity to deal with installations and \"physically\" reconfiguring hard drive space) and to test out files or websites that they don't necessarily trust (since it won't be able to infect your Windows operating system if it has malware)."
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bs0la0 | Why are there 2 types of screws/screwdrivers? Doesn't it just make it inconvenient to have to find a matching screwdriver? | Engineering | explainlikeimfive | {
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"Flatheads are older but also simpler to use. It's possible to screw a flathead with random stuff lying about like a key, coin or knife. If it's something that has to be opened often, this can be an advantage. That's why battery components usually have wide flats. Phillips can transfer way more strength without \"jumping\" much. But you need a tiny little bit of skill to screw it properly. Which is why ikea and other DIY furniture tends to use inbus screws. They don't jump at all when you provide the right tool, reducing the amount of broken screws and overscrewed boards. Inbus can greatly reduce the amount of service when dealing with laypeople. Other screws can improve on those designs but tend to be rare. tri-head aka nintendo screws are designed so you can't open up a nintendo unless you bought those specific screwdrivers, which almost nobody stocks. Before the internet, this slightly discouraged modding. Socket wrenches are better if it has to be real tight, like a car wheel. You really don't want to risk underscrewing a car wheel. Two big tips I can give you. Buy a toolbelt or work pants so you have a place to put the different tools you'll need, making it way less likely you have to search for the correct screwdriver. Secondly, buy a big box of a favoured screw type in different sizes. In my house, everything I fix, I try to exchange with phillips screws if possible.",
"Actually, there are many more than just two kinds. But let's leave that part out. Screws are important. Society uses a whole lot of them. Often in stuff manufactured by machinery. There has been ongoing development on screw heads for very many years. Aiming to make the screws better. Making the tools last longer. Increasing the force the tool is able to transfer to the screw. Those kinds of things. There are also screws that are made with the intention that it is supposed to be difficult to come by tools that fit them, bu that is usually a trick that only works for a handful of years. But most of it comes from the manufacturing industry and their demands. Everyone wants a cheap screw that is easy to screw in, won't wear down the tool much and is useful for applications when you have to apply a lot of force. Most newer screws seem to meet at least some of those expectations really well.",
"By “Two” do you mean the right one, and the wrong one? Heh there are quite a few different kinds, and to complicate it further, each one has multiple sizes too. I think it could an evolutionary thing over many years. Probably started with a slotted screw and evolved and got improved to Phillips, Pozi, Robertson, Torx, etc. If you’re further interested, read the history on this page: URL_1 In summary, slotted, outside hex head, and outside square heads came first. Then followed by Inside square (Robertson). Phillips followed after that. Also, another page on “drive types”: URL_0 Edit: I think what it all came down to initially was easy of machining them by tech available at the time.",
"Philips are actually designed to slip... They're meant to prevent you over torqueing the screw so the bit begins to slip out of the head."
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bs3ici | why do buses make that "PFSSSST" sound when they stop? | Engineering | explainlikeimfive | {
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"Many large vehicles have a system of brakes actuated by compressed air instead of hydraulic fluid or cables you would find in a lighter vehicle or passenger car. Parking/emergency brakes on such vehicles are usually \"normally closed\": to release the brake, air pressure must be applied to the brake. For these, a sudden release of air pressure will quickly activate that brake, but also will create a little bit of noise.",
"Air brakes. A tank of compressed air hold the brakes off, pressing the brake pedal relieves some pressure allowing the brakes to apply. The tank is pressurised by a pump on the engine. When stopped, the parking brake will allow the brakes to fully apply by releasing all pressure in the lines. It's far more complicated I'm sure! Edit: one reason they are used over hydraulic systems is fail-safe and maintenance. If something failed, the brakes will lock on, not dump fluid under pressure and facilitates road-side repair."
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bscn1n | Why do most electronics that run on two batteries require you to have them facing alternating directions? | Engineering | explainlikeimfive | {
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"It makes the wiring easier. The circuit starts at one end, runs through the first battery and across to the second battery, and back through the second to complete the circuit.",
"batteries come at fixed voltages (1.5v), however most electronics need higher voltage to function. You can stack batteries to increase the total voltage supplied. It is mechanically easier to build the stack when the connecting sides of the batteries are already laying close.",
"The batteries are wired in series. The positive terminal of one battery is wired to the negative terminal of next battery. If I connect two batteries in series I have doubled the voltage in the circuit while maintaining the same capacity rating (amp hours). If the batteries were facing the same way, they would be parallel. The positive terminal of one battery would be wired to the positive terminal of the next battery, and the same for the negative terminals. If I connect two batteries in parallel I double the capacity (amp hours) but the voltage is unchanged.",
"Each side has a different charge, and to power the device the circuit has to be complete. The energy flows through the batteries (I believe the negative to the device and back to positive, negative, positive, negative, and complete the circuit). It’s basically like a one way pipe that only takes certain electrons as electricity and doesn’t go backwards."
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bsgaob | How will the Starlink satellites move from their "blob" to be evenly spaced out in orbit? | Engineering | explainlikeimfive | {
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"Let's say there aren't 60, but 2 sats, and they're supposed to be on the exact opposite side of earth. The rocket releases them in an orbit where it takes them 1 hours to circle earth, and they need to go to an orbit where it takes them 2 hours. (those are not real numbers, I just made them up) Now the first satellite starts its thrusters and moves to the higher orbit. So when the second satellite has moved around earth exactly one time, the first satellite will only have moved halway around the earth. At that point, the second sat will starts it thrusters, which will bring it into the same orbit, just on the opposite side. It's of course a bit more complicated with 60 sats, and the timing will also not be as neatly. But it's the same principle: The sats will launch their thrusters one after another, timed just right so that they are evenly spaced apart."
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bshh20 | Why do heating and cooling systems use coils/curves? | I just saw a photo of a floor heating system, and there aren’t many “straight” heating parts, it’s all curved. Why? ^(Might’ve ^used ^the ^wrong ^flair) | Engineering | explainlikeimfive | {
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"Heat transferrence depends on surface area. If you just have a block, the surface area is only the outer areas. If you cut that block, you get all the area on each side of the cut as well. This is why heat sinks have all those fins. For heating and cooling systems like you've described, they need to use coils because the heating medium is a liquid that needs to keep moving through the system to transfer the heat.",
"Efficiency. You can heat a smaller area with less energy and keep it at that temp with less energy as well. Picture a tub of water, that water can hold it's heat better than if the water was spread out into a shallow trough."
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bslqw0 | Why do some batteries use kWh to define the capacity and other batteries use mAh? | Engineering | explainlikeimfive | {
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"Single cell batteries are typically rated with mAh since their voltages are always the same. IE: Lithium batteries are almost always 3.7v. A, D and C batteries are always 1.5v (Or 1.2v for rechargeable ones). So watts don't really matter as the voltage will stay the same. Where as multi-cell batteries like those in hybrids and EV's consist of several batteries wired together, which changes the voltage. These are usually rated with kWh since their voltages will often be different. Most EV's use around 350VDC, and most non-plugin hybrids are around 250VDC. & #x200B; PS: There are still multicell batteries such as some 12v and most 9v batteries that use mAh or Ah, but that's a common size of battery. So the voltage is still the same."
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bsokkx | Why do the calculator and the phone not share the same number placement/ pattern? | The numbers on the phone pad start with 1 in the upper left corner, going down to 9 in the bottom right corner. The numbers on a calculator start with 1 in the bottom left corn, going up to 9 in the top right corner. For example, the top left number on a phone pad is 1. The top left number on a calculator is 7. This difference makes it challenging to switch between the two. Why were they designed this way? | Engineering | explainlikeimfive | {
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"Both layouts were a result of a need to increase efficiency/productivity in their respective industries. The calculator layout was made for bookkeepers and found it increased their speed and efficiency. The phone layout was made to decrease the amount of wrong numbers that were dialed by people using phones, as that layout appeared to be more easily understood by most people and re-directing calls made to the wrong number caused increased workload on phone operators. Maybe I take for granted that I grew up with regular phones and texting with T9, but I never considered it would be challenging to switch between the two.",
"I long ago read (so don't recall the source) that when phones first moved from rotary to the standard layout, people with a lot of experience on calculators were dialing too fast and digits were being lost/skipped. They switched the layout to slow people down just long enough for the technology to catch up",
"Numberphile did a video on why the number layout is what it is on phones, and they talk a little bit about the calculator layout too. The calculator layout was not made for the average person, whereas the phone layout had to be easy to use for everyone. Here's the video: & #x200B; [ URL_0 ]( URL_0 )"
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bsq5ep | Why is it that tunnels and bridges don't rip themselves apart if the land is constantly changing and shifting | For example, the Channel Tunnel between the UK and France must be shifting, right? Even if it's only by a few centimetres each year. Wouldn't this eventually cause a catastrophic failure? | Engineering | explainlikeimfive | {
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"That's what the engineers do, is identify fault lines and make sure the tunnels don't pass through any of those areas. And no, the Chunnel is through one solid area of rock, and none of it is shifting. Besides, it's 250 feet below the bottom of the channel so there isn't really any way that a collapse or fracture that huge could happen."
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bt0xgw | What does your car radio sometimes lose signal when you come to a stop sign or stoplight, then comes in clear again when you roll forwards a few inches/feet? | see above | Engineering | explainlikeimfive | {
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"It's due to \"multipath interference\". On its way to your radio antenna, a radio wave can also bounce off various things (buildings, trees, cars, etc.). The reflected versions of these multiple paths take a little longer to get to your antenna than the most direct one, so they are out of phase with the original. (The peaks and troughs don't line up.) This can cause destructive interference to occur, degrading the radio signal. (It can also result in *constructive* interference.) If you move your car just a little bit, you change which reflections are hitting your antenna, and the destructive interference can be increased or reduced.",
"It is due to multipath interference. Radio waves bounce off metallic objects like other cars, buildings, sign poles, etc. If they arrive at your car antenna out of phase with the direct (not reflected) radio signal, they will cancel it out. A few inches can move you into a location where they no longer cancel. URL_0"
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btb4qb | What happens to an oil field after the oil is pumped out? Does it just leave a void/cavern? Isn't it today to leave that because it could collapse? | Engineering | explainlikeimfive | {
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"Oil isn't in a big cavern underground. It's seeped into the rock, and when a hole is drilled through the pressure of the Earth compressing the rock squeezes the oil out. So when there's no oil left, there's still plenty of rock down there. In some formations depleting the oil/gas can cause some ground subsidence, but usually nothing dangerous."
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btcxx4 | Why does NASA mission control 'lock the doors' when there's a tragedy? | Engineering | explainlikeimfive | {
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"text": [
"It doesn't literally mean lock the actually doors so no one is allowed in or out of the room. No doors are actually locked. It means flight controllers aren't supposed to leave the building and need to start preserving their data and writing up their logbook notes so everything possible can be used in a subsequent investigation.",
"“Lock the doors” is just a code phrase for post failure procedure, Back in the 50s and 60s the data on the computer terminals needed special procedures to retain accurate backups of the incident, and every station needed to be preserved in a fairy pristine state"
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btgmzn | How exactly do faucets work? They look like saxophones so how does water go up the pipes? | Engineering | explainlikeimfive | {
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"text": [
"Water pressure: either from a pump or water tower creates pressure and makes water come out the faucet"
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bth87z | What’s the problem with over cooling a car engine? | The new 2020 Supra is set to come out soonish and the car is covered in ‘fake’ vents. These vents aren’t functional (from the factory) but the plastic filler can be popped out and replaced with real (functional) vents for people that tune the car and make it faster. One of the reasons Toyota said they didn’t make all those vents functional to begin with, is because it would over cool the engine. Why would this be a bad thing? Edit: a word | Engineering | explainlikeimfive | {
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"The engine operates most efficiently when it is already moderately hot. Increasing it's ability to vent heat makes that sweet spot farther away (which is bad if you are just driving casually but good if you are constantly pushing the limit).",
"Combustion engines run better and more efficient if they are running at their operating temperature. This is usually at about 85°C for petrol engines. If you keep dissipating the heat generated from the combustion, the engine (or more precisely the controlling unit) will always try to heat the engine up to operating temp. To accomplish that it will use a richer mix (more fuel/less air) which means you'll burn more fuel than you would need to. A second factor is the viscosity of the oil lubricating the moving parts in the engine. It will flow better at higher temperatures. So with a cooler engine you will have more wear on your engine components and it needs repairs earlier. Toyota hybrids for example use oil which flows quicker at lower temperatures because their combustion engines don't get that hot because they're turned off so much"
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btna08 | How does 5G wireless technology work? | I keep hearing about 5G and I want to know how it works.I searched on this forum and only got answers talking about the benefits 5G will supposedly have, not the technology. 1G is basically a walkie-talkie. Inefficient use of frequency. 2G is the digitization of the spectrum that used it much more efficiently. You didn't jam the entire frequency when you talked. 3G is basically 2G for voice and the ability to send out packets in open spectrum. 4G is prioritizing packets to eliminate spikes in the network to increase capacity. But for the life of me, and I've spent a lot of time working it out, I can't figure out what 5G does. There are a couple ways of testing this out. If you go to the Wikipedia page for 4G, you'll see the standards listed out. If you go to the Wikipedia archive, you see how the page looked 10 years ago. And the people that wrote it then had a pretty good what 4G would be. But if you go the 5G Wikipedia page today, you'll see no standards. You'll see a bunch of guesses and ideas about what it *could* be, but no real standards. Is it beam forming wireless? MIMO? Edge-computing? What exactly is the standard? | Engineering | explainlikeimfive | {
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"You can find a complete outline of the most up to date 5G standards published by [3GPP]( URL_0 ). DR 21.915 provides a summary of each Release, The current standard, 1.1.0 can be found in release 15: The 5G requirements have been defined in terms of new services and markets by SA1, under the \"SMARTER\" work item. These are defined mostly in TS 22.261 [1], which describes different types of requirements for different 5G usage: - Enhanced Mobile Broadband (eMBB): the requirements are defined on high data rates, higher traffic or connection density, high user mobility, and the requirements related to various deployment and coverage scenarios. The scenarios address different service areas (e.g., indoor/outdoor , urban and rural areas, office and home, local and wide areas connectivity), and special deployments (e.g., massive gatherings, broadcast, residential, and high-speed vehicles). The scenarios and their performance requirements can be found in table 7.1-1 of TS 22.261 [1]. For instance, for the downlink, experienced data rate of up to 50 Mbps are expected outdoor and 1 Gbps indoor (5GLAN), and half of these values for the uplink. For services to an airplane, a bitrate of 1,2 Gbps is expected per plane. - Critical Communications (CC) and Ultra Reliable and Low Latency Communications (URLLC): Several scenarios require the support of very low latency and very high communications service availability. These are driven by the new services such as industrial automation. The overall service latency depends on the delay on the radio interface, transmission within the 5G system, transmission to a server which may be outside the 5G system, and data processing. Some of these factors depend directly on the 5G system itself, whereas for others the impact can be reduced by suitable interconnections between the 5G system and services or servers outside of the 5G system, for example, to allow local hosting of the services. The scenarios and their performance requirements can be found in table 7.2.2-1 of TS 22.261 [1]. For instance, in the context of remote control for process automation, a reliability of 99,9999% is expected, with a user experienced data rate up to 100 Mbps and an end-to-end latency of 50 ms. This is provided in particular through the Edge Computing capability described below. - Massive Internet of Things (mIoT). Several scenarios require the 5G system to support very high traffic densities of devices. The Massive Internet of Things requirements include the operational aspects that apply to the wide range of IoT devices and services anticipated in the 5G timeframe. - Flexible network operations. These are a set of specificities offered by the 5G system, as detailed in the following sections. It covers aspects such as network slicing, network capability exposure, scalability, and diverse mobility, security, efficient content delivery, and migration and interworking."
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btylfb | Why don’t we see more creativity in modern car design? | Engineering | explainlikeimfive | {
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"text": [
"Because engeneering came to an understanding of drag, air resistace and space organization so deep that most principles are shared among many different models. So fast cars are always gonna look in a way that reduces all the forces that would stop them (think of all F1 cars). Family cars are designed in a way to accommodate 5/6 people in the most comfortable way.. And so forth",
"The simplest answer is - they make what sells. Yeah, the Delorean was cool, but it didn't sell and failed. When cars were new, manufacturers tried making their cars \"cool\" and \"unique\", and for the most part those companies failed. When it comes to something as expensive as a car, the vast majority of consumers want reliability, safety, comfort, and efficiency in a \"nice looking\" package. They will skip on the \"really cool\" features like gullwing doors to get an easily maintained, safe and affordable vehicle"
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bu8e8m | Why are there clocks still made with the "ticking" noise, and not all silent? | Engineering | explainlikeimfive | {
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"ep8dm9o"
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"text": [
"They are mechanical, the ticking is also a good form of acoustic feedback so a person knows that the clock is ticking and if they want, count the seconds. You can buy silent mechanical clocks if you want.",
"Some people find the ticking to be quite satisfying. Either way, one of the components that makes the ticking sound are the gears that have been found in watches and clocks for centuries. These components are often more reliable than a computer chip telling the hands to move, which would probably make less sound."
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bu9bsc | why are wind turbines shaped like that? Would having wider blades or more than three blades give them more energy conversion for a given wind? | Engineering | explainlikeimfive | {
"a_id": [
"ep8suj6",
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"text": [
"It's about energy per unit cost. More blades extract more energy, but weigh more, so the energy is mostly spent making the big object rotate, not making electricity. It makes more sense where the momentum of the big wheel also helps deal with load changes, like a water pump. The load in a power generator is controlled and constant. Bigger structures also disrupt the wind. Thin structures slice through the air, and the time from blade #1 to blade #2 lets the wind stabilize. That way you can have rows without them fouling each other's airflow. One blade would be the best, but that leads to balance problems. Two blades have lots of harmonic interactions that cause wear in bearings. Three is the best compromise.",
"Wind turbines are an optimization problem You want the blades to be long so the tips generate as much torque as possible, but you also want them to be light since they'll be spinning. To get long light blades you end up needing to make them skinny and 3 blades helps keep everything balanced. You also don't necessarily want to catch all the wind. It's be nice on calm days but if you've got a dozen super wide blades then you're in for a world of hurt the everytime a big windy thunderstorm rolls through."
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buij31 | How are minutes used is sensitivity? What does 35 minutes per 2mm mean in leveling and engineering? | Engineering | explainlikeimfive | {
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"text": [
"Minutes are a part of circular measurement. 60 minutes equal one degree and 60 seconds equal one minute. So 35 minutes per 2mm means 2mm corresponds to 35/60 (or 0.58 degrees)",
"If it's on a production drawing, it's because someone hates you, because that's a virtually impossible standard to keep. There are 360 degrees in a circle. There are 60 minutes in a degree. So you're going for 35/60=0.58 Degrees off plane per 2mm. Listing it \"Per 2mm\" implies that you're going to keep adding 0.58 degrees every 2mm, creating a curve or series of staggered lines. I'd be guessing what the intention is, but it's probably obvious if we had the drawing to look at. Listing \"Minutes per 2mm\" is weird though. Typically it's either \"Degrees/Minutes\" or \"Xmm per 2mm\", giving you a triangle to solve for degrees if need be."
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buk4b8 | Why are culverts and drainage pipes “ribbed”? Wouldn’t a smooth pipe be better for letting stuff flow through? | Engineering | explainlikeimfive | {
"a_id": [
"epdc8qd"
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"text": [
"As the other answer, it is bendable in the lengthwise direction. But also, and possibly more importantly, it is far less able to collapse. The ribbing gives it strength in the circumferential direction. It's similar to corrugated iron sheets which bend in one direction, but not across the corrugations."
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burvwm | My apartment key opens my own door, but also the communal laundry room, communal basement and communal elevator keyhole. How does that work? | Engineering | explainlikeimfive | {
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"text": [
"Keys can be designed so that as locks become more complex, the more unique the area they're locking is. For example, imagine your key has 4 portions that equal a code of 1-3-5-7. Your room requires the code 1-3-5-7, so only your key will open your door. But perhaps the laundry only requires a key of 1-3-x-x. The latter parts can be any key. So your friend with key 1-3-4-6 can't open your door, but they have the same beginnings of the key that can access the laundry room. The more sophisticated the keys and locks, the more layers of complexity you can use to distinguish between tiers of security.",
"A single key has multiple different teeth cut into it, and those teeth match up with pins and tumblers inside the lock body. What you're noticing is that the lock body for the communal areas uses a smaller set of pins that match teeth that are common across all the keys, but other apartment doors have more pins inside that your key wouldn't be able to line up.",
"A lock works with pins that prevent the tumbler from turning. The pins are in two parts. When the key pushes the pins up to the right level, the top part of the pin is fully in the body of the lock, the bottom part remains in the tumbler. This allows the tumbler to turn. There are a few ways to make the system you have there work. Easy way is to only have one pin in the basement/elevator locks, and arrange for everyone's lock to have the same sized pin in that position. This makes the elevator/basement lock pretty insecure, but doesn't make every other lock much less secure. You can balance things by using more identical pins in everyone's locks, which makes the basement lock harder to pick, but other locks easier to guess - but guesses require you to get physical keys cut. A better way would be to have the pins in the common area locks to be in different positions along the key - say, everyone has a 6-pin tumbler, but there are extra positions cut between those 6 positions, identical in everyone's keys, that operate the pins in the common locks. But this would require a custom-built lock body and tumbler, which would make it expensive. So much easier to just put different pins into stock standard lock bodies. If you get the chance to compare the keys for 2 or 3 different apartments, it will be easy to see which pins are used to open the common doors.",
"The tumblers in the lock itself are set up with multiple pins, rather than just one set. Takes a little work to get used to laying them out at first, but it is pretty easy to do. I used to key locks years ago when I worked in a hardware store (still have a kit as well)."
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busyes | How are glass marbles mass produced? | I watched a video where a glass blower made a (larger) glass marble by twisting in all kinds of different colors, but it looked very time consuming and I know there's no way they do this for the millions of marbles they mass produce for sale for super cheap. So how exactly do they mass produce these things with all the twisty colors in them and whatnot? | Engineering | explainlikeimfive | {
"a_id": [
"ephe502"
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"text": [
"The first half of this video shows the machine which rolls hot chunks of glass while they cool to round them. [ URL_0 ]( URL_0 )"
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butnp6 | How/ why do rockets fly in one controlled direction rather than chaotically all over the place like a balloon when released? | Engineering | explainlikeimfive | {
"a_id": [
"ephfczn"
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"text": [
"The nozzle on a balloon is floppy - it flops around all chaotically as air wheezes out of it. The exhaust bells on a rocket are on gimbals - on giant motorized mounts that can aim the thrust coming out. Then, the problem becomes how do you balance a broom on your hand (aka the so called inverted pendulum), but as it turns out we have really good computers that have already solved that problem.. so [much so that you can easily do it at home]( URL_0 ) with a cheap computer and some spare parts."
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buvcak | Anti-Aircraft Guns WWII | Been watching Catch-22 on Hulu, and I'm seeing all kinds of AA fire going off all over the place. I know the show is based on the book and somewhat of a satire, but even in Band of Brothers, the AA seemed to have a somewhat low success rate. I know these are television/movies, but was there any accuracy to the amount of AA fire shown in the films? I'm not sure how exactly how they worked. I guess the true question is, "How did these work? Why didn't they try to fly above it? Was flying above an option? What kind of success rate did they provide? How have they improved over the years? | Engineering | explainlikeimfive | {
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"I would say that the AA fire is depicted fairly accurate. Flying above AA fire wasn't possible for heavy AA guns as they could reach 30,000 ft altitude relatively easy though with a roughly 30 second delay/flight time of the shells. As it wasn't really possible to get accurate hits at that altitude AA batteries would mostly just saturate the air space ahead of the bomber formations with well timed explosive shells that would go off all around the planes as you see it in those shows. Even though direct hits were relatively unlikely the shrapnel could still damage planes and wound/kill flight personnel, and a direct hit would most likely end in the plane going down. On a bombing run anywhere between 10-20% of planes would be shot down during the mission by AA fire and interceptor aircraft, and probably a similar percentage would be able to fly home with some damage. [This 1943 instructional video explains it quite well.]( URL_0 )",
"Most AA guns in WW2 were the fragmentation type, the most well known being the 'flak' (German 88mm AA cannon). This is basically a cannon that shoots an explosive shell with a fuse. The fuse is set so that the shell explodes at a certain time. By knowing the speed of the shell, they can calculate how long the shell takes to reach a certain altitude. When the fuse hits the explosive charge, the shell explodes and sends fragments everywhere. So the shell does not have to hit the plane, it just has to explode close enough that the fragments damage the plane. The Germans used a complex radar directed AA system. The radar stations would coordinate the AA batteries. The crew of the AA batteries would aim their cannons and set the fuses precisely according to instructions. This allowed the German's to inflict heavy casualties on US and British bomber crews as they could accurately track the altitude and heading of the incoming planes. The German flak could reach 32,000ft, the highest the B-17 could fly is 30,000ft, most other bombers couldn't reach higher than 25,000ft. Even if the bombers could fly over the flak, the higher they are, the less accurate their bombs are. & #x200B; & #x200B; Note: The allied bombers did fly higher to avoid other types of AA fire from smaller guns/cannons. This made bombing less accurate and resulted in many civilian casualties since the allies had to resort to carpet/saturation bombing.",
"They're essentially area denial. The point of flak guns isn't hitting the enemy, it's building a huge aerial danger mushroom meadow. Those danger mushrooms are relatively dense so by sheer chance they *will* hit at least some of the approaching bombers, if only with dropping shrapnel rather than the actual blast. In a way, they aren't supposed to hit, just scare and confuse the enemy into missing. This one is conjecture but I assume they also made for aerial depth charges. The explosions of those shells create pockets of vastly different air pressure which destabilizes the planes in their vicinity. Flying above wasn't viable for several reasons, first of which would be the depth charge effect. Airplanes also have a limited climbing height, especially heavy strategic bombers. It takes a lot of gas to climb and at some point will simply stall. Flak grenades were actually calibrated for the estimated stalling altitude of then-current bombers. Another point is that aiming becomes increasingly difficult due to target lag (as opposed to target lead, this is when you're aiming at a stationary target from a moving platform) and differences in wind speed and direction throughout the troposphere. The last reason is that bomber cabins weren't pressurized until very late in the war. That's why they're wearing breathing masks and those heavy flight suits. It's cold and there's barely any oxygen up there and you can only get so high before it damages whatever skin you have exposes.",
"So essentially, they’re just high flying grenade shotgun shells?",
"The success rates of AA for most of the second world war for most of the combatants were spectacularly low. I can look up some exact numbers if you want but it's a lot of work. Something in the order of 12,000 rounds spent per aircraft downed iirc. There was light, medium and heavy AA (short, medium and long range). Above those the defence would often have fighters. The fighters would attack the bombers and try to push them down into the AA. The higher the bombers stayed the lower their accuracy was (which was already terrible in WW II), but the lower they went the more AA they would be exposed to. There were also batteries of large searchlights, AA-balloons, early radar systems, and ground observers involved. There were great improvements made during the war, on all sides, and since. Two of the biggest in WW II would be the improved radar systems, and the Variable Time fuse, in my opinion. And with ubiquitous guided rocketry AA has become far more deadly since."
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bv40c8 | How the power grid is able to work even when some circuits are not closed | As far as I'm aware, for electricity to flow, a circuit has to be closed. How is it that if I flip off a light the entire city'w power doesn't go down. How does the power grid isolate circuits while still allowing a circuit to be closed? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The circuits are connected in parallel. If you cut off one of the circuits, the others are still connected. Consider [this diagram]( URL_0 ). If you remove one of the bulbs it only cuts off that circuit, but electricity can still flow through the other bulbs.",
"I would look on Wiki for the difference between parallel and series circuits. It would be weird if everything was wired in series, meaning every light switch in the city, every outlet, every single thing needed to be on for anything whatsoever to be on."
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bv4i69 | How does running water reach the higher floors of skyscrapers? | I don't really know how plumbing works but there's no way it just makes it all the way up in one shot without gravity interfering, right? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"There are booster pumps throughout that aid the water to reach the top, simultaneously there are pumps in the drainage to slow down the drop of water/waste",
"pumps can only push water up so far before it becomes a struggle (inefficient) to fight against the weight of the water pushing down. like in a deep mine, there will be a series of water tanks leading up to the top. a pump would only have to push the water to the first tank, where the second pump would push it to the third tank, and the third one up again etc."
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bv9f4x | Wrinkle resistant/non-iron clothing | What makes clothes wrinkle-resistant/non-iron? Why wouldn't all clothing be made this way? This seems like a relatively modern thing -- why is that? | Engineering | explainlikeimfive | {
"a_id": [
"epn4gat"
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"text": [
"It depends on the material. Natural fibers like cotton and linen wrinkle easily, though wool does not. Basically, cotton fibers (for example) have little elasticity - check a shirt or jeans, if you can find some with 100% cotton and see how well they stretch compared to other fabrics. They do have a little, but not much. Cotton more than linen, for example. That is why they don't bounce back as easily to their original shape - winkle free. Most microfibers (like polyester) are the opposite - like sports clothing. It doesn't wrinkle, and has a \"memory\" of it's original shape; as it's really stretchy, it can bounce back to the memory position of the fibers - unwrinkled. That's why it seems \"modern\" - we haven't been able to produce microfibers for all that long. Edit: Not all cloths are made that way because natural fibers have other benefits (e.g lack of smell development for cotton, lightness of the fabric for hot climates for linen) and many people feel more comfortable with them than with synthetic fibers."
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bvdhbq | How do automatic blood pressure cuffs/machines know when to stop inflating the cuff for each individual person? | Engineering | explainlikeimfive | {
"a_id": [
"epoh2pl"
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"text": [
"Basically, vibrations from blood pumping through the arteries are detected by the device, which let it know how far to inflate and when to deflate. \"The new models use “fuzzy logic” to decide how much the cuff should be inflated to reach a pressure about 20 mm Hg above systolic pressure for any individual. When the cuff is fully inflated to this pressure, no blood flow occurs through the artery. As the cuff is deflated below the systolic pressure, the reducing pressure exerted on the artery allows blood to flow through it and sets up a detectable vibration in the arterial wall. When the cuff pressure falls below the patient's diastolic pressure, blood flows smoothly through the artery in the usual pulses, without any vibration being set up in the wall. Vibrations occur at any point where the cuff pressure is sufficiently high that the blood has to push the arterial wall open in order to flow through the artery. The vibrations are transferred from the arterial wall, through the air inside the cuff, into a transducer in the monitor that converts the measurements into electrical signals.\" Source: URL_0"
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bvgggo | Does increased load on a generator require more mechanical work. | ECE major here that slept through all his power classes. Say I have a basic single-phase generator like the kind you get at Home Depot. If I have long string of irons and light bulbs (essentially purely resistive loads) and draw more than the rated wattage, what happens? My intuition says that the engine must work harder, but what is the specific mechanism that causes this. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Current flowing through the coils of a generator makes an magnetic field. The more current, the stronger the magnetic field. The higher the load, the more current. This magnetic field is opposite to the one generated by the magnets of the generator. The gasoline motor is trying to move the magnets past the magnetic field generated the the coil. The stronger this field is, the more work the gasoline motor needs to do."
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bviw04 | Why do escalator handrails never run at the same speed as the escalator itself does? | I assume some of you observed this before. When using an escalator I mostly notice that the handrails run just slightly faster/slower than the escalator itself. This is especially noticable when leaning against the handrail at the beginning; when at the finish you'll most likely be tilted either up- or downwards. I noticed this at multiple escalators around the world. It seems like this is a worldwide problem. Can someone explain this difference in speed between the escalator and the handrail? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"As Don-Slade has already kind of pointed out (at least in Germany) escalator handrails have to run a certain percentage faster than the escalators itself to pull your point of weight forward. By being just slightly faster, when you grab a hold of them, your weight will be distributed more to the front, thusly reducing the risk of you falling backwards down the escalator. Likewise, when you’re going downwards, the handrails tend to run a bit slower to pull your weight back so you don’t fall down.",
"I ride on an escalator every day and the handrail moves at the same speed as everything else.",
"The handrails move faster than the escalator itself to get ahead of wear. Since the belt is only friction driven, it will slow down after some time and if the handrails move slower than the escalator, they will push the person riding back which may cause them to fall over",
"I could see the point of other commenters, but I was wondering if it had something to do with the handrail belt being a different circumference than the steps belt yet being driven by the same motor therefore it would run at a different rate of speed."
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bvsi0l | how do cameras in movies get a shot of someone looking into a mirror from behind without the camera being in the shot? | Engineering | explainlikeimfive | {
"a_id": [
"eps9eu1"
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"text": [
"Usually, it's just angle trickery, the mirror is angled to not have the camera in it. Other times, it's removed via CGI. Other times it's very complex with multiple mirrors and identical sets through windows giving the illusion of a reflection."
],
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bvtldj | Why do nuts, drills, or tools that are used to punch/attach things always rotate to the right? | or is there any factory that produces it in the opposite direction? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Left-handed screws are a thing, they're just not as common. Generally you'd only use them in places where you're going to have something spinning that would work to loosen a right-handed screw. It's just more economical to primarily produce right-handed screws than to produce the same amount of both (not because right-handed screws are easier to make, just because that's already what most things use).",
"They don't always go right tighty lefty loosy, some go lefty tighty. Convention has them go the same way as it stops confusion, but certain applications require the opposite thread rotation. I believe gas lines are generally left handed threads where as water or vent lines are right handed. The Austin Healey had left handed threads on the wheel nuts on the right side of the car so that the rotation of the wheels didn't cause them to come undone!",
"When using a hand tool in the right hand to tighten a screw, bolt, or nut it is easier to rotate it in the direction of your fingers. Since most people are right handed, most screws, bolt, and nuts are made to be right handed. Since most were, it became standard. Left handed threads exist. Usually they are only used on motor shafts, so the spinning of the motor doesn’t loosen the nut."
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3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
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