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652sfe | Before bomb disposal robots, how did technicians train to actually defuse a bomb? | Surely it wasn't as simple as cutting a certain colored wire. We all see it in movies. Before it was as simple as sending in a robot to blow it up, how did they train? How simple was it? | Engineering | explainlikeimfive | {
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"Bombs at their core are essentially the same, a power source, a source for detonation, an explosive and a casing. The basic goal of an EOD tech is to remove the bombs ability to detonate and to do that, you usually cut the wire linking the detonation method and the explosive. A tech would carefully open the case and examine the bomb for its basic parts and use their training of various build methods the military and law enforcement has gleaned through disassembling and assembling either failed to explode bombs or putting the pieces back together of successful bombs to determine build methods.",
"Well, to give you an idea, even now the EOD pipeline is about 54 weeks of training. Navy EOD goes to further schooling, dive school, jump school."
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6557zx | when you flush a toilet, how does the water get sucked? Is it by a vacuum or the just the additional water that is added | I'm asking in regards to conventional toilets not airplanes | Engineering | explainlikeimfive | {
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"Conventional toilets work on water being added from above. The force of the water rushing in and then pouring over the top of the S-bend sucks the contents of the bowl out. When the flush cycle completes, the toilet trickle-fills the bowl a bit more in order to wash the sides of the bowl and fill the S-bend to the point that an air seal is created to keep the smell out. Conventional toilets do **not** work on siphons. If this were the case, when one toilet in the house flushed, all of them would, because they are all connected to a common sewer stack. In reality, the stack is vented to the outside above the rooftops to allow pressure to equalize, preventing one flush from causing a cascade. **TL;DR:** Toilets flush from the action of the water surging into the bowl and over the S-bend. No vacuum, suction, or siphon is involved, as sewer systems are not designed for that. **Edit: I've been corrected by people more knowledgable in plumbing. There is a siphon involved, but only through the S-bend.**",
"Depends on the toilet. Nearly all flush toilets have piping that goes like a un shape, with the bowl at the top of the u and the drain out the bottom of the n. The bottom of the u is filled with water, the top of the n and the drain is air. In the 'washdown' design it is just the force of the water falling down from the tank that flushes. It makes the water level rise in the u, go over the top of the n, and flow away. The water level won't change much when you flush. This design is the norm in Europe. In the 'siphon' design part of the pipe is narrowed and the water rushes in. This makes the water level in the bowl rise rapidly while the water moves into the pipe more slowly and totally fills it. The water level in the pipe goes round the top of the n and this starts a siphon, pulling the water round and out of the bowl. Only once the water in the bowl drops to the bottom of the U can air get in and break the siphon. This design is the norm in North America. And yes, it's a siphon. It doesn't affect the rest of the toilets because the siphoning water flow is only in the pipework for that toilet, with air further down the drains. There are some other designs, but those are the main ones. EDIT: To be clear. A difference is that in the washdown design, the top of the un bend is always an air space even during the flush. In the siphonic design it fills completely with water when it flushes."
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657wo6 | How do you come to a full stop in a stick shift vehicle? | I hear from people "Don't depress the clutch when you are breaking. Just depress to change gears." And "just break when you are coming to a stop". Okay so I depress the clutch and downshift, and go to first, or neutral, and then I slowly take my left foot of the clutch while my right foot is already braking. However I thought because I'm at a stop I can't take my foot off the clutch because the minute I do it'll stall, since you can't use gas on a full stop? I'm so confused [I'd post this in cars but they don't allow me because I'm too new] | Engineering | explainlikeimfive | {
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"Brake as normal. Leave the gearstick alone. When the engine is about to stall, depress the clutch. If you don't want to keep your foot on the clutch, you can choose to put the car in neutral and then release it. An alternative technique is to shift down through each gear as you're braking. That was used more with older cars that didn't have such good brakes, shifting down meant the engine could help slow the car. With modern cars most drivers don't bother. EDIT: And in fact organisations that teach driving, for both new learners and 'advanced' driver training, favour the 'block shifting' method where you brake down to your new speed then change into the gear for that speed. For example doing 70 mph in 6th gear, brake to 30 mph, then select 4th gear.",
"The wear you put on a vehicle by holding the clutch down completely is negligible. If it is a long stop, put it in neutral, otherwise just make sure you are not halfway on the clutch.",
"You just put the car in neutral and brake like normal. The car will only stall if it's in gear and you release the clutch. If it's not in gear nothing will happen when you release it.",
"The car must be in neutral if you want to release the clutch and stay still. This is a good plan, as just holding in the clutch can cause throwout bearing wear. To start moving again, you depress the clutch, put the car in gear, and move the right foot from the brake to the gas."
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658q49 | The difference and correlation between horsepower, torque, acceleration, and top speed in a vehicle. | Engineering | explainlikeimfive | {
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"Horsepower is a unit of Power, which is a physics term. Its equivalent in Metric is the Watt. Power means force multiplied by speed. (Something that is *powerful* can move something very heavy, very fast.) Torque is similar to Power, except it means it's spinning, and doesn't matter how quickly the energy is being transferred. Acceleration means how quickly something can change speed. (Does it take 5 seconds to go from 0 to 10mph? 2 seconds? 1 second?) Acceleration *feels* like how much you get pushed into your seat. High acceleration means you can reach a high speed in a short amount of time. The top speed doesn't really depend on any one particular factor: it's often a combination of many things. Combustion engines can only go as fast as the pistons allow before they break. Cars sometimes can only go as fast as their aerodynamics permit them, or else they would lose grip and flip over. Electric cars can only go as fast as the amperage of the batteries permit.",
"Horsepower is directly proportional to torque. An engine that makes a constant amount of torque over its entire RPM range will produce twice as much horsepower at 4000 RPMs as it will at 2000 RPMs. This is why low-revving engines produce lots of torque with little horsepower and why high-revving engines produce a lot of horsepower with little torque. Torque, by itself, is somewhat meaningless because transmission gearing allows the engine to trade rotation speed for more torque. If you have a 2:1 gearing, an engine rotating at 4000 RPM will rotate a driveshaft at 2000 RPM. The engine will effectively put out twice the torque but at half the speed. Similarly, a 100:1 ratio will produce 100x as much torque but only at 1/100 the speed. In either case, the horsepower is the same. This is why dyno tests are done in the gear where the ratio is as close to 1:1 as possible, so as to measure the engine's torque output most accurately. Acceleration is the direct result of horsepower applied to the mass of the car. The more horsepower, the faster the acceleration. The more massive the car, the slower the acceleration. Practically, acceleration will be limited by the grip available to the tires as well as air resistance and whatnot. Top speed is the point at which the produced horsepower is insufficient to accelerate the vehicle any faster, most significantly against the increasing resistance produced by the vehicle moving faster through the air. To sum things up, all four elements are directly proportional. All other things being equal, an increase in torque will mean an increase in horsepower, acceleration, and top speed (limited, of course, by grip and aerodynamic drag)."
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659za9 | How did people cut their nails in ancient/medieval times when there were no nail-cutters? | How were hairs cut without scissors in stone age or till the time blades/scissors were invented? Were haircuts costly before there were scissors etc? Was a good haircut measure of attractiveness in stone age? | Engineering | explainlikeimfive | {
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"Assuming by caveman you mean early humans (homo sapiens sapiens), the answer is stone tools. Humans have had stone tools since before we became 'humans' - i.e. since about a million years ago (and some are argued to be over 3million years old). Stone tools were the standard item for cutting and trimming - including nails and hair. Despite popular imagination of them as just rocks they were highly crafted and sophisticated tools, carefully shaped for purpose. We can see this behaviour described in the historical record when different cultures meet. People did also of course wear/break nails through daily use and tie their hair back, both of which happen today. Some cultures used animal fat in their hair as a kind of grease to hold it back or make it stick up and make them look bigger. Medieval people used scissors for hair but the scissors that existed were too big for nails. They did it the same way Romans did - with small knives (think paring knives rather than daggers). Source: my degree in archaeology and history.",
"Cavemen didn't cut their hair as hair provided extra warmth. As for nails they were used as tools so they were worn down naturally, if they became too long they probably chewed them or filed them with rocks. In medieval times they had scissors that they used to cut their nails.",
"I have not once cut my 2.5 year old son's nails. He apparently wears them down naturally, or that is what his pediatrician says. So weird. I am inclined to believe the other poster who said that cavemen wore them down working with tools.",
"I'm so confused why people would think you'd need tools or teeth to cut nails here. My entire life I've been able to cut my nails using my finger nails like it's the easiest thing in the world. I can't imagine why you would bite them unless it's somehow more pleasant, but I think that's bad for your teeth so I've never been tempted.",
"If you think about it, the lifestyle of the primitive humans allowed them to succesfully pass on their genes and live in harmony with the world for hundreds of thousands of years. Here we are completely fucking everything up in a tenth of the time, wondering \"were our ancestors capable of basic hygienic maintenance?\". Yet we don't ever ask \"how did they live in such a sustainable way in complete harmony with every other species on earth for so long?\" *i should not have said \"complete harmony with every other species\". What I really meant was that we weren't causing extinction at a massively increasing rate",
"I don't use nail-cutters or tools to cut my nails. You can bite off the ones on your fingers and carefully tear the ones on your toes. It's really not hard and it means I don't have to try and remember where I put the nail-cutters every time I want them trimmed EDIT: Why the downvotes? I gave an example of a perfectly simple way to trim your nails without nail-cutters. I'm not saying that's necessarily what they did or if they even them trimmed at all. I'm saying that it's very easy to cut your nails without tools...",
"They could probably just chew down the nail, or break it and tear off the excess. > How were hairs cut without scissors in stone age Sharp edges have always existed, even if we assume that cavemen cant produce one (go break a rock) you could still use animal claws or something. You can still cut hair with a blade.",
"Lindow man (Pete Marsh) was from around 2 BC to 119 AD and had manicured nails according to investigations. I believe that the microscope revealed that his nails had been cut with an instrument which may have been scissor-like. \"In life, Lindow Man would have measured between 5'6\" and 5'8\" (1.68 and 1.73 m) tall and weighed about 132 pounds (60 kg). It was possible to ascertain that his age at death was around the mid-20s. The body retains a trimmed beard, moustache, and sideburns of brown hair, as well as healthy teeth with no visible cavities, and manicured fingernails, indicating he did little heavy or rough work. \" URL_0"
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65abgg | How do they build tunnels that go underneath rivers? | I go through the holland tunnel or the lincoln tunnel at least once a week. So, at least once a week I reflect on a) How awful it would be if the tunnel broke and b) How in the world did it get built?? So..help? | Engineering | explainlikeimfive | {
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"There are [tunnel-boring machines]( URL_0 ), which are essentially huge metal walls the shape of the tunnel that slowly chew into the dirt/rock ahead of them, throwing it behind the wall. From there, conveyor belts or carts move the dirt/rock back to the surface, where they dump it somewhere. Right behind the boring machine, workers line the tunnel with concrete and support structures to seal and strengthen it. The boring goes pretty slowly, so the fresh tunnel gets concrete pretty much as soon as it is excavated. Engineers design the tunnel so the finished structure (after concrete application) doesn't collapse.",
"They don't go \"underwater\" they dig through the ground hundreds of feet below the bottom of the river",
"Mining engineer here. If there is a river of some watery grounds you need to go deeper and use water pumps (a lot of pumps, and people still work in knee high water) to get rid of water while drilling with tunnel boring machine or blasting with explosions . While you go further you cover the inside of a tunnel with supports (concrete or premade parts of tube). For example if you compare Moscow and St.Petersburg metro stations most of the St.Petersburg stations are located 3-4 times deeper and are mostly closed type stations (the train and the station are separated by a wall leaving only space for doors) due to watery grounds."
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65c1c5 | Why on boats are the propellors at the back yet on planes they are on the front? | Engineering | explainlikeimfive | {
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"Some issues: 1. Turbulence. When the medium through which your propeller moves is turbulent, you get wildly varying power levels. So you want to avoid feeding very turbulent air/water into your propeller. On a plane, the airframe itself generates a good deal of turbulence. On a boat, the hull alone generally won't impart enough energy to the water to create significant turbulence because water is much more dense than air. 2. Steerage. If you place the engine at the front, the resistance of the medium around your craft will tend to cause the craft to align along the direction of travel. If you place the engine at the back, the resistance of the medium will tend to deflect the craft from the direction of travel. With a plane, you need some pretty significant control surfaces to overcome this effect because air doesn't pose much of an obstacle to yawing uncontrollably. On a boat, it's nearly impossible to deflect its course in this manner because you'd need to displace enormous amounts of water to move sideways. 3. Boat propellers only work underwater. Even with the denser medium, it still makes sense to put the propeller on the front of the boat - the water just makes it less impractical to put the propeller on the back, it doesn't make it *better*. What makes it better is that the front of your boat leaves the water in situations where you need powered propulsion (climbing up a wave) while the back of your boat leaves the water in situations where you don't (climbing back down the wave). In the first case, gravity is opposing your direction of travel so a loss of propulsion means you fall back. In the latter case, gravity is assisting your direction of travel so a loss of propulsion means you keep moving forward anyways.",
"One reason on ships, and small boats with fixed engines, is that the water from the propellor flows directly onto the rudder. That means that the steering effect is greater as the concentrated water stream from the prop is deflected by the rudder blade to turn the boat. Aeroplanes are to a large part steered by banking the wings to change the direction of the \"lift\".",
"The propeller hits the ground when the plane takes off. But you want that to happen with a boat.",
"Well I'm no expert, but when a boat goes on plane you wouldn't have much prop if none at all in the water. Plus you don't want to much weight on the front of the boat either. Trolling motors go almost exclusively on the front of the boat because why not? They can't get on plane. Also, if the motor was on the front you wouldn't be able to beach your boat. Source: I'm a Floridian. Edit: Another reason popped in my head."
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65eah2 | How can a microwave be made of metal, but metal can't be inside a microwave. | Engineering | explainlikeimfive | {
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"Metal reflects microwaves. The boundaries of the oven contain the microwaves, allowing them to bounce around inside until they hit food. Metal can be inside the microwave as well, just you have to be careful with it, as it can build up an electric potential and eventually arc, creating sparks. You can often find metal grills for the microwave or microwaveable products that use metal-lined lids, but these are designed to mitigate the chance of sparks by using wide gaps and flat surfaces."
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65hcmf | If cranes are needed to build skyscrapers, who builds the cranes? | Engineering | explainlikeimfive | {
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"If you ask how the crane get higher and higher the answer is that is that you have a larger frame that is outside the mast that you can use to lift the crane with hydraulic jacks and insert another mast segment See URL_0 how it is done on a real crane or URL_1 for a more detailed animation"
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65jdxt | How did coating a weapon like a dagger in poison work? wouldn't the poison fall off if the weapon is too fast, like an arrow? | Engineering | explainlikeimfive | {
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"You dip the weapon in and dry the poison against the metal in layers, glazing it. The effect is somewhat like when you have fruit juice that's dried to a laminate counter. Somewhat sticky and easily dissolved or removed.",
"Typically I believe weapons that were coated in actual venom or poison were allowed to air dry. However its a lot easier and cheaper to smear shit on your arrows and that bacteria is obviously bad news if it finds a new home in an open wound Edit: apparently obligatory *I'm not a fucking expert and most of my knowledge comes from historical fiction of varying degrees of accuracy* Edit: removal of distinction of poison vs venom, it was irrelevant here. My apologies",
"Since you seem to be focused on the physics of it, just think about how dirty cars get - and stay - even though they regularly reach high speeds. Dirt, mud, bugs, bird poop, and even exhaust particles get on there and require specific conditions to be removed. Even driving quickly through rain doesn't do much to clean a car. Matter tends to get stuck to matter (with the exception of repellant substances, e.g. oil vs water), including at the microscopic level.",
"The San people of southern Africa are likely some of the earliest users of poisoned arrows, IIRC there have been arrowheads found with poison residues on them from 50,000 years ago. They use a number of poisonous plants in their recipes, but the most effective toxin comes [from the larva of a small beetle]( URL_0 ). The beetle larva is harmless if eaten, unless you have a cut in your mouth. You can imagine what happened to the poor guy who first discovered this. The way that the San (who still hunt with poisoned arrows today) get the poison to stick is that their recipe always includes some resin from the acacia tree. This acacia gum is a very effective glue when it dries, so they basically first make poisoned glue and then apply it to the arrowheads.",
"Some states still allow poisoned arrows for archery hunting. I know Mississippi is one state that does. The poison is released from a little pod placed on the arrow shaft an inch or so behind the broadhead. The pod itself is a little rubber tube that fits over the shaft. The poison in powder form is put inside the rubber pod (think almost condom like). When the arrow penetrates the animal the pod rolls inside out depositing the poison into the wound. The poison used is the fast working skeletal paralyzing chemical [suxamethonium chloride]( URL_0 ), also known as suxamethonium or succinylcholine sold as Anectine®. It's used by doctors in surgery to paralyze skeletal muscles. Enzymes in the blood quickly break down the chemical and the meat can be eaten.",
"A lot of toxic substances can stay toxic even when they dry out. Then once the weapon pierces skin and the toxin mixes with blood, they dissolve back in and enter the victim's system directly through the open wound. To make it easier in the case of an arrow, you might put dings and dents in the arrowhead. Think of the surface of a golf ball; those can go flying at speeds much greater than an arrow, but the dimples still hold dried dirt and grass stains.",
"It is . It is made by mixing kwuarm and dragon scale dust in a vial of water. Then you just apply it to your weapon of choice. It only comes off with a cleaning cloth.",
"You guys are getting way too complicated with this. They would just dip the tip in poison, let it dry, take them to battle and then shoot. They would prepare them ahead of time.",
"You wouldn't be asking this question from a computer assembled from the prison's computer disassembling program that you occasionally hide in a roof panel, would you?",
"Years ago I saw an excellent demonstration of this in a documentary about African tribesmen. They would prepare a gord shell full of what looked like cotton or other absorbent plant fiber and they would milk venomous snakes into the absorbent. The tribesmen would carry this corked with them to keep the venom from drying and when it was time to shoot would simply dip the arrow tip into the venom. Using sharpened wood arrows the wood was absorbent enough to hold a fair amount of venom for their prey.",
"> Edit2: Can you guys stop asking personal questions like if I'm a murderer or not? I wasn't aware this was a personal question. Hmm. My suspicions grow.",
"In table-top role-playing games, like Dungeons & Dragons, this will come up for rogue type classes. For poison that going to be delivered by a weapon will need to be fairly thick and sticky like tar or sap. If the poison is to be ingested liquid would be best. Inhaled poison would need to be a powder.",
"Reminds me of that meme of a show where the guy says his blade is dipped on poison then he licks it",
"To jump onto OP's question: what about older (medieval) stories where Kings/Rulers were given poisoned crowns or cloaks? Was that an exaggeration, or did it actually happen? How was it done and, more importantly, how did it poison the victim (i.e. was it just so potent that it overwhelmed the target?)?",
"Not a real world example but it seems pretty sound, in the night angel trilogy there's a part where it describes a character taking a knife with holes in the tip of the blade, stuffing cotton into the holes, and soaking the holes in poison. I believe the tip of the sheath held the poison so it could be reapplied in the run. Anyway, idea was as he stabbed someone the poison(venom) soaked cotton would pass through the wound and get in the blood stream. Again, not a real world example, but it makes sense and I can't think of why it wouldn't work."
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65k1qa | Why the MOAB (Massive Ordnance Air Blast) bomb is orange? | Engineering | explainlikeimfive | {
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"Orange is the color for trial and evaluation weapons. Most pictures, such as the main one on Wikipedia are of test bombs. The adopted, production MOABs are green with yellow bands/markings, which is the standard color coding for high explosive ordnance. Example of a [production MOAB.]( URL_1 ) Ordnance follow established color coding charts as much as possible to help identify their type easily. Technically the label of \"MOAB\" on the side should be yellow not white according to the chart, but whoever approved it may have figured white was easier to read and the munition was very recognizable anyway. Here is a page with a chart that helps give you [an idea of what's what for US munitions.]( URL_0 ) These color conventions are occasionally updated, and different countries use different color charts, so don't apply this universally.",
"The orange one you've seen is a test unit. Airborne test weapons are often brightly painted so that they can be spotted by cameras for better evaluation of the test. You don't want to do a multi-million-dollar test and then find out that the camera operator couldn't see the device and was pointing the wrong way!"
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65kgsz | Why Intel (and AMD) puts Integrated GPUs on HighEnd CPUs? If you need an I7 why wouldn't you buy a GPU? | Engineering | explainlikeimfive | {
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"There are plenty of things that you'd use an i7 for that would not in any way need significant graphics processing power that would require a separate GPU. Also, the GPUs are built into the CPUs for ease of use as well, that you don't *need* to buy a separate (often expensive) GPU to use the system. GPUs have very specialized and limited uses. Primarily gaming, and some complex math operations that work better on a dedicated GPU, outside of that, the need for a separate GPU is almost nil"
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65m752 | What's the point of stove range hoods that don't vent outside? | Engineering | explainlikeimfive | {
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"They contain a filter that removes the worst of the smoke so you don't end up getting a stained ceiling when you cook. Also, they use a fan that slightly spreads out the hot air they collect, reducing the chance of scorching your cabinets."
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65ofpx | Why are bumpers in cars made from plastic? | Engineering | explainlikeimfive | {
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"The plastic portion you can see is actually a bumper cover. Underneath the plastic there is a strong steel bumper bolted to the frame of the car. The bumper cover is meant to be attractive, suitable for minor collisions and easy to replace. Plastic is a great material for all three of these requirements. Edit: Here are photos of the bumper behind the plastic cover on a Chevrolet Cobalt. The first image shows the bumper with impact absorbing foam still attached. URL_0",
"Couple reasons, first and foremost, plastic is cheap. The bumpers of the car are the most likely place you'll see damage in a small accident, so they're cheaper and easier to replace. Second, when you're in a crash (kind of counterintuitively) it's actually safer for the car to have what's called a 'crumple effect'. If you use a less rigid material, it'll give way and the kinetic energy from the impact will all be absorbed by it and not transferred to you, the driver."
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65pltd | How do disc brakes work? | Why do they function better than drum? | Engineering | explainlikeimfive | {
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"Not an engineer, but to break pads get push together with a viceclamp (lack of a better term) and they squeeze the rotating disk that turns your tire. Creating a bunch of friction until the car vehicle comes to a stop."
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65q3ud | How does an autonomous vehicle decide who dies in an unavoidable crash? | Say I'm in an autonomous vehicle and there is a situation where the car has no evasive maneuvers available that won't end up in a death. Say the car is about to hit and kill a pedestrian and the only way to avoid it would mean to drive the car off a cliff and likely kill me. What would an autonomous car choose in this situation? | Engineering | explainlikeimfive | {
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"They aren't that complex. They just try to stop the vehicle and avoid collision as best they can, they don't make assessments of likelihood of death. Once they can it will likely be legislated to judge in a certain manner.",
"The car's programming is very simple. 1. Object in path. 2. Can I stop in time? Yes = stop. 3. If no to 2 = Can i safely swerve to avoid obstacle? Yes = swerve. 4. If no to 3 then attempt to stop and sound horn. Or something like that. Basically the car will never take a positive action that is unsafe. It doesn't know, care, or matter to the car whether the \"obstruction\" that starts this whole thing is a bag of garbage, a just reliest from jail on a technicaliy child rapist, or Jesus Christ returned to earth. If it can stop, it will. If it can swerve safely it will. If no to both, it hits.",
"So, I love your title. however your followup took something away. From what I understand, and I am pretty up to date. If the crash in not avoidable, it will simply attempt to stop. So say 3 people randomly jump to the left, right and center of its path, it wont swerve the middle and hit the left, it will simply conclude no alt path, and break. So, whoever was in the direct path of it would still get hit. Hope that helps. (btw, we are not up to iRobots yet, so these cars predict and calculate travel, not life expectancy in a crash ,not yet anyway"
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65sjgm | Why haven't we invented artificial gills yet? It seems like breathing underwater would be a huge breakthrough. | Engineering | explainlikeimfive | {
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"you can pull oxygen out of water, but simple fact is that there isnt that much oxygen there to pull, and its not super efficient, so its the least efficient method vs just carrying your own air, pumping it from the surface, or recycling it."
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661af2 | why dont car manufactures make their cars out of stainless steel? | Rust seems to be a problem with alot of cars, so wouldnt making cars out of stainless steel solve a big problem without changing much? | Engineering | explainlikeimfive | {
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"Because rust isn't a big deal on cars anymore. Most people don't drive cars for 30-40 years anymore. Stainless steel is also more expensive than other steels without bringing any specific strength other than anti-rust (which may not actually be a big deal anyway)",
"I'm going to be that guy and point out that car manufacturers don't particularly want to sell cars that last long periods of time. The sooner the thing wears out and winds up in the junkyard, the sooner they can sell a replacement.",
"The delorean was made of stainless steel but despite back to the future, the car company flopped. Sometimes when ideas don't work out, they are not tried again.",
"The DeLorean (as featured in Back to the future movies) had a stainless steel body. It was not a commercial success. Generally the extra cost of building a car that way do not justify the benefits. Modern cars don't have enough problem with rust to make it worthwhile."
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662lkv | How are underground subways in big cities designed? Do they actually dig and drill to open up tunnels for the subway or was it already prepped when the city we designed years ago? As old as some cities are I find it amazing this would have been thought out way back when. | Engineering | explainlikeimfive | {
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"London Underground is a good one to research. In some cases the tunnels were dug along the routes of existing roads, and they created a big trench, but the railway in the bottom and covered it over, then put the road back on top (\"cut and cover\"). In other cases, like where the railway had to go under big buildings, they mined it, in the same way that some coal mines are built, by digging a tunnel and reinforcing it as you go.",
"I don't think there has ever been a major city where the city planners were foresighted enough to plan for mass transit before they built the city, so *all* major subway lines have been built after the city they service was already established. Pretty crazy. In some instances they're built just below street level, which, yea, is a massive undertaking, but modern cities have had to be rebuilt on that level anyway due to the foundation requirements of a large modern buildings. Depending on the substrate, they can be bored under existing construction, though obviously you have to be careful in that case not to undermine the structures above.",
"There's different ways. Some subways are built by tunnelling through the earth beneath the city. Some subways are built by excavating the line (digging a huge trench) and then building roads and buildings on top. Most subways are a combination of both methods.",
"Yes, they actually dig and drill to open up tunnels for the subway. One of the biggest construction projects in Britain at the moment is \"Crossrail\", a railway that includes about 22 km (14 miles) of tunnel through central London. Construction started in 2009 and the line is due to be completed next year -- that is, it's expected to over take nine years to build it. Several buildings have had to be demolished, including a few famous music venues."
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6651lk | How do weapons shoot accurately when the sights are above the barrel? | Engineering | explainlikeimfive | {
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"Because light is straight and bullets follow an arc (it's where the term ballistics or ballistic flight come from). The [barrel is aimed upwards]( URL_1 ) so it \"tosses\" the bullet up to or through the light path of the scope at one or two distances. The shooter chooses the distances, in advance, when setting aim, then either adjusts his scope for any other distances, or makes an adjustment to the sight picture to vary the range. In the language of shooting, the near distance chosen is the range at which the gun is \"sighted\" \"zeroed\" or \"sighted in\" and the cross hairs mark the intended point of impact. That's why accurately estimating distances have long been a part of the skill set required to be a good shot (so the proper distance adjustment to the sights could be made). On older guns (using slow, heavy bullets that need to arc more at long distances), the [rear sight]( URL_0 ) was designed to rise significantly above the barrel, so the gun's angle would rise pretty considerably.",
"The sights can be adjusted or zeroed for different ranges. This movement in the sight compensates for the difference in elevation between the barrel and sight. The same applies for left and right movement as not everyone shoots the same and there are other factors such as wind for long distance shooting. For example if you shoot at 600m when you are zeroed at 100m you will shoot low. Take a shot at 100m when zeroed at 600m you will shoot high.",
"Weapons are \"zeroed\" to a specific distance. Think of it as like a triangle. Your optic sight path and bullet path meet at the specifically zeroed distance. For a weapon like an M4 that distance is usually 25 meters.",
"The sites are adjusted to point slightly down. Since a bullet drops while it is in flight, there is no one setting where the sites will be accurate at all ranges. The site are set of a particular range, and the shooter must compensate for the others. Also, the sites are about a half inch from the where the bullet leaves the gun. If that is your greatest source of inaccuracy, you are doing pretty good."
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665t17 | Valves in engine | When car manuf. say things like hey look my gt500 has a 32 valve engine, what does that mean? | Engineering | explainlikeimfive | {
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"Engines have intake valves and exhaust valves. The intake valves open as the piston is traveling down during the \"Intake stroke\" to allow air (and fuel in some cases) to enter the combustion chamber, then the valves close. The piston then travels back up and compresses the air (and fuel in some cases) during the \"Compression stroke\". The fuel is added at this point (if it hasn't been already) and it either ignites (diesel) or is ignited by a spark plug (gasoline) and the resulting explosion forces the piston back down during the \"Power stroke\". Finally, the exhaust valves open and the piston travels up to expel the spent combustion byproducts during the \"Exhaust stroke\". This process is repeated thousands of times per minute and produces the rotational force to the transmission or transaxle and moves the vehicle. Someone discovered along the way that more valves is usually better to an extent. Two smaller valves will flow better than one larger valve, and things usually fit better that way as well. So when you hear about a 32-valve engine, it means that each of the eight cylinders has two intake and two exhaust valves. There is a lot more to this, but this is the best simplified answer I could come up with. Also, the four stages of a four stroke engine are sometimes referred to as suck, squeeze, bang, blow."
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668dzi | why is it that technology is so advanced and we still can't use water or other liquids to run cars? | Water running cars | Engineering | explainlikeimfive | {
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"You need energy. Water doesn't have any extra energy just sitting there. You CAN use Hydrogen as a fuel, reacting it with Oxygen to make water releases energy. So if you have water, you need to split it into Hydrogen and Oxygen which, get this, *requires energy*. We can use say, a centralized power plant to provide electricity to split water into Hydrogen and Oxygen, then ship the Hydrogen in tanks to fueling stations, and use a Hydrogen fuel cell to power a vehicle. such vehicles have been in operation for over a decade. (google \"hydrogen fuel cell\"). It was technically possible years ago but a huge project to make Hydrogen fuel stations on every street corner and set up the whole interconnected system to switch to Hydrogen. The thing is, though, if we need to start with electicity, or another source of Hydrogen, you might as well just use electricity to power the car, and you can go and buy as consumer product electric car right now."
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66h7mh | How do companies design their products such that they are very likely to break/malfunction/deteriorate short after warranty ends? | Engineering | explainlikeimfive | {
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"There are a handful of examples where a company builds an expiry date into a product. The companies that do this are assholes that everyone hates and are opening themselves up to massive, massive, government fines and penalties (which include class action lawsuits, etc.). It is actually really hard for companies to \"get away\" with doing much that you would find despicable if you were truly informed of all the facts and issues at play. It happens, don't get me wrong, but its far less common than you think, its far harder for them to get away with it, and its seldom as overtly evil as one might think. However... Every physical object is going to have tradeoffs. Would you like your remote control to weigh twenty pounds but never wear out or need batteries - or would you like it to weigh five ounces and wear out after 10 years of average use? Customers have spoken and they want cheaper, lighter, fancier shit - and they are wiling to pay for it. So really what companies do is design the product so that in average use conditions it lasts a reasonable period of time, and then give consumers a warranty that covers a shorter, but still reasonable, period of time. And then if your toaster, or television, or jeans wear out sooner they replace them with an apology, and if they last longer... good everyone is happy. The real issue though... Seven years ago you went to the store and bought a computer for \"word processing and browsing the internet\", and now \"browsing the internet\" means streaming netflix and you are trying to use a computer capable of opening Word, and reading CNN, to run a home media center. And its not up to the task.",
"This is done through MTBF prediction( Mean Time Between Failure). There are several methods based on field(real data) and some physics ones or simulation with which you can predict when something is going to break/fail. Best is if you have field(real) data based on previous product designs, but if none are existing then you can make accelerated lifetime tests (temperature, humidity, vibration .... anything you can think about) and then based on this how severe were the conditions during the test you can round up/predict in approximately how many hours/cycles you will get to failure. The more data is available the more accurate is the prediction. P.S. This is not used only to design the product to break after the warranty. It is vital to the maintenance of life support systems, airplanes, power plants and etc.",
"Despite all the negative responses here, we don't design products to fail. We design products so that ~98+% will last until at least the end of the warranty period. But we also design them as cheaply as possible, and this often results in one of the parts failing shortly after the warranty period has expired. So if you want a product to last longer, buy the product with the longer warranty."
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66iv50 | Why do large military ships/vessels use nuclear power but same size or larger cruise/cargo ships don't? | Engineering | explainlikeimfive | {
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"Nuclear power is difficult to do safely and the government will allow its own ships to do things private organizations can't. Also nuclear power means a warship can't be starved for fuel which is of strategic importance while cargo ships don't really worry about enemy forces cutting off their supply lines.",
"The military values long endurance (years between refueling) over cost because long endurance improves their mission success. Largo ship and cruise line owners value low cost over endurance. With their longest voyages taking weeks rather than years, nuclear power doesn't buy them anything that they want.",
"The advantage of nuclear power is you don't need to refuel. The drawback is it's expensive because it's heavily regulated for safety. Not worth it for a cargo ship, considering they can cross oceans on one load of fuel anyway. Sometimes worth it for a warship because refuelling could mean either leaving the warzone or meeting up with a vulnerable tanker ship. There have been a few civilian ships with nuclear power. It's good for icebreakers because they need lots of power, a Russian company called Atomflot has about five or six of them in use.",
"Nuclear power is heavily regulated by governments, who in general do not want nuclear reactors in the hands of private companies. Particularly mobile nuclear reactors. The US has one nuclear powered merchant vessel, *The Savannah*, which operated for about ten years. It was more of a proof of concept that a practical cargo ship, and was decommissioned after it proved too expensive to operate.",
"Because a cruise ship doesn't mind having to refuel every time it goes into port. A military vessel doesn't always have that luxury, and not having to constantly refuel simplifies the supply lines for your navy.",
"There was a US flagged Cargo Ship built with a Nuclear reactor in the 60's. The issue with it was not the training or even regulations surround the vessel. The Issue was that it was not allowed into many foreign ports. The ship itself is now a museum. The ship was N/S Savannah. Not being aloud into foreign ports is an issue for military nuclear ships as well with regard to port of calls for liberty. Here is the wiki for the ship and associated museum. URL_0",
"The differences are the Pros/Cons. For a cruise liner, they value a return on investment from their business. A nuclear reactor provides power for many years into the future, but using diesel engines and fuel is cheaper. They recoup their costs and generate greater profit before the end of life of their ship. The US Govt. doesn't generate money with the ship, so ROI isn't of much consequence. The EOL of the ship is 30+ years, and the reduction in refueling times needed (coming to port) is a much greater tactical advantage than saving money in the outset."
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66owsa | What's causing the very high pitched engine noise and bangs usually Rally cars produce? | I come across videos of Rally cars, and played Dirt Rally, and in almost every documentation I see Rally cars have a different, high pitch and powerful sound, accompanied by loud bangs. What's happening? different engines or engine enhancments? | Engineering | explainlikeimfive | {
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"Straight cut gears (used because stronger than the quieter helical cut gears used in most road cars)will whine\" at higher road speeds. A blow off valve or BOV will vent excess turbo boost pressure when the throttle is closed, this generally produces a high pitched \"squeak\" An anti lag system will delay the ignition after the throttle is closed so that the fuel/air mix is still burning when it enters the exhaust manifold so keeps the turbine spinning so full boost can be made sooner when the throttle is opened again. This makes the loud pops and bangs. Also massively shortens turbo life to around 1000km.",
"I've been a gearhead all my life and a huge rally fan (I sadly live in America where it's hard to partake in anything not football or nascar). I worked on Blackhawks in the army and have been around card ALL of my life... That said I still learned a lot from the responses!",
"The high pitched noise is the turbo (basically a vacuum cleaner to suck more air into the motor). The bangs are excess gas/air igniting in the exhaust when they let off the gas, because when you are sucking that much air & gas through the motor, it can't stop following instantly when you lift off the accelerator.",
"No sound deadening, long travel heavy duty suspension, and rough terrain all add up to lots of noises you won't hear from circuit racing cars. Also all the components are much more sturdy to handle the punishment of rallying, which leads to a much more heavy handed driving style."
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66sw3z | how was the transatlantic telegraph line maintained? | Since that wire lay on the ocean floor, and submarines didn't exist then, how was that cable maintained? What would have happened if it broke? How would the have been able to get down there to fix it? Amazing technology at the time, but was provisions were made to properly keep it in smooth working order until better technology came around? Thanks | Engineering | explainlikeimfive | {
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"Similarly to [this video]( URL_0 ), but with appropriately older technology. Effectively, they'll winch it up with some kind of rope, chain, or other line w/ a hook. Then they splice or repair the communications cable(s) as necessary. Cables today are far more complex, dense, and even durable, but this is an extremely regular occurrence around the world, probably on a daily basis. Whales, submarines, seismic events, and other things can damage or destroy these cables. There's a LOT of transoceanic fiber [optic] out there, so it's only a matter of time before something disrupts one or more."
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66t0qy | How does p2p file sharing work exactly? And why aren't "hosts" like PopcornTime illegal? | Engineering | explainlikeimfive | {
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"text": [
"P2P is just using software to find another person who has the thing you want instead of going to a website or server that distributes it. Software for file sharing has never been illegal. The issue is that people are using it to trade copyrighted material, which makes it an illegal activity. Sort of like how hammers aren't illegal, but killing someone with a hammer is."
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66u1qb | Why is it recommended to have an odd/prime number of stators in each stage in a jet engine? | According to several sources in the design of high-efficiency turbomachinery and gas turbines, when designing the blades and rotors, it is common to use an even number of rotors for balancing reasons, and an odd ("preferably prime") number of stators. This "preferably prime" statement is found in different sources. As far as I can tell it is for mechanical vibration reduction and minimizing resonances. Can anyone explain why an odd number, and why prime numbers? | Engineering | explainlikeimfive | {
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"Imagine one rotor blade passing by a sequence of stators. As it passes by each stator there's some change in pressure. That change in pressure will be similar for each stator it passes by. On its own that rotor blade gets some vibration with a frequency equal to the frequency at which it passes by stators. Exactly what that vibration looks like isn't important, just that it exists and is based on the frequency of passing by stators. Now imagine that you have exactly as many rotor blades as you do stators. Every single one of the blades will be at the exact same point in their vibration at the same time. If, for example, the blades are pushed forward when the rotor and stator are aligned then the entire rotor is being pushed forward all at once. Now imagine that you have exactly 1/2 as many rotor blades as there are stators. Once again you have exactly the same problem: every rotor is lining up at the same time. You could do the same with 2/3 as many blades, but now the blades line up in groups. If you have N rotor blades and M stator blades and you reduce the fraction N/M as far as you can to n/m then you'll have n groups of rotor blades that are experiencing the same vibration at the same time. The goal is to make n as large as possible. At best n = N. One way to guarantee that n = N is if N is prime. A less restrictive way of making that that guarantee is to make sure that N and M are coprime (i.e. there is no number greater than 1 that both are divisible by), and a simple way of approximating that for relatively small numbers is to make N odd and M even (or vice versa)."
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66vx02 | Why does the temperature of the water in the shower get significantly hotter or colder when the toilet flushes? And why have we still not overcome this problem technologically? | Engineering | explainlikeimfive | {
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"If you have a small pipe feeding a bathroom (or multiple bathrooms), then when you flush the water the cold water pressure drops. Lets say before you had a mix of 50/50 hot cold, when somebody flushes the toilet you then have a 60/40 mix of hot and cold water, so the shower gets hotter. We have solved the problem. A lot of new showers have a thermostatic mixing valve, when the cold water pressure drops, the shower will allow less hot water. The water pressure will drop, but the temperature will not change much. Also, a lot of new low flow toilets are designed to fill slower than old toilets (since they only use 1.28 gallons you can flush more than once without filling the tank, so you don't need to fill as fast (and by filling slower they are quieter). Also, and easy solution if this is a problem is to slightly close the valve to the toilet supply. You can force it to fill slower, and the shower temp will not change as much."
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66y6mq | Will my solar panel be a backup? | I have solar panels installed on my roof. Whatever is produced I am using and surplus is going back to the grid. In case supply is lost and its a sunny day would I have some power in my house? | Engineering | explainlikeimfive | {
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"text": [
"Probably not. Most grid connected solar systems will automatically shut down if the grid power is lost. This is to prevent danger for anyone who might be working on the lines. Off the grid systems are generally tied to banks and banks of batteries."
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66z4w9 | Why aren't clear gun magazines more common in the military? | Don't you want to see how many bullets you have? | Engineering | explainlikeimfive | {
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"Metal is more durable than whatever plastic you would make the magazine out of. It's stronger and dents instead of cracks. Also you can just have a slit in the side to see the bullets.",
"The plastics in clear gun magazines have several problems, some that come to mind are as follows: The plastics have lower strenght than the stamped sheet metal. The plastic can degrade over time and have limited field service life The plastics are flammable and can burn And At elevated temperature conditions, the plastics tend to deform and fail Plus, they need a totally different manufacturing technique. I have actually observed the stamping of small arms magazines, plastic, transparent magazines require complex injection molding techniques.",
"In the military (at least in the infantry) you are trained to count your rounds as you fire. I did have a couple magpul mags while deployed with the window, but I always depended on my count rather than trying to peer through a small window and try to count the rounds. Plus I had a tracer every 10 rounds."
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674edh | Why does this modern jet have to fly at such and angle to go slowly? (pic below) | URL_0 A Spitfire and a Typhoon, in formation, but why does the juet have to be at such an angle? | Engineering | explainlikeimfive | {
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"The Typhoon is built for speed. This means that the designers have outfitted it with small thin wings. This reduce the aerodynamic drag so it can go faster. However it also reduces lift so it have to go faster to maintain its altitude. If you look at the front of the wings of the Typhoon you notice that it have its slats fully extended. Both slats and flaps are parts of the wings that can extend the surface area and thickness of the wing when extended. This allows the aircraft to have more lift which allows it to go at a slower speed. However that alone is not enough to make it fly level at the speed the picture is taken at. So the pilot have to increase the angle of attack. This will force even more air under the wing to increase the pressure and give more lift. It also change the angle of the engine so the engine also produce some lift. The problem is that if the angle of attack is too great then the air above the wing might separate from the surface of the wing which reduces lift considerably, this is called a stall. In fact on a normal airplane the control surfaces would likely have gotten into a stall just by the slight adjustments by the pilots but the Typhoon have advanced computers and multiple different control methods to prevent this from happening. The Spitfire were a very fast airplane so it should be able to fly at a much more comfortable speed for the Typhoon. I suspect the limiting speed here is the camera airplane which is likely a C-130 which is built for heavy cargo and therefore have huge thick wings which limits its top speed. In addition the camera man is likely laying on the edge of the open cargo door which puts further restrictions on the airspeed. The Typhoon pilot is comfortable with this though as he is still carrying the spare fuel tank which adds extra weight and makes flying at low speeds harder.",
"The top speed of this WW2 aircraft was only 340 mph at 20,000ft. So the Typhoon is struggling to go slow enough, as the other answers say. However, it's actually a [Hawker Hurricane]( URL_0 ), not a Spitfire."
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674tv5 | Why haven't cars gas mileage improved over the years? | My grandfather's first car was purchased in 1948 and got 30-31 mpg. And those cars were made of heavy steel, rather than the light aluminum and composites we see today. Well 60 years later, why hasn't technology improved for cars fuel efficiency? | Engineering | explainlikeimfive | {
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"Judging by sources such as [this]( URL_0 ), I wonder if you/your grandfather might have misremembered the mileage he got out of it. 30 mpg in 1948 sounds implausible. (And if accurate, it certainly wasn't an average car) It seems like most cars of that era got around 15-20 MPG from what I've been able to find.",
"You are not buying new cars it seems. 40 and 50 mpg is common for sedans, and 60 or more is common for hybrids.",
"Gas mileage improved significantly after the oil crisis in 1973 until the mid 1980s. From there, they didn't increase much until 2006, when serious legislation regarding vehicle efficiency were introduced. Cars nowadays have much higher gas economy, but the average mileage of vehicle ownership has been kept low due to the slow propagation of efficient cars and the increase in sales of larger vehicles such as pickup trucks and SUVs.",
"A thing to note is that you should not look at mpg for fule efficiency. The values are correct but it is hard to identify improvement. It is not obvious that a change from 10 to 20 MPG is significantly higher then a change from 20 to 50 MPG. The fule used for a 10,00 mile trip would be 10 MPG = 1000 gallons 20 MPG = 500 gallons 50 MPG = 200 gallons So the first change of 10 MPG result in 500 gallons reduction if fule consumption but the second change of 30 MPG is only a reduction of 300 gallons. You should convert them to Gallons per Mile (or 10,000 or 1000 mile) to ger a value that is easy to understand. Europe and most other parts of the world used litres per 100 km that system is equivalent to Gallons per Mile. If you use that system is the the same difference in number result in the same improvement regardless of the value of the number"
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6765hu | Why do some airplanes leave an exhaust trail but others do not? | Engineering | explainlikeimfive | {
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"text": [
"It isn't exhaust. It is disturbed air that essentially creates clouds from the turbulence. And it isn't the type of plane, it is the elevation and air conditions at those elevations on that particular day.",
"If you're talking about [contrails]( URL_0 ), those are not from exhaust. Or at least, not strictly exhaust. Contrails form when conditions are right, involving humidity, temperature, and air pressure. Small particulates from the exhaust create [nucleation sites]( URL_1 ) for ice crystals to form. Nucleation is kind of its own ELI5, but the short version is that ice can't form unless there's a place to start from. Once a little bit of ice starts, the rest of the water can stick to that to make the clump bigger, but generally something has to be there to start it. When conditions are just right, the water vapor in the air kind of primed to become thicker clouds of ice crystals, but it's not quite cold enough for ice to form without help. As the plane flies through the air, the tiny particulates provide the last bit needed for the vapor to condense into clouds of ice particles. Those clouds form the trails behind the engines. When conditions are *just* right, planes can also cause trails to form at the wingtips as the turbulence from the aerodynamics changes the air pressure, causing a trail to form. Why it happens to some planes and not others depends on the air conditions around the plane. The altitude changes those conditions, so altitude matter, airspeed matters, and small changes make a big difference so that not all planes can create them all the time."
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677hhe | Why do most websites forward you to the www subdomain? | For instance, if you go to URL_0 , you'll be forwarded to www. URL_0 . Does this convention do anything useful? Wouldn't it be simpler if we collectively agreed to stop doing it? | Engineering | explainlikeimfive | {
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"text": [
"It's purely historical. In the old days other protocols such as ftp or telnet might have been allocated to URL_0 and URL_1 . In the '90s everyone got used to websites beginning with www. At this point it's just silly except some people still expect it. When you say 'we all collectively agree', well that isn't going to happen. We all is everyone who uses the internet.",
"A domain name is required to resolve to a specific IP address (from the DNS, called an A-record), but a sub-domain name can be resolved to another domain/sub-domain name (called a CNAME-record). By forwarding to the sub-domain, a CNAME record can then be used to get the web-site's content from another server altogether (such as a CDN or Cloud platform server). For example, if I ping URL_3 , I get the IP address: 151.101.193.140 But if I ping URL_2 , I get the IP address: 151.101.61.140 And checking URL_2 on URL_0 , it shows that it is a CNAME record to reddit.map. URL_1 , and URL_1 is a Cloud platform"
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"fastly.net",
"www.reddit.com",
"reddit.com",
"reddit.map.fastly.net"
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67c6ux | How come that ships developed their own measurement systems for distance and speed (nautical miles and knots) different from the measurements for any other form of transportation? | Engineering | explainlikeimfive | {
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"text": [
"The system of using degrees, minutes and seconds to measure angles predates the system of celestial navigation we've developed and which is still in use. There are 360 degrees in a circle, 60 minutes in a degree and 60 seconds in a minute. Modern sextants (and predecessor instruments) measure the height of objects above the horizon in degrees and minutes of arc. The nautical mile is defined so that 1 minute of arc corresponds to 1 nautical mile. In this way, the angular measures can be easily equated to distances on the map. The makes the earth's circumference 360×60=21600 nautical miles. The latitude scale on the sides of mercator maps shows minutes of latitude which can be used as a scale of nautical miles. (The scale varies with latitude, so you need to use the scale at the same latitude as your location.) Arc seconds are not used by navigators. Often the first decimal of seconds of arc is recorded: tenths of a nautical mile correspond to 1 cable which is close to 100 fathoms or 600 feet and which is the traditional length of anchor cables. The metric definition is 1852 metres to the nautical mile and 185.2 metres to the cable. The term knots arose from the log line, a rope attached to a \"log\" thrown into the sea behind a ship with the rope wound on a reel. As the first knot unwinds off the reel a 30- (or 28-) second sand glass is turned and the seaman starts counting the number of additional knots which are spaced 51 (or 47.25) feet apart. The number of knots counted by the time the sand glass runs out gives the ship's speed directly in nautical miles per hour, AKA knots.",
"The sea was the only FAST means of travel for centuries. It needed to measure speed, not just in a few miles each hour, but more as we do today. Water is wet, messy stuff, so by sticking a fairly static floating lump in the stuff and dealing out twine with knots in it whilst counting off the time it took, gave you nautical knots. It isn't the same as miles, quite, but has it's roots in 'chains' and other olden measurement systems. The metric system using base ten is less factorable (divisible) than one with base twelve or sixteen, as the old 'imperial' systems were divided. There is considerable history to each measuring system, often with different trades using different systems, so I won't go any further off track."
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67f8si | Why do elevators have an "up" and "down" call button, when you can choose any floor inside the elevator? | Engineering | explainlikeimfive | {
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"text": [
"Imagine you're in a building with 20 floors. Someone in floor 2 decided to click \"floor 20\", so the elevator isn't gonna stop going up until it hits floor 20. Let's say you're in floor 4 and want to go to floor 3. If you pick this elevator, you'll do 4 - > 20 - > 3. So, avoiding this elevator by only pressing the \"down\" button, you'll catch an elevator going down, and you'll do straight from 4 to 3.",
"To explain it briefly, if you push the down call button, only an elevator on its way down or a vacant elevator will stop in your floor. An elevator on its way up will not stop in your floor. The up will call a vacant elevator or stop an elevator on its way up. An elevator on its way down will not stop in your floor.",
"So that an occupied elevator going the opposite direction as you doesn't stop to pick you up."
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67gqui | The electric hand mixer has two almost identical blenders but they have two specific locations, why is this? | Engineering | explainlikeimfive | {
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"text": [
"There's no difference between the beaters on most models where they are removable. They circulate in opposite directions to draw batter between them, to break up any chunks and make the blended batter more homogeneous."
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67i6mv | why does charging your phone while using the headphone jack cause interference, but not when the audio is playing through your USB cord? | I mainly notice this in cars. I understand EM fields and how cheaper auxiliary cords have less shielding for the audio signal. But why does the USB cord not cause interference with itself? | Engineering | explainlikeimfive | {
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"text": [
"USB is digital, while 3.5mm jacks transmit an analog signal. The digital signal can tolerate some noise without losing quality, while the analog signal starts losing details right away. Think of the USB signal like a novel while the analog signal is a bunch of pictures. The interference causes some random noise to show up in the signal. The novel is made up of letters, and there's only 26 letters in the English alphabet. Even if the letters get messed up a little bit, you'll still be able to tell what letters its supposed to be and be able to read the entire novel. If it gets too messed up, you won't be able to read it at all but you can tolerate a little noise without losing anything. With the pictures, on the other hand, you start losing details as soon as it gets a little messed up. You can still get the gist of it with quite a bit of noise (think of old TV signals with static if you have a bad signal), but you lose some details with even a small amount of noise."
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67je6k | Why do commercial buildings have flat roofs while residential buildings have sloped ones? | Maybe this is unique to the city I'm in, but pretty much all houses have sloped roofs - because you want the snow or rain to slide off it. Makes sense. But pretty much all commercial buildings I see - ranging from 40 story sky scrapers to a single story convenience store - pretty much all have flat roofs, The buildings are built pretty much entirely with 90 degree angles. Why is this? I can kinda see skyscrapers because I understand how concentrating the rainwater and letting it fall 40 stories might cause *problems* but you get all these commercial buildings, schools, some small apartment complexes that are only one or two stories tall, and they all have flat roofs. | Engineering | explainlikeimfive | {
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"text": [
"The slope of something is defined as the height divided by the width. A roof needs to be at least a certain slope for snow to slide off of it (rain generally will slide off a gentle slope). This slope is easy to make if the roof is small. However, if the roof is commercial sized (large width) and you want the same steepness throughout, you will end up with a VERY TALL slopped roof (large height). It's just not feasible. Secondly, the amount of material needed to cover a flat roof is less than for a sloped roof (the flat side of a rectangle is always smaller than the diagonal). When you need to cover a lot of roof area in commercial buildings, price becomes a factor. Next, a flat roof allows you to put things on there. Air conditioners and other ventilation systems are much larger for commercial buildings compared to smaller ones and generally they are placed on the roof. These would be very difficult to install on a sloped roof. Lastly, depending on the weather, a flat roof is fine. If it doesn't rain or snow much a flat roof will do. A sloped roof just looks more pleasing on a house (and it can add attic space) so residential houses have them simply to increase property value.",
"So there could be several reasons, I can think of 3 off the top of my head. 1: Residential buildings have attics for storage. 2: Having an attic allows for more insulation, since a house has to be heated pretty much 24/7, while a school only really needs to be heated 8-12 hours a day. 3: As a home owner it's easier to replace a patch of shingles or even replace all your shingles in the event your house had some damage. But a flat roof requires a thick and heavy layer of tar to seal it from water damage. This usually needs special equipment and professional insulation."
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67m9vu | How do manufacturers make artificial flavors taste almost exactly like the real thing!? | For example: How do they get grape flavored soda with 0 calories, 0 sugar? How do they match all these different flavors? | Engineering | explainlikeimfive | {
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"text": [
"**TL;DR**: *They usually concentrate on including a very special family of chemicals called 'esters' that are at the core of the flavour they're trying to duplicate, and top it up with sweeteners that are so low in calories they can legally market them as having zero.* Flavours are caused by a mix of chemicals that affect two of your senses (let's ignore stuff like texture, as 'crunch' or 'chewy' is not a flavour.) There's stuff that affects your taste and that your tongue picks up, like salt or sugar. And there's stuff that you smell and that your nasal passages pick up, like the smell of food cooking or that freshly cut pear. Both of them combined are released when you bite and chew, and that's why a good steak tastes stronger it smells. *(**Sidebar eli5**: when you have a cold and your nasal passages are all frigged up, you lose this second sense and that's why food is often more tasteless when you're ill.)* You usually only need a small trace of the latter type of nose-friendly chemical to influence the flavour of food, and certain chemicals are really strongly associated with certain foods. These are often 'esters', a complex chemical that our nose picks up and we know is quite distinctive. Bananas have one ester, oranges another, and some fruits like strawberries have a bunch that give a new smell when combined. Duplicate that chemical or mix in the lab, or get even close to it (for example, by using orange squash to flavour orange soda), and you have your flavour. Because only traces are required to make a food taste like a pineapple, they have essentially zero calories until you start adding sugars and other stuff to make it \"tongue friendly too\". And by adding artificial sweeteners or natural stronger sweeteners like Stevia that have a lot less calories than sugar, you can keep the calorie count so low that it's okay legally to say \"this product has 0 calories\".",
"A chemical is a chemical. The source of it doesn't make it \"real\" or \"not real\". If there was a good tasting plant that derived its flavor from a complex of Fluorine, Uranium, Carbon, and Potassium, it would be no different than making that same complex in a chemical factory."
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67q1nc | How are police able to retrieve Snapchat messages when they are inaccessible to the public ? | Snapchat isn't being truthful when they tell you it will be deleted forever. Is there a trick I can learn if I want to look at old photos? | Engineering | explainlikeimfive | {
"a_id": [
"dgsbcmp"
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"text": [
"> Snapchat isn't being truthful when they tell you it will be deleted forever. > Their policy clearly states they keep it for 30 days: URL_0"
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"text_urls": [
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"https://www.snap.com/en-US/news/post/how-snaps-are-stored-and-deleted/"
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67qp50 | Why does NYC have so many of those tall orange cones on the roads spewing steam? | Engineering | explainlikeimfive | {
"a_id": [
"dgsgoo3"
],
"text": [
"A combination of the fact a lot of energy created in Manhattan is steam powered, as well as releases from hydrology steam systems in subways. The cones are so homeless people dont lay on the grates for warmth. Which sounds cruel, but it's vapor, which soaks people over time causing pneumonia, thus compounding greater issues. Manhatten is huge, so there's lots of them."
],
"score": [
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|
67rs3a | Why do we screw clockwise and unscrew counter-clockwise? | Engineering | explainlikeimfive | {
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"text": [
"There's two ways I believe your question can be interpreted, and I'll start with the easier, more concrete one to answer. If you're asking why there aren't screws that tighten clockwise as well as counterclockwise circulating the market together, first off there are, but typically only for specialty items. But the main reason is just for uniformity. If both kinds were made, that would also mean that things such as bolts/nuts would HAVE to be paired with a nut/bolt respectively that was made to fit it. A counterclockwise to tighten bolt would not fit a clockwise to tighten nut, the threads wouldn't line up, so companies would have to have two machines instead of one to make their product. This is irrelevant to screws going into wood, but uniformity would dictate that it should be the same direction as with bolts. Now, the way I believe you're intending your question is why is it the standard that it's clockwise to tighen and counterclockwise is to loosen, instead of being standard to turn clockwise to loosen and counterclockwise to tighten, and although the answer to that isn't 100% certain, at least not to my knowledge, the predominantly accepted answer is that right-handed people can turn with a stronger force clockwise, so it was made uniform to tighten clockwise so a tighter grip could be made with the screw/bolt (because the vast majority of people are right-handed, sorry lefties).",
"I have to imagine that for the predominantly right handed society, you have more muscle to pull something as apposed to push it. So it makes sense to screw things in towards your body. Plus it's been that way for so long that there's no valid reason besides personal preference or spite to actually change it."
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67syu8 | Where do the machines that manufacture the machines that manufacture actual consumer items come from? | I have a metal cooking bowl. Some machine made it. Who and where did the machine that made the machine that made the metal bowl come from? ... and so on, *ad infinitum*. | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Most machines and tools can be made by a person using a simpler machine or tool, which was made by a person using an even simpler one, and so on. Until you reach the point where the first tool is somebody's bare hands bashing rocks together. Now they might not *actually* have been made that way. Nowadays most simple tools (hammers, chisels, saws, etc) are made in complex factories themselves. So the true chain kind of goes up and down in complexity as you look back. (Oh, and it's more of a branching tree too.) But eventually it will reach something a person did with their bare hands."
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67yg1m | Why can't robots move exactly like humans yet? What is holding engineers back? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"The trouble is software. We have the technology to build the physical machine itself. We could build an artificial skeleton with artificial tendons and muscles and the necessary sensors, but developing the software to control it all simultaneously in a way that duplicates human movement is a daunting task.",
"My uneducated (somewhat) guess would be rapid fine tuning of balance and equilibrium of a bipedal body. If you really try and \"feel\" your muscles as you move, or even stay in place, you can quickly see that a LOT of stabilizing autonomous activity is going on. This is all going on very quickly in your body and automatically, programming that in a robot is likely extremely complex."
],
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68190g | Why can't cars go reverse full speed ? | Engineering | explainlikeimfive | {
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"text": [
"To go full speed cars have gears, first, second, third, fourth and often a fifth for economy on motorway driving. There is little point in having gears for going backwards because most people would feel uncomfortable reversing at 120 miles per hour. So it only has one reverse gear which is the equivalent of first gear. Most cars in europe would struggle to go 30 miles per hour in first gear (normal cars) so that would be the same limit on reverse speed for the same reason.",
"Adding multiple reverse gears would add a lot of parts (and weight and cost). And there are very few usage cases where going fast in reverse could be justified.",
"Some vehicles can. It is all a question of what gears you have. Since with normal cars you usually don't ever have a good reason to drive backwards at anything other than slow speed, most car-makers don't built them with more than one reverse gear. Some vehicles like Mercedes' Unimog have multiple backward gears 8 forward and 6 backward gears is something I have seen. This is usually not to drive backwards very fast but to give you different option of driving backwards slowly and very slowly because you are moving something incredibly heavy like a couple of train cars."
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682rid | Why do all big cities have a highway or series of highways making a circle around the center? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"These are commonly called Ring Roads and they're simply an efficient way to move traffic around a city. The centers of these cities are generally dense and hard to build in. So, when developing a high speed road it's easier to build it outside the city instead of straight through the middle.",
"Bypass highways are to prevent traffic bottlenecking in the center of town... while clearly some people need to get to the center of town (ie. commuters) many are simply passing through on their way elsewhere. Rather than have them unnecessarily add to the traffic congestion, they can pass around the most crowded areas of town. They are also useful for people trying to get to various parts of the metro area from other parts, again without needing to go all the way downtown and back out, while not tying up surface streets."
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685bbm | How do electronics switch things on and off? | For example, on a typical flashlight you physically slide a switch, completing a circuit and opening the flow of electricity to the bulb. But how does that work on something like an iPhone torch. How does the circuitry 'open the flow'? Does something move inside? What moves that?! Cheers everyone | Engineering | explainlikeimfive | {
"a_id": [
"dgvt3p5"
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"text": [
"There are electrical components called transistors that can be used as switch or amplifiers. A transistor has three terminals, applying a voltage or current at one terminal (called the base or gate depending on the type of transistor) controls the amount of current flowing through the other two terminals (call the drain and source or collector and emitter depending on the type). There are other components that can act as switches. Relays are an example. They use an electromagnet to attract a piece of metal and close a circuit. SCRs (silicon controlled rectifiers) are similar to transistors except that they latch on and stay on until the voltage through them drops below a threshold value. Thyristors are similar to SCRs, except that they work with AC. Vacuum tubes can also be used as switches, but they're obsolete for most applications."
],
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685s8m | Why do the majority of automatic guns have 30 bullets in their magazines? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Military clips come with 10 rounds a piece. A magazine using them is best off loading in multiples of 10 rounds. So you're looking at choosing between 20, 30, or 40 rounds. 40 is just too much for standard use. It makes the magazine stick down too far to shoot from prone (a 30 round AR-15 mag sits almost even with the bottom of the pistol grip), and it makes the rifle too heavy (especially something like the steel magazines in a 7.62x39 AK). 30 rounds is as many rounds as you can put in while not sacrificing pointability and the ability to carry it. Additionally, it is harder to actually put larger mags into loadbearing equipment- especially something like a large curved 7.62x39 magazine. Look at the large RPK mags and imagine trying to carry a lot of them on your chest as a rifleman. As an aside, notice that larger full power rifles like the FAL more commonly used 20 round magazines because for them, a 30 round magazine was too heavy and large for standard issue.",
"For a rifle in an intermediate caliber with a box magazine on the underside of the receiver 30 cartridges is about the most you can fit in the magazine and still be able to fire the rifle comfortably from a prone (laying down) position. If the mag is too long it forces you to hold the rifle higher off the ground, which makes it difficult to shoot comfortably and accurately. Side or top-mounted magazines have their own set of problems that make them not really desirable for a modern rifle."
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6891rx | How does an automatic transmission work? | Also, why are automatics considered to be more complex and costly to work on? | Engineering | explainlikeimfive | {
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"Manual transmissions are quite basic. You have an input shaft with gears on it that turns and an output shaft with different sized gears on it and clutches to select which one you want to change the gear ratio. Stuff can be spaced out and there are limited parts In an automatic transmission you have planetary gear. There is a large gear in the middle (sun gear), a big ring gear(ring) on the outside, and smaller gears(planets) that connect the ring to the sun. Gear ratios are changed by choosing which gear is the input, which is output, and which is locked in place. All of these gears are packed together and a modern automatic could have up to 4 sets of planetary gears resulting in lots of parts, all of which are covered in oil. Transmissions have a rather low rate of problems and a rather high skill requirement to properly fix which results in there being few shops being willing or able to work on them which drives up the price",
"I think this question is better answered by watching a youtube video explaining all the basics."
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68anu4 | Why can't we fly a plane as high as it can go and launch a rocket off the back of it, using less fuel and weight, plus using the momentum it already has with the plane? Kinda like a giant missile to space. | Engineering | explainlikeimfive | {
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"We can but it is not terribly practical. In very rough terms lowest possible orbital speed is about 25,000 km/hr. A rocket achieves that by throwing mass out the back and letting conservation of momentum do its thing. The difference between a rocket and an (airbreathing) jet engine is that all the propellant mass has to be aboard at the beginning of the flight to accelerate not just the payload but, at earlier stages of the flight, all the rest of the propellant too resulting in the Tsiolkovsky rocket equation. As a result, the F9 requires about 500,000 kg of fuel to raise 20,000 kg to LEO. An extremely fast aircraft (SR-71) might achieve 4000 km/hr with a few hundred kg of payload and mid-air refueling. A B-2 goes about 1000 km/hr with about 18,000kg payload (again with mid-air refueling). Now if you look at the numbers above you can see that, from a speed perspective, a jet aircraft is roughly stationary compared to an orbiting spacecraft. You can also see that a rocket small enough to be carried by a B-2 would only be able to lift a few hundred kg to orbit and that it doesn't make much difference (at least in terms of momentum) whether you launch that rocket from the surface, from a balloon or from a jet aircraft.",
"It is called Pegasus and run by Orbital ATK They have been doing it for awhile URL_0 Here is a recent launch URL_1",
"Because the plane adds almost nothing to the momentum of the rocket, and because the planes we have are too small to give a significant payload to the rocket once you factor in the need to load it up with close to the same amount of fuel as you would in a normal launch. The hard part isn't getting to orbit, but getting a high enough speed to maintain that orbit. For example, the Space Shuttle had to hit 17,500 mph relative to Earth's surface; putting it on top of a plane would have only accounted for the first few 500 mph or so, and would have severely compromised the payload. Granted, you can try to get the plane moving faster, as what you're talking about has *some* merit, but the US hasn't tried anything like what you're suggesting since the [MD-21 incident]( URL_0 ).",
"You would still need so much fuel and such large rockets that there are no planes even close to big enough to do what you are suggesting. It would take a truly massive plane to make this work.",
"That's what we (Firefly Space Systems) were trying to do. The advantages of an air launch means there is a lot lower max Q during the launch so a lot less stress of the vehicle, the ability to launch anywhere and not be tied to a launch pad, and faster turn around between launches. The downside to launching any sizable vehicle is weight. Do you plan on launching something small like a Pegasus (do-able) or a Falcon 9 (impossible) from a plane? Our rocket was designed completely with carbon fiber to reduce weight, and even with that, we needed the largest plane to ever be build in order to do that (Stratolaunch).",
"A transport plane might get to roughly 500 mph with a rocket strapped onto it. The velocity needed to exit Earth's orbit is around 17500 mph. That's less than 3% of what it would need. You'd also have to make the plane really powerful and the rocket very small and light-weight to even be able to lift it off the ground."
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68c3j1 | Why are turbulences harmless for a plane? What's the physics behind that? | Engineering | explainlikeimfive | {
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"Simply put, the small bumps are negligible and the plane is strong enough to ignore it. Strong enough turbulence can do damage, but that's uncommon (they don't normally fly through the worst weather). What is turbulence? It's air that is flowing in a turbulent way, there's no smooth movement and it moves in eddies and abruptly changes direction. This jerkily-moving air literally just jostles the air about. This is contrasted with laminar flow, which is smooth and in nice neat layers. Think of water in a pool. If you move your arm through it when it's undisturbed you glide smoothly, if everyone near you is splashing you'll hit places where the current is moving with your arm and places where its against your arm so your arm gets pushed and pulled about more. Here's a picture contrasting the two: URL_0 URL_1"
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68czjp | Why are 9 volt batteries rectangular, while other small voltage batteries are round? | Engineering | explainlikeimfive | {
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"Because they are actually a little box containing up to 6 round batteries. [Here is one cut up.]( URL_0 )",
"9 volt batteries are actually batteries. A battery is a number of electrolytic cells connected together, almost always to increase the voltage. In this case, six 1.5 volt cells are joined to give the 9 volts. Strictly speaking, 1.5 volt \"batteries\" such as \"double As\" are just cells and shouldn't be called batteries at all. Popular usage over the years has changed the meaning. In the early days of electronics everything used vacuum tubes (AKA valves) which needed much higher voltages than transistors and so batteries, as opposed to cells, were much more common. Battery is used in the same sense for batteries of guns, i.e., a group of guns working together. Cells tend to be round because a cylinder is the most efficient way to arrange the metals and electrolyte. For a 9 volt battery, since each cell in the stack is relatively flat, the efficiency of a cylindrical shape is less important so it's worthwhile to push the battery into a rectangular shape to make it easier to fit inside compact electronic devices."
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68d8xp | Why is it so hard for road workers to set manhole covers flush with the road surface? | Engineering | explainlikeimfive | {
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"Also, it may have been level(ish?) when the road was new. Same way potholes form (road+water+constant heating and cooling) things move slowly all the time, especially objects of different densities.",
"Because they're attached to the pipes and conduits under the road, not the road itself, and the two things aren't always perfectly parallel."
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68di9c | Why haven't we been able to make leafblowers, etc silent / much quieter? | Engineering | explainlikeimfive | {
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"The noise occurs where the high speed exhaust starts mixing with the low-speed ambient air. Basically, the jet of air coming out of the blower needs to puncture through and rub against all the rest of the air. That causes friction and turbulence, which causes noise. There are some things you can do to improve the noise *quality* (see the [chevrons]( URL_0 ) on new aircraft engines), but reducing the overall noise level is generally only possible by reducing the speed difference between the exhaust and the ambient air; that is to say, turn the leaf blower off.",
"It's not that we *can't*, it's that it *drastically* increases the price without largely impacting the ability to do the job. People who are leafblowing would rather spend $200 for a loud cheap one than spend $450 on a silent one.",
"Actually the noise of leaf blowers and lawn mowers comes from the motor or engine, and whether electrical or gasoline-powered, they need to concentrate a lot of power into a generally small engine or motor. Power generates heat, so the motor or engine needs quite a bit of air flow to cool it down, and this makes it somewhat difficult to add padding or insulation that would absorb and lower the noise. You CAN find quieter devices, but you have to specifically look for noise ratings rather than performance ratings, so they're both more expensive and under-performing."
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68drp0 | Do heat-seeking missiles ever accidentally lock onto the sun? | I don't know how they exactly work - but do they recognize the sun as a hot object? | Engineering | explainlikeimfive | {
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"Usually, a heat-seeking missile has been programmed to change its trajectory based on various things, and so it can usually tell if it's detecting the sun (or, for example, infrared light from the sun scattered off of clouds) or if it's detecting its actual intended target. Compared to a person or a vehicle, the sun outputs a very obvious signal in infrared, since it's pretty much always going to be the same level of infrared light and in the same shape, provided it isn't getting partially obscured by things. If a missile simply ignores the brightest source of infrared light (or, if it's searching for super-heated jet engine outputs, ignores anything less bright than that) if it appears to be the size and intensity of the sun, it wouldn't be tricked by the sun. Of course, it isn't always going to be perfect, and there are conditions where the missile will mistake various things for its target - clouds, heat from sandy ground, and so on. Better and better technology and imaging techniques helps to mitigate this. The most sophisticated heat-seeking missiles basically make an infrared image of the surroundings and analyze it. Of course, even that isn't going to be perfect, yet. That's why we use \"identify the pictures that have signs in them!\" as ways to prove you're not a robot - computers are pretty bad at correctly interpreting visual data.",
"Yes, this is actually a known problem with primitive heat-seeking missiles, and pilots would occasionally try to get between the missile and the sun in order to transfer the missile's focus onto the sun. Modern missiles are specifically programmed to avoid this."
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68npm6 | What exactly does a land surveyor do? | Also, how does their equipment, such as the tripod/telescope-looking thing, help them do it? | Engineering | explainlikeimfive | {
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"They make sure facts on paper agree with facts on the ground. If you want to build a fence, you want to make sure it is on your side of the property line, otherwise your neighbor can tear it down if they like. You call a surveyor, they will review the property records, and so you exactly where the line is. Or maybe you are building a new shopping complex. You bought the land, you have decided where to put all the buildings, roads, and parking lots, and now you need someone to take those plans and put stakes in the ground so the builders build in the right place. The equipment lets them do this. The property records/building plans will reference some known landmark or coordinates. The surveyor starts there, sites their instrument in the correct direction, then measures off a certain number of feet, according to whatever they are working off of. Eventually, the set markers in all the key locations so the next people to come along know where everything belongs.",
"Land surveyors measure and record where things are on the surface of the earth. Usually in relation to a known geodetic grid. They also layout for new construction, such as roads, buildings, and even parking lots. As a former instrument operator, the instrument is usually called a total station, and it performs many tasks, such as measuring angles, elevation, as well as distance. The more common instruments can collect data, but that is usually done on a handled unit almost like a scientific calculator with special programming and memory that allows points to be stored, calculated, and even uploaded for laying out on the ground. Once a given point on the earth is known, the surveyor can then follow calculated angles and distances to get where they need to be to layout whatever it is they are tasked to do that day. Sometimes it is just about recording where something is, so that the civil engineers know where it is and are able to incorporate that into whatever they are working on. Things like houses, fences, curb and gutters, streets, utilities, drainage inlets and outlets, as well as any other permanent structures that can't be moved. Now with the invention of GPS, the same job that took a 3-4 man crew a week to do can be done by 2 people in half the time. I have been out of the field for several years, and this was to the best of my recollection, I hope it helps."
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68r6xj | Why are pistol bullets usually wider than rifle bullets? | A smaller Pistol caliber is 9mm. While a larger size rifle caliber is only 7.62mm. Why is that? | Engineering | explainlikeimfive | {
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"Bullets have both length and width that contribute to their volume, and therefore weight and power. In a rifle, the magazine can generally be whatever dimensions are convenient for the designer to make them. For a handgun however, the magazine goes inside the grip, and so must fit within a human hand. This restricts the forward-to-back dimension of the cartridge so that pistol bullets need to be short and stubbier than rifle bullets to fit. In order for the bullets to stay big, they just make them wider to compensate. On another point, because the case, and therefore powder volume of a rifle is so much larger, rifle bullets tend to go close to 3x as fast as a handgun bullet. Even so, at the extreme ranges that a rifle is used, the bullets can fall over 3 feet, making it important to keep that velocity up. Lower bullet mass and narrower bullets help with that. Since a handgun is so much more difficult to shoot accurately, its not really important that it's terribly effective past a few tens of meters. Thirdly, since the bullets move slower, (this is a little controversial) it has fewer mechanisms for wounding. Rifle bullets will send a shockwave through flesh, damaging organs even far away from the wound channel. Handgun bullets are slow enough that they don't really do that. In order for an organ to get damaged by a handgun bullet, the bullet has to actually pass through it. Making the bullet wider increases this chance. TL;DR Handgun bullets need to be short to fit in the grip, they are slow because they don't need range, and they are wide so that they still have adequate wounding potential at low energy.",
"With a rifle's intended long range, bullet speed is important -- and a heavy but slow-moving bullet may not reach its distant target. So they use a moderate-weight bullet with a relatively large explosive charge. Rifles using a large bullet, then, require a *very* large explosive charge, making them harder to handle and heavier. Also, pistols don't have a lot of length in the chamber simply because they are compact, so a wider rather than longer bullet is the way to add mass."
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68sf4f | What is the international space station for? | Engineering | explainlikeimfive | {
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"It's an ideal - indeed, almost the only - platform on which to perform scientific experiments where having (nearly) no gravity is important - for example, they have sent animals and plants up there to see how they react to a lack of gravity; this can teach us something about how they work which in itself has nothing to do with space, but relies on removing the variable of gravity from the equation. Beyond that, it's very useful for developing technology for space travel in a *relatively* safe but useful environment. The ISS is build with a lot of locks in place which means that a problem in one area can be isolated. This way they can send up test functions and see if they work \"in situ\" (rather than in a lab on earth), safe in the knowledge that if the worst comes to the worst the astronauts aboard can jump into their Soyez and get the hell out. One example of this is the Bigelow inflatable module, which is basically a giant balloon that's stuck to the side of the ISS. This may later be used for long-duration missions (for example to Mars) so that the astronauts have a lot more space for the journey without being limited by the size of what they can send up there (because it's inflated in space). Thirdly, it enables us to study the long term impacts of low gravity on the human body. One thing we have learned is that the eyeballs actually change shape slightly after extended periods in low gravity. It's obviously better that we discover this in the relatively safe surroundings of Low Earth Orbit rather than, say, half way to Mars. Fourthly, the *international* part of the ISS has three major benefits: i) It fosters international cooperation between countries that haven't always seen eye to eye. ii) It keeps the costs down for all the countries involved, who have access to a large space that they either couldn't afford normally or would eat up a larger part of their budget due to the pooling of resources and iii) It enables smaller countries to develop their own space technology and concentrate on small, specialised areas that, developed on their own, would be pointless. For example, the ESA - the combined European Space Agency - contributed (amongst other things) a supply vehicle (the ATV) to the ISS, which sent up supplies. This vehicle would have been largely useless without the ISS, as it would have no where to go and the ESA could not really afford (or justify) their own space station. This vehicle, however, it being incorporated into NASA's Orion space craft which will (all things going well!) go to Mars at some point. So, by being part of the ISS, the ESA is able to gain this specialism and experience in space travel it wouldn't otherwise get.",
"Research. There's dozens of science experiments being performed at any one time up there. From how plants and animals grow, to research of diseases, as well as research into new technologies that will be used to hep us explore further into space."
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68tok2 | how a bridge built to hold a mag lev train and track would work | Would the bridge only need to support the weight of the track? | Engineering | explainlikeimfive | {
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"The train's weight doesn't disappear anywhere, and it has to be supported by something. Regular trains have wheels, hovercraft have a cushion of air, and maglev trains have magnetic fields. The latter case just means that the magnets are pushed down as the train passes."
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68uajz | What do you do when the check engine light in your car comes on? | Engineering | explainlikeimfive | {
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"Generally, take it to your mechanic. Some auto parts stores may also provide services to read and tell you the code. There are also devices you can buy to read the codes.",
"It could be something serious, or it could be a small issue....that's the trouble with just having a light. It basically means that the computer has recorded an error code. To find out what went wrong, you need to read that code. Auto parts stores will often read your codes for free. A repair shop or dealership can certainly read it, although it might not be free. You can buy a code reader and read it yourself. Typically, the readers have been sort of expensive. I've seen $60 to $300. You can get an adapter to connect to the OBD port on the vehicle, and then read the codes with a smart phone. I bought one for $25 and it connects to a phone via wifi or Bluetooth. It also allows me to have the phone display gauges while driving. You do need an app, which may or may not be free. Either way, once you get the code read....you will know what error message was generated. That might not tell you what to do about it....but from there you can find out more information on how to proceed.",
"1) Get an OBD-II reader, which will cost $20 and let you read the trouble codes off of the ECU. 2) Identify the issue through the combination of trouble codes. 3) Fix the issue yourself, or bring it into a shop.",
"It's easy: 1) Find out why the light is on. This could be a loose gas cap or a real problem. There is a [$14 code reader gizmo]( URL_0 ) for this. 2) Fix the problem. This of course depends on what th problem is. 3) Reset the MIL (that's the real name of the \"check engine\" light). Your reader gizmo can also do this."
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68vwzo | Why is there no market for transportation that fits between a normal city car and a motorcycle? | Engineering | explainlikeimfive | {
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"There is: it's called Uber. Or Lyft or [insert rideshare service]. > It struck me how wasteful it is, that I carry around 840kg of metal just to transport 70kg of me 30 miles, every day. The problem with cars isn't their size, because you need that size when you need to move multiple people. The problem with cars is that you don't know when or how you will need to use them, so they are bigger than necessary for many uses and, worse, they _sit unused_ most of the day. You spend 30-45 minutes driving to and from work. The rest of your day, the car sits unused. The solution is not smaller vehicles. The solution is moving away from the concept that each individual needs a _dedicated_ vehicle. In the past, the challenge to this has been that the most efficient way to get a vehicle _when you need it_ has been to own a dedicated vehicle, and one that is large enough for your most common needs. You may only have one person in it when commuting to work, but taking the family of five to the park on Saturday requires all the seats. Technology will solve that in two ways: 1. By dispatch technology that can match the person needing transport with the nearest available appropriate vehicle of the appropriate size to transport them. This is what Uber/Lyft/etc are _close_ to doing today, but they're still stuck with repurposing existing dedicated-vehicles to this purpose. 2. By driverless technology that makes the matching of rider and vehicle not dependent on the needs of a human driver. Driverless technology also has the advantage of being more efficient, i.e. vehicles in dedicated-driverless lanes can all be communicating with one another, which will allow them to drive just a foot or two apart like a train, and slow down or accelerate all at once. Ever been in a long line of cars at a red light, the light turns green, then the first car accelerates, then the second, then the third, and so on, until by the time the car in front of you accelerates, the light has turned red again? Driverless cars don't have to behave like that because they could be in constant communication -- the light turns green, they _all_ move forward at the same time with the same acceleration. Matter of fact, if you can get human drivers off the road entirely, you don't even need stoplights (at least not for vehicular traffic -- you still need them for human pedestrians). Such technology reduces the overall number of cars on the road. In this scenario, cars might even become bigger and more luxurious, because the primary reason cars have been shrinking in size over the last 50-70 years is to reduce weight to reduce fuel consumption, which is only a problem because of the dedicated-vehicle model. EDIT: a couple edits to clarify and correct grammar.",
"There is. It's called the [Renault Twizy]( URL_0 ); it's not a car, it's not a motorcycle. It's a *quadricycle* - electric powered with a range of about 60km, windows and doors an optional extra",
"Pick any two: Big enough, fuel efficient, or cheap. I think most people are going to opt for \"big enough to accomplish what I need in a given day\". So if you're a family with two working parents and kid(s), you're going to want 2 cars that are both large enough to hold the kids and friends/groceries/luggage/sports equipment. You could also ask yourself why trucks are so popular. The majority of the time, the beds are empty. People buy them because either they like the look, they like being up high, or they like the *option* to tow or carry large items. I'd be really interested in an [Elio]( URL_0 ) at some point. There's at least a little bit of a market, as 65,000 people have reservations. They are cheap and small and have good gas mileage. It would make a great second car. But if we have kids, I'd need something that could tote them around in case I was unable to switch cars."
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68wq28 | Why Dixon Ticonderoga pencils can erase better than other pencils. | Engineering | explainlikeimfive | {
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"You kids should stop playing with rubbers. Serious answer, it has to do with the composition of the rubber. I've noticed that the rubber on those erasers rolls off it into little cylinders. This is important because it increases the surface area of the rubber. Imagine wiping up a desk with a Clorox wipe. You use one side until it's black. What do you do? You flip it over and use the other side! The rolling effect of the rubber flips the dirty side and the clean side, and because the rubber is strong enough to remain connected to itself, you can roll those little suckers around and wipe up your mistakes! On other lower quality erasers, the rubber doesn't quite hold together and just kinda breaks apart and disintegrates(not a literal disintegration, but it gets the point across). Now you have all these tiny itsy bitsy chunks which in theory have more surface area than the cylinders from before because they can use their sides and front and back and top and bottom, whereas the cylinders can only use front and back. Buuuuut, because the chunks break apart and scatter (and because there is no compression force acting upon them) they don't do shit. They don't have the structural integrity to withstand the pressure you are applying to them, so they they turn into dust and make it even more difficult to erase things."
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68y7dx | how do large ships with large anchors lift anchor to move again? | I'm wondering how a ship's anchor or anchors, which obviously need to be dig in deep enough to stop and hold a large ship, are able to then be pulled back up? | Engineering | explainlikeimfive | {
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"The anchor is designed to dig in when the ship is at some distance, so the anchor chain is at a shallow angle (far from vertical). To weigh anchor (re-raise the anchor), you move the ship close to the anchor so the chain is near vertical, then you winch it up."
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68zec3 | How does a "dead man's switch" work? | Some public figures like Edward Snowden has said that if he happens to die, his death would automatically leak very secret information, using this as a way to keep him from being asassinated. How does the information get leaked right after the person dies? | Engineering | explainlikeimfive | {
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"He probably has a program on a computer that will leak the information if a password isn't entered every so often. So if he dies he can't enter the password and the information gets leaked after a period of time automatically.",
"Usually a dead man's switch, when used in the context of machinery its something you need to actively and consciously do to keep everything running. If something happens to the user, they can't do it anymore. Unlike an accelerator where you could pass out while leaning on it. Trains use a button that needs pressing regularly, but not just held in, so if something happens to the driver, they can't press it anymore and the train emergency stops. Despite the name, it doesn't have to be a \"dead man\", the train case is more for drivers just having a nap than anything! In Snowden's case, or anything else to do with computers, it's likley as /u/Fishandchips321 said. If he hasn't checked in, for whatever reason, the automatic processes will kick in.",
"You can give a document to a lawyer and pre-pay for him to post that information upon an event. Keep the document sealed. If you're up against people that will go to quite extreme lengths, tell lawyer 1, ideally from a different country, to give the letter to lawyer 2 BUT NOT TELL YOU WHO LAWYER 2 IS - and for him to tell lawyer 2 to follow the above instructions (then take his money and walk away). That way if you're caught and tortured you still don't know who has got your 'reveal all' letter - poised and ready to post (well, possibly 30 letters, ready to post to a county-barrel load of respectable media outlets). And whomever is after you and the information suppression has the prospect of kidnapping and torturing innocent lawyer #1 who are in a different country - to add into the mix if they want to go with a black-bag operation - an unholy nightmare of a task!",
"you basically set up a program that executes unless it gets a signal that it shouldn't every X hours. These days you can rent servers in the cloud pretty anonymously. So you do that, upload your dangerous data there, hook it up to a script that uploads the data to... wherever, pirate bay or something. and set it to do that in 24 hours. Now you have a deadman switch, the script will upload the data unless you log in to the server, and reschedule the task.",
"There is a person, or an organization that is instructed to leak that information upon Edward Snowden being dead, or not heard of for X amount of time. Other types of dead man's switch are just holding a button pressed (or a pedal stepped on). If the person dies, they can't do that anymore and the train they are driving (or whatever) will automatically stop.",
"Edward Snowden is not the only guy with access to all those secrets, but the only one sitting in the lime light. So when the shit hits the fan and Snowden gets assassinated, another guy will step forward and eventually continue Snowden's work or to disclose all information at once - no matter how destructive the outcome.",
"There are three options for a Dead Man Switch: 1. Mechanical. You need to constantly or once-in-a-while press button or else something happens. You find those not only in movies, but also in trains: The driver has to press some pedal in short intervals or the train stops. 2. Computerized. You need to log into a certain service once in a while or something happens. You find those not only in movies, but also in your homebanking or many other sites. If you are not active for a certain amount of minutes/days/weeks, you are automatically logged off. Snowden might have one of those. 3. Social. Either you need to call a person once in a while or, in the case of Snowden, that person basically watches the news or follows you elsewise and if nothing happens for a certain amount of time, something happens. Snowden might have one of those. I expect that Snowden actually has several of 3, it might be people he trusts or pre-paid lawyers in possibly different countries, instructed to become active should he get killed, arrested or simply vanish. This is way easier and more foolproof than you having to log in somewhere, the issue with \"trust\" is you do not know what happens if years go by or when your friends are pressured, using lawyers (even large law firms not based in the US) might mitigate this."
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6909q7 | The taller a building, the deeper you have to dig into the ground, why? | Engineering | explainlikeimfive | {
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"You can look at a building like a lever e.g. imagine a long crowbar stuck the the ground. The taller the crowbar, the easier it is to tip it over, because the length magnifies the force exerted by the buried part. So a tall building's foundations should be deep to resist the bending forces.",
"Pushing dominoes over is easy unless the base is buried in the ground, the bigger the domino the more you need to bury them to stop them being pushed over."
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693329 | Nuclear Fusion Reactors | Reading about the nuclear fusion reactor in the UK . What I can't understand is how these reactors can contain temperatures as high as these folks are saying, 100 million degrees Celsius? Wouldn't that melt any material known to man? Edit 1: thank you for all the great answers! Okay, so I can understand that it's not actually touching anything, but then wouldn't the heat generated by the plasma still be cause for concern? I understand that this heat is where we are getting the energy, but then if we're constantly pulling it, wouldn't that drastically reduce the temperature of the plasma? | Engineering | explainlikeimfive | {
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"The part of the reactor that is 100 million degrees Celsius is plasma (the state of matter past air) and it is contained in a magnetic field. The magnetic field keeps the plasma from touching anything, which means it can only heat things up through radiating heat, which is a slow way to transfer heat (though at 100 million degrees it would transfer heat very fast even through radiation). Why this won't melt the reactor is how the reactor generates energy. Basically you flow a lot of water around the reactor to cool it off. The water boils into steam which turns a turbine. The turbine generates electricity. Now in the actual reactor they aren't using water, but a mineral salt that melts.",
"This is the reason why the reactors do not have any material close to the fusion material. The reactor core is suspended in vacuum by magnets and will slowly release its energy to the surrounding cooling pipes in a controlled manner. The problem people are facing when designing these reactors is that either the core produce too much energy for the system to dissipate though power generation or there is not enough energy being produced to give a net gain in power generation. So people are working on slowing down the reaction rate so the energy can be safely harvested and power the strong lasers and magnets required to get the ignition to start. There is a proposal that have been out for quite a few years to build a massive fusion reactor from known technology. There are however a few problems. It would take the entire US government annual budget to construct one reactor, the power grid is not big enough to handle the output and the power requirements is not high enough to be able to use all the power. To solve the two last problems there are some well known chemical processes that use CO2 and converts it into oil using power. The problem is that these processes are very inefficient and you would typically only get 1% of the energy back. The reactor would still be able to produce more oil then Saudi Arabia even with the massive loss in efficiency."
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69362t | If New Orleans is surrounded by man-made levees, then how was the city built below sea level hundreds of years ago? | Engineering | explainlikeimfive | {
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"Not all of it is below sea level. The French Quarter, which is the part that was originally settled by the French, is several feet above sea level. It still has a levee or sea wall between it and the Mississippi River to protect it during river floods, but it generally does not go underwater during storms. Even during Hurricane Katrina the French Quarter stayed high and dry. The parts of the city that flood are those that were established after levee protection and/or the drainage pumps came into existence. The levees have been around for a surprisingly long time and the pumping stations started getting built in earnest in the early 1900's, which allowed the city to expand even further into what was previously swampland. (Here is a Wikipedia article on[ drainage in the city]( URL_1 ). It also includes a [map]( URL_0 ) showing elevation in different parts of the city.) Finally, the city is built largely on river sediment and we don't allow the river to flood its banks anymore. Because river sediment contains a lot of organic material, the ground is slowly sinking as the organic material in the sediment decays. This is called compactional subsidence and it is pretty bad in some parts of the city. There are some areas where you have to fill your yard in with river sand every year or so and you have to replace your driveway every few years because it will sink with the sediment but your house will stay at the same elevation (houses are built on pilings so they don't move). Hope that answers your question",
"There are a few things. The biggest is that the city is subsiding, similar to what is happening to Venice in Italy. New Orleans is built on very moist, swampy land. Soil can act like a sponge and it increases in volume when it is wet, and decreases when it dries out. Man made changes on the Mississippi River and the delta, along with development and draining of the swampy land in the city proper, have caused the ground to literally sink beneath their feet. When in doubt read the NASA study I always say hehe. URL_0 It might surprise you to learn that this kind of action is going on all over rivers and coast lines around the world and it's very common even before we started changing the land to fit our needs. Coastline areas are always in a state of flux due to changes in river flow, sea levels, deltas and sand dumping at river mouths etc. One of the very first colonies in North America, Jamestown, was along side a river and that site is now completely under water even though it wasn't developed or changed much as we grew our cities. The wikipedia article mentions \" In the early 1900s, a seawall was constructed with the intention of preserving the site around the original \"James Fort\", even though the actual location of the original 1607 fort was thought to be underwater and lost to erosion. \" Waterfront properties over geologic time scales are always temporary."
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698510 | How does a computer know what device is attached to it ? | I understand all the workings of the memory and the processor and why they are required. No doubts. Crystal clear. I still do not understand how does the generalization in input/output come from. How does a computer know whether it is a keyboard that is connected or a a mouse that is connected or something else when the USB port remains the same. Can someone give me real life examples of computer interfaces. Are these interfaces the USB ports, PCIe ports, HDMI ports etc. etc. and does a processor restrict how many and what types of ports can a computer possess. And after all this why are drivers required ? If someone can point me to the right resources that would give me more insight, I would be grateful. Please help. A little detail is appreciated. I have banged my head on these questions long enough and still don't get them. | Engineering | explainlikeimfive | {
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"USB is more than just a connector, it's a whole set of protocols. One of the functions a USB device must support is the \"Get Descriptor\" request. The computer sends the Get Descriptor request through the USB, and the device must respond to it with a variety of information that identifies itself. The computer then looks up that information in a database and decides whether to treat the device as a keyboard, as speakers, or whatever. Drivers are components that operate directly with the hardware. If you tell your device \"Read this file for me\", the driver translates that into a series of requests for the disk drive, it schedules that read request in among all the others, it deals with failures, and it combines the data that the disk driver returns (which may be in weirdly sized pieces) into a full file for you."
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69880o | How/why are PC's better at playing video games when a playstation or xbox are made just to play games? | Engineering | explainlikeimfive | {
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"Compare it to buying a cheeseburger in McDonald's instead of making one yourself at home. Even if McDonald's employees are trained specifically to make burgers, the burger made in home will always be more nutritive and tasty, because you can choose the better ingredients, while McDonald's will use the best availability/cost/benefit ratio in order to boost their profit. The reason people buy consoles to play is the same reason why people eat at McDonald's, making a cheeseburger requires knowledge about ingredients and cooking, just like building a PC require knowledge in computer parts, also, a burger made of high quality fresh ingredients will probably cost more than a BigMac made of frozen \"meat\" and fake cheese. Consoles are simply low-end computers fabricated in a production line, while PCs can be build by hand using the highest technology available.",
"Because a recent ish gaming PC is more powerful than a console. The current generation of consoles are essentially low spec gaming PCs running a custom OS. They get better performance than an equivalent spec PC because the OS is more streamlined, and developers know exactly what hardware it has so they can optimise it specifically for that. But even a fairly cheap gaming PC will have better specs, so many games will run better on it than their console equivalents.",
"Playstation and xbox cost what? $300-$400 or so? I bet a PC that costs that much is not great for playing games. On the other hand a real gaming PC may have a video card alone more expensive than the whole console."
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6992k4 | What is the difference between an engineer and a scientist? | Engineering | explainlikeimfive | {
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"The line is a little blurry. Generally a scientist is someone who performs and publishes research, and engineers are the ones who apply that research to build things and create new technology. But there lots of engineers with PhD's who perform their own research. I consider engineers to be \"applied scientists\".",
"Engineers apply the results of science. A scientist's role is to develop knowledge, and an engineer's to use it. These can overlap, but which one is a person's *primary* responsibility is usually relatively clear.",
"Scientists figure out how things work. Engineers apply this knowledge into real world applications. Example: A scientist figured out that electricity can be used to convey information from one point to another. An engineer then designed the circuit board based on this observation.",
"Scientists apply specific methods to try to figure out how the universe works. Engineers apply what scientists have discovered about the universe to solve problems. In practice, there is often overlap so that individual people work as both scientists and engineers, frequently at the same time."
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69dfrg | One day they're there and the other day gone after construction! How on earth are cranes made!?? | Engineering | explainlikeimfive | {
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"I presume you're talking about tower cranes - the type with the tall metal lattice tower? They actually build themselves. The very first thing that's done is that the bottom section of the tower is put in and, on top of that they put a special section of the tower that can move up and down, before plonking the top bit of the crane on top of that. To do this, they use a mobile crane, but that's only good for the bottom, as mobile cranes generally aren't as tall as tower cranes can be. So, once they've built a little tiny tower crane, the special tower section that I mentioned jacks itself up, leaving a space where a new section of lattice tower can be slotted in. The tower crane itself lifts up the new section to where it's needed. Once this new section is bolted in, the whole thing happens again - the top parts of the crane are lifted up on the movable section at the top, a new bit is slotted in, and so on... Edit: And here's a video, which shows it quite nicely URL_0"
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69e5ie | How come water will break your phone, and how do companies make the phone completely water proof? | Engineering | explainlikeimfive | {
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"Phones work by electricity. Water conducts electricity, which means the electricity can get into the wrong places, and in the wrong amounts! To make something waterproof can be tricky, but the basic principle isn't very complicated. You just need to close all of the gaps. This might mean putting a rubber gasket around the edges of the device, and providing rubber plugs for the ports.",
"Think of the circuit board inside your phone as a complex system of roads, streets,and highways. In your car there are lines on the road to say where to go, stop signs, traffic lights, and such. Water conducts electricity which are the cars in this metaphor. Now imagine what it would be like if there were no roads everywhere, just a giant sheet of pavement spanning entire cities and you just go wherever you feel like going. Boom suddenly a whole bunch of accidents are occurring and cars are going everywhere and exploding. That's why :)"
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69e6op | How do combination lock manufacturing companies (ex. Master Lock, Dudley, etc...) choose the combination numbers of each lock? | I'm at a high school where we all have the same lock so I'm wondering if they would/could ever double up and how the combinations are generated. | Engineering | explainlikeimfive | {
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"The combinations in a Master lock can't be changed. There are different pieces of metal for each number (actually 12 different choices for each of the 3 numbers). that's not very many possible combinations, so there is a good chance that two locks have the same combination. [This fine site]( URL_0 ) explains the mechanical insides pretty well. You can do better, from a security perspective, with a lock where you set the combination. There are lots of old S & G padlocks on eBay."
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69exkm | What are the differences between engines with same engine power(hp) but different volumes(cc). | What are advantages or disadvantages of 2200cc 150kw engine compared to 3000cc 150kw engine? Both diesel engines. | Engineering | explainlikeimfive | {
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"An engine that is larger for a given horsepower will *usually* be less extremely tuned, and will usually last longer. As much as it is fun to engage in Jeremy Clarkson style bashing of old American engines that make 120 horsepower out of five liters, it's not beyond reason to tune those same engines to make 400-500+ horsepower. They also tend to last longer when they aren't being stressed. 200 thousand miles isn't difficult to achieve on those old engines.",
"Engine cc refers to an area of volume, the raw size that a particular part of the engine is. HP refers to how much actual power that engine can produce. So if an engine is built badly but is huge, it may have lower hp than an engine that is built well but is smaller. In the 60s there were 8000 cc engines being built that were so inefficient, a modern 1600cc engine actually has more pulling power than it. GENERALLY .. its easier for engineers to get a higher HP, the larger that bit of an engine described in CC is."
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69frsd | How do car key-fobs work and why do we not see machines that can mass-spoof unlock signals like computer passwords? | Engineering | explainlikeimfive | {
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"text": [
"The fob sends a very large number very slowly. It takes about 25ms to send the number, so that's only 40 per second, max. Most cars require 50ms of no signal to restart their receivers. That's about 13 guesses per second. It takes a long darn time to send a trillion numbers at 13 guesses per second.",
"modern keyfobs use a rolling code with trillions of possible combinations. even if you stood in a huge parking garage and rolled through codes at light speed youd take centuries to get even 1 car to respond. and then what? congratulations, you've unlocked the door, you could have managed that with a rock... there are easier ways anyway, sniff out a wireless key transmission and relay it outside to the owners car. with this method you can even start the car and drive it away."
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69hm2g | Why do some toilet seats fall down instead of staying up? | I don't want to urinate on the seat. But it seems like they want it, and it's difficult to hold it the whole time. | Engineering | explainlikeimfive | {
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"I’ve always figured it was due to design and/or installation errors leading the center of balance for the lifted lid to be too far “forward” (bowl side) resulting it them falling over. I very much doubt it’s by design to have them “auto-shut”, if that’s what you’re asking."
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69lp2y | Why most motorcycles don't come with a reverse gear, like they do in cars? | Engineering | explainlikeimfive | {
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"text": [
"It's very difficult to actually ride backwards. The front fork of basically all bikes has an angle and \"rake\", which assist in keeping it going straight and make it easy to correct balance without falling over. This doesn't work in reverse very well, as the rear wheel is fixed. You can train yourself to ride backwards, but it's very difficult. And it would be dangerous on a motorcycle, and fairly pointless since motorcycles have a tight turning radius plus you can simply push it backwards with your feet. Some heavy touring bikes do have a reverse gear, to assist in getting out of parking spaces only. It uses the starter motor, not the engine, to give it a slow push.",
"With a car, if you want to go backward, you have to put it into a special gear because it's too heavy to scoot, like you can do with a motorcycle. Also, you can easily turn a motorcycle around but a car has a very high turn radius."
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69r7n6 | What is the difference between a rechargeable battery and a capacitor? | Engineering | explainlikeimfive | {
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"A battery stores energy to be released relatively slowly and stored for extended periods of time. A capacitor is exactly the opposite. It stores energy for short periods of time to be released quickly.",
"Batteries store energy with chemicals to release the energy with chemical reactions when there is a load connected. Capacitors are electrical devices made from dielectric (read: partially insulating) that can store electricity temporarily in the form of static electricity because of the insulation and the charge that was previously applied to the capacitor.",
"Batteries store energy in chemicals. See: electrochemistry. Capacitors store the energy in a electric field. See: electrostatics.",
"The \"chemistry vs physics\" difference that others have mentioned leads to a practical difference: as a capacitor discharges, its voltage drops in proportion to the amount of charge that's been lost. In a battery, the voltage remains (fairly) constant."
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69tx3w | What determines which cities appear on highway signs? | It seems almost random which cities are listed on interstate signs. Of course Boston should show up on interstate signs that pass through the state's capital, but who decides what lesser cities are listed alongside it? | Engineering | explainlikeimfive | {
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"These are called [control cities]( URL_0 ). > The control cities on the Interstate Highway network are selected by the states and contained in the \"List of Control Cities for Use in Guide Signs on Interstate Highways,\" published and available from American Association of State Highway and Transportation Officials.[3] Control cities on other US roads are often selected on the basis of general principles, as opposed to specific lists of towns. > > US federal lists are in practice not always followed[citation needed]. This may be the result of towns having gained importance since the list was last updated or in order to have local (intrastate) interests prevail over towns elsewhere. On the other hand, there are also instances where intrastate control cities have been left out so that long-distance focal points could be added. There are also instances where the name of another state has prevailed over the official control city, e.g. the signs in Boston heading to the state of Maine. > > On the US federal list, control cities have often been selected by virtue of being located close to an intersection of two US-interstates. This has resulted in a number of very minor localities having control city status"
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69uzg7 | How does gyroscopic stability work on a tanks main gun. | I saw a video yesterday of a tank holding a beer on the end of it's main gun while going over bumps and the beer didn't budge. I was wondering what kind of technology would be necessary for this to be possible. | Engineering | explainlikeimfive | {
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"Gyroscopic sensors detect movement of the tank in 3 dimensions. Computers convert that information into movement of the tank barrel, and signal hydraulic systems to move the gun in the opposite direction. The system can't compensate for linear movement (the straight up and down component, as opposed to rotation), so it's possible that there was some sort of trickery involved. The _effect_ is valid, the tank can fire accurately while moving to evade return fire."
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69z4ry | What determines a car's distinctive engine pitch? | For example, how come the distinctive sound of a Mustang's V8 differs from the V8 of a Range Rover? Or even the V12 of a Ferrari? | Engineering | explainlikeimfive | {
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"A number of factors determine actual pitch and harmonics: RPM, the number of cylinders, engine and exhaust layout. RPM: This one's pretty simple, it's like playing two different keys on a piano. The V6 in an F1 car at 16,000rpm will sound roughly 2 octaves higher than your car with a V6 at 4,000rpm. Number of Cylinders: More cylinders means more explosions per second (higher pitch) being pushed out the tailpipe. That V12 Ferrari has a lot more cylinders firing per revolution at idle, then my 4 cylinder does. Layout: Depending on the type of engine, the layout of the cylinders will dictate different needs for the exhaust system. Essential, the air being moved away from the cylinders starts in individual pipes. These pipes need to join up in some way into one pipe and go out the exhaust. Depending on how the firing of the cylinders is timed, and how long each pipe is before they all join up, means that you might not be hearing the firing of each cylinder as it really happens. [This video]( URL_0 ) does a good job of showing how the lengths of pipes can cause the pulses coming down the exhaust to stack unevenly. Making the intervals between firings to appear uneven. Outside of those factors that really affect pitch, the size, weight, and materials of all the components in the engine and exhaust have their own resonant frequencies. Just like instruments, wood and metal and strings all have their own unique qualities because their materials have different natural properties. edit: LOL"
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6a3hq5 | why does putting my headphones in the wrong ears make the mix sound like it has less bass? | Ive always noticed that if I put my headphones in/on backwards it makes it sound like the music has more treble in the mix. Why does that happen? | Engineering | explainlikeimfive | {
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"text": [
"If you're talking about \"ear\" phones, manufacturers generally mold each bud to fit in a specific L or R auditory canal. If you put them on the wrong way, they do not seal the canal, allowing the pressure waves to travel out instead of to your drum."
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6a3p3w | 'Desalination' and the difficulties associated with performing it on a large scale? | Thank you. | Engineering | explainlikeimfive | {
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"text": [
"[This diagram shows the desalination process done at one of the plants in Singapore]( URL_0 ) [Website Source]( URL_1 ) Hope that helps!"
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6a6uqu | In a manual car, is it wrong to use neutral to get up to speed when descending hills? | Engineering | explainlikeimfive | {
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"No, not necessarily \"wrong\" per se, but perhaps against practice. People will say if you are in neutral you will have to use your breaks more, which technically is true, however I think it's negligible. The only thing I would worry about is if it was a large hill, and you were coasting for a while, and then went to shift into a gear, unless you know your car really well, you could shift a gear too high or low, which could cause your engine to redline or struggle. In the end, its your car bro; you do you.",
"First off, I don't think using your engine to \"save your breaks\" is a great idea. Brakes are made to be used and replaced, cheaply. Why would one opt to put additional wear on their engine internals? But speaking for myself, I like to stay in gear in case I need to accelerate or anything. Furthermore, I find it that when a car in neutral has accelerated and the engine is revving up on its own a little bit it's a tad more sloppy when you do finally schlap it into gear. I don't see an issue with descending in neutral though, not enough to make it the wrong thing to do at least."
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6aaar7 | How do solar panels work? | Engineering | explainlikeimfive | {
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"Think of electrons like kids at a waterslide. The flow of kids down the slide is like electrons moving through a wire. Now imagine that there is no ladder to the slide and only way to get to the top of the slide is for a big guy to throw them up one by one. They land on the slide instead of falling back onto the ground. The sunlight takes the role of the big guy. Each photon of light hits an individual electron, jumping it up. Instead of the electron falling back to where it was, it hits the other side of the solar cell and makes its way back via a wire, giving you flowing electricity.",
"A common kind of solar panel is the photovoltaic cell, that is made of an n-type semiconductor and p-type semiconductor. When sunlight hits the n-type semiconductor, electrons pretty much jump out of it and try to make their way to the p-type semiconductor. However, there's a buildup of charge between the semiconductors that stops the electrons from moving directly across; instead, the electrons have to travel through an external circuit, which is how we get a current from it. These solar panels are good for anything that uses electricity. Solar heating panels are also a kind of solar panel, and they basically just heat water by shining light on it. This is pretty much only good as a water heater.",
"Another question, (I live in a 3rd world country so I don't know alot about it right now) How useful and efficient is it now and how efficient can it get in the future? (Compared to fuel)"
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6ad4o1 | Where does electricity come from | My four year old asked me where electricity comes from. I explained from power plants that generate it in different ways and they send it to our house via electrical lines. I also explained that there are different ways that we generate electricity (solar, hydro, coal, etc) but I couldn't simply explain how electricity gets created from heating water to electricity. Anyone able to boil that down? (pun intended) | Engineering | explainlikeimfive | {
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"The idea behind (most) modern power plants is you heat up water so it turns into steam. That steam rises through turbines who spin magnets in in an electrical field like the inside of a roll of copper wire. That creates the electrical current.",
"Some people have done a good job of this but left out a couple important parts. A turbine is used to spin a rotor (think of something like a long axle) that is connected to the generator which actually spins the magnets in a copper field which creates the electricity. Historically these turbines have been mostly steam powered, where a power producer will burn something like coal, trash, or even byproducts of oil; use the heat from the burning to create steam. The steam runs through a series of blades attached to the rotor which spins the generator Present day, a lot electricity is created as part of a combined cycle. A combined cycle starts with a combustion turbine (oftentimes Natural Gas). A combustion turbine will take a fuel (NG) and compress it, burn it, and use the resultant heat escaping to push blades on a rotor, which is attached to a generator. The exhaust from 1-3 natural gas turbines then heats up steam which will power a steam turbine. *Apolitical commentary coming* This is largely why coal jobs are disappearing and likely won't ever come back. Natural Gas is easier/cheaper to extract from the ground, burns much more cleanly, and creates energy more efficiently due to the combined cycle. *Fun trivia* Everyone in the power industry pronounces the word 'turbine' as (ter-bihn) not (ter-bine). The word comes from the french word turbinem (ter-bihn-um), which meant swirling or spinning water, and eventually the /m/ fell off, leaving the word we use today.",
"The hot water produces steam, which spins a turbine. This turbine is essentially identical to the alternator in a car, albeit at a much larger scale. It contains a stator, which is a stationary set of electrical conductors wound in tight coils around an iron core; and a rotor; a magnet that spins around the stator. By spinning the magnet around the coil, electricity is generated via the law of electromagnetic induction. In short, the moving magnetic field induces electrical current in the coil, which creates AC power.",
"_Everything_ has electrons. \"Electricity\" is what happens when we force those electrons to _move_ by literally pushing them with magnets. So for your literal 5 year old, I'd suggest going to a pet store and looking at one of those trapped-ball cat toys. The ball is always there, but it just sits there until someone pushes it along. So a generator is a loop (well, many loops) of wire and a strong magnet (well many magnets). By moving the wire or the magnet (depending on the design, in modern generators we tend to move the wire loops) the magnet pushes the electrons in the wire. In \"AC\" -- \"Alternating Current\" -- the pushing is back-and-forth. The direction of the push alternates, because the magnets and loops are arranged to go from magnetic-north (which pushes in one direction) to magnetic-south (which pushes in the other) and then back again. Now since magnets push electrons, it turns out that electrons push back on magnets. This is that whole \"equal and opposite forces\" thing. So the electricity in a loop of wire from the power plant to my house and back is like a bicycle chain of electrons. Each electron pushes its neighbor just like the links of the chain move each other. So you move the pedals and the tire turns. (It's actually like having that captured ball toy being full of balls since only \"pushing\" happens, but from here on out I'll be using the chain to stand in for the crowded ball toy.) A motor in your house is like a generator. So much like a generator that in many uses they are interchangeable. When the power plant turns its generator the chain-of-electrons moves the motor in your house. But if that motor doesn't want to turn it pushes back and factually tries to slow the generator at the power plant. So like the bicycle chain, it's harder to pedal up hill because the wheel pushes back on the chain which pushes back on the pedals which makes your legs have to work harder. Same deal with generators. So who or what is doing the pedaling? Well we use falling water in dams; or we boil water with coal, oil, gas, or nuclear heat; or we use wind pushing against blades in windmills. As long as something is on the other end turning the pedals the electricity flows. This is also why turning things off saves energy. When things are off they are not pushing back, so its easier to turn the generator, which in turn means it takes less water, heat, or wind to keep things running. So one last side-thing about solar... Clearly there is no magnet nor is there anything spinning around, so WTF amirite? You know that thing when you are on a bike and you push the pedal a little then ratchet back then push the pedal again? You never turn the pedals all the way around but you keep adding just a little force then click back then add a little force? That's how solar panels work. Photons (packets of light) are very like electrons. They can push electrons around and create momentary \"electromagnetic\" forces as they arrive. And diodes and such can act like ratchets, where they only let the electrons move in one direction. Solar panels are just giant diodes. The electrons can only easily move from the front (sun-facing) side to the back side. The photons from the sun shove the electrons to the back of the panel. The only way they can get back to the front is by going the long way around through the wire. This produces a single-direction, non-alternating current, called a \"direct current\" or \"DC\". Just like a battery produces DC. So the force of any one photon moving any one electron is tiny... so the panels are made quite large and they work best in strong light. Just massive numbers of tiny events ratcheting electrons along one at a time. In the end, electrons push and get pushed. You find something that can push, be it photons or steam or falling water. You give it something to push against, like a turbine. You hook that to a magnet/coil deal so that the pushing translates from physical shove to electrical shove, and you pipe that shove into your house by using wires where it can shove motors. Or shove photons (LEDs) directly. Or shove its way through difficult wires, causing heat because the electrons are bumping into things (your electric fire, stove, etc). Or shove through thin wires that are also resisting the shove creating so much heat that that everything glows white hot (old fashioned light bulbs)."
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6agt69 | what's the difference between a car that runs on diesel and another that runs on gasoline? | Engineering | explainlikeimfive | {
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"Diesel fuel engines use compression to create heat and pressure, which causes the fuel to \"autoignite.\" Gas engines use a spark. Octane is a combustible liquid that gasoline is compared to. Octane is resistant to igniting under pressure, and the higher resistance to igniting under pressure gasoline has, the higher the \"octane rating.\" Gas is bought at the pump with three different choices of octane rating. \"100 octane gas\" is gasoline that has the same resistance to igniting under pressure as pure octane. Cetane, on the other hand, is what diesel is compared to. Cetane ignites very easily under pressure. Diesel only comes from a pump in one cetane rating, (I believe) it's 27. Diesel fuel can preignite in a gas engine, causing it to \"knock.\" (Pressure moving against the direction of the engine, breaking shit) while in a diesel engine, gasoline will not burn at all. Further, gasoline engines use (nowadays) fuel injection to spray for into the intake manifold, where the air and fuel mix before entering the engine, vs. a diesel engine which injects fuel at the height of compression. That's because, if diesel engines had a fuel system like gasoline engines do, the diesel fuel would ignite before the height of compression, and the engine would (at best) backfire and turn off, or at worst, knock hard and tear itself apart. Gasoline, on the other hand, will not ignite without a spark due to its high octane rating. Diesel fuel does have an octane rating, just as gas has a cetane rating, but they are both respectively very low."
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6ajvml | Why do most bipedal robots always keep their knees bent a bit when standing? | See for example the robots in [this]( URL_0 ) and [this]( URL_1 ). As humans, we don't stand like that very often because it would be tiring since we would have to be tensing muscles the whole time, Instead we can rely on ligaments/tendons to support us. I suppose a robot doesn't have to use energy to keep muscles tensed for that knees-bent pose, but what benefit does it bring to stay in that position and never get truly upright? | Engineering | explainlikeimfive | {
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"I'm still an industrial electronics student but if I had to guess I would say that it is because when engineers program robots they are given a \"home position\" that the robot stays in. In this case the home position is the one that best allows the robot to react to varying conditions. Like if the robot were to step into a hole and the knees were locked straight it would have trouble being able to step down into the hole because that joint can't rotate any further. But if the knee is in the middle of its rotation then it can straighten to step down into the hole or rotate further to step up onto something. Basically it's the position that allows a robot to do as much as possible and as far efficiency goes we are still just getting the kinks worked out of getting a robot walking. So it's not the most efficient way to stand but it's the easiest.",
"Has to do with the way they walk. It's called Zero-Moment-Point movement. Basically they position their legs, so that they do not produce any moment in horizontal direction, thus the robot cannot flip over. The drawback of the calculation behind this is that you cannot allow two axles to be co linear because then you have a singularity that you cannot calculate, because you then have two axles that could cancel out a momentum but you cannot chose which. The easiest solution is to forbid the joint to be stretched. Edit: To put it more ELI5: IF you have two axles that are in line the robot brain cannot chose which one should move in what direction to make the next step since they have the same direction. So they forbid them to be in line.",
"Because they are trying to model them off humans, because our bodies have adapted to walking on two legs and the closer we get to mimicking that, the more functional they will be. As humans we actually do stand with our knees slightly bent. Try standing in one place with your knees locked. It gets very tiring very fast, and if you are in a very hot environment or thick clothing, you can actually pass out because of it. I don't know the exact reasoning but it was what they always told us in military school during stationary reward parades. And I saw many a person drop like a fly because they didn't listen and locked their knees."
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6amgal | What it means to rebuild an engine. | Engineering | explainlikeimfive | {
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"Disconnect everything including all of the hoses, tubes and wires. Remove it from the machine or vehicle. Take it apart, removing all moving parts. Clean out the cylinders and any other component that might be clogged or gummed up. Replace any part that is worn or broken. Put it all back together.",
"It means disassembling it, replacing all worn parts, gaskets, re-honing cylinders, upgrading parts (sometimes, it's the easiest time to do it) for performance, etc, and reassembling it into an essentially \"new\" engine."
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6amx44 | Why do we not harness the energy produced from workout equipment in a gym? Is that not the same as a wind turbine? | Engineering | explainlikeimfive | {
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"A professional cyclist can produce about 400W of power with his legs during a stage in a race (like the Tour de France.) Sprinters can hit about 2000W during a short period of time. If you imagine a cyclist on the stationary bike at the gym, he can maybe produce 300W. If he rides for an hour, he is producing 0.3 kWhr of power. In my province, that's less than 2 cents worth of electricity.",
"Because then I'm not doing it for me, now I want to get paid for my service that I'm providing.",
"Mainly because the amount of energy is so small. You only produce around 200 Watts of energy while exercising vigorously, which means you'd have to work our for five whole hours just to produce 10 cents to 25 cents worth of electricity.",
"[We do]( URL_0 ) There are many places that do this, but the problem is the rather large upfront cost.",
"I actually thought this was a genius idea as a kid, funnily enough! As someone who's worked with a bunch of electrical engineers, there's a reason this hasn't been invented yet, and the reason why most arm-chair energy production concepts haven't been applied: the law of exergy efficiency. As others have pointed out, we exert quite a pathetic amount of energy during a workout. Not only that, but a certain amount of energy is lost during all energy conversions (in this case, kinetic to electrical). So, not only is a very low amount of usable energy expended, but an even lessor amount of electrical energy would be captured and stored. Then there's the massive expenditure in building gym equipment that converts kinetic energy to electrical and then store said energy into a central grid. There's a zillion different ways in which we can convert and store everyday energy expenditure that's otherwise lost, hence why the exergy efficiency formula was developed for thermodynamics to tell engineer's \"hey, this shit has a poor expenditure-to-return ratio, come up with something else\".",
"The energy gained from the equipment in the gym wouldn't be worth the equipment cost. Think about how much gym equipment already costs, and how much of it is unused even at peak hours.",
"If we were to assume that equipment was under 100% utilization with athletes working at full output, with 100% efficiency, we still could not expect more than about $0.05 per hour per machine in electricity output. Real numbers are likely to be a whole lot less than that, and would make the return on investment terrible."
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6andnw | How does a gaming AI enemy work? How does it know to attack you or your friend in co-op? | I know there is such a thing as Aggro or some technical term like that. But in co-op it should be more than that, right? AI enemies do their own calculation right? So I want to know how do they work. Before I get someone saying "Google it!", I rather ask the community to learn different live opinions. Thanks y'all in advance for your comments. | Engineering | explainlikeimfive | {
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"It really depends on the game. Computers are dumb. They can't make decisions on their own, and can only follow instructions that were given to them. A very simple AI in a shooter might have instructions that say: If the player is visible and in range, shoot at the player. Otherwise, walk along a patrol route. This is a \"conditional statement.\" The computer checks to see if the condition (player is in range) is true. If it is, an action (shoot at the player) is performed. If it isn't, another action (walk) occurs. You can add complexity by expanding the set of conditions that the AI reacts to, and providing actions. For example: If health is below 30%, find cover. Otherwise, if an enemy is visible and in range, shoot at the enemy. Otherwise, if the player is visible and out of range, run toward the player. Otherwise, if a nearby teammate is in combat, run toward the teammate. Otherwise, if a sound is heard, move toward the source of the sound. Otherwise, walk along a patrol route. The conditions are checked in order, and if any one of them is true, that behavior happens and the rest of the conditions are ignored. Conditions might also be nested inside of each other. You can add even further complexity by randomizing the behavior. Maybe each enemy has a \"bravery\" attribute that affects how much health they have to lose before seeking cover. Each enemy can also have its own method of selecting a target among multiple options. This can be either random or deterministic. A lot of MMOs are based on a \"threat\" mechanic, which calculates which player the enemy perceives as most dangerous. Others might attack whichever player is nearest. But finding a target is just another set of conditions. The more conditions you give an AI, the more complex its behavior can become."
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6antpf | If the charger is plugged in with the switch on, does it still take up power even if nothing is connected to it? | For example, leaving my phone charger switched on at all times in the office, despite only charging my phone a few hours each day. | Engineering | explainlikeimfive | {
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"Yes it does. The charger isn't off, it's still draining power from the wall outlet. Part of the voltage transformer is still active. The USB connection sensor circuit is still active.",
"After it has been plugged in for a while (hours), hold it in your hand. Is it warm? If it is then its drawing power, if it isn't then it isn't drawing power (or to such a small degree that it doesn't matter). Conservation of energy dictates that if you are using energy you are getting something for it in return. If there isn't a light, a movement, a sound, etc. the only thing left (and in fact a necessary by-product of producing any of those other things) is heat. So if its warm its drawing power, if its cold it isn't."
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6aozei | what makes an airplane "lightning proof?" | Engineering | explainlikeimfive | {
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"Airplanes are almost all metal on the outside. They are hit by lightning all the time, but the current flows around the plane's skin and down to the ground. Some systems kick off, but the pilots switch them on again and make a note in the logbook for maintenance to check for damage. No big deal, but not \"lightning proof\".",
"I'm not entirely certain if *all* aircraft have these, but many have \"Static dischargers\", small (relative to the aircraft) horizontal metal antennas scattered around the plane (usually on the wings) that the lightning will pass through because it's the path of least resistance. The frame of the airplane is also designed in such a way there's very little metal (from the outside \"shell\") contacting the parts on the inside. When a plane is hit by lightning usually it travels down the frame of the aircraft and out the static dischargers on the wings/tail (Path of least resistance), doing minimal to no damage to the aircraft itself, aside from usually destroying the discharger it left on. Now, having said that, **this isn't actually the function of the static dischargers**, it's actually (just as the name sounds) to discharge static from in/around the aircraft so the radio and navigation systems work correctly/more accurately. But, because of the nature of them, they tend to be where lightning also leaves the aircraft (and in turn, this usually damages the discharger). I suppose if you put aside the dischargers (I'm probably getting way too specific anyway), basically the big metal frame of the aircraft is usually in minimal direct-contact with the electronics inside, and thus as the lightning leaves through the path of least resistance it tends to avoid the electronics, and then usually leaves out a mounted antenna, light (rarely), or discharger and then back outside into the humid air to find its way to the ground. EDIT: Clarified it a bit.",
"Surprised nobody has mentioned they essentially operate as a giant Faraday cage. The same reason you are safer in a car during lightning storm (no, it's not that the tires are rubber).",
"Another thing to help with a lightning strike is that composite parts (fiberglass/carbon fiber) have a conductive coating under the paint to spread electricity through the panel. Lightning strikes happen all the time."
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6aripy | Why is it preferable to have a handmade car (e.g. Rolls Royce) than one made by robots, when robots are more precise than human hands? | Engineering | explainlikeimfive | {
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"I would say in short, rarity. These cars have low production numbers and variations can be made more frequently or tailored to each buyer. And at least based on their marketing, each car is unique, like a work of art. Factory cars by contrast offset the cost of the machinery and design through economy of scale. Everyone has the same thing. As with luxury cars in general, noone buys them for reliability, it only makes sense to own as long it's under warranty.",
"Humans are not robots Humans are social beings Before automation buyers wanted absolute perfection. Not because perfection was better but because it was rare. After automation buyers want hand craftsmanship. Not because hand craftsmanship is better but because it is rare. Rare things are better because they are more desirable (just from being rare/exclusive). Desire creates status, status is important to social beings.",
"Most of the answers in this thread cover different yet equally valid points, and certainly for the automotive industry they hold a lot of water. One thing I would like to point out is that \"handmade\" may not mean what you would assume. These days most of the time it's means that most of the assembly work is done by hand rather than robots. In modern luxury niche handed vehicles, the majority of what you see is production scale parts covered by hand with leather. Everything behind it will be made on a large injection moulding, milling, or casting scale. These days, \"handmade\" refers largely to the assembly method as opposed to the production method. It's there because as someone else mentioned, if you're making low volume high profit products it's hard to front the cash for big production systems, especially when you can use it as a selling point. If you can pay someone a low-medium hourly rate to assemble a car you can then sell for a higher price, why wouldn't you? Source: have worked for a number of years in the automotive world designing niche luxury (very fast) products.",
"I can give my 2 cents here. I'm a robotics engineer for automotive companies. Also, I've been to where some Rolls are built. Very skilled workers are much better than robots in certain areas. I'm saying better in the sense of quality. I'll use an example I'm familiar with. It's applying sealer to various seams of the car where metal comes together. If you open your hood or trunk you can probably see some a bead of sealer around the edges. They're applied everywhere almost and on a Rolls they have to be absolutely perfect. Robots can do this but they are used for speed and quantity. Compared to a skilled human the seams a robot applies are just ok. Humans have an instant feedback loop that robots do not. Many variables like humidity, changing viscosity of material, metal fit tolerances affect the quality of the seam. Humans can feel it, see it as it's happening and adjust their application on the fly. A robot is just going to lay it down the same no matter what.",
"Partly it's that some things cannot be done as well by robots as by a skilled person. Robots can make precise programmed movements, but they're less good at responding to their environment. When working with materials with natural variation like wood and leather, being able to use the individual pieces in the best way counts. Partly it's just that some buyers will pay a premium for something made in a more expensive way even if that more expensive way doesn't 'objectively' produce a better quality product. Work by a skilled person is valued in a way the output of a machine is not, and 'imperfections' can be seen instead as something that makes each individual car a little bit unique.",
"You can get much more customization with a handbuilt car than an automated car. Rolls Royce prides themselves on creating cars that match what the buyer wants. They can put custom star constellations in the roof. They can find the exact materials you want for your seat. They can do custom stitching. Automation works best when you have limited variations, because each variation requires the automation to be designed to handle it. So it works great and can deliver extremely tight tolerances over and over again, but you can't go outside the designed variations.",
"Robots are not more precise than a human. They're just more consistent. Engineering tolerances can be much tighter when something is hand built. On an automated line, the manufacturing tolerances are such that you can build a high volume of parts in the shortest amount of time possible while ensuring the least amount of fallout and downtime. Efficiency and cost trumps all. Design tolerances are relaxed to accommodate that throughput - and things like rattles and trim that doesn't fit just right is the result. The design philosophy behind a Rolls Royce is a bit different where manufacturing throughput and cost are not the primary design considerations.",
"I can't speak to that, but I can say that in my experience, hand made shoes are far superior and last longer than machine made ones (In the US there are only 2 sizable companies that do this Alden and Allen Edmunds). Additionally, you can have them re-soled when the bottoms wear out.",
"Robots are great at spot welding a frame together. However, they lack the finesse to install many of the interior parts. And when it comes to fitting doors, they're useless. Because metal expands & contacts during various stages of vehicle assembly, no two bodies are identical by the time the vehicle gets down the line to door fits. This must be done by human hands... and craftsmanship is key here. Source: I've worked in vehicle assembly for 23 years.",
"Engineering tolerances. Generally speaking, automated production produces things within tolerances- machines shift over time, actuators might be slightly imprecise, etc. But the cars are designed to work within those tolerances so there's little human intervention needed to ensure that you have a car that works. When it comes to hand made cars, you have human oversight at every point checking, double checking, and even triple checking each little detail to ensure that everything is exactly correct. Because humans are capable of being self correcting in ways that typical automated assembly machines are not, it is possible (and only really achievable on the very high end cars) to produce a hand made car that exceeds the build quality of an automatically assembled car. However, really, these differences are minute, and not worth considering to the majority of car buyers. What hand made cars gets you is a very expensive car, because you have to make back all those man hours spent getting everything perfect. What makes all those cars more desirable are two things: 1: These cars are constructed as luxury cars, they have many little features and engineering tricks packed in that the average car does not. 2: These cars are status symbols, owning one marks you out as someone who is elite, affluent, powerful. It is a statement of wealth.",
"ITT: a bunch of talk of robotics and engineering and shit. Real answer: if you're rich as fuck and can afford a Rolls-Royce, you're rich as fuck and can afford to take it to a service shop who knows how to service a Rolls-Royce. Because... if you own a Rolls-fuckin'-Royce, you don't take it to Midas for an oil change or a brake job. Because you're rich as fuck and you take your rich-ass car to a rich-ass shop so they can fondle your rich-ass balls and serve you rich-ass coffee while your rich-ass Rolls gets ITS rich-ass balls fondled. And rubbed with a diaper. You rich bastards.",
"When you want to sell something at a high price, you know most people won't be able to afford it, so putting money into designing a factory to produce it can seem like a waste of money in itself, unless you have enough people ready to buy it. You don't want a surplus of super expensive cars. If you want to make something truly special, something that maybe, not everyone will buy, something that even people with lots of money won't buy, you can't just build a factory for it. You'll end up using it only a few times a year, even if the result is perfect. Making a robot costs a LOT of money. You can source most parts from other major factories, but the custom parts, the parts that make your car special and unique, you will find the cheapest way to make it is by hand vs making a precision robot to do it perfectly over and over again. You don't make a robot unless you plan to make a lot of something with it. Toyota sells 10 million cars in a year. Rolls Royce sells 4000 a year and that's a \"new record.\" Most of the handmade cars have engines and big parts made in major automated factories, then they hand tune it themselves and make the charm of the car by hand. Body work. Engine and exhaust noise. Interior. Ride comfort. And now I'll share what was on my mind as I typed this: [A Review of the Alfa Romeo Disco Volante. Hand built by Touring in Milan.]( URL_0 ) **\"I'm not gonna say it's the best car in the world. It certainly isn't the nicest to drive. The brakes are spongey, you can see *nothing* out of the back, but...as a tool for making you feel special, really nothing gets close. Nothing at all.\"**",
"Because we petrolheads ( car enthusiasts) like to think, that when a car is handmade it has been given a soul. Yes it while breakdown sometimes, and yes you can't really get spare parts. But it has this sort of flare. It is like driving a Ferrari instead of a GTR. It doesn't matter if the GTR is faster and better in every way. You driving the Ferrari because it is Ferrari. It is quiet hard to explain something like this to someone who is not interested in cars, so this is probably the best explanation that I can give to you.",
"A different example where automation is less desirable: musical instruments. For the instruments that you buy in school, they were made primarily with machines (although a lot more human interaction than with cars). This makes the instrument affordable to amateurs. But for a professional, the instrument must be perfect and unique. The tone has to match their aesthetic, the instrument has to feel right to play, and it has to match with the people that the musician is playing with (like a Trumpet player in the opera would want a different horn than a jazz musician). Thus producing a series of identical instruments becomes undesirable simply because it's not fit for them. This is why a flute player will shell out $10k (sometimes) for a flute, or a violinist will pay $10k for their *bow*. Fun fact: the most expensive instrument ever sold was a Guarnieri violin for $3.9m",
"Cars off the line aren't built with high grade materials and do not go through the quality control that say, a Rolls Royce does. They get the bare minimum necessary for comfort and control so they can be flung out of the dealerships at a high rate of sale. Once it's sold the bog-standard of-the-line vehicle is nothing more than a slowly decaying corpse, waiting for you to buy the new, better version so it can be recycled through second hand buyers and auctions. Eventually landing in the hands of a collector 30 years down the line or ending up in a scrap pile. It's actually worse for some of the high end cars where once it reaches an unknown expiry date, nobody want to touch it. Shit, that didn't really answer your question. [tl;dr]( URL_0 ) Because the robot built vehicles often use lower grade materials than hand-built or higher end vehicles so they can be sold quicker with a reasonable price tag. They are for the masses to use and abuse.",
"It's not \"preferable\" thats just marketing working. It's a status symbol, it's not a better product just more expensive. You can compare it to the Iphone app that was only a sreen saver but it costs $999.",
"Same with anything handmade rather than assembly line. If someone is going to spend time making something by hand that could be made cheaper on an assembly line, chances are they're using higher quality materials. Assembly lines are more precise, but they don't really know when something goes wrong. A robot knows to screw a nut onto a bolt, but can't really tell if that nut is broken or whatnot. As to the car specifically, it's a lot about name brand too."
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6av9u0 | Why was the downtown portion of Los Angeles built so far from the pacific ocean water front in contrast to cities like San Diego or San Fransisco? | Engineering | explainlikeimfive | {
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"It's built on the banks of the Los Angeles River probably chose that site as it was the best to build. The river would have supplied the fledgling city with water and there may have been other reasons it's there maybe a convergence of wagon trails or something. Originally it was a Spanish settlement surrounded by other Spanish settlements (Santa Monica for example) which grew together over time and became \"incorporated\" into L.A. I don't know the specifics but the reason L.A. grew into the surroundings and kept it's name probably due to it being the biggest city in the area."
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6azoo3 | Why does using cruise control hurt your fuel economy? | Wouldn't staying at a consistent speed save fuel? | Engineering | explainlikeimfive | {
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"On a modern car, cruise control should be more economical. One of the problems with cruise control is that it can't see the road ahead. So, the car will change gears on sudden inclines or declines too late and will, therefore, use more fuel - because of inefficient gearing.",
"What saves fuel is not as much a matter if constant speed, but constant RPMs. Because it is rare to find a perfectly flat road, often the engine with have to change it's RPMs to maintain the constant speed. Higher RPMs will mean more fuel used.",
"Overall I think cruise control improves fuel economy for most vehicles and driving conditions. Human drivers tend to change speed and drive inconsistently, thereby reducing fuel economy. On an incline and decline however, cruise control may cost you some gas."
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6azs7o | Why do tires have whiskers? | Engineering | explainlikeimfive | {
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"Just looked it up. They're called 'vent spews.' When they fill the mold the tire is made in, they want to ensure there are no air bubbles or pockets in the tire, so they have small holes in the mold to allow the air to escape and some of the rubber gets spewed out of those holes, causing the little hairs/whiskers.",
"Do you mean the little bits sticking out on new tires? They are called risers and help the rubber fill the mold fully in the manufacturing process."
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6b1b6k | Why do. American cities lack the tram and subway systems that are prevalent in Europe? | Engineering | explainlikeimfive | {
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"**lots** of reasons The American rail system is focused on shipping freight which it does very well. Westward expansion took over a century which meant it was difficult to plan where new population centers would be cropping up in relation to the older cities. Lobbying and scheming by motor companies to make America based around the car, the documentary *Taken for a Ride* does a good job covering this. Many states are mostly rural areas which negates the usefulness of light rail somewhat. And finally I think that many people just prefer the freedom and independence afforded by using automobiles.",
"A very large number of American cities were built (or expanded into cities from being towns) after the invention of the Car. As such they were designed for people to use cars to navigate them, not for them to be walked on foot. When most people have and use cars there is very little that you can do to justify spending tax money on a public transit system, and very little motivation for a private company to provide it.",
"People use cars for pretty much any journey in the US. When I went there on business, I was asked by a colleague what I was doing for lunch and I said I'd probably pick up a sandwich from the supermarket which was less than 200 yards away across the office car park. He asked me how I was getting there and I said walking and he was having none of that insisted on driving me there, all 20 seconds of the journey. He seemed oblivious to the fact that it might be nice to get some fresh air. Another day I thought about visiting a store which was about three miles away. I do a lot of walking/hiking so it's a distance I walk regularly and I figured there'd be a route I could take to it and it would make a nice walk after being sat in an office all day. Not a chance in hell. I'd have to take a car to get there because of the road systems.",
"Mainly because those systems are only profitable in very densely populated areas, particularly when several very dense cities are located very close to each other. Most of the cities in the US just aren't as dense as European cities, and they tend to spread out more. Of course, the really dense American cities -- New York, Chicago, etc. -- do have subway systems.",
"There are a lot of factors listed here. One in cities like Houston, Texas is that it is massive and spread out. Houston is the 4th most populated city in the US and is a little larger than London at 1630 sq km, but has 25% of the population. People work far from where they live and have to commute all over the city. Light rail trains, buses, and high occupancy vehicle lanes cut down on the amount of vehicles on the road, but some drive distances/locations are not practical without allowing 2+ hours commute each way daily. Downtown Houston is only about 50 feet above sea level, so underground subway systems are not practical. Here is a quick guide to why the US sucks at public Transportation. Largest cities in the world ranked by land area in sqKm 1. NY metro 8683 2. Tokyo 6993 3. Chicago 5,498 4. Atlanta 5,083 5. Philadelphia 4,661 6. Boston 4,497 7. Los Angeles 4,320 8. Dallas/Fort Worth 3,644 9. Houston 3,355 10. Detroit 3,267 11. Washington DC 2,996 12. Miami 2,891 You have to get to 13th to find the 2nd city not in the US. We are the 3rd most populated country in the world but the 179th in population density. TLDR. We are really freaking big and spread out.",
"A lot of it really has to do when cities were developed. Major cities like SF, NY, Chicago have solid public transit. But once you get outside of the centers its a lot of open space. A good example would be San Jose California. 3rd largest city in California. More people than San Francisco. Public transit in San Jose isn't that great and the reality is you need a car. The reason why is it was mostly orchids and stuff like that 50 years ago. Then the tech boom hit and it grew rapidly. Well most people really weren't trying to move into cities so suburbs happened. Having a home with a yard was all part of that American dream.",
"The main plot of Who Framed Rodger Rabbit happened for real. URL_0 Although, my hometown city, San Diego, still had a really good public transit system (trolleys and buses) when I lived there, and I have been to and used public transit in Boston, New York, Chicago and Washington D.C., with little to no complaints, except for the smell, and sometimes the heat.",
"US was built in the car era. The government provided big subsidies for motorway systems, and happily drove them through downtown (European cities tend to have a ring road out beyond the suburbs). At the same time new zoning laws required plenty of parking for all those cars, prevented densification of existing suburbs (driving growth out with new suburbs) and city councils encouraged things like very wide roads (which are both convenient for drivers and difficult to cross for pedestrians). Houston is a good example of this. Built on a massive motorway network, development laws requiring huge plots even for single homes, minimum parking requirements, etc. The result of all this is US cities are overwhelming car centric. They can't support transit ridership the way European and Asian cities can without completely changing their geography.",
"Many cities did. It was systematically killed off and purchased by companies like General Motors to sell cars. There's a good documentary on it on YouTube. URL_0",
"Major cities have subway, bus, rail, and ferry systems where applicable - e.g., Boston, NYC, Chicago, LA, DC, etc. However there are *so many cities* in the US, and the US is massive. It does not make logistical sense to have subway systems in a city that does not have the same level of population as some of those cities. The cost of running the system has to be offset by the rider usage. If there aren't enough riders - like in many rural area cities, where most everyone has a car - it would not be cost effective.",
"How do American (from southern US) deal with the lack of consistency of their \"transport\" policies ? One one hand it seems they do everything to prevent you to take the car (toll road, expensive parking like $20 a day) but on the other hand there is no/few public transportation (I think I saw one Tram line in Dallas downtown, and one \"monorail\" in Jacksonville Downtown to name some place) and I don't talk about the lack of pedestrian sidewalks... I understand that most of the US cities are extended and have low density area which make hard to build efficient public transportation network. But If I compare (for example) to Paris suburb, in low density place you have a big parking near the urban train station which allow people to drive only the 2-5 km from their house to the station and avoid the traffic by taking the train.",
"Hey, do you know how European cities have these amazing, elaborate tram and subway systems in the first place? We had the \"opportunity\" to completely restructre our cities, oh, about 70 odd years ago. Turns out, when pretty much all your city is obliterated after WW2, and you have to rebuild anyways, there is a lot of free space where you can stick those transportation systems. Basically, you did the demolition for us. All the building and zoneing people had to do was clear the rubble and now we have parks in inner cities, zoos near the city centres, and relatively broad roadways. Plus, the space-consumeing railways. American cities were, for the most part, never destroyed that completely. You had to integrate public transport into living cities, which is almost impossible to do. Construction takes that much longer and is therefore that much more expensive because you can only do it in increments. Plus, shutting down certain parts of the city can become nigh-impossible because they are major traffic arteries. And there is the matter of aquiring the property you need to do construction on or underneath. If anyone gets wind of the project the prices are going to rocket sky high. Plus, what good is it to maintain old tram systems, even when they are profitable, when they're just going to be stuck in the traffic created by the cars? The more cars became prelevant, the less useful the tram becomes. Therefore, you need either subway systems (tunneling) or some sort of monorail / a bridge system to get your tram around. And those are way more expensive to build than tram systems on the ground. See also: The problem of aquiring the land in a city that is already completely owned by a hundred thousand different people. Even those support beams have to stand on somebody's land. And every time you attempt to do these project, the prices are going to go up. Plus, no-one is happy to live next to the subway, right? Those property prices are going to plummet because of noise polution. So you always have the big-construction-problem of groups forming to protest your new railway plans. Possibly to the point of stonewaling you and voting you out of office before you can make significant progress.",
"A related question for Americans: How do you do when you go out and grab a beer or ten? That is the #1 reason I'm so happy to have a good underground train system.",
"After reading many of these comments I am surprised no one mentioned oil industry lobbyists.",
"In addition to the other things mentioned here there's a general stigma surrounding public transport which causes a lack of support for creating public transport that would remove said stigma.",
"Trains are too expensive for what you get. (Both long distance and local). Trains in the city, your with a crowd of people in an enclose area and it cost around the same for a ride share app that is more convenient by dropping you off at a specific location. Long distance train fares are outrageous you might as well get an airline ticket.",
"Well our highway, interstates, and roads are basically everywhere and its easy to go with about 10 different ways to get there. Also big oil had a lot to do with it. Thats why trains are used a lot on the east coast and basically used purely for frieght out west despite the size of California and the benefits it would gain from a subway.",
"Wealth in European cities is concentrated in the city center, but wealth in American cities is concentrated in the suburbs. City metros & subways in Europe are much more profitable compared to America due to the higher traffic"
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