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g2z9hq | How do tower cranes not tip over and stay in balance? | I've always wondered that since one side is very short and the other side is very long relative to its center point. | Engineering | explainlikeimfive | {
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"Look at a tower crane and you should see the large counterweight on the back end of the jib, the other side of the upright. Movable to balance different loads on the main arm and a load as it moves inwards and outwards. Sometimes they get it wrong. This small mobile one uses a tension system at the rear end of the jib instead of a counterweight. URL_0"
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g30eo5 | why is it easier to balance something on your hand when it’s top heavy, but it’s more stable on the ground when it’s bottom heavy? | Engineering | explainlikeimfive | {
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"When you try to balance something like a broom in your hand, you have what is known as an [inverted pendulum]( URL_1 ). The physics for ***any*** pendulum, inverted or not, dictates that the longer (or heavier) the pendulum is - the harder it is getting it to move because it has a greater [moment of inertia]( URL_0 ). The moment of inertia for a pendulum can be determined using a bit of maths, including integrals, but a simplified case is that the inertia of motion is proportional to mass and distance squared: I=mr^(2) This means that if the distance from the pivot point to the centre of mass doubles, the moment of inertia is going to quadruple. This is why a top heavy object is easier to balance. Try turning said broom upside-down (right side up?) and you have a pendulum of equal length and mass, but with a shorter distance to its centre of mass, and it's going to be much harder to balance. In regards to the second part of your question: every object has a [support polygon]( URL_3 ). As long as (the extension of) the resulting force acting on an object passes through the support polygon, it's going be stable. You can choose to make the support polygon bigger (e.g. spreading your legs) in order to make something more stable, or you can lower the centre of mass - because that's where the resulting force acts on the object in question. \\- Sidenote: both of these things, inertia of motion and and a lower centre of mass, is why it's easier to walk in a tight rope if you have one of those [really long sticks]( URL_4 ) to hold onto! The stick is very long, meaning the r^(2) increases and thus also your moment of inertia, but they also bend due to gravity, which lowers your centre of mass. It's also how those seemingly impossible [balancing birds]( URL_2 ) work."
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g39ulx | How do hand soap dispensers turn liquids into foam? | Engineering | explainlikeimfive | {
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"Have ya ever blown bubbles? That is how the foam soap dispensers work, they blow the soap into a foam with compressed air similarly to how you blow bubbles. It just makes a lot of little bubbles instead of a few large ones."
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g3gzol | Why do they construct manholes in the middle of the roads? | Engineering | explainlikeimfive | {
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"Manholes usually cover deep trenches used for sewage or storm systems. They work best in the middle of the road because they can service both sides of the road while leaving the areas on the shoulder/sidewalk free for shallow systems like electricity or gas that are typically used for buildings near the sidewalk anyway.",
"Civil Engineer here, the code for water main and sewer (includes both sanitary and storm) require at least 8 feet of separation. By putting the sanitary manholes in the center of the road that allows us to have water main on one side and storm on the other if present. Let me know if you have any other questions!"
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g3kdo7 | How do cars powered by hydrogen, water or compressed air work? | Trying to help my sibling with her homework while knowing nothing about cars. Why would these be better or worse than the electric or plug-in alternatives? Thanks in advance. | Engineering | explainlikeimfive | {
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"Hydrogen engines are better for the environment and more efficient, yet costly, harder to maintain and EXTREMELY flammable.",
"How they work: * Hydrogen is a fuel that you can burn instead of petrol (gasoline) * Compressed air is mechanically stored energy that can be released to drive a turbine or pistons like steam does * Water on its own cannot power a car Pollutants from the vehicle: * Hydrogen is cleaner burning than hydrocarbons and bio fuels. However it still produces nitrogen based pollutants. If you could feed you engine hydrogen and pure oxygen instead of atmospheric air it would only emit water vapour with very small traces of other pollution from the lubricants * Compressed air emits only air Pollutants produced in production for both: * Depends on processes used and energy sources for those. Ideally you would use renewable electricity as a primary energy source. Compared to electric cars: * Many practical problems still to be solved for hydrogen fuelling * Hydrogen still has exhaust emission problems * Compressed air is very inefficient * Full electric plug-in cars are the 'cleanest' using current technology",
"Well, hydrogen is burned in an exotherm reaction with oxygen, much like diesel in other cars. Hydrogen and oxygen react to water, which is the only emission that comes out.",
"Cars powered by hydrogen usually work by reacting it with air in a fuel cell to produce electricity to run an electric motor. That is good environmentally but hydrogen is flammable in a crash and needs extra energy to cart around heavy pressure cylinders. It would be theoretically possible to use hydrogen in an internal combustion engine but it's not as efficient as petrol. You can run steam engines on water (or compressed air) but those are not the prime source of power, just an intermediary. You need to burn a fuel or use electricity to boil the water or compress the air."
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g3oi53 | Why do doors at businesses open outward, but residential doors open inwards? | Engineering | explainlikeimfive | {
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"If your house door opened outward, the hinges would be on the outside, and a thief could just take the door off the hinges and walk right in. So it's a security thing.",
"For commercial doors, it's a safety thing - if a mob rushes an exit, like when there's a fire, they could be pressed up against inward swinging doors, preventing them from opening.",
"Residential door hinges are almost always the pin type. On the inside of your house they work well and are secure. On the outside someone could pop the pins and enter your home. They would have to make more secure hinges to make residential doors open outwards. If you look at commercial doors they have a more complex hinge and are not as nice looking.",
"Businesses doors open out so that in case of fire a stampede to get out the exit door won’t block the door from being opened.",
"All of these are great answers. Another factor is that if doors open inward for a business then they waste valuable retail space.",
"I was always told it had to do with fire safety and the groups involved. Might be wrong, but made sense at the time. Fire crew can't bash an outward swinging door as easily if you are incapacitated in a burning house. For businesses, if there was a fire then people would be rushing outward and an inward swinging door would be a hazard. No written knowledge here. Only hear say. Take it with a grain of salt, but it makes sense.",
"OSHA regulation require establishment doors to open outward to aid in a quick exit during an emergency. These regulations dont apply to your house which will likely never see the same level of occupancy and all the occupants are likely to know where the means of egress are located.",
"Just guessing, I think it's a safety thing. If someone is trying to get into your home unwanted, it's easier to block an inside opening door than an outside opening door.",
"Building Codes. Generally, in the US, if the computed occupant load serving the door is greater than 49 the door must swing outward."
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g3sttz | How did the Apollo 11 astronauts survive through the Van Allen Belt? | Engineering | explainlikeimfive | {
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"The flight path to the moon was calculated to fly through the thinnest part of the belt. There’s an inner belt and an outer belt. The flight path skipped in inner belt completely.",
"The Van Allen Belt isn't a constant stream of radiation surrounding the entire planet. It is more intense in certain areas at certain times. After measuring the radiation over extended periods of time, they were able to figure out the best time, and relative location of the moon, to launch that would pass the shuttle in areas with the least radiation. Combined with lead and other radiation shielding over sensitive components, and they managed to get the astronauts through with minimal radiation exposure.",
"The Van Allen Belts are clouds of instant death or some impenetrable barrier of deadly radiation imprisoning us on our plane, they're just rings of charged particles trapped in the Earth's magnetic field lines. You wouldn't want to spend a lot of time in there, but it's nothing like what moon landing hoax believers make it seem like. The Apollo spacecraft went through the thinnest part of the belts, they were traveling very fast so went through the belts very quickly, and the metal that made up the spacecraft provides decent shielding against that type of radiation. The astronauts worse radiation dosimeters during their missions, and their time in the Van Allen belts gave them about the same radiation dose as a chest CT scan."
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g476rf | how does Velcro work? | Engineering | explainlikeimfive | {
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"[Hook-and-loop]( URL_0 ) is the actual name, with Velcro being the brand. It works with soft loops and hard hooks.",
"if you look very closely, you will see that the soft side is all loops, and the rough side is hooks. but the hooks are flexible enough to let go of the loops if you pull hard enough. it's actually very satisfying to watch closely/slowly lol"
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g4b839 | Why do laptop chargers come in two parts and not one cord? | Engineering | explainlikeimfive | {
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"Laptops and chargers are usually distributed all over the world. There are dozens of different wall plug types, AC line frequencies (I.e. 50 Hz/60Hz) and voltages (I.e. 110/220/240 volts). Electrical designers have engineered a charger that will accept any combination of line voltages and frequencies within the ranges specified above, so they need to manufacture only a single power supply regardless of where in the world the laptop is used. What is not universal is the wall plug. So the manufacturers make a single universal charger as one piece and then ship the laptop with the locally-required plug type.",
"A whole host of reasons actually. 1. Power bricks for laptops are normally voltage interchangeable between 120/220/240v depending on where you at in the world and each country or area has its own standard wall socket they use. It's cheaper to make one universal brick then just make the cords for each country you plan on selling the laptop in. 2. They are required to get certain approvals from certain places. (Various regulatory bodies and UL and stuff like that) 3. Strain relief. It's a good way to build in strain relief on the higher voltage side instead of just soldering the wires on. 4. This one only applies to things like Toughbooks and things used in industrial environments. It's better at keeping water/chemical ingress out and less chance of it shorting the hot and neutral together. As the conductors are covered."
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g4cm0v | How do they crack games? | Actually im a computer engineer senior student. I have a few idea but this is a subject that im not very familiar with. (You can use computer science terminology) | Engineering | explainlikeimfive | {
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"ELI5: We use a tool that tells us what bits do what, and we change those bits to do what we want them to. ELI15: Software gets compiled down to machine language. We have tools, such as IDA Pro (what I used, but there are other popular ones) to reverse engineer this machine language into something readable (Assembly, usually, but I hear there are ways to get C code these days). We can then read this to understand how the anti-piracy mechanisms work, such as \"this function call checks for a legitimate copy\" or \"this function takes in a key, checks it, and calls one of two functions depending on the status of the check\". We can then write back some assembly in the right spot to coax it into the right behavior, such as \"this function now always returns a good result\" or removing a function call by writing null bytes in its place. This at least works on a very basic level. I imagine trying to crack something like Denuvo requires more sophisticated tools, but I'm not familiar with them.",
"A lot of the anti piracy stuff these days rely on calling home and denying an account or hardware ID if something fishy is found. Its a lot \"safer\" than putting any sort of protection on the software where you can use code analysis and decompilation to skip the checks. The game still functions but their login servers won't let you login, or you can't find a match, or no user data is sent to you, etc. This renders the game unplayable without doing anything client side. The basic attacks against this is to circumvent the call home. Classic cracking technique (decompiling and manually editing the binaries) will do this. Of course this fails if you need any sort of data from their servers. If the game has online components your only real long term solution is to spoof the server. This is actually really easy client side. You find out which IPs the game is calling and just redirect calls to those address to your own server, localhost most likely. Then the hard part will be figuring out what the game is expecting back and mimicking it. Also, because so many games these days have an online component, a lot of the software protection is more about cheating than ensuring you paid for the software. Map hacks though are often easily done client side since its a matter of messing with the rendering system, the client is already getting all the data you need to know where everything is, its just not showing it to you. Similarly aimbots are often image processing and automated mouse controls. Depending on how much the servers trust the client, a lot can be done. To combat this anti cheat does check sums to verify if the software has been tampered with. Many also check to see if there are suspicious programs also running, using a database and heuristic system cribbed from anti virus software. The server may also do sanity checks to see if you are sending questionable data. Does all this sound incredibly tedious? It is! And often very time consuming. Maybe its worth $60 to just not have to do all that. The technical challenge is interesting though."
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g4qm5n | Why do fans (and propellers) have different numbers of blades? What advantage is there to more or less blades? | An actual question my five year old asked me and I couldn't answer, please help! | Engineering | explainlikeimfive | {
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"It's always a balance. Number of blades: * Fewer blades = More efficient shoveling of air because of turbulence (air swirls) created by other blades reduces efficiency. Usually simpler to make. * More blades = More stable because the force is spread out over more blades and shovels more air compared to how long the propellers are. Propeller tips breaking sound barrier is bad (because of lots of turbulence). The longer the propeller the faster the tips go compared to the center. But having too short blades means more loss of energy at the blade tips: * Longer blades = Better at generating lift, shoveling more air at lower speeds. Longer propellers also less stable and vibrate more. * Smaller blades = Allows higher top speeds since the propeller can go much faster without breaking the soundbarrier with the wingtips. More stable. So basicly.WW1 airplane: We can't make so good engines. So we're gonna go with efficient short two-bladed propellers because that gives is the most thrust for our weak engines. WW2 airplane: We gots a lot better engines now. But two-bladed propellers can't shovel enough air to take our planes as fast as we're going to go. So we're going to go with 4 short blades! Helicopter: We gotta generate lots of lift. So we're going to go with longer and slower rotating blades! Modern helicopter: Uh. Those blades aren't generating enough lift. MORE BLADES! More blades is harder to make, but more stable too. Modern turboprop: Too noisy! We're making special 6 bladed propellers that are much quieter. And computer power and advanced materials allows us to make them special advanced shapes that generate even less noise and more power. So now they look more like ship propellers. But for air! Still kinda short blades because we gotta go fast! Ship propellers: Water dense yo. So we gotta make blades short (or they'll break!) but we make them much wider to shovel a lot of water backwards. P.S: Jet engines work entirely differently, even if they do have fans at the front they're for compressing air into the engine, not generating thrust. P.P.S: For ceiling fan. You're moving lots of air, but you want to do it slowly and silently. So lots of wide blades. How long the blades are depends on how mobile you want the fan to be. Big fan = more air silently. Small fan = Noisier, but more mobile.",
"Next time you’re in a swimming pool try moving your hand through the water as fast as you can. Change the angle a bit and notice that you push more or less water around. Now try it again with your whole arm under water. You can push more water around but it also requires much more effort. Propellor optimization (fans are just propellers) involves striking a balance between the amount of fluid you want to move at the energy used to move it. Increasing the surface area of the propellor will move more fluid but require more energy to operate. This can be achieved by increasing either the size of the blades, the number of blades, or both. A house fan only needs to move relatively little air at high efficiency. A speedboat propeller is going to be optimized to move water. Many airplanes also have the ability to change the angle of their blades, taking a larger or smaller “bite” out of the air without changing the surface area exposed to the medium.",
"Here's my best shot at an ELIF: Generally, the more blades you have (and the larger they are) the slower and quieter the fan will be. It all has to do with resistance. You'll notice that a lot of helicopters only have four really skinny blades; Super fast, and SUPER loud. Very interesting question, kid! Edited to say it wasn't as hard as I thought to make it simple lol",
"Its a balance between a lot of factors Each additional blade adds more weight and cost which requires stronger($$$) engine components to overcome the increased drag from additional blades trying to move through the air. They also disturb the air they pass through so having 8 blades instead of 4 won't give you twice the power because the extra blades are now passing through disturbed air and not working as efficiently. Generally you get better results from increasing the length of the propeller but this requires a stronger propeller($$$) Generally the better option is to have a second cheap engine/propeller set (think twin engine propeller planes or the Chinook), or to use more elaborate propeller setups like [Contra-Rotating propellers]( URL_0 ) which boosts propeller efficiency giving you more thrust with the same horsepower despite driving two different sets of blades. This was used on the later Spitfires to get the most power possible out of their limited propeller diameter.",
"One video I remember and is kind of relevant (wind turbines) could maybe help you slightly. I don't know how to link on mobile but the video is on YouTube by \"Real Engineering\" and is called \"why do wind turbines have three blades\". There's also a second video with the same title on the channel called \"DOB-Academy studio\". They give you some more info. The videos should take you around 3 minutes to watch and they can explain the topic much better than me.",
"Aero engineer here, albeit late in the thread. While everything I’m reading is true for propeller design, it all boils down to mass flow rate. The true ELI5 answer is you can change the propeller’s overall diameter while pushing the same amount of air. Each blade moves some air mass proportional to its surface area. Assume two long blades move about the same amount of air mass as four short blades half the size. Design constraints determine the rest which goes above the ELI5: max prop diameter to the ground, excess power required for performance, engine efficiency, blade tip speed, etc. Edit: clarified size— > diameter",
"Right up my alley because I'm about to do this for a living. There are two big reasons props have more or less blades. One is ground clearance and two, power dissipation. You know how some cars can be slow, but some are really fast? The slow car has less power than the fast one. So the same goes for propellers. The slow ones have two blades and the fast have three, four or even five. The more powerful the engine, the more blades you can have. The other has to do with how high the engine is off the ground. The lower the engine is to the ground, the smaller the propeller is. The big reason you don't see huge two blade propellers on aircraft is because they'd be too close to the ground and they'd break apart if they started turning.",
"\"When a fan has fewer blades, there is less drag on the motor and it can go faster and move more air more [efficiently]( URL_0 ). This results in much more airflow and will create a better wind chill effect, making your space feel cooler.\"",
"Propellers are matched to the engine output and that combo is matched to the aircraft. A four-bladed prop of otherwise equal dimensions can impart twice the power of its two bladed version but it will be heavier and more expensive. If you have fewer blades the setup will be lighter but you generally need to make the blades longer and some aircraft are too low to the ground to cope with that, so the designers will give them more blades at a reduced radius/chord length.",
"There is a tangent point to this that you might also be interested in knowing. Fans tend to be built with an odd number of blades because of harmonics. A fan with 5 or 7 blades will sound like it makes less noise than a fan with 6 blades.",
"all the other answers are wrong. its actually quite complicated, you can have 2, 3 or 4. sometimes 5, but never 1 (except in extreme cases) 2 or 3 are usually most efficient for anything from a small pedestal fan to a giant turbine. the reason why a 10MW Turbine has 3 blades and not 2, is different than the reason why a plane prop has 4 blades instead of 3. or a outboard prop has 3 instead of 2 in the first case the big turbine blades are optimised to squeeze maximum efficiency the second case has to do with lower tip speed and lower noise (keeping it under speed of sound) TL:DR: It depends!",
"Radio control hobbiest checking in. A propeller works just like a wing except instead of generating lift by gliding through the air it generates it by rotating through the air. Like a regular wing, the more wing there is, the more lift that is generated, but also the more drag or aerodynamic resistance. You can either have a little bit of wing move a whole lot of air, or a lot of wing move just a little bit of air. Each has it's advantages and disadvantages with respect to efficiency, power, etc. The main reason a prop might use more than 2 blades is because of constraints to how long each blade can be so you're not hitting the ground or the fuselage with ridiculously oversized blades. There are other ways to generate more thrust with a propeller though and each has advantages and drawbacks. To create more power from a propeller you can do one of the following: Spin it through the air faster. (losses from friction as it spins faster and limit to how fast it can spin) Make each blade longer (The blade has to clear the ground during takeoff so you can't make them too long) Have more blades (increases aerodynamic drag and more chaotic air reduce effectiveness of extra blades) Use an airfoil shape for each blade that moves more air. (requires much more engine torque for a given RPM, harder on the engine, allows for higher speed but less climbing ability, think of prop pitch like the gear on a car, higher pitch is like being in fifth gear which is great for speed, but not so much for hill climbing)",
"Good answers here already. I will add that some fans don't look like what you consider to be a fan at all, if you look online at pictures of industrial exhaust fans you'll see what I mean, but here's what I want to say about that: As others have said, how much air a fan moves depends on a few things: diameter of the fan, the angle of the blades in relation to the fluid you want to move, number of blades, the horsepower of the motor that's turning the fan, and how many rotations the fan makes per minute. In a factory with, say, a very dusty process, if you want to control that dusty air by sucking it away from the work area, you would need one kind of fan. Generally speaking a very big one with a big motor, because sucking is very expensive (lol). Especially if you are sucking large volumes of air heavy with dust you want to move from one place to another. Try blowing a small piece of paper across a table with a straw. Easy. Now try sucking the same piece of paper up from a distance of an inch or more. Not so easy. So part of what determines how many blades a propellor or fan will have is, as others described, what's it for? How much fluid does it have to displace, and in what timeframe? What is the density of the fluid? Air? Water? Wet concrete? Think about/look at the motor on a celling fan. Then go outside and look at the outside unit for your air conditioner. It has a fan that you can see and hear up close. (There's also a compressor that makes it's own noise) Would you want that fan in your living room? Why not? Big, loud, blows too much air. Can you propel a 4000lb boat with a celling fan? No. Why? Well, the motor for one. But also the orientation of the blades relative to the fluid being displaced. A boat propeller is shaped more like a screw, or like an auger. That's about the direction you want to move, and is beyond what I can eli5."
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g50dam | Why are phones water resistant only for certain amount time or depth? | Eg: IPhone SE is said to be water resistant only upto 30 minutes and 1m depth. When something is water resistant, shouldn't it be resistant irrespective of how long its soaked? What happens post the time limit or depth? | Engineering | explainlikeimfive | {
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"In that amount of time, the sealants may dissolve. At greater depths, the pressure would overcome the resistance of said seals, and water would push in to anywhere it would fit.",
"There is an international standard for testing water resistance. The parameters given reflect the test that the device was able to pass. No doubt, Apple considered subjecting the device to more stringent tests, and presumably didn't think that it would pass reliably. If you exceed the parameters of the test, \"nobody knows\" (which means \"nobody is willing to guarantee\") what might happen. It might be fine, it might get water inside. Regardless, you exceeded the listed water resistance, so if something bad happens it's \"your fault\" and Apple doesn't have to fix it under warrantee."
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g54smn | What triggers gas pumps to shut off once your tank is full, or even in a simple gas can? | Engineering | explainlikeimfive | {
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"the round bump on the top of the handle actually contains a little diaphragm connected to a second little tube that, once you've got enough in the tank, begins to suck up overflowing gas, and tells the diaphragm you're full. see: URL_0 so it comes down to the handle knowing how much pressure is pushing back against the pump."
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g5872o | Why do computers heat up/need cooling | Engineering | explainlikeimfive | {
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"The bits inside the computer that do the, well, computing? They depends on electrical current moving around in conductive (but not perfectly conductive) materials. Moving a current through some resistance generates heat. It might be minimal for any given computational operation, but even small computers perform *loads* of operations over time. Without some means of getting the heat elsewhere (since it would simply move into nearby computer parts/air in the case if left alone), the cumulative heat buildup in a computer case or in specific components can become so great that it damages said components. So we devise ways of moving the hot air around, giving heat more efficient pathways away from the originating parts, etc."
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g5cxj6 | Why does water pressure in the showers changes when temperature changes? | Engineering | explainlikeimfive | {
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"The water pressure is being generated either by the city water pumps or your home well pump. But the pressure felt at the outlet of the pump is not what is felt at the faucet; with every inch of pipe it flows through, every pipe bend, etc., it reduces somewhat. This is sometimes referred to as \"pressure drop\" or \"head loss\". The cold water in your home flows directly from the well pump or city supply connection at your house. The hot water, on the other hand, flows first through your water heater; this incurs greater head loss, since it's a longer and more tortuous flowpath. So your hot water at the tap has a somewhat lower pressure. Consequently, when you adjust temperature, you also adjust pressure.",
"This depends heavily on the country you're in. Many countries have separate lines for hot and cold water. At least where I live the hot water has less pressure so the hotter you turn the water, the less pressure it'll have. Though I don't know if this is a safety feature or just because of the way the water is heated.",
"Hi, I am a plumber of over 4 years. Basically there are tons of different types of valves and they all act differently. Since you are specifically asking about a shower, those valves have a point where the hot and cold water meet (mixing valve). The pressure of the water doesn't change. On older shower valves there if nothing to prevent the hot water to flow into the cold water side of the valve or vice versa. This is where the problem is for example if someone were to flush a toilet close to the shower it would feel like there's less cold water pressure but the hot water is actually backfeeding into the cold water line. Or if someone turned on only the hot water to wash their hands at that bathrooms sink the water in the shower may feel colder or \"less pressure\" but it's the cold water backfeeding into the hot water line. On newer shower valves, kitchen faucets, etc (especially single handled valves) there is a part called a pressure balancing spool. This is similar to a backflow device or a check valve where it will only let water flow in one direction. This eliminates the effect of \"less water pressure\". . . Edit: And now that I'm reading your question again for the third time I'm realizing I read it wrong and gave you the wrong answer as well as a bunch of useless information. Instead I should have asked what you meant by temperature changes. Do you mean weather or temperature in the house?"
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g5dm4d | How can the police find the gun just by having the bullet that's been shot from it? | Engineering | explainlikeimfive | {
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"They can't \"find\" the gun, what they can do is test a gun and see if it makes the same marks on a new bullet as does the old bullet the marks or lands and grooves are created as the bullet moves down the barrel of the gun and are unique to each gun.",
"Well first thing they can do is tell what type of gun fired the bullet by the bullet size. (i.e a 9mm bullet was fired from a gun that fires 9mm bullets so they know what type of guns their looking for). Next when they find a gun they fire a bullet from this gun. In the barrel of every gun is corkscrew like grooves which make the bullet spin as it leaves the chamber. This leaves an imprint on the bullet which is individual to that particular gun, think of it like a thumbprint. So they test fire the gun they think was used in the crime and then compare it to any bullets found at the scene. If the bullets match then that’s your weapon and the case goes on from there",
"They can't. Just having the bullet tells you almost nothing useful. However, they can use that with other information to locate a gun. Perhaps that gun has been used to commit a crime before, and it was sold at auction; there will be a record of that. So the ballistics from the previous crime and the auction data could provide a starting point. Or perhaps you don't just have the bullet, you have it embedded in a wall; tracing that damage back through other points, like a broken window, could lead to where the shot was fired from; perhaps the shooter abandoned the gun there or close by. Or perhaps the bullet itself is unusual; for example, it may be a .40S & W with a jacket swaged from 9MM brass. That's almost certainly the product of a handloader, so they might start asking around about people who do custom handloading, or who have purchased bullet swaging equipment. That could lead them to who made the round, which could lead them to who bought and fired it."
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g5ekbe | why don’t people who disarm bombs (with wires) not cut all of them at once | Engineering | explainlikeimfive | {
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"Bomb difusal in movies is very different from real life bomb difusal. Most bombs will be disarmed just by cutting a random wire and does not contain any traps for bomb disposal crews. However a big problem is that you might accidentally short circuit some wires so the bomb goes off unintentionally. The best way to prevent this is to cut one wire at a time and make sure it is safe before you cut the next wire. Cutting them all at once carries a huge risk of short circuiting them. There was one notable bombing in August 1980 which did look like a classic plot for a movie and did include traps for the bomb disposal team. Instead of trying to defuse the bomb using wire cutters and risking someone blowing themselves up in the process the FBI decided to cut all the wires at once using an explosive charge. Nobody knows exactly what went wrong, if they used too little or too much or if they placed their charges wrong. In any case it did not work as well as they had hoped an the bomb detonated.",
"Actual former bomb tech here (USAF EOD). Some of the other things people are saying are right to varying degrees. Another very important point I didn't really see mentioned is that a bomb tech's life is a valuable thing. The military spent hundreds of thousands of dollars and a solid year training me before I was considered anything more than an apprentice. So they wouldn't risk my life over something trivial. If a job could be done remotely, by a robot, or by placing a tool and activating it after I was safely away, that would always be priority 1. My team leader in Iraq did a \"hand entry\" on a device that he really did not need to. He disarmed it successfully, and was thoroughly chewed out by leadership afterward. He was very nearly dismissed and sent home. As a final fun fact, in one of our advanced IEDs classes, we learned a relatively simple way to make a firing circuit that could detonate a bomb through the wire that you just cut.",
"Long story short, because disarmament is dangerous and bomb disposal is not only easier, but safer. Its actually pretty rare to see true “disarmament.” Usually a bomb tech will elect to blow-in-place, or BIP the device after securing is under a blast shield, or use what’s called a disruptor charge which is essentially a shotgun shell filled with water to destroy the bomb’s trigger mechanism without causing detonation.",
"Most machines are made 'fail safe', meaning they will shut down if some part of the system fails. Think of a lawnmower - you have to hold down the handle for it to work. That's so if the owner say collapses while using it, it doesn't continue to spin it's lethal blade. A bomb designer, depending on the level of evil, could have designed their bomb around the opposite principle. The circuit or mechanism is actually *preventing* the bomb from going off, so it will explode of the interrupted. If this is the case, bomb disposal needs to be carefully planned and carried out. More likely, they will detonate it under controlled conditions.",
"Other reasons aside, cutting all at once is almost impossible when compared to the speed of electric current. So unless you're lucky enough to cut them in correct sequence, you're boomed."
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g5l3mg | why hearing aids can't be used by normal people to get even better hearing? | Engineering | explainlikeimfive | {
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"They can. Hearing aids just make sounds louder. My shooting earmuffs do the same thing, and with them turned all the way up I can clearly hear people speaking 50+ feet away.",
"People can get over the counter hearing aides at a pharmacy, but your grandpa's hearing aides were most likely specifically calibrated for his specific type of hearing loss. Some people have a general hearing loss, where everything is muffled, but other people can have a muteness of certain tones, pitches or frequencies, not all hearing loss is the same. Also if everyone were to unnecessarily use hearing aides, it would make your hearing worse, hearing aides put decibels (sound volume) too high into the eardrum for someone with normal hearing, in fact most headphones do as well. I think there's been a study that hearing loss has increased since earbud/headphones became popular.",
"You can, but it's got the potential to make some things you could hear before become inaudible, or dangerously loud."
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g69iyv | How do people modify cars like supras and GTRs to have insane horsepower (around 1200+ hp)? | Engineering | explainlikeimfive | {
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"Usually larger turbos, free-er flowing down pipes/exhaust, larger intakes etc. You also need to upgrade internals on most engines once you hit 1k hp. Serious work involves increasing displacement as well. Some use superchargers, but that is much less common"
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g6nr45 | Why do some lights flicker first before completely turning on? | Engineering | explainlikeimfive | {
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"Some kinds of light such as fluorescent ones, need heating to be able to move enough electricity through the contained gas. I think what happens is that gas is ionised, emits light and loses so much energy in the process, that it needs a moment until it is ionised again. Ionisation is when electrons are pulled off the gas atoms."
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g6plfo | . How can the Hubble Telescope see billions of lights years away? | A distance so big our brains cannot comprehend it. | Engineering | explainlikeimfive | {
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"Because the objects that it is viewing are BILLIONS of light years long and wide. All of those nebulas you see are absolutely massive, they just not be incredibly bright. This is in contrast to Pluto which cannot be seen very well from the hubble space telescope. It is bright enough, but too small. Fun fact, you can see the [orion nebula]( URL_0 ) with just a camera."
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g6plt2 | Why can't fighter jets just fly straight into space? | Edit: I didn't understand how a jet engine worked, but now that I do, the question has been amended to this... "Why does a rocket have to travel faster and faster the higher up it goes? Shouldn't it require less and less speed as it is further from the earth it gets because there is a non-zero number(very small) of negative gravity change the higher you are?" Edit #2: I think I suck at asking this so I'll ask it like a 5 year old. We have all seen videos of rockets taking off. They start very slowly, and then build in speed. Although, at first, they build up in speed. It's not as if they torque off the earth at 20,000mph, although that would be ASTOUNDING to see. So here's my super drawn out really dumb question that I cannot wrap my head around the answer for the life of me. Let's say you have a rocket going 100mph going 90 degrees straight up from the surface of the earth. Why can't it just keep going 100mph straight up. Just keep going and going. Up, straight up. Up up up and away? Why can it move up starting from zero miles an hour? If it can move up at 5mph even for an instant, why can't it continue at that velocity all the way up. All the answers have been wonderful if I was asking how to get something in orbit. I'm asking why 100mph 90 degrees going straight up works down here, but not up there? I cannot find a straight answer to this question no matter what I google. I appear to be bad at research or this is just a stupid ass question. I really just don't understand the physics of this at all. Let's try this another way. Say I threw a magic baseball that whatever velocity it was tossed at, it maintained until it hit a object. It doesn't disregard gravity. It just has a magic anaerobic motor that maintains the speed. Like cruise control. Say I throw it 90 degrees straight up at 35mph. Will it leave Earth? Why or why not? | Engineering | explainlikeimfive | {
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"The way jet engines work is by pushing air backward. As you get higher, the air gets thinner and jet engines become less effective. Once you get high enough, a jet engine won't work at all. That being said, if a fighter jet used a rocket instead, there would still be issues. Space ships are CRAZY fast. Just to be able to stay in space where the international space station is, you have to go over mach 20. That takes way more fuel than a jet can hold.. at least for now :P. If you want to go slower and stay in space you have to go higher, and again, have more fuel. Final note, since there's no air in space an airplane's wings won't work either. The plane won't be able to turn or pitch, and anything that helped it stay in the air before won't do it much good now",
"Because a jet engine takes in air at the front and shoves it out the back to make thrust. There isn't air in space to suck in. I mean, with the right conditions you might be able to get it into space. But without a rocket or some other propulsion you're either going to fly off into the void or more likely get pulled back by gravity",
"As an aside... it is quite easy to build a rocket to get to space. You can basically launch one from your back yard. The problem is that to STAY in space, you need to get going 25,000mph laterally. That is the tricky part. Next to you watch a rocket launch notice that they don't go straight up. Almost immediately they start flying sideways in order to build lateral velocity.",
"That’s like asking why can’t a submarine drive above water. There is a lack of air density and oxygen at high altitudes. You need air density for lift to be created by wings, and you need oxygen for the engines to create combustion.",
"To answer your edit, The ISS experiences 99% of the gravity we do, IIRC. Even the moon experiences a lot of Earth's pull. Edit: Apparently I misremembered. [this]( URL_0 ) article says 88%. point still stands To stay in space, you have to enter an orbit. the ELI5 answer to this is, you have to go so fast, that by the time earth pulls you down, you go far enough to the side to miss it. Of course it's much more complicated than that. Orbital mechanics can be very daunting, but if you are willing to put in some effort, KSP can make you a rocket scientist before you even notice.",
"As other people have pointed out, rockets need to travel fast enough to maintain an orbit. The velocity is not about how fast you are going \"up\", but rather \"across'. People have explained that part well enough. The ELI5 is that your rocket will run out of fuel, so your rocket engine will shut down. The question is not \"how fast does the rocket need to go the higher it gets\", the question is \"how fast do you need to be going when your rocket engine runs out of fuel\". If you had a magic rocket engine that had a limitless source of fuel and enough thrust to lift the rocket, you could fly up into space at a nice, leisurely pace, like as slow as a person walks if you really wanted to take your time. Then you could stay above the Earth at any point regardless of whether you were in atmosphere or above the atmosphere. You would just use the always-on rocket to keep you in position. At that point the rocket is keeping you from falling back to the ground.",
"> \"Why does a rocket have to travel faster and faster the higher up it goes? Shouldn't it require less and less speed as it is further from the earth it gets because there is a non-zero number(very small) of negative gravity change the higher you are?\" You are right that the speed needed to overcome gravity (escape velocity) reduces as you climb...but not substantially until you've gone several hundred miles already. (Gravitational force is half at sqrt(2) earth Radii, or about 1600 miles above the surface.) And if you've made it that far you're going pretty fast already.",
"I don't think rockets *have* to travel faster and faster the higher it goes - I think they just *do*, since it's a byproduct of rocket engine design. Rockets burn fuel at a constant rate (at least solid fuel rockets do); however, the weight of the rocket goes down as fuel is burned, and air resistance goes down as the rocket climbs and the atmosphere thins. Therefore, the rocket keeps burning fuel and keeps accelerating, and accelerates at an even faster rate as weight and air resistance decrease.",
"You don’t need to move faster the higher up you go. But in order to stay up you need enough speed to stay in orbit or you will fall to the earth. To understand this, you have to understand orbit. An object in orbit is actually not “driving itself”, it’s constantly falling. It’s similar to swinging an object around with a string. The objects velocity keeps it moving and the string keeps it from moving away from the object it’s tied to. For orbit around the earth, gravity acts as the string. For it to work, your speed and height need to be calibrated correctly. Too fast and you’ll keep going out into space, and too slow and you’ll dive back to earth. The further away from the earth you are, the less the force of gravity acts on you and the slower you need to go to stay in orbit."
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g6qz07 | Why are skyscrapers nearly always covered in glass completely in contrast to small buildings? | Like is there a specific reason or is it just a design choice? Or do they have so many tall windows to let as much sunlight in as possible? It just occurred to me since the futuristic full glass look of skyscrapers really stands out against normal building surrounding them. | Engineering | explainlikeimfive | {
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"It's for both aesthetic and practical reasons. Aesthetically it looks stylish, and allows for a lot of options for colors and tinting. It also makes the offices inside more desirable when they have big windows with nice views and lots of natural light. Practically glass is lighter and easier to install and maintain than a lot of other cladding materials. Skyscrapers also almost always carry their weight on internal support beams so structural strength isn't a big concern for the exterior walls.",
"Glass isn't always windows. Glass is cheap, very durable, and not that heavy. It makes a much better cladding for a building that the marble/granite facades of early skyscrapers.",
"Skyscrapers are steel-framed. Leaving the option of all glass or not. Smaller buildings 2- 5 stories are usually wood framed. And more space is taken up by structure and the need for solid sheer walls. Leaving less room for Windows.",
"Since people have listed advantages already I request someone to list the disadvantages as well",
"Cheaper, easier to build, easier maintenance (it’s a pain to tick point a tall concrete/stone building), less busy design, less issue with privacy/people seeing in.",
"Doing brick, concrete or cladding systems is not really practical at skyscraper height mostly because of weight. Glass and aluminum extrusions is so much lighter and easier to get up there and install. Most of the load bearing elements of tall structures is concentrated within the building core, putting heavier materials at the perimeter could make for an unbalanced structure."
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g6uod1 | How do we construct things in water? Things like bridges or roads that need support pillars that go into the water. If they're made from concrete, how does the concrete ever dry if it's underwater? If it's in the ocean, does the very bottom of the pillar touch the seafloor? | Engineering | explainlikeimfive | {
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"Concrete curing is a chemical reaction that actually requires water to complete, although excess water in the mixture can yield a weaker cured concrete. Special concrete mixtures are used which are more resistant to chlorides (when pouring in seawater), and care is taken not to agitate an underwater concrete pour too much so that the mix doesn't thin out. You don't need concrete to dry to cure it. In fact, keeping a pour damp throughout the curing process will generally lead to a more complete cure, because the process generates heat that can evaporate water away from the surface, leading to slightly weaker concrete at the surface. Underwater you don't have that problem, though you do need to take care to keep the concrete and the surrounding water at its surface from being agitated and intermingling too much. Bridge pillars and the like are often constructed using caissons, which is like a waterproof shoring form that extends to the riverbed / seabed, and then has all the water pumped out so that dry construction techniques can be used.",
"Usually they build caissons, which are temporary dams that seal to the bottom or to a sealed bottom of some sort, then they pump out the water. That's not absolutely necessary, however, as concrete can be poured under water and will cure under water just fine. It's the people that don't like being under water."
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g6zwe4 | Why do I need to start/run my car every once in a while when it's not in use? | A *certain situation* has brought me back home to my parents house, but my car is across the country at my school, not being used until \~September. Why does everyone keep insisting it needs to be turned on/driven every once in a while? (Which it is, my landlords a pretty cool guy and offered to do it! | Engineering | explainlikeimfive | {
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"Cars that sit fall apart. Al;l the parts that need oil and grease on te=hem dry up and start to rust. Driving the car spreads the oil and grease where it belongs in the engine, the wheel bearings and on the seals that sotp the oil and grease from leaking out. If they sit for a long time those seals dry out and crack and start to leak. Also the brakes rust, and the brake seals dry out. And so on and so forth. The worst thing you can do to a car is let it sit for a long time. That is before we even talk about the battery going dead over time so if you left it until September it would not even start. And the battery likes a little exercise too. Your landlord is a good chap, take him a small token of appreciation, preferable beer."
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g71zw2 | Why do houses have a triangle shaped roof? Why not flat? | Engineering | explainlikeimfive | {
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"Houses have triangle roof so that rain and snow can fall down the sides and not create a big puddle on top",
"As someone with a flat roof I will tell you that it is very difficult to maintain. Because water does not so simply roll off the sides it will collect on the top and can seep into your ceiling. We have had to do repairs because of it Also animals like raccoons and squirrels can get on top easier and do damage to the roof.",
"Some houses do - but many would be found in drier parts of the world. In more temperate and cooler parts, you would need to be able to have snow/rain easily disperse from the roof instead of it pooling. If this happens, especially with snow, the weight of it might be structurally damaging. With rain, this would cause puddles to form which could leak into the house."
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g73e66 | how did the USA made the atomic bomb so quickly? Were the German scientists from operation paperclip already working on it for the Nazis? | Engineering | explainlikeimfive | {
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"A Norwegian special-forces ski-team infiltrated a Norwegian power-plant that was making heavy-water, which is what the Germans were using for their research, and sabotaged all the vats and sunk a ship carrying supplies ... killing a number of innocent countrymen in the process. URL_0 This slowed down the already hamstrung German research effort. Meanwhile in the US they built a new city, school-system and all, dedicated to supporting the staff to create the bomb."
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g73kqu | how are buildings with a rotating top floor wired? | i know this is random but it’s driving me crazy trying to figure it out. so there is a building in my city that the top floor rotated 360 degrees. how does the wiring, piping, etc. work? wouldn’t it get twisted up or break as the top floor spun but the rest of the building stayed in the same spot? (obviously it doesn’t but i just want to know how it’s done). if someone could explain this to me that would be fantastic and save me from hurting my brain lol. thanks. | Engineering | explainlikeimfive | {
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"Because the floor looks like it’s rotating doesn’t mean it does 100%. Usually it’s the outer portion with tables and eating area, to give customers the best view. This can be simply rotated via a disc mechanism under the floor. This is also not external. It’s all done inside. The Center portion of that area is usually fixed and does not rotate. Kitchen, bathroom, elevators, all are fixed. Also the ceiling is fixed where all lighting and air ducts go. So you basically have a fixed enveloppe with a moving “turntable” disc with a hole in its center. It’s called a rotating top floor but it’s really overall fixed (would be super dangerous in windy situations) with an internal rotating mechanism.",
"Although I don't know about buildings, the same thing happens in your steering wheel. There are a few places where electricity doesn't rely on a fixed, immovable connection. Trolley and subway cars have connections that slide along a straight path, and I imagine buildings like this would have something similar, just in a circle."
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g73kqv | How do RPG, PILA and such missiles "know" when to explode? | Engineering | explainlikeimfive | {
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"There is a number of different types of fuses depending on the ammunition. For example a shaped charge intended for burning through armor will have a contact fuse in its tip which detonates the explosives when it gets into contact with the target. A shrapnel charge intended to cause damage over a greater area will usually have a time fuse which gets lit when you fire and then detonates the explosives at a set distance.",
"Depends on the missile, explosive. Most Grenade launchers, for example need to be fired a certain distance before the round is primed. RPGs actually have a button on the end that, when pushed, causes the explosion. Some use impact. Some are remote. Its different per platform",
"They don't, but luckily we do! Fuses vary by device and purpose. Contact fuses rely on an impact. * This can be as simple as the front of your warhead having a little stick or striker in the front. Warhead hits something, that gets driven in, the thing goes off. * It can be more advanced though, like the piezoelectric trigger on an APILAS. Think a modern electronic scale; the pressure or shock on some materials like various forms of quartz creates a voltage (electricity), which means even if it glances the shock will have a good chance of setting the thing off. Timed fuses are as exactly what they sound like. They may be analog (tick tick tick tick tick) or digital (usually without the big bright number panel) but in either case when the set time has elapsed the charge goes off. * It still doesn't \"know\" whether or not it ought to blow though, it just does. But with a little math you know where your munition's going to be at any point in time in its trajectory... so if you know how far the target is... Lot of simple RPGs use a combination of these two. A contact fuse, but also a timer (just a few short seconds) so that worst case scenario you don't have a dangerous dud lying around six months from now. You usually build'em such that it won't arm until it's in flight, because you don't want a contact fuse ready to go while you're running around with it all day. Daffy Duck just gets a little singed but you would get a little fragged. That's also why some launchers need a battery; both to set off the rocket motor and sometimes to start up the electronic timer too. But those aren't the only ones around. Here's just two more: * Radar or Infrared missiles can be designed or programmed to detonate at a certain distance for maximum effect. With radar, for example the time between the emission and reception of the pulses is a factor of how close you are after all. * GPS guidance can simply have coordinates plugged in. You don't even need a known target; when it reaches the desired position (according to your satellites) and altitude it detonates."
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g75ycw | What is the difference between 7nm or 14nm processes? Why the lower one better? | I stumbled upon the new AMD Ryzen chips and that they are made in a 7nm process? And this makes them more efficient than the new Intel chips, which is supposed 14nm. Please help me understand. Thanks in advance | Engineering | explainlikeimfive | {
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"The switches are twice as close to one another from the 14 to the 7, this means the electric travels faster between them, shorter trips are faster, use less power, and generate less heat.",
"In general, the nanometer number that goes with a processor tells you which process it was built on. A 7 nm process should let you have gates as close as 7 nm from their neighbors while a 14 nanometer process permits just 14 nanometers. Since you can put the transistors half as far apart it means you can fit 4x as many in the same die area which lets you have either a smaller die (cheaper process and better yields) or more transistors in the same sized die (useful for multiple cores) Smaller transistors come with a couple power tradeoffs. They can change states at lower voltages so flipping the state of a transistor uses less power and your processor runs cooler, but they leak more current so your standby power is going to be higher. This makes using the smallest node best on desktop processors which can use 150W at peak and using 3 watts instead of 2 at standby isn't a deal breaker, but its less idea for phones which shut off whole portions of the chip and would lose significant battery power to the leakage Now earlier on I said \"In general\", a lot of these things have fallen apart as we've gotten down to low nanometers. 7 nm is more the official name of the process than the actual results that it yields, and Intel's 10 nm process is comparable to many other 7 nm process in terms of transistor density. There are also different processes within a single fab TSMC (on of the major chip makers) offers 3 different 7 nm processes and a 6 nm process. Which one of these were the new AMD chips made on ¯\\\\\\_(ツ)_/¯"
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g78cap | When the electricity is negative, why can't power companies 'destroy' the excess electricity instead of paying to deliver it to the grid? | Due to the increased market penetration of intermittent renewable energy and the inflexibility of nuclear and ~~fossil fuel~~ **some conventional power** plants, many electricity markets occasionally have negative electricity prices when demand is low and supply is high. See for instance [this article]( URL_0 ) about German electricity prices: > The inflexibility or financial infeasibility to shut down or ramp up/down base-load power stations – during hours of high renewable energy generation – only aggravates the imbalance between demand and supply. It might seem counter intuitive, but in some cases paying the buyer for purchasing electricity is cheaper than turning off power stations. I understand that it can be more profitable keep the power plant running due to the costs of ramping up or down. But I wonder why electricity suppliers (pay to) deliver their electricity to the net rather than destroy it via grounding or leakage to the earth? | Engineering | explainlikeimfive | {
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"We are talking on the scale of megawatts here. Grounding is a safety feature to prevent people from being accidentally electrocuted, and the earth is not intended to be an electrical dumping ground for enormous and constant amounts of electricity. Mythbusters showed that when a power line falls down the ground is electrified to the point that a human walking on the ground near it would be fried. So let's not do that sort of thing intentionally. As for dealing with the excess, I heard a story about one power company that could, when there was excess capacity, have the city turn on street lights during the day to use the excess capacity. Can't remember where I read that but sounds easy to find. Germany's position (geographically) in Europe probably lets it sell excess capacity to its neighbouring EU countries as well. All this highlights a problem with the grid: there's almost zero storage. Tesla's Power Wall and similar products help but should be more widely available. Plus we'd need some kind of signalling that it's happening and that the price of electricity just went negative to signal those power walls and other power consumers (eg: electric cars plugged in waiting for time to charge) to begin consuming some electricity, and how much.",
"One mechanism available for energy storage involves a hydroelectric dam with a pumping arrangement. During peak usage; water is allowed to flow freely into an afterbay downhill; but later when demand drops; power (pulled from the grid) is used to pump the water back uphill into the reservoir. Source: spent way too much time in Oroville, CA where the reservoir is set up like this.",
"You cannot \"destroy\" the electrical energy, you can convert it to something else, usually heat. If you connect your power output to ground (earth) the the electricity will convert into heat. Megawatts of electrical energy will turn into megawatts of heat. This is perfectly feasible, if you have something that can handle that much heat. If you simple connect the wires to ground then lots of current will flow, and either the circuit breakers trip, or the wires melt from all that heat. If this situation happened often it might make sense for the power company to build a device to convert excess electricity into heat. That would cost money to build, and money to operate. It would probably use a lot of cooling water. The price of electricity would have to go negative often and by a large amount to make building a way to dump the electricity cost effective.",
"You can't just \"destroy\" electricity. This is fundamental physics here, energy cannot be created or destroyed, merely change form. To get rid of electric energy, you need to convert it into some other type of energy. There's a couple of options for this. Thermal energy: we can turn electricity into heat by simply pushing it through a resistive load. However, we're taking about *millions* of watts of power here, that amount of heat is almost impossible to deal with. You'd end up heating a large area around the energy dump. The most viable solution would probably be a man made lake with huge heating coils sunk in the bottom. That much water can store a massive amount of heat, but it would be ecologically harmful. Chemical energy: batteries, basically. You convert the electric energy into chemical energy stored between molecules to be recovered later. This is *hideously* expensive to do at the kind of scale we need. It's simply not viable on a nationwide scale at this time. Maybe in the near future. Potential/kinetic energy: very similar things here, we use the electricity to move something. Later on, that thing can be moved back to release the energy back into the electric grid. One major technology right now is water resivoirs. You build two big resivoirs, one as high above the other as the landscape can provide. You use excess energy to pump water uphill, then later you can let the water fall back down through a turbine to generate electricity. The bad part about this is that you actually can't store as much energy as you'd think. It doesn't scale well because it requires so much land area in a very special landscape. Sinking the current back into the ground is essentially shorting out the generator. This will generate a *lot* of heat in a real big hurry. Whatever wires you use will likely vaporize, causing an extremely dangerous arc that can blind, burn, electrocute, and otherwise kill the fuck out of anyone nearby. Tldr, we can't just get rid of excess electricity. The energy has to go *somewhere*, and there is simply way, WAY too much energy to dispose of in a reasonable way.",
"Electricity is never 'negative'. Demand rises and falls but doesn't normally drop below what's called the \"base load\", which represents things that are always on like refrigerators and such. There always needs to be enough power in the grid to supply this base load. Utilities regulate how much electricity goes to the grid by taking generators offline, so that they only put the minimum amount of energy into the grid that they need to in order to keep things from browning or blacking out. The most expensive generators typically get shut down first. This is why you'll often see wind turbines not spinning... because the grid doesn't need all the power. Excess electricity sometimes **does** end up going to ground at the end of circuits, which essentially 'destroys' it. There is an entire industry dedicated to minimizing the amount of power \"wasted\" to the earth or storing it somehow for future use. In summary, the grid is never at zero demand, and this is the most efficient way to provide the energy to service the load. Any additional action taken to 'destroy' energy other than simply grounding it would just add cost. Edit: Added sometimes.",
"One basic thing about energy in this universe, is that it can’t be destroyed. My knowledge is a little shaky, but as my teachers had described it: the amount of energy in the universe is set, and energy can never be destroyed, only transferred. I feel that it would be infinitely more expensive for the power company to ground out your negative electricity (meaning they would have to generate that to sell themselves while disposing of your charge for no good reason), and pump out their own. The power system (in the United States Atleast) is designed to be able to handle the back flow. So nobody can destroy energy, and it would cost the energy company more money to get rid of the energy you pump in, than it is to pay you a mild sum for it and sell it for more"
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g7andg | What do you mean by mobilizaiton and demobilization costs? | Trying to understand this in the context of construction of wind projects.. | Engineering | explainlikeimfive | {
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"Mobilization cost is the actual cost of accumulating and coordinating all the necessary equipment, tools, materials, people, etc to get a job started. Demobilization cost means all costs and expenses caused by the project management suspending or terminating work under this contract, including travel expenses, penalties, fees and other costs associated with terminating, suspending, or making change orders to contracts.",
"Mobilization is the cost of setting up the job site. Office trailers, temp toilets, construction fence, etc Demobilization is the cost to remove all of that at the end of the project."
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g7opon | Why do some machine guns fire faster than others? | So I understand how an automatic machine gun works in the first place, where there is a separate chamber that utilizes the gas from the bullet leaving the gun to pull the action back in order to fire the next round. My question regards why some guns do this faster than others? I'm thinking of these huge rate of fire differences like you see with the Kriss Vector vs MP40. Could it be due to gas chamber size? Is this done purposefully? Thanks! | Engineering | explainlikeimfive | {
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"There are a wide variety of things that can be changed. In general, increasing the forces or decreasing the distances involved will cause faster fire. Not all machine guns are gas-piston operated either. For instance, having a stronger return spring for the chambering system can cause the gun to fire faster. The piston pushes the bolt back, and the spring then returns it forward faster because it is stronger. Increasing the pressure of the gas piston as well as decreasing its length also can speed things up."
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g7tf8c | When a gun has the description of for example, 9mm or 7mm. What does that actually mean? | Engineering | explainlikeimfive | {
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"This measures the diameter of the bullet. Sometimes you'll see the length of the cartridge, too, like 9x18mm or 7.62x54mm. Then there are some local variations, like measuring the neck of the casing instead of the bullet, but by and large it's < bullet diameter > [x case length]",
"Diameter of the case, but more accurately the size of the bore. You will often see the case length following the diameter. 5.45x39mm=5.45mm in diameter, 39mm in length."
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g7xxz3 | What is a space elevator and how does it work? | I’ve seen some games, movies, discussions, etc that have/mention space elevators. What are space elevators exactly and what does it do? | Engineering | explainlikeimfive | {
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"It is a theoretical idea that you could effectively lower a rope from a satellite in a geo stationary orbit to a point on the earth surface and that loads could climb the rope to get into space. The problem is that the rope would have to be thousands of miles long, super strong and incredibly light, because it will need to hold its own weight as well as anything climbing it. At the moment there are no materials with anything like the properties that are needed. Nice idea. Not likely to be possible."
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g7zv3d | How do combustion engines (for example all 4 cylinder unleaded gasoline car engines) have varying levels of efficiency if the concept and design is relatively the same? What improves the efficiency? | Engineering | explainlikeimfive | {
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"Gasoline engines control power by restricting the amount of air that can enter the engine. This reduces efficiency because you’re wasting some energy to pull air in past the restriction, as well as reducing peak temperature/pressure and other factors that would allow the engine to work at its peak efficiency. So an oversized engine run at a small fraction of its possible power is often less efficient than a small engine run near its full power. Gasoline engines also have limits on how much they can compress the air/fuel mixture (compression ratio) as well as the use of turbo pressure, and limits on the ratio of air to fuel. These are *all* related to the issue of fuel burning before it is supposed to (preignition or detonation) or failing to burn. Modern direct-injection systems (which share some of these benefits with Diesel engines) get around these limitations by waiting to inject fuel until the moment it’s supposed to burn, and combined with advanced spark systems make sure it burns even in less than ideal conditions. Fuel injection itself was already an improvement over carburetors, with the advantages of simply making sure all the fuel was mixed with air so that it could burn, and allowing more precise control over air/fuel mixture in different cases.",
"There are 3 main factors. How efficiently the fuel is burned, how well the energy is extracted from the hit gas, and energy used to keep the engine running Ideally you want the fuel well atomized so when you ignite it the flame front moved smoothly through it and you burn all the fuel. If you have big fuel droplets or poorly spaced droplets you don't get an even burn and don't get all the energy out of the fuel. Modern direct injection engines get better dispersion than old carburetor engines or even fuel injected into the intake port Next up is how well you can capture that energy. This comes down to letting the gas expand as much as possible, heat engine efficiency is determined by the difference between peak and exhaust temperature, the more you expand the gas the more energy you capture and the cooler it gets. Atkinson cycle engines are used in hybrids and have a longer expansion stroke than compression stroke so they can extract more energy than a symmetrical Otto cycle engine Finally you've got inefficiencies in the engine. If your car needs 20 HP while cruising on the highway but the oil pump, water pump, and cams take 3 HP to run then your engine needs to generate 23 HP. If we move to a thinner oil, better tubing, and light electronically controlled cams then you can shave that down to 1 and your engine only need to make 21 HP so your engine efficiency has improved by nearly 10%!"
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g81kyu | why do you sound better in the shower? | Engineering | explainlikeimfive | {
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"You're surrounded by hard surfaces that bounce the sound around. This creates miniature echos which makes sounds reach you ear over a longer period of time which, in turn, makes you louder, and more importantly, creates a fuller and more robust sound."
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g84rbf | How can an outlet which supplies a certain voltage generate enough power to charge 6-8 different pieces of equipment. | Engineering | explainlikeimfive | {
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"Power=voltage\\*current If you plug in more stuff, then you'll draw more current from the system.",
"First of all, an outlet does not generate power. electrical power in the easiest way can be calculated by current * voltage ( P=I*V; Power = Current* Voltage) Following that, a higher current is drawn from the grid when connecting more equipment which requires more power. ( addition: parallel supply of equipment, which is the standard, states after ohm's law, that the voltage is equal at each part of equipment and the current gets divided.)"
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g8ag01 | How does air conditioning work? | Engineering | explainlikeimfive | {
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"A device called a compressor takes a gas (like freon) and puts it under pressure until it's converted to a liquid. This liquid is run through pipes called coils. Warm air is pulled from the room through a vent and is blown over the coils by a fan called the blower. The heat from the air is sucked up to convert the liquid back to a gas. Then the cooled air is pumped through other vents to cool your house. The gas cycles back to the compressor and is turned into liquid again, over and over.",
"Squashing something releases heat. Unsquashing something releases cold. Air conditioners squash something on the outside of the house, move it inside, then unsquash it, releasing cold inside the house."
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g8spuj | Why are so many electrical plugs designed in such a way that they cover adjacent sockets? | Engineering | explainlikeimfive | {
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"Ease and durability, mostly. The part that generally covers adjacent sockets is the *rectifier* and *transformer,* the generally blocky bit that converts AC power into DC power at the proper voltage and amperage. It's better for the cable to have the mass at the end that generally doesn't move.",
"It's a common problem when using devices that run off a low voltage direct current, as your house is wired to supply alternating current at a higher voltage. That 115/230 volt alternating current has to be converted to a lower voltage and rectified into direct current. The electronics that do this take up a bit of space. That space can be built into the device (making it larger and outputting more heat), somewhere along the middle of the cable (typically expensive and annoying to deal with sometimes), or at the wall plug end (cheap and very practical, but can block adjacent slots).",
"Does this relate specifically to US plugs? I’m from Ireland and don’t understand the question and the various responses",
"In product development there are engineers and there are designers. Engineers make sure a product works and designers make sure people enjoy using the product. Charging cables are usually bought \"off the shelf\" to accompany products since they are regulated and not considered necessary to redesign with every new product design. Since power cables are often overlooked as contributing to a user experience they are often not designed in a user friendly manner.",
"The answer is that one person's genius idea conflicts with another person's genius idea. This is what a \"traditional\" North American power strip looks like. URL_2 When you try to plug in a \"traditional\" wall wart / ac adapter - this is what happens - URL_4 (ignore the bottom part with the short cords). Everyone realized that this was a problem. So, power strip manufacturers rotated their sockets 90 degrees. This works really well. URL_0 Device manufacturers also rotated their plugs like 90 degrees and made them skinny, like this. This also works well. URL_3 But the two solutions are generally incompatible. If you try to put a rotated plug into a rotated power strip, you end up with the same problem all over again - with a plug covering multiple sockets. URL_1 So now everything just sucks. The \"solutions\" are to: * make the adapters small enough to not take up more space than the socket itself (only possible with low power adapters like USB chargers) * add a cord to the adapter instead of plugging it into the wall (increases cost and contributes to \"rat's nests\" of wires) As a consumer, you can buy short extension cords, a power strip large enough to handle both types of plugs, or multiple power strips. But all of those cost money.",
"Plug in power bricks are built that size for two reasons. One is that they often need the space for the circuitry inside. Another is that they all produce some heat. Many people have places where multiple of these power bricks are needed, and they are tempted to connect them to the same power board. If they all packed together, all of them as wide as they can be, with no space between them - they would overheat, maybe enough to cause a fire. So building them so that they take up more than one socket forces some space between them, so they can cool properly.",
"All the electric devices that have this issue run on different power than that which comes out of the socket. So they are build like this: * A plug that connects to the socket * A chunk that converts normal socket power to what the device needs * The device itself Take a desktop computer vs a laptop computer. The desktop simply connects to the socket with a cable. Everything else is inside the desktop itself. This is possible because the desktop is already pretty big and heavy and doesn't need to be portable. So what you get is plug - > cable - > device (internal converter) For a laptop on the other hand people want it to be as small and light as possible, so the converter needs to be outside the computer itself. The converter is generally too big tough to realistically fit into a blocky plug. So what you get is plug - > cable - > converter - > cable - > device Now for a lot of smaller devices you don't need a converter as big but the device itself is so small that you really dont want the converter inside the device either. Even considering how small a phone charger is you probably wouldn't want it permanently attached to your phone. But the charger IS small enough that you *can* integrate it into a blocky plug. This way you get plug - > converter - > cable - > device and save yourself the thick cable. This keeps your device small, saves money on the thick cable, reduces the box size by not having to include the large cable and simplifies the design. Is it going to inconvenience your customers by blocking adjacent sockets? Yes, but everyone is doing it so you're not standing out in a negative way. And anything you can do about it would make your device more expensive and thus less competitive.",
"Because the makers of the low-voltage \"wall wart\" type power supplies want to keep it as cheap as possible on their end. Good ones have 6\" or so of cord between the transformer/switch mode power supple and the plug.",
"The real ELI5 answer is \"It just be like that sometimes.\" It's cheaper to manufacture when the rectifier (the box shaped bit) contains the blades that plug into the outlet. There are 2 common methods of delivering electricity to your appliances. Most large appliances use the kind flowing through the wires in your wall(AC). Most electronics use the other kind(DC). Most of the small electronics have the box plugs that contain the circuitry, called a rectifier, to switch from AC to DC. Bigger electronics like PCs and TVs have the rectifier built in rather than in the box plug. If this is a reaction to you experiencing this issue, there exists small 1 ft, 2 ft etc extension cords. Mostly they're made for when you want to plug something in behind a piece of furniture where that plug prevents the furniture from sitting flush against the wall. They will solve your problem if you can't fit 2 plugs into the same outlet due to size or shape.",
"Poor design. It's long been possible to make a power supply narrow enough to ameliorate that problem, but too often companies rely on stock designs which have shortcomings, that among them.",
"There are a lot of comments that are correct from an engineering standpoint. There's also a consumer choice aspect. When was the last time you seriously considered the plug when buying an electronic item? Until consumers start to decline a purchase due to the plug, manufacturers have no incentive to change the plug shape."
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g95ako | Why does different parts of the world have different voltages? | Just that, why? Wouldn't be easier to have the same voltage all over the world so we don't have to use adapters and things like that? | Engineering | explainlikeimfive | {
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"When electrical grids were being constructed, the idea of globalization was still far away. There was no benefit to someone in Europe trying to legislate that they should use the same voltage and connectors as the US and Canada. Each made their own decisions independently. In today's world, those decisions stand because trying to change everything would be impossible.",
"Early electric was 100 volts for no particular reason. Radios needed 90v power for tubes, so that's what we went with. Most electric service worldwide occurred during the WWII reconstruction, so 230 volts was used, being more efficient and using less copper in the process. Japan was an outlier, they used the older 100v US system, which by now was 110 volts. Today North America is 120v (with the US and Canada also having 240v service for large appliances) and most of the world running at about 240 volts, with Japan remaining the only outlier."
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g9frav | How exactly do vacuums suck up air? | All I see is a spinning cloud of dust. How do vacuum cleaners and chambers work? | Engineering | explainlikeimfive | {
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"We think of fans as blowing air, but if you look from the back side of the fan, it is sucking air in. Hold a candle behind the fan and you can see the smoke get sucked into the fan. All fans suck on one side and blow on the other side. There are lots of ways to make fans, and some designs are really good at sucking. A vacuum cleaner uses the kind of fan that really sucks. It's still just a fan, though.",
"Vacuum occurs when there is a lack of matter in a space. All the nearby matter starts fighting to get into that empty space. A vacuum works by evacuating as much matter out of itself as it can using a fan or air pump. Once enough air has been moved out hen all the outside air rushes in to that newly empty space.",
"> How do vacuum cleaners and chambers work? Inside the chamber is a filter and on the other side of that filter is a powerful fan that draws air from the chamber side and blows it out the other side into the room. When it draws the air from the chamber it creates a low pressure, and as u/ToFuuVEVO mentioned, it tries to reach equilibrium... easiest way is through the hose, or the bottom of the vacuum. High pressure air (relative to the chamber) travels to low pressure in the chamber, and draws in dirt and crap along with it. The spinning cloud of dirt is because the dirt enters the chamber at an angle (by design), creating a vortex, in order to keep the dirt on the edges of the chamber. The filter is in the middle of the chamber and often located at the top, so it helps keep the filter clean longer before you have to empty it."
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g9n3fy | How are bridges tested for how much weight they can hold without breaking the bridge? | Engineering | explainlikeimfive | {
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"It's not like they build the bridge and THEN test it for strength. The architecture of the bridge was designed under the principles of engineering in such a manner that the mathematics and physics behind the design equate to a certain amount of load capacity, above and beyond what the structure will ever be expected to hold during its life. By the time it is actually built the engineers know very well what the limits of the design are.",
"The design studies know know the strength of materials, the load the bridge is required to support and the safety margin that they need to build in. They don't physically test a completed bridge like that although the periodically inspect structures for cracks, corrosion or other safety-related problems",
"We know the material properties of all things involved(steel and concrete mostly), we did a ton of testing of those since those are very common material. Then structural engineers will take this data and figure out how thick concrete and steel you will need at what places. Also bridges are built with a safety factor. That means theoretically they can hold up more weight than they would ever experience in real life so any imperfections during construction are accounted for",
"disregard all other answers, the true answer is & #x200B; they make the bridge so fuckin big that they know it cant possibly break with a sensible number of cars on it"
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gbchuk | How do rockets launched into space not collide with satellites? | Engineering | explainlikeimfive | {
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"They track possible satellite collisions from earth. Additionally, the odds of hitting a large man-made satellite (which number in the thousands) are astronomically low given the volume of space around earth. That said, collisions with space debris are increasingly a problem as countries send more stuff into orbit. Every orbiting satellite (which means anything that orbits the planet) is an additional factor they have to take into account when launching a new satellite.",
"Space is enormous. You have the entire width and height of the earth to fit a satellite inside, plus altitude. It’s the same reason planes going opposite directions don’t collide, you stick them in on different paths"
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gbq1em | How do toilet pipes work? | Engineering | explainlikeimfive | {
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"There is a large pipe under the toilet for waste. It connects to a larger, vertical pipe called the main stack. Thence out to septic or sewer or the president’s Twitter account. Fresh water comes in to the tank ready for the next flush. It knows when to stop filling when a float hits the right spot and cuts the flow. The water in the bowl helps to ensure that no gas comes into the house from the sewer. Bada bing bada boom."
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gbrl5o | How is a sniper rifle precise with the scope on a different position on the weapon than the muzzle over various distances? | The scope is on the top and the muzzle is a little below and in the front. How does the gun shoot at the scope's point of focus accurately? | Engineering | explainlikeimfive | {
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"The scope is only accurate at a certain, fixed distance. The shooter has to adjust the calibration of the scope so that it's accurate at 50m, or 100m, or 200m, or whatever. Otherwise you'd be correct, the scope and the barrel couldn't both be pointed at the same spot for any distance, since the scope is starting from a point above the barrel.",
"When you put the scope on it, you adjust it for the range you intend to aim at. You can shoot closer or further by aiming down or up to compensate. This diagram is for a shorter range, but shows the principle. In this diagram, the sights are adjusted to be accurate at 200 yards. If your target is closer, you can see how it would hit high; if it were further away, the bullet will hit low. [Bullet trajectory]( URL_0 )",
"The scope (or sights) on a rifle, and not just a sniper's rifle, have to be adjusted to shoot accurately at various distances. Alternatively, the scope or sight can include markings to show the user where to look to shoot correctly over different distances (in a scope, these markings are often called the \"reticle\"). For really long distance shots, many other factors also have to be taken into account. Many top snipers actually shoot with a partner, who keeps track of things like wind position, elevation, and sometimes even accounts for the rotation of the earth; over an extremely long shot, the earth can rotate your target out of position while the bullet is in the air.",
"Math. Lots and lots of math. The shooter must understand the relationship between the optics and their function, along with the ballistics of the weapon.",
"Guns have to be sighted in for various distances. So the scope and barrel will be lined up so they meet at a specific distance. From there, the various notches on the site are used for distances shorter/longer than the center.",
"In sniping, as you may have expected, there are a ton of variables to account for. Some of the major ones include distance to target, bullet drop, bullet velocity, bullet drag, wind speed along the flight path, if the bullet has a chance of hitting any obstacles along the way, proper shooting techniques, etc., and some of the minor but still significant variables include temperature, humidity, bullet spin drift (as the bullet spins, it tends to drift towards one direction), air pressure, and even the rotation of the Earth. To answer your question, we’ll focus specifically on distance to the target. Guns are essentially just very, very long range mortars. The moment the bullet leaves the barrel, it starts dropping very quickly. A 5.56mm NATO round going at roughly 3000 feet per second can drop as much as a foot at 300 meters from gravity. As a result, snipers who shoot at targets over extremely long distances can either “zero” the scope by adjusting the scope crosshairs’ windage (sideways) and elevation (vertical) so that the bullet hits exactly where the scope is aiming at at roughly X meters with the bullet drop accounted for. The bullet will then essentially be lobbed over the crosshairs along its flight path so that it drops and lands squarely on the crosshairs at X meters. However, sometimes you don’t have the luxury of time to adjust your scope, maybe fire some test shots, etc. As a result, snipers can adjust for the bullet drop themselves over a distance by estimating the distance to target or being assisted by a spotter with a rangefinder. From many range sessions and years of practice, snipers already have a strong idea of what bullet trajectories are like over, say, 500 meters, 800 meters, 1000 meters, etc. and they can account for bullet drop accordingly by aiming the crosshairs above the target a few notches. That way, even if the bullet does drop significantly and deviate from the center of the crosshairs, it’ll still hit its target if the sniper’s rough mental calculations were correct. To give a real life example, the (now third) longest recorded sniper shot was made by Corporal Craig Harrison of the British Army. He took 11 shots to take down 2 taliban insurgents - 9 shots to properly range the distance to the target, and then 1 shot for each insurgent once the distance was accurately determined. The distance was 1.5 miles. Even with a massive 25x scope, a target at that range will appear smaller than the period at the end of this sentence. The bullet will take 6 seconds to reach the target and will drop 300+ feet according to my rough calculations. He had to hold almost a football field’s worth of “holdover” (aiming above the target to compensate for bullet drop) in order to lob the bullet accurately into the target. This is why long range sniping is in a completely different league of its own from something like competitive marksmanship where you don’t have to jump through dozens of variables to land your bullet on target."
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gc5fn1 | How do jet engine-powered helicopters avoid generating thrust from the jet engines themselves? | I understand that most helicopters use turboshaft engines, wherein a jet engine is used to turn a transmission that's connected to the main rotors. My question is, wouldn't there still be directional thrust generated by the exhaust gases from the jet turbine? Wikipedia doesn't really address this, and I can see exhaust vents on helicopter designs but how is it possible avoid any thrust from the hot gases? | Engineering | explainlikeimfive | {
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"All the thrust is used up by the turbine. Calling a helicopter engine a jet engine is a bit misleading. The correct term is really gas turbine engine. They are used all over the place from helicopter to tanks to ships. They fire hot exhaust gasses into a series of turbines that slow the gas down, and the energy is used to rotate the turbines.",
"The engine exhaust does produce thrust but it is not designed to generate the same type of thrust as a regular jet engine. They may share a name but not the same function. The rapidly expanding gas drives the turbine blades which rotate the shaft and is used to power the chopper. Your car if it has rear facing exhaust produces thrust by expelling hot gasses but your car does not move because of it. URL_0",
"While others are correct, large helicopter engines do push a lot of air out the back. For example a Chinook with engines at flight speed could probably knock you over if you were not paying attention. Source: have nearly been knocked over by Chinook engine.",
"> My question is, wouldn't there still be directional thrust generated by the exhaust gases from the jet turbine? Very little. A turbine doesn't actually need to generate thrust if you fully expand the gas prior to exhausting it, which is what you do when all you care about is mechanical/electrical power, which is the case for a helicopter where you want all of the energy going to the main rotors. In jet engines, the exhaust is only *partially* expanded on the tail end of the turbine (in order to provide a small amount of electrical power for the aircraft's systems), and the remaining energy in the exhaust gas translates into thrust."
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gc5p5o | Sometimes, when headphones "break", they work properly if we bend the wire a certain way. Why is this? Is it a result of build quality? Can we do something to prevent/delay it? | Engineering | explainlikeimfive | {
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"The copper wires inside snap if subjected to too much mechanical stress either suddenly or over time. Avoid bending the cable too sharply, yanking on it (especially at the connector/headphone/volume control pod joints where the wire is fixed to a rigid object), getting them knotted up or suspending weight from them..",
"sometimes the broken wires are just close enough, that's why when you bent them in certain way they regain connection.",
"As others have already said, repeated bending/pulling of the wires eventually breaks the conductors. If they're decent headphones (worth fixing rather than tossing), it's often not too difficult to open them up and replace the wire with a new one. Amazon and others will sell you a new cable with connector (and mic/volume buttons if you need them) for a few bucks. Check Youtube for helpful videos. Often the hardest part is figuring out how to get them open without breaking them."
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gcakki | Why are drop ceilings so commonly used in public buildings? | Engineering | explainlikeimfive | {
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"Tldr, it makes it cheaper and easier to maintain and install various bits of wiring and ducting, especially if you're adding those things to an older building after the fact.",
"It is easier to hide electronics, piping, air ducts, etc in a drop ceiling and easier to modify, replace, and repair them in a drop ceiling. It is also easier to soundproof with modified tiles than it is to add soundproofing to a different ceiling model. As such they are a better ceiling choice for public buildings."
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gcgzj4 | What are Tesla Coils, and how do they work? | So, recently I have been seeing **a lot** of tesla coil videos on YouTube, and here on Reddit too. Now don't get me wrong, these are *tesla* ***cool***, but I have no idea how they work, what they do, and, well, what in the world they are. Hopefully one of you can appreciate my pun, and Explain Like I'm Five! Thanks! | Engineering | explainlikeimfive | {
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"A Tesla coil is actually just a very big transformer that creates and immense charge difference between the top loop of the coil and the ground. The loop gets \"overcharged\" with electrons and, in comparison to its surroundings, is charged negatively. Because of the laws of physics, this difference in charge needs to even out, so the coil gives off electrons in the form of lightning to the air and ground surrounding it. Please correct me if I got something wrong.",
"Usually, when you make a circuit, the electricity has a clear path through a connecting wire, if you break the wire, no electrons can flow. However, this doesn't mean that they can NEVER flow. Metal just tends to be a good material for them to go through. If electricity has enough energy, it can go through materials that are a little more difficult to move through, but usually, they will try to find the path of least resistance. Electrons are lazy, just like us. Enter, Tesla coils! Telsa coils have a lot of electrical energy because of how they are constructed, it's part magnetism (because the flow of electricity can change magnetic fields) and part electricity. When one Telsa coil gets enough energy, they need to find a way to discharge that energy, and the best way is usually through the other tesla coil that is close by. Heres where things get cool. Most of the videos you probably see are people playing music on tesla coils, and while keeping this at a low context, its because electrons move kind of like sound. With sound waves, they can be fast or slow, big or small, and that affects how they make our eardrums vibrate, which in turn changes how we think they sound. Since electricity is energy, and energy transfer isn't a perfect process, they tend to make some soundwaves too. By changing the amount or quality of energy, you change the type of sound you get. Hope that's clear!"
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gcifk4 | Why are cars designed such that their batteries go dead instead of cutting off current to everything except the starter? | Engineering | explainlikeimfive | {
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"Short answer: they type of battery, lead acid battery is designed to operate best with a floating charge very near to full. Seems like a good idea though, perhaps doing some research and design could rectify such an issue.",
"Modern cars have a lot of electrical devices that need constant power. Proximity key detection, clock, alarm, air suspension",
"You can't really detect it until its too late Your battery gets charged back up to full every time you drive, and most of your car electronics really don't consume much power. You might pull 100W for all the lights on your car, your battery can supply this low current level (~10A) for several hours. But then you go to start your car and you need 4,800 watts (400A) right now! Whoops! Turns out your battery's internal resistance is a bit too high and it couldn't sustain that current level quite long enough to start the engine. You've now drained it wayyyyy too far to succeed on a second attempt The starter motor is such a ludicrously large load compared to anything else in the car that its very difficult to tell when the battery has transitioned from \"Yes, I can start the car no problem!\" to \"Ehhh, might not work this time, good luck!\""
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gcpkha | Why we don't ground a device at the neutral wire? | I am a grade 11 student and I live in a place that has a separate ground wire and the British power plug is huge and bulky because of it. I have searched about why we don't merge them on google but the results returned are mostly about how one is current carrying and another is a safety mechinism, there are also conflicting results from people saying that the neutral wire can shock people while some others saying that it won't. There is also a very sophisticated answer on r/AskEngineers that I failed to comprehend but I digressed. Theoretically tbe neutral should be at the same level a ground, they could have just grounded the chassis to the neutral instead, it will trip the fuse when it is shorted and there is less complications in the device, they can also regulate it so that the neutral wire is always rugged so that it won't fall off. Why bother making a separate wire just to ground the device to. Edit: I noticed that mistake in the title, don't sweat the detail , it's not important. Edit P.S. : I am asking if the neutral wire can be used for grounding a device since it has the same potential as ground anyway, not the other way around. My original question also assumes that I didn't know anything about grounding at the neutral wire at the plug and I am using a plug with a separate grounding wire pin. You can comment on the following answers instead if you think they can be expanded. | Engineering | explainlikeimfive | {
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"Electrician here. We do. It's known as an Main Earth Neutral link (MEN link). And it's for all the reasons you currently know. It helps balance the neutral and earth voltages and it assists in the operation of things like circuit breakers, rcd's and fuses. Let me perfectly clear with one thing. Neutral wires CAN and WILL shock people. Even if the active wire is switched off, voltage can hang around on the neutral line and zap people if they touch it. It's known as a 'floating neutral' and it has killed people before. Another reason why MEN links are essential and required by law in Australia. Edit: Let me add one more thing. We only place the MEN link at the main switchboard (the start of every circuit in your house). This is because if we placed any other links, then it can cause nuisance tripping."
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gct1vr | why is E85 used in some automotive performance applications when standard gasoline is more energy dense? | Engineering | explainlikeimfive | {
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"E85 is used in many high horsepower boosted applications. It is more resistant to pre-detonation(basically exploding before the spark plug ignites it). This means these cars can run higher boost levels making more power. If I remember right it also runs cooler which helps. For instance, my bud went from 93 to e85 in his S2000 and after the tune made over another 100 horsepower."
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gcv8zy | ()Specific Impulse for Rockets | Hey guys, I’m writing a paper on different propulsion systems for rockets and had a question about the formula for Specific Impulse. Before saying anything else i’d like to clarify that i’m a freshman engineering student so i’m not too bright lol. But anyways, I’m reading a journal where it compares Chemical, Nuclear Thermal and Electric propulsion and they all list their exhaust speeds. Is the exhaust speed equal to the thrust? or the mass flow rate of the propellant. Again I’m sorry if this sounds like a retarded question. Thank you all. | Engineering | explainlikeimfive | {
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"If you have a rocket engine with X kg of stuff to throw out, there are several possible designs. You can through it out fast or slow; and you can throw it out in a big burst or gradually over a longer time. Thrust is a force, so f=ma says it depends on both the mass and the amount of acceleration. Mass flow rate is a combination of the mass element of thrust and duration of the rocket burn. Exhaust speed is a gauge of how fast the particles of stuff are moving when they leave the rocket nozzle. There is a relationship to thrust, as the duration of the time the thrust was applied to the particles gives their speed according to v=at. Specific impulse is thrust/mass flow rate ; and in many rocket designs it's more directly useful as a design parameter than either parameter separately. In some expressions it uses \"weight flow rate\", by expressing mass in pounds or some other weight unit."
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gcvv47 | when you’re showering and the water suddenly turns icy cold or scalding hot for a few seconds before returning to its previous temperature, what’s happening? | Engineering | explainlikeimfive | {
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"Water temperature in the shower is determined by the mixing of cold water + hot water from the two different pipes in your house. If the water pressure suddenly changes, like for say someone flushes the toilet, the cold water pressure in the shower drops and the temperature increases. Most showers these days have valves designed to minimize this effect. Because suddenly having nothing but scalding water can be dangerous. The valve mechanically senses the drop in pressure and adjusts the pressure of the other pipe to compensate, but there's still a fluctuation in pressure and temperature change. It just isn't as bad as without the valve. Your valve might also be worn out.",
"Somebody opens a tap somewhere else. The water prefers the other way if pressure loss is smaller that way. Therefore, no hot or cold water arrives at your tap anymore.",
"Water is only heated at a set temperature. Cold water is mixed with that one temperature. Sometimes the water isn't constant, so it hiccups, usually just a pressure drop or increase from the water main, through the valve changing the temperature for a second."
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gcxzb5 | Why is the electric motor in kitchen mixer/grinders so noisy compared to the motor in a ceiling fan or the motors in an electric car? | Engineering | explainlikeimfive | {
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"Ok, firstly the ceiling fan has an induction motor that has no physically touching parts, the fan has permanent magnets that work with the electro magnets in the fan to produce motion, as a fact they are low torque high speed units. In your food processor, you need high torque and noise is not a problem because it wont be working for very long, the motor in the food processor has brushes, and the spindle has not got permanent magnets but electro magnets, when the electro magnets work against each other they produce way more torque but as a result you can hear the brushes feeding on the electricity as they produce friction. More expensive motors have brushless action but you wont find this in cheap electronics in the home.",
"Both those items have gearboxes that are designed to reduce the speed of the motor, and consequently increase the torque (or turning force) so they can do what they can do. Gearboxes are noisy devices, basically. They have meshing mechanical parts, and many many more bearings each of which will make a little noise itself. It all adds up.",
"In short is because a consumer wants to buy a powerful blender but a silent fan, and that drives the engineering efforts. Due to high torques (more power) involved and inter exchangeable parts (think loose connectors vibrating) they will be noisier almost by default. That said they could be engineered to be much more silent, but that would cost more and bring almost no benefit since they are only used for a short amount of time and all the slicing they do is already very noisy."
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gcy5pl | Why are bulletproof vests not stabproof? | Engineering | explainlikeimfive | {
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"For a start, vests are not really bulletproof. They are bullet resistant. They work one of two ways. The lightest and most flexible ones use multiple layers of material, usually kevlar, that are strong enough to resist the bullet traveling through them. With each layer, the force gets spread over a wider and wider area, until it reaches the user and is (hopefully) spread out enough to not do lethal damage. A knife, though, just cuts the fibers; that being said, the vest will slow a blade down. The other method uses high-strength armor plates, usually ceramic that absorb the impact but crack (and must be replaced); these plates are quite stab-resistant."
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gd6l7q | Why are trucks and planes controlled from the front, but most big ships controlled from the back? | Engineering | explainlikeimfive | {
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"Many modern ships have aft accommodations because it simplifies construction. The accommodation is the big structure that contains the sleeping cabins, the galley, the bridge, etc. Under the accommodation, is the engine room casing. It is a cheaper and easier construction to place the accommodation directly on top of the engine room casing. You don't need to build additional bulkheads, thus cutting down on weight. Less ship weight means more cargo. If the engine room casing and accommodations are places forward of the ship instead of aft, then you need to construct a long shaft that goes from all the way forward to aft. This shaft connects the engine to the propeller. By building a shaft, you add more weight to the ship, take away room (a shaft needs a shaft tunnel) and you increase the amount of moving parts which need to be maintained. Even if you want to use a long shaft, you would still need an aft compartment for certain pieces of machinery. Many ships use a CPP (controllable pitch propeller). This is a hydraulic setup which changes the pitch (angle) of the propeller blades to adjust the speed of the ship, and you can also make the ship go astern. You would also need a steering flat, which is a hydraulic pump setup which turns the rudder. According to regulations, you need bulkheads at the aft, forward, and in front and aft of the engine room casing. With an aft house, the aft bulkhead and the aft casing bulkhead can be the same one, meaning you need one less bulk head. With an engine not aft, you need that extra bulkhead. So, even if you have a forward engine room, you would still need a lot of machinery aft. There is also a safety consideration. Ships have a limited amount of engineers, sometimes there aren't any on watch at the time. Should something happen, like a steering failure, it could take a long time for an engineer to make it all the way back aft to the steering flat and activate the emergency steering mode. In an after accommodation ship, you only need to go down the stairs. As for maneuvering and navigation, there may not be a definite advantage. Many of the older ships on the Great Lakes had forward wheelhouses. The guys that sailed most of their time on them swear by them and claim that is the best way to sail. Myself, I have never been on a front end job and don't see any positives. There might be an objectively better setup, but then it might come down to preference.",
"It may be hard to see the path in front of you if you are stuck behind the cargo compartment. But if you sit in front of the vehicle you do not see the sides for when you are turning. So in all of the vehicle types you mention the operator sits as far back as possible while still being able to see in front of him. For example on a cruise ship the bridge is at the front. However on an agricultural tractor the drivers seat is often right over the rear axle. A lot of sports cars put the drivers seat close to the center of the car or even a bit behind the center. Some planes now have taxi cameras mounted at the tail allowing the pilot to taxi from the vantage point of the tail instead of only looking out the cockpit windows in the front. Cargo ships is different from cruise ships as cargo is heavier then the mostly empty space of a cruise ship. And because the weight of a ship equals its displacement you can not stack containers as high as a cruise ship so you can mount the bridge further back so you can see over the containers and still boats and docks on the side of the ship."
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gd7m2y | How does stretch wrap manage to be so lightweight and easy to tear yet durable enough to keep a 1 ton pallet from spilling? | I use stretch wrap at work a lot to wrap pallets of merchandise, fixtures, paper records, etc. The heaviest of these pallets are probably stacks of water bottles that weigh just over a ton each. Now I can rip stretch wrap with my fingers easily, even several layers of it. Yet when you properly wrap a pallet, this seemingly weak, fragile plastic wrap can easily restrain a ton of water from shifting during transit. I’ve seen heavy pallets of pool salt and water shift drastically but the wrap held them. How does that work? | Engineering | explainlikeimfive | {
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"It acts as a skin to distribute forces and therefore lessen them. Those stacks of heavy objects should be pretty damn stable because of their weight when at rest. What screws them up is sudden jolts. The wrap takes those jolts and makes the pallet act as one combined object rather than several individual objects making it much more resilient. It's also the case that different materials act in different ways to different forces. Having a high load capacity under tension (like wrap does because it can withstand a lot of pulling force) doesn't have any bearing on its ability to withstand piercing forces like your fingers"
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gdei4x | What is horsepower and torque and how do they relate to a car being fast or a truck having a towing capacity? | Engineering | explainlikeimfive | {
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"Let's draw an analogy. If Torque and horsepower were people, Torque would be Arnold Schwarzenegger while HP would be Usain Bolt. Now both of them are tasked with carrying a 100 bricks across a bridge. Now Arnold, given his sheer power, can carry 20 bricks at a time, making 5 trips in total, which take him 50 mins in total, or 10 min per trip. Now Bolt, though not as strong as Arnold, can run like a cheetah. So though he only carries 5 bricks at a time, he only takes 2.5 mins per trip, doing the task in 50 mins. So, horse power is the amount of work done in a given time, measured in HP or Kilowatts. In order to do the same amount of task, i.e. achieve same amount of horsepower, you can either increase your Tourqe (strength/force) or revolutions per minute (RPM). HP is a function of Torque and revolutions. When judging a car, compare the HP, the work it gets done, whether by brute force (torque) or RPM, not just torque. No point having Mark Henry in your team if he can't see when Ray Mysterio kicks his ass because he's too heavy.",
"Horsepower is a product of speed and force (it also depends on the direction of these things aswell). Or of rotational speed (rpm) and torque (Nm, lbft, etc.) Let's look at them separately first. rotational speed is how fast something is spinning, how many times it rotates every minute. Torque is \"how much force is behind that turning motion\". A Nm (newton-meter) is just 1 newton of force with a lever that's 1 m long. (or 2 Newtons of force with 0.5 meter lever). And one lbft (foot-pound) is the torque that 1 lb for force makes with a 1 foot long lever (or 2 foot long lever with half pound force). These 2 units are essentially the same thing, only one is bigger than the other, like seconds to minutes. There's this thing called a gearbox that can speed up rotation at the cost of torque; or increase the torque of something, but at the cost of speed. Doubling the torque means halfing the rotational speed. Because we have this, it makes sense to talk about the product of speed and torque; something that stays constant no matter what kind of gearbox you put it through (ignoring the losses of course). That's called power. And horsepower or kW (kilowatt) is a unit of power. If you have an engine with a lot of torque and low speed you can put a gearbox behind it to make it \"seem like\" it has more speed and less torque. Similarly, if you have a fast engine with low torque, you can still put a different gearbox behind it so it seems to have more torque, but less speed. If you want a fast car then power (in horsepowers or kW) is the most important thing, since you need to put down a lot of force (or torque) at high speed. And that means a lot of power. If you want to tow, then horsepower is still the most important factor of the engine. Yes, you need more torque at the wheels, but that's exactly why the gearbox is there. It takes the fast speed of the engine, slows it down and increases the torque by a lot, so you can tow stuff. & #x200B; However, with towing the mass (or weight) of your car is also very important, because a light car can have trouble pulling up a heavy trailer up a hill. Even though it has enough power (and torqe) to do the job, but the wheels would just slip.",
"Imagine a lever centered on a fulcrum. When you push down the left side, the right side rises an equal distance, with equal force. Move the lever to the left, so you are pushing on the longer end: the right side rises relatively little, but with greater force. You have traded horsepower for torque. Move the lever to the right, so you are pushing on the shorter end: the right side moves relatively further, but with less force. You have traded torque for horsepower. This tradeoff of leverage between force (torque) and speed (horsepower) is exactly what happens with the gears in a car's transmission - gears are just continuously rotating levers.",
"Torque is the twisting force of the wheels, and Horsepower is how much work is done. When you wring a towel out, torque is how hard you can twist it, HP is kind of like much water comes out. transmissions exist, which is like putting the towel in a mechanical twister that you spin by hand, every 2 turns of your arm is one turn on the twister. You can apply twice the pressure. The torque measurement is coming from your arm though. The 2 turns is great, but you want more, so you upgraded it to 4 turns per, to double the pressure on the towel again, but the little wooden dowels that hold it in place snapped. So you get metal dowels. Upgrade again to 8 turns per, and something else breaks. And you replace it for something a little more durable. You keep this up, and before you know it, your towel wringer is top notch. durable, plus really bulky. ^That’s the truck that can tow. Another person says, what if Make a device that spins the towel really fast? One arm turn is 5 spins of the towel. Still applying the same torque with your arm. This design puts more wear on Bearings and anything that is slightly off balance. You upgrade to smaller, more precise parts. Spin faster. Upgrade, faster, upgrade. ^This is like the fast car. Remember, you’re the engine here, same torque for both, only the design is different. Both can produce the same horsepower, and can have the same torque, but you can get a different engine that is better at doing that task. As well as computers making it so we can customize the timing of how much power you have at what speed. A car’s engine would be designed to have the torque be low in the beginning, then highest when it’s going fast so it can go even faster. A trucks engine would be designed to have high torque at the start so it can start moving a large load from a stop."
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gdfhey | Why are school busses not required to have seatbelts from a safety perspective? | Engineering | explainlikeimfive | {
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"People have debated the merits of providing seat belts in school buses for a long time, but statistics of collisions involving school buses tend to show seat belts wouldn't make much of a difference. In reality, despite the lack of belts, school buses are already quite safe relative to regular passenger cars ( > 10x better). School bus collisions tend to be at lower speeds ( < 80 km/h / 50 mph), and tend to involve other cars that are much shorter in height. The shorter, smaller cars tend to 'submarine' under the frame of the school bus anyway, so the kinetic energy tends not to be transferred to the body of the bus and the passengers within. Furthermore people who have tested seat belts in buses have found they may cause more severe injuries than not having them at all. To keep kids belted into the seats the seat frames themselves have to be built to be stronger and stiffer, otherwise they may slip out of the belts. Without shoulder belts the kids are more likely to hit their heads against the back of the seat in front of them in a frontal collision (which are relatively rare occurrences anyway), whereas it would somewhat counter-intuitively be *less* severe to the kids if their entire bodies slide into the back of a flimsier seat in front of them.",
"I will add something to the comments above: a bus seat can burn very very quickly. It would take a long, long, *long* time to get 72 terrified grade-schoolers out of 72 seat belts.",
"Small children are not good at buckling/unbuckling seat belts without assistance. They are also not good about ensuring that the seat belt is positioned correctly. Children will also use them as weapons, toys, experiments, etc",
"Because they don't provide any significant increase in passenger safety regarding a bus. Passengers are typically high up, and busses are both large and heavy. So if something slams into them the engine block is below the passengers, they aren't going to tip or roll easily, and they don't crumple like modern cars are designed to",
"They are required in some places — we had them when I was growing up (suburbs of Chicago, but not sure how widespread law was, like district, county or state). But buses are higher up, much heavier mass, driven by trained professionals, mostly travel at low speeds, have other safety features like high padded seat backs in front of passengers that all help minimize risk in case of an accident. Additionally, for young kids in a panic situation, they might trap kids unable to undo their own buckle and risk them being killed by fire or smoke vs dealing with bumps and broken bones.",
"They’re compulsory in Ireland since a rather tragic crash. In which five were killed and many more injured. [link]( URL_0 )",
"I always thought it went something like this: \"Hey fiftey 8 year olds the bus is now on fire, unbuckle yourself in a calm manner and exit the bus before the flames get ya.\" panic ensues and a majority of them die",
"Buses are huge. A physics fight between a school bus and a car is like a heavyweight boxer versus a baby. I've actually been in two buses that got hit by cars--one time I had no idea we'd even been hit, the other time it felt like a small tap. The bigger danger is when buses roll over or catch on fire (buses actually catch on fire a lot). In neither case do you want the kids attached to their seats.",
"I drove a special Ed school bus for a year. we only had enough seat belts for the severely handicapped kids. each day i would sit them down and put on their seat belt. and they would immediately take it off. until one day one of them stood up as i was stopping and crashed in the isle. they principal ask me what happened and why they didn't have their seat-belt on. i explained i put it on him every day and he took it off, because the other kids didn't wear them. the next week we had enough belts for every kid.",
"School buses in the uk all have seatbelts, I don’t remember seeing anyone actually use them though",
"Because kids are expendable. Face it, he/she is only 8 years old, you can't be *THAT* attached to him/her.",
"Interesting side note...in Texas all 2018 model year an newer school buses are required to be equipped with three point seatbelts. Now a waiver can be obtained if the district can prove it can't budget a new bus with seatbelts but can budget one without. Also, older buses are not being required to be retrofit.",
"Mostly because school buses don’t get in many accidents and the accidents that do occur are not as serious because 1. Bus drivers are not generally yahoos 2. Buses mostly avoid highway speeds reducing the energy involved. 3. Other drivers are typically more cautious around school buses. 4. Inertia - bus companies, kids, parents and administrators don’t want to change. Newer buses are equipped with belts.",
"For the type of accidents that buses are usually involved (aka, with much smaller vehicles) the seat belts add only minimal safety benefits. Sure, there's probably some where they would make a huge difference, but they're very rare. On the other hand, they would drastically increase the time it takes to evacuate the bus in case of emergency, since kids aren't always that great at undoing them, and are probably even worse when under stress."
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gdp9e1 | What does "Cocking the gun" actually do in movie scenes. Why wouldn't you just pull the trigger? | Engineering | explainlikeimfive | {
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"First off, this depends greatly on the type of gun involved. I'll break that down after I explain your original question. A round of ammo for a modern firearm contains a \"primer\". This is a little piece in the butt of the round that contains a \"percussive explosive\", meaning that if you hit it, it will explode. That explosion ignites the gun powder, and propels the bullet forward. Your gun basically contains a little needle that slams into the primer and causes it to fire. When you \"cock\" the gun, are pulling back the \"hammer\" that will hit that needle, and putting tension on a spring that will cause the hammer to move forward and hit that needle. A mechanism engages to hold the hammer back, and pulling the trigger removes that mechanism, allowing the hammer to jump forward. Now for the \"it depends on the type of gun part\". Not all guns have an external hammer in this day and age. For example, Glocks are \"striker fired\", which means that instead of normal \"hammer\" that you can touch, it's all internal. Meaning that you can't \"cock\" a Glock, except for when you cycle the action to load a round into the chamber. So a Glock is basically \"always ready to go\", and you can't \"cock\" it for dramatic effect. However, you will hear cocking sounds in a lot of movies when the character is using a Glock, because it excites the audience.",
"In the movies, it’s show of force from one character to another. For the audience, it escalates the tension in the scene. Just pulling the trigger would not have the same effect. In real life, cocking the gun reduces the amount of force you have to put on the trigger to make it fire."
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gdxft6 | How is dynamic range increased on newer cameras and why does the human eye not get blown out highlights like cameras do? | Engineering | explainlikeimfive | {
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"For the human eye part, the explanation is that it does not work like a camera. You do not capture a single high definition image of all you see. Most of the eye has quite low resolution and there is a single spot the fovea with high resolution. It covers a 2-degree area and you get a clear image of stuff by moving the eye around and building up a clear image ow what you see. When you do that you change the amount of light that reaches the retina as the exposure is correct for the area you focus at. Search for \"human eye-tracking heat map\" and images and you will see how human eye skips around and target the part we thing it interesting Your brain take this small clear area in combination with the less clear surrounding and build up a single stable image even if the eye moves around. If you did not look wit the fovea on a part the brain adds in information from the low-resolution data and your experience of the world. Lots of what you see in a way guesses by your brain. An optical illusion is in large part exploiting the way that the brain interprets the world. The [black and blue, or white and gold dress]( URL_0 ) is an example of how our brain manipulate information, som will use the overexposed background as information that it is overexposed and unconsciously change out the perception of color to match the perceived lighting condition but other do not and you get a different result The [Checker\\_shadow\\_illusion]( URL_1 ) is another example of how we look at stuff. Two scares with the same color white or gray depending on the surrounding square and the clear shadow. So in a simple image like that, your brain does a lot to an image. If you print the image and cut out the squares is very clear that the color is identical. This is a very clear example of how our brain manipulate what we see. Yo do the same when you look at the real world Human vision or even interpretation if an image of a screen is very complex. If fixes a lot of problems but add stuff that is not there. So it is an imperfect but quite useful system. & #x200B; I away out vision work more like if you create panorama with many images of a smaller are each correctly exposed to get a single large image. You then have the correct exposure of each part of the image. This is a lot closer to how a human eye looks at the world.",
"With more processing power onboard a camera, many of them utilize high dynamic range (HDR) processing to get more dynamic range. The standard HDR method requires capturing multiple images with different exposures. Suppose a scene has brightness levels from 1 - 1000. Your camera's dynamic range can only distinguish 1 - 10 levels. To capture the full dynamic range, you take one image at a low exposure to capture the 1 - 10 brightness, increase exposure by 10 to capture 10 - 100, and increase exposure by 100 to capture 100 - 1000. In software, you combine the three images into one image with higher dynamic range. A camera sensor's dynamic range is determined by the bit depth. In the example above, the sensor could report 1, 2, 3, ... 10 values for brightness. When you increase the exposure by 10x, it reports 10, 20, 30, ... 100 so you can see that the spacing changes but the ratio between the smallest and the largest value is the same (1 to 10). If you had a camera that could capture the whole 1 - 1000 range, you wouldn't need to perform the HDR combination with multiple images! With new technology, more advanced SLR cameras have bit depths of 10 - 15 bits which equate to 2^10 = 1024 and 2^15 = 32,768 levels of brightness. Our human eye is still better. In the proper lighting conditions, we can achieve about 1,000,000 levels of brightness which is about a 20 bit depth. Cameras simply haven't reached this point yet but with a combination of better sensors and HDR software processing, they are getting closer."
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gdxwzq | Why can’t the F-35B take off vertically? | The F-35B variant is capible of vertical landing, but unlike the AV-8B, it only has short takeoff instead of vertical takeoff. However, the F-35B is capible of sustained hovering, so what’s preventing it from taking off vertically? | Engineering | explainlikeimfive | {
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"The F-35B is actually capable of a vertical takeoff. However, to do so, it has to shed weight. They remove the armaments and much of the fuel. It isn't practical to use the vertical takeoff mode for most reasons why you would want to use the plane in the first place."
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gdyeth | Why do older homes, like everything pre 70's especially, seem to have more smaller rooms? Is it a generational thing or what? | Engineering | explainlikeimfive | {
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"Several things going on with this: Expectations of homes were very different pre-1970s so they were built a fair bit smaller. In a lot of regions brick was the material of choice pre-1970s, but it’s quite expensive, so smaller homes were more financially viable. In the late 70’ and early 80’s the timber industry really took off in home construction, enabled in part by development of new systems for construction such as more economical sheathing systems and mass produced metal connection systems like [Joist Hangers]( URL_1 ) that enabled rapid and economical framing as carpenters didn’t have to go cutting individual connections for every member on a job. This reduced the cost per square foot of timber construction significantly, and a lot of people wanted to put those savings into more living space. One controlling factor is how far floor joists can span. Smaller joists are more economical but can span over smaller rooms. The big rooms you see in modern houses are often made possible by manufactured products - for example [truss joists]( URL_0 ). These enable much deeper joists that can span significantly further than readily available joists cut direct from a tree. /Edited to fix link edit hugged to death and reordered paragraphs",
"The basic concepts of home design have changed from function to fashion. Older kitchens are smaller and more isolated because they were akin to utility rooms. You didn't want the heat, noise, and odor of cooking to get into the rest of the house, so food was prepared in the kitchen and then brought into the dining room for consumption. Now, kitchens are viewed as fancy hubs of entertaining and socializing, which has resulted in modern \"open floorplans\" where everyone is milling about in one large space. Older houses have more bedrooms because people had more children during the periods in which they were designed, and families were more likely to have multiple generations living under one roof.",
"It also depends on how old a home is. I live in a home in northern new england that was built in 1901. The rooms are smaller than modern homes. I cannot imagine the nightmare that would come with trying to heat an open floor plan home 120 years ago. Even now, we heat rooms at different temperatures depending on usage. It saves us a lot of $$. Also, queen or king beds weren't a thing back then.",
"Check out [this history of closed rooms]( URL_1 ) from Kate Wagner (of [McMansion Hell]( URL_0 )). Some snippets: > Structural reasons in general were why, in common houses, open spaces would not become more widespread until changes in construction made them more affordable. & #x200B; > Today’s style of framing, platform framing, enabled more flexible room shapes and sizes. & #x200B; > Even as plans in elite houses continued to open up throughout the 1920s, the common house retained its interior walls. Why? In many respects, closed rooms existed to maintain a semblance of privacy. ... > > Work areas, such as the kitchen, and private spaces, like bedrooms and bathrooms, were always closed off to avoid guests seeing the mess of meal-making or, heaven forbid, the “unmentionable room” (the bathroom). & #x200B; > Kitchens began to open up and become public spaces in the home because of cultural shifts regarding consumption. & #x200B; > If closed floor plans are considered such a nuisance these days, why did they prevail for almost 100 years in single-family working- and middle-class suburban housing? The answer: closed floor plans make a lot of sense, from both an environmental and a living perspective.",
"Lol, this is clearly not someone from the UK! Rooms in houses in the UK since the 70s have gotten smaller and fewer!",
"We have much more stuff now than we did 30 years ago We have more money and thus... We have higher expectations. Expectations of space to live and expectations of of space to put all of our shit. I saw somebody on reddit recently make the claim that 4000 sqft house was barely enough for a couple! I live alone in a two bedroom apartment in Chicago built in the late 1800s maybe early 1900. The dining room is twice as big as the second bedroom. A hundred years ago a family of four probably lived here and the kids shared the second bedroom. Maybe more...",
"My house was built in the 50s, and I don't get the impression closets or bathrooms were a priority....so small. Ppl prolly owned less clothes then?",
"This also has to do with the costs of infrastructure and with building permitting, at least in suburban USA. Land costs, sewer hookups, and development rights have risen and are relatively fixed for any individual single-family home lot. The only way to make that high price seem like a better value is to increase the overall square footage of the house itself. For $500k, a 3,000 sq ft house sounds like a much better deal than a 1,200 sq foot one. New tweaks to balloon-frame building techniques allow this to happen relatively cheaply. But cities typically restrict how many bedrooms each new home can have as a way to manage growth, in particular the effect on schools (which are a big local expense in the US). So both the 3k sq ft house and the 1.2k sq ft house will have 3 bedrooms (or maybe the 3k house will have 4, but that is still not proportional to the overall size). All that room has to go somewhere, and it often goes to bigger bedrooms, gigantic open kitchens, \"bonus\" rooms, and big wasteful spaces like entry foyers. Giant houses--with few bedrooms and lots of wasted space--situated on small lots is the result.",
"Economics was a large factor. Consider back then, one-income households was common vs. today it's almost a required to have two to buy an average home. Mortgages were shorter and interest rates were higher. Linger effects of economic instability (two world wars, Korean and Vietnam, and a great depression). All that contributed to folks being more careful about how much home they purchased.",
"I admit that I didn’t read through every answer you’ve gotten, but aside from the structural reasons, people back then actually preferred closed floor plans, more often than not. Back then, people tended to live their lives MUCH closer to their home turf, wherever “home” was, and life in general was much more closely knitted and more small community centric. Not even *nearly* the habits of relocations and cross-country (much less global!) moves that are so much a part of society today. As a result, you tended to live your life where you knew everyone and everyone knew you, and even if you happened to be one of the few who moved, you THEN tended to stay out. That meant you were so surrounded by extended family and lifelong friends that people were inevitably “dropping by” to say hi, share gossip, borrow something, return something, drink coffee, whatever. This aunt or that cousin or one friend or another could pop in unexpectedly at any time. Thus, every home started with an entry hall/foyer, coat closet, and a formal living room that stayed clean. There was no walking in a front door with a giant, open living / dining / kitchen arrangement where just anyone could see that you hadn’t cleaned up from breakfast yet! One reason you can do that today is because most people *don’t* tend to live in the same place forever, so they don’t have to worry about unexpected drop-ins at unexpected times. Plus, the age of relocations has led to much stricter etiquette against “dropping in” at all. I live in Dallas, TX (**not** where either my hubs OR I grew up, by the way) and no one just pops over without warning. They just don’t. But in small town Oklahoma, where I was born — and where my mother was born, where my grandparents had lived since statehood, where I had 3 great uncles with their families, 3 great aunts with their families, countless cousins, and my grandparents’ nearly lifelong friends whose children were my mom’s *literal* lifelong friends whose children were my older sisters’ best friends, etc. — **there**, every house was a virtual revolving door of neighborly traffic, and “company rooms” were much appreciated.",
"Seems to be the opposite in the UK, old Victorian homes when we had an empire and money are huge, big grand ceilings and what have you. Our newly built houses are a lot smaller.",
"We had a lot less stuff back when those houses were built. No computers, TV's, air-conditioning, much fewer clothes, less nickknacks, no board games, no DVDs, no gaming systems, just the essentials in the kitchen, no microwave or electric gadgets. Modern people just have a lot more stuff then people did 100 years ago.",
"Of interest, perhaps. In the neighborhood I lived in New Orleans, (near Bayou St. John and City Park), the driveways are steep from the street, and narrow as hell. Houses built 1910-1930. The cars back then had high clearance and narrow frames. And very few people even owned cars, so may of the houses in my neighborhood had no driveway at all. Modern cars trying to park in those driveways have to approach it at an angle, and ease up onto the driveway itself. Otherwise you'll scrape your oil pan or lower body units. - I like knowing why things are how they are.",
"Here in the UK its reversed. Older houses tend to have large rooms while new build houses tend to be very small and boxy because in the UK the main factor people look at when buying a house is number of bedrooms. So if you can make a small 2 or 3 bedroom house then you can fit more of them into a given area. When a company builds a whole road or estate they will cram in as many houses as they can with small bedrooms and a small garden because they still tick the checkboxes that people require. Trying to find a big 2 or 3 bedroom house made in the last 40 years is basically impossible here. In other countries buyers might first focus on other aspects (i hear the US usually looks at floorsize above all else).",
"Middle class life X decades ago would be considered poverty life today. We lived in much smaller houses, had fewer cars, had fewer home amenities (including AC), ate out much less, ate meat much less, and so on and so on. A lot of things we take for granted today used to be luxuries yesterday.",
"In addition to the construction factors, there was a social component as well. Prior to the 1970s (especially homes built in the first half of the 20th Century), it was very common for people to live with their parents much later in life, as well as elderly parents living with their grown children. So in a home that might have four bedrooms, it wasn't expected that each kid would get their own bedroom and you'd have an office space. It was expected that the kids would double up, and maybe nana lived in one of the bedrooms, and maybe you even had a boarder or extended family member renting a room, which was common as well. So the social priority in home design was privacy. A kitchen was a place where people worked cooking, and the ladies of the house would congregate and socialize. The idea of an open living room - dining room was unattractive, because if you are living with that many people in a relatively small space, you want the ability not have to see everyone all the time. Breaking up the space was good. Now, the ideal is nuclear families in single family homes, so having an open floorplan feels more social (dad can be in the \"kitchen\" and mom can be in the \"dining room\" and junior can be in the \"living room\" and everyone can still hear and see one another). Also, roles have changed and thoughts about cooking as a social activity have changed, so the idea of a kitchen and living room being one large space has a lot more appeal.",
"It's actually the opposite in my country. Most antiquated houses have very large rooms in comparison to modern day apartments.",
"Where the hell do you live? Houses have got ever smaller since the 70’s",
"Because people went outside to do things back then. Now, everything people are conditioned to like can be done in the room.",
"Funny I always think of \"older homes\" as windy large rambling houses with tall echoey ceilings, oversized doorways, mysterious basements and attics and secret passageways and forgotten nooks. But then i live in central new orleans where alot of the housing stock is 1890s-1920s. I find them almost impractically oversized but very pleasant and spacious. Maybe youre thinking of suburban tract houses from 50s to 70s as \"older\" homes. When i go back to my dads house (bought with a VA loan after ww2 ) in tennessee it feels like Im living in a crackerbox with ceilings you can touch just by extending your arm up.",
"What country is this? Where I live houses are getting smaller every day for insulation and more efficient heating and cleaning. My mum's ceilings are so high getting the cobwebs make me cry, and if we turn the heating off for half an hour in APRIL on a cold day, several hours' worth of heating is suddenly out of the window",
"Hello from Portugal. Our older homes have smaller rooms, because none of them were built with central heating (not really a thing here, until very recently). So, you basically just heated the room you were in, while you needed to. This may be the same for your country. If the house in question was built back when you heated rooms instead of heating a whole house.",
"Top-level comments all have good points, but a factor I haven't seen discussed is family size. With the advent of widely-available birth control and a reduction in the social stigmas of using it, people planned their families more and more. And that often meant smaller families. Instead of building a home to accommodate as many people as practical within a space you can afford to heat and maintain, people built it to accommodate a smaller family more comfortably. Same space, fewer divisions. I'm sure the decline of common-spaces for relaxation, replaced by in-home entertainment like TV, had an effect as well.",
"Occasionalredditor had a good answer, but there is a deeper answer. As a largely accurate generality, people move out of apartments and into houses when they get married and want to have kids. This is particularly true in low density heteronormative environments—aka the vast majority of post WWII United States. Post WWII and post Korea, it’s important to know a few other demographic characteristics of “home buyers”. First, they were generally very poor. As a generation, they had been made destitute as children by the Great Depression and has the first few years of their young adulthood spent in the non-earning and non-career-establishing activities of killing NAZI’s, Imperial Japanese, and then Chicom’s and North Koreans. Second, they were mentally tough, self disciplined, and defiantly self reliant in a way that is very difficult for us to fully grasp today. They wanted what they wanted and having ground their way into Normandy and Iwo Jima they knew that just by working they could get more than they’d ever had using only a fraction of the will they had extended while manning a machine gun at 2am on some mountain ridge when it was a billion degrees below zero. But they had no money and no safety net: they had will. So this was the market. The builders of homes responded to that market by building suitable homes. What was a suitable home? Well, it would have to bigger than a foxhole or a tent and big enough for a bedroom and a babies room. But cheap enough to fit the mortgage these guys could take on. Did I mention that the men had nothing? MAYBE 2 suits and 3 shirts and two pairs of shoes. The wife had maybe three dresses plus 1 for funerals and one for special occasions-maybe. That’s the size closet they needed. They didn’t show up to the closing with a TV and two kitchens worth of dishes and blenders. They wanted solid and they needed cheap and didn’t NEED “big”. put those three together and there’s your answer. Look at the homes built in the 1980’s and you see the results of the wealth generated in the process of 1950’s era 20 somethings building a modern world in the 50’s, 60’s, and 70’s. Bigger, roomier, more extravagant.",
"This is just speculation. But pre 70’s, interest rates were very high. When interest rates are high, demand for renting increases. Rental units with an increased number of bedrooms (not sq footage) are more favorable. This is just my best guess. The builders were developing with a rental market in mind.",
"This is kind of funny to me. I just bought a place in Metro Vancouver...it's early 1970s, 1100 sqft, 3 bedrooms. To me it seems like it's absolutely HUGE because \\*they don't build three bedroom units this big here any more\\*. Now they build them way smaller and just cram everything together to sell more units.",
"Generally older house layouts had more compartmentalized spaces. Walled off dining area, living room, kitchen, study, etc.. More walls - less square footage overall. Modern House layouts tend to generally be more open, dining rooms are part of the kitchen, or the living/dining/kitchen are just one big room now. Families are generally smaller as well, so you don’t need to make 5 economy sized rooms and you can have 2-3 larger rooms instead.",
"Until the 1970s banks would only consider one income. The thought of course is the woman would become a homemaker. Just that fact made houses more modest. Families were larger so more rooms while smaller served a purpose. In the 80s and then even more so in the 90s loan packages were developed to let people borrow more by stretching out payment length or getting lower initial interest rates. When my Grandmother had bought a house in the 1930s the longest loan time available was 5 years. By the late 80s some banks were playing with 40 year loans. You never paid the loan amount down but home values kept going up so it was ok In the end the whole thimg collapsed I remember peoples expectations changing so much. Every bedroom had to have a bathroom. Saving for a rainy day was just not in the thinking.",
"Combo a few things: 1) people were physically smaller. Take a look at vintage clothing. People were smaller even back in the 1950s. A lot of this had to do with nutritional deficiency in some product (FDA did not exist back then and there were a lot of unappetizing fillers in food) and food accessibility. 2) as the top comment eloquently lays out, things were built differently back then. 3) stuff. People had less stuff. Therefore, less room needed to fill the stuff. [brief video by the university of California study on space usage.]( URL_0 ) 4) HVAC. I shudder to think what the heating bill would be for a radiator to heat an open concept space with 15 foot ceilings. 5) post WWII boom was focused on the car and the residual home ec movement that very much focused on the kitchen as a workspace/command center for a homemaker. This applies to everything from sight lines from the kitchen into the yard and living room to why the garage often goes straight into the kitchen area.",
"I remember my grand dad putting up “storm” windows every fall. Sometimes stapled plastic over that",
"People of healthy weight don’t need as spacious of a home in order to not feel cramped. Tl;dr: obesity happened",
"Looking around at my 1 bedroom NYC apartment with 350 square feet at $3k per month in rent... I have no idea what you're talking about.",
"I live in a Victorian two story built in 1878. The rooms are huge. Like 24x24ft with 12ft ceilings. Not all older homes have small rooms.",
"I saw a makeover tv show that said that people would re do their homes just bc they wanted it to be different from their mothers’. They pulled up carpet , under that was linoleum, then hard wood. Now everyone wants hardwood again.",
"One reason (so I was told) was that the rooms are smaller because someone added a closet into the room at some point after the house was built. Before that the room was much larger. They didn't build in closets since closets were considered another \"room\" and that increased property taxes. They used furniture instead.",
"In the south i have noticed the opposite. All the older houses have huge rooms. A nursery is the size of a master bedroom. But newer houses all the rooms are the size of my walk in closet (which isn't very big). We went with a 1980 house because the rooms were huge. Closets were huge. 2 living rooms. 2 dinningrooms. 3 bathrooms. All while still being affordable.",
"What’s more, houses built in the 1970s and 1980s commonly had eight-foot first-floor flat ceilings due to the energy crisis that gripped the country. (Unrest in the Middle East led to an embargo on oil exports to the United States.) In an effort to stem heating/cooling costs, houses were constructed with less interior space by shortening ceilings My parents house was built mid 70s. I think ceilings were 7' 6\". A simple way to save on heating costs.",
"Wild speculation here. I've noticed that a lot of new development areas over the years had architecture restrictions on the minimum size of the houses that were allowed to be built. I've seen residential lots advertising the restriction as high as around 2200 square feet for some acreage developments just outside my city. Perhaps the increase in square footage was a bit of a byproduct of trying to keep the poors out of the new neighbourhood or a simple keeping up with the Joneses thing?",
"It's all about the aliens. See, pre 1970, the aliens visited and studied us much more frequently (this is before they realized that 75% of the human race is retarded and pointless). Since beaming into a new home requires a bit of guesswork, the tiny rooms would make it harder for the aliens to enter uninvited, for fear of beaming halfway into a wall. Additionally, the larger number of rooms meant a greater number of armed militia members (also own a children) could be stationed there without sharing quarters. This was especially useful when the female guards entered their teenage years, where they would periodically transform into violent hormone monsters and require isolation to calm down."
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ge4ku2 | how the same key opens both the front door of my apartment building, laundry room and my apartment door but not any other apartment door | Engineering | explainlikeimfive | {
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"For many setups like these, the common area door locks only check one or two pins/positions of the key, which will be the same for everyone.",
"Keys have multiple teeth. Each tooth raises a tumbler inside the lock to a specific position so that the lock can be turned. These tumblers can be made into \"dummy\" tumblers where any size tooth can open them. Your apartment building's door only needs certain teeth. Your laundry room and apartment door require other teeth (and usually more than the shared door) which are unique to your key. Your neighbor's keys will have matching teeth to open the shared building door, but then unique teeth for their individual doors."
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ge7dqn | How are powergrids able to synchronize the power generated from different stations/generators? | Engineering | explainlikeimfive | {
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"Assuming a stable grid all sources are in sync meaning the voltage waves all peak at the same time. When connecting a new source there are measurements taken on both sides of the open breaker that prevents it from closing unless the voltage waves are peaking at the same time. Once the breaker is closed the system finds the new normal and everything remains in sync until there is a disturbance."
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ge7xc5 | Why does usb c on phones have the female part on the phone and the male on the cable? (This makes the part in the phone have a small nipple that can break.) It just seems simpler and and more natural to put the male part into the female part then sticking the female into the male one. | Engineering | explainlikeimfive | {
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"With most connectors one side wears more than the other. For USB-C that's the male part because it contains a number of flexible contacts. It makes sense to put the more wear-resistant side (the female connector) into the phone, because a cable can easily be replaced if the connector wears out, but replacing the connector inside the phone is much harder."
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genc1u | Why do phones make that screeching sound when put on speaker next to each other and something is being transmitted to both microphones? | They are basically playing the same sound,so why is there screeching? | Engineering | explainlikeimfive | {
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"It’s a feedback loop. Phone 1’s microphone picks up a noise, then the speakers play it on the other phone. Phone 1’s microphone picks up that noise, and then plays it louder. Phone 2 picks up that louder noise, plays it louder, and the cycle continues until you have horrid, angry phones screaming at each other.",
"Audio feedback loop! It's the same thing that happens when you hear a squealing microphone at an event. The sound comes out of the speakers, and the mic picks up the sound it just gave. The sound goes out of the speakers again and is amplified. The same sound being constantly amplified leads to a degraded horrible squealing sound. This is why speakers at events are placed in particular spots, usually just in front and to the side of the stage, so the main PA speakers arent pointed directly at the mic. Point a mic at a speaker and you're in feedback city! Which is what happens when you put two phones next to each other"
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geq7k1 | Why are crowbars made from a hexagonal bar? | Does a hex shaped bar have any benefit in any way? | Engineering | explainlikeimfive | {
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"It's so the bar doesn't roll when placed on the fulcrum and it spreads the force of the bar over a larger portion of the fulcrum. Less likely to deform the fulcrum if you can reduce the pressure by spreading out the force."
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gesbvm | What’s the difference between all wheel drive and 4 wheel drive? | Engineering | explainlikeimfive | {
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"4WD typically refers to part-time, where you can select and engage it or turn it off. AWD all 4 wheels are just always powered no matter the conditions and may not be able to be turned off. AWD is specifically designed to be used on all surfaces while 4WD the instructions typically tell you not to use it on things like say dry pavement, because the different mechanical components are more susceptible to wear or failure (particularly from what is called drivetrain binding) when run on surfaces that don't have some slip to them. It's also generally argued that 4WD drivetrains are tougher than AWD and can handle more abuse or load, though with modern advances in materials and tech I can't speak as to whether that's actually true these days. One of the biggest differences and the cause of that drivetrain binding is the way they get power up to the front (or the rear). A 2WD vehicle has a differential between the 2 wheels allowing them to spin at different rates no problem. AWD extends this idea to allow the front and back sets of wheels to spin at different speeds no problem. 4WD usually uses a solid mechanical link forcing the drive shaft to the front and to the back to spin at the same speed, so when you take a turn on dry pavement and all 4 wheels are going different speeds it can cause damage.",
"The terms used to be synonymous and they are often confused for each other. But the way these terms are used now 4WD refers to vehicles with a transfer case that locks the movement of the front wheels and the rear wheels. AWD on the other hand use a differential to transfer torque to the front and rear wheels allowing the front wheels to move independently from the rear wheels while still providing torque to all wheels. The problem with 4WD is that you can not go through corners without spinning a wheel which makes the handling worse. The most common solution is to allow the driver to disconnect drive to one of the axles turning the car into a 2WD while on road. The problem with AWD is that if one wheel loses traction it gets all the torque and you are unable to move. A common solution is to allow the driver to lock the center differential turning the car into a 4WD when needed. There is a host of other solutions that tries to do this smooth and automatically."
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gf9ycm | How does the F-35 transition to flight after vertical takeoff? | Wouldn’t they need immediate speed for any lift over their wings? Why do they not just drop out of the sky immediately? | Engineering | explainlikeimfive | {
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"Well first off they don't really use vertical takeoff operationally (same as the Harrier). But for transitioning between hover and horizontal flight its not like the engine snaps between normal position and hover. It puts it a few degrees back to get a bit of thrust to get a bit of speed to get a bit of lift so it can put the engine a few degrees more back... repeat until in normal flight. See [here]( URL_0 )."
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gfkfso | How does the pump at the gas station know when to stop when you fill up? | Engineering | explainlikeimfive | {
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"[Here's a video]( URL_0 ) that shows the internal parts. As you pump gas, the air inside the tank gets pushed out, and there's a little tube inside the pump that detects the pressure of what's coming up out of the tank, air or liquid.",
"There is a float inside the handle of the pump. As you are pumping gas in the air that is being replaced is coming out and back up into the handle. When the fuel gets high enough to block that return the float surges in the handle shutting off the flow of fuel",
"There is a small hole on the tip of gas nozzles with a tiny vacuum in it. This tiny vacuum flips a switch in the gas nozzle to turn it off once the gas reaches it. Think about it this way- when you're vacuuming and your vacuum tries to eat a large piece of cloth it has to suck really, really, really hard all of the sudden. The same goes for the little tiny vacuum in gas nozzles- when the gas reaches the little tiny vacuum, the little tiny vacuum has to work a lot harder to suck things up all of the sudden. This increased work by the tiny vacuum causes an increase in pressure to build up behind it, which then causes a lever in the handle to switch to the off position, which then stops the gas from flowing."
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gfl228 | In a shower or a sink, Why can water go from hot to cold so fast, but much slower to go cold to hot? | Engineering | explainlikeimfive | {
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"You have water at two temperatures, the hot water in your heater and the cold water everywhere else. It takes awhile to heat up because the hot water has to get there from the heater. Everything in the pipe between the heater and the shower is cold at first. However, switching to cold is no problem. You've got cold water right there from the pipe."
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gfnt98 | How did we make the first machine? | Engineering | explainlikeimfive | {
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"Wood. Weaving looms, windmills, all kinds of early machines were made out of wood. Also, you can cast metal using nothing more than clay and fire. It's just inefficient and difficult. We can also forge metal parts with hammers and other tools on heated-up metal, like a blacksmith does. We've been making metal things like swords and axes since before history began. The Colossus of Rhodes was cast in pits dug into dirt. It's well within human capability to make metal things without using metal."
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gftyzw | If computer screens render different colours by filtering white background light through red, green and blue pixels, and black is the absence of colour, how do computer screens reproduce the colour black? | The most intuitive answer would seem that black pixels get "switched off", but I know that's not true because I can tell when a monitor is switched on and off even if the screen is just black. There's a sort of "black glow" to them. | Engineering | explainlikeimfive | {
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"So this applies to LCD, and other screen panel types where the pixels dont produce their own light. On an lcd the backlight is always on in some form, and the way they make \"blacks\" can be done in a few diffetent ways and a combination of ways. LCDs generally have a layer behind the pixels that is a polarizing layer, that can be turned on and off to block the backlight from going through that zone of pixels. What you reference when you know your monitor is on but supposed to be black is called \"backlight bleeding\" Fancier LCDs use a technique called Local dimming where the backlight is a panel of millions of white LEDs broken into a grod of zones,i beleive current high end lcds have 192+zones of dimming. This is where the tv will actually shut off areas of the backlight to produce a much deeper black, though this effect can create \"halos\" most noticible on white text on a black background.",
"Not all screens work this way. OLED displays don’t have a backlight; they use red/green/blue pixels that are individually self-illuminating. So if that pixel needs to be black, it just doesn’t light up at all, and it really does look black. But cheaper displays do work with a backlight, and the red/green/blue pixels control how much of the backlight gets through. To display black, a pixel will reduce the light coming through it by the maximum amount possible. Since this isn’t perfect, you actually get a slightly glowing dark gray color instead of black - but you perceive it as black because you’re comparing it to the other colors on the screen. Fancier displays have what’s called “local dimming” where sections of the backlight can be made dimmer or turned off, to make the black areas closer to black."
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gfvvrg | Why are some smartphones not compatible with certain carriers? | Why does it matter what SIM card I put into a device? | Engineering | explainlikeimfive | {
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"It's not so much the SIM card as it is the radio frequencies and the communications protocol that each carrier uses. On the older systems there were two main protocols, CDMA and GSM, and they were not compatible at all. In about 2010, LTE became the dominant protocol, and the CDMA and GSM networks are beginning to go the way of the dodo bird, with all but a few planned for shutdown by the end of 2020. That will take away the protocol problem, but the frequency problem will still be there, because different carriers are allotted different frequencies for operation.",
"Or rather, why is your phone locked to a particular carrier? No smartphones that I can think of in recent memory are actually restricted to or from a carrier on the basis of technology - it used to be, CDMA vs. GSM vs. whatever... but now many mobile chipsets are capable of talking most wireless technologies and frequency bands.... back when I worked in wireless there were some differences between frequency bands between NA, Europe and Asia, so you had to have slightly different models for each market, but Im pretty sure that's not the case anymore. Rather, the reason your phone is locked to a carrier is because of customer-lock in. Carriers don't actually make money on phone sales - they lose money; the phone is a loss leader to get you to sign up for a monthly plan. Thats what a Device Tab is, essentially you're paying off the purchase price of your phone. There is also the question of carrier exclusivity - AT & T may pay Apple $$$ to be able to sell iPhoneY exclusively in the US for a time period, they don't want you to buy an iPhoneY (remember they lose money on that) and then switch to BargainBasement Carrier, they want to keep you on $ExpensivePlan."
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gg0se0 | Why don’t AA batteries shock you? | If you hold both the + and - with your hand, why doesn’t it shock you? Is it just too weak, or what? | Engineering | explainlikeimfive | {
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"Yes, the voltage is just too weak, along with your high skin resistance. On the other hand, if you were to put the battery in your mouth, you would definitely feel a slight shock. This is even more noticeable with a 9v battery.",
"Your skin is a somewhat decent insulator for the voltages you come across daily, AA batteries are 1.5V, but even car batteries at 12V, or even voltages as high as 30V aren’t enough to be felt by most people However some areas, most notably your mouth, eyes and nose, have lower resistance and there you can feel even voltages as low as a AA, although not very much, at about 5-10V it starts becoming pretty painful on your tongue",
"Best way to explain this is with a quick explanation of how electricity moves, and best way to do that is with water analogy. You got a water hose, you pinch it off, the water wants to get out but cant. Water pressure from your spigot isnt really that high, so it just stops and sits there. Now you got a water hose hooked up to the bottom of Hoover Dam. Thats like...a lot of water pressure. You could try to pinch it off if you want, but the water will probably blow right through the hose and through you. In simple terms, Voltage is the water pressure, the higher it is, the more likely the electricity is to blow through something. AA batteries are very low voltage and arent able to blow through the insulating properties of your skin. Fin."
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gg3kru | How do boats stay safe from lightning? | Sailboats in particular, but also all metal boats | Engineering | explainlikeimfive | {
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"text": [
"It's not uncommon for ships to get hit by lighting. If a lighting storm approaches, everyone goes inside. The ship is a big [Faraday Cage]( URL_0 ), so we are safe if we stay inside. Hopefully, the lighting won't hit the mast or an antennae and fry the equipment, but it happens.",
"They often have lightening rods like buildings do. A strip of metal running from the top to the bottom to hopefully direct the current away from sensitive equipment or people."
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gg5ovw | How are Teslas able to increase the battery range by OTA update? | Beyond the restrictions limit they put on to extend battery life, how are they able to do it just by software update? | Engineering | explainlikeimfive | {
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"Well the first part is obvious like you said, adjust the restrictions on things like max draw and how far it will allow the batteries to deplete before demanding a recharges. That is probably the big one right there actually, since the drive motor(s) are far and away going to be your biggest power draws. There might be other adjustments like to regenerative braking if that's software-controlled. Other less noticeable stuff might be adjustments to say the levels of dimming available on dash instruments, or blower motor speeds for the HVAC (it's increasingly common in a lot of cars to use a MOSFET to digitally control the fan instead of a resistor pack), if the motors or batteries have active cooling that is powered by battery, maybe some adjustments to the speeds of the fans there or at what temp the fans turn on. Being that a lot of cars use a bunch of local control modules to operate things like the power windows etc (linked by a CANBUS or some other communication so your driver door module can tell the back door module that you're pushing a button to roll down the window), perhaps some adjustments to the sleep states on those."
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ggilwe | Why do some stainless steel skillets have a copper bottom, how does it work vs a stainless steel skillet that doesn't have a copper bottom? | Engineering | explainlikeimfive | {
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"In general, all metals are good heat conductors but some are much better than others. Stainless steel is an alloy that's among the not-so-good metals as far as heat conduction so it tends to get hot spots rather than spreading heat out along its surface. Copper is the best heat conductor among metals useful for cookware. The copper bottom helps spread the heat out across the bottom of the pan allowing for more even heating.",
"When talking about heat and how it affects materials, there are two important properties: how much heat energy it can hold (specific heat) and how fast it can transfer heat (heat conductivity). Iron based alloys (including stainless steel) tend to have higher specific heats, but lower heat conductivities. So you can cram a lot of heat energy into them, and they'll release it back at a slow rate. This is optimal for when you want to heat things consistently and evenly. Cast iron pans are much better at this than stainless steel; stainless steel pans are designed more for their anti-corrosive properties (hence \"stainless\"). But stainless steel kind of falls into this camp. Copper is an element with *extremely* good heat conductivity, but has a relatively poor specific heat. Give a piece of copper some heat energy and it will disperse that energy throughout itself. Look at any device that needs to move significant amounts of heat (high performance electronics, air conditioners, refrigerators) and you'll likely find their heat-moving components ([heat pipes]( URL_0 )) are made of copper. So if you combine the two metals into one object, you can get both of their properties. The heat from a stove is on the bottom, so you can put the copper there to ferry the heat all across the bottom of the pan. The rest of the pan, the part that contacts the food, can be made of stainless steel, which is resistant to damage and can cook the food more steadily. Stainless steel is also much stronger and creates most of the strength of the pan -- there's a reason you don't see pans made entirely of copper."
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ggmwq9 | How is one individual staple connected to other staples? (english is my 2nd language so please don’t mind my grammatical mistakes) | Engineering | explainlikeimfive | {
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"text": [
"staples start as 80 (or however many is on one strip) strips of wire that are glued together into a flat solid chunk. when dry they then get cut and bent into the U shaped bar you see when you open the box."
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6
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ggqj00 | Why does solid bulk cargo liquefaction affect ships? | Engineering | explainlikeimfive | {
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"Taken from the article you linked: > Solid bulk cargoes – defined as granular materials loaded directly into a ship’s hold – can suddenly turn from a solid state into a liquid state, a process known as liquefaction So they aren't in containers but a single hold. They expect it to barely shift at all. When it liquefied suddenly your cargo hold is now a sloshing ballast tank. Since its center of gravity now moves with the motion of a ship, when the ship lists the center of gravity will move too, which can tip the ship over and cause it to capsize.",
"I think usually that kind of stuff isn't in containers. It's just thrown into a giant hold, which means it can slosh around from one side of the ship to the other."
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ggyyjg | Why do we need DACs with high sampling rate? | My understanding: * Human hearing range is 20Hz-20kHz, * CD sampling rate is 44.1kHz, which is chosen based on Nyquist–Shannon sampling theorem, so that all frequencies that people can hear can be captured. but why do they keep making DACs with higher and higher sampling rate? I've seen DACs with 96kHz, 192kHz, 384kHz and even 768kHz sampling rate. And what happens (regarding sound quality) when an audio stream with lower sampling rate passes through a DAC with higher sampling rate? (e.g. playing a 44.1kHz MP3 file using a 192kHz DAC) I've searched reddit (not an exhaustive search) and found the following related topics: * [ELI5: Why do we listen to songs above 20,000hz]( URL_2 ) * [ELI5: Whats the difference between 44kHz and 48kHz when the human ear can only hear up to 20kHz ?]( URL_0 ) * [Eli5: Why are high quality speakers and headphones built to reproduce frequencies outside the audible range?]( URL_1 ) but they don't seem to answer my question (or I'm too dumb to get the answer). I've read some articles online but they are too complicated for me, and I don't know if they are telling the truth or just trying to market/sell their equipment. | Engineering | explainlikeimfive | {
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"Sometimes you’ll record something at a higher sample rate to playback at 44.1kHz. This is how a lot of ‘slow motion’ audio is done in the movies.",
"One argument for higher sampling rate is that you can achieve more precise timing of the signal components and therefore capture the original signal more closely, timing-wise. 44100 kHz, was picked to be easily attached to video standards in times of analog TV ([ URL_1 ]( URL_0 )). The trick is that your sample rate is an integer multiple of your basic frequency so you don't have to adjust samples timing-wise. That is where things get tricky with modern DACs and interfaces. You sort of mentioned the problem yourself (i.e. playing a 44100Hz through a 192 kHz DAC). You have to resample it, means convert/interpolate the samples such that they fit the target sampling rate. Interpolation to 48kHz can only infer loss because there is no integer factor between 44100 and 48000. 48000Hz to 192kHz works pretty well in comparison since the upsampling factor is 4. Alright. The following is my personal opinion. Do not use 44100 kHz on your DAC connected to your PC. Why? USB DACs are fed with a USB data stream. All of the embedded USB chips I experimented on had a 12 MHz base clock, and that is trivially divided down to 48000Hz by 250. Means: Your USB DAC is most likely to cope better with 48kHz signals than with 44100 because it does not need to perform expensive resampling and has a stable clock for your data input signal to work with. (Really expensive DACs buffer the data stream asynchronously first, and then convert with a separate clock...but that needs separate hardware, thus cost). Set your sound card (DAC) to 48000 Hz. If you need to resample, let your computer do it, it has more processing power and can handle more sophisticated resampling algorithms. Your raw digital output is most likely filtered to get rid of the artifacts caused by the analog conversion process. Moving the output filter effects away from the audible signal is good, therefore sampling higher first, then you can let your filter operate on high-frequency signal parts. The filter then will not affect your lower frequencies. While the effect is desirable, I doubt that oversampling higher and higher gets any benefit from it. Looking at the high end range of DACs, they don't use more than 768 kHz sampling. (At least none that I am aware of, and no I do not have one). Last point: Do not underestimate how different converters (from different manufacturers) sound at the same sampling rate. The difference in circuit design can have a considerable effect on the chip's performance (e.g. linearity, distortion). Maintaining constant quality in these chips is what makes them expensive by the way. Hope that helps, kindly tell if I should elaborate on one or the other point :)"
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gh0r8b | Why are flathead screws a good design idea? | Engineering | explainlikeimfive | {
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"They're a lot easier to sand and paint over, and they disappear under paint and such. Can give a more minimalistic finish.",
"They prevent you from overtightening the screws. It feels frustrating when you need to tighten one and the screwdriver jumps out, but it's actually intended. That's the reason why they still exist to this day. The reason why they exist in the first place is that they are way easier to manufacture, and because of that they were the first to be mass produced."
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gh4uaw | Concorde burned two tonnes of fuel just taxiing to the runway. Why wasn't it towed there to save fuel? | Engineering | explainlikeimfive | {
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"It also warmed up the engine and pressurized hydraulic accumulators. The towing wouldn't have saved enough to impact the ginormous cost of Concorde.",
"Ironically, jet fuel is some of the cheapest fuel on the planet. It's so abundant that the primary cost behind it is just getting it to and inside aircraft safely. It literally can't be efficiently used on anything else because it only effectively burns at high altitude. The fuel you get at your local fuel pump for your volkswagon is FAR more expensive than jet fuel. & #x200B; The primary cost of aircraft is in parts becoming \"timed out\" When an aircraft reaches higher altitudes, it pressurizes it's cabin. This puts an enormous amount of stress on the frame / chassis of the aircraft, and these things need to be inspected and replaced by very specialized technicians to a very high standard. This accounts for the overwhelming majority of aircraft expense. Fuel is a drop in the bucket.",
"Fuel consumption was not really an issue. Fuel was and still is quite cheap compared to the equipment and crew required to tow it to the runway. In addition to the cost of delay it would cause for what was the expensive and fast way to travel. Towing aircraft to the runway due to fuel savings have not been done since the end of World War 2. However with modern technology there is a push to have automatic aircraft tugs that would be able to help aircraft taxi. This could reduce the amount of ground crew required to push it to the runway which could make this economically feasible. So we might see it in the future."
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gh5igg | Why do hand-held string instruments need to be tuned so often? | I know pianos need to be tuned every so often, but why are instruments like guitars and violins tuned everyday or every time you play? Do the strings not stay in the same place? | Engineering | explainlikeimfive | {
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"When the temperature changes, the wood expands and contracts, sometimes up to a half step. So you gotta retune. Also, since the tuning keys are on the outside, some jerkwad like a cat could jump on them and change the tuning. Also, lots of people like to change their guitars to have nonstandard tunings, so they have to start over every time. All in all, it’s just a good idea",
"Strings stretch over time making them looser. So you need to be tightening them up again until they gets worn out and snap. This is less of a problem on strong steel strings like a piano use but it is much harder to play those so most string instruments use softer strings. But the biggest issue is that hand held instruments are usually made of wood which expands and contract depending on the temperature and humidity. So even just moving between two rooms is enough to change the size of the instrument and therefore the amount of force on the strings so you have to tune them again. Pianos usually have a steel frame and high end pianos even come with air conditioners in them to keep the temperatures and humidity stable.",
"The strings stretch out over time under the tension. When I put a brand new string on my guitar, it goes about 1/2 a note flat the first few days until it's been sufficiently stretched. I once saw a professional guitarist have to put on a brand new string before a concert, and he was manually pulling on it to try to stretch it out so it wouldn't go flat mid-song. I suppose if the guitar has crappy quality tuning legs, they might untwist a bit too under the tension."
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gh7dcs | Why do some homes have amazing water pressure and water at some homes barely makes it out of the nozzle? | Engineering | explainlikeimfive | {
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"Lots of things. The floor you’re on, how many lines come off of that one, regulator to save water and more but i’m too dumb to explain but that’s what i would assume",
"Screw off your kitchen aerator and see if it has a flow-restriction disk. You can also take the showerhead off and see if there is a restrictor right at the inlet.",
"Few possible reasons. & #x200B; 1. You have a leak near your house/apartment. 2. You have a more restrictive regulator to cut costs/consumption rates. 3. There are more people on that water supply than it can sustain."
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gh97fn | why are cars made to be able to go speeds well above any speed limit, when they aren't made for reaching? | Engineering | explainlikeimfive | {
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"A lot of road cars are designed to be efficient. They want to be working as little as possible at the speeds they are most likely to go at. An engine that can only get a car to 60mph/100km/h will be working as hard as possible all the time if you were on an open highway. This would wear the engine down and lead to more faults as the parts are pushed to their absolute limit. An engine that can get the vehicle to 140mph/225km/h will effectively be working way less when keeping at 60/100. This results in less fuel usage, less wear and tear, less part failure and less hassle for the consumer.",
"Keep in mind that a lot of European cars are expected to use the autobahn which has no speed limit at all in some areas. They get slightly different versions over there but are mostly the same. My audi doesn’t go 170mph because I need it, it’s because Klaus needs it. I wish I was klaus.",
"Simply put: marketing. There was a movement in the 80’s where car speedos only went to like 85 or so. It was not a popular outcome.",
"There are plenty of engineering reasons why a car that's efficient at 70 will be able to go a lot faster, as other people have explained. Of course, there comes a point where going quickly isn't a result of efficiency, but just for it's own sake.For a lot of cars that's a marketing thing, you own this marvel of engineering that can go well over100mph, even if it never will. It's also worth noting that speed limits only apply to public roads; go to a race track and your can drive as fast as your car can go. Not a common use case, but it's there."
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ghcmwb | 360 camera rotation | Hello everyone, I was watching a video filmed from the camera underneath a helicopter and I was wondering how can the camera rotate 360° and send a direct image inside the cabin. Wouldn't the cables connecting the camera to the screen of the copilot get intertwined? Does the camera need to turn the other way around once a certain limit passed to "reset" its position? | Engineering | explainlikeimfive | {
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"It depends on the camera, but it probably points down through a Pechan prism to a mirror. That way the whole rotating mechanism is mechanical, no wires to tangle.",
"The other explanation with a mirror might be how it works but another option is a slip ring. Have an electrical connector as ring around the axis and connect to them with wire brushes and you can rotate and never twist wires. [Look at this image]( URL_0 ) for an example. It is not that different from a 3.5 mm headphone connector that you can rotate around. For rotating stuff, an option is a wireless communication and only power through a slip ring."
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ghdvjc | why does car doors have that middle position where the door is not fully closed nor fully opened | Engineering | explainlikeimfive | {
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"To clarify, this is asking why sometimes when you close your car door with insufficient force it doesn't close completely and is not flush with the rest of the body, but at the same time it's latched into place requiring you to pull the handle mechanism to unlatch it to open it again. Not closed to the point the car accepts that it's closed, but not open to the point that it swings freely. I usually slam my butt into it to close it all the way. Correct? (At this time there's 2 answers that don't seem to have the same interpretation of the question)"
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ghgap7 | Why are missiles and torpedoes shaped differently? | When designing each, how does the design differ depending on the fluid it travels through? | Engineering | explainlikeimfive | {
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"Water is far more dense than air, limiting the speed of torpedoes while raising the speed of sound. Furthermore, torpedoes and missiles have different propulsions systems. Missiles are consistently supersonic - they travel faster than sound and are shaped accordingly. This is in contrast to torpedoes which move much slower. They also have different warheads and guidance systems as their targets are different and because radar/heat-cameras don't work underwater. Missiles are propelled by either jets or rockets rockets and a rocket does not need air from the outside to operate. As such, missiles tend to have flat backs where the exhaust comes out. The alternative is jets, which must have an intake up front to suck in air. Torpedoes do not need an intake, and this redirection of water would further increase drag, but they *do* need water flowing over their propellers, and so they have a tapered back with a prop sticking out, as well as a ring around the prop to improve efficiency and reduce noise.",
"Honestly they're pretty similar in principle. But the resistance of water vs air necessitates some changes in design as water is much denser. As does the different guidance systems. Most missiles also use rocket propulsion, while most modern torpedoes use what's basically a jet engine in water, so more design changes there. Also torpedoes need to be quiet as sonar is used to detect them. Missiles don't need to be quiet, but being a slim radar profile helps. Add all that together and you end up with two weapons that have many principles in common but need a very different form to be most effective.",
"Rounded noses have the lowest coefficient of form drag, while pointy noses have the lowest coefficient of wave drag. For an object traveling below the speed of sound (like a torpedo, or a 737 jet liner or a handgun bullet) the form drag is the main type of drag that applies, so a blunt nose that minimizes form drag is superior to a pointy nose. For an object traveling faster than the speed of sound (like a missile or a jet fighter or a high powered rifle bullet) the wave drag is the main type of drag, so a point noise that minimizes wave drag is superior to a blunt nose. Generally, look at anything designed to go fast and you'll see that, if it is designed to stay under the speed of sound it'll have a blunt nose and if it's designed to exceed the speed of sound, it'll have a pointy one."
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ghl20f | Why average car brands does not make their cars shaped like porsche/lamborghini sports cars? | What I want to ask is, why opel/toyota/fiat etc. doesnt make their regular car with the same engine and parts, but shape it look like a sports car which considered "cool" Is it that hard to make a car look like that? Edit: thanks a lot to everyone who took a time to answer. cheers! | Engineering | explainlikeimfive | {
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"I’d imagine it’s easier to make a car in the less sporty style, but I don’t think that’s the main reason. Firstly, there are different markets for cars: a mum of 3 probably isn’t going to want a typical Ferrari looking things. But if you’re asking why doesn’t fiat make a cheap sports car (as well as other models). I’d say because it dilutes the brand/ image of a sports car. When people see a car like that, they expect it to be fast and built to a high standard. If these “knock offs” become common it will probably ruin the image of what a nice car is. In the case of fiat, they also make actual sports cars, so they’d also be undercutting themselves. Dunno if this answer is allowed as it’s not hard fact, just going off common sense. Although I have wondered this sometimes so there’s probably a better answer coming.",
"Because nobody buys those cars because of how they look- they buy them so everyone knows how rich they are",
"Not hard, just completely impractical. A regular hatchback, by comparison, is able to seat 4-5 people comfortably and carry their luggage. All in a package that’s economical to run and “cheap” to produce. A car shaped like a lambo or Ferrari is far less practical. It’s close to the ground - reducing ride comfort unless you equip much more expensive suspension components - and unable to fit as many passengers or luggage. They’re also much bigger vehicles, increasing cost to produce and thus sell. This is a very basic explanation, if you want more detail I can try and go into specifics but the end answer is the same - cost and comfort.",
"There are lots of reasons. Those aren't ideal shapes for the kinds of cars they're trying to sell. While they might look cool to some they don't look cool to everyone. The people looking for their cars are looking for something more practical which necessitates a different shape. They could be sued for copying the other companies brand. They want to establish their own identity as a car manufacturer. The components they want to include and the features don't actually fit within that space and would need to be seriously distorted to make it work so why bother copying something you have to ruin to make fit your purpose when you can design something that's actually meant to fit your need?"
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gi0bzb | the difference between an automatic center punch and a hammer/nail | Engineering | explainlikeimfive | {
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"Technically? Alot. If your question is there ultimately any difference in functionality, then not so much. If you're careful, you can start a guide dimple with a hammer and nail easily. The advantage of the auto punch is that it's smaller, lightweight, and since it uses the force of the internal spring for the punch, a hammer isn't needed. This all means that you can theoretically do more punches faster and more accurately, and use less energy to do it."
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gi7ios | Why do helicopters have only four blades and not six or eight of them? | Engineering | explainlikeimfive | {
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"Some helicopters do have 6 blades, and some have as many as 12, split between 2 rotors. The reason for not having as many as possible is a question of weight and necessity. If your engine is capable of flying efficiently with 4, adding 2 more just adds weight, cost, and complexity.",
"One of the reasons why helicopter can't have \"too many\" blades is that each blade creates an area of turbulent air behind it as it moves trough air. If the next blade is too close this turbulence can reduce efficiency, lift, induce vibrations. All this needs to be considered when designing a helicopter. Also, helicopter parts are mass produced so when a helicopter is being designed the engineers might just chose parts that are already available, tested and cheaper than demanding a new part is developed. That means if a 4 blade design is \"popular\" it might influence future designs to use 4 blades as well simply because the manufacture and maintenance infrastructure already exists.",
"I suppose the exact number of blades isn't what you are asking. I assume it's the \"*Why exactly that number, and not more or not fewer blades*\". The number is decided based on how much air needs to be pushed down so the helicopter can fly or at least stay in the air. It's like balancing \"*How many steps (rungs/crossbars) do you need on a ladder?*\" Too few and you can't stretch your leg far enough and you will fall off because you can't balance yourself. Too many steps and your feet won't fit in the gaps and you will move too slowly. Too many blades on the copter means each blade doesn't catch enough air to push it down, and too few blades means it will not push the air fast enough to lift the helicopter.",
"They don't, all. Helicopters can have as few as two. Some have as many as seven. How mnay depends on what you want from your 'copter. Lift, speed, whatever..."
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gijgp7 | Why armies just stood in front of each other and fired? | While watching the movie The Patriot I keep seeing major battles where the 2 armies just stand in front of each other and fire. Why did they do this? This seems like a very stupid way to fight a war causing the most deaths possible | Engineering | explainlikeimfive | {
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"Because the accuracy and firing rate of their weapons was very poor. Keeping your men together and organized allowed them to fire in a more organized way that allowed them to fire volleys in succession and en-mass, that allowed for more hits on the enemy. If everyone hid behind cover separately, and fired sporadically at individual fleeting targets that were also hidden behind cover, then no one would ever hit anything. So, you sacrificed your own concealment in an effort to actually inflict damage consistently.",
"Short version: Giving your enemy more stuff than they can deal with is an effective way to win battles. And a large group of guys shooting at you is a lot to deal with. Long version: Before the industrialization of war (mostly modern artillery and the machine gun) it was REALLY hard to win a battle by just killing a lot of people. Instead what you would hope to do is make your opponent unwilling or unable to continue the fight. Ideally you would do this by inflicting \"shock\" on the enemy, which in ELI5 terms would be some combination of \"scare your enemy into running away\" and \"traumatize them so badly that they can't respond correctly\". Now it turns out that not all weapons are equal when it comes to inflicting shock. Melee weapons are pretty good at inflicting shock, having some guy come up to you with a big pointy stick and try to shove it into your gut is a significant emotional event, so for a lot of early battles there wasn't much of a problem here. Things changed when firearms came to dominate the battlefield. Firearms are nice because any schmuck off the street can be trained to use one pretty quickly which made raising large armies fairly easy. The down side is that early firearms are, on an individual basis, kinda shit at inflicting shock. An individual musket often doesn't do anything (e.g. misses its target) and the rate of fire is slow enough that if it did do something you have time to recover (or the NCO in charge of your unit has time to harass you back into shape). There are a few ways to overcome this. Limiting yourself to the straight forward approaches a smallish unit might have, one approach is that you pack a whole bunch of people together who all fire their weapons at once. Smoke, and fire, and watching a bunch of your friends get shot at the same time is a more traumatic event then a few people doping at random. The 2nd is that you find some way to go back to the whole \"shove a sword in someones gut\" approach to warfare, which is what the \"Bayonet charge\" was all about. Once you get your enemy to break you can then follow up with reserves to make the victory decisive. So to answer your question, the reason you have two armies \"stand in front of each other and fire\" is because that was one of the few ways at the scale of small units of doing decisive. A similar idea continues even into modern war. We've advanced beyond \"line up and fire\" approach to warfare, but \"Hit your enemy with more stuff than they can handle\" is alive and well. One oft-quoted difference in the \"quality\" of troops is the number of forms of \"contact\" that they can withstand before breaking. \"Contact\" in this case being a way you are interacting with your enemy (I think the US Army defines contact as something that \"requires a passive or active response to the enemy\"). Forms of contact are: observation, direct fire, indirect fire, obstacles, aircraft, NBC, and EW. Basically, it turns out that combat is hard, and troops can only deal with so much at one time, and their level of training plays a big part in how many things you can hit them with at once before they become overwhelmed and are combat ineffective. So you might expect poorly trained conscripts to break after 2 forms of simultaneous contact, while very good special forces might be able to handle 4. \"Combat ineffective\" can be something as simple as \"fail to respond to a threat\" (e.g. be so distracted by fighting with enemy infantry that you don't notice an airplane about to bomb the hell out of your unit) or something more traumatic like a full rout.",
"Weapons in the early modern era (post reformation to the 1840s) were fairly crude mechanisms with an extremely low rate of fire, even for the best drilled musketeers in the world. So, to produce a volume of fire capable of killing the men necessary to make one side or the other a winner, masses of hundreds of guns firing simultaneously were necessary. To best deliver these volleys of deadly fire, military doctrine at that time dictated that you would approach very close to the enemy and fire as fast as possible. Getting soldiers to stand this close and fling flying death balls at each other took rigorous drilling, so that in the heat of battle terrified soldiers could fall on muscle memory to perform the complicated task of loading a black powder weapon. Thus, early modern battles became the characteristic rectangle on rectangle bloodbath we associate with the wars of Spanish and Austrian succession, the French and Indian war, the revolution and, and the napoleonic wars. TL;DR Because it was the best way to utilize the technology they had access to.",
"If you notice, this is why the Indian tribes were so effective in the French and Indian war. No one on that side really met in open battle, mostly combat through trees and brush, concealed. If you notice the scene where they rescue heath ledger, they fought in the trees and behind cover, a couple of kids and Mel Gibson took them all out. That’s completely plausible",
"A musket is generally just not a great gun. You get 1-3 shots a minute in good weather, and without anyone shooting back; every shot you take creates a loud bang and a big cloud of smoke; and you're only really accurate against a man-sized target out to about 100 yards. So one guy with a musket is going to get stomped. He's got one shot, and if he misses there's a decent chance whoever he's shooting at will just run over and stab him before he reloads. Doubly so if that other guy is riding a horse. Then there's the problem of noise, smoke, and confusion. Muskets are terrifyingly loud and make big clouds of thick smoke. After a few shots you either have to move or hope for a breeze because you won't be able to see anything through your own smoke cloud. A bunch of deaf guys all wandering around willy-nilly in smoke with guns and swords is a recipe for chaos. So you wear a big bright uniform and follow a big shiny flag in a tight formation. That way you don't lose your team and accidentally get lost or wander too close to the other team and get stabbed.",
"The muskets of the 1700s were basically spears that could also fire 1 shot every minute or so. If you only had a couple people in your army firing at a time, it would be relatively easy for the enemy to just charge at you and stab you with their spears. So, the solution to this was to have everybody in your unit reload together and then fire all at once, so that there were enough bullets heading downrange at the same time to actually knock down a charge. It didn't help that they weren't really accurate enough to make aiming at a specific enemy soldier worthwhile, you'd always miss. So instead, you just pointed it generally at the direction of the enemy and hoped for the best, so again, more bullets at once was important. Finally, the effective range of everything except big cannons was only around a hundred yards, so you couldn't really damage the enemy until you were almost right on top of them, and at that point its important to not get cut off, isolated, surrounded, etc. A single soldier would go down quickly to massed-fire, but an army could protect itself by returning fire and keeping the enemy at arms length.",
"To add, A barrel of a gun is a tube, you know this. The drilling process is called boring, and the result is the hole called the bore. The barrel exists to direct the gasses pushing the projectile in one direction long enough to get it up to speed. Getting to my point, this alone describes what's called a smooth bore barrel. The problem is a projectile is inherently unstable, it's being pushed forward, not pulled, and it's just going to bounce down the barrel and will squirrel around as it pushes its way through the air. What you have is a very inaccurate weapon. You could hope to hit a 20\" square at 100 yards, that sounds about the breadth of a man's torso but it's still hard to hit. And if your targets are further out than that, then forget it. The point of a firing line and volleys - the additional point I wanted to make, is to affect a wall of bullets that would stand a greater chance of hitting the opposing army's line, who are themselves trying to do the same thing - and this is in addition to what others have said, about managing and maneuvering your troops, and all the other effects of war and combat. You can't just thin out your line, making your troops hard to hit, without also losing your ability to fend off the approaching enemy in formation, who is an encroaching wall of bullets to contend with. Rifles get their name because the barrel of the weapon is itself \"rifled\". That is to say, you carve helical grooves into the bore, and what this will do is catch the projectile as it's being shot out, and impart spin. That spin imparts gyroscopic stability. It's the difference between a knuckle-ball and a fast-ball throw in baseball. The problem with muzzle loaded rifles is that they load slower, slow enough to make a damning difference. A musket could be fired 3x a minute. Snipers existed then, and used rifles, and they were hated for it. Because how dare you shoot these gentlemen who are merely trying to maneuver their troops. It was considered uncouth.",
"More fundamentally, the reason why you don't see \"major battles\" where one side doesn't fire en masse is because, fundamentally, that isn't a major battle. A bunch of snipers behind trees isn't an army, and (generally speaking) can't stop an army from doing army stuff, like occupying positions or seizing supplies (such guerrilla tactics can certainly make an army's job a whole lot harder and contribute to the failure of an army's campaign, but normally they can't by themselves defeat and destroy an army). The best way to stop an army is to organize your own bigger and/or better army, and defeat them in battle. Commanding an army is an extremely difficult coordination problem. You can't just tell each soldier to get out there and give it their best shot. Soldiers working together in coordinated groups are \\*vastly\\* more effective than individuals just fighting however they see fit. As a commander, you need to be able to command large crowds of people all at the same time, to all work together in coordinated masses to execute maneuvers and perform combat actions (e.g. advance, withdraw, attack, change formation, charge, etc.). So you arrange your soldiers together in units, train them very thoroughly to perform coordinated actions, put officers in charge of them to keep them organized, and have a signal system so that you can tell the officers what to do. Before the advent of radio communication and extremely effective infantry firearms in the 20th century, that looked like big blocks of troops, all trained to maneuver and fire according to strict drills, and directed by signals like bugle calls, flags, and drum-and-fife music. The best way to maximize the deadliness of your army's musket fire was to train them to march and fire in ranks. If the enemy army isn't trained to do likewise, they will lose. That's all there is to it. Troops taking cover and popping off shots at will cannot do enough damage to trained infantry masses to make any serious difference. So major battles -- which by definition are two armies fighting one another -- are going to look like big blocks of troops lining up and blasting at each other in coordinated barrages. Because the army that can do that better will beat the army that does it worse."
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gj1wq7 | what's the difference between diesel fuel and regular gasoline? Do the engines function differently? Is diesel more powerful? | Engineering | explainlikeimfive | {
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"Diesel is more dense and has a higher energy density than gasoline does. So diesel produces more energy for the engines it’s used in. It also is a lot harder to light on fire. Gas engines use spark plugs to ignite the fuel-air mixture. The plug produces a spark, which causes the gas to explode, forcing the piston back down. Diesels do it through brute force by compressing the diesel-air mixture until it gets so hot that it explodes. You can’t run diesel through a gas engine because it won’t burn - the spark plugs don’t produce enough heat to light it. You could run gas through a diesel, but it reaaaallly won’t like it.",
"Crude oil is distilled into different products. It is heated various temperatures and the vapor is collected and allowed to cool. Gasoline is what you get at around 150 C, diesel at around 300 C. Diesel and gasoline engines function in largely the same way, but there are differences. Diesel will reliably ignite under compression without the need for a spark, so diesel engines don't use spark plugs. Per volume, diesel has about a 15% higher energy density than gasoline."
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gj7lf4 | How do scissors "know" when you're using the wrong hand to operate them? | Is it unequal pressure within the handle or something along those lines? Was curious when I was cutting sausages. Thanks! | Engineering | explainlikeimfive | {
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"You slightly push with your thumb and pull with your index, this normally gets the blades closer together, however if you use them with the other hand the blades will get pushed apart and won’t cut as well"
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gjcyrx | How does a fridge make things cold? | I have had this question in my head for the longest time, and I just can’t wrap my mind around it. How does a fridge make what is inside it cold? I am familiar already with the concept of adding heat by adding energy, but the other way around just doesn’t seem to work... Do refrigerators just subtract (?) energy from within themselves? Do they just rely on wind and cold air? | Engineering | explainlikeimfive | {
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"It was already known that compressing a gas makes it hot. Someone got the neat idea that, well, what if we let it cool down, then uncompress it again? It'll be really cold! That's basically how refrigerator and air conditioning compressors work.",
"You take refrigerant in the form of a gas, compress it, condense it into liquid form, send it through an expansion valve where pressure and temperature drop ( URL_0 ), blow air over a bunch of coils full of the cold refrigerant. Do this in a cycle, and now your fridge is cold. Energy is added to the cycle by the compressor and cooling coils, and rejected in the condenser. The reason why the cycle needs a compressor is the 2nd law of thermodynamics. Expressed by Clausius as \"Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time\"",
"1. A refrigerant gas is compressed. Compressing a gas heats it up. The refridgerant is now hotter than the surrounding air outside the fridge. 2. The hot refreidgerent is pumped through a coil on the back of the fridge and is cooled down by the surrounding air until it reaches close to room temperature. 3. The room temperature gas is now decompressed. Expanding it will cool it down, like how a deoderant can will spray cold gas/liquid even if its at room temperature. Now the gas is cold. 4. The cold gas will get pumped through the fridge and the warmer air in the fridge will heat up the gas. However the gas is still going to be cooler than room temperature so we need to repeat step 1.",
"Refrigeration systems (just like air conditioning units) exploiting thermodynamic properties of the phase changes between liquid and gas of the refrigerant used, in order to pump heat from the cold side (inside the fridge) and discard it to the hot side (outside fridge). (When a gas expands, it draws heat from the surroundings. When a gas is compressed, it releases energy as heat)."
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gjeaxn | Why are guillotine blades angular rather than rectangular shaped? | Guillotines chop heads. If you look at the guillotine blade, it is angled, with one side of the blade much higher than the other end. I would think the guillotine blade would be shaped more rectangular. | Engineering | explainlikeimfive | {
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"A straight blade such as a rectangular shape is designed for chopping, while an angled blade is designed for slicing. The human neck is not hard to cut through, but there are pieces that are tougher than others (the spine for example). Imagining a tomato, the skin is tougher to slice than the flesh. Imagine taking your knife, flat against the skin and pushing down. It would squash the tomato, not cut it. Now imagine the same scenario, but you angle the knife in the direction of the resistance, suddenly the skin and flesh of the fruit becomes much easier to cut in one clean slice. A guillotine is the exact same concept. It's a slice, not a chop.",
"So that it actually slices as it drops. If it was rectangular, the cut would be a lot more brutal and gory.",
"I feel like this would be a pressure = force/area thing. So if the full blade makes connection at once, the force is evenly spread over a larger area. Kinda like how if push on a peice of wood with your thumb nothing happens. But apply the same force with a small area (like a pin) you can push into the wood. So by having an angle, you have the same force on a smaller area at the start, so a much higher pressure.",
"I’m not a historian, and you might want to ask this question at r/askahistorian, but I some blades were flat at the bottom, and if I’m not mistaken some were triangular, so the point was in the middle. The engineers that design this sort of thing figured out pretty quick that the angled blade works best. Take for example a great loaf of bread if you took a sharp flat blade and brought it down on the bread would it cut? Yeah, maybe but there is going to be a whole lot of smooshing going on too... not good... the point in the center blade would direct the force out to both sides of the retaining block which holds the head in place, allowing it to slice but also smoosh, there are stories about the blade not going all the thru and the executioner having to jump on top of the blade to get it thru... ( I think I heard that on hardcore history) The angled blade was perfect, as it dropped it pushed the neck to one side of the retaining block and allowed the blade to cut smaller amount and still get the job done.... I think I’m close, others much smarter and more awake than I would probably have greater insight ...",
"i can explain this like you are a five year old. Take a butter knife and take a tomato and chop straight down into it. It'll squash it, juices and seeds will leak everywhere. But hold the knife on an angle and slide down into the tomato and you'll get clean cut. Concentrating the pressuring into one point of the blade on an angle is better than trying to spread the same amount of pressure across the whole blade surface.",
"When you chop vegetables or fruits, do you knife those things parallel to the chopping board? Or do you tilt your end a bit higher?",
"you want more slice less choppy chop. think about cutting a tomatoe. if you just bring the knife down on it, even if its super sharp, it will bruise and squish the tomato. if you cut in a slicing motion, that tomatoe slice is just fine and ready for a sandwhich. just like a guillotine that is angled is ready for a revolution."
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