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e73v6p | How do stops in a pipe organ work? | Context: I work in a museum with a Baroque-era European pipe organ from between 1670-1770. Every week, some students from a local university’s music program come by and play it. Thing sounds awesome. On it, there are 10-12 knobs that, when pulled, totally change the sound of the organ, which I now know are called stops. What I don’t know, and have not learnt through Google, is how these stops so dramatically change the timbre of the organ. It goes from sounding like Phantom of the Opera, to a giant flute, to a Beethoven-esque sound... it just does not compute. Can someone ELI5? | Engineering | explainlikeimfive | {
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"Those are literally valves that direct air to different sets of pipes. Depending on the material, shape, length, etc., of the pipes, you can get different sounds. If you pull a stop, it opens a valve, and when you push it back in, it closes it.",
"Organs are very complicated instruments. Larger ones have hundreds of different sets of pipes. Each set is keyed to one of the keyboards (there's probably a technical term, but I don't know it) so when you pull out the stop that opens the valve, you can trigger the pipes associated with a particular note across several different sets of pipes. Some organs have semi-programmable buttons where you can engage a group of stops mid-song. This is how you can get such complicated sounds from a single performer. [This]( URL_0 ) video gives a nice tour of a large organ. It's really spectacular the effort that goes into such a massive instrument.",
"The reason why you can get such a variable sound by changing the stops is that an organ is quite literally a physical synthesizer. The sound that an instrument makes (its timbre) can be decomposed into multiple tones: a fundamental frequency that determines the note that is being played, and a bunch of harmonics at multiples of it (e.g. 2×, 3×, etc). The volume of these parts relative to each other is what makes an instrument sound one way or another. For example, you might have a 500Hz tone, a 1000Hz tone, a 1500Hz tone, etc, at different volumes. Computer synthesizers often work by mixing together tones like this to produce a given sound. Changing which note you play changes the base note and all the harmonics along with it, but the pattern remains roughly the same for a given sound/instrument. The stops of an organ literally correspond to these harmonics (or combinations of them). So by configuring them differently you can make it sound closer to a flute, to a violin, etc."
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e749u5 | How do houses made out of brick collapse when on fire? | Engineering | explainlikeimfive | {
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"They are brick with timber supports the bricks stay in place the timber burns placing stress and strain on various parts of the brickwork, alternatively the bricks may get hit when parts of the building collapse.",
"In the US at least most \"brick\" houses are really just \"masonry facade\" homes - wood framed and brick exterior for long term weather resistance. When the home burns down, the wooden ceiling and interior frame that the facade was tied to is destroyed leaving only a completely unsupported sheet of bricks. This provides little structural strength on its own and falls over under its own weight. True masonry structures like cinder block or concrete warehouses are pretty tough to light on fire, but if you do manage it the intense heat can eventually chemically destroy them and collapse the building. They don't burn, but they will disintegrate under excessive heat.",
"Brick houses in most places (in the US) is not structural, it is a masonry facade placed outside a standard timber framed wall. But fire can damage bricks. Bricks not intended for use in a kiln or other place intended to be lit on fire can have somewhat uneven expansion when heated due to moisture content of the brick and materials used in its creations. This is true even for fired bricks if the extra steps and standards used for kiln bricks are not used in their creation. This uneven expansion can cause the mortar to crumble as well as cause the bricks to crack. The mortar itself can also \"over dry\" and become crumbly on its own if it is not a mix intended for high heat or fires even without uneven expansion of the bricks which can cause enough structural weakness for the wall to collapse. You also have the fact that even houses that are structurally Brick will often have timber interior walls, timber flooring, and timber roofing. When those burn out, even if the exterior walls survive the roof and everything inside will collapse."
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e74ob6 | How do bullet classifications work? I’ve seen 5.56, .44 and 50 Caliber in video games but I have no idea what any of these numbers represent or how it works. | Engineering | explainlikeimfive | {
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".44 and .50 are the diameter of the bullet in inches - except .44 magnum is actually more like .42 inches, but it's still called .44 because it is based off of the .44 Special, which in turn was based off of the .44 Smith & Wesson American, which actually was .44 inches. 5.56 is the diameter of that bullet in mm. A 5.56x45 mm round is 5.56 mm in diameter, which is around .224 inches. Basically, they're usually either the diameter in inches, or the diameter in mm.",
"Oh boy... Chambering nomenclature is an absolute Charlie Foxtrot, even for people that nerd out over guns. They are basically all semi-arbitrary and half branding. About the only semi-consistent point is that the first number is the bullet diamete... unless it's the bore diameter... and the bore diameter might be measured groove-to-groove or land-to-land. Also, the power of the round is only loosely correlated to the bullet/bore diameter, as the amount of powder behind the bullet matters a lot more for power. That said, there are a few locally-consistant conventions that are used, such as by NATO. NATO chambering designation lists the bullet diameter in millimeters followed by the case length in millimeters, separated by an \"x\" (pronounced \"by\") For example: the NATO .30 caliber round is designated \"7.62x51mm\" compared to the Russian .30 caliber rounds which are designated by NATO as \"7.62x39mm\" (used in the AK-47) and \"7.62x54R\" (used in the PKM).",
"Generally, the caliber refers to the diameter of the bullet itself, either in mm (5.56, for example) or inches (.45). Now, the actual diameter can vary significantly from what the name states. And the exact same diameter, and often the exact same bullet, can be used in a variety of different kinds of ammunition; for example, many bullets used in .40S & W can also be used in 10mm. The only real easy hard rule is that there are no easy hard rules. Ammunition loading handbooks contain literally thousands of measurements, variations, and sub-types.",
"No one has mentioned shotgun gauges yet, and they're a little more complicated. The number represents how many lead spheres with a diameter equal to that of the gun bore make one US pound. Twelve lead balls with diameter equal to the bore of a 12 gauge make one pound. The only shotgun that does not fit this schema is the .410; it is measured in inches like many other small arms. It's really a bit bigger though because you can shoot a .44 Long Colt pistol round with it.",
"The number is the diameter of the bullet but is a mix of mm and inches. 5.56 is in mm and .44 and 50 that is 0.50 is in inches so 10.9mm and 12.7 mm But just the bullet diameter is just one factor. It says nothing about the length of the bullet of the size of the propellant changes that determine the speed/energy of the bullet. I used the specification with bullet diameter x length of the cartridge. And added the typical weight, speed, and energy of the bullet. The smallest common pistol/revolver calibre is .22 Long Rifle with the same diameter as the 5.56 that is the most common military assault rifle calibre in the west. The energy difference in the tow is a factor of 10x. So just the diameter of the bullet says nothing. There is two main categories for cartridges rifles and handguns. Rifles have long bullets with relative small diameter and a lot of propellant for a fast bullet. Handguns cartridges have a larger diameter and less propellant designed and speed. The reason for the difference is that you like a handgun to be physically smaller and light so you can handle it with one hand. For pistols, the magazine is in the handgrip. The other reason that you like less energy in a handgun because it is hard to handle high recoil without stock to your shoulder. Submachinguns uses handguns calibres even if you have a stock. & #x200B; Military assault rifles has in the west 5.56 mm or 7.62 mm bullet. Pistols most of the time have 9mm or larger bullets. & #x200B; * 5.56×45mm NATO (0.223 inches) an intermediate cartridge with a 4 g, 948 m/s, 1797 J * .44 Magnum (10.9×33mmR) a revolver cartridge with a 16 g, 360 m/s, 1005 J * .50 BMG (12.7×99mm NATO) heavy machinegun cartridge with a 42 g, 923 m/s, 18100 J So you can see that similar bullet diameter like .44 and .50 have an enormous difference in bullies energy with a factor of 18x. So 5.56 is a small light and fast bullet for military automatic rifles. .44 is a have and slow revolver bullet and 50 calibre is a very large fast bullet for heavy machineguns or in antimatter rifles, for computer games the would be a heavy sniper rifle, [An image]( URL_0 ) both .50 that is the largest and 5.56 that is the second from the right.",
"Well some are in millimeters some in inches. The 5.56 is 5.56mm .50 and .44 are inches. Then there's also the length of each but I won't go into that. Depending on who you ask 5.56mm might also be called .223 because it's .223in",
"[Previously asked, I answered. Cartridge nomenclature is kinda fun]( URL_0 )",
"And all of this gets really fun when you look at the muzzle velocities for a .22 long rifle and a .223. A .22LR travels at about 1200 feet per second while a .223 (the NATO 5.56x45 mentioned earlier) travels at over 3200 feet per second. A .22 won't always kill a small animal and a .223 is the most common round used in \"AR-15\" style guns. You can google search a side by side image of the 2 for a visual representation of the cartridgesizes, despite a .003\" difference in the diameter of th he bullet itself."
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e760n3 | Why passenger trains in the US are often delayed while passenger trains in Europe and Asia have much better on-time performance. | I’m sitting here in 30th St Station in Philadelphia and almost all the Amtrak trains are delayed. How can train networks in other countries run so efficiently and we can’t seem to get our act together here. | Engineering | explainlikeimfive | {
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"Outside of the Northeast Corridor (Washington DC to Boston), there are almost no rails dedicated primarily to passenger rail. Freight companies own most of the country's rail networks, and they don't always give Amtrak trains the highest priority.",
"There is only one passenger rail service in the US, and it owns very little track. Amtrak operates on tracks owned by freight companies, and so must give priority to freight trains using the tracks. Amtrak also receives very little funding compared to European rail systems, and US freight companies do only the bare minimum to maintain and upgrade their lines, which leads to delays and reroutings due to damage or degradation of track.",
"Passenger trains run on same tracks as freight, and the freight carriers own the tracks and prioritize their traffic.",
"About 60 years ago, jet travel replaced rail as the primary intercity passenger service in Canada and the United States. Not only was it a lot faster (due to the large distances involved), it ended up being cheaper too. Up to that point, most passenger rail services were operated by private companies. Jets made passenger service unprofitable, so the railroads divested it to focus strictly on freight. Bulk cargo still being more cost effective to ship overland versus by aircraft. When the railroads finally phased out their passenger service in the late 60's, government agencies, VIA Rail and Amtrak, purchased the rolling stock (passenger cars) and took over service on the most popular routes. They now owned the trains and stations, but the private railroads still owned the tracks, signalling systems, and other infrastructure. VIA and Amtrak simply leased the track from them. However, under that agreement, profitable freight traffic had to be given priority. Since that's ultimately what pays for the upkeep of the lines. If a freight train wants by, they have to wait, which causes delays. It's sort of like letting your neighbour borrow your truck any time they like, but only if you aren't using it, and only if they return it with a full tank of gas. Europe and Asia are a little different. For starters, major cities aren't as far apart. So airplanes don't have the same advantages they do in the Americas, where major cities have vast distances between them. You can fit all of Europe inside the continental United States or Canada. The other thing is that public railroads also invested heavily in building their own infrastructure as part of post-war spending programs. Which was done in Japan with their bullet trains. The Shinkansen have their own dedicated lines that no other train can use. Building new railroads though, especially ones that cover long distances, is incredibly expensive. Land has to be expropriated, varying levels of local and state/provincial bureaucracy have to be dealt with, etc. before even an inch of track is laid. It'd probably be cheaper and easier to go to the Moon again. Even private freight railroads rarely, if ever, do it anymore. Hence why most North American rail lines date back to the 19th century. Even if they do get built, there's no guarantee they'll make a return on the initial investment. VIA and Amtrak don't make money as is. There's no advantage to taking the train over flying, so very few people do. And due to the huge operating and maintenance costs involved, any new dedicated intercity passenger rail line would become a huge money pit pretty darn quickly. Which taxpayers won't tolerate. So leasing is really the only practical option. It's worth noting that even the Shinkansen, though successful in the long run, also faced a large amount of opposition due to the cost of its construction. But what about China? They're building a ton of new intercity passenger rail lines over long distances. Well China is run by an authoritarian regime ,and has a lot of wealth floating around. So they can just ram things through without concern for money or what taxpayers and landowners think. Nobody has property rights after all. So it's easier to get big infrastructure projects done. Plus few people can afford to fly or drive via private car, so trains are a more practical way to get from city to city."
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e7dxcd | How do single propeller planes counter the torque from the propeller. | I was playing kerbal space program last night and my single prop planes kept flipping over. I understand that having a second propeller spinning the opposite way can counteract this, but how do single propeller planes do this? | Engineering | explainlikeimfive | {
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"The only way to stop the plane veering up and to the left is actively steering against it. Modern single-prop aircraft have automatic systems to counteract this issue in a manner relative to the speed the propeller/plane is moving, so the pilot doesn’t have to correct it. It most often can be felt during changes in speed (i.e. during takeoff/landing), due to the larger difference between the speed of the propeller and the speed of the aircraft. This also means that in many light aircraft - particularly older fighter planes - it’s actually quicker and easier to turn left than it is to turn right. This is called a ‘rotary turn’.",
"One way is to offset the angle of the propeller shaft. As the propeller's torque rolls the plane to the left, the increased offset traction pulls the plane to the right. Or it can be left to the pilot to adjust, by trimming the ailerons and rudder depending on the throttle. The effect of propeller torque is usually small enough for a pilot to counter by feel and instinct without a problem. Other planes use other outputs of the engines. For instance, the engine's exhaust comes out of the engine enough to create some thrust, so you can adjust the locations of the exhaust to exert a force that counters the propeller's torque.",
"In WWII several RAF Spitfire pilots died when their squadrons ungraded to Griffon engines from the original Merlins. Great care was needed applying throttle to allow for the massive torque, and the new engines turned in the opposite direction. They simply forgot."
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e7eqmh | How does a battery store charge? | Engineering | explainlikeimfive | {
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"They decide if they accept cash, check, and credit. Then they ask you to pay for the battery you have chosen based on its size and brand. Source: worked at a battery store.",
"A battery stores charge using the materials it's made of. In your typical battery, one end uses zinc metal, and the other uses something called manganese dioxide. In between is a thick paste, usually something called potassium hydroxide. When you connect a battery to a circuit, the zinc metal reacts with the hydroxide and gives up electrons. These electrons flow into the circuit, then reach the other end of the battery, where the manganese dioxide reacts with the hydroxide and accepts them. A battery \"has charge\" as long as it has enough of each initial chemical to sustain the reactions.",
"Negatively charged electrons (-) really don't want to be together, but would much rather hang out with positively charged protons (+). Usually, they pair up one to one, and you'll have no net charge. In a battery, the electrons are separated from the protons and are crammed into the negative pole of the battery. The positive side has all the protons. Inside the battery, there isn't any way for the electrons to get back to the protons. The more of them you cram together, the less happy about it they become. Also, the more electrons you separate from the proton, the stronger their electromagnetic pull will become. This difference is called a **voltage**. A higher voltage means a greater difference in charge between the positive and negative side. When you put a battery inside an electrical appliance and turn it on, you create a complete circuit - a path for the electrons to get back to the protons. The electrons start flowing back towards the protons in the plus side of the battery - and electrons flowing is a **current**, which is passed through lots of circuits and components to make whatever electronic it's in to do its thing. Once all the electrons are back at the protons the battery is depleted of energy, i.e. it's dead. If it's a single use battery you recycle it. If it's rechargeable, you can reverse the process. Instead of allowing the electrons to flow and induce a current, you use a current (from the charger) to make the electrons go back to the negative side. Keep in mind that this is a **gross oversimplification**, but unfortunately electrochemistry is hard to explain at a simple level. It's quite a tricky subject.",
"Chemical potential energy. There's two chemicals in a battery that want to interact and discharge energy, but until you complete the circuit, that can't easily happen."
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e7fw9n | What makes a smartphone vibrate? | Engineering | explainlikeimfive | {
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"There is a very tiny electric motor inside that has a little weight attached to the output shaft which is off balance. When the motor spins it vibrates like having something off balance in your washing machine.",
"A tiny motor turning a deliberately off center and unbalanced weight. Thus makes the motor, and the phone it's mounted to, vibrate."
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e7idjb | If there are pipelines that can move oil thousands of miles, why can’t the same be done to move water thousands of miles to areas that experience frequent drought? | Engineering | explainlikeimfive | {
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"They do For example much of California's water comes from as far away as Colorado. The problem is much of California is basically a desert and we're trying to keep it a lush garden. That takes a lot of water to maintain indefinitely, which simply doesn't exist.",
"They can, when there is big money, like watering Los Angeles. However, in general oil is valuable and water is not. Water costs $0.001 per gallon in most cities. That's not raw water, but chlorinated drinking-quality water. Crude oil closed Friday at $1.31 per gallon.",
"Um, there *are*. For example, Los Angeles and Las Vegas rely heavily on water pipeline use. A key problem with water pipelines is when you deliver water via a pipeline, you're effectively taking away water from somewhere else, and when that \"somewhere else\" is also staring down the barrel of a drought, they're not too happy about having to give up their water to people who decided to make a home where they knew there wasn't any water in the first place.",
"Because there’s no financial gain for those that would be involved in making and maintaining said pipelines",
"We've been doing that for over 2000 years. [ URL_0 ]( URL_0 )",
"It’s worth adding that some places have rules about this because if you move water thousands of miles, you take it out of the natural water cycle of the local area and eventually there will be none left for the locals. The Great Lakes has very strict rules about this, so much so that in certain states, people living just a few miles from the lakes cannot pipe the water from them, as their water discharge heads to the Mississippi and not back into the Great Lakes.",
"It could be, as is, done. But it's not a complete solution to the problem. The issue is more our demand for fresh, usable water. The earth is about 70% water, but most of that is locked up in the ocean, in ice caps, in the ground and in the atmosphere, so it can't be used for watering your plants or for filling your water bottle up with. About 0.3% of water is usable for our needs, and that water has to be processed and transported. This also uses a lot of energy. Time, money and water availability puts a limitation on our supply of water, compared to our incredibly high demands."
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e7koc4 | Why are washing machines usually smaller than dryers? (Have way less space for clothes in them) | Engineering | explainlikeimfive | {
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"Dryers need to tumble the clothes apart from each other more. Washing machines can have clothes very close to each other. They rub against each their helping to clean each other with friction. Dryers need to get the clothes more separated, to get the heat in. If a pile of wet clothes had heat blowing on them but they stayed close to each other, they wouldn’t dry as quickly. So while dryers may look like they can take more clothes, they’re at their most effective with a load that matches the size of the washing machine. This is true with blankets and comforters as well. Allowing the blanket to get a loose tumble is what dries it. Not very scientific sounding, but it’s the basic answer. I’m sure someone smarter could explain heat dispersion, and give us a more technical answer, but this is the gist.",
"Appliance tech here: Dryers have very low RPMs (rotation per minute) compared to washers, about 50-60 RPM. This is because dryers use heat, ventilation (unless it's a condenser dryer), and the tumbling action to dry the clothes. If it spun faster the clothes wouldn't tumble and would instead get flattened along the drum due to centrifugal force. A top load washer peaks at about 800 RPM and a front load washer is anywhere from 1000-1200 RPM. This is because unlike dryers washers rely on this high speed to create enough centrifugal force to remove the water. They aren't trying to remove all the water just most of it. Washers fill with water which is very heavy compared to the wet clothes you put in the dryer. What this means is that washers are much higher stress and energy machines compared to dryers. This affects the drum design. In a dryer there's a single drum. It sits on rollers (they 100% look like rollerblade wheels), felt and plastic guides, and in some models a bearing at the rear. Washers, both front and top load, use a double drum design. The inner drum is what rotates and where you put your clothes. The outer drum doesn't rotate and is suspended by dampers and shocks. This suspension system is absolutely critical to absorb the tremendous energy and vibration that comes with rotating a heavy wet load at high RPM. In fact this is why forgetting to remove the shipping bolts can be lethal to washers. When washers are delivered they don't want the drum banging around during transport. Both top and front load washers have shipping bolts to secure the drums. When customers forget to remove them and run the washer it will shake so violently it will start walking along the floor. This happens way more often than you think - despite warning labels, brightly coloured shipping bolts with tags on them, lots of folks don't read the manual and take them out. This can crack or otherwise damage the drums. It's a very expensive ($500-$800 Canadian) to fix and will take 2 technicians 2-3 hours to repair. To sum up: washers have less available working internal volume compared to dryers due to the double versus single drum. The double drum is necessary to allow the outer drum to be suspended to absorb the higher stress and energy associated with washing versus drying.",
"Dryers tumble clothing to allow the hot air to move through and around them and doing this requires more space for the same amount of clothing. As such a washing machine paired with a dryer set to do the same sized loads will be smaller than the dryer."
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e7o60k | how can phone screens tell the difference between your fingerprint and something like a stick? | Engineering | explainlikeimfive | {
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"In a word, capacitance. The human body is a significant amount water, and that water has a specific range that is measurable by the phone. The phone puts a very small electrical charge on the screen and when it's disrupted by your finger, the phone \"knows\" that it fits the capacitance range, and assumes it's an input."
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e7s3s8 | Why do cinemas use projectors on a huge wall instead of a huge screen? | Engineering | explainlikeimfive | {
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"To make a huge image, it's much cheaper to get a powerful projector than to build a high-resolution video screen that big.",
"Price of a screen goes up exponencially the bigger it is. Its WAY cheaper to buy projector than a big ass screen.",
"Besides cost, a projector has a scalable size, so a theater with multiple cineplexes can use one type of projector to display different distances and different sizes. It would be impossible for a company to produce enough size options for all of the different size theaters out there."
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e7t4xa | How do technicians fix wires or systems that are buried inside walls? | Engineering | explainlikeimfive | {
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"Ultimately we are either able to fish a new wire down the wall, or we have to cut a big whole in the wall. If everything os done right, there are no wire joints behind a wall. All joints are required to be in a junction box, which is in an accessible location. All devices mounted on walls or ceilings can be taken apart so their workings are accessible. Did that answer your question?",
"They’re almost never “buried” inside walls. There are access panels which are sometimes hidden. In the rare case that it is inside the wall, they would cut a hole in the wall, do the work, then patch the hole."
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e7vvrb | How do they make dams watertight if the cement is underwater and wet? | Engineering | explainlikeimfive | {
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"Dams are typically built with roller compacted concrete. While it is porous at a technical level and not \"water tight\", it's not going to result in water seeping through it any more (significantly less in reality) than natural environment materials that do things like hold water into lakes. It's easy to hear things like \"concrete isn't water tight\" that come out of things like residential construction where you're worried about warping of your fine hardwood floors. That concern for a 6\" concrete pad just doesn't play out for the needs of damns, the type of concrete used and their size.",
"The setting of cement is a chemical reaction, it's not just drying out. In fact, if you are laying bricks or cement on a hot day, you put covering over the wet cement so it sets properly. If it dries it doesn't form a hard layer, but will break up easily. The most common type of cement powder, Portland Cement, made from limestone, clay and gypsum will set underwater.",
"If you want to make sure your concrete cures properly you need to leave it underwater. If concrete dries it will cease to harden until it gets wet again. There is a chemical reaction with the water which makes it harden, no water no harden (other than absorbing water vapour from the atmosphere. Edit- adding flue dust or fly ash which have very small particles which fill in the spaces around the aggregate makes it more waterproof.",
"Concrete is water tight once it has cured. There are also special types of concrete which can be poured and cured underwater. Generally instead of using the expensive underwater concrete, they divert the river and build the dam dry, then redirect the river into the new watertight dam.",
"You make the place where the dam is going to go unwet by building a temporary damn with wood or lots of dirt around it and pumping out the water (or diverting the water from where the dam will go). Then, after the dam has set, you take away the temporary dam."
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e7wwzg | How do Cuban heels in riding boots help you stay in the stirrup? | Engineering | explainlikeimfive | {
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"It's the shape and length of the Cuban that makes it good for riding. They should be at least 2\" tall and strong pitch (the slant on the back side of the heel itself). The nook of that slant is designed very specifically for hooking into a stirrup, and it does it better than most other types of heels. Not only does angled heel settle into a stirrup better than a straight heel, it also causes less friction against the horse. The slant is a lot gentler on the horse, too, because it doesn't have a hard edge that can jab into the creature when you're moving faster than a walk. You don't absolutely need something specifically called \"Cuban\", standard \"Riding boots\" have the exact same heel. They're a bit tougher to walk in, but they're better for riding. But as a ranch hand/wrangler, you're going to be walking a lot, too. You'll probably want to get a fairly standard \"Fowler with pitch\" or \"Cowboy\" boot, with 1 1/2\" to 2\" heel and a gentler slant than the Cuban, but noticeably slanted."
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e7yujr | . Why are large passenger/cargo aircraft designed with up swept low mounted wings and large military cargo planes designed with down swept high mounted wings? I tried to research this myself but there was alot of science words... Dihedral, anhedral, occilations, the dihedral effect. | Engineering | explainlikeimfive | {
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"Military cargo aircraft use high mounted wings because it allows them to use unprepared or hastily prepared runways. Keeping the engines up high helps with not sucking in a bunch of dirt and rocks. Passenger aircraft operate pretty much exclusively from well maintain airports, so that isn't a big deal for them. Upswept wings make a plane more stable in a roll. The aerodynamics work out so the plane's natural tendency is to want to roll back to wings-level. This makes the plane easier to fly, and generally more comfortable, but limits the rate at which it can roll. High-wing large transports usually already have quite a lot of roll stability, so downswept wings are used to give them slightly more responsive handling, which helps when landing in adverse conditions.",
"Military cargo planes are desired to be very close to the ground for easy loading and unloading of extremely heavy cargo. So the whole plane is reconfigured to avoid banging the wings and engines into the ground. also they are used sometimes on bad quality runways which may contain dirt and gravel, so again there is a desire to pull the engines up away from debris.",
"Military transports have a high-mounted wing in order to get the bottom of the fuselage as close to the ground as possible, so you can drive vehicles into them via a built-in ramp. It also reduces the obstacle clearance requirements on crudely-built forward-area runways. The higher the wing is on the fuselage, the more stable the aircraft is in the yaw and roll axes. Airliners have dihedral (upswept wings) to take advantage of this. Military transports, with their high-mounted wings, would be *too* stable with dihedral -- so they have anhedral (downswept wings) to offset it. There is one airliner with high, anhedral wings, the BAe146. Many of its passengers can't see the scenery because the engines are in the way -- worse, its only emergency exits are at the ends, because if you tried to abandon it amidships you'd run into a hot engine.",
"Airliners prefer to have low mounted wings and low mounted engines because lower engines are much easier to reach. In fact, a big selling point is often that the low engines don't need much complex equipment to reach. Just an elevated platform and you can basically strip the thing down if you have to. Low mounted wings are also much easier to land as the ground effect is much more pronounced, but a disadvantage is not being able to have a lot of clearance between the wings and the ground on the ground. So you can't have lots of people darting around under the plane the same way you could with a military cargo plane. & #x200B; Speaking of cargo, cargo is a huge factor that goes into how you build a plane. Every plane wants to carry as much cargo and as efficiently as possible. For commercial planes like the 747, they are a mix of carrying passengers in the crew compartments and luggage, mail, or other goods in cargo areas. & #x200B; For a military transport, you basically have to carry extremes, either a huge amount of passengers like paratroopers or no passengers and only tanks or vehicles, so 1 giant cargo hold is better than having the plane cut in half for specific loads. & #x200B; Also you want to be able to access said cargo. You could use a lift like a commercial plane, but having high mounted wings means the fuselage can be MUCH closer to the ground. So you can literally just drive off the plane. For a 747 or A380, you could carry vehicles in it, but you would almost certainly need a crane to get it out, a C-150 could just open up and you could drive the car off.",
"About \"dihedral\" and \"anhedral\": Those words just refer to the wing design shape you're talking about. Wings bent down is anhedral and wings bent up is dihedral. Dihedral is good because it improves the plane's stability while flying while anhedral makes it worse. We like our civilian passenger planes nice and safe and stable so we design them with dihedral. Military planes, like the c-5 and c-17, use anhedral not because they are made to be unstable, but actually because the wings create so much lift to make such a heavily loaded plane fly that they actually bend upward and have a slight dihedral while in flight",
"Can someone eli5 the question? My stupid ass knows 0 of those airplane terms.",
"One thing nobody else has mentioned is the durability of the aircraft when making a crash landing. The body of a plane is pretty fragile and tears apart when skidding across the ground or water. When the B-24 (high wing) crash landed, it usually cheese-gratered the crew as it came to a stop. When the B-17 (low wing) crash landed, the reinforcements that held the body to the wings is under the plane, protecting the crew/plane a lot better and often. My grandfather flew bombers in WW2 and he said landing a damaged B-24 was nearly a suicide mission but they landed damaged B-17s all the time with a lot better survivor rates because the underbody of the plane would take the brunt of the scraping or ocean waves. On the question of it just having to do with damaged landing gear - Your landing gear can be working fine, but if you have to put your bomber down in a field or brush, landing gear is going to snap off instantly and didn't help whatsoever anyway. One factor that makes commercial airliners safer is to have wings under the body. That way if the landing gear fails or they have to ditch right after takeoff, they can slide a lot longer before the thing takes everybody's legs off.",
"They are built with and anhedral instead of a dihedral. They are built up high for engine clearance, and if they are up high like that a dihedral wouldn't work, hence the anhedral. Take a fw190 vs an antonov. Low wing dihedral, high wing anhedral. Dihedral and anhedral both add roll stability, but in different ways. This video gives a way better look into than I can give in a short text. URL_0",
"While stability and cargo loading are a significant factor in the design of military cargo transport aircraft, there are additional factors at play for passenger operations. Noise is a significant factor for passenger operations. If you’ve ever ridden on a high wing aircraft, you would immediately notice the increased engine and aerodynamic noise present in the cabin. The BAe-146 is likely the most successful high-wing passenger aircraft of all time. The noise during flap extension and retraction is startling, if you’re not used to it. Boxes don’t seem to notice the noise. Passengers don’t like it at all. Another factor at play in cargo operation is the ability to use ground effect for added lift in short/unimproved takeoff and landing. Basically, this is extra lift developed by the wing when the aircraft is close to the ground. Think of a layer of air smashed between the ground and wing. The larger space between the ground and wing in a high-wing design takes better advantage of this aerodynamic effect. Lastly, there are high speed aerodynamic forces that tend to favor a low wing design. Most cargo aircraft are relatively slow compared to modern passenger airliners. TLDR; High-Wing cargo aircraft are optimized for heavy lift capability, while passenger airliners are optimized for comfort and efficiency.",
"All that being said, most commercial cargo aircraft are re-purposed passenger planes, or were born from them. Military cargo planes are designed with purpose alone.",
"Anhedral is angling downwards from the centre: /\\\\, while dihedral is angling upwards from the centre: \\\\/.",
"Raising the wings raises the engines and lowers the floor of the aircraft, allowing for a ramp to drive cargo on and off.",
"Not sure if this is allowed but [this video]( URL_0 ) explains it very well. TL;DR its complicated and its based on seemingly arbitrary conditions sometimes"
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e7zs5h | how do faucets not explode from the water pressure? | Engineering | explainlikeimfive | {
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"Once you close a faucet, that's the pressure it will remain. Your water system has a certain pressure that is maintained. Closing the faucet doesn't make the pressure continue to build up to infinity. Think of your blood pressure. The pressure is generated by your heart pumping and your vessels squeezing. You could temporarily decrease the pressure by giving yourself a big cut and bleeding. Once you stop the bleeding, your pressure doesn't just rise to infinity.",
"Fluid pressure in a closed system like the pipes between the water supply and your closed faucet is not cumulative. That is to say it doesn't build up and become greater over time. The water supply pump can only push out the water to a certain pressure level that it's capable of. Once the pipe is packed full of enough water, the pump just doesn't have enough power to put more water into the pipe. At that point the system reaches an equilibrium and the water stops going into the pipe. Then the whole system just sits there with no water going into the pipe and the pressure stays constant at that level until you open the faucet. The water supply and the faucet valve are designed so that the faucet valve can withstand this constant, un-changing pressure level pretty much forever."
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e857te | How are dams built? How do they get the water behind the dam like that? | Engineering | explainlikeimfive | {
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"You'll have to change your perspective a little bit; dams are built over rivers, there is no large body of water at all at this point. When completed, the dam blocks the river, causing the area upstream to flood and create a lake, but this takes a very long time. The Hoover dam, built across the Colorado River in 1936, blocked all the water from flowing for six whole years, creating Lake Mead. This lake covers nearly 250 square miles, and simply didn't exist until the dam was completed.",
"Usually a temporary cofferdam and diversion channel are built to direct water away from the dam site. Then the dam is built, and when it is completed the cofferdam is removed and water is allowed to fill up the reservoir."
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e86odf | How can micro SD cards range from 1 gig to 1tb while being the exact same size? | It feels like only a few years ago when the biggest micro SD card you could get was 64gb how do they keep fitting more and more into the same size? Is there a theoretical limit? | Engineering | explainlikeimfive | {
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"When you're making a chip, you etch transistors into the silicon. If you're clever, you can develop ways to etch smaller and smaller transistors in the same area (this is very difficult and requires new, very expensive equipment, and people still want to get the maximum money out of their old kit so will continue to make and sell the older technology for some time). That means the max capacity of the cards can increase over time in the same area of chip. The other factor is that when you're etching a chip, a certain amount of the etch will fail. That's fine and expected, so they design the chips in a modular way so if there is a fault in one module, the rest of the chip still works, it's just got a lower capacity than a fully working one. So that's two ways to get lower capacity identically sized chips - the final way is that the vendor intentionally turns off sections of the chip because once you've invested in the very expensive machinery to make them, the chips themselves are very cheap to make. They'd much rather sell 100m of them at varying prices than sell 100k of the most expensive ones (how many people do you know with 1TB microsd cards?).",
"The size of microsd cards is set by human standards, not technological standards. You can make a 64gb chip much smaller these days, but you wouldn't be able to handle it. You'd lose it, or be unable to insert it into the slot.",
"Ok easiest way to explain it... Those micro SD cards have a chip on them. There is only a certain amount of size to work with. The difference is that in the smaller capacity cards(256mb,1gb, etcetera) the components that make it are able to be larger and spread out, but still use the same amount of space. In the higher cards all those parts inside that one chip have to be alot smaller, and even more compact so that the 1tb of components fits inside roughly the same size chip on the card. Tldr the chip that is on them is more compact on the inside of the bigger capacity cards."
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e8ei6a | Exactly how do bullet proof vests work? | Engineering | explainlikeimfive | {
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"They help to redistribute the kinetic energy that the bullet uses to penetrate so it essentially takes all the momentum and energy from the bullet and spreads it across the vest so that the bullet just flattens and knocks you down",
"Bulletproof breasts are designed to stop projectiles by dispersing the energy accross its whole surface, preventing it from penetrating too far. In addition they have ablative materials that absorb energy by being destroyed. It's Important to note that being shot in a vest isn't painless. It will likely floor you and will often break a rib or two. It will however save you from death.",
"Bullets are small and moving very fast. However, they don't hit that physically hard - at least smaller ones. The momentum of a smaller bullet may be comparable to a thrown baseball. If something could spread the impact of a bullet out and reduce its energy, then the momentum will be much less of a problem. This is either done with thick metal/ceramic plates, or kevlar. The plates just absorb the impact with the awesome strength of steel. They reduce the bullet's energy by distributing its momentum through the large and heavy plate. They are, however, quite heavy. Kevlar, meanwhile, essentially transmits all of that momentum directly to your body but over a much larger area and it still reduces the energy quite a bit by stretching and deforming. As such, it can be extremely painful since the bullet *will* continue moving into your body a tad before it is fully caught.",
"the main goal of a bullet resistant vest is making sure the bullet doesnt achieve penetration it does this by stacking layers of a material that can \" catch\" the bullet(basically as somethnig strong enough and light enough ot be woven) and hold it there while the kinetic force is dsitributed in a wider area, instead of the focused line it would normally follow. for most vests as long as the bullet doesnt pass thru they are good enough, ubut this doesnt mean youll get out unscathed, broken ribs and bruising are very common, but th the lesser of 2 evils."
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e8tknh | Do submarines have anchors? | Engineering | explainlikeimfive | {
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"Yes, they do. But they rarely use them. Source: 4.5 years on board a submarine. NEVER used the anchor."
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e98v2h | how do engineers make memory cards/HDD/SSD have bigger storage space every year yet retain it's size/get smaller? | Engineering | explainlikeimfive | {
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"The processes, mostly semiconductor fabrication processes, strive to make smaller logic units every year. As a result, more of them will fit into a consumer part at an affordable yield rate. Today, they are probably making test parts 4X the capacity of the parts they are selling. Those parts only work a small fraction of the time, so they aren't something that customers are willing to pay for, today. The engineers work to improve process yield, in hopes that in the future the yield will come up enough that the part can be sold for a profit.",
"To reference a [previous ELI5]( URL_0 ) > Let's talk about regular hard drives first. Imagine a regular hard drive is just a piece of paper, a pen, and a magnifying glass. Lets say we have some information we want to save (like a word document or video). A regular hard drive takes all of the data that Microsoft Word is asking to save, and writes in on the paper with a pen. It has actual moving parts, and the pen moves along the paper as it writes. Later on, when Microsoft Word wants to get to that data, it takes the magnifying glass and moves along the paper until it finds what it needs. Again, moving parts. We have gotten pretty good at getting the pen and the magnifying glass to work reliably, and they read/write really fast compared to ancient computer times. We have also gotten really good at writing short-hand, so it takes less paper to save the same amount of information. Now let's talk about solid state drives. Solid state drives don't have moving parts, so no pen, and no magnifying glass. Instead, they have electric circuits. It's kinda hard to explain for a 5 year old, but basically these circuits are designed to work like paper, meaning we can store information on these circuits. The cool part about these circuits, is instead of a pen being used to put information on them, we use electricity instead. Electricity travels super duper fast, so instead of moving a clunky and slow pen, we just put an electric current on the circuit, and if we use the correct current we store the correct information. This means that we can access that information very quickly, because instead of the magnifying glass going to page 10, then to page 130, then to page 140592, we send electric currents and they can go to page 10, 130 and 140592 much faster than the pen can move (almost instantly for practical purposes). So that should help with some context. As for retaining the size, this is because the circuits which make up the SSD are becoming smaller. If you can fit a smaller circuit in the same space - you'll be able to store more information."
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e9fbkg | Why aren't kitchens fitted with air conditioning units to cool down the staff from the heat | Engineering | explainlikeimfive | {
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"Cold air makes hot food cold faster. -chef of 20 years -owner of 3 restaurants -always hot",
"Because kitchens have constantly running exhaust fans, cooling the air would do very little — the cool air would be discarded right away. The real problem is the *radiant* heat, the infrared coming off the hot cooking surfaces, and air conditioning doesn't block that."
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e9mel2 | Could we use thermopiles to efficiently reuse heat generated from computer hardware and cool components down? If not, why? | Engineering | explainlikeimfive | {
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"Computers need to be kept cool. If you put anything between the heatsink and the chip, it is going to make it harder for the heat to get to the heatsink and escape, making the CPU hotter. And a hotter CPU uses more power, is less efficient. And thermopiles are very inefficient, so you are playing a losing game. But sometimes people do use thermopiles to cool electronics. When they need to be cool, but don't use much power and don't make much heat, a thermopile or peltier device can be used to cool it down. But if it makes a lot of heat, the amount of power that thermopile needs to move the heat away gets too high."
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e9s2jb | in avionics, what causes spiral instability? | Engineering | explainlikeimfive | {
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"Spiral instability isn't caused by avionics. It's caused by the aerodynamics of the aircraft. Recall back to how an aircraft wing generates lift. If I pitch the wing up at an angle relative to the airflow, I create a lift force perpendicular to the airflow. Now instead of thinking about the wing, picture the aircraft from a top down view, and think of the aircraft fuselage as your lifting surface. The effect is the same. If the aircraft \"sideslips\", a force is created that pushes the aircraft in the direction perpendicular to the airflow. This force is uncreatively called \"side-force\". If the center of pressure of side force is closer to the nose than your center of gravity (the point where the aircraft will rotate around), then an increase in side force will also create a torque that will increase the slipslip angle, which will further increase the side slip force, which will increase the sideslip angle, which will increase the slideslip force, etc. This makes the aircraft unstable. If the center of pressure is located behind the center of gravity, the side force will create a torque that restores the rotation back in line with the airflow. This makes the aircraft stable. The fuselage of the aircraft will tend to push the center of pressure of side force torwards towards the nose, so a vertical tail is placed to make the plane stable. The tail acts like a wing to create a restoring torque whenever the aircraft sideslips. If you have an aircraft that's unstable in the yaw axis (like a B2 Spirit Bomber, which does not have a tail ), the aircraft cannot fly without constant adjustments being made to some sort of yaw control system (differential thrust and wing flaps in the B2 case). Since it's difficult for a pilot to do this while still having his/her mental capacity freed up to do more important things associated with flying the plane, this task is given over to some sort of automatic flight system."
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e9sa69 | Why are back wheel brakes on cars on the front of the brake and front wheel brakes are on the back of the brake? | Engineering | explainlikeimfive | {
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"They're actually usually not that way. It's close to 50/50 with a slight preference for the opposite. 53% of passenger cars have their rear brake on the rear of the rear wheel, and only 47% have the rear brake on the front of the rear wheel. 51% of cars have the front brake on the front of the front wheel, and 49% have it on the rear of the front wheel. Engineering Explained did a video on this. [ URL_0 ]( URL_0 ) In short, it depends on a lot of things. Adequate cooling of the brakes, purpose of the vehicle, cost, and other design factors like the suspension system."
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e9uayi | Why some electronics, like old TVs, start working again after they're hit. | Engineering | explainlikeimfive | {
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"Percussive maintenance causes all of the parts to jiggle around. Many problems arise when a connection somewhere is shoddy and has slid out of place, but the jiggling can knock this connection back into place."
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e9utut | why are bathtubs always slightly smaller than an adult? | basic common bathtubs are always specifically 5 1/2 feet long and 2 feet wide (ish), but wouldn't 6 feet by 3 feet make more sense, since humans are taller than back when bathtubs were made? | Engineering | explainlikeimfive | {
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"A standard alcove style bathtub (the one surrounded by 3 sides, possibly it AND the alcove are one big piece?) is more typically 60\" long, or 5 ft. Which, for most people, is still \"long enough\". Remember, bathtub sizes aren't designed for people to be able to lie flat out in. They're designed to be long enough so your butt and legs are flat. While humans are getting taller, over half of your body height (typically) is in your hips downard, say 60%. And 5\" less the two inches of lip around the outside is still enough for anyone who isn't 7\" tall or has freakishly outsized legs to sit comfortably. To submerge the rest of you on the other hand... Anyways - the reason why so many bathtubs (and sinks and toilets for that matter) fit a standardized profile of sizes is because they're hard to change. If you go and get a larger sofa, who cares. You don't have to renovate your entire living room, maybe just move some other stuff around. If you go an get a bitter bathtub or a toilet or sink... you're doing a who renovation on your bathtub and most likely some walls are moving. So to allow homeowners to replace or change fixtures without having to reno the entire bathroom, vendors stick to similar sizes and conventions. I feel your pain tho. I'm 6' 2\" with most of that in long legs. I can have a nice relaxing bath submerged with my legs folded up sticking up and out. If I want to wash my legs the rest of me is getting cold.",
"1) You are not suppose to be able to lay down in a bathtub. They are designed for the average person to sit in them at an angle with their head and shoulders out of the water. 2) Bathrooms are designed to be as small as possible and still fit all the needed things into them unless you specifically spend the money to make a larger bathroom. As such once the standard size of tub was established that is the size a bathroom becomes. 3) In the US at least most people prefer showers so there is not a lot of pressure to change the standard size of a bathtub.",
"Because basic/common usually means cheap. People buying cheap tubs probably have cheap (ie, small) bathrooms."
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eadjwh | Why do school buses have the "overhang" on the back? | School buses seem to cantilever past the rear axis a lot more than other "trucks" and "buses" of similar size. Is it that the body extends past the rear axis a lot more, or that the space between the two axis is shorter than other buses and trucks, and why? | Engineering | explainlikeimfive | {
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"Shorter turning radius, to give more maneuverability in neighborhoods and school parking lots/dropoff zones. The drivers are very experienced with the vehicle and the specific route traveled while moving at low speed, this generally prevents the situation from becoming as unsafe as it would be in general for a truck.",
"In addition to what others have mentioned, I'll also point out that city buses tend to have the front wheels somewhere behind the driver. School buses tend to have wheels in front of the driver. This also increases maneuverability and safety.",
"Increases maneuverability. The longer the wheelbase is, the longer the turning circle is, and these things are designed to operate in residential neighbourhoods, not big open city streets like a normal bus. The overhang is the solution to the problem."
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eag5bs | how do usb plugs built in to outlets work with phones and other devices that use usb? Don’t you need to convert AC to DC? | Isn’t the reason we use those cube power plugs to plug phone chargers in because they change from the ac of the wall to dc that our devices use. So how do USB ports built in to the outlet and powered by ac work? [Example]( URL_0 ) | Engineering | explainlikeimfive | {
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"There is either a converter built into the wall before the usb. So it goes wires > converter > USB. Or the cube is used because the normal outlet uses the two prongs and not USB.",
"Yes you need a rectifier. They are so small these days, they are build in a small board the size of a dime."
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eak8wr | How do cable lines on telephone poles transmit and receive data along thousands of houses and not get interference? | Engineering | explainlikeimfive | {
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"The answer is multiplexing. [There are many ways to do it.]( URL_0 ) In really simple terms, you can put multiple individual 'data streams' into the same signal by various means. You can give each data stream its own frequency or its own time slice on the channel etc and then reassemble them back into the individual streams on the receiving end. A really simple eli5 example of multiplexing over fiber would be to give a different colour laser to each stream and shoot them down the fiber. The receiver could then use colour filters to single out the individual colours again to recover each stream.",
"In metro areas data is transmitted mainly via one of two different cable types: Fiber Optic and Coax. Get back to these in second. Interference in data transmissions come from Radio Frequency (RF). The biggest source of RF noise that causes inference is power or electricity. One of the easiest ways and common to cut down on interference is to keep power lines away from data transmission lines. This is why if there are power poles in an area then the data lines are buried. Or the other way around if there are telephones poles then the power lines are buried. However keeping power lines away from data lines is not always possible. So that is where the two different cable types come into play and they treat interference completely differently. Coax is older technology and has been around for awhile. This is the same cable type that brought TV and Cable to the home since the 1960’s. Coax addresses interference basically through a ton of shielding wrapped around the central core cable. If you ever cut into a coax cable. There is a central copper wire surrounded by thick plastic and then a metal jacket and then more plastic. It is only the central copper wire that carries data. The plastic and metal surrounding the copper wire protect the copper wire. There are several grades of Coax some with more metal and plastic protection that limit interference even more. Coax is cheap and easy to produce and the transmission of tried and technology. Fiber is newer technology and is based on the transmission of light (lasers). Great thing about Fiber is that the light is virtually immune to RF interference because light is different then radio frequency. Power lines literally do not change the direction of light therefore you can for the most part ignore interference when it comes to fiber lines. So why not do everything over fiber? Well for the most part that is the direction data transmission is going. Fiber used to be very expensive both in the cabling and the equipment needed to use fiber. It has only been in the last decade or so that fiber has become cheap enough to be used everywhere. Coax has been around for a long time and there is a lot of it. It will take time to replace the Coax with Fiber. This still may not happen completely because Coax technology is still being improved. This plays into the getting fiber to the home or getting cable to the home. Probably still way more then an ELI5, but what I could come up with. RF is hard to explain. Think of it as static on a radio station. If there is too much static then you can’t hear the music. Electricity is the main source of this static when it comes to data transmission.",
"I guess it depends on what sort of setup you are talking about. I am a telecommunications engineer in the UK. How things are fed here is you get dial tone from the exchange in a pair of wires that are twisted together. The twists help resist any interference from other circuits. These cables generally go to a street cabinet which, again generally speaking, will be close to your house. At the green cabinet there is a DSLAM which is a box that had a fibre connection in it that your phone line runs through fibre ports which then when it comes out it has your dial tone and broadband service on it. This is then on a pair of wires to your house via different connections. In your house you should have a micro filter which is really a splitter that splits the different frequencies the one you can hear for the phone and one that's beyond your hearing range for broadband. I have worked on lines that have a lot of cable above ground on poles and when using my test phone I can hear the radio on the line. But this can be filtered out by phone sockets. TLDR. Basically from the exchange you have one pair of wires all they way to your house. Having them twisted makes a big difference in reducing any interference.",
"We are talking about billions of possible frequencies. Think of it like this, you have a bag of sand. Only one size grain is meant for you though. So you have two sifters, one that lets through all grains all grains smaller than yours, one that holds back all grains bigger. So you pour the sand through the first sifter, and boom, no grains smaller than yours get through. You pour the leftover contents through the other sifter, and only the ones meant for you get through. Boom. Out of billions of grains, you get the ones meant for you, no matter how mixed they were before. Edit, since I apparently wasn't clear enough. The information is split into different frequencies. Each frequency being the grains of sand. They can be mixed together, yet still singled back out through bandpass filtration, aka, the holes in the sieve here.",
"The interference part of your question. Edit: Actually a different side of it to consider. The other answers already cover the signals interfering with each other. There is a lot of interference. Cracks in cable, bad connectors, faulty hardware and other issues can all lead to signal egress and ingress that can lead to interference with external RF signals from leakage and internal interference from outside sources getting in. These issues increase the amount of signal noise in the system, which essentially makes the signal dirty by reducing the amount of signal above the noise floor (SNR). It is maintained by technicians in the field and an office crew that monitors the plant for those and other issues. The long range work is done almost entirely on fiber-optic cable, but that still requires a lot of work. Fiber splicing is hard work that requires a clean room to prevent dust and other debris from getting inside of the splice and blocking or (even slightly) redirecting the light. With a coax network, every piece of cable, connector, splitter, directional coupler, amplifier, mini-bridger, and literally any other piece of hardware can cause interference. Even electrical issues in homes can cause problems. I can't tell you how many intermittent area outages I've seen that were caused by people using old electronics that were causing interference. Everything has to be perfect, because there is just so much on these networks. Basically, it's done with a lot of work. A lot. The other answers regarding multiplexing and the like should explain the parts that I would have to Google.",
"It's not a matter of not having interference, it's a matter of keeping the level of interference low enough that the signal can be recovered at the other end. A more technical term would be \"Signal to Noise Ratio\" SNR. Here are a few techniques you can use to work around noise: 1. **shielding**. co-ax cables and shielded cables use a foil or mesh layer surrounding the signal wire. Outside electromagnetic interference is absorbed by the shield and never reaches the signal wires on the inside. It's the same principle as a *Faraday Cage*, just extended over the whole length of a wire. Cable TV typically comes over a co-ax wire. 2. **twisted pairs**. Take two wires and twist them together, so that any electro-magnetic interference affects both wires equally. Send your signal down one wire. At the receiver, you subtract the value of the \"dummy\" wire from the signal wire, giving you a clean signal again. Telephone and ethernet cables use twisted pairs (and wires for very long distances also have shielding around the twisted pairs). 3. **repeating**. After fixed distances, receive the signal into a device, and re-transmit the signal again with more power and no noise. Since SNR is a function of distance in the wire, keeping your wires short and repeating the signal can help avoid problems. 4. **modulation**. There are three basic modulation schemes you can use to transmit a signal over a wire: amplitude, frequence and phase. The first two are used by AM and FM radio, respectively. AM can be susceptible to noise while FM is more resistant (which is part of the reason why music stations tend to use FM while talk stations tend to use AM, and why AM radio quality decreased gradually with distance from the antenna while FM tends to either be perfect or static with nothing in between). Fiber optic cables don't have to worry so much about electromagnetic interference. Glass fibers have multiple layers which reflect light back into the center of the fiber, and then are surrounded by shielding to keep external light out. You can get longer distances with fiber optics than you can with most metal wires, but you still need repeaters to keep the light intensity high.",
"Eli5 answer: There is interference. But the content can be transformed into a format that is easier to send. Additionally the sent signal is processed to minimize the impact of the interference.",
"They do get interference. Look up ingress and egress for cable. The FCC is very strict about this and signal leaks are almost immediately taken care of",
"They can and do. Especially with the old analog lines. Now there is a lot more digital lines. Over the digital, the interference is ignored. But over analog some times you can hear someone else's convo. Also, a strong enough radio signal can go over the phone line and be heard. For instance, a ham operator may be heard in a near by home over the phone when transmitting.",
"They do! It’s an annoying problem. The two types of lines you’re probably thinking of are twisted pair telephone lines (for DSL) and coaxial cable TV (DOCSIS/cable). The first works around interference with some basic arithmetic by forming what’s called a Balanced Pair. Lets say you want to send the number 3 down the line, but there’s interference on the way that makes it look like 4. The solution is to send 3 on one wire and -3 on the other wire. When the signal arrives to you, the interference is still 1, but it’s 1 on both wires, so the signal you see is 4 and -2. Invert -2 into 2 and take the average (4+2 / 2) and you get 3 again! There’s a little more to it but this form of interference rejection is commonly used, it’s the reason a good quality microphone has 3 pins instead of 2. On coaxial cable there’s an inside part that is basically a radio antenna. The outside part is a shield to protect against interference. Another way to work around this problem is to cut the signal into pieces and assign each one a different frequency. Most interference isn’t at all frequencies - just a few. By segmenting things up you can use math to determine that certain frequencies are bad and avoid them. Think of this like a courier company and lanes on a road: instead of using a single massive delivery truck that takes up all the lanes, they use smaller trucks and can avoid potholes. These days the simplest solution is to avoid interference in the first place. All signals used to come from a large centralized location (telephone central office) so you would have thousands of conversations on wires running next to each other. Today the equipment is getting moved to the neighbourhood and you might only have to deal with a hundred or so, and much shorter wires."
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eapmlq | How do planes turn? | So cars turn by turning the wheels. But planes don’t have wheels: how do planes turn left or right or whatever in the air? | Engineering | explainlikeimfive | {
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"To start with, it's important to define *turn*, which means defining their orientation in 3D space. There is **pitch**, which is pointing the nose/tail up and down; **roll** which is moving the wings up/down (the nose doesn't move); and **yaw**, which is moving the nose/tail left and right. Yaw is controlled by the rudder, roll by the ailerons, and pitch by the elevators; [see this diagram]( URL_0 ). In order to change its *heading* - meaning, what direction the plane is going - planes can do a couple things. One is to just turn the rudder, which will cause the plane to yaw in that direction, which changes the heading. One problem with this is that it's uncomfortable inside the plane. Inertia makes the plane (and everyone in it) want to keep going straight, so centrifugal force throws them sideways. Another problem is that the outside wing has to take a farther path than the inside wing at the same speed. That means the outside wing generates more lift, which causes the plane to roll. But that rolling can be used as a good thing. The other way a plane can change heading is by rolling in that direction. Imagine an arrow pointing perpendicular upwards from the wing, which represents the direction of lift provided by the wings. If the plane rolls, the arrow stays perpendicular to the wings, which means that arrow rolls with the plane. Now instead of straight up, it's a little bit sideways. So the lift from the wings is pulling the plane to the side, which is changing its heading. You also lose a tiny bit of lift, which makes the nose pitch down. That's fine, just move the elevators to keep the nose pitched up. The farther the plane rolls, the faster it will change heading and less lift is opposing gravity. The advantage of this is that the passengers roll with the plane, so that now the centrifugal force is pushing them towards the bottom of the plane, into their seats instead of sideways towards the wall. That's a lot more comfortable. Most passenger planes do what is called a *coordinated turn* - they begin the turn with a little bit of rudder input and allow the plane to roll into the turn. If they need to, they will add a little bit of aileron input to roll the plane more. Once the plane is at the desired angle and changing heading as fast as they want it to, they add opposing aileron input to stop the roll and hold the plane at that angle. Some elevator input is added to keep the nose level. Once the desired heading is reached, aileron input is added to roll the plane back to level flight.",
"By tilting the back edge of some wing or fin, so that the air rushing past the plane pushes harder on one side than the other. For example the tail (vertical stabilizer) has a *rudder* on the back that swings left and right, controlled by the pilot's pedals. URL_0"
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eaq01w | With the sheer volume how are bridges logged & monitored for erosion so they are deemed to be safe? | Engineering | explainlikeimfive | {
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"They are not. That is the simple truth. When a concerned user makes a report to a governmental body, it may be investigated. Multiple reports = greater likelihood of inspection. For that to happen though -- the level of concern has to get high enough to overcome the \"I really don't want to get involved\", \"not my job\", and \"wow this system is a pain in the ass to navigate\" thresholds. As such, it really doesn't happen often enough. The more complex answer is that there are infrastructure departments, but they are horrendously understaffed, for the amount of work that needs to be done. There is more \"research\" work done than actual inspection. If a bridge was built in 1940, with typical 1940 technology, there is a known / assumed life expectancy based on the construction type and materials available at the time. That gives urban planners / inspectors an idea of when to expect inspections to be required, maintenance to be done, components to fail, etc."
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eaq8jx | how do spaceships and shuttles turn? | After asking how planes turn I’ve been wondering the same about space vessels. How do spaceships like the Apollo’s and Shuttles like Atlantis turn? Do they use rudders? Do they both use rudders? Do they both use the same turning mechanisms, or different ones? | Engineering | explainlikeimfive | {
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"At each end they have tiny rockets or thrusters, which push out gas at very high speed. This causes that end of the vehicle to go the other way.",
"While in atmosphere, rockets can use fins to steer like planes. Once out of the atmosphere, they have to get creative. The simplest answer is having tiny steering rockets on the front and back of your ship. By firing these rockets you can rotate your ship. Thrust vectoring, which allows the entire rocket engine to rotate slightly, is often used when the rocket is currently using its engine. However, many more creative solutions exist. There's reaction wheels, where the rocket spins little wheels inside itself to rotate itself. There's even the yo-yo despin, which allows certain rockets to stop spinning once they've launched (worth note that this only works once and only to *stop* spinning*)."
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eavg6w | Why do urinals need gallons of water to eliminate only a few mLs of urine? | Engineering | explainlikeimfive | {
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"Because otherwise they smell RANCID. -I have a job as a janitor. -Men don’t always flush -🤢🤮",
"To ensure the entirety of the urine is washed away and displaced requires that volume. Leaving any urine unflushed will create odours."
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eb6j4h | Why are there different types of helmets if you're riding a bicycle, a motorcycle or a snowboard etc? | Hi everyone, I was looking around me today and noticed the obvious : bikers helmets are quite different from cyclists helmets, is there a reason? Isn't the goal the same? I mean protecting the head from a commotion in case of a road accident? Yet the design as shape and material doesn't really look similar | Engineering | explainlikeimfive | {
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"To have as little protection as is safe for the activity. More protection just gets in the way if you dont need it",
"Most helmets are pretty similar in basic construction, actually. They're made of a layer of impact protection (frequently polystyrene) with padding for comfort/fit and a shell to spread out the impact, and to cover and protect the impact layer. After that, the design varies to suit the activity. A motorcycle helmet has to handle more force in an accident than a bicycle helmet, so it's built heavier and stronger to match. On the flip side, a bicyclist is sweating more, and isn't going fast enough for the wind to cool a motorcycle helmet, so they have something lighter with good ventilation and airflow, but sacrificing some coverage (although there's exceptions - downhill riders, for example, wear something similar to a motorcycle helmet)",
"They are built for different purposes. Both use Polystrene. Polystyrene is great at absorbing impacts but is really only a one time use - try pushing down on some and you'll see it won't return to its normal shape. A bicycle helmet is made of plastic and some polystyrene. The outer plastic shell will absorb most of the impact from a standard bicycle crash because it is usually quite thick. Anything else will be absorbed by the polystyrene. It does not need to have a large amount of polystyrene because it doesn't need to absorb a huge amount of impact. A motorcycle helmet has much more polystyrene and uses a thin fibreglass shell. It uses way more polystyrene because in the event of an impact it'll need to absorb much more to keep the rider safe. The fibreglass will barely absorb anything. This is why it is important motorbike riders replace helmets after ANY impact. Even if you just drop it from a few feet, replace it - more damage to the polystyrene is more damage to your head if you crash."
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eb721d | How do sinks with sensors avoid sensing the water? | Engineering | explainlikeimfive | {
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"Taking a wild guess but it's likely IR light and doesn't reflect through water well but is better reflected into the sensor by your hands."
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eb7gn6 | How do washers (for screws) work, and why? | Engineering | explainlikeimfive | {
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"Do you mean what purpose do they serve? They provide a surface for the bolt head to rotate against, so it doesn't mar the surface by rubbing against it. They also distribute the pressure from the head across a wider area, so you can tighten further without worrying you might indent the area around the hole. By spreading out the force, you both protect the object underneath, and you can hold it more securely. Also can provide a surface against which a lock washer can press. Lock washers essentially provide pressure and/or friction against the bottom of the bolt head, preventing the bolt from working itself loose.",
"they have a few functions. the most obvious is that they keep the head of the screw from being pulled into whatever they're screwed into. since the washer is wider than the screw head, it distributes the force over a wider area. they also maintain tightness. because they can expand and contract independent of what they're screwed into, the washer can maintain pressure even while things are vibrating.",
"Both of the two main purposes of the washer according to the common description are - providing a larger surface area to press on, and allowing pressure to be applied better on uneven surfaces - but these can be be built into the screw itself. Just make the screw head larger in diameter so that it's its own washer. In real life it doesn't work well. These types of screws do exist and they tend to suck just as bad as a screw with no washer. The important part is that the washer isn't a part of the surface or a part of the screw. If a screw can't go into a surface anymore, it means that it can still be backed out fairly easily (even just from vibration). Also if you keep reefing on it to prevent that you will just break the screw. The washer mediates the tension and lets the screw press down harder than it could if it were all one solid piece. Since there isn't a clear stopping point it isn't easy for it to be backed out, which is what is desired. Fittings with NPT threads work in a similar way without a washer, because the threads are tapered (hard to see but they are, very slightly). As you thread one fitting into another the resistance is graduated. There is no clear stopping point, so it can't be backed out easily nor will it break easily unless you go way too far. The \"washer\" in this case is that the threads themselves are very gradually distorted as you apply more pressure, so there is no clear stop point."
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eb8ol8 | How energy deparments know exactly where to fix a fault in the electrical energy distribution. | For example a wire going along a remote road. | Engineering | explainlikeimfive | {
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"The fault impedance can be measured at the time of the fault. The power line has a given impedance per length, the distance to the fault is the first divided by the second. Newer systems can measure a wave reflected from the fault and the travel time of the wave corresponds to the distance to the fault. These two are used mostly on transmission lines. For distribution, networks of sensors are deployed. These are usually only used in sensitive areas, though. Many places will not know there is an issue unless a customer calls. If an area is reported as a problem, a particular feeder to that area can be identified then inspected pole by pole."
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eb8qnq | Why do cook times vary by oven when the temp setting is the same? | Engineering | explainlikeimfive | {
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"Aside from differences in temperature regulation, ovens differ in two ways: * How much radiant heat the heating elements put out * How air-tight they are If you have an oven with an exposed heating element and poor insulation, the air temperature inside may be 200°C, but the surface of the food will be hotter since it's exposed to radiant heat from the heating element. And that heating element will be on for longer periods of time to maintain the selected air temperature due to the poor insulation. In addition to that, food that you're baking will release steam, and depending on how air-tight the oven is, trapped steam will help the food cook faster since humid air is much better at transferring heat than dry air. That's also why professional bakers' ovens have a function to inject steam. Bread gets a much nicer crust that way.",
"Not all ovens have their temperature controls calibrated exactly the same. I’ve personally seen many that are a full 50F over or under a calibrated reference source Also, the span between the cut-in and cut-out temperatures may vary. It may be as precise as 5 degrees or as much as 30 degrees (or more)"
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ebm3ta | How do wire nuts work? | The same nut fits on various size wires and holds it very tight! | Engineering | explainlikeimfive | {
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"They are designed to fit certain ranges of wire gauge and are typically color coded for what gauges they will fit. They are able to fit multiple gauges of wire because they are tapered. The metal threads inside grip the stripped wire and twist it together with the screwing action pulling the wire to the top where it gets smaller causing the wires to compress and hold."
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ebpr12 | What actually makes the power go out during a thunderstorm? | So here I sit in the dark wondering. Other than power lines going down, what actually causes the power to go out during bad thunderstorms? | Engineering | explainlikeimfive | {
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"Lightning may strike poles, causing a surge that makes circuit breakers in the line activate to protect the stuff down the line. Wind may blow lines into branches. Lots of stuff can happen."
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ebr7z4 | why is there a small hole in aircraft window glass and why does the cabin crew ask us to open the shutters when taking off and landing? | Engineering | explainlikeimfive | {
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"OK so these are 2 different questions The small hole is called a bleed hole. Airplane windows have 2 or more panes, the inner pane is designed as a insulating barrier, aka not let the cold air freeze your ass off, while the outer pane is the one that actually handles the structural load, aka higher pressure from the cabin pushing against the lower pressure of the outside. The bleed hole allows pressure to equalize and makes sure that pressure is only applied to the outer pane. Opening the shutters is to allow your eyes to be accustomed to the light level for the outside environment, such that when you get to the emergency exit you don't suddenly get blinded by the change in light level, this is also why they dim the lights during nighttime takeoffs. Keeping the shutters open also allows the cabin crew to easily look out the window to see if there are any evacuation hazards(e.g. Fire) on that side of the aircraft in case of an emergency Edit: evacuation hazards Edit 2: to whoever gave the gold, thanks so much, I really appreciate it!!!:D",
"Also the blinds are so the emergency services can see into the aircraft from the outside if needed",
"The open shutters also allows more passenger eyes to see if there is something wrong during takeoff/landing (e.g. fire) and alert the crew quickly.",
"I asked the stewardess once why they keep the shutters open for take off and landing. She said, highest chance of malfunction is during take off and landing, the shutters are kept open so we have extra eyes on the wings etc for fire or damage since the pilots don't have clear visual",
"The main reason why they ask you to open the shutters on take off and landing is that if something were to go wrong, theres a high chance of a passenger seeing it, freaking out and letting the stewards know. It's essentially creating an indicating system using the passengers as audible alarms. And the reason why its only during takeoff and landing is that's when theres a higher chance of things going pair shape as the aircraft isnt in its prime flying conditions (slow airspeed, engines running at a higher rpm trying to gain lift etc).",
"Hmmph I take a couple flights a year and have never heard them ask anyone to open or close the shutters.",
"You open the shutters so the rescue people can see in if you crash. And so if the crew needs to check out the plane, they can, but mostly for rescuers."
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ebrtr7 | Why do programs have to be manually optimized for multiple CPU cores? Why is single-core performance such a bottleneck? | For a long time, single core performance has been the most important feature for gaming. Though we are getting better multi-threaded games, we are still pushing for the maximum single core performance instead of cores. Why can't 16* 2ghz cores do roughly as good job as 8* 4ghz (of the same CPU architecture), especially in gaming? They say that software programmers have to manually split the jobs for multiple cores. Why? Why does the OS even need to operate multiple cores in the first place? To me this sounds like bad workplace management, where the results depend on pushing the limits of the same few people (cores) instead of splitting the work. I feel like making just a big bunch of cheap cores would give better performance for the money than doing tons of research for the best possible elite cores. This works for encoding jobs but not for snappy game performance. Now, one limitation that comes to mind is sequential jobs. Things where the steps need to be done in a certain order, depending on the results of the previous step. In this case, higher clock speed has an advantage and you wouldn't even be able to utilize multiple cores. However, I still feel like the clock speeds like 4 000 000 000 cycles per second can't be the limiting factor for running a game over 150 frames per second. Or is it? Are the CPU jobs in game programming just so sequential? Is there any way to increase the speed of simple sequential jobs with the help of more cores? Bonus question: How do multiple instructions per cycle work if a job is sequential? Bonus question 2: GPUs have tons of low power cores. Why is this okay? Is it just because the job of rendering is not sequential at all? | Engineering | explainlikeimfive | {
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"It's hard to convey to someone just how difficult multi-core programming is if they don't have a strong programming background. > instead of splitting the work And therein lies the rub: splitting work across cores is extremely difficult. Without programmer assistance the CPU cannot meaningfully understand the program structure to extract significant work. > Are the CPU jobs in game programming just so sequential? To put it simply, yes. Working across multiple cores is immensely difficult for the bulk of the work a game does. > Is there any way to increase the speed of simple sequential jobs with the help of more cores? This depends entirely on the specific details of the jobs. > How do multiple instructions per cycle work if a job is sequential? Each individual instruction engages different parts of the CPU at different times. So you can have to instructions \"executing\" simultaneously so long as they are using different parts of the CPU. > GPUs have tons of low power cores. Why is this okay? Is it just because the job of rendering is not sequential at all? Correct. Graphics rendering is a whole lot of \"do this operation on every pixel\" and each operation is independent of all others. You can have a thousand running simultaneously without much work by the programmer.",
"Imagine you're changing all the tires on a car. With just one person, it takes forever. With two people, you can work on two tires at once. But why stop there? If we throw 16 or 64 people at it we can change it faster than an Indy 500 team, right? Well not really. You're still limited by your equipment, just like single-core performance. It doesn't matter how many people you have or how fast the other steps are if your jack is a slow scissor jack. And you need a human to decide which tasks get grouped in parallel so you don't have one guy trying to screw lug nuts on a new tire before another guy gets the old tire off. However, having help on each tire can speed things up, but not because you're creating more core teams to handle more groups of tasks, but because you've got a pipeline so one person can be readying the next task while the last person is finishing his old task. (There are actually some attempts to let the CPU decide what can be run in parallel in a pipeline instead of the programmer through techniques like hyperthreading. But this happens per instruction, and may affect data in the instructions right before or after the hyperthreaded line, which makes this practice a bad candidate for parallelization across cores) It's also worth pointing out here that not only is upgrading equipment (like a hydraulic jack) faster, it's also more efficient. Even if you could change four tires with 100 low-paid guys using cheap equipment, imagine the amount of body heat that mosh pit crew would create. But what if we had to do a really repetitive job, like buffing and polishing the car. If we got 50 people to polish at once, we'd get done way faster than a skilled team of three people. This is the idea behind GPUs: that certain tasks like graphics can have dozens or thousands of the same calculation done in parallel.",
"Short answer, because multithreaded programming is *extremely* hard and often complicates things. You can have threads that overlap on the same job. You can have threads that wait upon each other to finish a task before continuing, in and endless loop (known as a deadlock) You can have threads that have access to the same data and both try to modify it at the same time, leading to a \"race condition\" You can have starved threads resulting from having tons of threads with low resources. Predictability is a problem with multithreaded programs. You have no idea how the program will execute in a multithreaded program, so you in turn have no idea how threads will act with data and if/when they will cause the issues above. All of these things require different algorithms and features to resolve. Yes, overall it is faster but only if done correctly, so it's more desirable to have faster cores to limit the need of multi threading. ELI5: You are building a house. You have 2 builders, who are experienced and work well together. The house is taking too long, so why not hire 4 more to speed it up? These builders don't know who is working on what. They start both trying to take the same brick at the same time, so now the building is halted until one of them concedes the brick. The builders start to wait on one person to finish the frame, but the person building the frame is waiting for the other builders to finish their part. And now, with more builders, you have 2 builders sitting around doing nothing because there's not enough bricks anymore. To solve it, you hire a manager to manage the site. He keeps tabs on the builders and decides who does what and adds systems to prevent conflict. The builders are threads. The bricks are processes. The manager is the process management system."
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eby2mi | Why do airplane cabins need to be pressurised? | So, when the cabin is sealed, the interior pressure is equal to the atmospheric pressure at sea level. When the plane lands, the exterior pressure is equal to the interior pressure. So why does the plane need to be pressurised for the duration of the trip? | Engineering | explainlikeimfive | {
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"Because the air pressure is extremely low at typical cruising altitudes. You'd lose consciousness from lack of oxygen in less than a minute, and would die not long after. That's why planes have oxygen masks that drop down in case the plane loses pressure. It's also cold. Like, really cold. Upwards of -60C cold. As an aside, plane cabins are pressurized, but not to sea level. Usually they're pressurized to somewhere between 6,000ft - 8,000ft. This is enough to be comfortable for people while also reducing stress on the aircraft from the pressure differential.",
"A lot of people have misunderstood that question. So i'll leave out the \"why humans do bad at low oxygen pressure and why we shouldn't do that\" bit. The cabin is not sealed - the air is actually being constantly replenished, under pressure. Think of it like a balloon with a pinprick leak. If you blow into it faster than it is leaking out, then the balloon will stay inflated. This is important because as people breathe in the cabin, oxygen would slowly be replaced with carbon dioxide. You could filter this, spacecraft style, but that's heavy and expensive. Much easier to just replace the air with fresh (compressed) outside air. Even if that wasn't an issue, having a perfectly sealed cabin would spell trouble on flights to different cities. They are at different elevations, and this different ambient pressures. A flight from Los Angeles to Denver would leave the airplane pressurized relative to the outside, creating hazards and a very uncomfortable sudden jump when the doors are opened.",
"At 30-50,000 feet cruising altitude (higher than Mt. Everest) the atmosphere is perilously thin. This is great for the plane since it dramatically decreases wind resistance, but it's not so great for the people inside who like to breathe. Such low atmospheric pressures cause hyperventilation and possible loss of consciousness with prolonged exposure, especially if you're from a low-altitude region and not acclimated to it. The plane isn't perfectly airtight (nor would you want it to be with 200 people breathing inside) so the cabin pressure needs to be continually vented and boosted.",
"At 30,000 feet there is very little air. It's low pressure and would be very hard to breathe. Without pressurizing the air we would have to breathe very quickly in order to get enough oxygen and it would be extremely uncomfortable. Even with the pressurized cabins I get horrible ear and sinus pain. Without the pressure I'd be in agony.",
"> cabin is sealed The cabin is not sealed. There is a small vent at the back. You can see it here, with the red border around it: URL_0 The engines provide fresh air to the cabin (or in the case of the 787, electric compressors). The air pressure inside the aircraft is equal to the pressure at about 8,000 ft. Keeping the pressure lower than ground level puts less stress on the airframe and is less weight in air to carry around."
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ec57va | Why do air conditioners function properly even when precipitation(snow, sleet, hail, ice, rain) gets in? | I've wondered about the outer part of the ac that sticks out the window gets water inside(the rectangular slots). Doesn't it(precipitation/water/melting snow or ice) damage the components of an ac inside? Also, when I am talking about the air conditioner, I am talking about window mounted acs(with one half sticking out the window and the other half mounted inside). ______________________ This is especially interesting when it pours outside(not just a drizzle, but when it rains heavily). | Engineering | explainlikeimfive | {
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"Air conditioner units use radiators (like the car radiators in front of the engine) to concentrate the heat or the cold, and a fan behind the radiator to push the air through and transfer the heat (or the cold) to the air. So water (snow sleet rain ice) has a much higher heat capacity than air, and moves heat BETTER. The AC unit is designed so that the water doesn't get into the electrical parts (unless you submerge it in water), and if some rain gets in the radiator, it's made of metal so it won't be damaged, and will actually bleed off heat quite a bit better. [Here's what it looks like]( URL_0 ). The electrical parts are protected, probably in box labeled 7."
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ec8io3 | How are roads on steep cliffs built? | Whenever I am driving through the mountains I always end up on a road going along the middle of a steep cliff and I've never understood how the road crews and engineers built the road on the first place. | Engineering | explainlikeimfive | {
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"Dynamite. I remember going on a hike somewhere in Utah and there was a trail that was originally going to be turned into a road but they just left it unfinished and made it a trail instead. You could see where they drilled the holes and were going to blow the cliffside. It takes a lot of precision to keep it somewhat level and prevent the whole side of the cliff from just crumbling. To level the road, they'll just use all the dirt and small rock debris to make a flat surface, then pour asphalt over it"
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ecc1np | Manual transmission - what does changing the gear actually do? | Engineering | explainlikeimfive | {
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"It literally changes the gear. There’s one gear spinning from the clutch plate, and three or four or whatever other gears around it that engage with the drive shaft. It’s a little more tricky than that, but for ELi5... When you change gears, you disengage one of the driveshaft gears and engage another. Mechanically, the shifter lever has a guided fork that follows a path to where the gears can be pushed or pulled into place. This helps ensure only one gear can be engaged at a time, although they can be engaged in any order. The gears have different diameters, so they’ll spin at different speeds relative to each other, giving different output to the driveshaft given the same input from the motor. That’s why in first gear you’re barely moving, but have a lot of power to accelerate, and in fifth gear you’re really flying, but speeding up is slower.",
"Changes your gear ratio from the original 1:1 of the engine, to a ratio with more torque. Look at it as adding “leverage” to the engine. As you drive faster in first gear, your rpm’s rise to a point that you need a taller gear ratio. For sake of conversation et’s call 1st gear 100:1, then 2nd gear could be 75:1, 3rd 50:1, 4th 25:1, 5th 1:1 (that’s called direct drive because you are back to 1:1 meaning there is no gear reduction). Some transmissions will then have another gear that’s called “overdrive” in which the engine makes enough power to where it can run at at say 0.5:1 which allows you to go highway speeds at a lower RPM which can help you save fuel as long as your RPM’s don’t drop to the point that your engine has too much load on it. That in which will cause the engine to “lug” and heat up past the point of normal operating temp, which can be harmful to your engine. Some vehicles even have a second overdrive gear."
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ecgrn0 | How magnified gun optics work? | How does the reticle on the scope always point at the target? What makes it more accurate than just using the front post iron sight? And how does turning one handle make the zoom go from something like 6× down to 1× on adjustable zoom scopes? | Engineering | explainlikeimfive | {
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"Curved glass (a lens) bends the light going through it, allowing you to magnify the image. Adjusting sights have two lenses, so that you can change the distance between them and adjust the magnification. They're not necessarily more accurate than the iron sights (and can be vastly worse if you haven't aligned the scope correctly) but for longer shots they make it easier to see the target. If a marksman expects to be shooting at very long range, they'll adjust the angle of the scope to account for bullet drop. This means the gun will actually tip up slightly so that gravity brings the bullet back down to the target.",
"> How does the reticle on the scope always point at the target? It doesn't. Rifles (and other guns) fire bullets in a parabolic arc; when you sight in your rifle, you go through a few rounds either on your own or, if you're more of a novice, using a machine rest, and you use dials on the top and side of the scope to correct up/down and left/right as needed. In the scopes I've used (see: exactly 2) there were gross controls and fine controls; the gross controls were used to get you in the same average area, and then the fine controls to dial closer; there was also some mechanism that would allow the control knobs to be re-set to \"center\" once you sighted it in in a controlled environment, as those controls are *also* used when you're adjusting for range and wind in the field. And this is the important part: Long-distance shooting, at a point, isn't just \"point and shoot\"; it's weaponized trigonometry. > What makes it more accurate than just using the front post iron sight? The fact that you can see your target in a larger % of your field of vision is pretty much the long and the short of it; if you are aiming at a target that is several hundreds of yards away, it will probably be completely covered by your front sight, making it nearly impossible to accurately gain a sight picture. > And how does turning one handle make the zoom go from something like 6× down to 1× on adjustable zoom scopes? Scopes have a bunch of different lenses that serve different purposes; one of these is the magnification lens, and using that control either pulls the lens further from your eye to make the image bigger, or pushes it closer to make it smaller. Same principle as when you take a magnifying glass and move it closer or further from your face, just much more precise on a scope, with different adjustments adjusting different lenses to do things like focus/correct for parallax, un-flip the image, magnify, etc."
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ecicvg | Turning on the AC in the car affects your MPG due to the added power needs, but what about charging your phone? Would using a 2.1 or a 3.1 amp or even a USB-C PD charger change your MPG? | Engineering | explainlikeimfive | {
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"It's a matter of scale When you're cruising down the highway you might need 20 horsepower from the engine (14.9 kW). Your phone charger might need 50 W if it's a big USB-PD one, that's an increase of 0.33%(likely less than 0.1%). When your AC compressor and fan are running they could require up to 3 hp (2.2 kW) of power and about 1 (745 kW) on average. That's an increase in total power of ~5% which would take you from 30 mpg to 28.5 or even lower if the compressor is running more.",
"Yes, but no. In theory it increases the load on the alternator, which increases the load on the engine, which increases fuel consumption. In practice though the impact is completely negligible. Your average 2.1A charger delivers 10.5 Watts to the phone and draws about 12W from the electrical system (because the DC-DC converter inside is about 85-90% efficient). In turn the alternator would put an extra 15 Watts of (mechanical) load on the engine. Meanwhile the engine is putting out somewhere in the neighborhood of 20 horsepower (~15,000 Watts) to maintain a constant speed on the highway. That means you will use about 0.1% more fuel while charging the phone. So a car that would normally get 30 mpg would now get 29.97 mpg. In other words, it's not worth worrying about.",
"Your AC has a compressor driven by a belt that is connected to your crankshaft. When not in use, the ac clutch disengages and the resistance added is minimal. When turned on, the ac clutch engages and disengages repeatedly to move refrigerant around the ac system at a set pressure. This adds a lot of resistance to the engine and decreases your available power/ mileage due to the extra strain. Your phone battery charger gets power from your alternator, which is creating electrical power anytime the car is running as it is also run by a belt attached to the crank. It however, doesn't have a clutch and runs all the time. This charges your battery and runs the lights, computer, etc at all times. The alternator creates more power than the car uses and adding some electrical strain to the system will not affect your cars performance. If you added a lot of electrical strain, you could potentially surpass what the alternator can create and give yourself problems with a weak firing system or computer malfunctions, but you would have to do some serious dumb stuff to get to that point. So tldr- no. Your phone charger doesn't affect gas mileage."
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eckzrk | How do air conditioners and heaters work to change the temperature of the air? | Engineering | explainlikeimfive | {
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"There are two main types of AC -- Evaporative and Compressor. Evaporative coolers, aka Swamp Coolers, work in very dry areas, like deserts. They work by moving hot air through a duct, and spraying cool water on the hot duct. The heat in the air gets puled out of the air and causes the water to evaporate, thus cooling the air (heat transfer from air to water). The water vapor is vented outside and the newly-cool air is blown in to the house. Compressor coolers work just like your kitchen refrigerator. They compress air in to a high-pressure tank, then spray it out through a very small nozzle. This is a neat physics thing where air that is under pressure, and then is blown out a tiny nozzle expands quickly, gets very cold. You can try this with your mouth -- blow air out with a wide open mouth on to your hand. the air will be hot. But if you mak a small opening with your mouth and blow air out fast, it will be cold air on your hand. The act of compressing the air down and then expanding it through the small nozzle (your mouth) cools it off. Anyway, this new cool air, through some various mechanics we don't need to get in to, cools the air circulating in to your house. Heating is more simple. Furnaces use electricity or burn gas to create heat, then pump this heat in to your house's air.",
"Heaters: use electricity to generate heat, use a fan to transfer heat to air. Air conditioners use a property of gases that when you compress a gas it heats up, and when you decompress a gas it cools down. So the air conditioner has a gas inside (used to be freon, now it's a more environmentally-friendly mixture) and a compressor to pressurize it. When pressurized, the gas gets very hot, hotter than outside, so this hot gas gets cooled down as it passes through the radiator element outside. Then the (now cold) gas gets depressurized and becomes freezing-cold, and thus can absorb heat from the room when it passes through the radiator element inside the room. Absorbing heat from the room heats up the gas a bit, to where it's warm. Then the gas gets pressurized again, making it very hot, and the cycle repeats. Refrigerators work on the same principle."
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ecnzh8 | I know about the boiler that makes the hot water that come out of my tap hot, but what determines the temperature of cold water coming out of my tap? | Is it just not affected? Is there a water cooler somewhere in my building? | Engineering | explainlikeimfive | {
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"There is no chiller for cold water before it comes to your tap. The ground that the pipes are in cools the pipes & water. Basically mother nature controls the cold water temperature.",
"It determined by the ground water temperature. Depending on the season and where you live, ground water can be anywhere from just above freezing (32°F or 0°C) to near 80°F (26°C)"
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ecq84v | How airplanes are able to fly even with one failed engine? | Wouldn't it create torque and force airplane to spin? | Engineering | explainlikeimfive | {
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"The torque is counteracted mostly by trimming the rudder. On a prop plane the failed engine is 'feathered', changing the pitch of the blades so as to minimise drag on that engine.",
"short answer no. long answer it does in a way but that can be offset. planes dont really fly in a straight line all the time. they can do something called crabbing which is where the nose is pointing to the left or right of the direction of travel. this is used for example during high winds and is really visible at landing where the plane will be flying straight down the runway and the nose will be maybe 20 degrees off to the side and the pilot will straighten up just at touchdown. also planes engines really just give them the speed to keep enough air pressure over the wings as long as the remaining engine can create enough forward momentum ant torque created can be combated by using the rudder to compensate, much in the same way a helecopters tail rotor stops that from spinning like a top by providing thrust on the tail in the opposite direction of the rotation of the main rotor."
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ectpy9 | Why is it important to let an engine warm up in winter? | What could happen if someone doesn't let an engine warm up? | Engineering | explainlikeimfive | {
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"Back when engines used carburetors, cold engines would need to be warmed in order to get the proper fuel-air mixture for sustained ignition/combustion. Nowadays, however, it's entirely unnecessary; engines have fuel injectors and sensitive instrumentation that adjusts the mixture for optimal combustion.",
"Car manufacturers generally recommend against idling engines to warm them up, beyond letting it run for 30 seconds or so to let the oil circulate. Idling an engine to warm it up can cause extra wear because you're prolonging the time the engine is running below operating temp. Driving it with moderate amounts of throttle and revs will warm it up more quickly. While the engine is still cold a lot of unburnt fuel and condensation is going to make its way into the oil and exhaust system, so you don't want to have it running in this state any longer than is necessary. There's also the issue that while the coolant is going to heat up if you idle the engine, the engine oil takes much longer to get up to temperature if the engine isn't doing anything.",
"It's not. You are wasting energy for nothing. Start engine, accelerate moderately. That's it.",
"Unless it’s very cold there is no need to warm an engine up for cars. All the fluids and the engine transmission are design to work fully right after starting. If it’s super cold just limit speed and acceleration for the first five minutes.",
"This was mostly a thing for old cars. Cars have a desired temperature to work at and being cold makes them inefficient as there are larger gaps in the pistons that mean it doesn't convert it all to power. In the old days you'd have a choke that allowed more fuel into the engine to combat this and as such it needed to be left a little while. & #x200B; Engineering is now precise enough that this is basically irrelevant.",
"I always thought warming up the car meant turning it on and getting the heater on the inside going.",
"Mainly to get the oil circulating. In cold weather, oil increases in viscosity (thickens) and after sitting at the bottom of the engine all night, it’s hard to pump up to the very top. Multi-viscosity oil (10W-30 — 10 *Winter*, 30 Normal) help mitigate this, but just because it’s better than it was before doesn’t mean you can just ignore it. Regardless of the weather though, the majority of the wear and tear an engine suffers is during startup because it’s not properly lubricated. Engines also have little rubber seals and O-rings that do their jobs better when they are warm and oiled. But on a much more practical level, the engine warms up the coolant which is where the heater gets the heat from, so a lot of people let their car warm up just so the cabin has heat.",
"It used to be the case that you'd manually adjust the AFR (air fuel ratio) of the engine when starting it with the choke during a cold day, and then let it warm up so that it could idle unsupported. when it first started, it wouldn't be able to self-sustain without using the choke. after it was warm you could drive. nowadays a computer controls the AFR and automatically adjusts it according to tempurature. the other part of it is oil circulation, which is something that still makes me cringe. Watching someone start an engine and immediately start driving it. The oil pump will not have sufficient pressure to lubricate the engine properly for at least a couple of seconds, as oil falls back into the sump after a short while of the engine being off. When i start a modern vehicle, i let the engine run for at least 10 seconds before moving. Normally i just start the engine, then get my gloves and helmet on. this provides a convenient time measure, enough for oil to circulate. In general, engines just like to be at their operating tempurature. their parts are machined to the correct tolerances for a given tempurature. for example the piston rings are set to provide a good seal at around 150-250 degrees, so when they're dead cold, they're slightly too small and don't provide a good fit.",
"OK but which of these answers are relevant to me, a resident of the Canadian prairie winter hellscape, which gets down to -40° ? Are the answers still generally relevant or are there additional considerations at that temperature?",
"People have mentioned what is happening inside the engine, there is a practical safety concern. If you don't warm up your car, your windshield defroster won't work. The interior heat is waste heat from the engine. Even if you scrape frost off of the windshield, your breath can condense on a cold windshield and blind you. You don't have to warm your car up for very long. If the windshield is clear when you get in, it won't fog up immediately, and your engine generates heat quickly while you're driving. But the defroster is a safety system, it is considered bad luck to drive blind. Warm up your car so that the defroster can work.",
"I don't even own a sweater where I live. I still let my car warm up though. Glad to know this is completely unnecessary.",
"A lot of people are mentioning fluids and air-fuel ratios, but I think the other issue is also the metal that makes up a lot of the engine parts that need to warm up. Taking cold metal and applying a sudden increase in temperature and pressure to it could potentially lead to catastrophic (and premature) failure of those parts.",
"Everyone here is pretty much spot on about not really \"warming up\" gasoline cars, but driving them conservatively until warm. But yeah, that does mean there is still a \"warm up\" period. The engines are designed to run at a specific temperature. The various parts all expand and contract at slightly different rates, and you don't want to put sudden changes in load on it until everything is at the temp it's designed for. But yeah, just driving it is better than not, because it heats things up faster.",
"I found this... *When an internal combustion engine sets overnight the mechanical components will be cooler than when at “ideal” operating temperature. Engine wear is most experienced at cold start due to the lack of oil available to engine components. The dimensional tolerances will be at the non-ideal design limits. Maximum clearances in all bearing and piston to wall specifications. The piston will be an oval shape having not expanded to true oval for minimal clearance. Some piston slap will cause some wear on the piston skirts until thermal expansion maximizes. No lubrication oil will be top side or on the cylinder walls. This is where the most “wear “ occurs. Metal to metal and no lubrication. Why? The oil pump galleries may be dry with no oil present. Today 99% of the cars on the road use mechanical oil pumps. This means the pump oil pump cannot deliver oil pressure until it has sucked up the oil from the oil pan sump and has begun pushing the oil through the oil galleries. From cold start until the engine warms up and the oil fills all the oil galleries and we have a steady oil pressure reading we do not have proper lubrication. It was true that we suffered a lot of cylinder / piston wear about 20 years ago. The cylinder walls used to be honed and finished with many peaks and valleys remaining in the surface profile. The introduction of Plateau Honing meant the peaks were knocked down on final hone pass so the engine break in time was a lot shorter and we had significantly more valleys to retain oil. Todays computerized fuel monitoring means we do not have excessive fuel splashing on cold cylinders at start up unlike the day of the “choke”. Your assumption that ”thicker oil” does better lubrication is not true today with the introduction of synthetic oils. Cold start lubrication is best achieved from an oil with good cold flow Properties. The reason the 98C wear is the least is the engine is functioning properly. At 20C the engine is way too cold and piston rings are permitting too much blow, washing the lubricating oil off the cylinder walls. The piston is not thermally expanding for a tight piston ring seal. When the oil is not heated to proper temperature harmful deposits, moisture, and acid accumulate rapidly, then eat away at the inside of your engine. There is a lot of chemical things happening during the combustion process so you must change engine oil at least every 3 months regardless of the miles driven. You literally have acid and sludge developing in the crankcase.*"
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ecxgaq | Why can't we catapult rockets? | Well, I've always asked myself why can't we use some kind of train or catapult to help the rockets to save fuel or to go further. Can anyone explain me why? | Engineering | explainlikeimfive | {
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"They need to get up to 28,000km/hr to get into orbit. Starting at 0km/hr or 40km/hr or even 400km/hr is practically insignificant (especially when the Earth's own rotation adds more than that) and only adds complexity and failure points. When your plan is to accelerate hundreds of tons of rocket fuel in a literal missile to 28,000km/hr, minimizing failure - especially on the ground with people around - is important.",
"There are actual ideas along those lines, but they are still theoretical because they would need to be extremely huge beyond anything we can easily build today. The important thing is that it is not so much about getting into space (which is only a 100 km up) but getting into orbit which means going several dozen times the speed of sound on earth. Rockets are difficult because you need to carry fuel to carry more fuel around, so that your typical rocket that goes into space is mostly fuel and very little actual payload. This had let many to think of how we can do this easier, better and cheaper. The most famous idea for an alternate orbital insertion system is the space elevator, basically climbing a rope up into space high enough that you reach the point where orbital velocity which you need to stay up is the same speed that you are already going thanks to the rotation of the planet. Everyone agrees that such a space elevator would be wonderful and cheap and easy and generally much better than rockets with just the minor problem that we don't have any materials strong enough to build one. Other famous ideas include shooting up your spaceship in a giant gun. This is an idea that actually predates modern rocketry and another thing that would work in theory. One problem is that chemical explosion based guns accelerate their projectile really really hard, so that would not work for anything fragile like humans. Magnet based rail guns could work with a much lower acceleration though. The bigger problem is that any space gun would need to be enormous. It is another thing that would work in theory but that we don't have the right tech for yet to actually build it. The last guy to actually spend serious money on building anything like that was Saddam Hussein and he was more concerned with reaching some place more down to earth rather than the stars. (Things didn't work out well for him.) Another thing that might be come close to a catapult would be a space bola or rotating space tether. It is basically a cut down version of a space elevator that rotates in orbit and has its ends reach down into the atmosphere where a fast flying plane could attack a payload to be catapulted up into higher orbit by the spinning death strand. It is close technology wise to what we might actually be able to build with current tech, but would still be a major undertaking. In any case, anything that shoots or catapults stuff into space could save some rocket fuel but you would always need some rockets to make an actual orbit out of it. The point is that people have thought along the lines you suggested, come up with ways that would work, but ended up not being able to built the things they came up with because we don't have the materials or the money for that yet."
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ed0k5d | Why is engine braking safer than normal braking on slippery roads? | Engineering | explainlikeimfive | {
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"Engine braking is LESS safe on slippery roads, at least in cars that don't have permanent all-wheel drive or four-wheel drive. If you use engine braking in a RWD or FWD car, it's only the two driven wheels that have to do all the braking while the other two are doing nothing. That means you're not using all of the available traction, leading to worse braking performance, and it's potentially dangerous because the drive wheels will have less grip available to transmit cornerning forces. With FWD that means added understeer, and with RWD that means a higher tendency to oversteer. The safest way to slow down when a road is very slippery is to use the brakes (carefully), because you're not just using two wheels to slow down, you're making use of the grip of all four wheels. Not only will the car stop much better, it will also be easier to control.",
"Modern braking systems provide ABS, as well as additional stability/Vector controls to ensure you are safely slowing down. For these reasons, prioritize your regular brakes for almost every situation... except long downhill grades or if your brakes start failing. Engine braking bypasses normal braking design, and forces the wheels to push through the additional engine resistance provided. Additionally, being in a lower gear means the provided power when applied will likely cause a loss of traction compared to using a higher gear that would provide less wheel power and gradually change its speed. [Wiki: Engine Braking ]( URL_0 ) > Improper engine braking technique can cause the wheels to skid (also called shift-locking), especially on slippery surfaces, as a result of too much deceleration. As in a skid caused by overbraking, the vehicle will not regain traction until the wheels are allowed to turn more quickly. If the driver reduces engine braking by shifting back up, or disengaging the clutch on a manual transmission, traction can be regained."
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ed74ug | Bypass capacitors on electronics. | Engineering | explainlikeimfive | {
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"Capacitors allow a little bit of charge to flow through them before filling up and stopping more. Because of this, they only slightly impede oscillating charges that move in and out, but completely block a constant movement of charge. By adding them between components, they can cause all faster oscillating charges to move through them and 'skip' the rest of the circuit, filtering it out so the rest of the circuit has less of this oscillation."
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ed9yat | Why is oversteering bad on tarmac racing but advantageous on loose road racing like rallying? | Engineering | explainlikeimfive | {
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"This is due to the friction characteristics of the tire and road surface. Take a look at this diagram: [ URL_0 ]( URL_0 ) The blue line is for asphalt, the orange one for a loose off-road surface. It shows you how much force the tire can transmit for a given slip angle. On asphalt you get peak at a relatively low slip angle, and if you increase the slip angle, the grip drops off pretty sharply. So a low slip angle is ideal for asphalt. On a loose surface there's no such peak, instead the grip increases as the slip angle increases, which means going through a corner sideways is faster than with a low slip angle."
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edc3mp | How does condensation drying work? | Engineering | explainlikeimfive | {
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"Condensation drying is often used to remove moisture from compressed air. It relies on the fact that the water capacity of cold air is lower than the water capacity of warmer air. The air is chilled by a refrigerant process (much like a small refrigerator) at which point the moisture will condense into a liquid and drip away from the system. The colder the air gets, the more the moisture will condense. The air is then fed to the system that uses it and the condensed moisture is taken away in a drain system."
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eddmc3 | can someone please explain impedance to me? | I’m trying to understand impedance and I’ve found lots of different answers with no set definition. Could someone please explain it in a more general sense? | Engineering | explainlikeimfive | {
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"When you try to push electrons through a wire, it takes some force. Some of that force is required to overcome the resistance of the wire, and this resistance is the same for DC (constant voltage) and AC (oscillating voltage). However, that's not all the force required. As electrons run through a wire, they produce a magnetic field. That magnetic field makes it harder to change the speed of the electrons, requiring more force. This effect is called impedance. Most interestingly, the effect depends on the geometry of the arrangement of wires and the frequency of oscillation for AC currents."
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ede79g | How does a cruise ship have enough hot water for 2,000 people to take a shower every morning? | Engineering | explainlikeimfive | {
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"Ships of those size would have several boilers and other forms of heat exchangers. It's not hard to get hot water on ships because main engines and many auxiliary machines require cooling water. When this cooling water is heated, it can pass through a heat exchanger and heat up the potable water for the showers."
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edf23t | How does the security of cellular data and of shared networks where everyone logs in with a different account compare to a typical password-protected home network? | Engineering | explainlikeimfive | {
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"The cell networks are basically open to anyone, like a road is. If you have a car you can get where you want to go. Security is achieved not on the network itself, but between you and the destination you are communicating with. This is why you enter your bank password on that website itself, not to your cell network. Once you've made a secure connection to a site, all the network sees is the destination of your data, and the data itself is hidden in a black box of encryption. An armored car if you will. Private networks like home wifi are basically the same, just with one extra step between you and the open network. It's like how you have to go through the garage before you can hit the road, but you need a key to the garage first."
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edf3sn | Why don’t electric cars (like Teslas) all have solar panels built in to the roof that could add to the battery’s charge all day? Is it just cost prohibitive for the panels themselves? Would the surface area of such small panels not contribute enough power throughout the day to justify them? | Engineering | explainlikeimfive | {
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"The latter - panels that small would generate so little power that you might only get a 1 or 2% charge over the course of a sunny day (and zilch on a cloudy one). It just isn't worth it for such a minor improvement.",
"The Fisker Karma had such a roof. The main purpose was to assist the climate control system and keeping the car cool when parked. I think they estimated it only added a few miles *per week* to the car's range.",
"I was on a R & D design team for Fisker 10 years ago. We researched all sorts of ideas on how to generate power from solar power collecting paint, regenerative breaking, turning heat into electricity....(I actually wrote a book on it!)....it actually takes a lot to make and store power. So the best thing we found was how to be more efficient (aerodynamics, better tires, better bearings, smarter motors, new battery technology....)",
"A rough rule of thumb: while it's driving, an electric car uses about as much electricity as you'd get from a tennis court covered with solar panels.",
"Solar power just isn't efficient enough (yet?) to justify the cost. Add to it the cost of replacement/repair, and adding hundreds of dollars to the cost in order to maybe someday getting a return on that investment doesn't make sense.",
"One modern solar panel generates about 1/3kW-hr in one hour. A Tesla battery stores about 70kW-hr, so it would take this much sunny time to get a full charge from one pane: time_to_full = 70 kW-hr / (1/3 kW) = 210 hours of sunshine = more than 30 sunny days Now, you don’t always need to fully charge your car - what is the normal battery usage per day? I typically commute and use maybe 10% charge in a day, so that would take around three sunny days to charge. If solar panels were ten times more efficient, then it would only take 2 hours, which would work, but solar panels are already around 22% of maximum possible efficiency, so we can’t improve them enough to make one panel work. So you know, solar panels generate electricity using the “Einstein Photovoltaic Effect”, where light particles hit the silicon and knock an electron loose, creating a voltage - an “electric pressure” that can push energy into a battery. This effect has a known “maximum performance” based on the physics, so the solar panel designers know that they aren’t perfect until they get 100% of that efficiency. Currently, the best technology is able to get maybe 30%, but the ones you can buy now are about 22% efficient.",
"Nissan Leaf had one, but it was mainly useless. Theoretically it could help with the climate control system, but it was mainly a talking point.",
"Well, most of them do not. But have a look at here: [Sion, 25,5k€ EV]( URL_0 ) . It is supposedly also very essily maintained and repaired by the owners. As you can see though, the solar panels do not give too much extra range and the system complicates the design exponentially per cell-structure, and adds weight. There is also the rather fast improvement happening NOT in solar panels, but energy storage, which in return doesn’t really incentivise you to sink money to irreplacable panels. It is more desirable to make your EV use less energy instead of trying to create it on its own.",
"Elon claimed they could make the bed cover on the Cybertruck generate 15miles equivalent per day. That seems unlikely but heck I’d buy it.",
"one thing most of these comments are missing is simply the extra weight of the panels: solar panels are heavy. they wouldnt generate enough power to compensate for their own weight, let alone spare any for the car.",
"Look at the Lightyear One. It’s a concept as you described, I went to a show that they were showing off the car at and I think the guy said a full 8 hour day (I.e parked at work) in the sun would give about 4 miles of charge.",
"There is not enough surface area to mount the panel(s) in any meaningful way. A 0.1kW solar panel attempting to charge a 30+kW battery would be like you trying to fill the Grand Canyon by throwing bricks into it. A better question would be why doesn't every flat, South-facing surface (for Northern hemisphere structures) have solar panels mounted on them.",
"let's say the panel is one meter by one meter (pretty large to be on a car). So, annual solar irradiance at this surface is 1000 Watts. So the maximum perfect energy would be enough to light 10 light bulbs. Actual result when you figure in clouds, latitude, efficiency, etc, it could probably run one or two light bulbs.",
"I would love to see them added as an option as a sort of \"limp home mode\". Until charging stations are more common it would be cool if worst case you ran out of juice somewhere and could just hit a local restaurant for a glass of tea and slice of cake while you car built up enough charge to get to the nearest charging station.",
"A square meter of sun, after the atmosphere, generates about 1000 watts per hour. The average panels operates at 20%, and the average usable hours of sunlight per day is six. So per meter, you get 1,200 watts per day. A car is maybe three square meter so top surface area. So about 3.6kW per day The Tesla Cyber truck is a 200kW battery. **So it would take 55 days to fill the battery.** Should we put solar panels on the surfaces? I think there should be an option to be able to. It is less about charging the car to drive, and more about being able to run subsystems from the car. I could run an xbox and big screen for months if my car sat in the sun. ' Even on a small farm, sometimes trucks only have to move a kilometer over a few days, so in many cases I think it would be useful. Electric vehicle can and should be designed to be the battery pack for the entire home, so the more solar panels you have closer to the battery storage, the better."
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edj6sg | How does a weedwhacker transmit power from the engine to the rotating piece? | Specifically on weedwhackers with a curved arm connecting the engine to the cutting section. It baffles my ignorant brain lol Thanks! | Engineering | explainlikeimfive | {
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"I found this article to explain it very well: [link here]( URL_0 ) \"In both curved and straight shaft trimmers, a motor connects to a cutting head by way of a shaft. The shaft on both models is going to be where the handle and the throttle are mounted. Within the metal shaft, a drive cable runs the length of the shaft, spun by the engine, and turns the cutting head at the other end of the trimmer. The curve of the shaft, or lack thereof, will influence the drive cable. In a curved model, the drive cable will need to be flexible to accommodate the curve in the shaft. This will have a direct effect on the durability of the cable, as the drive cable constantly bends and spins within the metal shaft.\"",
"The motor delivers the power the same way the motor does in a car. The motor is connected to a drive shaft. In the curved necked weed whacker, I believe there's a cable that's connected between the drive shaft and cutting head."
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edkyvt | how do they get the giant cranes on buildings | Hi Reddit! My family and I would like to know how they get those giant cranes onto the top of the tall buildings they are constructing. Thanks! | Engineering | explainlikeimfive | {
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"[Here is a good gif]( URL_0 ) that explains the process.",
"[Here]( URL_0 ) is an explanation. The gist is that they assemble the basic parts with other shorter cranes, and then the super-tall crane builds *itself*.",
"The cranes build themselves up piece by piece. Constructs the building around itself. The Squareish body of the crane eventually becomes the elevator shaft that it disassembles itself down. There are some great timelapse videos online of them. Crazy amount of engineering and hard work.",
"Crane operator here. Just wanted to add in that while very tall cranes climb/jack up, most cranes I operate is erected only by a mobile crane and is the same height during the entire construction time. This is usually the cheapest and most effective way for cranes 100 m (300 ft) or lower.",
"How does a crane not tip over? Isn’t it top heavy?"
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edrifm | CPUs seem to hit its limit of 3.5-4Ghz before they generate too much heat. why dont companies just make bigger CPUs instead of adding 8+ cores? | Engineering | explainlikeimfive | {
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"Hold out your hand, and spread your thumb and pinky finger out as far from each other as they'll go. The distance, tip to tip, is, *very roughly,* how far light can travel in a nanosecond. In order for the signals in a chip to get from place to place fast, the chip has to be very small; the smaller you can make a transistor, the closer together you can pack them, and the more overall you can pack in, but more components means more heat."
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edrj6s | How are ski lifts designed so they can pass through the support beams? | Engineering | explainlikeimfive | {
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"Ski lifts look lke question marks. That way the center of Gravity stays under the cable but one side of the cable is not blocked",
"Ski lifts not pass through support beams. You attach the cabin, T-Bas to the wire with a metal beam on one side of the wire So the whole system is designed so one side of the wire is never covered and there is the attached stuff sticks out."
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edum69 | Why do some small electronics such as a router have a bulky adapter plug, but a large appliance such as a vacuum cleaner have a regular plug? | Engineering | explainlikeimfive | {
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"Your small electronic devices all need low voltage DC power, they generally run off 24V or less so they need a power supply that can take the 120V or 230V AC power from the wall and convert it into the 5/12/24V DC that the device needs. This can be done with a wall wart(big plug on the wall), a power brick in the middle of the power cord, or inside the device. If you want to make a small device then you want to move the bulky power supply to a power brick or a wall wart so it doesn't bulk up your primary device. Your vacuum just runs straight off the AC. AC runs into the motor, AC runs to the secondary motors, everything runs directly off of power provided from the wall. Even for bigger things like a stove which may have a display, they're large enough that fitting a small power supply inside the device isn't going to require a larger device.",
"Because the router runs on low-voltage DC current and needs an adapter to convert the 120 volt AC current coming out of the wall. The vacuum cleaner is a large appliance and all its components just run on the standard 120 volt AC current.",
"Because small appliances run on low voltage DC power which requires a converter that's normally integrated into the plug. The makers of these appliances only want to make one model that they can sell all over the world that has different power standards and plugs. They just package a different wall wart in the box for different markets.",
"Some things run on AC power which is what the power outlet in the wall provides. It’s alternating voltage like a sine wave. The wall provides 110-120v AC which is a lot. Waay to much voltage for small electronics. The bulky adapter takes the 120VAC and will step it down and “rectify” it into a DC source (constant voltage like a battery, not a sine wave like AC). The circuit required to do this is a step down transformer which is ratio of a lot of coiled wires around a magnet, followed by other component to make up the rectifier circuit. You vacuum cleaner motor runs off the large 110-120VAC because it needs the power and has built in conditioning circuitry"
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eduyim | What exactly produces the noise in an electric motor? | Electric locomotives for example make a lot of noise, where does this noise come from, other than mechanical motion and friction? | Engineering | explainlikeimfive | {
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"I can't speak to electric locomotives, but most electric motors are actually super quiet. Things that do make noise tend to be mechanical components, such as the commutator or bearings or gears.",
"In addition to the noise from mechanical parts, there's also noise from vibration caused by the changing electromagnetic fields in the motors and power system. It's the same phenomenon as transformer hum and coil whine."
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ee6k3x | Why are most microphones black? Would there be a difference if they were pink, blue etc? | Engineering | explainlikeimfive | {
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"Because they don't reflect spotlight on stage, especially useful for photography/cam work that does not reflect. They also blend in better in dark setting, without standing out. That's my theory. But mics are all kinds of colors these days."
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ee8c9g | Why is it faster to charge your phone from 0% to 50% than it is from 50% to 100%? | Or even, why is it faster to charge from 50% to 75% than it is to charge from 75% to 100%? | Engineering | explainlikeimfive | {
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"Lithium ion batteries very sensitive to over-voltage which could cause unwanted chemical reactions start to happen inside them. They can cause damage, overheating or even an explosion. To avoid over-voltage, the charger charges the battery at full speed (current) first, and slows it down as the voltage approaches the maximum voltage.",
"Imagine filling a large box with many smaller boxes. When you first start to fill the large box up, you can just toss the smaller boxes in really quickly. But as you start to fill the large box up, you realize you have to slow down and take more time to line the smaller boxes up in order to fit more in. The more smaller boxes you want to add, the more time it takes you to re-arrange the boxes that are already inside to fit more in."
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ee95b1 | When people say electric car batteries are “just as harmful as fossil fuels” is there any truth to that? Why is this claim made? | Whether it be true or not, what is the reason people say batteries are harmful for the environment? | Engineering | explainlikeimfive | {
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"All the responses in this thread so far are correct in spirit but wrong in overall outcome. Electric vehicles (EVs) are overall better for the environment than conventional vehicles. Yes, making a battery is harmful for the environment, you are mining various metals that result in water pollution etc. And charging them can be bad if the grid you are on is 100% coal (unlikely and grids will improve constantly over the life of your car). But even on a polluting grid we can compare how much CO2 (or other harmful pollutant) a vehicle makes starting with mining the metals all the way to recycling it at end of life. It's called Life Cycle Assessment (LCA). And because EVs are more efficient than conventional cars, when you look at their entire life cycle, they make less pollution. Check this [interactive graph]( URL_0 ) based on a peer reviewed article. You can customize the energy grid and see that even when an EV is charged on 100% coal it is cleaner over its lifetime than a normal car. Cars are of course still bad for the environment and EVs are no exception. Take a bus or ride a bike if you want what's best. But unless you only care about aquatic pollution, and not climate change, respiratory disease, ocean acidification etc., then EVs are a huge improvement. Source: PhD student studying climate change mitigation",
"\"What kind of batteries are used in electric cars? Most lithium-ion batteries in electric vehicles in Europe in 2016 were produced in Japan and South Korea, where approximately 25%–40% of electricity generation is from coal. ... This emissions recovery period is no more than 3 years even in countries with relatively higher-carbon electricity such as in Germany.\" I literally just googled this. It's the pollution involved in the production of the batteries. Because a lot of coal is used.",
"No truth whatsoever. This argument is much older than you think - it was [first directed at the Prius twelve years ago]( URL_1 ), back when the Prius was the de facto green car. All those talking points were debunked repeatedly, but the thing about false claims is that it has a tendency to persist even after being corrected. That’s why those claims were then made against EVs as well, even though it’s not true - lifecycle analyses demonstrate that even if you account for the batteries, EVs are [still better for the environment than normal cars]( URL_0 ). The most truth you’ll find in that claim is that EVs are also harmful to the environment - however, that is also true of every method of transportation or locomotion ever, so it doesn’t mean much.",
"It's not true. My experience is that this claim is made by people who want to feel better about driving a fossil-burning car."
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eedv4b | Why do car windows freeze up and sometimes they don't at the same temp or colder? | Engineering | explainlikeimfive | {
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"Depends on the relative humidity, dew point, and wind in addition to just temperature. The moisture in the air condensates on the glass like a cold glass of water, and the temp and wind chill can freeze it even above a relative freezing temp as the glass is colder."
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eeex15 | Why do old instruments such as a Stradivarius violin “play” better than modern instruments? | Engineering | explainlikeimfive | {
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"There is no inherent reason for this to be true. You could copy the exact techniques used to make a Stradivarius today and end up with a Stradivarius that functions like a Stradivarius. Humans tend to conflate price with quality, so will trick themselves into hearing a good sound on an expensive instrument due to the sheer fact it's expensive. Plus of course, not to mention that people's tastes vary a lot. Just because one person might prefer the sound of a particular instrument doesn't mean everyone does. It's probably worth considering that there's quite a lot of natural selection going on here though. For an old instrument to still exist, it must have been kept in great condition and received painstakingly delicate repairs over the years. And you would only go to this effort in the first place if the instrument you're preserving is a good quality one. The idea that old instruments sound better may just be a product of the fact that old instruments that sound bad aren't used at all. Additionally, since old instruments tend to be much more expensive, you usually only find them being played by people who already know what they're doing, whereas lower grade players are likely using cheaper, newer instruments. Therefore creating the illusion that old instruments are good because only good players are playing old instruments.",
"Stradivarius violins being \"better\" than modern made instruments is pretty much just a myth now, not real. Stradivarius violins just have a big history behind them that they sounded the best, but compared to modern instruments, again, its a myth that they are better.",
"Actually, that is a myth debunked years ago. A few years back, there were a series of studies done proving that a modern violin, say in the $30,000 price range, is indistinguishable from a Stradivarius. That is both according to the perceptions of a blindfolded violinist playing the violin, and listeners in the audience. Lutiers find it insulting to think they’ve learned nothing in the past 300 years since Stradivarius. URL_0"
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eejpfv | How is Starlink not counter-productive to SpaceX's plan to go to space, would putting 40 000+ satellites in orbit not impede any attempts to exit the atmosphere? | Engineering | explainlikeimfive | {
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"Space is bigger than you think. There are already 29,000 or so objects (larger than 10cm) in orbit around the planet."
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eevheh | Why does every vehicle have a top speed? As in, if a car has a top speed of 250, what prevents it from achieving 251? | Engineering | explainlikeimfive | {
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"There are three basic reasons cars have a top speed: 1. Electronically limited: a car manufacturer sets a limit where the car’s computer won’t let it go faster (eg 155). This is done for safety reasons, because the car is technically capable of going faster than is safe because of tires, handling, or aerodynamics. 2. Gear-limited: basically the car can hit the engine redline in top gear and cannot go any faster without another gear or exceeding the redline. 3. Drag Limited: the car doesn’t have enough power to go any faster. Aerodynamic drag is exponential, so at high speeds it requires MUCH more power to continue to accelerate. Any one of these could prevent you from going faster- and there is a limit where even 1 mph can’t be obtained without some sort of assistance like a tailwind or downhill.",
"In real life, a governor. It's a device that limits fuel and oxygen into your engine, capping its maximum speed well below your speedometer's max. If you remove it, your engine can only create so much power by combining fuel, oxygen and fire. More cylinders can get you more power (so a v8 is faster than a d6 generally). A better air intake and exhaust system can get you more power (that's the rumble from a muscle car or race car). A more aerodynamic body makes the car move easier per unit of power (which is why race cars aren't shaped like school buses). Speedometers are generally numbered according to the real top speed if you remove the governor.",
"To continue off what previous reply-ers stated, basically at a certain speed the air resistance will equal the amount of force provided by the engine. Theoretically it could go 251 if the engine was more powerful (assuming that there is no governor and the only thing keeping it from going faster is drag). That is precisely what terminal velocity is... look it up it is quite interesting."
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ef019o | How do Bridges get built across canyons, ravines and rivers in Ancient times? | Engineering | explainlikeimfive | {
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"In general, the same way they are built now. It just took more time and more people/animal power. You can build up for bridges over rivers or relatively shallow canyons. Sink some supports, add scaffolding and start laying masonry or building wooden tresses on top on your supports. For longer expanses, just treat each completed section as the new bank and start another section further out. Build a cofferdam or (partially) divert the river during construction if needed/desired. You can build out for bridges over deeper canyons. Pass some ropes from one bank to another. Use these to support people and wooden frames as you build from one bank to another. Eventually you have either a wooden bridge or a frame to start laying masonry. These processes can also happen incrementally over hundreds of years. It might start with a rope bridge to allow traders to periodically ford a river. Later, a town improves this crossing by building a wooden bridge, allowing oxcarts to more easily traverse. Even later a local lord wanting to show his largesse or improve transit for his armed forces, replaces the wooden bridge with stonework. In each case, the older bridge can be used to help construct the new one.",
"In Julius Caesar’s book ‘Commentary on the Gallic War’ he describes exactly how they built a bridge across the Rhine. This was in 55BC and again in 53BC. First one took him 10 days and the second ‘a few days’. They both managed to get his Legions to the other side and back. This is the wiki entry but I’d highly recommend the book as a whole if you’re interested in many other military engineering feats. The Roman engineers were masters and very quick! URL_0",
"Even in more modern times, people had to be creative. I think the holding of the \"Kite Contest\" to start the bridge over Niagara Falls has to be one of the most ingenious (and cost effective) ways I have ever heard URL_0",
"Note also that a lot of ancient structures were somewhat overbuilt. Lots of support, lots of building materials expended. It’s said that anybody can build a bridge that will stand up. It takes an engineer to build a bridge that will *barely* stand up.",
"Bows, arrows, and rope... one you have the rope in place you can start building with nothing but rope or upgrade to actual wood... doesn't take as long as you may think but you do need people on two sides and THAT takes time.",
"Lots are talking about the construction, but it should be noted that the engineering tools and devices aren't that modern. It's a bit like asking hiw did essays get written without modern writing tools like word processors. The math for bridges is ancient and the buolding levels and sighting equipment is only slightly newer. The stuff used today only make the job easier or allow more complex forms."
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ef4s57 | How do water towers not freeze up in the winter time. | For context I live in Minnesota | Engineering | explainlikeimfive | {
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"In Idaho, the tanks have pumps that keep the water moving around inside. We aren't as cold as Minnesota so that is enough, but adding insulation and heaters would also be an option."
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ef625o | Why do newer cars have a horrible, painful sound, almost like the cabin is being pressurized and depressurized rapidly when you open the window at speeds above 30mph? | Engineering | explainlikeimfive | {
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"helmholtz resonance (or wind throb) is the phenomenon of air resonance in a cavity, such as when one blows across the top of an empty bottle. you turn your car into a simple instrument essentially.",
"I've noticed this happening for decades, grasshopper. It's a resonance, created as the air entering encounters the air being forced out. With more than one window open, the air flows in and out without doubling back upon itself.",
"The phenomenon is called Helmholtz Resonance, and it's for it part to the shape and size of car cabins. It's also due to the fact that newer car cabins are much better sealed than older cars. The air rushes in the open window when the vortices got the back edges of the window, until it builds up enough pressure in the car to where it has to escape, then it resonates as that cycle continues.",
"By “newer” do you mean in the last 40 or so years? Because this has been a thing longer than I’ve been alive.",
"Newer cars probably seal the cabin better, adding to the likelihood of this effect at lower speeds.",
"Happened in my 1982 Accord, my 1992 Audi my 1996 Toyota, my 1999 Subaru, didn’t happen in my 2003 Ford pickup, but it also did in my 2007 Subaru and my 2011 BMW."
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efckqc | Why do some cars have 3 tubes protruding out of the hood engine of the car? | Engineering | explainlikeimfive | {
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"It's an air intake for a supercharger A supercharger is basically an air compressor cranked by the engine. More air being forced into the engine (boost) means the engine can make more power.",
"Do you mean one of these? URL_0 It’s called a bug catcher scoop. It feeds the engine air for a supercharger system, a part of some engines that force extra air into the engine which helps it make a lot more power."
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eff4fg | Why does driving in reverse not have that typical motor sound? | Engineering | explainlikeimfive | {
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"All the forward gears in a gearbox are helically cut, which means each 'tooth' wraps in a spiral around the centre of the gear. This means that there is always a point of contact between the driven and driving gears, making them much smoother sounding and quieter. In contrast a reverse gear is 'straight' or 'spur' cut, meaning it resembles a classical gear, and the teeth of two interlocking gears smack into each other as they turn, producing a whining noise at higher RPMs."
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efgql5 | Why does the same note sound different on different instruments? | Engineering | explainlikeimfive | {
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"The sound you hear from an instrument is made from a fundamental frequency which determines the note you're playing and several 'overtones', which are multiples of the fundamental frequency. Each instrument will amplify some of these overtones and dampen others depending on many factors such as its construction, the materials used, and the specific way the player plucked, pressed or blew into them. The configuration of these overtones is what gives the instrument its 'timbre'. There's another important property of the waves produced and that is their shape. Two waves can have the same frequency but not the same shape. For instance a sine wave is smooth whereas a square wave is choppy and a sawtooth is pointy. The shape of the wave is also unique to each instrument, even when producing the same frequency.",
"Instruments don't just produce a single wave of sound. The loudest wave is the one that determines the note, but the shape and material of the instrument also produce sound waves according to their natural frequencies which is what makes them sound different from one another."
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efpzx6 | How do river locks work? | This Christmas, my family spent an hour discussing and trying to understand how river locks operate. Backstory: My grandparents went on a Danube river cruise this year and my grandfather was in astonished by the operations of river locks moving the boat up the hillside. How do river locks work? | Engineering | explainlikeimfive | {
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"Think of a river lock like a water fall. It is a discrete location where the elevation of a river changes a set amount. The lock itself is like a bathtub in which the water can be filled (to raise the water level inside) or emptied (to lower the water level inside). A boat sails into the lock. The doors on both sides are shut watertight. River water is then added to the lock or removed from the lock to change the water level within the lock to match the upstream or downstream water elevation. This procedure lets a boat jump up elevations like a salmon going upstream to spawn or go downstream without having to go over a waterfall.",
"The water can be stored and pumped an infinite number of times. But the quantity of water in a lock would be infinitesimally small compared to the volume in the river."
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efq1gg | The torque number on the car | Everytime I see car ads they talk about horsepower and torque. I get horsepower being how fast a car is but what is the torque and why does it matter? | Engineering | explainlikeimfive | {
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"Horsepower is a calculated value based on torque and speed (engine RPM). Horsepower = (Torque in ft-lbs X Engine RPM) /5252. At 5252 RPM, horsepower and torque will be equal. High strung race engines in Formula 1 make big power numbers by spinning to an absurd RPM...like 18000 rpms fee years ago. Their torque isn't super high, but they spin 3X as fast as regular engines (ultra exotic lightweight materials and components, strong enough to last a couple of races, maybe 1000 miles total). 175 ft lbs X 18000 RPM / 5252 = 600 HP (not exact numbers, but in the ballpark). A large 15 liter diesel engine in a semi truck makes a lot of power by producing huge torque, but can't spin very fast (heavy, overbuilt components made to run millions of miles). 1968 ft lbs X 1600 RPM / 5252 = 600 HP (again, estimates, but close to real specs). Both engines make similar power but in different ways. You wouldn't put a 2000 lb diesel engine in a F1 car though...nor would you put an F1 engine in a semi truck pulling 80k lbs. You can produce 200 ft lbs worth of torque on a long ratchet wrench without much trouble. But you can't spin it at 6000 RPM's like an engine. Wind turbines produce immense power at very low RPMs...like 1.5 MW, or about 2000 horsepower worth of electricity at 20 RPMs. This works out to 525000 foot pounds of torque that the blades are applying to the center shaft. Nuts. Source: engineer working at a diesel engine manufacturer"
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efqsls | Why do new electronic devices need to be charged overnight before their first use? | Engineering | explainlikeimfive | {
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"They don't, it's just recommended to fully charge them for use because they're just factory charged and then shipped. So they recommend a full charge before setting it up so it doesn't die or malfunction during set up.",
"When u first get the device, the battery level shown might not be accurate due to battery discharge, so charging the device up to full ensures that the battery is full"
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efri6i | Why do cars jerk right before coming to a complete stop? | Engineering | explainlikeimfive | {
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"There is a point at which the inertia of a car under braking force will fail to overcome the friction of the brake pads on the rotors or drums, and the car will come to a stop. The car is not totally devoid of inertia yet, so it comes to a stop with a jerk that is absorbed by the suspension and the friction of the tires against the ground. That jerk is what you're feeling."
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efu56c | some modern car sensors | There are so many, but specifically I'm thinking of: The sensor that can tell I'm inside the lane. The sensor that can tell what the speed limit is without having a gps. The sensor that can regulate the headlights if there is an approaching car. The sensor that controls the wipers based on a very small amount of water. The sensor that can tell if I have my hands on the wheel, even if I'm just steering using 1 finger. | Engineering | explainlikeimfive | {
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"For the first three they use camera's and AI in the form of neural networks to recognize objects like cars, lane markings, and road signs. The automatic wipers use a sensor that is generally located in the rearview mirror mount. The sensor shines light on the windshield under an angle, and then measures how much is reflected. When there is a drop of water on the glass a bigger portion of the light is reflected elsewhere, and the computer will turn on the wipers. And the last one I believe works using a torque sensor that measures the amount of torque that is applied to the steering wheel."
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efvynh | When watches/clocks were first invented, how did we know how quickly the second hand needed to move in order to keep time accurately? | A second is a very small, very precise measurement. I take for granted that my devices can keep perfect time, but how did they track a single second prior to actually making the first clock and/or watch? EDIT: Most successful thread ever for me. I’ve been reading everything and got a lot of amazing information. I probably have more questions related to what you guys have said, but I need time to think on it. | Engineering | explainlikeimfive | {
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"Early clocks didn't have second hands, early watches were not very accurate and not until navigational prizes were handed out did watches improve dramatically.",
"Clocks are just a geared mechanism. So first you figure out the gear ratios needed to make 60 movements of the second hand = 1 rotation round the dial and 60 rotations of the second hand = 1 rotation of the minute hand and 60 rotations of the minute hand = 5 steps round the dial for the hour hand. Then you fine tune the pendulum length to set the second duration by checking the time against a sundial over hours/days.",
"The definitive story about this has already been written by several people much smarter than any of us. Over 200 years ago, the navigation of ships was a matter of intense government interest in England. The \"latitude\" was very easy to calculate. However, the \"longitude\" was based on time, so a very accurate clock was needed. The longer you were at sea, the more accurate the clock needed to be. Here is a 3-hour movie that explains the issue, and how it was solved. [ URL_0 ]( URL_0 )",
"A second is 1/60th of a minute which is 1/60th of an hour which is 1/24th of a day. A day can be measured with good precision by observing the sky. Then you simply subdivide that measurement.",
"Clocks don’t measure time they run concurrently in time so the construct was mathematically determined and then the clocks set accordingly to the construct",
"Background first: When geared clocks were invented, we already had water clocks & sundials capable of showing accurate days and hours. There had even been advanced clocks capable of dividing the hours into smaller divisions since the ancient Babylonians, who chose 60 divisions because it made math much easier in their base 12 counting system. Industrial manufacture of gears came along, and people designed clocks that could indicate these smaller divisions simply by gearing another hand to make 60 full rotations each time the hour hand did 1/12 of a rotation. These smaller (more minute) divisions of the day were called \"minute divisions\". Finally we get to seconds. Gear-making had exploded, growing much more accurate, and it wasn't long before they were capable of making clocks with a second division of the hour, even smaller than the \"minute divisions\", simply by inserting a new hand & more gears with ratios so that the \"second division\" hand would rotate 60 times as the \"minute division\" hand did one rotation. These mechanical clocks could be adjusted to slightly speed them up or slow them down, and each clock would be adjusted until it matched another clock deemed to be accurate. Once the clock accurately reflected one day, gear ratios meant hours, minutes and seconds automatically became accurate (as accurate as you could get in those days, anyway).",
"The first clocks did not have second hands. Sundials measured hours accurately from ancient times, and minutes are 1/60 of that, so you can tell if 60 min pass you should be precisely on the next hour. When they started doing seconds, same thing. When it moves the right speed, exactly 1 minute should pass after 60 seconds and I’d that’s not the case, you need to adjust the speed.",
"One handy fact about physics is that any pendulum of a given length and weight, in a given gravitational environment, will have a specific period. The kicker her is that *this is independent of how big the pendulum’s swing is*. You can try it now. Just take something heavy on a string, or anything that can swing freely, and hold it out in front of you. Pull way up to the right, 100% of how far it can go right, and let it swing, and see how long it takes to swing all the way left and all the way back right again. Now stop it, and move it just a little bit to the right, maybe 50% as far as you moved it before, and let it swing. Now note how long it takes to get all the way through its swing. Try it again with letting it go from 25% to the right. It’s the same time, no matter how far you displace it to start. That’s it’s *period*. A given pendulum of some shape and size, in a given gravitational field, has a constant period, independent of the pendulum’s starting displacement. Or independent of how much kinetic and potential energy it has. What this means is that you can start a pendulum swinging, and it will slow down and slow down and slow down from friction, but as it’s slowing down from wide swings to tiny little swings, the amount of time between the swings will remain constant. You can see where this is going. If you make a pendulum of a certain weight and length, you can get a pendulum that takes exactly 1 second to go through a swing. You grab that pendulum and pull it off center and let it start swinging, and now you have an accurate, super precise and reliable clock that counts off seconds for you. Now you make a gear with 60 teeth, and you put a ratchet on it, and you attach the pendulum to the ratchet so that each time it swings right it slips the ratchet by one gear tooth, and when it swings left, it pulls that gear and rotates it by one tooth’s distance. Since there are 60 teeth, you’ll be moving that gear full circle once every 60 swings. And since you’re using a 1 second pendulum to move the gear, every time the gear turns it’ll be a minute gone by. Now you run a peg coming off the front of the gear, and you get your clock face with a hole in the middle and you put the clock face over the peg off the front of the gear. And you mount your enemy’s mummified finger on that peg, and *voila*, you have a clock with a functioning second hand. Now even if you don’t agree yet on how long a second is, you can standardize time across your kingdom by ordering the artisans to make all of the pendulums of the exact same size and weight. You could even standardize time by having all pendulums made by a central factory and then shipped around to other clockmakers who put all sorts of varied and custom housing on it. Or better yet, you define the pendulum’s shape and weight distribution and just decree that clock makers start with that standard.",
"Because watches are mechanical the speed of the second hand was governed by gearing moving 60 times faster than the minute hand. Before watches were available short periods of time were often counted by using heartbeats which often average around 60 per minute.",
"Read Longitude, Dava Sobel's great book about the quest for an accurate chronometer: ***Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time*** is a best-selling book by [Dava Sobel]( URL_4 ) about [John Harrison]( URL_6 ), an 18th-century [clockmaker]( URL_7 ) who created the first clock ([chronometer]( URL_0 )) sufficiently accurate to be used to determine [longitude]( URL_2 ) at sea—an important development in [navigation]( URL_5 ). The book was made into a television series entitled [*Longitude*]( URL_2 _(TV_series)).[\\[1\\]]( URL_2 _(book)#cite_note-1) In 1998, *The Illustrated Longitude* was published, supplementing the earlier text with 180 images of characters, events, instruments, maps and publications. URL_1",
"Gears and Ratios existed well before Clocks. Also keep in mind that there were actual Clocks before their were watches. This means the gear ratio is the same, but the size of the gears are all that changes.",
"You can not measure time the much same way a piano metronome can’t measure music but you can use the predictive rhythm to set a standard base, clocks are devices that a predetermined mathematical rhythm and are set accordingly to run alongside through space time",
"Trial and error. You have something like a sundial which will give you absolute(ish) time. Early clocks were actually things like \"a bowl with a small hole in the bottom\", which would give you some specific period of time. If you want something like a modern pendulum clock, you can just build one. Run it for a day, and count how many times the pendulum goes back and forth. If (when) it's wrong, you need to make the pendulum longer or shorter, until it's right. The duration names are actually historical. Hours are.. well, hours. Minutes are \"*pars minuta prima*, or the \"first small part\". Seconds are \"*pars minuta secunda*, or the \"second small part\". Dividing by 60 each time was something an Arab scholar decided would be neat in the 1000's or so. So, *by definition*, there are 3600 seconds in an hour, and 24 hours in a day. You just need to keep fixing your clock until it counts out 86,400 seconds in each day.",
"You don't start off trying to measure seconds, or even minutes. It's an evolutionary process. Let's say you're dumped on an alien planet one day. You have no clock and you need to keep track of time. That's pretty much the situation our ancestors were in. First, you look at the day. You stand in a particular spot and push a long stick vertically into the sand. Then you watch and note as the sun comes over the horizon and first casts a shadow on the stick. You track the progress of the shadow on the sand and note when it vanishes at the end of the day. You might notice that the next day and the next, the shadows are slightly different. So you record that too. Eventually, you realise that the time from the shortest day that you record, to the next time the day is just as short, is 365 days (or 360 if you weren't counting very well!). You call that a \"year\". Then you divide the time in the day up. On the most average day of the year you mark the ground with your new \"shadow clock\" (or \"sun dial\") into a convenient number of parts. 24 sounds good - It divides up well. You watch the shadow on the stick as it passes each mark in the sand, and adjust the marks until they are equally spaced. Maybe you use an hourglass with sand in it to help you make sure each \"hour\" is the same length. Then divide up each \"hour\" into 60 \"minutes\" and repeat. Now repeat that with each minute being divided into 60 \"seconds\". THAT's how you know how long a second is. When you design your new-fangled mechanical \"clock\", you design it so that it runs at the same speed as all the things you've measured. Measuring the length of a second is hard, so you just work back up. Does your clock count 60 seconds in a minute? And 360 seconds in an hour? And 8640 seconds in a day? If it's 8641, then you need to adjust and make it smaller. THAT's how you make sure your second hand is right."
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efx87u | How is lithium mined exactly and why does it consume so much fresh water? | My understanding of lithium mining is that there are underground salt lakes which contain a lot of lithium. This salt water is pumped to the surface and is then left to evaporate for several months in the sun. The remains can then be further processed to lithium. What I don't understand is that a lot of articles state that there is a very high consumption of fresh water. Since the actual water from the salt lake most likely doesn't count as fresh water, what exactly is the fresh water then needed for? | Engineering | explainlikeimfive | {
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"text": [
"The brine (salt water) isn’t pumped out. They pump in fresh water, and the brine comes out somewhere else. The freshwater can also dissolve some of the rock salts underground and becomes more brine.",
"From what little I've read, the problem is that mining up the lithium brine also depletes nearby aquifers of fresh water. There was one study done in Chile in which they measured an increase in the levels of the brine pools (water being pumped in) matched a decrease in water levels in nearby freshwater lagoons. So essentially, the problem is that when you remove the salt water brine from the Earth, it leaves space for nearby freshwater to move in and drains surface pools which many rural communities in South America (where most Lithium is mined) depend on. It will also theoretically have an effect on the local ecology as wildlife loses access to water. [Source]( URL_0 )"
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efxqv4 | How did early automatic transmissions know when to shift gears? | I know that in modern automatic cars the transmission knows when to shift gears through a computer system, but how did mid-century classic cars with automatic transmissions know when to shift gears without a computer system? | Engineering | explainlikeimfive | {
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"Early automatic transmissions had computers. But they didn't use electricity, they used vacuum, oils, pressure, levers, and gears to do the same things that modern cars do with electronics. Do a Google image search for \"automatic transmission valve body\" and you'll see exactly what I mean - automatic transmissions are a nightmare of passages that make sure input signals (vacuum) gets translated into oil pressure going to the right place at the right time.",
"Usually through vacuum. The harder the engine is working, the higher the vacuum pressure on the intake manifold (and consequently, less vacuum if the engine is not working hard). The transmission had linkages and valves that would make the transmission change gears in response to the engine work load.",
"I'll try to keep things simple. Let's say this is only a two speed transmission. There is a valve that can either be shifted to the left (low gear), or to the right (high gear). There would be a spring pushing it to the left, and hydraulic pressure pushing it to the right. The hydraulic pressure is created by a pump driven by the output of the transmission. As the output spins faster, pressure increases, and the valve moves to the right. Eventually, the pressure increases enough to shift the transmission into high gear. There is also some sort of mechanism for applying extra force to the left as you press the throttle more. So if you press the throttle, it shifts into high gear later. This is a very very simplified model, but that's basically it. Hydraulic pressure from various sources acting on valves. It's actually kindof a hydraulic computer."
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efzj0c | why are there so many types of tires and how are they all different? | Engineering | explainlikeimfive | {
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"Because there's a lot of different types of cars and road surfaces You could have slick tires with no tread for racing on hot smooth race tracks, these give the best grip but terrible water performance. You could have semi slicks which give you better water performance but less traction Normal street tires come in three basic forms 1. Summer tires - meant for hot roads with limited rain. They're hard when cold but soft when warm and quite and give a nice ride, but don't ever let them encounter snow 2. All-Seasons - they're meant for All-Seasons. They give decent performance in all weather conditions and they're your most common type of tire. They'll have deep groves for moving water away but still be a fairly smooth and quite ride. They'll give much better snow performance than summer tires and better wet performance. 3. Snow tires - These tires are meant for cold weather and snow. They give much much better snow performance than All-Season tires because they stay soft and grippy even at cold temperatures. They have a rougher tread pattern which makes them noisier but more effective in bad road conditions Then you have all the different classifications like Touring, Grand Touring, etc. These are ways to grade what the tire may have focused in, some opt to be cost effective while others opt for premium performance with no regard for cost. You also have speed ratings(the tire will get too hot and rip apart if it goes too fast) and weight ratings and treadlift ratings. All of these things are traded with each other and cost. No one tire is great at all road conditions, let alone being great for all road conditions on all vehicles so having options lets you pick the right tires for your needs. Snow tires in Texas would just wear down crazy fast and Summer tires in Maine would try to kill you 11 months of the year."
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egajrq | pulleys. I am a physics major and I am generally familiar with how pulleys should theoretically work. But in practice if you try to attach a few pulleys in a linear fashion to the same mass, something weird happens. The pulleys closer to the pulled side rise faster, why? | There is a pretty clear demonstration on a smarter everyday video. [ URL_0 ]( URL_0 ) , that's the link, skip to minute 5:40. There is no explanation anywhere on the internet. I am assuming this is a result of some "real world" factor that I am ignoring. Does someone Have an explanation for this? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The string is slightly elastic. The closer it is from the source, the more linear tension in the string, the more crooked it become"
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egbrnz | If a power strip has multiple USB ports, why can't they all charge at max power at the same time? | Engineering | explainlikeimfive | {
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"text": [
"Apologies, but this sounds like a question specific to your power strip that you are asking for a ubiquitous answer for. A power strip with USB ports can be designed so each port could output whatever power the designer desired and USB supports. Your specific power strip probably has something like a 5V 10W supply shared amongst all USB ports. Regardless of how many USB plugs are available or how many things you have plugged in, if it can only supply 10W, you'll only ever get 10W out. Maybe that is a 2A draw for one phone or a .5A draw for 4 phones."
],
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egc4sc | In construction why do they put rock on top of various pipes instead of dirt? | By my understanding they put rock because the dirt would crack or break the pipe because of weight, is this even correct? If so how does the rock not allow the same thing to happen? | Engineering | explainlikeimfive | {
"a_id": [
"fc5j8wg"
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"text": [
"Because the rock won't settle as much. If the dirt under the pipe settles, there won't be anything supporting the pipe underneath and settling dirt on top will increase in weight and stress it. Rock allows water to drain and settled less."
],
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egea5q | Why are slick tyres illegal on road cars yet racing cars use them because they are grippy? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Flat tires are grippy on dry flat asphalt, but super slippery when it rains or really anything else, so they’re dangerous on the road.",
"Race tracks are carefully maintained and cleaned. Roads that regular cars drive on are full of debris. We also drive in heavy rain and weather. Tires that we use on regular cars are designed to still reach the ground to create grip under these conditions.",
"Because slicks Don't work in the rain or even damp conditions it's why almost all racing series either don't run in the rain or have to switch to rain tires. That and they don't last very long like a couple hundred miles at most.",
"Professional race tracks are meticulously maintained. They also use different tires for different weather conditions. Slicks are used in dry conditions. Different rubber compounds can be used. Soft rubber gives more grip at the expense of speed. Hard rubber gives less friction for more speed, and drifting, but at the expense of grip. They also do use treaded rain and snow tires for wet/icy conditions. Road cars though need one set of tires that can work in multiple weather conditions. You're not going to be swapping to new tires every time it rains. Plus most drivers aren't typically as experienced as professional racing drivers. They're more likely to lose control on bald tires, which poses a threat to other drivers.",
"Slick tires with soft material grip well on dry, smooth pavement. Tires with tread grip better on rough, wet pavement."
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egg4n8 | What does material risk mean? | Someone asked me to check whether a system materially increases the risk of operating and maintaining a project. | Engineering | explainlikeimfive | {
"a_id": [
"fc6cu5y"
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"text": [
"It's a non-quantified way of describing a risk that is meaningfully large - that is, the risk is large enough to be worth considering. It is risk that is important enough that it should be managed."
],
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egkxh4 | The difference between particle board, pressed board, MDF, plywood, engineered wood, and other common names of "not solid wood" that are used in common household furniture and shelving these days? | Engineering | explainlikeimfive | {
"a_id": [
"fc7b4sx"
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"text": [
"The difference is in the ingredients, glue, and pressure. Have a lot of sawdust, but low pressure? You can make MDF. More pressure and glue? HDF! Have big shards of wood handy? Lay them in opposing directions before adding glue and pressure and you have OSB! Like a chef would use different ingredients to make different meals, each of these products is suited for different purposes. MDF is without wood grain — so it preforms uniformly in all three directions. These sheets are good for cabinets, because the have a small distance to span, but look the same no matter which direction you cut. In contrast, OSB uses wood that retains a grain — so it is strong enough to span flooring and roofing distances. GluLam retains the largest chunks of wood grain: it can usually span the furthest. That glue is strong, go GluLam can span further than lumber, and is a nice alternative to steel! Bonus! Most of these products UP-cycle industrial waste! The ingredients would be thrown in the garbage (or furnace) if not reused like this. So! Using MDF in you next cabinet potentially diverts sawdust from being burned, and sequesters that carbon in a building - not the atmosphere."
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egszys | Why are zinc-carbon batteries cheaper than alkaline batteries? Are there any uses for zinc-carbon batteries that make them the better choice over other types? | Engineering | explainlikeimfive | {
"a_id": [
"fcadqhu"
],
"text": [
"They are less expensive because they are of a simpler design and require less costly materials that are easier to handle. However, they hold less than half the charge, have a shorter shelf life, and are more prone to leakage. For some low drain applications, their price/hour might come out ahead of alkaline, especially when shelf life limited rather than charge limited. But when you consider the hassle factor of changing batteries or being caught with dead batteries, they rarely come out ahead. Their primary use is for manufacturers who want to include a battery with their product but want it to be the cheapest possible (I'm looking at you, Panasonic). IMHO, there is no reason for a consumer to buy a zinc-carbon battery unless they only have a dollar in their pocket and need a battery immediately."
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egwjva | How are military aircraft carriers transported to the ocean initially? | Do they get assembled at the port? Considering their massive size and weight they can't possibly be 'driven' down on any street, like the space shuttle. What I'm I missing. | Engineering | explainlikeimfive | {
"a_id": [
"fcagf0f",
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"text": [
"They are assembled in dry docks, like most large ship. It's like a bassin that is below the water level, but it's enclose so the water can't come him. They build the ship there and when they are ready, they open the valve, flood the dry dock until the ship can float by itself. After that they open the big door to the river or bay where the dry dock is, the ship can get out and reach the ocean. [ URL_0 ]( URL_0 )",
"They're built and repaired in a drydock facility like all other large ships. Basically a large empty pit that has all the cranes and other facilities needed to make a ship. Once the ship is built/repaired the dock can be flooded making the ship float. Then it can be towed out of the facility (usually located in an estuary) out to sea where it can then move under it's own power."
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egy610 | How is a train able to pull many cargos? | I tried to Google but the answers are over my head. Here is one I am trying to understand. URL_0 | Engineering | explainlikeimfive | {
"a_id": [
"fcauazi",
"fcauht4",
"fcawmhl"
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"text": [
"There isn’t really that much friction on rails, so it doesn’t take that much force to get it started, to help with traction, all the wheels on locomotives are driven, so effectively they can be 8 or more wheel drive, also they might put several locomotives together",
"To move something you only need to overcome the resistance of it not moving. In this case, since a train is on smooth metal rails, with smooth metal wheels, there is very little resistance to the train moving.",
"Trains only accelerate one car at a time. There is slight give in the joints between the cars. So when the engine starts moving forward, only the first car moves. Then the coupling between the first and second car goes taught and pulls it forward. This dominos through all of the cars. Trying to find a video that explains this and can't"
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eh0szl | why do arrows need to have the feathers on their ends? | Engineering | explainlikeimfive | {
"a_id": [
"fcbsjp7",
"fcbribl",
"fcclk6h"
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"text": [
"The idea behind this is to make the arrow more stable as it flies. Imagine the arrow as it flies. One would generally imagine it flying straight, but no one's perfect so imagine you just chucked it ( or yeeted if you prefer) ahead of you and it tumbles slightly end over end. The end with the feather has more drag which will slow the tumbling as it catches more air. On a smaller scale, this is what happens on a normal shot. The feather causes drag to enact a force on the back of the arrow turning the feather end away from the direction the arrow is going.",
"To add drag on the back side and keep the back side on the back. Without a fin on the back it will tumble through the air; the fletching (the fin or feather on the back) pulls the arrow back with drag as it goes through the air keeping it stable.",
"Throw a stick overarm like a baseball and throw a piece of paper (don't crumple it) in the same manner. The stick will travel farther than the paper because it has enough weight to overcome air resistance, but it will also tumble and you'll have trouble hitting anything you throw it at with a specific part of the stick. Importantly the stick will reliably move in the direction you throw it. Hard to predict how it will specifically tumble, but easy to predict what general direction it will travel in. The paper won't travel worth a damn, it will be incredibly inaccurate and their is a good chance the paper ends up going the complete opposite direction in which you tried to throw it. If you watch the paper you should notice that the paper always travels by its edges leading. The paper is so lightweight that moving through the air by it's face encounters too much resistance from the air to it travels by it's edges and cuts through the air. Mechanically it's the same reason it's easier to cut something with the blade of a knife instead of the flat of the blade. Align pieces of paper on a specially shaped stick and you can combine these properties. The feathers on an arrow will prevent the arrow from tumbling because the \"edge\" of the feathers will resist any attempts to travel by their face and since they are fixed to the arrow that \"edge\" is pointed in a specific direction. The shaft of the arrow has weight like the stick and is heavy enough to overcome wind resistance and travel far."
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