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8ypnip | How does current and voltage get "stepped down" from a wall socket? | In Australia, wall sockets are rated at 240V and 10A. On my laptop charger, it's input is 100-240V 1.8A and output is 20V 3A. How does the laptop charger only draw 1.8A from the power supply? Is this through the resistor and how does the resistor draw the certain amount of current? And if the input power is 240\*1.8 (432W) and the output is 20\*3(60W), where does this additional power go to? I know transformers can change voltage and current, however they will account for most power and little will be lost. Thanks | Engineering | explainlikeimfive | {
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"It uses a transformer. A transformer has two independent coils which are coupled magnetically. The ratio of the turns in the secondary to turns in the primary is the factor which the voltage is reduced by. So 100 secondary/1000 primary gives 0.1x240 or 24V. Ignoring losses in the transformer, the energy in the primary is equal to the energy in the secondary. Since the secondary is lower voltage, it has higher current (by the same 10/1 ratio). Laptop supplies don't use 50/60 Hz transformers because they are heavy and inefficient. They convert 240VAC to 340VDC then switch it off/on at around 100 kHz before sending it to a transformer. Edit; the other part of your question > if the input power is 240*1.8 (432W) and the output is 20*3(60W), where does this additional power go to? The input current rating is worst case which would be at 100V (100x1.8=180W). That only accounts for part of the discrepancy. The other part is likely due to [power factor]( URL_0 ) (voltage and current not in phase) and power-on surge rating. The power adapter is about 85% efficient.",
"There are a few ways. Transformers change voltage quite efficiently, but they only work with AC. DC can be changed with things like voltage dividers and multipliers (stepping it down and up, respectively), or DC-DC converters. The thing about the current is that a device will draw a given amount, and no more, based on the applied voltage and its internal characteristics. The simplest to understand is a resistor. The amount of current that will flow though it is a function of the applied voltage and its resistance and nothing more. If I apply 12 volts to a light bulb from a source that can supply 1 amp, or 1 million amps, either way the bulb will draw the same current from that 12 volt source. Looking at your power converter, first multiply the 1.8 amps by the 100 volts it can accept; that gives it 180 watts. It can draw less current at higher voltages to get the power it needs, but it has to be rated for the most current it might need to draw, which will be at the lowest voltage. There's also going to be a fair bit of internal loss (that's why it gets hot), and it will be overengineered so that little manufacturing flaws or other things don't melt it. Even with all that, it's not drawing 180 watts and supplying 60. Those are just working numbers for rating purposes, not the actual exact figures."
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8yq2zv | Why do some countries use 220v outlets and what are their pros? | Engineering | explainlikeimfive | {
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"The higher voltage means smaller wires can be used which is cheaper. It is cheaper for everyone in the country. This saves a lot of money. The higher voltage requires tougher safety rules, more ground fault outlets, smaller permitted extension cords, thicker insulation, whatever it take to reduce injuries.",
"Power = Voltage * Current. So 220V can deliver more power (for ovens, space heaters) without more current (current heats up wires). So that's the pro. The con is that 220V can be lethal, whereas 120V hurts a lot but usually isn't. In any case, if even more power is needed, typically what you see is multiple phases being used, compounding 2 x 120 into a 240, or 2 x 220 into a 480."
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8yws6p | What is the difference between centrifugal force and centripetal force | I have heard that people often confuse the two but I have never gotten a clear explanation between the two. | Engineering | explainlikeimfive | {
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"If you take a ball on a string and spin it around in your hand really fast - centrifugal force feels like it's pulling the ball away from you, centripetal force is being privided by the string to keep the ball from wandering off on it's own course.",
"First of all, centripetal means \"toward the center\"; centrifugal means \"away from the center\". (Think \"fugitive\") When you spin a ball around on a string, the ball doesn't go in a straight line because *centripetal* force, exerted by the string, is acting on it. By Newton's Third Law, the ball exerts an equal and opposite *centrifugal* force on the string, which transmits it to your hand. Centrifugal force can also be described as a *pseudoforce* that transforms a dynamics problem to a statics problem, but I think that's out of ELI5 range.",
"Centrifugal force is a phrase in place of what in reality is inertia. If you don’t know what inertia is, it’s the resistance of an object to change in its position and state of motion. So a ball will have less inertia than say a brick wall if you tried to move one of them. Centrifugal force is also known as a fictitious or pseudo force. It is usually present in a centrifuge among other instruments. A centripetal force is a force that makes an object follow a curved path and gravity is an example of this. Source: Wikipedia/google",
"Let's say there is a spinning ring structure in space and you're standing on the inside of it. From an outside (inertial) frame of reference an observer would clearly say: It is a spinning ring, and the (structure of the) ring is exerting a force onto you overcoming your inertia so that you move in a circle in space, ergo there is a centripetal force accelerating you towards the centre of the ring. From your (rotating) frame of reference the ring does not move with respect to you but you experience a downward force away from the centre of the ring, ergo there is a centrifugal force. = Same thing , different frame of reference"
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8ywt8b | Fitting only two tyres in a car | I read the Greek official driving test and it stated that if you can only change two tires it should be the front ones.why so? Doesn't it depend if its is front wheel drive, rear or 4x4? | Engineering | explainlikeimfive | {
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"That's just bad advice. Two fresh tires go on the rear, always Your rear tires keep you traveling in a straight line. Traction on the rear tires keep you from spinning out when cornering or braking. Your front tires help you steer, and brake but neither of those are helpful if your rear tires slip and you spin. You're better off continuing to travel in a forward direction than traveling sideways off the road > [\"When tires are replaced in pairs...the new tires should always be installed on the rear axle and the partially worn tires moved to the front.\"]( URL_0 ) > -Tirerack",
"Front tires tend to do most of the breaking as weight of the car shifts forward under breaking due to the momentum. That said, you should still make sure all tires are good condition."
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8yx2tv | Do cars use up petrol due to speed or rpms? | Say I'm driving down the highway at 75 mph @ 2500 rpm. Then I decide to speed up to 80 mph. Even though my rpms increased to accelerate to 80, they soon fall back to 2500 rpm. Am I essentially, at that moment, using the same amount of petrol at 80 mph as I was at 75 mph? | Engineering | explainlikeimfive | {
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"RPMS and the motor curve matched with the transmission. Motors are more efficient at certain RPMS. Along with the load on the engine. Steep hill vs flat ground. To check the load vs certain gears and rpms you need exhaust temp. Lower temp is better and more efficient less fuel being blown out.",
"> Even though my rpms increased to accelerate to 80, they soon fall back to 2500 rpm That's where you're wrong. If you're doing 75 at 2500rpm, in the same gear, 80 would be 2666rpm. Your tach might be imprecise or whatever, but to go faster, either you need to upshift or increase engine speed. Now, that's only part of the equation. Another aspect is your engine ECU and your fuel injection system. There's a balancing act between the air resistance and your engine. Most cars have optimal MPG somewhere in the 40-60mph range. Say you're going 30mph at 2500rpm in 4th gear (these are hypothetical numbers that would differ depending on the transmission, but it works) and you're getting 25mpg. If you increase your speed to 60mph and go up into 5th gear at 2500rpm, you're going twice as fast at the same rpm, so you might think you'll get double the mpg, right? Not quite. Air resistance is higher and your engine has to push more, so your fuel injection system is going to put in more fuel in order to maintain that speed. It's probably not going to be twice as much, so you might get something like 40mpg. Mileage drops when you get past your optimal speed as the resistance becomes higher and higher, so above 60mph would decline from that 40mpg."
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8z0g3n | How do Sniper Rifle Scopes work? | Engineering | explainlikeimfive | {
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"Scopes **are not** parallel to the barrel. That would be fairly useless because bullets drop due to gravity. What you do instead is angle the scope downwards slightly and \"zero it in\" so that it correctly matched up with the arc of the bullet at a particular range. [You can see a diagram on this page]( URL_0 ). If you want to shoot a target at some other range, you need to compensate. Some scopes have a range adjustment that changes the alignment. Some scopes have markings that represent changes in range (eg - look up a \"mil-dot scope\")",
"You are standing on your mates shoulders. Both of you are shining a laser pointer straight in front of you. The lasers are hitting a wall 50 meters away. Of course, your lasers don't hit the same spot. To do that you lower your laser until it matches your mate's spot. Now, so long as you don't change your angles, you can move around all day shining your lasers at things and they will always match up at 50 meters. If you want to hit something at a different range then you will need to change your angle again.",
"Scopes are aligned slightly off from parallel to the barrel so that they intersect at a particular distance – a hunting rifle might be \"sighted in\" at around 100 yards, for instance. At longer ranges, The shooter needs to take into account factors like wind speed, air resistance, and the vertical drop of the bullet, and long range scopes have scales and adjustment tools to accommodate these considerations."
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8z44t1 | Why can’t the Panama Canal just dig a deep canal and remove the locks? | Engineering | explainlikeimfive | {
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"Oceans are in constant motion. This means that they surge up and down. Because the Pacific and Atlantic Ocean aren't connected anywhere *but* the Panama Canal, you're channeling the entire difference in wave height at any given time through the canal. Without the locks, that means you'd mostly get a fast running channel from the Pacific to the Atlantic... that reversed from time to time to run the other way. Navigating that channel would be an enormous effort. Instead, they install locks to prevent the water from flowing unchecked from one end to the other.",
"The middle part of the canal system is 85 feet above sea level. So you'd need to dig the rest of the canal 85 feet deeper. For about 40 miles. So that would be an enormous amount of earth and rocks to dig and move, much more than was dug to place the locks as they currently are. That's not even the biggest issue, though. Look at the map: URL_0 See all that water in the middle? The canal isn't a single cut across Panama, it's two canals, with locks, with **a huge ass lake in the middle**. Gatun Lake *is* the canal's middle, you enter the lake at one end and scoot across. Leveling the canal would be draining the entire lake (which itself was filled to create the canal) and drastically changing everything in the area, which now has created a large healthy rainforest area. That lake is the source of drinking water for Panama City. Weirdest part is, the mean sea level at the Pacific side is 20 feet higher than the Atlantic side owing to differences in tides. I have no idea what would happen exactly if you were to make a singe level clean cut across Panama but I wouldn't want to be standing in the middle of it when the Pacific Ocean decides it's time to be 20 feet higher than the water on the other end."
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8zbs9t | Does leaving a phone or battery pack plugged in after it’s fully charged damage the battery? | Engineering | explainlikeimfive | {
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"No. A lithium-based battery can not be overcharged even if you leave it plugged in at all times because as soon as it is fully charged (100%), the internal circuit prevents further charging until there is a drop in the voltage. Source: URL_0"
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8zh8bu | Why do large commercial ships use diesel engines to produce electricity, to then power the turbines? | Engineering | explainlikeimfive | {
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"Ships go fast and slow. Diesel is more efficient at particular engine speeds (ask the engineer). Keeping the diesel at the efficient point and using electricity to power the propeller turns out to be a good idea.",
"Point 1. Electric motors don't need transmissions. Having a generator and a motor is more efficient than having a motor and a transmission. Point 2. At least for cruise ships, in the mornings, around 75% of the generated power is used for the people, not thrust. (heating water for showers, blow dryers, cooking, etc) If you need that much power generation, it doesn't make sense to have generators, diesel motors, and transmissions.",
"To take the already-mentioned issue of efficiency to an extreme, a diesel engine **cannot** operate at 0 RPM. You need to start it moving and this gives it enough energy to ignite fuel and continue moving. If you want to couple a moving engine to stationary wheels, there are a few ways to do this including the torque converter used in automatic transmissions, but these all involve some inefficiency and if you want them to be large, they’re expensive. In cars that works out OK, but in ships *and trains* where you have the space/money to invest in an electric generator/motor system and the amount of fuel was high enough to justify those fuel savings, it ends up making sense to use the system you mention (which is more efficient).",
"Moving extreme mass (cargo ships, trains) at comparatively low speed is best done by electric motors because they generate maximum torque at zero RPM. Their power is maximized near the starting line. Diesel internal combustion OTOH generates maximum torque midway through its powerband and is most efficient when running at a particular steady speed which is NOT zero. This makes the diesel powerplant-electric drive configuration sort of magical because by applying maximum torque where it is most needed it can move gargantuan loads with the most economy and reliability.",
"This is more common on trains. It is beneficial because diesel engine efficiency is difficult to manage during times of acceleration or especially climbing a hill. An electric motor revs quicker than a diesel so response time is lessened. With this setup, the electric motor draws power from the battery which is then recharged by the diesel/ generator. So the battery is acting as a buffer allowing the diesel engine to recharge the battery at a more gradual pace. More gradual of a pace means lower surge in demand equals more efficiency. Also, having a giant generator makes it more cost effective to feed power take offs such as thrusters or compartment doors, cranes etc.",
"This isn't used all the time. It's common to have the diesel engine connected directly to the propeller shaft, so that the engine runs at the same speed and direction of the propeller. So, if you want to reverse or do emergency braking. You'd stop the engine, then restart it running in reverse. This can be time consuming so makes precise navigation difficult. You are also limited because the engine has minimum speed so extremely fine control is also difficult. These days, better mobility with advanced steerable propellers or additional thrusters are available. For example, cruise ships which are designed for comfort, or scientific/industrial ships which need precise positioning may have additional propellers at the front and sides. This allows the ship to spin around or move sideways without moving forward. In this type of ship you can't have a big diesel on each propeller so, you have electric motors on each with diesel generators for power. In addition to the flexibility of multiple thrusters, electronic speed control gives much more precise control of motor speed making these ships much more steerable."
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8zk5v4 | Why EU and AUS use same octane rating (RON) but cars in Australia can run on 91 while EU cars need 95? | Engineering | explainlikeimfive | {
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"Mostly it's due to regulations. Europe has much stricter regulations about what sort of fuel can be sold than Australia does, as well as much stricter regulations about the quality of the fuel (I believe EU has a limit on Sulphur content in ~~Diesel~~ petrol fuel of a max. 10ppm, whereas Australia has a limit of 150ppm for 91 RON and 50ppm for 95 and 98 RON). This means that Australia has a cheaper fuel option (91 RON, as you've mentioned) but also means that Australia tends to get cars optioned with lower tech engines (the Honda Jazz in Australia, for instance, gets an older SOHC engine that runs on 91 RON, compared to the higher tech, more powerful DOHC engines for Japan and Europe) or where the engine is the same, it'll get tuned so it makes lower power to be able to run on the lower quality of fuel. In terms of *why* the Australian government has done this: - lobbying from the former manufacturing industry, who were able to make cars for the local market that were suited to the lower quality fuel - Regional characteristics - the countries around australia all have similar fuel quality, so maintaining the same level means common tunes for vehicles, and lower costs through not having to re-tune for the local market - Lobbying from fuel providers, who are resistant to change It looks like this will be changing soon though, as the car manufacturing industry is dead in Australia, and most car companies now want Australia to more in line with the more dominant European market, especially as the new [fuel and emissions standards]( URL_0 ) are coming into effect, which will make it even harder to run on 91 RON fuel and still pass Euro emissions. As a result, there's likely to be a phase out of 91 RON fuel in Australia in the next few years (assuming it's agreed upon by parliament, and gets through all the red tape) otherwise Australia could see itself become even more of a dumping ground for older, inferior engines as the next generation aren't able to run on 91 RON fuel. [edited for accuracy]",
"Most cars in Germany used to run on RON 91 as well in the old days. Then came stricter emission norms, which were largely implemented using higher compression. Now RON is a measure how likely a fuel mixture is to ignite without a spark. Higher compression makes this more likely. Hence, you need higher RON (less likely to spontaneously ignite) fuel. Now just looking around Australia it looks to me like the emission standards aren’t even remotely as strict as they are in Europe. Hence I guess you can still get back with RON 91 consuming engines.",
"ELI5 for people who dont know cars/fuels Question: Why are cars in Australia able to run on lower quality fuel compared to cars in Europe? Answer: Europe has strict rules on car emissions. To achieve this cars need high tech engines, which needs higher quality fuels to run. Aussie rules arent so strict regarding emissions so they can still use low quality fuel for low tech engine cars.",
"Why does the one I use say 87?",
"Interesting. In South Africa we have 93 and 95 inland (higher altitudes and lower air pressures), and 95 and 97 on the coast.",
"As a side question, why is fuel in Europe so damn expensive? Here on a holiday now and paying the equivalent of $2.40 a litre! Average in Sydney is rarely above $1.50",
"Engines suck air in, mix it with fuel, compress that mixture by moving a piston up, and then use a spark to ignite it, which pushes the piston back down and makes the car go. The problem is that compressing fuel can cause it to ignite without a spark, which means the fire starts early and pushes the piston down while it still wants to move up. This can cause damage, or at the very least force the car's computer to change its settings in a way that hurts gas milage. \"Octane rating\" is just a way of telling how resistant a fuel is to igniting without a spark. The more an engine compresses the air, the higher octane fuel it needs to run properly. This rating is increased by adding ingredients to the fuel that make it cost more. Now, there are two main ways to increase the power of an engine. First, you can increase space inside the engine by adding more or bigger pistons. Second, you can increase the amount that you compress the air/fuel mixture, so you burn more fuel in the same amount of space. As a general rule, it is cheaper to use the first option, so the cheapest way to build a car is to keep compression low, and make the engine as big as it needs to be. In most places, increasing the amount of compression is only used in more expensive and higher performance engines. In Europe, they tend to tax engines based on how much space they have inside for burning fuel, so manufacturers try to minimize that. By increasing compression, they can use a smaller engine for any given power level, so it is worth the cost to do so in order to save tax money. As a result of this, cars in Europe tend to have higher compression, and thus need higher octane fuel than other parts of the world."
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8zooqt | What would happen if a Nuclear Power Plant was left unattended? | Engineering | explainlikeimfive | {
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"There are safeguards that would trigger and shut the whole thing down safely. They'd just turn off. If you're asking about potential for meltdown, that's possible but exceedingly unlikely. Even in that case, most reactors (all American reactors) are designed to meltdown as safely as possible. Most people don't know that a \"meltdown\" is actually a safety feature. The reactor is positioned over a huge block of cement. In the event of an uncontrolled reactor (it's still not a bomb), the heat generated melts the cement, the reactor sinks, and the cement hardens behind it, \"melting down\" into a cement tomb designed to contain the reactor and radiation for as long as it has to.",
"To add to what's been said, the vast majority of land based nuclear reactors are designed in such a way that the water surrounding the core is necessary for the chain reaction to continue. Even if every SCRAM fail-safe fails, once the water boils off the core, the reaction stops. That doesn’t prevent a meltdown, but it does limit the danger of one. The fuel would melt and pool at the bottom of the reaction vessel. It might leak and it might make it into the water table (all of which would be bad but for chemical and not radiological reasons, mainly). Pretty quickly, however, the molten core would cool and solidify. It would remain dangerously radioactive for millennia, but it would never “go off” like a nuclear bomb. Naval and some Soviet designs don’t work this way. They're essentially slow burning bombs, as I understand them. The good news is that water is just about the best shielding against radiation you could ever ask for and as long as the ship goes down in deep water, there's no problem. This has, in fact, happened. A submarine at the bottom of the ocean is probably a better containment vessel than anything we could engineer for the task. Even then, they wouldn’t go off like a nuclear weapon. They’d melt down and continue reacting until the fuel was dispersed or depleted. Chernobyl style reactors, however? Don’t be down wind of them if civilization collapses. They explode, but still not a nuclear explosion. They'll kick a whole cloud if radioactive death into the atmosphere though. They're closest to what we would call a “dirty bomb”. I’m not a professional. I’m just a nuclear hobbyist. Some people collect stamps.",
"Most of these things are designed to shut themselves down if they don't receive maintenance. So probably they won't be the huge problem shown in, like, 'last man on earth'",
"A nuclear plant with modern safety systems would likely eventually encounter some sort of fault scenario and shut itself down. They are designed to be *extremely* failsafe now, both due to the actual threat presented, and the perception of threat presented.",
"My former nuclear engineering roommate explained it to me like this: without monitoring it may overheat. When this happens there are automated emergency processes that try to make it not overheat anymore and stop the reaction. If those fail it will keep getting hotter and things will start to melt down through the floor. There's no nuclear explosion but it's possible for there to be a sudden release of pressurized steam or hydrogen if things have gone really bad."
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8zpzi0 | Why do drones usually have 2 blades on each propeller? | It's obvious why they don't use 1 blade (It can't be balanced and will just vibrate). But why not 3 or more blades? Does it have something to do with efficiency of flying, or something else? | Engineering | explainlikeimfive | {
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"For a given amount of weight, the fewer blades, the better, as more blades start to interfere with each other aerodynamically. You point out why one blade is impractical, so two is going to be your starting point. Three and four are sometimes used on aircraft, but that is mostly to save space, as the blades can be shorter."
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8zsyny | How do they get huge cranes off the top of tall buildings? | Engineering | explainlikeimfive | {
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"Above 200 feet, the cranes, called tower cranes, build themselves. A hydraulic unit is installed when the crane is first built and is pulled into position by the crane itself. The crane then lifts the next section of tower from the ground and onto the hydraulic unit. A team of workers unpins the crane sections and the hydraulic “climber” lifts the top of the crane enough for the next section to be inserted. The team pins that section into place and secures the crane to the building. To come down, the process is reversed. Below 200 feet, usually a large Hydraulic crane can build the tower crane. The “hydro” cranes have more capacity, but also take up more room on the ground. [Erecting]( URL_1 ) [Climbing]( URL_0 )",
"Bringing in an ever taller portable crane to lower them down. The highest truck-mounted crane can reach 550 feet up. Or in extreme heights, by helicopter."
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8zvi9s | How those transparency changing windows work. | Engineering | explainlikeimfive | {
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"Liquid crystal displays— passing electricity can orient crystals in ways that let them pass light. When electricity isn’t applied, the crystals “relax” to a random state, blurring light as it passes. Other designs would have them totally shut out light. It’s VERY similar to how phone or computer screens work. Except for one particular type of screen (OLED), light isn’t produced as needed, where needed, in the colors needed. Instead light shines from the back of the screen, and LCD technology is used to block some colors and allow others through to create the right color/brightness when where it’s needed. The windows are (hopefully) cheaper than computer screens because they uniformly apply power to change the color/transparency of the whole window, rather than needing to control each pixel individually."
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8zxriq | What is the difference between a bore and a valve in a car engine? | I can't seem to tell the difference. I'm trying to learn about car engines and some places say valve others say bore. So what's the difference? Thanks! | Engineering | explainlikeimfive | {
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"They are two completely separate measurements. The bore is a measurement of the size of the hole that the Piston goes up and down in, and valves are very small piston like rods that open and close to allow the air-fuel mixture in and the exhaust out.",
"They're completely different things. The \"bore\" of an engine cylinder is the measure of the cylinder's diameter. \"Stroke\" is how far the piston moves up & down inside the cylinder. The valves are the openings at the top that open & close to allow fuel in, compression to happen & exhaust to escape."
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901wan | Why did it seem to be the protocol during WWII to fly so many bombers together in such tight formations? It seems in doing so, it was easier for them to be taken out by Flak and other defenses. Would it not have been more effective to have the sorties spread out? | Engineering | explainlikeimfive | {
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"From URL_0 : There are a number of advantages to flying in formation. In the case of the bombers, it was to help with defending against fighters and it also helped with navigation. For example, in Europe, B-17s could cover each other's blind spots while they were flying in formation. It also made it easier for fighters to provide cover to the heavy bombers. It's easier to defend a large formation of planes than it is to defend a single plane. The formations of planes also ensured better coverage of the areas that the allies wished to bomb and they helped ensure that bombers didn't get bombed by each other. In the Pacific, flak wasn't as much of an issue. The Japanese produced less than 200 guns that were capable of reaching the B-29s that raided the home islands. and much much much more from there."
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904a82 | How does Silicon Wafer Production actually work | ELI5: How does Silicon Wafer Production actually work, I am currently working in the Industry (support staff) and I cannot get my head around the process of creating a wafer and once it is created how is it turned into a chip we see in devices? | Engineering | explainlikeimfive | {
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"1. First they take a little Crystal of silicon and put it in a vat of melted silicon,and spin in slowly,after a while a YUGE perfect crystal forms around the small crystal,about 30cm in diameter.its internal structure is perfect. Then this crystal is cut up into 30cm discs and polished and shipped to the Chip makers. 2. Now the chipmakers coat the silicon wafer disc in photo resist material,then they take a “stencil” of whatever electronic design they have come up with for the chip and shine UV light through a lens(to miniaturize the design to like 1cm or less) onto the wafer Coated with photoresists,UV Light reacts with photoresist changing its chemical composition.Later in the parts with the UV light based patterns are washed away using a solvent,exposing the silicon underneath. Next other solvents are used to etch the exposed silicon,not the remaining photoresists. Once the silicon is etched, the rest of the photo resist is also washed off leaving only the etched silicon shape 3. Again the same photoresist is applied/patterned/washed/etched off only this time the exposed silicon areas are bombarded by ions,called doping. Doping changes the electrical characteristics of silicon to be conductive or non conductive. 4. Again the same photoresist is applied/patterned/washed/etched off.This time the removed photoresist makes way for copper deposition,used to connect the various sub components of the chip,copper is deposited in vapor form by a machine.Photoresist applied,Photoresist removed,excess copper removed,rinse and repeat.This process is repeated until actual interconnects are formed between various parts. 5. Now the over 9000 chips on the wafer are tested,then cut up and shipped to a packaging facility where they are placed in little black packages of plastic or resin or epoxy idk what the material is called,here a machine connects tiny gold wires to the pads of the tiny silicon chips,there wires connect to the pins that are outside the black packaging,which you can see and use. 6. Now these packaged and tested black chips are sold to electronics makers who use these chips in their own products,these chips are attached to PCB boards using solder,which is a Tin/Lead alloy that melts at 200C 7. Now these electronics products are used for a wide variety of things,like for example the evil automod bot that deletes all my posts on this sub,for example Oh also,all the over 9000 chips on a given wafer aren't 100% pristine and working correctly,so their non-working damaged parts are shut off,and sold as cheaper and low performance versions compared to the top-tier All OK high end,high performance,high price versions.This is called binning,and this is what causes the difference between your Intel i3 and intel i7 processor variants"
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9056b6 | How did WW2 proximity fuzes work? | Engineering | explainlikeimfive | {
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"Proximity fuses on what? Marine mines? There are two mechanisms I know off. Either by measuring vibrations in water and detonating when vibrations match frequency of ship engine or by measuring distortion in electromagneitc field and detonating when large metal mass approaches. Is this what you are asking about? & nbsp; EDIT: Assuming you mean proximity fuses on sea mines. There are two mechanisms I know of. **Mechanic resonation** Each physical object has something called resonance frequency. That means if you mechanically vibrate this object at this frewuency it will vibrate more than at any other frequency. It is like the object \"wants\" to vibrate. This alows you to design delicate switching mechanism that if submited to vibrations like this switches electric circuit or detonates a mine. Now each ship needs to be propelled somehow so it has engine room that turns the screws. Operation of this engine room causes vibrations that travel trough the hull of the ship into the sea and can be detected at relatively far distance. These vibrations would trigger the mechanism and detonate the mine. **Electromagnetic** If you take a compass and put large piece of metal near it the compass will be affected by it. The arrow will point different direction. Since ships are huge hunks of metal this principle can be used in proximity fuse to detonate the payload.",
"There were a few types, but the most important were the ones which used radio waves. They had a radio transmitter/receiver combination which picked up reflections from the nearby aircraft. Since the shell was moving rapidly towards the aircraft, the reflected waves were shifted in frequency due to the Doppler effect (police radars use the same principle). The frequency shift was detected and triggered the fuse.",
"If you are talking about artillery and anti-aircraft shells, they used small radar sets inside the shell. Since the distance they wanted between detonation and target was small, they didn’t need to be big or powerful, so they could fit them in larger shells. The principle they used is called the Doppler effect. This is when radar or sound waves you send out bounce back at you faster the closer you get to an obstruction. So they programmed the fuze to detonate once the radar bounceback is fast enough."
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907z7u | what is the difference in functionality between flat head screws and phillips head screws? | Engineering | explainlikeimfive | {
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"You're less likely to slip out of a Philips head thereby making it faster and safer. The trade off is you need what was once considered a special device whereas before you could have used anything from a coin to a knife.",
"The earliest screws are slot-head, because they're easy to make. A blacksmith can make one by hand, just by cutting a slot into the top, and the appropriate tool is basically a pointed stick. They're also fairly attractive screws, so they're often used for finishing touches. However, it takes some dexterity to keep the screwdriver centered in the slot, so they're not the fastest to use, and they really can't be driven with power tools effectively. If you over-torque them, the head will often strip out and become unusable. Phillips screws are designed specifically for use with power tools. The shape is self-centering so you can run them in quickly, and the driving surfaces are actually slightly tapered so if you try to over-tighten them, the tool will slip out without seriously damaging either the screw or the tool. They need specialized equipment to manufacture, but the head can be formed in a single operation by a press, so they're still pretty cheap. There are other screw designs which also have the self-centering features of Phillips but *don't* slip under load. Robertson (square-drive) screws, Torx, and internal hex are all like this. They're honestly better for most things, especially now that technology allows us to build torque-limiting screwdrivers, but they don't have the dominance of Phillips. For Robertson, that's a patent issue; for the other kinds it's more because they're newer and more expensive to produce."
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90cdsi | Why the nut does not unscrew itself from the bolt? | Engineering | explainlikeimfive | {
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"They can, if subjected to vibration, which is why in critical applications they are secured with a twisted piece of wire.",
"Ig because there is enough friction holding it to the screw. A lot of the time the nut will unscrew over time if it's being shaken or jarred."
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90gtqc | how does a tugboat have the power to tug or haul such big tankers or boats? | Engineering | explainlikeimfive | {
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"A tuboat is basically a small shell wrapped around a very powerful engine. It also moved very slowly, and sometimes multiple tugboats are required.",
"To add to the rest, it's really easy to start the movement of something in the water. You can push a pretty heavy boat and start a movement in it, slow but surely. On land, the force to initiate a movement is really big. You'd be able to keep a car moving much easier than you'd start it to move from a stop. For the boat it is less relevent."
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90k93t | Why aren't shaving razors made with carbide or industrial diamond? Wouldn't they stay sharp almost indefinitely? | Engineering | explainlikeimfive | {
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"\"modern\" razors are disposable razors. Before that people used a straight razor. If you make an incredibly sharp razor it will be incredibly brittle, if you make it of something sharp and not brittle it will be incredibly expensive. If it rusts, it'll rust in the bathroom and oxidation dulls a blade far more than use will. The other option is to have a blade head that you can use a few times and get a new one. If you chip a carbide razor, it's expensive trash.",
"The very nature of razors means they **have** to wear out quickly. Razor edges are **microns** thin, which means they're prone to corrosion and wear very quickly, there's literally no other option; and all razors are about the same. It doesn't matter if it's a $0.99 Bic disposable or a $30 a pack five blade vibrating number. The 5 Bladed one might stay sharp longer (less use on each blade per shave). You can make your razors last longer by thoroughly washing and drying them after each use (oil on skin and moisture corrodes them faster). Ultimately, the best option is to grab a well made straight razor and a stropping strap. A single straight razor can last literally a lifetime, and when stropped correctly will retain its sharpness indefinitely.",
"Diamond that thin would be incredibly brittle. The material needs to be hard enough to maintain an edge, but it also needs to be tough enough to not chip. Same goes for carbide.",
"It absolutely matters what kind of material razor blades are made out of. The bulk material can be different, and you can put very hard wear resistant coatings on that material. For example, The Mach 3 kind have something called diamond like carbon on them (bonded like carbon but amorphous, and easy to deposit.) This used to be advertised. This really helps with reducing corrosion and improving wear. I have found that at least rinsing them and isopropyl alcohol to make sure they are totally dry really helps keep them alive. It absolutely matters what materials these are made out of, and the highest rated comment on here right now is totally wrong. I stick with Mach 3s because I have found them to be the longest lasting, and it's probably because of that coating. No I do not work for that company :-). But I am a materials scientist and I used to work on DLC and diamond thin films.",
"Diamonds are *hard*, but they're not *sharp* in the way razors need to be. Carbide steel won't last any longer - as others have noted. However, if you want to escape the expensive razor blade gimmick (which you may not - a Mach 3 is a good razor that will almost never cut you), you can get a traditional double-edged razor. The blades are about 10-15 cents each if bought online in bulk, and you can usually get 10-15 shaves out of each one. More, if you're careful about the blades. Much easier than a straight razor, and much less maintenance. I've used one for six or seven years now for shaving at home. I keep a Mach 3 for travel or when I'm in a hurry. /r/wicked_edge can help you. There's no real need to spend a fortune (although you can, if you like, and the fancy stuff sure is nice). A basic kit of razor, blades, brush, and shaving soap can be had for under $50 if you're trying to economize, and it will last you for a long, long, long time. Seriously: I bought a sampler pack of 50-100 blades (somewhere in there, can't remember) to try different brands when I started double-edge shaving, and I still haven't used them all. I've used maybe five blades on my Mach 3 in that time for travel or quick shaves. I did switch from shaving in the morning in the shower (shaving as necessary task) to shaving in the evening at the sink (shaving as pleasant grooming experience).",
"My rotary electric razor is probably ten years old and still on the same set of blades. They cut by shearing rather than relying on an extremely sharp blade. That sharpness means it wears out faster. Even diamond knives need resharpening and they are very fragile. Plus they cost too much. Carbide is cheaper, but very brittle.",
"Disposable razors have really come a long long way. High end ones ($3-$8 per cartridge) should last you a month now and use higher quality steal that won't rust quickly. Low end ones ($0.10 - $1 for 10 pack at local dollar store) are really only good for one or two shaves and will rust overnight. Thin metal strips are used because they are flexible and easier to contour to your face. It also means less metal is being used there by driving down the cost. Diamond is brittle and much more expensive. The industry is highly competitive and they're constantly trying to come up with new and better razors in order to pitch them to the market. I've personally tried every razor on the market that I know of. this includes everything from what I can find in dollar stores all the way up to the highest price razor. I tried old-fashioned methods and new methods and I'm always willing to try something else. My facial hair is really thick. My personal conclusion is that different razors have different advantages. For day to day shaving before work I shave in the shower with a Gillette Fusion. However, if it's the end of the day and I have sunscreen on my face I will use something a lot cheaper with 3 blades because the Gillete will get clogged and become useless. This is because the blades are too close together to handle thicker pasty materials. I've used other five blade razors, but find they rust faster as I leave them in the shower. Im a really hairy guy and I'll use other razors for different body parts. For example, I'll use a woman's razor with guide wires when I shave my balls. My back does well with the Hydro.",
"Razor manufacturers are trying to make money. Not much money in a product that lasts forever, ask Singer. Like the story about the two guys and the bear, you only need to be better than your next best competition and everybody only needs to be good enough."
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90o885 | Why do some submarines have diving planes on the sail, while some have them at the bow? | Engineering | explainlikeimfive | {
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"Fair water planes, on the sail, are less desirable from an operational standpoint. They don’t contribute to keeping you surfaced once they clear the waterline on the surface. At periscope depth, they tend to broach, increasing a submarines visibility while simultaneously reducing the crews ability to control depth. Their only advantage is that they are out of the way when the submarine is brought along pier side or other ships. Bow planes are better in that they are never out of the water during operations. They can be locked at an up angle on the surface to help keep the submarine on the surface at speed. They don’t broach at periscope depth. Their disadvantage is an engineering one, they need to be retractable or foldable in order for the submarine to moor. Generally, if your naval architects have mastered bow plane technology, that is what your submariners want for ship control."
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90r03b | How do train rails how up such heavy train carts? Won't they buckle under the extreme weight? | Engineering | explainlikeimfive | {
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"The rails (at least the ones used today, rather than the ones in the 1800s) themselves are very strong, they just transfer the force into the ground. But you are correct, the ground needs to be engineered properly to be stable. The soil is compacted, and gravel put on top of it to allow for slight movement.",
"Train rails are steel sitting on huge wooden blocks supported by coarse gravel. The entire structure is designed to bear weight without shifting, spreading it out into materials selected to be able to withstand the weight."
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90w9yb | Why aren't modern refrigerator / freezers made to be vacuum sealed if things only spoil with oxygen? | Wouldn't it save a lot of energy too if there was only a very small section cooling things that you desire to be cool like particular produce, cold dishes and beverages, with everything else in the larger space simply preserved at room temperature? Then the only power used otherwise would be the vacuum process every time you opened and closed the door. Or would all our food explode? | Engineering | explainlikeimfive | {
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"The bacteria in the food need oxygen, true. However, not all of them do. The ones that do need it can still make energy when they're deprived of it, at least for a short time. This happens in humans when we exercise, and some of our cells start starving for oxygen. The process to create extra energy produces the lactic acid that makes our muscles burn. All the bacteria need is a few minutes to start the degradation of the food. They can get any nutrients they need from the food they're in, and there will definitely be some oxygen in the food itself. So, even if the fridge or freezer door is closed for a long time, not all the bacteria will die. The reason we keep food at cold temperatures is because this either kills the bacteria or forces it into something like hibernation, where it's too cold for the bacteria to be able to do anything. I also imagine the power needed to vacuum seal a container of that size would be expensive. People might not want to pay for an appliance that costs that much. It could also pose structural issues, as a strong vacuum might be too much for a typical box-shaped fridge. The vacuum of the container may also make things like yogurt, which usually has an aluminum lid, explode. Drinks might explode as well. I'm not entirely sure about solid foods like meats, but I imagine much of the food would lose its moisture more easily. This would be because the vacuum would pull water molecules out of the air and food, drying them out and ruining the taste and texture.",
"to couple on to the other responses pulling a vacuum on a fridge would cause any container inside to explode"
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90y7d4 | How are dams built? It seems to me like the issue of all the water they must hold back would make it extremely difficult. | Would they have to build it with all that water rushing over them? Or from the top down? I’ve always kind of wondered this, thanks! | Engineering | explainlikeimfive | {
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"Sometimes the river is temporarily redirected during construction, but remember that the massive wall of water only exists *after* the dam is finished. Before that it's just a river at the bottom of a valley. If the dam has a bypass at the bottom, it can remain open until the dam is completed so the water level doesn't rise. Once the dam is closed, the reservoir will fill.",
"They build diversion channels to get the water to flow around the site where the dam will go, and then they build the dam itself.",
"From what I’ve seen they divert the river from its normal course by digging a man made bypass. It allows the water to go around the area where they are building the dam",
"The reason you build a dam in the first place is so that you can control the flow of water out from the dam independently from the water inlet naturally provided by the river. In other words, no matter how you build the dam, there is a tunnel or a canal that lets water bypass the dam. Build the tunnel first. Place all the hatches on it so that you can control the use of it, then let the water take that manmade route instead, unhindered. Then build the dam. It’ll be dry and safe to do so, as long as you pay attention to spring flooding and such (if the amount of water coming exceeds what the tunnel can swallow, your’ in trouble with the dam construction) that the dam is later supposed to catch and make into an even flow. Once the dam is finished, let the next spring flood fill the dam by limiting the flow that goes through the tunnel."
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9107ig | How did mechanical slot machines work to allow for randomness? What mechanically went on inside of them that insured randomness? Were they also constructed in ways to guarantee an average win/loss rate over a long enough period? | For the win/loss rate question what I mean is that currently slot machines can be set to have a certain payout rate, such as on average, it will pay out (fake numbers) 40% of the time, but will still bring in money 60% of the time. Did old mechanical slot machines have the ability to change this payout percentage as well? | Engineering | explainlikeimfive | {
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"Most of them use a spinning wheel that's geared to the dial you see. The wheel has notches on it such that (to extend your fake numbers) 40% of the wheel is notch. The notches are \"randomly\" arranged on the wheel in the sense that you don't know the pattern and the pattern has a long repeat relative to the dials you can see. It's a brass analog pseudo random number generator. That said, there is also quite a bit of random vibration in the machine, that's really random, which further randomizes the wheel PRNG.",
"Check out [this video.] ( URL_0 ) It explains the inner workings of a mechanical slot machine."
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910hgg | How do laundry dryers collect lint? | Engineering | explainlikeimfive | {
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"Hot air is blown in through a vent in the drum, the air exits the drum by a second vent which has the lint catcher placed between the drum and the rest of the exhaust system. Since the hot air has to travel though all your clothes, it picks up the lint and is blown towards the exhaust vent and lint catcher"
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9115bq | When shooting a full blow sniper rifle, how does the scope not hurt the eye/head? | Engineering | explainlikeimfive | {
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"A rifle scope isn't put up to the eye like a telescope. You will keep a gap between the eye and the scope lens, this is called correct eye relief. That said, you can see loads of videos on YouTube of people using scopes wrong who do get themselves hit in the eye, this is called being a knob.",
"You don’t actually put the thing on your eye it’s like an inch and a half away. Also when the gun kicks back it will be in your shoulder so it doesn’t really move much.",
"Avoid contact with the scope with your eye or head before pulling the trigger. And if you're braced and positioned properly, your head will recoil with your shoulders(recoil will also be minimal) the gun is braced on, keeping about the same distance from the scope."
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9125rv | How do people and animals not impale themselves on tranquilizer darts when they fall? | Engineering | explainlikeimfive | {
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"Nobody uses tranquilizer darts on people. Unlike in movies, in real life a darted animal doesn't just fall over. It slowly gets sleepier and more lethargic, and usually lays down.",
"The darts are relatively small. They’re often used on larger animals so even if the animal fell on the dart while laying down, there’s very little additional damage that could be done."
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915vx1 | why is it that wind farms stop their turbines from spinning? | I understand that they will be stopped for maintenance reasons, but I feel like I see more turbines stopped then spinning, and I’m wondering why that is. | Engineering | explainlikeimfive | {
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"Two most plausible reasons: 1) Too much power in the grid right now. 2) Too strong winds right now, they have to secure it against spinning out of control.",
"Related to wind, - the wind is a bit too gentle. Running the turbine costs more in maintenance than the actual production would give in income. - the wind is too strong. There is a maximum rotational speed. Exceeding it will damage the machinery. As a result, it pulls the brakes. Related to maintenance, - every minute of production counts. It is after all an advanced piece of machinery sitting waaay up in the air on top of a tower. Once the mill has been operating a specified number of hours, it calls for maintenance. And stops while waiting. Because the last precious hours of production until maintenance should be spent making as much money as possible. If the maintenance guy is expected to show up a week later, it makes sense to compare the production output you can have now with the production output you can have later the same week if the wind is stronger. - something can actually break down and cause a full stop. Related to production, - the power grid connects producers and consumers with each other. The production is spent In real-time. In other words, if no customer wants the production right now, it’s senseless to produce. - some wind farms have a power grid connection where the grid can’t have the full production served to it if all the mills in the farm are active at the same time. The mills will then cooperate. Establish which one is running and which one is halted. Keep tabs on which ones are close to maintenance, figure out if one got a more favourable wind and another ought to be shut down. And so on.",
"They need to match the electricity output to demand, if there is not enough then that energy will go to waste, or even cause surges that could damage the grid. This is a problem a lot of people are looking into, ways to use or store that spare electricity, like pumped storage hydro or even using electric car batteries. But for now they have to just turn them off"
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916vjx | How did they stop water to build the Hoover dam? | Engineering | explainlikeimfive | {
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"First, they had to divert away the water. This is usually done by building a tunnel upstream and letting the water flow through it instead of the construction site. Next, they form the dam and let the concrete set for a couple of weeks. After the concrete is sufficiently strong, the tunnel is plugged up and the water is directed back to the dam.",
"First, a series of tunnels were dug from below where the new dam would be, going upstream through the rock - four tunnels, each 50 feet in diameter. The entrances were cleared LAST, of course, so they wouldn't flood, and were protected by cofferdams, which are temporary dams around a riverbank that are basically just walls stuck into the bottom of the river. When the tunnels were ready, the cofferdams were literally blown up. Once the tunnels were built and the water diverted, NEW cofferdams were built across the river at the tunnels to protect the Hoover Dam construction site and keep it dry. Then build the dam, close the diversion tunnels, and let the river fill up the space behind the dam. The cofferdams protecting the Hoover Dam construction site didn't actually have to be taken out, because, remember, Lake Mead is deep but the river was not.",
"Great video from Modern Marvels on Hoover Dam construction. Four tunnels were created out of solid rock to channel the river around the dam site. [ URL_0 ]( URL_0 ) Skip to 16:49 to see how the Colorado River was diverted around the dam site. Edit: skip to 13:53 for animation of the construction process showing the tunnels and coffer dams. Life was cheap during construction, 112 men died. The first to die and last to die were father and son, J. G. Tierney and Patrick Tierney. If you visit Hoover Dam, take a tour, you get to go inside the dam and walk along one of the inspection tunnels.",
"First you create a diversion channel that goes around the site of the dam. Depending on the location of the dam, this can be a tunnel through rock, or just digging a temporary riverbed around the site. Next, you install a cofferdam upstream and downstream of the location of the dam. This forces the water into the diversion channel(s) and leaves a dry area for the dam to be built. Once the dam is finished, you collapse the cofferdams and the diversion channels and the river flow returns to normal, just with the dam restricting flow causing a reservoir to build up behind it.",
"They started off building two tunnels going around the site of the dam. These tunnels were built above the waterline. They then dumped truckloads of rock and dirt into the river blocking it and creating a small temporary dam. The water level behind this dam rose until it came up to the tunnels which were built and diverted the water away from the construction site. This allowed the construction workers to work on the dam on the dry river floor. The dam includes valves which allows the river to flow under the dam if needed. The diversion tunnels also have valves which allows them to be sealed. When the dam construction were done the valves were closed off and the water level were allowed to rise to the top of the dam."
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91ejtg | Why do automakers make interference engines if they can destroy themselves if the timing belt fails. | Engineering | explainlikeimfive | {
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"It allows engine manufacturers to optimize various performance features of the engine. One that comes to mind is compression ratio, which is good for a wide variety of performance situations, such as fuel efficiency or raw power."
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91mibq | Why aren't 2x4s, 1.75x3.5, or 1.5x3, so that when you put 2 of them together in framing they are square? | Engineering | explainlikeimfive | {
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"In the old days they dried the wood before cutting it so a 2x4 was actually 2x4. Then they realized they could save money cutting wood before it dried. Makes it easier to cut and they get more wood from same log. You can still buy a true 2x4 but it’ll cost you more."
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91r2pn | When 2 or more sound wave met, it produces sounds from the initial waves despite its form is altered to something else. How is that even possible? | (*Not sure if these fits here. Please point me to another sub when it isn't).* I understand that when waves (lets say sinewave and squarewave) met they produce a new waveform that has characteristic of its sources but they will sound quite different. However, when I open an audio file with audio processing software, all the original sounds is still there. What is actually happen here? I'm so confused | Engineering | explainlikeimfive | {
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"The two waves are only altered *where* they meet. Once the waves move passed each other, they go back to being just a single wave. Remember what sound waves are, vibrating molecules, most often for us, air molecules. At the point where two waves meet, each wave is trying to get the air molecules at that one point to move a certain way. The result of the two forces acting on those molecules is that they move a way that is different from each of the waves. But once the waves pass each other there is now only one wave acting on the molecules. So basically waves can pass through each other and come out the other side unaltered."
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91wa94 | How do they lay the foundation for structures in water without it being pushed away by the water? | Engineering | explainlikeimfive | {
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"They generally divert the water to another area or build a coffer dam in the middle of the body of water and then pump the water out. Really going to depend on the specifics of the project."
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91xppv | How does a turbocharge in a car work? Does it really facilitate the engine that much? | Engineering | explainlikeimfive | {
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"Fuel burns much more efficiently when the air that's used to facilitate the combustion is compressed. Every molecule of fuel needs to find a molecule of oxygen for fire to happen. If there's too much fuel, it clogs up the reaction, so you can't just add more fuel. But if you add more oxygen first, then every fuel molecule (or at least, more of them) can still find the necessary oxygen, and because they're so close together so it happens more quickly. What's more, the air heats up from the compression so it's already hot *before* the combustion. The hot air already wants to expand before the combustion, which makes the reaction much more powerful. This is what [turbo]jet engines are doing with the big fans on the front of the engine: those fans compress the air before it reaches the ignition chamber, making the engine more powerful. Part of the energy of the exhaust blasting out of the back is captured using fans on the back and used to turn the fans on the front. That's what your cylinder is doing during the [compression stroke]( URL_0 ) right before the fuel is ignited. The more compressed the air is, the more fuel you can add, and the more efficient your engine is. But air resists compression. Your cylinders can only push so hard, not least because you still need room for fuel to be injected. The best option would be to \"pre-compress\" the air before it gets put into the cylinder. A turbocharger does exactly that. *Exactly* like a jet engine, the exhaust blasting out of your engine block provides some power, captured with fans, which are linked to another fan on the front of the air intake for your engine. That fan compresses the air on the way into your engine, so your cylinders don't have to do as much work, and you get hotter, more compressed air into the engine with less loss of power to do it. Superchargers do the same thing, but fan is connected to the crankshaft coming from the engine, so it's powered directly from the engine output instead of siphoning power from the exhaust.",
"As load is put on the engine, the exhaust pressure increases. The causes the turbo to 'spool up (whirring noise). When the turbo spools up it is forcing air into the combustion chamber. As there is more air, you can add more fuel and have more power output of the engine. This can greatly increase output power of the engine. But this creates extra stresses on the engine, so it must be built to deal with the extra stresses."
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921swn | What is the purpose of having multiple gears in a transmission in a vehicle? | Engineering | explainlikeimfive | {
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"This is how I explained it to my learner driver son. To move a stationary car you need a tough, high powered gear (1st). It's like wearing a boot to climb a mountain. It uses more energy per unit of distance traveled. However, once the terrain becomes less difficult you may want to change your footwear to give you more speed and become more energy efficient. When you're well on your way a sports trainer will give you more speed. Sorry, now that I've written this it sounds a bit daft. It's better explained in person.",
"If you've ever ridden a bike with gears - that's why! You need a low gear to start off or go up a steep hill, but your legs can only go so fast so then you need a higher gear once you're rolling to go faster without wearing yourself out. The engine has a range where it's happy and working at its best (all the little moving parts are moving at their happy speed) - outside that, too slow and the engine can't keep turning, too fast and the moving parts can't move any faster so the whole thing stops working, or the forces make it fall apart.",
"If you only had one gear, you're gonna have to choose between a low gear with high acceleration but a slow ass speed like 40 mph, or a high gear that'll get you to top speed but takes a full minute to 0-100 mph, and wrecks your clutch after 6 uses. Or something in between with neither speed nor acceleration. Having multiple gears means you don't have to choose."
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9240vx | Why are space rockets so hard to handle? | Here are more questions just to clarify my point. Why does every rocket need its own calculations for the launch? Why is it so hard (impossible?) to set constant variables to succeed every time in rocket launch? | Engineering | explainlikeimfive | {
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"You need to look up what they call \"the rocket equation\". Lets say you want to throw 10kg into orbit. Orbit speed means you have to accelerate it to something like 9.4 km/s (thats per _second_). Thats pretty fast. To accerlate your 10kg AND your rocket to that speed you need a certain amount of thrust. That means bigger engines, or engines that burn longer both of which requires more fuel. But that fuel has mass that you ALSO have to accelerate so now you have to bring MORE fuel to accelerate the other fuel, but wait the mass you have to accelerate drops as you burn fuel so now you need less fuel to accelerate it..... and now you have a 2nd or 3rd order differential equation. Now throw in multiple stages (why multiple stages I won't get into), the reserve you need to maybe land your rocket like SpaceX, and you have some hard math. If your payload changes weight at all, you have to recalculate the whole shebang. As for the control - the aerodynamic forces acting on a rocket that is accelerating to that kind of speed - and before it leaves the atmosphere - are tremendous; and even relatively minute shifts in center of gravity of your rocket (as the fuel gets burned up) or a shift in payload (remember that resupply rocket in The Martian that blew up?) means you have to have control surfaces or nozzle gymbols to constantly adjust the thrust so its through the center of mass or things start tumbling and the forces rip it apart.",
"If you launched the same rocket from the same spot in the same weather at the dame time of day on the same day of the year, the math *would* be the same. Since we're impatient and computers are good at math, it's easier to recalculate for a launch tomorrow than to wait for the variables to match. Rocket science is complex, but ultimately predictable. That's precisely why we're able to launch so many rockets every year with minimal failures. The failures that do occur are generally hardware failures, not failures due to miscalculation. Rockets are metal cans full of explosives after all, there's a lot that can go wrong. Most of the difficulties are not i the math but in the manufacturing."
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92udyj | A toothpick is 2mm in diameter and a small kerf rotary saw blade is 2.4mm. Does this mean there is as much weight made in saw dust during manufacture? | Engineering | explainlikeimfive | {
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"Check out this video: URL_0 Looks like they use a 1.06mm blade to cut strips, and then a punch press to break it into individual toothpicks. So there's no sawing, per se. That first step where they \"unravel\" the log looks like mostly pressure and a sharp wedge used to pry the wood apart, which would be pretty low waste. And the punch press that splits into toothpick shapes looks very low waste as well. Looks like the majority of the waste would be removing the bark/smoothing the log, and then throwing out all the defective toothpicks, but that doesn't look like it will be very close to 1:1 at all."
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92wy9z | How do combined power sources on Cars and Bikes work with each other?(Electric bike example) | I have en electric bike. If I pedal and pin the throttle, the bike accelerates faster than if I pin the throttle alone. When going up a hill, if I pedal, and throttle it's far easier and faster for the bike than just the electric motor alone. I can hold the throttle steady, shift up to match the motor's output, and pedal to help the motor out, its far easier to pedal at speed but I can still feel work being done by my legs. Alone neither, the motor nor myself can "wheelie" the bike, but if I pin the throttle and am in a low enough gear and pedal hard, I can pick the front wheel up off the ground without trying. This is all 1 system going to the same rear wheel. My pedals are connected via gears and a chain, my motor is in the hub of the wheel and spins itself against the wheel mounts. 2 different sources of power to the same drift shaft. I do not have a pedal assist system. Both my chain and my hubmotor are independent power sources from one another. And on that same note, how do 2 Piston engines, or Electric motors, ect. drive the same driveshaft or chain drive in hybrid piston+Electric engine cars to achieve greater total torque and horsepower? Lately I've been seeing some sports cars come out that have electric drive motors combined into the drivetrain along with a very powerful piston engine to produce an even greater amount of power. How on earth does this work? How does combining sources of power like this ease up the workload on the motor and my legs, and generates greater output than either by itself? In my head, one should overpower the other's input and become useless, but that's obviously not correct because my own experience shows that's not true. | Engineering | explainlikeimfive | {
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"Both are pushing the wheel around the axle at the same time. There's no problem with that. It's the same as if two people are pushing a stalled car. Whatever torque the motor is applying against the mounts (or mounts against the wheel, however you wanna look at it) is added to the torque applied by the gear cassette. It's as simple as 5 ft•lb + 10 ft•lb = 15 ft•lb."
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934vos | How do tunnel booring machines navigate under ground to such precision that they can dig from two sides and meet in the middle, almost dead on? | Engineering | explainlikeimfive | {
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"You can measure angles. distance and change in incline to a high precipitation so you can know where the machine is. Today you use laser based system to fixed points to measure distance, angles is measured with high precision in the instrument that is called a [ Total station] ( URL_0 ). the older non distance measuring instrument is a [Theodolite]( URL_1 ) that have existed since the 16 century. There have been other similar devices in the past. So by using instrument like that you can know the path of the tunnel. You also need to know the starting point. [Surveying]( URL_2 ) metods by measuring angles from multiple point and create triangles are called triangulation. You only need to measure a single distance to calculate all other. The measured distance is done on some flate area. Large scale surveying with high accuracy have been done on continent scale areas from the 19th century laser distance meter have accuracy of 1.5 mm for distances of up to 1500 m. The angel measurement is up to 0.5 arc second. A arc second is 1/3600 of a degree. So the measuring equipment we have today manage what is need without a problem. Digging from two sides in a mountain was already done by the romans for aqueducts. The sometimes missed a bit but manage to connect them. So when it was possible with the equipment back then it is relative easy with modern surveying equipment."
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935xbq | There are buildings in Europe, Asia, Africa, and South America which have been around for centuries or millennia. Why can't build those kind of quality, time lasting structures today in the USA? | Engineering | explainlikeimfive | {
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"* They would cost a fortune in materials and labor * They aren't well insulated * They make it very difficult and expensive to use modern technology (heating, cooling, electricity, networking, plumbing, Wi-Fi) * They have limits on size (you can't create a highrise/skyscraper) * They are difficult to change/remodel once created"
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939w1n | How is the temperature of tap water regulated? | Engineering | explainlikeimfive | {
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"The hot water temperature is regulated by the thermostat on the water heater in the building. The cold water is regulated by the ambient ground temperature that the supply pipes run through. The ground is quite cold below the surface layer even on the hottest of days."
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93bway | Why do bicycle helmets have holes? | isn't it better for helmets to be like . [instead of this] . Edit: added bicycle helmet to show the difference | Engineering | explainlikeimfive | {
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"Sweat. On a bicycle you are presumably exercising. With a fully closed helmet it would get uncomfortably hot and wet under the helmet as you are trying to shed the heat you generate by sweating. The bicycle helmet allows lots of air to reach your head so your sweat can evaporate properly."
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93iq8a | How do they make iridescent stainless steel cutlery? How does the light effect work? Will it wash off? | Engineering | explainlikeimfive | {
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"Do you mean those rainbow looking knives? A lot of those are covered with a layer of titanium oxide. When heat or an electrical current is used on titanium, it will change colors. Since this is a coating, it is possible to wash off. Compared to pure titanium which the color can be reapplied with the correct set up. [Here is a color chart for pure titanium colors done at various voltage.]( URL_0 )",
"This is typically done by applying a thin layer of titanium nitride to the surface of the metal. This is done by a process called [Chemical Vapor Deposition.]( URL_1 ) The layer is very thin, comparable to the wavelength of light. Depending on the thickness, the coating causes [interference effects]( URL_0 ) with incoming light reflecting off the underlying metal surface. Certain colors interfere more than others, since different colors of light have different wavelengths. So some colors are reflected better in different areas depending on the thickness there. You can also produce a similar effect just by heating stainless steel carefully in air. This causes chromium in the steel to form a similar layer of chromium oxide which produces similar interference effects. This can be seen on welds on stainless steel or titanium. The oxide layer forms as the weld cools. However, titanium nitride is much harder and stronger than chromium oxide, so the coating better resists being scratched or rubbed off. In contrast, oxidation colors on steel are easily rubbed off."
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93jema | Why do train tracks have wooden planks between the rails, and why do they have a scattering of rocks? | Engineering | explainlikeimfive | {
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"Those pieces of wood (or sometimes concrete) maintain the proper spacing between the rails and held support the weight of the train. The gravel around it provides support for the ties or sleepers (the wooden or concrete bits) and provides good drainage so the ties aren't sitting in mud or water all the time."
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93qco5 | the difference between single phase and three phase power | I hear these terms thrown around a lot and just not sure what the difference is. | Engineering | explainlikeimfive | {
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"Both are forms of alternating current (AC) Alternating current cycles from +120V to -120V, 60 times per second (assuming you live somewhere that uses 120V 60 Hz for mains power) Single phase power means that all of the power in the wire alternates from +120V to -120V. Three phase power has three wires, all alternating from +120 to -120, all at the same frequency, but they are offset from each other. Basically, when Phase 1 is at its peak, Phase 2 is in the middle, and Phase 3 is at the bottom. So in 3 phase, there's virtually always a wire at 120V or very close to it. It delivers a steady stream of power, and that makes it much more useful for higher electrical loads.",
"If you are really 5 years old: * Imagine three people on a row boat. * Single-phase power: One guy is rowing, and each stroke takes three seconds. Stroke - 2 - 3. Stroke - 2 - 3. It's enough to move the boat. It's enough to power virtually any modern equipment -- whose power supply takes those strokes and converts it into useful energy. * Three-phase power: All three guys are rowing. Each person's stroke takes three seconds. But they each stroke exactly 1/3 after the last dude goes. So essentially, you are never more than a third of a stroke off the some guy's strongest. This explanation is not a literally 100% precise analogy, but it's reasonably good enough. One complication is that: (a) in the United States, where 3-phase power is commonly \"line-to-line\", the power of a 3-phase system (at a certain amperage) is not literally 3x the power of a single-phase system (at the same amperage). For reasons beyond the understanding of a 5-year-old, it is 1.732 times greater. (b) in Europe, where 3-phase power is commonly \"line-to-neutral\", it's a better analogy. But whatever, you are five.",
"From someone who has worked 30 plus years in industrial environments. Surprised that everyone in this thread is stating 120 volt 3 phase as if that's even a thing. Most 3 phase power in the U.S. is 480 VAC 3 phase. That's what most industry uses for powering moterized equipment. 240 volt 3 phase is also used but less common. I have never heard of 120 volt 3 phase.",
"Imagine you are holding a pole, and someone else has the other end. The other guy pushes you with the pole, then pulls, then pushes, then pulls, etc. etc. Really fast. You never go anywhere, but you get pushed back and forth. That's single phase power. Now imagine that there are 3 poles, attached to your belt at 120 degree spacing. Pole A pushes you, and then when they are pulling on you Pole B pushes you, and when Pole B is pulling on you Pole C pushes you. All of them push and pull you constantly, but out of synch. You never go anywhere, but you get pushed/pulled a lot. This is 3 phase power.",
"It is basically 3 lines of same voltage that are 1/3 out of phase with each other. AC is push/pull on the electrons created by (in traditional rotary style generators) magnets moving past a coil. The + side of magnets pulls the electrons, then the - side comes in a pushes the electrons, and this goes back and forth creating an alternating current in the form of sin wave. Now, within this generator the coils/magnets are arranged in such a way that as one coil's electrons are pushed another's is pulled and yet another is right in the middle, each of which is it's own phase. These 3 lines leave the powerhouse at super high voltages, 500KV+ and are distributed to the \"grid\". They run to sub stations that take in these high voltages and convert them down to say 10KV. These mid level lines are then distributed to points of use where there is another transformer that converts it down to 110V. Now, most homes and small businesses only need 1 phase, so the transformer for that location only pulls off of 1 of the 3 lines. Converts it to 110V and sends it into the building. However, big industry that uses big electrical motors and such will actually have all 3 phases come in and those 3 phases are fed to the motor. A 3 phase motor is much more efficient, creates less heat and can generate more power."
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93vcd7 | [deleted by user] | Engineering | explainlikeimfive | {
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"In a rear-wheel-drive car the \"hump\" is for the transmission and drive axle which delivers power to the rear wheels. In a front wheel drive car this is usually not the case, pretty clear, although there may be some styling decision based on what that center console is doing in the backseat - lots of backseat A/C, wiring etc. being delivered. I'm looking at the backseat of a '16 Toyota Camry and the floor is generally flat across the backseat but the center console/storage/a/c whatever thing protrudes.",
"It is there to keep the car lower to the ground if the car was built flat on top of all the components running below (driveshafts or exhaust pipe) the car would be a lot further from the ground which is probably bad for fuel efficiency and it’s probably bad for handling as well"
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940g5u | What does exactly clutch do in manual cars? | Engineering | explainlikeimfive | {
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"As simply put as possible; it separates the wheels from the engine. Your engine is constantly turning. That's how it runs. Your engine turns a gear that's connected to the wheels. However, the engine can only turn so fast before it damages itself. You fix this by changing the size of the gears. Smaller and smaller gears mean the engine can spin at the same speed while the wheels turn faster and faster. In order to change gears, the gear has to separate from the engine so another can be put in its place. That's what the clutch does. Automatic cars also have clutches, they just operate automatically."
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943wlx | How do speakers at rock concerts not blow out due to the sheer volume of sound they're outputting? | I was at a heavy metal concert last night (Five Finger Death Punch/Breaking Benjamin for those wondering) and the amount of sound that was coming out of the speakers at that concert seemed like it was going to blow them during the opening acts (Nothing More and Bad Wolves were opening. Great bands all around) and then they still were able to turn it up during 5FDP and BB and nothing seemed worse for wear. How are they able to do this? | Engineering | explainlikeimfive | {
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"The only answer is that they are designed not to. They are very expensive and made of very high grade materials that can withstand the vibrations and stressors they are put under. The loudest speaker in the world is capable of producing 165db of volume. That is louder than standing directly in front of a jet when it takes off at 25m and more than loud enough to rupture your eardrums. The rock concert speakers are no where near that volume",
"Two big things: * We use *a lot* of speakers. This spreads the load out. * The speakers are controlled with sophisticated hardware that helps get the most power out of each box and protects it from signals that are too high. Most speakers have several different sized elements that create the sound. We call these \"drivers\" as a short hand and each one is good at recreating a certain range of frequencies. At home, these speakers are fed from one amplifier and then a circuit inside the speaker called a crossover, splits that signal and sends the proper frequencies to each driver. In professional PA speakers at rock concerts, we use a separate amp for each of those drivers. We also use sophisticated hardware that controls which frequencies go to which amps/drivers. This gives us a tremendous amount of control of how the system sounds. These settings can be adapted for each concert venue we setup our system in. This is one of the major factors that allows pro PA speakers to get so loud. And as others have mentioned, that same hardware has a function called a \"limiter\" that will prevent the signal from ever getting louder than a certain preset limit. The more a system gets pushed into \"limiting\" the worse it sounds, eventually it will just sound like total garbage, but your won't destroy the speakers. Sometimes the systems don't have limiters built in or enabled. I know this because I am a former pro. audio engineer. At the very beginning of my career I destroyed a PA system by letting a touring engineer for a hip-hop artist push my system too loud and I did in fact blow out 12 out of the 16 speakers I had.",
"50kW is a lot of sound power. That is about the energy what is used. The woofers are kevlar reinforced, often liquid cooled, with high power rating. They are heavy and sacrifice some fidelity to efficiency. High frequencies are coming from compression drivers that increase efficiency further. We have tremendous losses in the system so we need to make a lot of compromises. Distortion is high, phase issues are a plenty (when several speakers produce the same sound from several different locations and they arrive at your ear at different times) and of course, distance is one huge factor. Sound works, roughly speaking, like any radiation source. The energy that starts from a point and radiates evenly to all directions work with the inverse square law. 2 times distance means 4 times less energy per every unit of area. This all means that we need a LOT of power and very efficient speakers that project their sound at precise angle so we don't end up covering areas that are too far or are already covered by another speaker. Line arrays do this quite well. These are the long line of speakers commonly hanging from the stage supports. They try to achieve an infinite long line of speakers, straight up and this allows us to for a wavefront, a unified soundwave that travels forward all in the same time. The sound comes out in quite narrow \"cones\" so that they don't overlap too much as they travel to the audience. With a bit of software magic, we can tune them to fit the space we are in. The added benefits are too many to list but one important is coverage. The lowest speakers in a line array are usually angled to the front rows. The curve gradually straightens and the higher up we go, the further the sound is going to travel. This allows us to control the coverage, how even it is and so that we don't need to use all power on a stack of speakers, having the front losing their hearing while at the back you can hold a tea party. Add to this the amount of bass that is put out; home systems just do not have the raw power to move massive amounts of air. The space doesn't support it even if the amps and speaker will. Large spaces allow longer waves to travel without interference. Interference is bad, one cause is the room that bounces of the long waves around so that you can get sound arriving multiple times from just single speaker. Nearly half of the total power is used for subwoofers that cover ~100hz from the full 20kHz bandwidth that we want. The rest of the system takes care of the rest of the 19900Hz but uses power in same magnitude than then subs alone. Sound energy vs frequency is not linear, we need more and more power the lower we go, worsened by our hearing that turns from ears to body and touch/pressure/vibration senses with decreasing sensitivity. High frequencies take additional hit; the air molecules themselves take a lot of energy from fast moving sound waves.The higher we go, the more distance affects sound power. Which is why we need high efficiency and choose compression drivers. High frequencies are also very directional; when with mids we have trouble making it narrow enough, the high frequencies starts to \"beam\" causing hotspots where the sound is uneven in the frequency domain. If we have even sound field, we can fix it.. If it is uneven, we can only fix some of the places while making the rest worse. Oh, and bass travels in all directions, also behind and on to the stage which is another headache (solved partially by using subwoofer arrays but that is another topic and is more about backstage comfort/communication and noise pollution in live events..) Which brings us to last point, software used to control all that and to even out the sound all across the room, from front to back and from side to side. Sidefills and delay towers for ex in stadiums and indoor icerink etc. places are used to project the sound to all paying customers (both the sound and ticket sales will battle this out... sound has a quality of service to think about which means less tickets to sides and far back, and venue and production want to sell tickets. Bad sound brings bad reviews so usually sound engineer knows the best place to draw the very literal line...). Delay towers are called that because the sound comes out delayed, so that it syncs with the main PA, they are behind the FoH, mixing engineers position (Front of House, a lot of terms come from theater...). They can extend the audience area even to places where there is not even a line of sight, like in very large events. In Woodstock, the furthest delay towers were something like half a mile away. Longest i've done was quarter of a mile and around a corner (and had to take it down while riot police were handling the situation nearby, co-incidence.. took a break until the worst fights were over..). The end result is a bit like if you imagine lights in the place of those speakers. Red, green and blue spotlights in each cabinet. Your goal is to make the room look white, combining all light so that the end result is even, nice and smooth, white light on the floor, same brightness and color on every square meter. That is about the same how line array tries to make it all even and smooth, all same \"color\" and amplitude (and no we can't cover the audience area with small speakers, sound wants to be single point source because of that phasing problem i said earlier, line array is maybe the next best thing after single point source, and single point source is impossible to build since it can't have any volume..) Not sure if this helps or not, it is not just one simple thing like \"big speakers\" but multiple technologies and advancements coming together. And to be fair, our speaker size decreased quite a bit when line arrays came to be popular. Before that it was stacks of speakers, long horizontal lines. I remember the last big gig before line arrays took over was Turbosound system that they tried to promote. I can be wrong but it was two horizontal arrays in a curved formation with 18 subs per side and they were about man size in height and about the same in depth.. And on top of that came the mids and highs. It was as wide as the audience area. Lugging that along must've been hell.",
"Line array speakers. Don't use one big speaker, use a lot of speakers. Then, don't focus on audiophile quality, focus on speaker xmax - make sure the drivers can handle a lot of excursion without breaking. If you want a powerful engine, don't use 1 really big cylinder - use many big cylinders.",
"In the early days of rock music, they blew speakers way more often since the manufacturers never intended them to be used at that level. Nowadays, there are plenty of companies building speakers specifically for extremely loud concerts, and those speakers can be used night after night for entire concert tours without even breaking a sweat.",
"There has been lots of talk about drivers so far, and rightly so because they are important. However I haven't seen anyone mention cabinet design. Obviously having cones that can handle the amount of volume they are required to generate is important, however the design of the box they are mounted in is just as important. Lots of research and science goes into the shape, size and features of the cabinet in order to get the best out of the drivers, including directing the sound where you want it to go, avoiding resonant frequencies, etc. You could take the best driver in the world and stick it in a poorly designed box and it will sound crap."
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94447r | If a car’s engine is flooded (filled with water) can it be fixed? | If a car engine gets filled with water, hydro locked I think it is, can it be brought back to life? Like if a car drives through a large puddle or river, can the engine be revived or is it pretty much done for? Edit: Also what happens internally to the engine? Are there specific parts that are more likely to be damaged? | Engineering | explainlikeimfive | {
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"It's possible, I've seen hydrolocked cars get fixed but it's a lot of work. You're going to have to tear down the engine to see what the damages are internally",
"Hydrolocking an engine is usually a total since it's normally cheaper to hoist in a new junkyard engine than do a full engine teardown. It mostly depends on if the engine was running when it got flooded. Water is incompressible and gasoline engines attempt to compress things, so if enough water got in the cylinders and the cylinders attempted to compress the water down you'll get broken seals and pistons. If the engine wasn't running, you can probably drain out and re-lube and re-assemble the engine fine.",
"Wow, I never knew this stuff. I guess it should be obvious about what happens when you try to compress water. I just never really thought that if you are driving and hit a big enough puddle to flood the engine intake with water that it would basically be an entire rebuild/replacement. I was expecting all the warnings about rusting and damaging parts, and lack of lubricant from the foaming. Never thought of the water hammer that would happen.",
"If you haven't bent any connecting rods or valves and you can get the water out and change the oil fast enough there's a chance. I've sunk ATVs I've owned on more than one occasion. I pull the spark plugs, turn it over to get the water out, put a little oil in through the spark plug hole, change oil, run for maybe 1-2 minutes. Then change the oil 2 more times while letting it run a little longer each time.",
"Depends. If you’re at an idle and somehow water gets in, the vehicles engine will shut off but slowly and may not have caused any damage. You would need to bring it to a shop quickly because the water will start to corrode and rust the internals that are supposed to stay lubricated. If you’re engines RPMs are pretty much anything higher than an idle, you’re engine is done. Water can not be compressed and the fo de of the piston going up and abruptly stopping is enough to bend and break internal components like the connecting rods and may actually smash a hole in the engine. When 1 piston stops abruptly, the all stop abruptly."
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945wwi | In golf, why is it easier to curve the ball with a lower lofted club? And by extension why do most people hit it straight with wedges when they go all over the place with longer clubs? | Engineering | explainlikeimfive | {
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"Short answer: backspin. Higher lofted clubs produce far more backspin which stabilizes the ball in flight and affect its path. A 56 degree wedge for example, even with a negative aoa, is probably striking the ball at a 50 degree angle. A 5 degree open or closed face will cause a push or pull, but won't change the axis of rotation much. With lower loft, say a 9 degree driver, with a positive aoa, might strike the ball at only 12 or 13 degrees. The same open or closed face here will alter the axis of rotation significantly causing a slice or hook (or ideally an intentional fade or draw). You can still 'work' a short iron, you just need to exaggerate the face angle."
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94691f | Why does bending the end of a semi-broken phone charger cable or earbuds sometimes fix the connection to the port if maintained in that orientation? | Engineering | explainlikeimfive | {
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"The cable is semi-broken because the smaller wires inside are damaged. If it suddenly starts to work when you hold it at a certain angle, it's because you're holding the damaged ends together.",
"The wires inside break over time, leaving a tiny gap. When you bend the end, you can move the wires just enough to close the gap and reconnect again. But you have to hold it in place to keep the wires touching each other.",
"Sometimes the problem is more that the charging port is filled with lint, and it takes the repositioning of the cord or bending it to get enough contact between the charger and the port to actually charge the phone."
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94e9mu | Why do roads continued to be made of asphalt give its proclivity to deform, and thus need constant repair? | Engineering | explainlikeimfive | {
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"Asphalt is incredibly cheap. It's also fairly durable and doesn't get too slick when it's wet.",
"The closest alternative to Asphalt Concrete is regular Concrete. This takes far longer to cure (months instead of a week), cement is more expensive than Bitumen, and has the same flaws (potholes, cracking due to weather conditions). Concrete is more resistant and costs less to maintain, but the upfront cost isn’t worth it.",
"The ground isn't as solid as it seems. It moves, expands and shrinks. Asphalt is good at adapting to these situations. You think it's cracking is bad, but it typically can last years before reaching this point. A more rigid material would take longer to put down and then wouldn't last very long."
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94gjun | why do most remotes run on two AAA batteries and not just one? | Engineering | explainlikeimfive | {
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94s5og | Why can't long cables be stretched perfectly straight? | I'm thinking about electricity cables for example. | Engineering | explainlikeimfive | {
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"Its 3 things combined. Weight, malleability, gravity. The wires themselves are heavy, and gravity is always trying to pull them down. In order to attempt to keep a wire stretched straight across you need to put on enough tension to over come gravitys attempts to pull it down, however all metals used for powerlines will stretch if enough tension is placed on them. The amount of tension required to over come gravity is more then what the wires will tolerate before they can't hold themselves together anymore and snap. Edit: as u/OVERHEAD1 points out below, there is also the issue of expansion and contraction due to temperature.",
"In the real world, you can only approach a straight cable, but never actually reach it. You can think about it in terms of the ratio of the force pulling down (gravity) vs the force pulling sideways (tension). A straight cable would have a ratio of zero, that is, zero units down to one unit sideways, which would only be possible with a weightless cable or an unbreakable cable with infinite tension, neither of which can exist on earth.",
"A rope can only be loaded with tension and only along the length of the rope. In order for a horizontal rope to bear any weight (even its own weight) there has to be some vertical component (i.e. it has to go a bit downwards in order to pull up). This diagram shows how much more force you need at the anchor points at a given angle: URL_1 This is also a nice illustration: URL_0",
"Also the next thing is temperature. Cables that long expand and shorten quite a bit from lets say -20 to +40. Even if you'd have some sort or strong cable than usual it'd eventually either snap or get destroyed some other way.",
"They can, and are, actually, when the situation demands it. Electric trains with overhead catenary wires must have the wires parallel to the ground. This is achived with a curved support wire and a straight wire underneath. [wiki on catenary wires]( URL_0 ) Edit because of rampant pedantry: They are not perfectly straight or parallel, they are relatively straight and parallel. Perfection is not achievable in real life, one must always draw the line at measurably good enough for the purpose at hand. Perhaps the 5yr old or laypersons definition of perfectly straight is straight to the eye from a distance?",
"Because the amount of energy required for lifting the middle of a cable increases exponentially. It's not worth the extreme amount of extra tension on the poles.",
"It mainly has to do with the physics of the cable. You would need infinite tension to overcome the force of gravity on the cable. I remember this being brought up in differential equations (a cable anchored at each end is modeled by the cosh function)"
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94sqm5 | how do big cities maintain water pressure despite the addition of hundreds of houses/condos every year? | Engineering | explainlikeimfive | {
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"Build more water towers—Water towers are tall to provide pressure. Each foot of height provides 0.43 PSI (pounds per square Inch) of pressure. A typical municipal water supply runs at between 50 and 100 PSI Hydrostatic pressure- google it",
"Sometimes they don't. Recently, a new community near Vaughan, outside of Toronto, Canada, had to have move-ins delayed because there was no water pressure. Planners had underestimated the demands on the system and the distance from Lake Ontario, which is the primary intake to the city.",
"ELI5 - if the pipes can’t move enough water, they will put in more pipes or bigger ones. More detail: Engineers use models to determine whether the existing water network will maintain pressure and flow at acceptable levels accounting for the increased demand from development. In the event that the network won’t manage the increased demand; new pipes, etc. will be constructed to service the new properties. In some cases, particularly where the network upgrades are only required to service a single development (i.e. a housing estate or a high rise building); developers may be required to construct the network upgrades as a condition of their development approvals. Further, planning engineers monitor growth projections/future development plans to ensure that major upgrades (larger pipes, water storages and treatment plans) can be planned, designed and constructed before the development occurs. This will be generally managed by the utility. At least this is the case in Australia. Source: water engineer",
"Usually water towers are part of the design of the building by place a large water storage container on the roof of the building.",
"Water is in a big water bowl. Under ground water pipes connect the big bowl to your house. As long as the big water bowl is higher than your house (not bigger, just higher like on a hill or on a tall tower), you will have water pressure.",
"Because it is ELI5: Booster station (actual) = pump (laymen term) Reservoir (actual) = water tower (laymen term) 1) Booster stations take water through feedermains to reservoirs. Think 500mm or larger pipe for a feedermain. Homes/businesses are not ‘tied’ to these. 2) Sometimes you don’t need pumps or booster stations if source of water is at a suitable elevation already. At these reservoirs there may be another pump to take water to the next higher reservoir. 3) Reservoirs then ‘drop’ water to homes through distribution mains. If pressures are over 80 psi you will have a PRV. If pressures are under 45 psi you may require a larger service to your home. Think 100mm to 400mm pipes for distribution mains. FYI -The need for water towers in towns has two parts: 1-supply from reservoir yes, 2-acts as a way of balancing the pressure in the system. As such you will typically put the water tower as far away as you can from the source. Imagine if there is a theoretical street of 100 homes. The family showering and using toilets in the morning at the very end experiences less pressure than the family at the start. By putting the water tower at the end of the street, you are helping to balance the dynamic pressure in the system when it is under action.",
"In part because when the water facilities were built they planned for that eventual growth. It isn't built for current needs but future expected needs.",
"Wait!!!!! I can answer this for NYC!!!!! I attended a PD on this! I’m NYC, the water source is the Catskills, which is much higher in elevation than NYC. the aqua duct that carry’s water to NYC is pressurized by the head water pressure from the higher elevation of the Catskills, so water pressure is just a matter of gravity trying to pull the water down, no pump needed! In fact, for a long time there was a limit to how tall buildings could be. Any building called something like a 3 story walk up is probably still pressurized by gravity. Also, if you go to Central Park, I think I’m the middle of the Jackie Onassis reservoir, you’ll see a fountain that shoots right up. That water is being pushed by the head water pressure from the Catskills!"
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94uhrc | Why do they make 3-prong electric plugs when they can still work with just 2? | Engineering | explainlikeimfive | {
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"The third prong is the ground, its there for safety not functionality Under normal conditions there should be no current flowing into that third prong, but if something goes wrong then that ground prong serves to provide a low resistance connection between the case and ground so the current flows through it rather than you."
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950ry8 | Why do bows have a longer range than crossbows (considering crossbows have more force)? | EDIT: I failed to mention that I was more curious about the physics of the bow and draw. It's good to highlight the arrow/quarrel(bolt) difference though. PS. This is my first ELI5 post, you guys are all amazing. Thank you! | Engineering | explainlikeimfive | {
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"Crossbows have a big disadvantage due to having short limbs compared to a bow. This is true for all types of bow, but it has to be balanced with how unwieldy it would be to have a huge longbow or crossbow. The biggest difference is the length of the power stroke. A fairly typical archer will have a draw length (the distance between the drawn string and the back of the bow) on their bow of about 27-31 inches, and a brace height (the distance between the undrawn string and the back of the bow) of about 6-8 inches. This gives you a power stroke of somewhere in the 19-25 inch range. Most crossbows have a power stroke somewhere in the 9-13 inch range. That dramatically reduces the amount of time the string is imparting force on the arrow. That's how you can have an arrow flying the same speed as a bolt despite having a much lower draw weight. There's also a penalty in efficiency for having short limbs that affect crossbows. All bows have a draw force curve that shows how much force the string is imparting compared to how far it is drawn back. In a typical longbow, this curve is shaped like an upward facing banana. That means that when it is barely drawn, almost no force is imparted, and as you draw it farther the force increases more and more. The flatter the curve, the more efficient because the force on the arrow isn't dropping off as much during the power stroke. Having longer limbs gives you a flatter curve, which is why longbows are so long. So, the crossbow with its very short limbs has the force drop off very quickly, giving less speed for the same amount of force. Finally, since crossbows need to have a lot more initial force to make up for the inefficiencies we've already talked about, they have to have shorter, thicker, heavier bolts so the initial shock of the force doesn't destroy them. Heavy bolts also need more fletching to straighten their flight path. The short, thick bolts are much less aerodynamic than the longer, skinnier arrows.",
"Crossbow bolts are thicker, heavier, and shorter, and crossbows have shorter strings, compared to arrows and bows. This makes them less aerodynamic and reduces the amount of maximum potential imparted by the weapon. The weight of the bolt is probably the most important factor here. A common, modern crossbow bolt can be in the 500 grain area (about 31 grams), whereas a common, modern arrow is usually in the 300 grain area (about 19 grams).",
"Crossbows are inefficient at making the arrow actually fly fast. A 500-pound crossbow hits about as hard as 150-pound longbow. This is largely because the crossbow is so short. Just like the short barrel of a carbine compared to the long barrel of a marksman's rifle, the weapon is pushing on the projectile for a shorter period of time.",
"A crossbow is a mid-range weapon that uses a short, heavy bolt meant to punch through plate armor. A bow is a long-range weapon meant to be (among other things) fired in volleys at lightly armored infantry.",
"I assume youre comparing bows and crossbows with equal draw weights in which case your statement is true but an added benefit of crossbows is that you can use drawweights that are impossible with a traditional bow. A crossbow uses cocking aids to draw the string back to its firing position which if using a rope cocker gives a 2 to 1 mechanical advantage and then there are crank aids which make it possible to draw a crossbow string back with one hand. My Crossbow has a D.W of 260 lbs so while the bolt is heavier and shorter the added energy of a crossbow more than makes up for it. Here's some numbers on record distances URL_0",
"Bolts are heavier so while their initial punch is greater, they lose more energy over distance than lighter arrows do.",
"If you're asking about historical, military bows & crossbows, some of the responses you've gotten are misleading. Not all crossbows have shorter ranges than all bows. There are different kinds of bows and crossbows, for different purposes, like, do you need to be able to shoot and reload while on a horse? Or what year/technology are we talking about - crossbow reloading technology allowed crossbow draw weights to go up about 4x. For bows, the kinds of arrows used in war are much more massive than the target arrows and hunting arrows people used to seeing today. Being much more massive, they won't fly as far. Likewise, the modern crossbow often just shoots arrows rather than bolts or quarrels, and shares many design elements of a bow, and is not that helpful in understanding the historical crossbow. As to your question, why might a 1,000+ pound crossbow not have 5 times the effectiveness of a 200 pound bow? The powerstroke: First of all, that draw weight number is merely a measure of the force needed to keep it pulled taught, at full extension, and doesn't tell you anything about how much kinetic energy will be in the bolt or arrow by the time it has left the crossbow or bow. More kinetic energy = shoots faster, further, and harder. Quite different than a modern crossbow, medieval crossbows get their string pulled back much less far than bows. As soon as the string is released, a bow or crossbow starts accelerating the arrow or bolt, but it can only do so for the distance that it was originally pulled back. This distance, over which the projectile is being accelerated, is the powerstroke. Powerstroke and force on the string work together to give the projectile kinetic energy. So a bow with a much longer powerstroke than a crossbow, but a much lower draw weight, is still effective. The non-ELI5 would use calculus to talk about each bit of (decreasing) force applied at each increment of the string getting closer to the original position, building up the kinetic energy and accelerating the projectile. There are other factors, but they are less important than the powerstroke. Two youtube channels I find to be reliable: [Tod's Stuff]( URL_1 ) \\- mostly crossbows. He builds modern recreations of historical european crossbows and other stuff. [Scholagladtoria]( URL_0 ) \\- historical combat, weapons, with some great videos on bows and crossbows.",
"Crossbows shoot bolts, bows shoot arrows. Bolts are much thicker and much shorter than arrows. Air resistance takes care of the rest.",
"Are you sure that they do? Where do you have that information from? I just looked into it, and it seems that there is not much different, neither in old, nor in modern equipment. If anything, then older crossbows were able to shoot further, due to heavier pull. Sorry to say, but the other 3 comments are partially wrong. Heavier bolts shot at the same speed as arrows should go further.",
"Crossbows have more range, higher velocity, heavier arrows, but less accuracy. You could shoot further but you will miss. Arrows are more stable than crossbow bolts due to their length and how they are carefully guided out of the bow. Crossbow bolts [390gn and 416gn]( URL_1 ) Crossbow speeds [400fps]( URL_0 )"
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"https://www.pse-archery.com/shop/bows/2018-pse-crossbows/pse-thrive-400-crossbow/",
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95176e | How can electronics withstand high G-Force environments e.g. missiles? | I'm wondering what it takes to make electronics that can withstand extreme g-forces, such as in a guided missile? I'm assuming that regular circuit boards and connectors would be instantly pulverised if you launched them in a guided missile. | Engineering | explainlikeimfive | {
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"Most missiles honestly don't accelerate too ridiculously quickly, where g-forces are concerned. As long as your circuit boards are not constructed with any particularly fragile appendages, they'll generally stay intact. The key to realize here is Newton's second law - Force = Mass * acceleration. Let's take an AIM-9 Sidewinder - a guided A2A missile. It's fuse is based on a 20g acceleration - which is about 200 m/s^2. I'm going to take a very simple example here which I've used myself - a PIC18f4550 microcontroller. It's a small computer-y thing that you might find on boards similar to an Arduino. URL_0 It weighs 6 grams. So 0.006 kg * 200 m/s^2 ~ 1.2 N. It would take 1.2 newtons of force to accelerate this microcontroller at 20g - about the equivalent of making it support a decently sized apple. Significant forces? Yes, of course. But would it pulverize it? Probably not. While a Sidewinder would proobably not have this particular thing in it, it does offer a nice demonstration of the comparisons of the amount of force involved. 20 G's is considered a lot because we humans are squishy and we require blood to go all throughout our bodies for us to even function correctly - and 20 G's is much more than our heart can take to properly distribute that blood all around, as well as creating troubles with various other softer bits of us."
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95ly4s | Despite the fact that railroad crossings are built to compensate for added weight of trains, how do they have such a short life expectancy compared to road and other rail structures? | Engineering | explainlikeimfive | {
"a_id": [
"e3tnu2x"
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"text": [
"They're basically built-in potholes. The passing vehicles jump the rail gap and slam their tires against the pavement on the other side millions of times a year. Usually the rail itself is still fine when the crossing gets repaved, but the pavement is obliterated from cars grinding away at it five thousand times a day."
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95tspw | What science in a car allows it to be able to tow heavy loads? | My 2.0L 4cyl sedan back in the day was rated to tow 1000kg but my current 5.0L V8 is not rated to tow at all, in-fact if I towed anything with it I'd void the warranty. I assumed that power is needed for the tow rating but it doesn't seem like it's the case. Is it all in the chassis? Or is there something else at play here? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Your engine has to be strong enough to pull the load. Your transmission has to be strong enough to handle the load. Your chassis has to be strong enough to carry the load. Your springs and shocks have to be strong enough to carry the load. Your brakes have to be strong enough to stop the load.",
"Bit of column A, bit of column B there. But really it's almost everything about the vehicle. Obviously the engine plays a big part in what the vehicle is capable of getting moving, but it's not everything. The transmission actually needs to be geared a certain way that general-use vehicles just aren't. The car/truck's frame and axles need to be strong enough to pull extra weight. Just because it can load a lot in the trunk or bed doesn't necessarily mean it can handle towing, because keep in mind that force is coming from a completely different direction. And then there's the brakes. Just because it can physically get moving doesn't mean it can stop."
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95u2j7 | How do beer cans (and pop cans) open without a sharp edge? | I've cut aluminum before and that stuff can be sharp. Yet I have never cut myself on a can. How!? | Engineering | explainlikeimfive | {
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"The amount of engineering that goes into the opening on coke cans and coke bottles is mind boggling. Ever single line is at a very precise angle to make it work. When you lift the tab on a can it flexes the top. If it was just simple leverage the tab would bend before the can opened, but the flexing of the top causes the score to break first. When you cut something you pinch down on it till it shears. This pinch creates an edge. A coke top basically rips open along a scored path. There is no pinching action.",
"Have you ever tried sticking your ginger throigh the opening of a can? That shit is incredibly sharp. It’s just that there’s a lip around where the hole is and you normally don’t stick your mouth through the hole so it’s hard to cut yourself on it without doing something stupid",
"others have explained it well, but here is a video of a guy going over all the physics of the soda can. its set to the point just about the pop top. URL_0",
"The opening is scored, so a sharp edge has already done its work, just not deep enough to open the can. When you flip the top, it punches through the scored area."
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95y5q3 | How are car doors able to be ajar but still be unable to be opened without opening the latch | Engineering | explainlikeimfive | {
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"text": [
"It's because the hook that is attached to the vehicle's door jam has 2 notches on it. The latch on the door goes over these two notches when you close it and it hooks the door closed. If you open the door just a little the door latch then catches on the second notch of the door jam and stays hooked and bounces between the 2 notches in the door jam."
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96cqgb | why buildings aren't all tethered together? wouldn't that just make for a sturdier structure? and if it would, could you then build onto that? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"From the engineering perspective, adding a skywalk doesn't add much reinforcing strength at all to a megastructure like a skyscraper. You'd need astoundingly heavy, super-expensive, and mega-thick beams to do that. But even so, society and human behaviour don't actually like to do that sort of stuff in all cases. Humans like their space, and they like to own things that are unique or special to them. That includes companies owning their own \"standalone\" buildings. Two unrelated businesses that are rich enough to own their own skyscrapers need a good reason to hook their skyscrapers to each other, and structural strength just isn't one. There are lots of cases of downtown cores that are partly connected by passageways such as skywalks, so the model can work... but it's usually connections between very close together buildings that have stores and pretty much go \"through\" tourist-friendly structures like malls. That description only applies to a few buildings, not most of them.",
"Buildings being tethered together increases risk of fire spreading, it makes them less resistant to earthquake as they no longer have the ability to shift so instead break, intensifies the wind tunnel effect already common in cities, makes owning or building new property difficult, and simply looks bad to most people. Skywalks are a slightly better thing, but they are for the most part only useful in situations where two buildings have reason to have a lot of traffic between each other such as a hotel and a convention center, or a parking garage and the building it is associated with."
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96ftwi | What is the role of a differential on a car? | Engineering | explainlikeimfive | {
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"text": [
"I'm not educated enough to speak about the different kinds, but the differential is there to provide balanced power to the wheels while allowing them to spin at different speeds. The reason it's necessary is because in a turn, the inner wheel takes a shorter path than the outer wheel, and thus spins more slowly, so having a rigid axle would cause severe handling issues. There's a video with 6 million views on Youtube that explains how and why it works. It's from 1937 so is extremely retro/Fallout style, but equally as educational and applicable today. URL_0",
"it transfers power from the transmission out to the wheels. it also allows the wheels to turn at different speeds while cornering. a limited slip differential, or \"positraction\", keeps both wheels locked in unison while going in straight lines. positraction has a set of clutches installed in the spider gears which keep the axles locked together until g-forces from cornering pull them out and allow the wheels to slip independently of each other."
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96knt4 | How does tap water come out cold? | There’s no cooling element in the house. Is it because the pipes in the ground cool the water? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Because the ground usually maintains a constant temperature year round. In some places that temperature is in the 50's. The water line runs mostly below ground, so it has a long time to balance to that temperature.",
"The pipes are underground, the water gets to ambient temperature underground, typically fairly cool",
"The farther you go underground, the more the earth regulates the temperature. At about 1m (3 ft) underground, the temperature is regulated to between 5-25°C (41-77°F). It's usually below room temperature, and definitely below body temperature. Most pipes (at least in the USA) are at this depth or more."
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96ncu9 | Where is my oil going when it gets low? | Where does the oil in your car go when it gets low? I thought it’s a closed system, so it can’t get out. But how does it burn off? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Leakage into the combustion chamber either by ill fitting rings or leaking valve seals. Once in the combustion chamber it is burned off similar to the way the gasoline burns."
],
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23
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96nm06 | How do companies repair the damage to the walls of hydroelectric dams? | Engineering | explainlikeimfive | {
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"text": [
"While I've never done this specifically, I am a civil engineer, so I know enough about it to get you started. First, there are actually techniques for injecting resins and grouts underwater. So they can do small leak repairs and seals pretty easily. Get a diver or robot down there with a hose and pump it into the cracks under pressure. Done. For bigger, structural repairs, where you have to replace the concrete or reinforcement, I'm pretty positive you'll have to be \"in the dry\". That's a much more difficult issue, and depends on the situation. Depending on the size of the dam and location of the leak, contractors may be able to isolate the repair. It's much like working with bridges, or doing deep foundations. They can install huge metal sheets vertically that extend into the ground. Put enough of them together, and you have a big wall around your worksite. Seal off the edges as best you can, and throw some really big pumps in there, and you'll have a dry work area. You just have to pump water out faster than it's leaking into your site. From there, you can carve out and replace some concrete. Again, depends on the situation. Because installing new concrete onto old concrete is a weaker bond than one continuous piece (\"dry joints\"). This would make the repair a weak point (again). So there's going to be some detailed structural analysis done. For a big enough dam, and a big enough defect, you're just going to have to divert all the water and rebuild the thing."
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96oiec | why concrete roads (and sidewalks) have seams but asphalt is laid in a seamless stretch? | Engineering | explainlikeimfive | {
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"Because asphalt is bendy and stretchy, elastic, so thermal expansion isn’t that much of an issue, but concrete is very brittle (breaks and cracks easily) so it needs expansion joints",
"Civil engineer here. Two things I've learned about concrete: It gets hard, and it cracks As others have said, concrete cracks due to shrinkage after placement and in response to fluctuations in ambient temperature throughout is design life (thermal expansion and contraction). The first cracks typically show up within 24 hours of placement as free water is lost to the hydration process (how concrete gains strength). Joints are an effort to tell the concrete where to crack by creating a plane of weakness. Depending on the joint type you may have additional reinforcement or smooth steel rods to allow the panels to expand and contract. Meanwhile asphalt has more elasticity meaning it has a greater ability to deform under load (i.e. thermal expansion/contraction) and return to its original size and shape more or less. Its ability to do this decreases as the pavement ages. Asphalt tends to be less durable than properly placed concrete and has a greater susceptibility to fatigue stress. Rutting in asphalt at stop lights or in parking stalls are examples fatigue distress due to repeated loading/unloading. Edit: grammar",
"The concrete is a harder material. It behaves different to asphalt when the surrounding temperature changes. You literally *need* to have seams here and there because if you don't the natural, temperature induced expansion will make the tiles expand towards each other. And eventually crack, because there is no room for more expansion. Then, of course, the concrete slabs can be manufactured in a factory and transported to the construction site. It's just like when you build a path in your garden. You buy concrete tiles and place them in a nice fashion all the way to your front door. Exactly the same principle with a road, except the tiles are huge in comparison. But, seriously though. Concrete roads tend to be built with fully automated machinery that pour concrete into a mobile molding form that is in slow constant motion all the time. Even then, it's important to \"break\" the tiles now and then so that the road won't immediately crack itself the first year.",
"Concrete has great compressive strength (ability to be pushed down), but poor tensile strength (ability to be stretched out). As temperatures rise and fall, it expands and contracts, and eventually one large slab of concrete will stretch itself until it cracks and breaks into smaller pieces. By cutting in expansion joints, you are essentially telling the concrete where to break. If done correctly, the concrete will crack beneath the expansion joint, where you cannot see it. This also causes less stress on the slab as it expands and contracts. Well made concrete slabs can easily stand for upwards of 40 years, requiring very little maintenance, whereas asphalt needs to be replaced (or at the very least maintained) far more often.",
"Why are sidewalks not made of aspahalt, then there wouldn't be seams right?",
"Concrete is a rigid pavement. As the ground below the pavement expands and contracts it will move whatever is on top of it. In the case of concrete, you need to put expansion joints in it or it will break apart. Asphalt is a flexible pavement and will move with the pavement below. If the underlying base is moving a lot you can see cracks in the asphalt but due to the materials flexibility they can self heal. Hot mix asphalt is dirt cheap ( 2c/lb) and if the road design has been done correctly should last 20 years",
"In Michigan, it's for the plow drivers to get a hold of and rip a good chunk off when they're pushing snow."
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96xbif | If a toilet is submerged in a flood does flushing it help lower the flood? | Engineering | explainlikeimfive | {
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"text": [
"No. If the bowl is submerged, then as much water as can drain through it is already *going* to do so, because that's how the flush works: it raises the water level in the bowl above the upper half of the U-bend, and so the water syphons away. Submerging the bowl does the same thing; running the flush just adds more water that it needs to get rid of, unless the sewers are also completely flooded, in which case the toilet simply won't flush at all, and you've just dumped more water into the room.",
"Dump a bucket of water into a toilet and watch it insta-flush. If it could flush, it would.",
"A toilet flush lets water from a tank into your toilet bowl. Once the water is in the toilet bowl, it flushes because of gravity pushing down on the water in the bowl - there is no sucking / vacuuming caused by the handle push. Once the water level is higher than the bend in the toilet, there is enough pressure from the water to push past that bend. It empties completely due to siphoning once the flush starts, which is when the empty space left by the water getting sucked down is filled by more water from the bowl. So if your toilet bowl is below the flood line, and there is empty space for it to drain into, it will drain whether you push down the flush handle or not. If it's not draining, it's because it's full on the other side.",
"There is drainage and runoff pipes in a lot of cities that redirect rain water and sewage to wherever it goes. When you get rain that is too heavy, these pipes cant move the water fast enough and it can back up to the point where water collects on the surface. Flushing the toilet would send water into these backed up pipes, where it would have nowhere to go but back to the surface. Nope, it isn't going to help. If these sewage systems are totally seperate from the runoff systems, then it might help a little, but the amount of water you would be moving would be nothing compared to the ampunt ofnwater needed to submerge your entire toilet.",
"When I’m dealing with houses that are flooded with storm water, not sewage, I sometimes pop the toilet off and let the water go down the drain"
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96yjs6 | How does a pull-start motor operate such that it sometimes needs many pulls to start it? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The smaller the engine, the more exact the balance has to be between the air, fuel and spark. Also, bigger engines have electric starters that spin the motor faster and longer allowing for the mixture to hit the right combo to explode. Modern car engines have the elements computer controlled so a multicylinder car engine will fire right away--all things equal. I've been a mechanic my whole life, but small engines, like mowers and weed trimmers are always a pain. Brand new, they should fire in 2 or 3 pulls, once the gas gets flowing. But, after a while, dust gets in the carb, the gas gets watered down due to condensation, or the gas goes bad because its got ethanol in it ( worse idea Congress ever had, less power, less mpg, and erosion of the internal fuel delivery system). Also, on a 2 cycle engine like a weed trimmer, gas has to be mixed with 2 cycle oil in a specific ratio to combust and to keep the engine from overheating. A small engine may fire once but until it gets a constant consistent delivery of fuel air and spark, it won't keep running. Each of those elements have a myriad of problems that can arise. On your 27th pull, everything finally mixed to create an explosion every 2nd rpm (2 cycle) or every 4th (4cycle) rpm. And, the engine has to go through enough cycles to get everything functioning before it can keep running on its own. Always use fresh fuel, drain the fuel before storing for more than a month (if using car gasoline) and replace the air filter as needed. The nice thing is that the carburetors are usually cheap enough on eBay, that it's easier and more effective to simply replace the carb, than to clean it or rebuild it. Feeling your frustration....",
"After reading all of your replies to comments, it's likely down to the fuel for you. When you have to pull multiple times, you either have too much or too little fuel. Too Much: If you take note of the color of the exhaust when it starts and you see any faint black smoke puffing out, it means you had too much fuel in there. This happens from pumping the primer bulb too much, having the choke on when it wasn't needed, or a dirty air filter or you need to adjust the jets on your carb (if possible). This means that liquid gasoline gets inside the engine and not enough air and, even though it's hard to believe, the spark wouldn't cause the fuel to burn because you didn't have enough air. As long as the choke is off, as you continue to pull and pull, it will eventually expel the extra gas and start up. If you have a way to hold the throttle wide open (full speed) without engaging the choke, you can speed this process up. Too Little: I think this is probably what's happening with yours but I'd really need to understand exactly how your engine is setup. Not all primer bulbs do the same thing. Some squirt some gas into the carb, while others ensure that the gas line from the tank to the carb is sufficiently full of fuel (no air bubbles in there). If yours actually squirts fuel into the carb, you will NOT want to pump it too much. If it just gets the air bubbles out of the fuel line, you can pump it many times extra. But, your primer bulb could be insufficiently doing its job. It could be that there's a slight crack in the bulb and it's not actually priming like it should (replace the bulb) or it could be that you need more than 3 pushes of it. If you notice that the primer bulb is full of gas, then 3x should be good. If all the gas has run out of the bulb, you might need to push it more to get the gas into the carb. You may also need to adjust the jets on your carb (once again, if yours is adjustable). As you continue pulling and pulling you're getting the engine to suck up that gas the hard way that the primer bulb is intended to make easier until it finally pulls it in and starts up."
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96zuix | Why is it when driving over bridges at a high speed it makes such a high pitched noise, unlike driving on a regular highway? | Sounds similar to URRRRRRRRR or EEEEEERRR... | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Concrete has a finer texture than asphalt and so creates a higher pitch noise. Regular asphalt creates a lot of noise, you just tune it out. You only realize it when you suddenly drive on to fresh quite pavement, or ride in a luxury car.",
"The part is seems others have failed to point out is - Most places, bridges are surfaced differently than the rest of the road. Due to things like icing, rain removal, infrastructure that may follow the roadway, and just the fact that unlike a road, bridges got nothing under them, they have to be built and surfaced differently than your normal roadway. This also causes them to sound different when travelling over them."
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971egz | How can a straight train car travel along a curved railroad track? | Engineering | explainlikeimfive | {
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"text": [
"The wheels have a slight conical shape. As the truck goes around the corner, it slides over slightly on the rail so the part of the outside wheel engages the rail at a slighter larger diameter, the inside wheel at a slightly lower diameter. You can seen Feynman talk about it here: URL_0",
"Train wheels are on swivels that can turn with track, not fixed in parallel with body of car. And cars have flexing hubs between them.",
"If you watch a video, both sets of wheels are on a swivel. Which allows it to move along the track."
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971lbl | How exactly does a posi-trac rear-end on a Plymouth work? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Positrac is a brand name for a [limited slip differential]( URL_0 ), which does two desirable things: 1) Allows the wheels on the axle (in this case the rear wheels) to spin at different speeds. (This is why it's called a differential.) 2) Has a mechanism that resists speed differences between the two axles. (This is the \"limited slip\" part.) Now, 1 and 2 may seem to contradict each other somewhat. However, they address different situations. 1 addresses normal driving like going around a corner. When you go around a corner, the outside wheel has further to travel than the inside wheel so it has to spin faster to avoid slipping. In a solid axle, this can't be accommodated so you are guaranteed to have some slip. But a differential helps avoid that. 2 helps address unusual situations where one wheel can spin with a lot less resistance than another wheel -- for example, if one wheel is on ice. A normal differential applies equal torque to both wheels. Without the mechanism to oppose a speed difference between the wheels, the wheel on the ice could spin extremely fast and damage your tire, because the resistance of the ice to your tire spinning is very low, so it doesn't take much torque to go very fast. The limited slip differential reduces torque to the wheel spinning quickly and increases torque to the wheel spinning slowly, which allows you to take the greatest advantage of the torque both wheels can support."
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972bv1 | I am really wasting 81W AC to create 10W? | Hello. As I know, power is P=U*I. From the label on charger I see that input AC 230V * 0.34A is used to create DC 5V * 2A. It looks like I am spending 81. 6W just to create 10W? Is my charger awful? Why so much power is wasted? How can I prevent wasting it? | Engineering | explainlikeimfive | {
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"text": [
"Your charger might draw 0.34A, but **not all the time**. Modern phone chargers usually use a \"switched mode power supply\". This works by drawing current from the AC power line in a brief \"gulp\", then switching it off, and repeating this this many thousands of times a second. It then converts the power into a constant flow at the 5V DC side. Your charger is probably repeatedly drawing 0.34 amps and 80some watts from the wall for a few microseconds, and zero amps and zero watts for a bunch more microseconds, for an average power draw of a bit more than 10 watts. [ URL_1 ]( URL_0 ) You can be sure you're not drawing 80 watts constantly. That's the power drawn by a large incandescent light bulb or a couple of soldering irons: it would get way too hot to touch.",
"No. Your charger is probably quite efficient. In an AC circuit, you cannot assume that V(rms) * I (rms) = P. This is because AC current and potential difference is reported as a form of time average (specifically, the root mean square over a period of time, typically 1 or more cycles). In many cases, this assumption that V * I = P holds is reasonable - and this is one of the reasons why rms is used, because it allows this assumption to be correct in more cases. The main situation when the assumption is correct is when I is proportional to V, which it is if you are powering a resistor (like a filament light bulb, or space heater). However, in certain cases (like electronic devices, like phone chargers), I is not proportional to V, and this means that calculating V(rms) * I(rms) overestimates P. To get around this electrical engineers came up with the idea of \"power factor\" which is a factor that corrects the estimate for a certain situation. P = Pf * V(rms) * I(rms). For some of these cheap chargers (and also things like LED lamps), Pf can be very low, like 0.25",
"According to those calculations, yes, that charger sounds horribly inefficient. I'd wager that the current rating is probably its maximum rating, not its average rating",
"In true ELI5 fashion, here we go. Your converter isn't using all of the current your wall socket can provide. If your converter is putting out 10W of power, it is only going to draw 10W, plus some small amount of overhead, from the outlet. Your wall outlet can provide a lot more current, but the converter isn't using it. The \"small amount\" will vary from converter to converter. I've seen web sites that assert that modern, consumer grade converters range between 65% and 85% efficiency - for every 1W of electricity that goes in, .65 to .85 watts of electricity comes out."
],
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97d6si | why does the initial stream of urine come out in a double helix? | Not sure if this also happens with women | Engineering | explainlikeimfive | {
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"The old Askreddit post /u/Lorikeeter found is wrong! Recent research on urine streams (yes, really) has shown that it's not a helix at all. Instead, it has the cross-section of an ellipse, because the opening of the urethra has a vertical slit shape. As the stream moves along, surface tension pulls the ellipse toward a circular cross-section, but it overshoots to form a horizontal ellipse, surface tension pulls it back toward a circle, it overshoots again to a vertical ellipse, and so on forming an oscillating elliptical wave, not a spiral. A picture's worth a thousand words: [ URL_0 ]( URL_0 ) [ URL_2 ]( URL_2 ) The article goes on to show that you can estimate whether someone has a healthy urine flow rate by just asking them about the shape of their pee stream, which avoids an awkward medical test. [ URL_1 ]( URL_1 )",
"URL_0 Short answer: 1) the shape of the opening, and 2) the stickiness of the liquid"
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"http://journals.plos.org/plosone/article/figure/image?size=large&id=10.1371/journal.pone.0047133.g002"
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97evh4 | If AC is a sine wave, how is the sine wave generated? | Also, when it is between negative and positive, what is generated? | Engineering | explainlikeimfive | {
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"text": [
"AC sine wave electricity is generated by moving magnet inside a coil of conductive wire. The magnet pulls and pushes the electrons in the coiled wire, making them move with the motion of the magnet. As electrons move back and forth, that's your voltage and your current."
],
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97gn14 | How can thunder contribute to a bridge collapsing? | Engineering | explainlikeimfive | {
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"text": [
"I assume you mean lighting? Lighting packs a huge amount of energy. I’ve seen examples of it melting some materials, stripping trees of their bark and leaves and even cracking rock. Theoretically, if it hit the bridge just right, it could have caused the concrete or even metal struts to warp or crack. With the amount of load being put on them even a small crack could be catastrophic if it occurred in the right place.",
"Thunder is the resulting sound caused by lightning. The bridge that collapsed in Italy was (it is claimed) struck by lightning just before collapsing. Lightning is a massive electrical current and when it grounds, it goes through the thing it touches first. Often a tree that's hit by lightning will split apart and burst into flames. This is because, firstly the sap instantly boils and the steam created inside the wood bursts the wood open. Then as the temperature rises because the tree has electrical resistance (which causes the electrical energy to dissipate into the tree and releases that energy by turning it into heat energy), it reaches the flash-point of wood and thus it self ignites. In the case of the bridge, the wet, porous concrete and rusty reinforcement steel, buried within, will have behaved very similarly to the tree, by heating up very suddenly, creating trapped steam which then bursts the concrete, over-heats and softens the steel inside it and as a consequence, causes the structure to fail. It seems that this particular bridge has a history of under-maintenance and over-use which will have contributed to the sort of domino effect that a single failure point can have by affecting the next section and then the next section and so forth."
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97gtd8 | Why do boxes that have a closing lid have those two little side flaps as well as the lid? | [These]( URL_0 ) | Engineering | explainlikeimfive | {
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"text": [
"Without them the box would be much weaker and no support for the sides at the top. Also, they avoid spillage from the sides, depending on what you use the boxes for."
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97gumf | What exactly does the neutral wire do in an AC electrical circuit? | I’m almost embarrassed because I am an electrician. However, you don’t need to know the science to it to know it goes on the silver screw. But my curiosity always gets to me and I can’t seem to understand the role the neutral wire plays in the circuit. | Engineering | explainlikeimfive | {
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"The neutral is the center tap of a transformer, also called the grounded conductor because the neutral and Grounds are bonded at the primary means of disconnect for a panel box. Electricity functions as a circular circuit with the 'hot'' leg completing it's journey back to the transformer through the neutral. Without a completed circuit, there is no difference in potential so the circuit doesn't work. When there is a load on the circuit (resistance), the neutral will spark when connected. If there is no load, the neutral doesn't exhibit this. With a single phase residential service in the US, there are two 'hot' legs 180 degrees out of phase with each other, providing ~240 Volts difference in potential. The center tapped Neutral allows for ~120 Volts difference in potential. Most appliances in a residence operate on 110-125 volts which a circuit consisting of one hot leg and the neutral. The circuit will also (by current code) have a protective ground which provides an emergency path back to the panel box if there is a short inside the plugged in device. However, some devices (meant to stay plugged in) like ovens, electrical water heaters, dryer, A/C condensers and electric furnaces use 220-250 volts and may or may not have a neutral. Usually, if a device does not have a digital display or require a circuit board, only the two hot legs are used. If the device does have circuits that requires voltage to be converted to low voltage DC, then it will. EDIT: typo",
"For an actual 5 year old... Electrical current flows... like water. Imagine electricity like a stream and the black wire is hose of water.... Now to power a waterwheel the water has to come up the hose, turn the wheel and then go down a different hose... that's the white/neutral wire. W/o that... the water has nowhere to go and the wheel wont move. This analogy also works w/ other explanations... Hose size and pressure is analogous to amps and volts.. which way the waterwheel turns if you hook up the hoses backwards etc."
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97irdz | What actually happens to make the power go out during a thunderstorm? | Engineering | explainlikeimfive | {
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"Powerlines are constantly monitored by electronics that measure current and load. This is done because you need to constantly ensure that there is no short circuit, and that the output voltage stays within a tolerable span. Because you want to avoid fires out along the line and because you don't want to get blamed for frying all of your customers electronics, respectively. What happens when a lightning strikes in the line or very, very close to is is that the fault detector detects a fault that...simply put, is not really there. And when it has been able to establish that it was a lightning, it's to late. The breaker has already started acting on it's order. The breaker is opened, and the power is out. This might seem a bit counterproductive, because it would probably be better if it didn't react to lightning. But, well. The thing is that from the fault detectors point of view, this could very well be a line that is frying a car with a totally innocent family in it. It has a programmed obligation to react to anything that could be lethal. And it has to act swiftly. The time it takes for the breaker alone to physically move from closed to open is a near-lethal exposure to a high-voltage line. There is simply not enough time to make the distinction between lightning and a lethal fault. The fault detector has to act on a half-truth, often as a regulatory requirement. The first thing the detector does after operating the breaker, though, is to contact the Network Operations Centre computer. The computer will, most of the time, tell it to wait 2 seconds, attempt to close the breaker again and see what happens. If the fault remains, it opens the breaker again, calls the attention of an operator at the NOC and says \"fault detected, disconnected. Auto-reconnect. Fault remains.\" There are a few technical and regulatory variants on this theme, but that is pretty much why lightning shuts down the power.",
"Often the wind from the storm will blow a tree limb into an electrical line and either short it to ground or between lines. Either way the short is detected and a breaker pops to cut power. Sometimes the breaker will wait a bit and then send some power down the line to check if the short is still present. If it is gone then power resumes, otherwise it stays off."
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97llzh | How does an ice cream maker work? | Engineering | explainlikeimfive | {
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"Ice cream needs to be constantly stirred while it freezes. That way you entrain air into the mixture and get a nice texture. A home ice cream maker has three parts - a bowl, a paddle, and a turntable. The bowl is filled with coolant, which you freeze. When you pour the ingredients into that bowl, they will eventually freeze. The turntable makes the bowl spin while the ingredients are freezing. The paddle stays stationary in the mixture. As the bowl turns, since the paddle is staying still, the mixture gets stirred by the paddle. That's really all there is to it.",
"Ice cream is frozen custard (or something similar to custard). However it's frozen in a special way. It's churned or starred constantly while it freezes. This process creates lots of tiny bubbles (basically it's frozen foam) for the special texture of ice cream. To do that you need a way to constantly stir ice cream, and freeze it very quickly. Home ice cream makers usually have a double bath, allowing very cold ice water (the salt added to the water allows the water to chill below 0C/32F while remaining liquid) and either a hand crank or a motor to spin a paddle that churns the custard as heat is transferred into the cold ice water and it freezes.",
"The air argument is not correct. It is the formation of specific forms of ice crystals in the mix that give its texture. The constant churning is what enables this. If you don't churn it while freezing, you get large chunks of ice forming. Not very smooth. URL_0 > ABSTRACT: The smoothness and perceived quality of an ice cream depends in large part on the small size of ice crystals in the product. Understanding the mechanisms responsible for producing the disc‐shaped crystals found in ice cream will greatly aid manufacturers in predicting how processing and formulation changes will affect their product. This is why refreezing meld ice cream is never the same. You would have to refreeze it in a churn to get it back."
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97njmw | Why are caster wheels offset just behind the verticle attachment point? | Engineering | explainlikeimfive | {
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"text": [
"This creates a dragging-behind motion that causes the wheels to automatically turn in the exact direction of travel."
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97nx2w | Why is there always two locomotives on a train, one facing forward and one backward? | Engineering | explainlikeimfive | {
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"text": [
"Part of this is relative to where you live, but they plain just need the power. Most engines are designed to be chained so both locomotives can actually be controlled from the front. They flip the second one around as this makes it easier to walk from one to the other since they nicely line up.",
"Some train companies do this so it makes it easy to turn the train around at the end of the line and go the other way. But some don't do this at all.",
"They don't always work this way. In general, there are two locomotives on any train, and often they face either way, but they frequently face the same direction as well. There are no hard and fast rules in regards to this. There are two locomotives in almost all cases, for two reasons. First, they need the horsepower to move the tonnage. Second, in case one of them fails, they still have some tractive effort available. There is no particular reason to have the second unit reversed on through freight trains. In some working trains it makes sense, like if you are taking 100 grain empties to an elevator, then once the cars are loaded, you can now just change ends and be facing the proper way to bring the loads back."
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97ozy8 | Why are home/domestic toilets made like they are, with a lot of nooks and crannies that are hard to clean? | Engineering | explainlikeimfive | {
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"The modern flush toilet is pretty much a near-perfect design. You're not going to be able to improve on it substantially given the limitations of the water pressure coming into most building. So with that said, the interior shape of the trap and bowl is going to stay the same no matter what it looks like on the outside. If you wanted to make a square toilet, which would be easier to clean, you would need to add additional material as the outside wall, which would increase weight and cost. There's no reason you *can't* do this, but most consumers have not shown a willingness to pay for this, which is why you only see toilets that do not conform to the standard shape at the high end of the market, which is less price sensitive.",
"Presumably you mean the sides of the P trap, so the bottom part in the back. From what I can tell, it's to reduce the amount of porcelain used to only what's functional: the bowl and the built-in \"pipe\" leading to the floor. Giving the fixture smooth sides would mean filling in with lots of clay, and more important, getting that clay to bake properly when the fixture is fired into porcelain. Some high-end toilets do have smooth sides, but they're typically panels added on rather than solid porcelain."
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97rozj | Why do combustion engines have a "sweet spot" in terms of efficiency, and why are they inefficient above or below that spot? | Engineering | explainlikeimfive | {
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"In addition to the optimal reaction the other guys have mentioned, there are other factors at work too. One of them is gas movement in engine peripherals. In your run of the mill combustion engine (a 4-stroke gasoline engine), only one of the piston strokes actually adds energy to the spinning motion of the crankshaft. The other 3 strokes essentially waste energy added during that one stroke. Now, both in the intake and in the exhaust, there is gas. Mainly air on the intake and mainly exhaust gas in the exhaust. Because the engine performs a repeating motion, it will set these gases in perpetual motion too. If the exhaust gas rebounds towards the cylinder in the wrong moment, it will rebound into the piston currently in the \"exhaust\" stroke, which will make the piston waste more energy to push out the fresh exhaust gas against this resistance of old exhaust gas. Same is true for the intake gas: When the fresh air and gasoline rebound away from the intake valve miliseconds before the intake valve opens, the piston will have to use up more energy to suck in the fresh intake gas, working against the intake gases movement away from the cylinder. There is an optimal timing here, at which the oscillating intake gas will push into the cylinder by itself (effectively supercharging the engine by a fraction). Equally, there is an optimal timing on the exhaust side, where the oscillating gas will actually help the piston by sucking out fresh exhaust gas. In those scenarios, your torque diagram will show a small local peak. This is not a huge effect but it has measurable impacts and automotive engineers do take it into account."
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97sfyo | Why does the brake pedal seem to stiffen up if the car is off, but then go back to normal the second the car is turned on? | Engineering | explainlikeimfive | {
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"text": [
"Because the pedal is assisted with power from the engine, and with the engine off that assistance is gone.",
"Power brakes are assisted with vacuum pressure either generated by the intake manifold (gas) or a pump (diesel). You usually get 2 to 3 presses of the brake pedal before all the pressure is released. If the engine is running, the pressure gets restored, otherwise it doesn't and the pedal gets still.",
"Because there's the brake servo (sorry, I'm not a native English speaker, Idon't know a correct word) - a thing that helps you to push the pedal easier. And this works only when the engine is running. Once it is stopped - you push the pedal with your own muscle power only - so it's harder. Edit: typos"
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97up9c | If we can use pipelines to transport oil across the country why can't we do the same for water? | Engineering | explainlikeimfive | {
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"Building pipes and piping liquids is expensive. It is basically always cheaper to use local sources, even if they are scarce.",
"You could, but we generally call it a canal rather than a pipeline. You'd need to funnel a lot of water into the canal to provide for California, it'd be the size of the Mississippi The big trick is the Rocky Mountains. You'd have to get the water up and over the mountains to get it to the west coast and that's quite a climb Even once you get the water to California you're back to the same problem. How do you get it everywhere you need it? How do you get billions of gallons of water sprayed throughout California to stop it from burning regularly",
"Im not sure of the relevance, but anything with the great lakes water has to be approved unanimously by all the states bordering a lake",
"Oil is very, very expensive. Water is not. It's not economically feasible to pump water thousands of miles to address temporary rainfall shortages. If you decide to invest billions of dollars into a pipeline to move water across the country because of a drought, then someday the drought ends and you have to economically compete with something that falls out of the sky for free.",
"This has already been done in some places already. The big issue is a combination of cost and terrain. The longer your pipeline is the more costly it becomes; for reference the Central Arizona Project, a 336 mi long canal pipeline cost about $4.7 Billion. The pipeline you are suggesting would need to be *much* longer. (And don’t forget that evaporation gets more the longer your canal is!) The terrain is also a *huge* factor. It’s fairly easy (albeit still extremely expensive) to make a canal that goes downhill, but it’s basically impossible to make one that goes uphill. You can’t easily get over, say the Rocky Mountains that are in the road. That said where the conditions are right and someone is willing to pay the money we certainly can and will pump water to places that need it.",
"Idk how much I can answer your question but I'll try. So the first issue is the main transporting. Water is a solvent that actively dissolves shit into it. This means you will get contamination in the pipeline from not only other sources but the pipe it self. Additionally you need to keep a pressure of 40+ psi in your water main to prevent growth and ensure enough water supply. As water travels through a pipe there is a loss of pressure called head, in order to over come this obstacle and also height differences, you need booster pumps between point A and B. This is expensive. You can transport via 3 ways: positive displacement, centrifugal and one more incant remember. Additionally water has dissolved organic and inorganic material and transferring this via long distances means you can actually send pathogens or invasive organisms great distances. Leaks in piping can be costly and do massive damage to the ecosystem. It's much easier to just use water from aquifers because then its atleast easu to extract. I know this was a mess but I'm in the phone and I dont like typing, if you have more questions feel free to message me and i can try to answer it better."
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97xs9d | How do the fluid dynamics of toilets work? Specifically, how is it you can successfully flush a toilet on a floor higher than ground level? | Engineering | explainlikeimfive | {
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"text": [
"That’s a really good question, actually. Most people don’t realize how complicated managing water pressure is in tall buildings. Most tall buildings incorporate water tanks and pumps to maintain appropriate pressure on every floor. Normal multi-story buildings that can’t get enough pressure on the top floor from city plumbing have a water tank on the roof and pumps to pump the water up to the tank, with valves adjusted to set the water pressure provided by that tank according to how far downhill the floor is (with the tank on the roof, bottom floors get too much pressure and have to be tightened down to protect the plumbing and people). Really tall buildings (skyscrapers) have tanks at intervals all the way up to the top.",
"The magic is not in flushing a toilet higher than ground level because that water coming from your tank flows down into the bowl pushing the water in the bowl and waste products down into the septic lines. This is done by gravity with a little bit of help from the tank water pushing down. The magic is when you have a toilet below ground level like in a basement and that's able to flush despite being lower than the ground. The reason being is that no construction is done with the toilet septic lines lower than the entry point to either a septic tank for Rural installations or the sewer system for urban installations. Gravity helps a lot in all kinds of sewage disposal. It's very rare that any type of setup has a pump to push sewage upward into an entry point. I'm sure underground bunkers and cave homes have those but it's a specialty thing. The broad Strokes is that gravity helps to feed down waste and the new water in your bowl from flushing pushed the old water in the bowl and all the waste below it downward into the sewer entry point. The water in the bowl is there to keep the smells trapped inside the piping."
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9812ef | why do galleries have a circular-shaped section? | Is that merely linked with machinery used to dig them, or is there (also) some static motivations? I would have used a catenary (if it were easy to make a hole with such shape). Edit: I meant “tunnels”, not “galleries”. I misused the term from my language. | Engineering | explainlikeimfive | {
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"Mainly because of the machine, you can regularly see tunnels (they aren’t called galleries in English) that are square, but they are mostly old ones. You could make a catenary, but most machines are round and rotate, you could make a catenary drill head, with many circles but it would be more complex and expensive But there is also another point, the facades, which on a circle are all the same, but on a catenary they need to be all different, again adding cost",
"Sorry, what kind of gallery are you talking about? Most commonly this word does not refer to something dug underground."
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9860cy | How do gas and electric companies get their product to your house if they all use the same systems like gas mains or long streched of wire? Also how is this detectable or easily changable via signing up for them, or ending your buisiness with them? | Please correct me because I'm probably very, very wrong about this, but I thought that all electricty that goes to your house is sent over big electrical cables that eventually go into your house, similar to gas mains or pipes. I also thought that the only way that they could tell that you're using the resource is via a meter that does a science thing to detect how much is being used, but I don't understand how the companies could detect whose gas/electricty it is. So reddit, how far off am I with this one and how do things actually work? | Engineering | explainlikeimfive | {
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"> I also thought that the only way that they could tell that you're using the resource is via a meter that does a science thing to detect how much is being used, but I don't understand how the companies could detect whose gas/electricty it is. This one has a simple answer. There's a separate meter for each customer, so your meter only reports how much you use. The meter is usually attached to the customer's house or building."
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98a330 | why dishwashers have sault compartment to soften water and washing machine do not ? | Why | Engineering | explainlikeimfive | {
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"The salt in the water can ruin the glass and dishes immediately but your clothes are more durable.",
"I like to think there's a portal to Sault St. Marie in my dishwasher, and that's where all the dirt goes. Serious answer though is that hard water leaves spots on your dishes. During the drying cycle, the water evaporates but the minerals in the water stay behind, leaving ugly residue on your glassware. Rinse aids and salt based water softeners help remove these minerals. The prime culprit is calcium carbonate, aka lime or chalk. Which is an abundant mineral in many inland lakes and groundwater sources. A softener works by bonding exchanging the calcium ions with sodium ones. Here's a little explanation on [how the process works]( URL_0 ). Hard water and mineral stains can also be a problem with your laundry, though it's often not as noticeable as it is with dishes. Though I personally have my washer hooked up to a water softener due to the high lime content in our water."
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98b6kc | How does a submarine submerge but can also float? | Engineering | explainlikeimfive | {
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"text": [
"Submarines have tanks called ballast tanks that control the ships buoyancy. They’re filled with air to make the submarine float, or filled with water to make the submarine sink, and the air ejected. Filling it with air requires tanks of compressed air on board to force the water out of those tanks.",
"Former submariner here. There are a set of ballast tanks in the front and back of the ship that are between the thick pressure hull and the thin outer hull. These tanks are open on the bottom and when air is forced into them the water flows out making the ship light enough to float. To submerge the ship, valves on the top are opened to let the air out. The water comes back in from the bottom and the ship is heavy enough to sink. The ship carries enough high pressure air to force the water out of the ballast tanks but we don't like to use up that air because it takes a long time for the air compressors to put it back into the air banks. The normal way is to come close to the surface and put up a snorkel mast which can be used to suck in air which is blown into the ballast tanks.",
"It contains ballast tanks to adjust this. Filled with water, they make it sink. Filled with air, they make it float. Partway, they make it neutral."
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98j5o6 | Why do suspension bridge decks curve upward? | On pictures of Suspension bridges, there is a noticeable curve on the road deck, is there a particular reason as to why it happens? | Engineering | explainlikeimfive | {
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"If it were flat, and any weight was added to it, it would bend downwards. Nothing can be perfectly stiff. By starting with an upwards bend, once it bends down it will either be flat or still bend upwards. Also, at any location of the bridge, the neighboring locations are curved away below/behind it. This helps distribute the load from where it’s located to neighboring parts of the bridge. This is the basic idea of an *arch*, which has been used with everything from basic stone construction to concrete dams and suspension bridges.",
"In additional the structural reasons discussed, there is also the fact that a large bridge over a major navigable waterway needs to be low enough to meet the road at each end, but be high enough for large ships to pass under it in the middle."
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98jlsm | Why are there so many different sizes of tires? | Engineering | explainlikeimfive | {
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"text": [
"There's a few reasons. First, tire size is highly related to vehicle performance and can be a factor in its design and cost. You see those crazy drag racer hot rods with the tiny tires out front and the giant donuts in the rear? That's a sort of extreme example of how tires can impact what a vehicle drives like and feels like. So for small cars like a mini Cooper which don't have a lot of room to stuff a big fat tire under the fenders, you want small tires, and for a big booming Mustang, you'll want a larger tire because the more muscular engine can rotate its larger mass and accelerate much faster. Second, tires look different. High performance tires with specialized rims make a vehicle look pretty damn awesome, and so there's demand for tires that look a certain way and have a certain size characterization. Third, there wasn't just one single car manufacturer so there wasn't one single tire size. As car companies made their own products, we kind of drifted into a market situation where all tires weren't interchangeable, and because nobody with the right level of authority put their hand up and said \"Hey world, stop this insanity! Standardize on tire sizes!\"... it never got addressed.",
"Among other things people may be looking for something with better traction, less rolling resistance, asthetics, snow tires, all season. Different duties result in different profiles. You're vehicle also may have different options for wheel/rim sizes from the factory.",
"The first thing you need to keep in mind about tire sizes is that they all depend on the rims. Rims are, according to some kind of general consensus, supposed to be as large as possible. Because that looks cooler, or whatever. But there is also a technical reason. There is something important that has to fit inside the rims: the brakes. The brakes will typically be more efficient, and safer, if they are larger. Many car manufacturers intentionally fit larger brakes on the more expensive engine alternatives, because with more power comes the need for better braking efficiency. And with that, they also need to go up a size or two on the rims, to fit the brakes. It's also worth nothing that brakes are, generally speaking, larger on heavier cars. Because braking power is all about how much weight is set in motion and how fast it has to be able to stop. Anyway. Brake size alone on different engine alternatives on otherwise exactly alike cars can typically mean that the same car comes from the factory with several rim alternatives in different sizes. But, well. The rim holds the tire. But despite the size of the rim, the tire is still supposed to have the same rotational diameter. Which means that if a car comes from factory with two possible rim sizes, it also comes with two tire size recommendations. And for those who feel that they want even larger rims, there are most likely tires on the market that work with those rims. Which adds one or two sizes more that has to go in the catalog. And still just for one single make and model combination. Next, let's talk a bit about traction. Traction, when it comes to tires, is a lot about the area of the surface of the car that is in contact with the ground. Because that rubber underneath the tire is the only place where you got any kind of grip on the surface. If you make your tire wider, you'll automatically add some traction. This is important if your engine is powerful. If you apply more power than your tires got grip for, they will instead just burn rubber and you will get nowhere. A wider tire means that you can apply more power as you try to take off, and get more acceleration out of it. This means that the standard car in our example above can all of a sudden have several non-standard rims that offer wider - or narrower - tire alternatives to it. And all of a sudden we are up to...whatsit, somewhere between 8 and 12 tire alternatives for the same car, depending on the chosen rims. And like this it goes on and on and on. For every bloody car on the market, there is somewhere between a handful and ten sensible manufacturer approved tire sizes, and two or three times as many extras that you may toy with. Every Single One. And let's not get started on tractors and construction machinery, where some farmers got several tire sets for their tractor to better fit the dirt types he encounters through different seasons. Or different comfort levels with perhaps one set of tires on dirt, and one for the road transports during the harvest season."
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98nlzm | why so many different pasta lengths and shapes? What do they even add to the dish? | Engineering | explainlikeimfive | {
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"text": [
"If I’m having a dryish pasta with lots of small bits (bacon, peas etc...) i’ll choose a smaller pasta like orzo or macaroni, so it all mixes better and the small bits don’t just drop to the bottom. With a pasta with more sauce I might choose a tubular pasta so the sauce fills it a bit. Long pastas like spaghetti and tagliatelle are also good with sauce, where the sauce coats the strands. I might choose a wider pasta like pappardelle with shredded meat dishes like ragu so the shreds cling to the long wide strands. These are just some examples, but the large variety of thickness, width, length and shape allows for a lot of customization to enhance particular dishes.",
"It can change a lot of things.. if you eat penne with some sauce like ragu, they can catch more of it. :)"
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98pmjw | Why when digging tunnels for trains and traffic do we use large boring machines rather than explosives like we do in mining? | Engineering | explainlikeimfive | {
"a_id": [
"e4htojo"
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"text": [
"In a mine you just want to get deep asap to get to the goods. A train tunnel needs stable walls so that the tunnel doesn't collapse on top of a train full of commuters. Just randomly blowing holes to make a tunnel does not yield stable walls..."
],
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98y3co | Are cabin windows on commercial jets literally just there for the passengers to lookout? If yes, then why are the windows always either too forward or too back? | Engineering | explainlikeimfive | {
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"e4jl3xz",
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"text": [
"Yes. They are just for the passengers. The plane hull would be stronger without the windows but then flying would be a more claustrophobic experience. The windows used to be aligned with the passengers' seats before airlines realized they could squeeze more people in a plane by compressing your legroom. Because the seats are closer, they don't line up with the windows very well.",
"Different airlines buy the basic jet and outfit it with their choice of seating. Seats may be different sizes, provide different amounts of leg room, have more/less/no first class (which has more space per row) and either some divider or maybe a bathroom between first class and economy sections. The windows are located where possible, based on the structure of the plane body itself (you can’t have a window where you have a metal “rib” holding the shape of the plane). It’s safe to assume this spacing is as reasonable as possible, based on the designer’s guesses of how the plane might be set up, but there’s no way for it to fit the location of every seat, with every way the plane could be set up."
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