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jw1sy0 | How do boats float? I've never actually thought about it before I've always accepted it but cruise ships are made of thousands of tonnes of metal. Do boats have a max weight capacity before they sink or can they bare whatever they can fit? | Engineering | explainlikeimfive | {
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"They push water out of the way(displace) which raises the level of the rest of the body of water so the boat experiences an upwards force equal to the weight of the water it has pushed out of the way. If you make the boat heavier, it will sit a bit lower in the water causing it to push more water out of the way so it stays afloat. As long as the average density of the boat is less than the density of water it will float. Consider something big like an Oasis Class cruise ship. Its 47 meters wide at the waterline and 360 meters long overall, but a lot of that pointy bow adds to length and not displacement so lets assume a foot print of 300 meters x 50 meters for easy math. How much weight do you need to put on the boat to lower it by 1 cm? Well 300 meters x 50 meters x 1 cm is 150 m^3, so you'd need to add about 150 tons onto the ship just to push it 1 cm deeper into the water. You can stake weight onto the boat until one of two things happens. Either you get to the first opening of the ship and it lets water pour in, or your ship becomes too unstable and goes for a barrel roll. Filling the air portions of the boat with water causes it to sink because it raises the average density of the boat causing it to sit deeper and deeper and deeper until it hits the bottom or water stops coming in.",
"Go to your kitchen sink. Fill it 3/4 with water. Get a bowl. put the bowl in the water so that it floats. Now... push down on the bowl. Feel the force increase? The more water you displace the more that pressure upwards increases. Water is really, really, heavy. So long as more weight of water is displaced than what is displacing it you will float.",
"Boats are filled with air and the combined mass of air and ships structure is less than the water so the mass displaces some of the water and floats on top as in Archimedes principle. - URL_0",
"[Steve Spangler Science]( URL_0 ) has a vid on buoyancy using bowling balls that explains it pretty well. How can you tell if an ant is male or female? Put it water, if it floats it’s boy-ant.",
"Low density floats on higher density If two volumes are the same but one has more mass, the bigger mass has higher density. When an object is placed in water it displaces the same volume as the object. If said object weighs less than the water displaced it will float. If it weighs more it sinks For example take a sealed pop bottle. When empty it floats, when full it sinks. Both bottles displace the same amount of water but the full bottle weighs more than the displaced water and so sinks",
"Two reasons: the buoyant force on the boat, and the air inside of the boat. When a boat is in water, gravity pushes it down, but the displacement of water causes a buoyant force that pushes up on the boat. Additionally, the air inside of the boat is less dense than the water outside, allowing it to reach an equilibrium point.",
"Things float because they weigh less than the water they displace. Cruise ships are very heavy, but they are very very big! If you had a big blob of water the size of a cruise ship, the water would weigh even more than the ship. Water is pretty heavy, and although a cruise ship is made of a lot of very heavy metal, it also has a lot of air inside it. The air doesn't weigh much, so overall, the ship is lighter than the water. If you crammed a lot of heavy stuff onto the ship, so that the ship was the same size, but heavier, then yeah, you could make it so heavy that it weighs more than the water and it can't float anymore. If you think about a ship like the Titanic sinking, that's because a hole let water into the ship. Some of the lightweight air in the ship got replaced with water, making the ship heavier, so it sank."
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jwqcpl | Can someone explain Square Cube Law and how would applying it to HVAC/Heater units save electricity? | Engineering | explainlikeimfive | {
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"Cube square law is like, if you have a square and then make it twice as long you have twice as much space, if you make it twice as wide you have twice as much space, but if you make the box twice as long and wide (make it twice as big entirely) that means you have 4x as much space in the box, not 2x. It's saying if you spread out an area the amount you need to use to fill it grows really fast. So a room that is twice as big has 4 times as much air in it."
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jwrbyh | Its said that cars are "weaker" because they're now made from a softer material proper to receive impact, thus providing safety to the driver. How will safety work with cybertruck's 30x 'ultrahard' stainless steel when crashing? | Engineering | explainlikeimfive | {
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"Hard is not the same as tough is not the same as strong. Cybertruck's stainless steel body panels are hard; they're probably also tough, although that's usually not very relevant for body panels. They're not any stronger than they need to be though (since that's what drives weight), so their crash behavior shouldn't be meaingingfully different. Hard = how easy it is to scratch. This is obviously really relevant for vehicle body panels, we want them to stay looking nice, harder materials are harder to scratch and stay good looking for longer. Tough = how easy it is for a crack to grow. Body panels don't usually crack so this isn't a big deal. It's a huge deal for fatigue-critical structure (stuff that goes through a lot of stress cycles) but that's also not usually a big deal for body panels, they're mostly decorative and not carrying nearly as much load as the chassis. Strong = how much stress it can carry without yielding (permanent deformation). Cybertruck doesn't need to be 30x stronger...it might be 1 or 2x stronger because of the extra battery weight, but nowhere near 30x. That would just be wasted weight, which drives down range and drives up costs, so there's no reason to do that.",
"There is probably a difference between the stuff and design used as the energy absorbent crash structure versus the internal frame that has to hold the load of the vehicle. You can absolutely make crash absorbent structures even out of very \"hard\" material - it is more about the shape than the materials used. Nonetheless, it would seem intelligent to only use the very strong and expensive material for load bearing internal structures and not the \"outer\" part of the vehicle.",
"Contrary to popular belief, modern cars are WAY safer than decades-old cars. Modern cars have stronger frames and stronger internal occupant protection cages, plus crumple zones that give way and safely absorb energy upon impact. Older cars have heavier external sheet metal, but their occupant compartments are far more easily compromised in the event of a collision and they are far less effective at safely dissipating energy bc they lack crumple zones. For anecdotal proof, ask an extrication specialist (think jaws of life) who regularly has to cut into the occupant compartments of crashed vehicles to remove injured or dead people. They’ll tell you that cutting into older cars is way easier bc the steel is softer. For a crash test, see URL_0 .",
"When a car hits something, it's coming to a very sudden stop and all that energy has to go somewhere. In older vehicles made mostly from steel, that energy usually ended up going into the passengers and cargo, which would cause serious injury. Gradually, cars began to be designed to crumple on impact instead, so the car would absorb most of the energy and the passengers would be less likely to get seriously hurt. I don't know how the Cybertruck is constructed but crumpling is only one of the possible ways to get the car to absorb the impact energy. It is possible to use a sturdier material while still achieving the same goal through different physics.",
"Rigid is dangerous, basically what you are interested in is a deceleration force (basically g force) if you stop from 30 MPH in 1/1000th of a second your body is subjected to a huge deceleration force and it can kill you if you have the same impact over 1 second then you are likely to survive. The crumple zone of the other vehicle really isn't what is saving your life here, the only extra risk with the crumple zone is if bits of the vehicle are pushed into the passenger space.",
"For the cybertruck, the intent is you can throw a brick at it and not dent it. However the force of a brick is nothing to the overall car, it's not going to hurt the driver if it hits the hood. Meanwhile driving into a brick wall will hurt the driver, it will dent the body panels, and it compress the crumble zones. This is because they just have steel plates on top of a frame with all the usual safety things and it doesn't rely on the body panels For safety.",
"The passenger compartment on today's cars is stronger than past cars. There is a ton of crash test data to support this. Body panels are weaker but their function is cosmetic and for aerodynamics, they don't contribute to much to crash resistance.",
"Those who say cars are \"Weaker\" are entirely incorrect. Classic cars will, very slightly, resist a sub 5-mph impact better as the bumpers are usually solid steel and bolted directly to the frame. Beyond that nearly every modern car will basically destroy a classic one in a head-on crash. As stated elsewhere, the Cybertruck's body has a high surface hardness, but it's not the major structure of the vehicle and will deform readily in a crash."
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jwv93z | The Boeing 737 MAX was cleared to fly again today by the FAA after being grounded for 20 months. The MCAS combined with faulty AoA indicators caused the initial two fatal crashes. What exactly was changed regarding these two systems to make the plane safe to fly again? | Engineering | explainlikeimfive | {
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"Boeing stated the changes to the MAX were mainly software based, adding warnings to alert pilots to sensor disagreements such as those that precipitated the two disasters that grounded the fleet initially, and making changes to the MCAS system itself to prevent inappropriate activation.",
"The 737 MAX has larger engines than prior 737 versions, and their power and location relative to the aerodynamic center and center of gravity of the aircraft caused the aircraft to pitch up and down excessively. This isn't dangerous or anything, but it's an additional frustration and workload to the pilots. To reduce this issue, the Maneuvering Characteristics Augmentation System (MCAS), was designed to adjust pitch trim (shift the horizontal stabilizer up and down) so that on engine power changes, the aircraft would pitch up or down like an earlier 737. There were a large number of mistakes in how MCAS was implemented. Since MCAS interacts with the pitch trim system, it's required MCAS undergo a thorough review that would have identified all these problems and prevented its implementation as designed. Unfortunately, Boeing engineers (may have) lied to the FAA and told them MCAS was limited to small pitch changes, avoiding a thorough design analysis. In reality, MCAS had no limits, and as designed, if it detected excessive AOA that pitch trim could not correct, it would simply rip the aircraft apart trying. MCAS was also designed so that it could not be turned off. The only way to *stop* MCAS from pushing the pitch to the point of airframe destruction was to disable the pitch trim motors. But the pilots *needed* the pitch trim motors to restore pitch to normal if MCAS had pushed pitch beyond the point where it could be manually controlled. Finally, MCAS only measured from one of two AOA sensors. MCAS had no way to determine if the AOA data was faulty or not, so it could and would issue dangerous pitch commands at random. And from a training perspective: There was very little documentation or training for MCAS - what it did, what hazards it might pose, how to deal with those situations - because the engineers who designed MCAS didn't really know these things either. Since MCAS was designed to mimic engine-related pitch changes, not trim changes, an MCAS fault did not behave like a pitch trim fault, making it very hard to isolate. The FAA required several changes, IMHO these are the most important ones: First, MCAS reads from both AOA sensors, and only activates if both sensors agree the AOA needs correction. Second, MCAS activates only once per AOA event, so it won't keep fighting the pilots after a faulty activation event. Third, MCAS is limited in pitch range. It cannot move pitch to the point where the pilots cannot fully compensate by moving the control column. Fourth, MCAS is limited in pitch speed. If it issues bad pitch commands, it does so at a speed slow enough the pilots will have time to notice and react. Even if they don't react, the amount of pitch change will be small enough that the recovery will be a gentle nudging of the column and not a life-or-death fight for control. Previously, pilots would only have a few seconds before MCAS put the aircraft in an irrecoverable situation. Fifth, MCAS does not fight the pilots. It monitors column movements and disables itself if the pilots resist an MCAS event by moving the column the opposite direction. There are additional training changes, which mostly recognize that MCAS events are similar to, but distinct from, a runaway stabilizer event. Training teaches pilots to be aware of both events and how to counter them."
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jx329p | how is sending a tube shaped rocket straight into space easier or more cost efficient than something that will take off and land like an airplane | Engineering | explainlikeimfive | {
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"Planes take off because they generate lift with their wings. They do this because the shape of the wing causes it to push more air under than over it. The problem with that is when you get to higher elevations, there isn't enough air to push under the wings to keep pushing it higher. This limits the height you can go with an airplane-like design.",
"The insane speeds involved with getting into orbit mean that the only feasible way to do it is with rocket power. To stay in a low earth orbit, you have to travel upwards of 7 km/s. As others have mentioned, a plane can only carry you so high up and so fast because it can only operate within the atmosphere. Jet engines need to breathe, and wings need air to push off. You could feasibly lift a smaller rocket on an airplane up into the atmosphere, then launch from a higher altitude. This is an air-launch to orbit ~~is called a Single-Stage to Orbit (or SSO)~~, and experiments and small scale operations have been done with them before. However rockets are heavy, which means you need lots of aerodynamic lift to lift them. The higher up in the atmosphere you go, the less lift you can generate. Meaning that lifting a rocket into the atmosphere quickly becomes infeasible. Any efficiency gains you could theoretically get are offset by the enormous added complexity of such a launch (as all experiments with air launch have discovered). As it turns out, the best way to lift a smaller rocket up high to reach orbit from there is with a bigger rocket. And that's basically what a 2-stage rocket is. Also we HAVE found lots of better ways to get into space in the last 70 years. They just have all involved improvements to our rocket technology. Rockets may look more or less the same to the casual observer than they did 70 years ago, but they are a lot different! We are way better at getting into space than we were 70 years ago!",
"The [concept exists since the 40s]( URL_0 ). The problem is, you gain very little from it. The plane can get you into the upper atmosphere, but it will do so at low speed. You still need to accelerate to orbital/escape velocity from there, and the small initial speed from the plane hardly makes a dent there. The only advantage here is that you start at a lower air pressure, meaning less resistance, and less pressure that the rocket needs to bear. Why dont build a plane that can go faster? Well, because then you loose the advantages of a plane. The first being airbreathing engines, which are more efficient but limited by oxygen intake and thus not capable of reaching high velocities. The second is lift - but this requires near-horizontal flight, which means you stay in the dense atmosphere longer and loose all your advantages. & #x200B; The counterintuitive thing about rockets is this: Ignoring the aspect of air pressure, it doesnt matter too much you start at a height of 0km or 100.000 - as long as your velocity is the same, you still have to accelerate by the same amount, and need a similar amount of fuel."
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jx9qcj | How does an electric motor work? | How does electricity turn into movement? | Engineering | explainlikeimfive | {
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"Motors use magnets to turn electricity into movement. I'm sure you've seen how a magnet repels and attracts another magnet depending on the orientation of their poles. Inside an electric motor are two magnets, one field magnet, and one rotor magnet. The field magnet is usually a permanent magnet in smaller or cheaper motors. The rotor magnet is an electromagnet. It is a coil of wire, fixed to the motor axle. When you apply a current to the rotor magnet, it becomes magnetised. The rotor magnet flips so that its north is attracted to the field magnet's south, and vice versa. Constant motion is achieved by reversing the polarity of the rotor magnet just as it finishes flipping into place. Doing this means that each pole of the rotor magnet is now attracted to the *other* pole of the field magnet, so it flips again. Then you reverse the polarity again and so on. For a more thorough explanation, see here: URL_0",
"To ELI5 this one we need to break it down a little bit into parts. The first part - electromagnetism Essentially what we want to do is make a magnet, but to be able to turn it off and on as and when we want. The reason for this is, just like a bar magnet you may have used to push metal fillings around, or to pick up certain coins, if we can make a magnet that we can turn on and off we can use it to push, or turn things as and when we want. Because this isn't possible with a \"normal\" magnet, we need to make an electromagnet. This is basically a special material, such as iron, that we wrap wires around and pass an electricity through, either from the socket in the wall or a battery. (The non ELIS part of this is that a changing electric field induces a magnetic field as defined by Maxwells equations). So now we have a magnet we can turn on and off (turn the electricity on or off) and also change the strength of (apply more or less electricity) we need to get it to push on something in a certain way so that we can make a motor spin. First imagine lots of these little electromagnets we have made arranged like the numbers on a clock face (i.e. spaced out on the perimeter of a circle). Next imagine the rod of the motor that we are going to spin as the centre of the clock face where all the hands of the clock are attached to. Finally imagine a chunk of magnetic material attached to that rod in the middle, but that extends straight down (like the hour hand of a clock facing 6 o-clock). If we turn on the electromagnet we made at the 5 o'clock position, we can push the chuck of material we attached to the rod towards the 7 o'clock position. After we have done this, we can then turn on the magnet at the 6 o'clock position and turn the magnet off at the 5 o'clock position. You can start to see that by turning these magnetd on and off in sequence we can push the hands of the clock (or the lump of metal we attached) all the way around the clock. If our lump of metal is attached rigidly to the central rod, this will turn the rod and make the motor spin. We can change the direction the motor spins by changing the direction of the electricity we apply to the motor (switching the positive and negative connections on our battery). We can also change the speed by increasing the strength of the power applied or by the rate at which we turn magnets on and off. As a final aside to this, we can actually run the motor in reverse. Let's say we push the hand of the clock with our finger, we are pushing the lump of magnetic material we attached there passed the other electromagnets. This will generate a electricity for us and is essentially how generators work (just think of a wind turbine using the wind to push the blades/hands off our clock). Hope that helps. I should also add, just like all ELI5 answers, this is a simplified answer and there are more complex design principles that go into modern electrical motors in terms (phase of magnets, brushless vs brushes magnets, etc..). Worth a Google and a read if you're interested. Essentially what we are saying here is that we can turn electricity, that we can get from a battery or a socket, into a magnetic field. This is done by I will also add that this isn't quite a complete answer as there are more complex designs for electric motors",
"Many types of electric motor exist, but the most common types all use electromagnetism. When electricity flows through a wire, it forms a magnetic field around the wire. Magnetic fields tug on things that make magnetic fields, so wires with electric current in them will push on other wires with electric current in them, as well as on magnets. This allows us to use electric currents to push magnets in a circle, or to push other wires in a circle. The simplest version of this is probably a brushless DC motor. In this setup, there is just a magnet and a coil (or more than one). The coil turns on to pull the magnet, then reverses direction to push the magnet, and it repeats every time the magnet comes around again."
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jxd4hn | Why do many tires come manufactured with hairs? | I've noticed it since I was young, but I guess I never questioned it until now -- most tires come with bits of rubber sticking off that look like tiny hairs and I'm wondering what the purpose of those hairs are. | Engineering | explainlikeimfive | {
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"When you're injecting rubber into the mold you're going to have air that's going to need to be displaced, right? And you can't exactly purge air from every nook and cranny easily. You can keep pushing rubber in but air compresses really well so you might end up with pockets that cause deformed tires. So instead you put little extra vents for the air to go into at regular intervals all over the mold. The air will compress within these vents instead, a little rubber will go up these little vents as well, et voila, hairs on your tires when they come out of the mold.",
"I would add one correction: Most tires are not injection molded, they are compression molded. Raw rubber is pre-formed into a rough tire shape, generally by adding many layers of flat rubber strip. Uncured rubber tends to be soft and stick (to itself) so as those strips are added, they are basically \"self gluing\" and the pre-form doesn't just fall apart. In complex tires, there may be additions to the pre-form like radial steel or canvas cords and \"beads\" of wire where extra stiffening is needed. Those pre-forms are placed in a compression mold where they are both compressed and heated, forcing the soft rubber into the various grooves, bumps, and tread shapes of a tire. The \"hairs\" are from vent holes where the soft rubber tries to squeeze out (trapped air would cause a void and therefore a reject tire--and that does happen when the vents sometimes clog). Heat cures (vulcanizes) the rubber from a squishy mess into the strong and durable material we are used to seeing. Rubber is not naturally black like car tires. In fact, the early car and bicycle tires were typically a natural white/cream color. Carbon black is now added to the raw rubber in processing because it gives the rubber some improved strength properties and helps prevent damage from UV in sunlight as your car sits outside.",
"Those are called nipples. When the tire is made the rubber is forced in to a mold that has the tire shape and tread pattern. The mold has hundreds of small holes in it to allow trapped air to escape so your tread doesn't have bubbles. Bits of rubber get squeezed into the holes and so you get tire nipples.",
"Why did I think they were for driving in water or something? Lol"
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jxhj1s | Why can a refrigerator from 1943 still function perfectly but cars need their air conditioning recharged after only a few years? | I always assumed they were both simply heat pumps, so why does one run out of juice so fast? | Engineering | explainlikeimfive | {
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"Automotive refrigeration uses many rubber seals and gaskets. Whereas domestic refrigeration is all copper or aluminum with brazed connections. There are no rubber gaskets or seals. It’s a hermetically sealed system.",
"In addition to what others have said, that fridge is probably made of lower-efficiency but higher-durability parts. Thicker metal that won't conduct heat as well and would cost a hell of a lot more if you were building it today, but will resist corrosion for a lot longer, for example. Also keep in mind that an awful lot of refrigerators from 1943 did not make it to 2020. The ones that did are probably exceptional for some reason or another. So there's a certain amount of survivor bias: don't assume that the fridges that are still operational are necessarily representative of typical fridges of the time. More simply: the old fridge probably costs way more to run and build, and probably just happened to be an unusually strongly-built one from the outset.",
"Refrigerators don’t sit outside battling the elements for years. They’re protected from the corrosion and weathering that disintegrates cars after twenty years. I doubt a fridge from the 40s would have actually made it this far without needing maintenance though.",
"Industrial Refrigeration Mechanic here, a fridge is constructed with steel tubing or copper tubing that has silver soldered joints totally sealed from outside contaminants. With no rubber hoses or driveshaft seals that leak microscopically, like a car system. The fridge is also in a dry location subject to a lot less vibration. The fridge is designed with a compressor which is designed to be durable, running at a constant speed, really optimum conditions for a long life.",
"One reason automotive A/C systems develop leaks is actually due to insufficient use. Rubber seals (such as the dynamic seal on the compressor) will eventually dry out if the A/C sits unused for long enough, and on the first use they wear out quite a bit and can easily develop a leak. Manufacturers developed a good solution to this. The A/C compressor in modern cars will engage whenever a cars defroster setting is selected. This ensures sufficient lubrication of the A/C systems during times of low usage, such as the winter time. However, this is not a cure-all. Vehicles that sit unused for long periods of time should be ran occasionally with the A/C turned on to ensure that the seals do not dry out.",
"That’s the thing. Cars generally don’t need AC recharges. It’s the things that keep the freon from leaking that slowly deteriorate. Such as O-Rings etc. Correct me if I’m wrong.",
"A few years on your car AC?! Neither my 11 year old Corolla, or my 16 year old Golf ever needed an AC recharge. Owned both from new and had them in Arizona and Texas, so good AC was essential.",
"Put your refrigerator inside your engine bay for 2 years and see how much refrigerant is left."
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jxr7zx | Why does computer parts like SMPS have metallic casing? Isn't there issue of shorting because of metal casing? | Engineering | explainlikeimfive | {
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"You do have to design your parts so that there is no risk of shorting out to the metallic case. However if there is a short you would much rather have it short to something you can control and make sure it is properly grounded rather then to have it short out to something that might kill someone or start a fire. There are other advantages to a metal case. It is much tougher so it does not get damaged as easily and it conducts heat much better so it cools the components on the inside better then plastic. However the main reason to use a metal case for a switch mode power supply is that it blocks any electromagnetic signals. These power supplies are quite noisy in the electromagnetic spectrum and will send out signals that disrupt your wifi, cell phone, speakers or even other electronics. To prevent this from happening they enclose all the noisy electronics in a metallic case which prevents these signals from going out.",
"Well, firstly, the actual power is insulated from the metal case, and secondly, the case itself should be connected to earth for safety reasons. Even if something goes wrong and the live power gets connected to the case, it will just cause the breaker to blow, not hurt anyone. As for why use it, metal is the strongest and lightest material they could use there. Plastic would have to be ridiculously thick to support something as heavy as a PSU."
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jxsq8g | How are components in car engines able to survive heavy rain/snow when smaller electronics like phones still aren't entirely waterproof? | Engineering | explainlikeimfive | {
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"Because a waterproof phone often includes the ability to be submerged up to a certain depth for some period of time, which means you need to account for water pressure. From an engineering perspective, that's tough to do without making the phone clunky or unwieldy. Electrical components in cars for the most part aren't submersible, and only need to deal with incidental water contact. That's a lot easier and simple to do from a design perspective.",
"Many aspects of a car engine can operate completely sealed. For example a headlight doesn't need to have any openings to the outside world, it can shine light through a clear shroud and get powered through sealed electrical connectors. In contrast a phone tends to need openings for various things. Microphones, speakers, buttons, and multipurpose connectors are all points where water might enter the device. The orientation of the device might change at any time as well; an automobile can be expect to remain upright or water intrusion is the least of your worries."
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jy5ul3 | How can RAM cost so much for amounts like 32GB but HDD/SSD cost the same price at 1TB. | I always see things like CPU Cache advertised at 16mb cache as well, can they not use the same amounts as storage memory? | Engineering | explainlikeimfive | {
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"Think of RAM like a super fast sports car and SSD like a pickup truck. The truck can hold more than the sports car, but cost less. They are not built the same way or designed to do the same thing.",
"Cache is fast enough to keep up the insanely high speeds of the cpu, and as such is more expensive than Ram. Ram is alot slower than cache but also alot faster than even the fastest SSD. All three are made with different, but similar technologies. faster designs are more expensive. this is not a perfect analogy but things you are currently using are in cache, things you will be using soon or have recently used are in RAM, and things you are not going to be using for a while are in SSD/HDD storage."
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jyi07p | How is it easier to send people into space then to reach the bottom of the deepest part of the ocean? | We've been going to space and landed on the moon a couple times I think, since the sixties but we are barely able to explore the deepest part of the ocean. What's this about? | Engineering | explainlikeimfive | {
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"Because we don't have much that can withstand the insane pressure. The deeper you go the more pressure.",
"Space is essentially a vacuum. Deep sea is the exact opposite. The crushing weight of the water and atmosphere above can crush steel and destroy vessels if they aren’t specialized",
"It’s not too much easier or harder; it’s mostly just vastly different. For the ocean, you have to deal with extreme pressures; at the bottom of the Mariana Trench, it’s about 1000x the atmosphere’s pressure. Many things don’t work the way it normally does at that pressure, and any vessel will shrink significantly on its way down, making design really important. In contrast, space vessels have to hold about 1 atmosphere’s worth of pressure against a the vacuum of space, so the pressure’s on the inside. That isn’t that difficult, really. The biggest issue is that the vessel has to get to space in the first place. And then things don’t necessarily work the same way, much like the submersible experiences. The big reason we visit space more often is because it provides a frontier of science that isn’t reproducible on the surface. Things tend to go weird when you take gravity out of the mix, and we don’t have a way to emulate that for more than a few seconds outside of space. For any high pressure experiments, we can usually just toss it in a pressure vessel instead of sending it to the bottom of the ocean."
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jyj23i | How songs get recorded on vinyls? | Engineering | explainlikeimfive | {
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"A master is created by picking up the soundwaves with a microphone that converts them to an electric signal. The signal is sent to a needle mounted on a rotating wax disc. This causes the needle to vibrate which etches the little grooves into the wax disc. The wax discs are then used to make metal molds for each side of the record. Those molds are then used to press the final vinyl disc (because vinyl is much more durable than wax and much lighter than metal). Playback is really just the reverse process -- the needle rides along the grooves and vibrates. Those vibrations are converted electronically into signals, and sent to speakers where they are converted back into soundwaves. EDIT: Note that this describes the \"old school\" way of *live* recording prior to tape or digital. As recording technology progressed the means of cutting the master has changed. But you still have to etch a recording, make a mold, and press the individual vinyl records."
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jyumtf | How were rope bridges formed when people needed them to cross a gap in the first place? | Engineering | explainlikeimfive | {
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"There's basically always a means to cross. It may be just a long, long way around. Now some guys take the long way around, some guys stay. Once everyone is in place, you get a light guide rope over the gap. Shoot it with an arrow, fly it over with a kite. Things like that. On the light guide rope, you pull over the final thick ropes, secure them and complete the structure.",
"Throw/shoot a thin rope over and use that to pull a thicker rope over. You'll definitely need people on both sides, so there must be a long way around to get to the other side. Or climb down and up again with a rope with you.",
"You get 2 people. The first one stands on one side. The second one takes the long way around to the otherside. You tie the rope to a spear or arrow and shoot it across the gap. Then the person on the other side secures it down. An you keep shooting rope until you can make a bridge",
"[Philippe Petit]( URL_0 ) was a high wire artist that strung a high wire between the two towers of the World Trade Center before it was destroyed, and walked across (several times in fact). \"To pass the cable across the void, Petit and his crew had settled on using a bow and arrow attached to a rope. They had to practice this many times to perfect their technique. They first shot across a fishing line, which was attached to larger ropes, and finally to the 450-pound (200 kg) steel cable. The team was delayed when the heavy cable sank too fast, and had to be pulled up manually for hours. Petit had already identified points at which to anchor two tiranti (guy lines) to other points to stabilize the cable and keep the swaying of the wire to a minimum.\"",
"In the army we would swim across with a lighter rope, use the lighter rope to haul a heavier rope across, and then anchor the heavy rope to start making the bridge. So the people saying shoot the rope across with an arrow/spear don't understand the weight of a rope.",
"An individual/small group would take one end over to the otherside. It's a rarity that those gaps were impassable to begin with.",
"The reason to build a bridge is to avoid a REALLY long walk. Someone took the walk so they could catch the rope."
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jyzvn5 | How do longer gun barrels translate to faster muzzle velocity? | This is one thkng that never made sense to me and seems (at least to me) counterintuitive even though the historical precedents speak for themselves (case in point, the long-barrelled Sherman Firefly variant which became a very effective weapon against WWII German armor that the ordinary Sherman wouldn't normally be able to penetrate) The way I see it, the projectile is in the barrel (and therefore engaging the rifling) for that much longer - in that time, more of the shell's kinetic energy is lost as friction in the barrel than it would be normally, wouldn't it? Is the effect of friction negligible and outweighed by the increased rotation imparted by the long barrel? I just don't understand how it makes as significant a difference as it does. | Engineering | explainlikeimfive | {
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"The Bullet is pushed through the barrel by the expanding gas from the gunpowder exploding. The more time the gasses pushes on the bullet the faster it goes. As long there is a higher pressure behind the bullet than in front of it, it will accelerate.",
"The longer the barrel the longer the explosive gasses get to push on the projectile. The longer the shell is pushed the more energy it has, the faster it will be traveling. As long as the barrel isn't so long that the gasses are able to fully expend, then the projectile is going to be getting more energy. This is why, when the projectile comes out of the end of the barrel, you see the gasses follow it out. On a pistol, if you have a short 4 inch barrel, the gasses only get to accelerate the bullet for 4 inches. If you have an 8 inch barrel, the gasses get to accelerates the bullet for twice the distance.",
"The gases from the propellant charge have more time to act on the projectile. The longer the projectile stays in the barrel, the lower the pressure behind the projectile (because the gases expand) and the higher the pressure in front of the projectile (because the air that was in the barrel gets compressed). At some point, the gain isn't worth the extra mass of the barrel.",
"Intuitively, I'd believe it's similar to using different lengths of rubber band. There's more thrust time or push time on the back of a longer/more stretched band than a smaller band. In a long barrel, the force continues to push outward excelling the speed of the bullet faster and faster. In a short barrel with the same force, that force loses its thrusting power as soon as it exits the barrel.",
"Imagine blowing a spitball with a straw. Now imagine blowing a spitball with a straw half the size. Now, again imagine blowing a spitball with half the size of that. Notice it starting to slow down yet? Why? You will intuitively know that a stub of a straw will be difficult to hit your older brother in the head from across the room. Your lungs want to accelerate the spitball. As long as you have forceful air in your lungs to push the spitball along its journey from start to end of the straw - the faster and bigger the splat! Be careful though - your brother with his bigger stronger lungs can have a longer straw that shoots even faster."
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jz2tg3 | Why do traditional cars lack any decent ability to warn the driver that the battery is low or about to die? | You can test a battery if you go under the hood and connect up the right meter to measure the battery integrity but why can’t a modern car employ the technology easily? (Or maybe it does and I need a new car) | Engineering | explainlikeimfive | {
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"The technical people answering are technically correct, that a voltmeter would indicate the voltage of a battery, but they’re missing what OP is after: when won’t a battery work anymore? In other words, they are wondering “why can’t I know the health of my battery?” With car batteries (the 12V lead acid type) the voltage isn’t really a good indicator of health. An old dead battery can read ~12V just fine. It would likely power most lights and equipment, too. The real test of health comes when trying to start the engine; the “load” test. An old battery can read 12V until asked to turn the starter, then immediately drops to an unusable voltage. The simple answer is that traditional 12V car batteries do not have the sophisticated tech to indicate their health like, say, laptop batteries. Nor is there a good way to test the health except for hooking the battery to a load, which isn’t an easy thing to build into a car’s circuitry. Basically, starting the engine IS the load test. Edit: To all those asking why a load tester couldn’t be added into the hardware or software of a car: it could. Nearly anything is possible with time and money. But I agree with the comments from those in the industry; it comes down to three basic things: 1) Added cost (automotive margins are very thin) 2) Added complexity and engineering effort for nearly no return (exactly who would truly want this?) 3) Service side (auto companies do not wish customers to have to think about maintenance beyond knowing to take the vehicle in when the light turns on) Edit 2: Since this blew up from my original simple answer, we’ve attracted the attention of my more astute engineering colleagues. It appears my answer is a little dated. The fact is that this diagnostic capability DOES exist in more modern vehicles. But just as auto companies have chosen to shroud engines in giant swaths of plastic to hide the ugly technical bits, so have they chosen to hide most of these diagnostic abilities from the consumer behind a simple light or “Service Soon” message. Good discussion!",
"There's a battery light that pops up when battery voltage is low on some cars. Diagnosing lead-acid battery health is not as simple as measuring voltage, it can be near full voltage and go down super low when you actually try and draw power. You're required to change batteries often enough that it shouldn't be a problem, but many people only change them when they die leaving them in a field.",
"Batteries in traditional (i.e. gasoline-powered internal combustion engine) cars are only used for (a) powering the starter motor to start the engine or (b) running electrical features (e.g. radio, lights) when the engine isn't running. Car batteries are automatically re-charged by the alternator, which uses power from the engine to generate electricity while the engine is running, both for re-charging the battery and running electrical features of the car. Traditional car batteries don't really store that much energy, since their primary purpose is only to power the starter motor that gets the combustion engine running. Basically, they need to put out one big boost to start the engine, then they get automatically re-charged once the engine is humming. So there are two reasons your car battery will die: 1. The alternator is failing to do it's job, so, while driving, anything that relies on electricity like lights or windshield wipers or radio will drain the battery instead of getting electricity from the alternator. 2. The engine isn't running, but something else is draining the battery. E.g. lights are left on while the car isn't running or there's a short somewhere in the electrical system. Most modern cars (at least in the US) *have* an alternator/battery-warning dashboard light that comes on when the alternator is failing to provide sufficient power to re-charge the battery. That takes care of #1. However, #2 occurs when the engine isn't running ... which usually means you aren't in the car. Since a car battery doesn't store all that much energy on its own, if you're away from the car for a few hours with something draining the battery, it's not going to start when you get back to the car. (And if it didn't drain the battery enough to prevent the car from starting, then the battery will be re-charged by the engine as soon as you start driving again.) So, as long as your alternator is working correctly, your battery generally won't have issues. Cars have warning lights to let the driver know if the alternator is failing. But if your battery loses its charge for some other reason (e.g. human error or electrical system problems), it's going to go from a usable charge to insufficient charge to start the car pretty quickly *while you're not driving and not in the car*, so a warning light isn't any help. TL;DR: if you leave your car lights on overnight, a warning light that you're draining the battery isn't much use while you're asleep in bed.",
"They don't lack this. Every car for many many years has a volt meter and most have a warning light or message if charging gets too low.",
"Even a bad battery can show you 12v. But as soon as a load is present, drop to 8v. When you test the battery in the shop, a big load is put on, for example some heating coils (inside the tester). It should be hard to automate this and not overstrain the battery.",
"Many cars measure voltage at turn-on and can signal you. The most important test, trying to start the car, already has a \"warning\", wken the car doesn't start. Without a more sophisyicated test, you can't tell \"low charge\" from \"bad battery\". A bad battery is pretty obvious, but predicting it doesn't work unlesss people are going to replace t_eir battery when the car says \"battery failure within a month\".",
"You give the example of using multimeter to check your battery, but that doesn't actually tell you anything about battery health. A battery can show 12v on a multimeter but not actually have enough capacity to start an engine. You should check voltage drop under load, you'll notice as a battery gets weaker the voltage will dip more when it is put under load like starting the engine. This is the idea of those battery capacity testers you can buy in store. They just have a big resistor in them that draws a huge load on the battery and you check what the voltage drops to. If you want to really check battery health you can do a capacity check. They aren't commonly done on vehicles but often done on aircraft. Basically you charge the battery fully, put a known load on the battery, and then time how long it takes to get below a certain voltage. You then compare that to the manufacturers numbers to see if your battery is low on capacity or not. It's not done on vehicles because in a vehicle a battery is primarily there to start the engine, if the engine doesn't start you know it's bad but no harm done besides the inconvenience. It's done often on aircraft because the battery is there to provide emergency power in the event of an alternator/generator going bad. You don't want to be flying through clouds with no visibility relying on your instruments for navigation and find out your battery is shot when you alternator goes out. Here is a video from Concorde about battery capacity testing. URL_0",
"I posted a somewhat similar question a few days ago and everyone acted like I was stupid. Maybe I worded it wrong but I was basically saying the same thing wondering how come we can't see percent of the car's battery. URL_0",
"So, mechanic here. Some (most?) trucks have a battery volt meter in the instrument cluster that reads the voltage at the battery (for simplicitys sake). Cars, not so much, but as stated theres a battery light in the cluster. Toyotas light up the abs and vsc light (if I'm not mistaken) when the alternator goes out and the car is running on battery power alone. Disclaimer: its been an interesting weekend with the kiddos, so my memory may not serve me correctly. If anyone has any corrections please feel free to comment.",
"Because batteries are quite good. My saturn had a 1.2 kW starter. A healthy battery dips to 10 volts during cranking, so that's 120 amps demanded. The battery for it was rated for 650 cold-cranking amps. To pass the test it has to supply 650 amps at 32 degrees *for thirty seconds*. It could do more amps for the three seconds it actually takes to start the car. One could test the battery annually and see a gradual decline, but it would still bump that starter over nicely. If it declined on a parabolic curve, which I bet it does, the fall-off would be dramatic by the point the car stopped starting. In the old days, starters were direct-drive, weighed 50 lbs, were 10 inches long, 5 inches in diameter, and guzzled amps, so you would in fact note the decay earlier via slower cranking. You'd have more warning because you were on a flatter part of the curve. Modern starters use gear reduction drives which draw fewer amps, making the failure point more binary. It's a miracle we're still getting batteries as big as we still do. This adds a smidge of reliability, and capacity to run things like the radio memory and remote keyless entry sensors if the car is parked for a week. Companies like Honda put skinny bullshit batteries in some of their cars to save fuel but the trays will have holes for bigger replacements.",
"Along with other answers, some vehicles are fitted with a voltmeter in the gauge cluster. This is expressly for warning the driver if the vehicles voltage drops too low!",
"In my Range rover there's a light that lights up when the battery or alternator are failing. It's broken. It's lit all the time. The battery and alternator are fine and have been for going on 8 years. Who watches the watchmen?",
"Car batteries don't tend to have a long and drawn-out death. In general they work normally until one of the plates inside develops a crack, which massively limits the current the battery can develop and stops it from starting the engine. Since there's no practical way of detecting this it's not worth checking.",
"On average, americans only own a car for about 7 years. A \"Dying battery\" sensor would be used only once or twice over the typical ownership span. Why are there no tire tread depth sensors? Timing belt wear sensors? Water pump fatigue sensors? Brake component wear sensors? Again, it's all just added cost for things one will rarely use",
"Mechanic here. The only thing your battery is really meant to do is START the car. Running electrical components and electronics while the car is running is not it's main purpose. The generator (most people call this the alternator, it's correctly called generator now buy the industry) keeps all those things working when the car is running. Ok so, testing a battery essentially tells you if it can hold enough charge to start the car after it's been left off for some time. So your question, why doesn't the car test the battery... Well they would theoretically involve determining if the battery can start the car... So, this would happen after you start the car? Or when you get in before you start it? Starting the car essentially is the test. If it starts, it's good. So, do you want to know if it's gonna start tomorrow morning? Well, testing it now won't really tell you that. So you see, \"testing\" the battery is kinda pointless when it's working. The reason we (mechanics) test your battery when the car won't start is to make sure the problem is ACTUALLY the battery and not something else like parasitic drain, starter, wiring etc...",
"Wtf cars are you driving? My 75 vette has factory a battery gauge...",
"Every single new car has a battery voltage meter light on the dashboard. Or am I crazy?",
"Use ur ears for Christ sake. If it’s struggling to start, and ur battery is more than three years old just replace it - don’t wait for it to die.",
"Because people don't like seeing useful information in their gauge cluster. Most cars used to have a variety of gauges including voltage and oil pressure. Now you're lucky if you even have a fuel gauge.",
"it isn't sufficiently profitable. most actual improvements are not sufficiently profitable. superficialities are what sells a vehicle. CEOs want a lot of profit so they can retire to the Bahamas before their employees get too pissed off at how they've been fucked over for decades. the only way to get something to happen is to inspire people's greed.",
"There is no need. When the engine is running the alternator produces all the needed electricity and recharges the battery. This is the important thing that is, in fact, being monitored and if charging fails you will see a red lamp on the dashboard. The battery will not go flat as long as the charging works properly unless it just fails due to malfunction. And in that case, charge indicator won't be enough to warn you in time because it can't predict failure.",
"Because the average person is too dumb to understand what they’re looking at. Heck, the automakers have simplified their gauge readings to not show real time data, and keep the needles in the same spot for an entire range of sensor values... if you even get a gauge. They don’t call it a dummy gauge for nothing. Ideally, the PCM or a similar control system would rapidly monitor the battery conduction voltage under cranking, and throw a flag of that was too low. Similarly, since there is always live 12v through the OBD port, it could flag if the battery voltage with the vehicle off is too low. State of health is a complex measure, that means different things to different people, and is contingent upon many factors. That’s probably easier said than done. But simple readings would go a long way.",
"Volts are just potential and *AMPS* are what start your car. Bigger the engine, generally means a higher amp rating and bigger battery is needed to start it. Testing for amps (classical type battery testers) get VERY hot, because of the high amount of AMPS that run through the tester, and putting one on a car could cause a fire or could kill the battery by testing it all the time. Cars for decades have come with a Battery gauge that tells you the VOLTS which can be used to tell you Electrical and Charging health of your car. You should be somewhere above 13V to 14.5 volts at all times or the Battery or *Alternator*(engine component used to recharge the battery as you drive) could be failing. If the volts drop to low, your car will likely stall out, even while driving.",
"TLDR: It isn't worth the effort, and would not be that accurate without even more effort. The only accurate way to test a battery is to apply a high current (\"heavy load\") to the battery and monitor both the amperage and voltage with the engine off, ideally with the battery disconnected. It is not possible to wire in an amperage measurement, nor valuable (it is possible) to disconnect the computer from the battery and supply power from a separate source (second battery) on most cars. High current draw is only possible through thick wires, and this would require a separate set of wires and human interaction to enable/disable them. Monitoring the system voltage when the engine is starting, saving a log of it, and setting a check engine (or check battery) light seems feasible, but not very valuable. Some other people mentioned the battery dying from a rapid drop in temperature, which is still possible with monitoring only voltage. Drivers in cold climates might get a false sense of security from expecting a warning and not getting one.",
"No answer for you but like question. I have a 2017 Jeep wrangler unlimited rubicon( can we use more words to describe the damn things?!?!) and the battery died Saturday. There was no light in the dash as others have mentioned, so not all newer cars have that. The only “indication” was a slightly off start sound Thursday afternoon. It wasn’t anything crazy, maybe a one second delay, but just enough delay that I thought that seemed odd. Since it started and got me home, I didn’t think much of it. AAA came out to my house Saturday, jumped it and it started up. Then he hooked whatever up to it and said it was operating at about 20% so it didn’t have enough power to crank it. So I bought a new one from them (which is convenient). I didn’t leave anything on in it. AAA said anymore batteries last 3-4 years in newer cars because all the computer bits. That tracks because in my wranglers, I have had to replace the battery every 3 years due to them randomly dying, never have any warning either.",
"The very first car I ever owned had a battery gauge inside it. The range was from \"10V\" to \"14V\", while the needle sat just below \"12V\" the majority of time I owned it. False sense of security, as one day, the battery refused to start my car despite showing nearly \"12V\" on the gauge. Turns out, a battery's ability to turn an engine over is measured in amperage, not voltage, which means that to start the car, the battery must be ready to push plenty of amps to start the ignition, something the gauge cannot measure. Cost, and customer confusion, were probably the two largest factors to remove the useless gauge from dashboards, and I'm rather thankful for that now since my gauge clearly didn't let me know my battery's charge was insufficient. Oh, the cause? Aging alternator, which wasn't charging the battery to its capacity, despite the battery being perfectly fine. & #x200B; On a side note: buy a boost charger. A small one costs about $40 and you don't need another car to jump your battery. Honestly, these should come standard with all cars sold.",
"Ironically cars used to have volt meters, which when starting a car (putting load on the battery) gave the exact indication of battery integrity as per the OP meter (another crude test in early cars with limited batteries was putting on the high-beam headlights and trying to honk the horn at the same time, which would fail with a weak battery, meaningless nowadays as even a weak battery does such). Consumers bought cars without voltmeter gauges in favor of \"idiot lights\" which do the same thing as a voltmeter but hide the impending battery doom from the driver in favor of lighting the failure light when it might be too late. Similar issue with oil pressure gauges cars used to have because it's so critical now having only an idiot light and folks spend thousands to replace engines due to oil issues obscured from them. There's also a combination of slight money saved per unit sold adds up to a fair amount of cost savings, and batteries are more robust than they used to be, and in some places lots of consumers have roadside service provided or pay for it. Then add that repair businesses profit from failures... Until consumers start purchasing based on features rather than looks/marketing...",
"That's actually a pretty good idea, and could be relatively easily implemented. That said, every time hardware and software is added to a car, it increases the cost to manufacture the car. A tiny increase in cost per car can have major effects because so many units are produced. I think the easiest /cheapest way to do it would be to measure the battery voltage at the battery immediately prior to cranking (to gauge the state of charge), and then while cranking (to gauge the battery's ability to maintain voltage while loaded). If you wanted to increase accuracy, you could also monitor starter current draw, battery temperature, and engine oil temperature. Some cars monitor Smart Key battery voltage to alert the driver when the key's battery is getting low, but I haven't seen a car with 12v battery monitoring. Edit: I just read the other replies that said battery monitoring isn't necessary because the alternator provides electrical power once the car is running. It is true that the alternator provides power for the car and recharges the battery once the engine is running, battery condition monitoring would still be beneficial. The battery's sole purposes are to start the engine and provide backup power for computer memory. Anybody who has been stuck in a parking lot with a dead battery is likely to think battery condition monitoring is a pretty good idea. As batteries age, they lose capacity. A 5 year old battery might use 90% of its capacity to start the car. The driver would have no clue the battery is degraded because the car starts, and once it does, the alternator takes over. Everything is fine until on day the engine doesn't start on the first try and the battery doesn't have enough capacity to crank the engine a second time. Or maybe the temperature has dropped. When the ambient temperature is lower, more power is needed to crank the engine. If the battery barely has the capacity to start the engine when it's warm, it won't be able to start the engine when it's cold."
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jzbujs | When we suck through a straw, the substance follows the suction to the source: our mouth. So how is it that when vacuum cleaners suck up crumbs, the particles fall into a dust bin instead of clinging to the fan or filter in front of it that causes the suction? | Engineering | explainlikeimfive | {
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"It's mostly to do with the large density difference between air and dirt. The vacuum cleaner is also sucking up air and the air easily flows past the solid particles. With a vacuum cleaner the speed of the air is fast enough to lift particles up in the hose, but when it enters a larger chamber the air speed slows down and the particles fall. There's also usually a \"cyclone\" effect which effectively makes things heavier (centrifugal/centripetal force) and amplifies the difference in density between the dirt and air making them separate easier. A straw only sucks up one fluid with no air so there's no separation based on density. If you've ever accidentally cracked a straw and had air leak into the side you find that it doesn't work nearly as well and you have to suck a lot harder. And you'll notice that inside your mouth the liquid falls to the bottom of your mouth which is why you don't fill your lungs with soda on accident. (Or when slurping soup)."
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jzrtoh | Why do Boeing number their planes with the middle digit increasing 737, 747, 757, etc.? Why not 737, 738, 739...? | Engineering | explainlikeimfive | {
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"The company’s engineering department divided the model numbers into blocks of 100 for each of the new product areas. For example, 300s and 400s represented aircraft, 500s were used on turbine engines, 600s for rockets and missiles, and 700s – you guessed it – were used for jet transport aircraft. It was an easy way to keep things organized. But the marketing department realized that the name Model 700 wasn’t exactly catchy, so instead they suggested the name 707. This started a long-standing pattern, starting with 727, 737 and finally today with the latest Boeing 787 Dreamliner models Sauce: URL_0",
"Well they kinda do use the 738 739 etc nomenclature you spoke of. The 737-800 or 738, when seen on an ATC flight strip or data tag, is a generation of the 737. That's all I can contribute to the discussion though.",
"it sounded sexy af. sauce: URL_0 When Boeing shifted from propeller airliners to jets in the late fifties, it began its numbering anew with the 707. Like pi, it’s a number familiar to many engineers: 7, 0 and 7 are the first three digits in both the sine and cosine of 45 degrees. Swept wings — wings that angle toward the back of a plane’s fuselage rather than sticking out at 90 degrees — were new at the time. Story goes that the name 707 came from the angle of the plane’s wings. It’d be a fitting tale if it was true, but the 707 wing sweep was only 35 degrees, not 45. Following the Second World War, Boeing’s president organized the company’s product lines into blocks of 100. For example, the 600s were reserved for rockets and missiles. Commercial aircraft were assigned numbers in the 700s. The first plane might well have been named the 700, but it just didn’t sound right to the marketing Mad Men of the era. “Seven-oh-seven” sounded sexier — with a ring like “double-oh-seven.” The naming tradition’s been carried down over the decades. Internally, Boeing is noncommittal before an aircraft is released. The 787 started out as the 7E7 — “E” standing for efficiency, though the 8 seemed predestined. Eight is considered good luck in China, where people will pay substantial sums for items like license plates with 8s. (Recall that the Beijing Summer Olympics began at 8 P.M on the date 8/8/08.) A plane with an 8 in the name certainly couldn’t hurt when selling to the expanding Chinese market. But the 787 also came with another name. Officials at Boeing were prepared to call it the Global Cruiser until it was decided to let the world’s population vote on a name. A short list of possibilities was put together and distributed globally. Over half-a-million people from 160 countries cast their ballots. And when the tally was completed, Dreamliner won by a margin of only 2500 votes."
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jzsy1f | how do you explain the mechanics of what a manual car does when it's emergency braking? | Engineering | explainlikeimfive | {
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"You don't need to wait till the car has almost stopped to push the clutch in. Just hit both right away."
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jztnlu | why can cars not keep the throttle open but not inject fuel, to reduce engine braking? | My understanding of how engine braking works is that, when you take your foot all the way off the gas, the throttle closes, and no air enters the cylinder. This creates a vacuum that the piston has to pull against (using the force from the wheels turning), which is what provides the braking force. At the same time, the fuel injector stops inputting fuel. But what if you don't want to engine brake and just want to coast? Why can't the car open the throttle but not inject gas, getting rid of this vacuum and allowing it to spin without resistance? Of course, you can put it in neutral, but then the car is having to spend fuel to idle because the engine isn't connected to the wheels. | Engineering | explainlikeimfive | {
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"The engine braking effect still happens with the throttle opened, and in my experimenting it actually more pronounced and slows down faster when you try and do what you describe. I have fuel injected motorcycles with cable driven throttles, you can hit the kill switch on them while riding, this will cut the injectors, and you can still actuate the throttle. I've played with it where hitting the kill switch and then going wide open with the throttle, the engine makes a deep sound from sucking in all the air and it rapidly loses RPMs, a lot faster than if I had the throttle closed. I was doing testing with that to figure out ways to optimize fuel economy. My 2000 Honda Insight hybrid has what is effectively an engine kill switch, I can pop it into neutral, kill the engine and coast without using any fuel or running down the battery, then it automatically restarts the engine once I put it back into gear."
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k00yqn | How do ships move in reverse? | Engineering | explainlikeimfive | {
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"Just spin the blades the other way. If a fan spins one way, it blows air. If it spins the other way it sucks air.",
"There are a few ways. First, you reverse the engine and spin the prop in the opposite direction. To do that, you engage the reversing gear, which essentially changes the timing of the engine cylinders, so that they ignite in a different sequence, and thus turn the crankshaft the other way. You will find this on older ship, or on ships that do longer slower ocean passages. The second way is with a CPP, or a controllable pitch propeller. Instead of the engine shaft rotating a different direction, a hydraulic system can reverse the pitch of the blades. Pitch is essentially the angle of the blade. Reverse pitch is basically the reverse of forward pitch. In fact, with a CPP, the propeller can turn at several RPM, but the ship won't move with the blades at neutral or stop pitch. You will find CPPs on faster ships that have to do more maneuvering (i.e. they are in and out of port more often). A third way is with azipods. An azipod is a propeller unit that rotates around. Instead of a the rudder move, the pods do. You can turn the pods are all the way and have them provide reversing thrust. You will find these on smaller work boats, such tugs, and on cruise ships.",
"By driving their propellers in reverse. In the case of ships with steam turbine propulsion they'll often have extra turbines specifically for the job, because turbines will only rotate in one direction and the forces involved are way too high to have something like a car's gearbox in there."
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k04bjy | When comparing USA to EUR electricity, what's the benefit of having 240v on two-phase vs the European single-phase? | I have a pretty strong grasp on household electricity for the USA and today I learned the European outlets are a single 240v line and a neutral where I erroneously thought it was two 120v phases without a neutral. What is the benefit of having 240v in two, 120v phases vs the European single phase 240v? | Engineering | explainlikeimfive | {
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"One benefit is that 120V is less lethal than 240V. Not that 120V is safe, but obviously the higher the voltage, the more dangerous it is, so proper installation/insulation and practices are more important with 240V systems. Other than that I can't think of many benefits. Keep in mind though that a lot of European homes have 3-phase supplies, so since each phase carries 240V, you can have far higher power loads. Tankless electric water heaters that are pretty common in Europe for example draw 15,000-21,000 Watts. 3-phase electric stoves can also be more powerful. It's possible to run these loads with 240V 2-phase of course, but that requires very heavy duty wiring, breakers and electrical panels, and sometimes even upgraded wiring to the house.",
"Today the only major benefit is not having to adapt the entire power system and every appliance to 240 V. The reason why the USA uses 110 V is historical. When electricity was introduced in the USA by Edison, his lamps worked best around 110 V and it was easier to generate 110 VDC than a higher voltage. In terms of efficiency 240 V is better due to the lower currents, but changing the entire system to 240 V would be a lot of work and the transition would not be well accepted by the manufacturers and the population.",
"Higher voltages enable - lower transmission losses - more power for the same current (wiring costs.) - the British can boil water for tea more quickly (3kW kettles) - only one plug style for all appliances It used to be 240V in UK/Ireland and 220V on the continent but the standards have been harmonised at 230V for Europe.",
"Technology connections had a nice video on this earlier in the year. One of the reasons for EUR 240v is because there was a considerable savings in the amount of copper needed for 240 over 120 which the US didn't have problems acquiring plenty of.",
"Ooh oooh! There's a great [Technology Connections]( URL_0 ) video on exactly this topic. As user bal00 pointed out though, one of the big benefits is it being a bit safer. Comparatively, I mean.",
"Don't know about USA standart, but here in Brazil its the same, two 110v phases to create 220v. The benefit i see is that it's a lot easier to convert an outlet from 220 to 110 by only switching on line to neutral."
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k04vft | - How do airplane engines/turbines stay waterproof while it's raining? | Engineering | explainlikeimfive | {
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"Good answers here already. But the big reason why THEY can take on a bunch of water while the one in your car can't is that turbines don't have a \"closed\" compression, which means hydrolock can't happen. It's a continuous flow of air rather than taking isolated gulps like a piston engine.",
"Since this is ELi5, I'll try to keep it basic. The most common type of turbine you'll see is a bypass type turbo fan engine. These engines have what is called the core engine which is the compressor in the front and the turbine in the back and is surrounded by the bypass ducts. For the sake of this explanation, I'll just say that the purpose of the core engine is solely to accomplish the suck-squeeze-bang-blow cycle and doesn't create any usable thrust in that process. The core engine drives the turbine fan in the front which is responsible for producing a majority of the thrust simply by accelerating a large volume of air as it goes through the fan and is blown out of the tail pipe without being involved in the combustion process, so all that needs to happen is to keep the water out of the core engine. Consider that at cruise power, that fan is turning at about ~5,000 RPM depending on the engine. When water initially hits the fan, the centrifugal force slings the majority of the water outwards to the ends of the fan blades, the water is blown through the bypassing air, and out the back of the engine never having gone through the core engine. Some water does make it into the compressor and goes through to the turbine section but it's not enough to interfere with the combustion process and cause a flame out. TLDR; When an a jet engine goes through heavy rain, the water doesn't make it into the part of the engine that keeps it running. Edit: Corrected fan RPM.",
"They are not waterproof. They are designed to funnel the rain through the fan blades, compressor blades, into the combustion chamber (where it is turned into steam), through the turbines, and out the back. (most of it goes through the front fan blades and bypasses the rest of the engine and get blown out the back.)",
"Both the fan that you see at the front of the engine as well as the blades within the compressor section are turning at mind numbingly fast speeds. Any water ingested in to the intake is QUICKLY thrown to the outside of the engine, where it is drained out through ports. No water actually makes it to the combustion section. The way that they test these engines is by pouring MULTIPLE firehouses of water in to them at full blast, and the engines don't skip a beat.",
"Engine tester for Boeing here, aircraft engines can ingest water into the fancase and compressor without a problem; the sensitive electronics are kept under a gasketed cowl around the fancase, and there is an anti-ice system that either pumps hot liquid or heats a filament around the forward part of the engine (the aft portion heats itself).",
"Gasturbines in powerplant can inject water to increase the output power as well. You just want a medium to which you can add energy. If you add a lot of heat into steam it gives more power when expanding over the turbine which drives the axle and generator.",
"Bonus fact: Purposefully injecting water into the jet engine can provide increased performance at low altitude. “Adding water increases the mass being accelerated out of the engine, increasing thrust and it also serves to cool the turbines. Since temperature is normally the limiting factor in turbine engine performance at low altitudes, the cooling effect lets the engine run at higher RPM with more fuel injected and more thrust created without overheating.” URL_0",
"Hello, helicopter pilot here. Many turbine engines have an inlet particle separator that works by using inertia to remove particulates from the air. In S-70 aircraft air is swirled at the intake and things like dust and water are dumped overboard. Some still gets in but usually not enough to cause issues. Turbo props usually have a similar system. The T-6 required air to make a sharp turn to get into the intake, this had the same effect. As was already mentioned, only about 30% of the air is used for combustion while the rest flows through the engine and cools it. Water that gets into the turbine is turned into steam immediately. There is hardly ever enough to affect the combustion process. In the pavehawk we will sometimes fly through a rain shaft after doing dusty landings or salt water operations to use this phenomenon to clean the inside of the motor. Salt and dust will eventually degrade the compressor and gas generator blades despite the particle separation system. Some old jets actually used water injection to increase their thrust, harnessing the expansion of the steam, but that was generally after the combustion section. However, there are operating limits placed on some aircraft regarding amounts of precipitation they can fly through. They usually sound like this “flight through heavy rain is prohibited”. My aircraft doesn’t have such a limit but I’ve flown through storms and seen my turbine gas temp indicate pretty low for the power setting I had. Made me uncomfortable. TLDR: Water droplets get separated because of centrifugal (yes I know) forces due to engineering tricks that spin the air as it enters the engine. Mostly clean air enters the engine and is combusted. Not enough water enters the combustion section to flame it out. . . Usually",
"Same way a ships prop stays waterproof underwater. It doesn't. The part (most of it) that gets wet isn't damaged by water.",
"I worked on aircraft engines the blades get heavily stained we mark it as environmental damage but its not really damage. In saying that youd be surprised how many broken blades are actually in engines and allowed to fly some companies even bribe to try get them signed off",
"When water ingress shuts off something like an internal combustion engine it usually does so because the ingress is heavy enough to reduce the oxygen supply sufficiently that the fuel in the engine cannot ignite. Jet engines are designed to have massive volumes of air flowing through them all the time so you need an almost ridiculously high rate of water ingress to cause them to shut down.",
"1) What you see when looking at a typical airliner engine up front is the \"fan\", essentially a large propellor that blows most of the air around the \"core\" of the engine through the so calles \"bypas duct [(you can]( URL_2 ) basically [look through]( URL_3 ) these[things]( URL_0 )!). Most of the water just gets flung to the outsode and through the bypass duct, having only erver interacted with the fan. 2) In the core, the air (and rain) first goes into the compressor stage where it is compressed (duh) and, in the process, gets very hot (couple 100°C; ever pump up a bicycle tire and feel the pump heat up? That, just a lot more). So even before it gets to the combusion chamber, it is no longer liquid, at that point, for the compressor, it is just a gas not too different from air. 3) After it has gone through the compressor, the air-steam mixture goes into the combustion chamber where kerosene is mixed in and the whole thing ignites. In a car's piston engine you try match the amount of fuel to the amount of air you have in the cylinder as closely as possible, so that all the air is used up to burn all of the fuel (more fuel means it cannot be burned and is wasted, more air means you could have produced more power). In a jet engine you have a lot more air than is needed for combustion (basically beacause otherwise everything ywould just melt, it is close enough as is). So even if you replace a significant portion of the air with water / steam, you still have plenty of air to burn your fuel. During Qantas flight 32 an A 380s engine had an uncontained failure, rupturing the controls to the outer engine on that wing, resulting in the flight crew being unable to shut it down. It took the firefighter hours(!) to douse the fire inside the engines combustion chambers to shut that engine off. Very intreseting incident due to other reasons as well, especially in how the [flight crew dealt with the extensive damage to the aircraft]( URL_1 ) . Love to see an autonomous aircraft do that."
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k08jpi | How does turbofan engines overcome the issues facing turboprop engines? | So [turboprop engines]( URL_0 ) have to have a reduction gearbox to slow down the propeller as the tips would hit the speed of sound and Bad Things Would Happen™. However, [turbofans]( URL_1 ) just slap a cowling around the "propeller" (fan), don't need the reduction gearbox any more, and problem solved... how? | Engineering | explainlikeimfive | {
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"As far as I know, the gearing isn't to prevent the tips from breaking the sound barrier. The purpose is to increase the torque to turn a larger, heavier propeller. Big propellers move a lot of air a little bit, which is more efficient at lower speeds. At higher speeds, it becomes difficult to move a lot of air so instead the turbofan and turbojet engines move less air but make it go faster. The danger of the propeller tips breaking the sound barrier *is* real, but it has more to do with the airspeed of the plane. The propeller's rotation alone isn't fast enough to break the sound barrier. Instead, it's the combined velocity of the rotation speed *plus* the plane moving forward through the air that presents the real danger. As the other comment points out, turbofan engines have cowling that slows down the air flowing into the engine such that regardless of how fast the plane is going the air in the engine will always be subsonic. That's was actually a very difficult design challenge for early supersonic jets, because the engine won't function if the air going in is supersonic.",
"Geared turbofans are starting to become a thing. Some of them do have gear boxes. In a normal turbofan, the fan is designed to spin optimally at the same rate as the low-pressure turbine / compressor. You don't want the fan blades to spin too fast, so this means that the rotational speed of the lower pressure turbine / compressor is limited. This means that sometimes more compressor stages are required, thus adding more weight and complexity to the design. You could use a gearbox to fix this, but gearboxes add weight and complexity too. The gearbox has to provide enough benefit to offset the costs associated with including the gearbox itself. Whether or not to have gearbox becomes an exercise in engineering trade-off. Each specific engine will take a different approach depending on it's application and how it was designed."
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k0e542 | How does jumping a dead car battery work? Are you losing electrons from the donor car? Are you losing long term battery life or damaging the donor car in any way? | Engineering | explainlikeimfive | {
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"No, you can't spill electrons on the ground. The current flows from the donor battery on one cable to the dead battery, through the car, to the starter, and them back through the other cable to the donor battery. Starting an extra time or two won't hurt anything, but it shouldn't be an every-day behavior.",
"A battery have two poles. One negative and one positive. In order to push electrons into the positive pole, the same amount is withdrawn from the negative pole. In other words, there will always be an equilibrium of electrons."
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k0j075 | Why do scissors only work in one hand and not the other? | Engineering | explainlikeimfive | {
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"The force you apply to the two handle pieces of a pair of scissors, isn't a totally flat force parallel to the cutting plane. You're also pushing with your thumb and pulling with your fingers laterally, to create a stabilizing pair of opposing sideways forces. When you're using the scissors in the correct hand, those opposing forces are directed so as to pinch the cutting edges together as they swivel. In the wrong hand, it splays them apart instead.",
"When cutting there is a slight sideways force not just the squeezing. In the opposite hand it's difficult to apply the opposite sideways force.",
"The primary difference between left and right handed scissors is the way the blades are connected. The special thing about scissors for left hands is that when you open them, the blade on the left hand side goes to the top. This means the blade on the right sits on the bottom."
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k0l9hn | Cold Cut Saw Blades | I'm talking about the blades that are cold cut metal blades, so they can cut without sparks etc, and leave a clean cold edge. What's the science behind them? How do they work so effectively? | Engineering | explainlikeimfive | {
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"Hard things cut soft things. Instead of cutting by heating the metal molten, it cuts out chunks with the blades the same way skilsaw cuts wood without burning it. The science is attaching really hard teeth like carbide (that like to shatter and don’t weld easy) to a flexible and strong blade with the right number of teeth and shape and speed to stay stable during cutting."
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k0ouae | How is horsepower actually measured for both wheel horsepower and brake horsepower? And are there limits to the technology that measures them? | Engineering | explainlikeimfive | {
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"Horsepower is measured with a dynamometer which is any device that can measure torque and rpm at the same time. For wheel horsepower it's a pair of drums that the car sits on top of that work kindof like a car treadmill. (With the car held firmly in place to keep it from jumping off) A very basic dyno will just be a heavy known weight and by measuring rpm vs time you can tell how much power is generated by how quickly the drum spins up. Usually though it's a motor/generator which can provide variable resistance and can calculate HP by measuring how much power is generated. Similar thing with brake horsepower though usually that's done with a motor mounted on a stand outside of a car with the motor bolted to the dynamometer."
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k156sg | How do processors work? How are a bunch of transistors able to make logical decisions? | Engineering | explainlikeimfive | {
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"If you have the time, I highly recommend a youtube series by Ben Eater, in which he shows how a simple CPU can be made almost from bare transistors. He shows how a few transistors (electronic switches) can be combined together to make _gates_. Gates usually have 2 inputs, and 1 output. With an XOR gate, for example, if one of the inputs is zero voltage, and the other is a positive voltage the output have a positive voltage; otherwise the output will have zero voltage. He then shows how a few gates can be connected to make a _flip-flip_. The key to a flip-flop is that the output of the gates are connected to to inputs of other gates, in a loop. This results in the flip-flops having state: the outputs can have a voltage even when the inputs have been switched off. Building from that, flip-flips can be combined to make _registers_, which are like tiny bits of RAM. Gates can also be connected together in a different way to make _arithmetic logic units_ and _control logic_. Control logic, which to me was the most mysterious part of a CPU, is actually the least interesting, I found. It’s just a lot of gates wired together so that any particular machine code instruction (just a series of on/off bits) results in a particular set of components inside the CPU being activated or not. Finally, everything is connected together with a _clock_, a device that pulses regularly, and causes all the other components to do their thing at the same time.",
"Transistors act like switches (transistor literally means trans-resistor, i.e. a resistor you can control, effectively controlling if the current flows or not). Switches are the easiest component to implement a logic function. Think about it: link two switches together and you have an AND gate, i.e. something that is on only if both switches are closed. Link two switches in parallel and you have an OR gate, i.e. something that is on when at least one switch is on. With this reasoning and some algorithms you can create every logic function you need. Now processors are a lot more complex, they are made of many smaller components called buses, but the most important ones are two: the ALU and the cache memory. ALUs are basically a big bundle of logic functions, you can add two inputs, you can compare them and many other things. Cache memories are extremely fast but very expensive memories, made with groups of transistors called flip-flops (which are called flip-flop because the first ones made this sound, fun fact) which the processor uses to elaborate all the data you ask, by using an address system to understand what piece of memory its being used. Basically you the programmer use a very simple language called Assembly to tell the computer exactly what to physically do when, for example, someone uses an add function. I know it sounds confusing so I'll make an example to help you understand: you want to make a program that sums whatever two numbers are written by the user, so you tell the processor to take the numbers from the cache memory (where they are stored once you input them, there's a bus in the processor whose job is to interpret the user interface input, i.e. your keyboard, your monitor etc.), send them to the ALU and tell the ALU to add whatever you sent and send you back the result, which is stored in another cell of the cache and sent back to your monitor. I simplified a lot and cut many things, but if you're interested I can go on forever, this is what I do for a living :)",
"I highly recommend the book called \"But how does it know?\" it is a great introduction on the topic which quite honestly is a bit too elaborate for an ELI5. On a very basic level a transistor does not know. It is how the transistors are arranged that lets it \"know\". Its applying simple rules to them on how they act and combining these small parts into more and more complex parts, which is of course extremly oversimplified to fit ELI5."
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k1b8dc | How does google search go so quickly? | Engineering | explainlikeimfive | {
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"Google doesn't search the internet when you make your query, they *already* searched it in advance. They make what are called \"indexes\" that function much like the index in a book, pointing to locations within a database without needing to look them up right then. The indexes are held in active memory so they can be accessed extremely quickly. Google has programs constantly crawling the web and creating the indexes, and this takes much longer than just referencing the ones already made."
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k1ivx0 | The cockpit of a large jet has a mind-boggling number of buttons, switches and gauges. How does a pilot keep up with all them and know if one has accidentally been hit or changed from its proper setting? | Engineering | explainlikeimfive | {
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"Each device that needs to be controlled have its own panel. So each panel only have a few buttons. And the panels are located in a systematic way based on how often they are used and what they do. So when pilots are looking for a specific button they only need to know what it does and can therefore find its panel and read the label on the buttons on that panel. Pilots have long checklists for everything they do which mainly consists of going through a bunch of settings to make sure they are set correctly for what they are doing. So that if a switch have accidentally been changed they will notice it when they go through the checklist. They do not have to go through every button for every checklist, only those that matter for whatever they are doing. In addition to this there is systems that are constantly monitoring everything and sound an alarm if something is wrong. Pilots are then able to notice the issue and fix it before it cause more harm.",
"Ironically we don't use most of those switches on a average flight. Starting a modern jet is actually pretty easy. It's a few switches and you're good to go. Mostly the airplane does it it self once you press the right buttons. Mainly its making sure that every switch is in the right place and knowing when to add fuel to the fire. Here is a video of the 737 start up procedure from someone's home sim. [ URL_0 ]( URL_0 ) Pretty simple if you know what you are looking for. (shocking this is someones battlestation in their home). Edit: here is a full start up procedure [** URL_1 **]( URL_1 ) An abbreviated version of the start check list is as follows **Preflight Procedure (Battery and APU On)** * Battery — on. * Standby power — on, guard closed. * Alternate flaps master switch — off, guard closed. * Wipers — off. * Electric hydraulic pumps — verify off. * Landing gear lever — down, lights on. * Weather radar — off. * Fire test and extinguisher test — perform. * Left aft fuel pump (used by APU) — On. * APU — Start * APU transfer bus — On. * BUS OFF, TRANSFER BUS OFF, APU MAINT, APU LOW PRESSURE, APU FAULT, APU OVERSPEED lights — extinguished. * Wheel well fire system — test. * Lights — as desired. * Recirculation fans — Auto. * Packs — Auto. * Isolation valve — Open. * Engine bleeds — On. * APU bleed — On. **Engine Start (APU)** * Packs — off. * Fuel pumps — On. * Electric hydraulic pumps — On. * Ignition switch — left. * Left engine start knob — START position. * When N2 reaches 25% or max motoring: Left fuel cutoff handle — Idle. * Monitor EGT, oil pressure, and N1 for proper start indications. * When left engine N1 stabilized, verify starter cutout and normal indications. * Left engine start knob — Ground position. Actually pretty simple once you know what you are looking for.",
"Pilots live and die by checklists. There are checklists for normal operations like engine startup and shutdown, and emergency checklists for things like engine fires or electrical power loss. Verifying the status of those switches or gauges, and adjusting them will be part of one or more checklists, and still others will be used during normal flight operations to verify the status of the engines or flight controls. This is all normal procedure that pilots are required to learn in order to fly an aircraft."
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k1lpdt | How does a computer chip "poll" the clock to see what time it is? | Engineering | explainlikeimfive | {
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"The computer holds a number internally that represents the current time. Most computers can reliably give you time with an accuracy of 1 microsecond. They can give a value that is more accurate (e.g. 1 nanosecond) but you can't trust this value due to complexities of the computer and OS. This number is incremented using a reference oscillator. These are crystals that produce a voltage that oscillates at a very well defined frequency. However this frequency isn't a 'nice' number (generally 32768Hz). This frequency doesn't fit nicely into our counting system, and is also quite slow. To solve this, we invented a digital circuit called a 'phase locked loop'. This circuit can use a lower frequency reference signal (our oscillator) and then generate a very accurate higher frequency oscillation. We can then run our CPU (and therefore our clock counter) from this higher frequency oscillation. As the number for time is stored within the CPU itself, there isn't really any polling happening. The CPU knows the address of a register that contains the current time, and can query that address whenever it wants to find out."
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k1phj4 | I understand why we have treads on tires, but why are specific shapes and positions of grooves what they are? | Engineering | explainlikeimfive | {
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"As far as I know, a more normal street tire has “arrow shaped” design that filters water in a way that aims prevents hydro planing . An off road tire, has grips that are meant to help the vehicle climb through dirt and mud and even snow. I am assuming the designs just differ from company to company based on their own take. That’s all I have for you!"
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k1q2ps | How exactly are air and fuel mixed in Bunsen Burners, Internal Combustion Engines, and the like? | Engineering | explainlikeimfive | {
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"They will be different. Bunsen burners, if my memory serves, have a series of vents near the bottom which let air flow into the burner from underneath. The high pressure of the fuel gas coming out of the nozzle will draw the surrounding air to flow with it; this is called entrainment. The gas combusts with the entrained air. The vents then let more air into the burner area from the bottom, and the process repeats.",
"In an old-style IC engine the piston going down sucked in air which passed over an orifice in the carburetor. The low pressure created by the flowing air sucked petrol droplets into the airflow which then evaporated to make the fuel/air mixture that the spark plug ignited. Nowadays the petrol droplets are sprayed directly into the cylinder by the injector to give more precise control over ratio and timing. The Bunsen Burner has gas going into the bottom of the vertical pipe through a narrow jet, increasing its speed. Also at the bottom of the pipe are (usually two) sizeable holes to the outside air which can be opened or closed by turning a collar. When they are closed, just gas flows up the pipe and burns in the air with a yellow, smokey flame due to the poor mixing. When the holes are open, air is pulled in due to the speed of the gas. That mixes into the fuel so it burns hotter and more completely."
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k24go0 | How are buildings that are higher then cranes built ? | Engineering | explainlikeimfive | {
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"You can place the cane on the building and move it up as the building goes up. When the building is taller than the available cable length, you can add another crane some place below, it can bring the item part way up, then drop the load off in a collection area and the next crane will collect the item and continue the items ascent.",
"The crane is modular can can build it's self as tall as needed to construct the building. URL_0"
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k2ghg1 | Why are bedpans in hospitals always kidney-shaped? | Engineering | explainlikeimfive | {
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"They're not. A bedpan is shaped [like this]( URL_0 ), similar to a toilet bowl so that the patient can sit on it or have it placed under them. You're thinking of one of [these]( URL_1 ) - a kidney dish for vomit or blood. It's for the other end, and is shaped the way it is so it can be tucked under the patient's chin or held closely against their body to catch whatever comes out."
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k2omjo | In regions that are "100% powered by renewable energy", what happens to the traditional power plants? | Engineering | explainlikeimfive | {
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"In general they have been decommissioned or repurposed most power plants have a life span of 20-30 years anyway before they need to be replaced. One of the most famous ones is in London Battersea power station. URL_0",
"In many cases they still have them and use them (particularly during peak usage or during times when renewable means aren’t producing enough like night/low wind for solar/wind) but much less. The trick is many “100% renewable” numbers are often “net” so if they make a ton of renewable energy during the day (more than they can use) and sell it to neighboring regions (and reduce those regions reliance and use of fossil fuels, etc) they count that as an offset to the limited use of fossile fuels they may still use.",
"Many are converted to run natural gas as backup for the renewable generators. Most 100% renewable energy regions are 100% for like 48 hours at most, but that will change as more renewable sources are added to the grid. I'm particularly excited about Eavor-loop geothermal energy generation, which could be outfitted to an existing steam driven turbine plant.",
"There are no sizeable regions outside Iceland with significant populations which achieve this claim. There are gas-fired peaking plants or separate industrial power plants. Old power plants are often recycled, you can take out a coal boiler plant and use a new gas-fired plant to feed steam into the coal plant's old turbines. Sometimes it's worth it to move the turbine to a new location, so the old facility can be sold on the real estate market.",
"Plenty of \"100% renewable\" regions use old coal plants on reserve when renewable is in short supply or demand spikes (snow storms, heat waves, etc). The exception is hydro, which is fairly reliable in its output.",
"To the best of my knowledge \"traditional\" power plants were never really a thing here in Iceland, except for 2 small islands that aren't connected to the main grid, they use diesel generators.",
"there are very few regions (or jurisdictions, in energy community parlance) that really use 100% renewable power. and that’s just electricity - you won’t find a jurisdiction with 100% renewable energy supply across *all sectors*. these are Albania, Iceland and Paraguay, with Norway at 97%. At least for Albania and Iceland, there never really was any fossil (or “conventional” power plants). “Old school” renewables such as hydro and geothermal have simply been abundant and cheaper. Where you actually see fossil fuel power plants (as well as nuclear) being driven out of the market is where modern renewables, primarily wind and solar Photovoltaic, have been deployed at scale. Germany, Spain and Denmark are your typical poster children. The rise of modern renewables has been part policy (most notably feed-in tarrifs and more recently, CO2-price), part advances in technology and costs (in turn also to a large extent driven by policy), and changes in market regulation, most notably liberalisation and vertical desintegration of power companies (again, policy). what this did to conventional power generators was to push them out of the market, and fast. UK is almost without coal at the moment, whereas it was a pillar of it power system a bit more than a decade ago. Germany has seen coal generation drop precepitously, as low marginal cost renewables have suppresed the power market prices and the CO2 price has risen recently. in many regions with good solar potentials it’s cheaper to *build new solar PV* than operate existing fossil generators. natural gas generators have been less badly hammered, and low gas prices have helped them, but they’ve also been suffering. so coal power plants are shutting down in many places simply because of economics. the irony of this that with rising share in the power mix of variable renewable sources such as wind and solar, you have to complement this with power generators that can be regulated. hydro is perfect, but potentials are limited almost everywhete in the world (with few exceptions such as Albania, Iceland, Paraguay and Norway). natural gas is the next best thing. but with whoselase power prices suppressed, new gas capacity is not comimg online. and there’s no easy fixes for this. in Germany, coal power plants that are due to go offline, will be kept in strategic reserve at billions of euro in costs, and at grave environmental consequences if they turn out to be needed. tl;dr fossil power generators are getting pushed out of market, but in case of natural gas, that’s not an unequivocally good thing. the whole power system needs to evolve beyond just adding renewables in order to be able to reach 100%. EDIT: apparently, this was understood by some as stating that a nearly 100% renewable energy supply across all sectors is not possible, or at least that we shouldn‘t rush it. in fact, it’s actually possible with today’s technologies. the harder questions are non-technical, e.g. how fast can we deploy, how do we re-organise markets to set the necessary incentives, how do we solve the IT side of a truly IoT energy system, how can we get away with such a massive change from a social and political perspective, etc. but if we can manage these non-technical aspects, different studies show we can achieve a global 100% renewable energy *across all sectors* by 2050 and not just that, it‘s cheaper than the current, largely fossil-based system if you put a monetary price on environmental destruction wrought on by unmitigated climate change. so the point many of the energy transition pioneers have been increasingly making lately is, don‘t worry about the last 10% of the fossil fuels you‘ll need to get out of the system 30 years down the road, where the non-technical problems make it look like an impossible thing from today‘s perspective. focus on the 90% that you can already achieve now and push ahead. don‘t make perfect the enemy of the good. that is because time is critical and even the 90% energy transition that we can achieve with today‘s technologies is an insanely complex challenge. there isn‘t one size fits all solution. batteries can be a big part of the solution - if they were another notch cheaper and could be scaled much, much fastet than what we are able to fo now. that is because, with the exception of places near the equator, you need to store power not for the night, but for the winter. if you have one charge-discharge cycle per year, the necessary quantities are huge and cost per unit of energy deployed is just not acceptable. pumped storage could play the same role but here too, capacity is limited almost everywhere. it‘s often said that Norway can store enough power in their high-above-the-sea-level dams to get at least Scandinavia through the winter. well, no, because you can’t pump sea warer into fresh water lakes if you’re not willing to kill off their entire ecosystems. electrolytic hydrogen and synthetic fuels (known as Power-to-X) look promising right now because they’re based on mature technologies and theoretically, enough renewable power can be converted into chemical energy to provide seasonal storage for entire continents. but here, you also have your problems, namely low efficiencies and high costs. hydrogen as such is also a nightmare to transport and store; if you go a step further and produce synthetic methane, diesel, kerosine or ammonia, you can use existing fossil-fuels infrastructure, but you’ll add furthet conversion losses and increase once more the costs. that’s why the current hydrogen hype is largely just that. hydrogen as such an synthetic fuels will probably end up occupying niches that electrification and other technologies can’t decarbonise, but won’t become the new oil. another solution to renewables’ intermittency is to build out the power grid. the sun always shines somewhere, after all. but this is neither cheap, fast or popular. you can always theoretically just build more renewables so that even in the winter, sun will provide enough energy to power your electric car and your heat pump, even if you’ll have to waste a lot of it in the summer because you’ll just have no need for it. modellings show this will actually likely be an important part of the solution for a 100% renewable system. at least PV (wind less so) is actaully on the track to het so dirt cheap that this would make economic sense on its own. the problem is what this does to your power *market* - if you have zero-marginal cost renewables covering your entire power need for 3/4 of the year, all the other technologies that you need to get you throught the winter only have have three months a year to refinance themselves. what else is there ... ah, nuclear. current gen4 reactors are too expensive and too slow to deploy. typically, a nuclear power plant takes 10 years from the where the investment decision is made to where it comes online. that’s just too long at the pace we need to decarbonise at. also, the investments are huge and companies all over the world have always been relying on governements to step in and bail them out when they had costs overruns. then, in EU, Japan and Korea, power markets got liberalised and companies in the nuclear business just didn’t have the chops to build new plants. all that said, as long as existing nuclear power plants are able to *safely* provide you carbon free power, they should do so and shutting them down early (as many countries are in the process of doing) is absurd from the standpoint of fighting climate change. on last thing that gets mentioned a lot is flexible demand. basically, use power when the sun is shining and the wind is blowing. that works to some extent but you probably won’t ask a hospital to go offline for a couple of hours. also, if you want to cram daily power demand into a few sunny and windy hours, you’ll need to transport much more at once, and the current power grid can‘t handle that. bulking it up enough to do that is far from your economic optimum. the last solution I will mention here which should perhaps be the first is energy efficiency. it‘s the least sexy of them all but absolutely essential to achieving a 100% renewable energy system, and the most economic partial solution across different sectors. a combination of these technologies and approaches is what a 100% renewable *power* system which is the backbone of a 100% renewable *energy supply across all sectors* could look like. i‘ve skipped some important parts but the point is that we already have the tools to get to at least 90% already. the last 10%, we can figure out as we go. not knowing how we‘ll manage the last 10% shouldn‘t be the reason not go full steam ahead with the first 90%.",
"Almost always, fossil fuel plants stay online to support renewables. Nuclear has the least fuel support, then hydro, but their mix hasn’t really changed over time. There are small, rare, rural examples of almost completely renewable.",
"Still needed for backup in case the wind doesn't blow or the sun doesn't shine. Forget renewable. How about green Nuclear?",
"I live right next to an old coal power station. It was decommissioned 6 or 7 years ago. It has been demolished slowly over the past year, mostly due to covid causing delay. It was part of a bigger site but 4 of the 8 cooling towers were demolished in the late 90's. The old boiler house was demolished near the beginning of the year. 4 cooling towers remain and one big chimney as well as some smaller buildings. The taller chimney is due to be demolished the beginning of January shortly followed by the remaining cooling towers and buildings. The land has plans already set in place for it to become housing and a few shops, schools too! It's pretty cool to watch them demolish parts, my sons especially enjoy it! Edit: Forgot to mention i am in the UK",
"Coal fired are decommissioned or repurposed to use gas. Gas fired will remain as short term (a couple of decades at most) solution for surge demand. Further down the road it *may* be possible to further repurpose them to run on hydrogen fuels. Use renewable to make hydrogen fuel in peak availability, later burn fuel to supply for surges. But by then it may be more cost effective to build a new more efficient plant. TLDR: They will all be scrapped eventually. In the long term surge demand will be provided by hydrogen power, batteries or pumped hydro. See: URL_1 URL_0",
"Manitoban here. 97% of our electricity comes from hydroelectric power. We also have 2 large wind farms. We have 2 plants that are natural gas (1 is mixed use with coal) powered, but are there for peak demand. There are also apparently 4 isolated communities that use diesel power generation, but they only make 3 or less megawatts of power each.",
"I live in Vancouver BC. We could get all our electricity from hydro electric dams, but we actually buy a lot of power from coal fired plants in Alberta. Here’s why: The coal power plants in Alberta burn coal to heat water to make steam, and then they use the steam to spin a generator. Just like boiling a kettle takes time, starting up a coal fired plant takes time. So they prefer to run coal power plants almost all the time. But in the middle of the night people don’t need much electricity. A hydro dam can go from zero to full power and back to zero much faster than a coal plant. So I’m the middle of the night BC buys power from Alberta and then in the morning when everyone in Calgary turns on their lights and coffee makers we sell them a bit of our hydro power. We also sell power into the United States during summertime heatwaves. In that case everyone in Los Angeles is turning on their air conditioning at the same time, so they need extra power. We just open the taps at the hydro dams make more and sell it. There are even bizarre times when BC is buying power from Alberta at the same time as they are selling power into the US. This happens because all the power companies are connected to the same electricity grid which spans all over North America and can buy and sell energy from each other.",
"I’m in the industry and am part of a group involved in answering this complicated question. I’m not sure if the answer you’re looking for is related to the impacts on jobs, on the local peer grid, the jobs in the local community, the environment, or power bills for customers. It impacts all of them in important ways, and those answers will be nuanced usually. My area is finance, so I’ll speak to that more specifically. In most of the US, electric utilities are are regulated monopoly, meaning since there is no competitive market the government audits the utility to ensure the rates being charged grant a reasonable profit and recovery of operating and maintenance costs. Accounting rules require plant and equipment to be depreciated over the course of the expected life of the asset. In other words, a utility that built a coal-fired power plant and expected it to operate for 40 years would make financing arrangements which allowed it to collect 1/40 of the cost of the plant through customer’s bills each year + the cost of capital (interest and dividends). When a major asset like a power plant shuts down ahead of the original depreciation schedule (less than 40 years in this case), power company and the regulator need to make decisions about how to pay off the remaining debts associated with the assets. Beyond the financial, there are important questions about what makes the most sense as a replacement power resource, requirements for environmental remediation, local workforce retraining resources, etc. Many complicated issues, and every state will address them differently.",
"I don't think it's possible to have a grid with only renewable energy. There has to be a coal plant or nuclear plant to keep the frequency steady else people connected to the grid will get broken appliances."
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k2qd1i | What are the physical/mechanical differences between an air conditioner and a heat pump? | Engineering | explainlikeimfive | {
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"Both a central AC unit and heat pump systems are considered a type of central air HVAC system as they transfer (or pump) heat from inside the structure to the outside to cool inside temperatures. The major difference between an AC unit and a heat pump is that heat pumps can reverse their air flow direction and transfer heat from the outside to raise indoor temperatures by utilizing a reversing valve built into the compressor. Edit: I sell the things.",
"There is almost no difference, besides having a pump that can be reversed and a thermal expansion valve capable of handling flow in either direction.",
"A heat pump generally have valves that allows it to swap the evaporator and expansion coils around in the circuit. This means that the inside coil can act as either a heater or a cooler depending on the temperature."
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k2tebs | What happend at the Deepwater Horizon? | Engineering | explainlikeimfive | {
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"Here’s my explanation as a petroleum engineer and recalling what my friend who is a drilling engineer for BP told me (he ended up drilling the relief well that finally allowed BP to kill the blowout). A deep water exploration well was being drilled. When you reach your target depth, through the oil producing zone, you then run metal tubing called casing into the hole and pump cement into it to completely seal the entire wellbore. In a later step, holes will be shot through the casing into the reservoir, but at this point it is imperative that the casing and cement seal the whole wellbore. The cement is pumped down trough the casing and when it reaches the end of the tube at the bottom of the well, it u-turns and comes up the backside between the outside of the casing and wellbore wall. This is the main seal that keeps all liquids and gas from entering the wellbore. As you can imagine, getting the cement to completely fill up the annulus between the outside of the casing and the inside of the wellbore over 10,000+ feet is not easy. Voids can be created, thief zones can cause the cement to flow into highly porous rocks, and contamination can prevent the cement from setting. So, when the cement job is done, there are a series of tests that are run to test the cement job. Cement bond log are run which is an acoustic tool that can measure how well the cement set (think of it like tapping on a wall to find a stud and listening to the response). You also then run pressure tests, where you pump into the casing, building up pressure to a set number and then shut in the well and watch to see if there is any pressure bleed off, which would indicate a leak. BP broke several standard operating procedures in an effort to hurry up the job (an offshore drilling rig like that costs about $1 million a day). They decided to skip the cement bond log that would have shown poor cement coverage. During the pressure test of the casing, they were seeing pressure bleed off, indicating that there was a leak. The rig supervisor, under intense pressure from BP to wrap things up, convinced himself that the leak was not in the casing, but that there was an issue with the tubing that connects to the casing. So, essentially they ignored the failed pressure test. At this point in a standard drilling operation, you are pretty much done. The last step is to circulate out the drilling mud and replace it with a clear brine water. When you are drilling a well, you are always circulating drilling mud through the wellbore. Drilling mud performs 2 major functions: to remove the rock cuttings from the wellbore and to exert enough pressure inside the wellbore to prevent any oil, water, or gas from flowing into the wellbore. Drilling mud is typically water or oil based with minerals mixed in to increase its weight. For instance fresh water is 8.3 pounds per gallon, where as drilling muds can weight 10 to 15 pounds per gallon. This fluid is very expensive and dirty, so you don’t want to leave it in the wellbore after drilling the well. When BP circulated the drilling mud out of the well, they were replacing it with a clear brine water. The brine weighs much less than the drilling mud. The weight of the drilling mud had been plugging up the leaks that were in the casing down-hole. Once they switch out the mud for the lighter brine, natural gas began to flow into the wellbore. Natural gas is lighter than water, so it flow up the casing. If it reaches the surface, that’s called a blowout... the uncontrolled release of oil or gas into the well and out at the surface. There is a safety system that is always used, called a blowout preventer. This is a series of hydraulically operated rams that have a series of blocks within it. Some rams close around the tubing to form a seal, some rams have cutting blades that cut the pipe, some rams are designed to seal the whole wellbore shut. When BP saw the blowout coming on their pressure gauges, they activated the blowout preventer, using the seal rams. These were not able to hold back the pressure. They then activated the shear rams to cut the pipe and seal the well bore. Unfortunately, there was a casing collar (the thick part of the tubing where the threads connect one length of tubing to the next) sitting across the shear rams. The shear rams are rated to cut through the body of the tubing, but not the thicker collar. So, all activation of the BOP failed. At this point there is no way to stop the natural gas and oil from flowing to the surface and spraying all over the rig. If that gas finds some form of a spark...boom. Sparks are easy to find on a huge rig. The last option is the emergency disconnect. This severs the pipe connection from the rig above the BOP (which is on the bottom of the ocean floor) and allows the rig to move away from the blow out well. There was a long delay in this being activated due to lack of decision making. This a multi-million / billion dollar decision. By the time the decision was made, the rig had already caught fire and the emergency disconnect was damaged and did not function. As a result, the rig burned down and the worst offshore drilling disaster was born. A confluence of illegal shortcuts, poor decision making, bad communication, and bad luck came together in just the right way to cause this disaster.",
"Deepwater was deep, 18,360 feet (5,600 m) deep. They were drilling into rock from the surface and doing all of what they needed to do remotely like building a ship at the end of a bottle with a 5,600 m long neck. Part of the process requires capping the hole they made with a water tight seal. Three tests were done to make sure that the seal was secure, and only 1 came back saying everything's fine. The seal wasn't fine. When they relied upon the seal to hold everything down, it instead erupted with oil and caused an explosion.",
"Like many industrial accidents, a lot of independent mistakes lined up all at once. The immediate cause was that they let a huge bubble of natural gas get into the well and up to the surface, where it got sucked into the rig's engines, ignited, and exploded. The explosion (plus some other failures) took out all the ways of sealing the well, so now they had a free-flowing hole directly into a significant oil/gas reservoir. This dumped a huge amount of oil and gas into the Gulf of Mexico. It kept doing that until another bunch of rigs could come in and plug the well. You know those old pictures of oil gushing out of the ground somewhere in Texas or Oklahoma? It was that, only much much much bigger, and underwater. Some of the major things that went wrong: \\-When they drilled through the oil/gas zone and cemented the pipe in place that was supposed to seal the oil & gas in, the cement didn't actually seal. \\-When they did the test that should have verified if the cement sealed, and the mechanical seals at the top of the pipe were working, they mis-interpreted the results and thought the seal was good when it wasn't. \\-When they resumed operations after the pressure test and started to get oil/gas coming into the well, they didn't realize it (this is harder than it sounds on large deepwater oil rigs). \\-When they finally realized that they were gaining fluid and tried to close the well (using a huge piece of equipment called a blowout preventer or \"BOP\") the BOP failed to fully seal because the drill pipe had been pushed out of position by the oncoming oil & gas \\-When the oil & gas got above the BOP (on the sea floor) into the larger pipe called the riser that connects the BOP to the rig, it began pushing all the fluid in the riser up and onto the rig. For reasons still unexplained, although there are theories, the rig staff didn't activate a piece of equipment designed to deal with this situation, called a \"diverter' that might have shunted all the incoming fluild/oil/gas safely overboard. \\-When the natural gas bubble engulfed the rig and exploded, it severed the electrical & hydraulic connections between the rig and the BOP. The BOP is supposed to respond by closing \\*all\\* the valves, including some that are explicitly designed to cut through any drill pipe in the way. But due to some deferred maintenance from several weeks/months earlier, two independent systems that were supposed to do that both failed. Had any one of the above not happened, the disaster would have been prevented or significantly less severe."
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k2tvba | Why aren’t any modern planes, biplanes? | Wouldn’t a biplane with a modern wing shape have the same amount of lift for about half the wing length? This would make the wings shorter, so more compact and more structurally secure than a longer piece of metal that is subject to large forces and only attached at one end. This all sounds cheaper and more fuel efficient, plus biplanes are cool EDIT: Thanks everyone! I assumed I wasn’t smarter than everyone at Boeing, Airbus etc but you never know 😀 | Engineering | explainlikeimfive | {
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"> Wouldn’t a biplane with a modern wing shape have the same amount of lift for about half the wing length? No. Due to aerodynamic interference between the two wings, a biplane configuration does not give twice the lift of a single wing of identical span. In addition, shorter wings have higher drag coefficient than longer wings of the same area. This means that if you were to replace a monoplane with a biplane of half the wingspan, it would have a lower lift coefficient and higher drag coefficient, which translates into more thrust (and hence fuel) needed to keep the plane airborne. It would be more structurally rigid, which is a major reason why early aircraft often used a biplane configuration. They had relatively primitive materials to work with and they weren't flying very fast, so drag wasn't such a big issue.",
"Two wings means more drag, both due to more surface area and interference drag between the wings. It also means a poor lift-to-drag ratio that results in pretty bad glide characteristics. If you have the technical capability to build a monoplane there's no reason to use a biplane configuration.",
"Wings are long because being long and thin makes them low drag. They could be much shorter and generate enough lift, but the drag would be higher. Add another wing on top and the drag is higher still. So the upshot is that biplanes would burn more fuel, making them more expensive to run.",
"The cons with biplanes outweigh the Pros. They are still being used for aerbatic shows but other than that, They are pretty far behind a modern Monoplane with the same capabilities.",
"The way biplanes are designed causes a lot of drag that cant be avoided, both in the way the wings are positioned and the supports holding them up. No amount of modern techniques or materials can overcome that fundamental inefficiency. They just use too much fuel and go too slowly. Of course, that doesn't mean there are no modern uses for such planes. Just that most of the time with a plane, the whole point is to go as fast as possible."
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k2xxmm | Why Are Airplane Engines Situation So Far Onto the Wings? | Wouldn't it make way more sense structurally to have the engines as close to the body as possible? I often see them at the centre of the wings, and sometimes I'll see missiles/fuel tanks at the wingtips of fighter jets which seem even more structurally unsound. They should have them either inside the fuselage somewhere or on top, like at the tail and such, or at the very least right next to the fuselage. What makes that position so optimal? Aren't the wings under unnecessary and enormous stress? | Engineering | explainlikeimfive | {
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"The short answer is that lift bends the wings upwards so engines underneath the wing halfway along both balance that upward force on the wings and have a relatively undisturbed flow of air coming into the engine.",
"Some smaller planes do put their engines closer to the body, typically not connected to the wings. You do need at least a little bit of clearance to get undisturbed airflow into the engines though so you can't mount it right on the fuselage, so they have little winglet things that distance it a bit, but not as much as a jetliner. > Wouldn't it make way more sense structurally to have the engines as close to the body as possible? This isn't quite true though. While on the ground, the fuselage bears the weight of the wings. While in the air, the wings bear the weight of the fuselage, so distributing the weight across the wing might be better for weight purposes, but the materials they use for it will support either positioning. I believe it is done though mainly because of sound. Keep the engine further from the cabin, it makes less noise, because those smaller planes with cabin mounted engines are pretty loud from the inside apparently. Smaller planes do not have the luxury of mounting their engines below their wings, the engines are too big, it would make the plane have a very high set of wheels which isn't optimal either."
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k2y8n4 | How are large ships(cargo, cruise) steered? Are they on autopilot most of the time, like large aircraft? | Also what considerations does the helmsman take when manually steering the ship(like navigating a strait)? Is it intuitive and eyeballing like driving a car, or are there strict guidance systems? | Engineering | explainlikeimfive | {
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"They are steered by a computer for 90 percent of the time. The crew is only there for docking and as a failsafe. There is no eyeballing when sailing these giant ships. With breaking distance measurement in kilometers they basically do a lot of math on board. Or rather let the computer do it.",
"In tight confines such as a narrow straight, busy city waterway, there are also typically tugboats or other small craft for the purpose of steering the large ships. A small ship pushing on the bow of a large ship can allow it to turn much more accurately, and those tugs would also be under the supervision of the port. For larger/busier ports, a Harbourmaster would have control over where each ship is heading likely using a computerized system not unlike an air traffic control. [ URL_1 ]( URL_0 )"
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k32454 | What happens when a transmission slips? | I have a six speed transmission in my truck. Often times when I accelerate immediately after slowing too a near stop, my truck will hesitate and lurch forward. One time I slammed the accelerator particularly heard from a dead stop and heard a clank and the truck moved like it had been hit from behind before it settled in and drove. Any diagnoses? Only happens after coming to a stop, never happens right after starting the truck. | Engineering | explainlikeimfive | {
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"I’d start by checking the fluid level if you haven’t done that lately. You can also empty the fluid into a clean bucket and see if there are any metal fragments or if the condition of the gear oil is acceptable or not.",
"The hesitation and clanking you felt is a symptom of slipping clutches in the transmission. By the sound of it, the transmission is worn out. Power passes from your engine to your wheels via the interaction of clutch disks spinning against each other. When you apply throttle, the transmission pushes the spinning clutches together and causes them to lock rotation due to friction. This transmits power to the wheels. When clutches get worn out, they lose their ability to lock together because the friction material has been worn away. This causes slippage as the transmission is forced to spin the clutches faster and push them together harder in order to achieve a friction lock. The sudden lurch and clanking you feel is the clutches suddenly finding friction and locking together- sending a pulse of energy down your driveline. What can you do? It really depends. Clutches can only be repaired with a transmission rebuild, and that's something you want to leave to a professional. Changing the transmission fluid might alleviate some of the symptoms, but it's never a sure thing. Looking at your other comments, you have a constellation of symptoms going on. The misfiring could be caused by a faulty coil, which is easy to rule out- swap it with a neighboring coil and see if it changes the misfiring cylinder. If it's not the coil then suspect the injector. The ticking is potentially troubling, but ecoboosts normally tick. So without knowing what area it's coming from, it's impossible to say with confidence. FWIW, not a mechanic but I've worked on a lot of Fords."
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k32cwp | What is a transistor??? | Engineering | explainlikeimfive | {
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"A transistor is an electronic switch. By powering one part of it, electricity can flow between two other parts of it. This makes it capable of producing boolean logic (think: binary) circuits and thus do math. Prior to transistors, something similar could be achieved with relays (basically a physical switch operated by an electromagnet), but at a million times the size/cost and one millionth the speed. Transistors are unique in that they have no moving parts, relying solely ob electrochemistry to operate."
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k35b5e | How is there always enough electricity to power our electronics, and assuming there’s extra where does it all go? | Engineering | explainlikeimfive | {
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"There’s always enough electricity because there are people managing the electrical power plants 24/7 to match supply with demand. They make their jobs easier by predicting when they need more supply and when they need less (such as they are prepared to need More when the sun sets, as people get home from worm and turn on their lights). In some places overflow electricity is diverted into battery banks, or put to some other extra use, but in times of “oh holy crap we really have made way to much we’re going to overload the system” there are ways to emergency discharge the excess electricity Into the ground."
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k3brea | Why are wind turbine blades not wider? Wouldn’t they catch more wind if they were? | Engineering | explainlikeimfive | {
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"A wider blade is significantly heavier and won't catch that much more energy, but a longer one will. A blade that's 10% thicker will catch more wind, maybe 10% but also weighs at least 10% more and won't necessarily give you 10% more power. Most of the energy capture is from the tips of the blades which capture wind from the largest area and can turn a given force from the wind into a much larger torque If you instead use that 10% weight increase to have longer blades they'll be a bit over 10% longer and capture a bit over 21% more wind(its the area of the disc, not just the length) so the goal is pretty much always to have longggg skinny lightweight blades so you can capture as large of a disc of wind as possible with the least material",
"The intention is not to catch wind, but to use the wind to rotate the blades. If they were bigger like a sail, the blades wouldn’t rotate. Hence they are designed aerodynamically so that they rotate with lesses wind speeds.",
"I'm not sure what the other answers here are talking about, I believe the reason that wind turbine blades are long and thin is to have a high aspect ratio. Wind turbine blades are basically wings, and in aerodynamics at low speeds a high aspect ratio, or a long and thin wing, will produce less drag for a given amount of lift then a lower aspect ratio, or a short and wide wing. On wind turbines, drag is a loss, as they are driven by lift, so minimizing drag by having a very high aspect ratio makes a wind turbine more efficient. The type of drag that is caused by generating lift is called induced drag, and it is generally inversely proportional with the aspect ratio of the wing. This is also why most subsonic airplanes have long and thin wings. In particular, if you look at gliders and sailplanes, they also have extremely high aspect ratio wings for the same reason. There are vertical axis wind turbines that use drag to drive the blades, which do have very wide, sail-like blades."
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k3eb81 | How do spaceship parts fall without damaging surrounding areas or hurting anyone? | Not sure if the right flair, but when you see a rocket ship take off some of the parts fall off as it goes up. How do those heavy pieces of metal fall back to earth safely without hurting anyone or destroying property? | Engineering | explainlikeimfive | {
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"Launches (US and Europe launchers) typically happen from a location where the discarded stages can fall in the ocean, and before a launch that area is cleared and people are warned to not enter. A similar thing is done in Russia's but over uninhabited desert. And China just... Doesn't really give a shit so their stuff falls near remote villages all the time. And stages discarded at higher altitudes burn up on reentry.",
"Generally speaking, rockets are launched over sparsely populated or uninhabited areas for exactly that reason. The US, for example, launches mostly from Cape Canaveral, which is on Florida's Atlantic coast. Rockets generally track east-northeast or east-southeast after launch, depending on the intended orbital inclination. Radio messages are broadcast prior to launch warning ships away from the rocket's downrange trajectory to reduce the risk of a booster falling on someone's head. The boosters fall into the ocean. The Soviet Union launched from Baikonur Cosmodrome in Kazakhstan. Rockets again tracked over sparsely inhabited desert (if I'm reading Google Maps correctly). The Soviet government being as secretive about literally everything as it was, I can only assume that any known inhabitants in harm's way would have been warned prior to launch--but then again, the Soviet Government's track record on human rights could charitably be described as \"no fucks given,\" so who knows?"
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k3ebsr | - What is limiting computer processors to operate beyond the current range of clock frequencies (from 3 to up 5GHz)? | Engineering | explainlikeimfive | {
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"Mostly heat generation and lack of dissipation. Faster things produce substantially more heat than slower things, and with as dense as we pack that stuff in, there's only so much heat we can get rid of so quickly. Eventually it'll just melt. Or at least it will cease to perform as a computer needs to perform. edit:: Making the CPU larger serves to increase the length between each transistor. This introduces a time delay that reduces overall clock speeds. CPU's are packed as densely as they are because that's what gives us these insanely fast clock speeds that we've become accustomed to.",
"The limitation on clock speed is caused by a concept known as the \"Critical Path\" through the CPU. Each of the 100s transistors used to make a calculation, (add, subtract, write to mem, read from mem, etc) need time to potentially change states. To go from a 1 to 0 or a 0 to a 1. The clock speed must be slower than the slowest possible calculation step so that in a worst case all operations can occur and fully complete within 1 cycle. Modern chip use tons of techniques, one of which is called pipelining, to try to run operations in stages to circumvent this limitation. For example while a math operation is calculated, the values for the next calculation can be loaded into place ready for the next cycle. This creates interesting challenges when the result of that second calculation depends on the second, but that is the price you pay for speed in that case. In addition as others have mentioned, beyond simplifying the structure for a shorter critical path (part of why Apples new M1 Chips are so much more efficient), you can make the switches flip faster. However this is a thermal issue. A stored 1 value or 0 value changing into the opposite requires current to flow in or out of the transistor, which generates heat which must be removed or the transistor will degrade or even melt. The more you have flipping faster, the more heat you get. Lastly, you can shorten the critical path physically but making it shorter but designing the CPU die so that components that talk to each other are close by or making the transistors themselves smaller through this cant be done in all cases. We have been building CPUs with components so small that the actual speed of electric voltage moving though wires is starting to become relevant. For context, an Intel i9 lists a 5.3 GHz clock speed. In one clock cycle, light - the fastest thing in the universe - travels only 5.66 centimeters and electric voltage (signals) moves much slower than that in metal, some where slightly slower than speed of light depending on other factors Edit: speed of light",
"First, Power Density (or Heat). Processors got exponentially faster over the last 50 years due to \"Moore's Law\" [ URL_7 ]( URL_5 ). This was an economic prediction made in 1965 that the number of transistors on chips will continue to double every 2 years. It became a self-fulfilling prophecy because Intel integrated that schedule as part of their business plan. Having more transistors available lets you clock faster because you're able to use the transistors for fancy tricks such as deep pipelining. EDIT: I got caught wearing my architecture hat. It's important to note that smaller transistors are just plain faster, so during this period, even with no tricks, the circuits would just magically get about 1.4x faster every generation. This doubling was possible because of \"Dennard Scaling\" [ URL_4 ]( URL_8 ) which at a high level means that due to the physics of the transistors, the power density of a transistor will stay constant as they decrease in size. This allows you to fit twice as many transistors on a chip while using the same cooling mechanisms. However, this broke down in the late 90s. The graph here is a great illustration of this (haven't read the rest of the article, but it's probably good: [ URL_6 ]( URL_6 )). Because Dennard scaling failed, we couldn't use those transistors to make it go faster, so instead the industry moved to multicore processors which were each clocked lower. Incidentally, this trend has also failed due to the \"Dark Silicon\" problem [ URL_1 ]( URL_2 ). This has resulted in huge innovation in the field, where custom hardware blocks are used for power efficiency rather than relying on a bulky CPU. Second, Power Efficiency. Power scales linearly with frequency, but quadratically with voltage. [ URL_3 ]( URL_3 ) Having a higher frequency requires a higher voltage. Conversely, underclocking the processor allows you to lower the voltage safely. This results in a cubic decrease in power consumption. So for similar performance, you might rather have several slower, cooler cores versus a single blazing fast and hot core. Third, the Memory Wall ([ URL_9 ]( URL_0 )) Most of the speed increase has gone to logic and not memory. This means that your CPU gets way faster, but the backing memory doesn't. If your CPU triples in speed, but your DRAM goes 1.4x, the CPU will just end up idling for long periods of time. This is inefficient and results in poor relative performance increases. This problem gets even worse with multicore processors, which is why it's still an active area of research.",
"The limiting factor for speed is simply the maximum frequency response of silicon. Most of the responses you are getting are more related to what are the bottlenecks to getting more throughput which is a little bit different question than raw maximum speed. It’s been 20 years since I took semiconductor physics in college but I still remember that and nothing has changed there. If you want a cpu with a 10 GHz clock you’re going to have to use something other than silicon. Radio circuitry that operates at higher frequencies use transistors made from different semiconductor material with a higher maximum frequency response. Gallium arsenide is one option. Silicon is still used for CPUs because we’ve gotten very good at making it with very few impurities which allow us to make smaller transistors and pack them in.",
"The speed is limited in part by capacitance, which you have to charge up for an amount of time to get to a desired voltage. Making the parts smaller also makes the capacitance go down, so they can run faster. Of course, insulation barriers can't handle as much voltage, so working voltages go down. At some point, you can't work with barriers that are thinner or voltages that are lower. That is a big reason that multiple cores are so popular now, one core at 5GHz can't do as much work as two cores at 3MHz if you can partition the work effectively."
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"https://en.wikipedia.org/wiki/Dark\\_silicon",
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k3jzxp | how does the suspension work in a car? | Engineering | explainlikeimfive | {
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"Get a glass of water. Hold it in your hand. Now bounce. Bend your knees up and down. The water doesn't spill, does it? Because you're using your muscles to balance everything out and keep the water still and in the glass. Bingo. That's what your car's suspension does. It's the car's knees and elbows and muscles absorbing many of the shocks and bumps. It keeps the passengers and cargo from bouncing around. Among other things.",
"The many parts of the suspension (control arms, shocks, springs, etc) are the only thing suspending the rest of the car (chassis, frame, etc) from the road. Without it, the bumps would be extremely hard, and eventually damage the car and maybe the people inside. Too soft of suspension, and it’d be an uncontrollable water bed floating down the road. An important part of the suspension is to keep the tires in contact with the road, while keeping the car easy and predictable to control."
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k3lpg2 | What is "halo" that saved F1 drivers life in that crash, and how does it work? | Hey reddit! So i guess you have all seen the video of a F1 driver surviving in fire for that long. And that crash was hard to watch, but everybody in the comments were talking about some halo that saved that drivers life. What is that and how does it work? | Engineering | explainlikeimfive | {
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"F1 cars like Indy Car are open cockpit which means there's no cockpit frame or crash structure surrounding the drivers head to protect them in a crash. It's just their head and crash helmet poking out from the chassis. The Halo is a titanium and carbon fiber tube that surrounds the drivers head to prevent certain types of debris and impacts from hitting them. In the case of today the Halo prevented Grosjean's head from hitting the Techpro barrier directly, which would have certainly killed him. Jules Bianchi was killed in a similar incident years before when his F1 car struck a tractor that was recovering another vehicle. His car plowed underneath the tractor and his head struck the tractor frame giving him a massive brain injury which eventually killed him. Similar María de Villota was test driving a Murassia F1 car and plowed underneath a trailer which resulted in a similar head injury. She survived but lost an eye in the crash, and died suddenly months later from a related blood clot. I think it was Fittipaldi that was killed when struck in the head by a bouncing tire at Indy. Having a halo on his Indy car would have absorbed the hit and he would have survived. One of the major concerns that led to the halo was another car landing on top of yours, which is exactly what happened at Spa in 2012, ironically it was Grosjean's car that flew over Alonso's car and nearly decapitated him. Alonso survived unscathed, but was within inches of being killed. The halo would have prevented that possible injury as well. Felipe Massa was struct in the head by a spring at the Hungaroring in 2009. He suffered a significant head injury as a result and was knocked unconscious with his foot on the accelerator. He survived, but they changed the helmet design after that to help prevent similar injuries. There's also a 50/50 chance the the halo would have deflected the spring.",
"It's a 20 pound titanium ring that has a support sloping up in the front and runs over the driver's head It's supposed to protect against stuff coming up the front by pushing it over the top and protects against straight down stuff like when a car flips or has another car land on top of it The drivers basically sit in a strong pod while the rest of the car will disintegrate around them to protect them"
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k3tgtu | Elecric blankets/sheets exist for heating but not cooling. What engeneering would be required to make a cooling one? I'd love a cold sheet to lie on in summer. | Engineering | explainlikeimfive | {
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"The biggest issue with that is that “cold”, at least from a physics standpoint, doesn’t actually exist. It’s just less heat. Because of that, you can’t really introduce cold to an environment, you can only remove heat. The other part is that it’s incredibly easy to make things hot. Heat is one of the most basic forms of energy, and a byproduct of inefficiency. Your computer needs a fan because there’s a nonzero amount of electrical energy that gets converted into heat energy through friction. Electric blankets take advantage of that fact by placing deliberately inefficient wiring in the fabric to generate more heat from less power.",
"Reverse principle, pump or chill water in tubes woven through the fabric. Complicated in that it poses a few safety challenges as well.",
"They are available, but expensive. Something like $600 for a small water+ice version. No idea what other liquid types are out there.",
"I once remodeled an old building into a bar. The kegs of beer were kept in an outer regrigerated building, but were a good distance away from the taps. The beer lines were wrapped with smaller refrigerated lines that were filled with glycol. The lines were a closed loop and returned to a refrigerated glycol bath. When I saw the system, my first thought was that this should be used for cooling bedding.",
"I imagine you could make a cooling blanket using a water cooling system - a system of pipes that water is continually pumped through to remove heat. The reason why this doesn't exist is probably because there's a high chance for it to fail. One little leak would soak your surroundings and ruin any nearby electronics including the pump element itself. It would be very dangerous. A pump to circulating a large amount of water is probably going to be pretty noisy too It's why waterbeds aren't as popular, they always seem to be leaking. Maybe a solution would be a blanket with pockets for ice packs?"
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k3xntd | Why are there no nuclear-powered civilian ships that can run indefinitely like the military ships? | Engineering | explainlikeimfive | {
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"Because nuclear power is uneconomical for civilian shipping. Running a reactor is incredibly expensive and the regulations are *very* restrictive. It's simply much cheaper to just run diesel or bunker fuel.",
"Nuclear power isn't used on ships because it is economical. Nuclear power is used on ships to avoid having to refuel. Civilian transport ships regularly go into ports where they can fuel up, so that isn't a necessity for them. On the other hand, an aircraft carrier or submarine will want to stay at sea for months at a time, so nuclear power is necessary for them.",
"Well there actually are/ were nuclear powered civilian ships. The first ones that come to mind are the Russian Arktika class ice breakers. Other civilian ships are the US built freighter NN Savannah and the German Otto Hahn. Both of them were eventually retired for the same reasons: nuclear powered ships are very expensive to maintain and operate, so as civilian vessels they simply can't make money. This is not a problem for the military. They also don't quite run indefinitely. The Arktika class for example needs new fuel about every 13 years.",
"It’s insanely expensive to build and maintain, so much so that they’re reserved only for roles that require extreme self-sufficiency like an aircraft carrier or submarine. No civilian ship will expect to remain deployed in hostile waters for months. There’s also security concerns with the fuel and equipment. This is already baked in on a military ship, but it would be weird to have heavily armed soldiers patrolling an oil tanker or cruise ship.",
"There are a few. The Russians operate a nuclear powered icebreaker, and several other countries have built nuclear powered \"demonstration\" vessels (i.e. ships to show off civilian nuclear propulsion). The big reason it isn't done is because it's expensive. There are a number of reasons for this. Some include: Getting a \"nuclear trained\" engineering crew is hard. One of the attempts at making a nuclear powered civilian ship had a strike because of wage complaints between the engineers and command crew. There are not many places that are setup to service nuclear ships, which makes maintenance, repairs and refueling costly. Insuring a nuclear ship is hard (\"normal\" insurance won't cover them as an incident could be an international disaster). There are also some security concerns (e.g. people stealing radioactive material or sabotaging the reactor to cause a disaster) and extra security costs money. Also, being able to \"run indefinitely\" is often of little value for a civilian ship, as their job is usually to bring things into a port. If your ship has to stop in a port every week to load/unload cargo then it isn't really much of a burden to load fuel too.",
"Civilian shipping is all about low cost. A giant cargo container ship uses 7 horsepower per container to slowly move them from place to place at ultra low cost. Add a couple of nuclear engineers to the crew, and you don't have a money-making voyage cost (even ignoring the cost of the reactor itself).",
"As an additional point to all of the great ones already here, a nuclear powered vessel may be restricted from entering port. All it takes is for the country in question to decide your company cannot be trusted to operate safely and suddenly you just lost a customer. This would be problematic for international shipping. Really, there are a lot of reasons this would be impractical. Maybe, just maybe, if nuclear became the predominant power source around the world you might see civilian vessels move away from fossil fuels.",
"It's all about cost and logistics. Nuclear power is going to cost more upfront, and add to the operational costs. Diesel mechanics are relatively cheap. People qualified to operate nuclear equipment are not common, nor are they cheap.",
"Ocean piracy is still a real problem and the safety of a mobile civilian nuclear reactor 2000 miles from help is far from guaranteed. Many countries are considered unsafe or unstable such that they are banned from having nuclear power. World powers are concerned about ba people from getting their hands on large amounts of nuclear material.",
"The NS Savannah was a nuclear-powered merchant ship built in the 1950's. The wikipedia article discusses a little of the politics and financial realities: URL_0",
"USN Aircraft Carriers and Subs like nuclear reactors because they can run indefinitely at maximum speed, or stay submerged for long periods of time. Cargo ships don't care about speed, they only care about cost efficiency. A Nimitz Class carrier clocks in around 100,000 tons, can do 30+ knots indefinitely, but has a crew of 3500 not including the airwing. A Maersk Triple E class container ship can hit almost 200,000 tons fully loaded, cruises at a mere 16 knots on two big ol' diesels, and does so with a crew of 13. The low crew requirement is part of what makes them sooooo cost efficient. A cargo ship can take a ton of cargo over 500 miles on a single gallon of fuel, and with only a dozen or so guys on board it costs *very little* to move huge amounts of cargo massive distances. A nuclear reactor would have significantly higher crew costs, while the fuel consumption would be basically zero, the super expensive initial construction would take a long time to pay for, and the high crew expenses makes it unlikely it could ever turn a profit. Even the NS Savanah was never intended to turn a profit."
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k497wb | How coil handles on my fireplace are cool to the touch | I’ve had my fireplace blazing and the coil handles are still cool to the touch even though they are attached and really close to the fireplace itself. How does this work? And does this have anything to do with why they use coils in electrical stuff | Engineering | explainlikeimfive | {
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"Those coils have a lot more surface area than a solid bar might have, plus they allow air to pass over a larger portion of that surface area unimpeded. This means they take longer to heat up and they cool down faster than a solid bar would. Ultimately, this means they don't ever get \"hot\" because they cool faster than they heat up, at that specific distance and with a standard log fire of appropriate size."
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k4ayrj | What is the difference between volts, amps, amperes, watts, etc.. | Engineering | explainlikeimfive | {
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"These are all different units for different physical properties. A volt is a unit for electric potential, or basically work needed to move an electric charge in an electric field. In ELI5 language, “how hard does the field ‘hold onto’ a charge”. An ampere is a unit for electric current - basically how many charges move through a conductor. A watt is a unit of power, both in electromagnetism and mechanics; basically how much energy is transferred. There is one more unit, the coulomb which is the unit of electric charge. They are all related - elementary electric charge is the charge of one proton or one electron, which is about 1.6x10^-19 C . One ampere is the current that moves one C in one second. One volt is basically the difference between electric potential where 1 A will cause 1 W of power. A watt is defined as J/s so you can also say that one volt is a difference in electric potential that will cause 1 J of energy to every 1 C of charge that move through it.",
"Volts are potential difference Amps and amperes are the same, how much electrons are flowing on something per a unit of time. Watts are how much electricity something is using, per a unit of time."
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k4b0qa | Diesel Exhaust Fluid | So, what is the purpose of diesel exhaust fluid? Why do older diesel vehicles not need it? | Engineering | explainlikeimfive | {
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"It's there to reduce NOX (nitrogen oxides), a pollutant in the exhaust from some diesel engines. NOX is created anytime you have incomplete or lean combustion (more air than needed to burn the fuel). The DEF reacts with the NOX in a special catalytic converter to turn the NOX into nitrogen, water, and CO2. It only works in engines that have the catalytic converter, so if an old engine doesn't have the converter there's no point in adding DEF."
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k4bead | Where do the huge cement poles that support bridges over deep bodies of water go? | Like, how do the engineers know where the bottom of the water is and how do they get them to stand up? How do they even get them vertical? | Engineering | explainlikeimfive | {
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"When they set them, they build a dam completely around the area it needs to go, drain all the water, and build them into the ground beneath. Built it vertically as normal, then take apart the dam and let them go back underwater.",
"They go down to the bedrock under the bottom of the water, and sometimes into it. They use divers, or pressurized work rooms to place their foundations. Then they use climbing forms to pour the concrete. Concrete is much heavier than water, and cures chemically underwater about as well as it cures in air (better in some ways due to better temperature control). Set the forms, pour a layer, slide the forms up, pour a layer, ... until you are above the water."
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k4hhgk | There are so many kinds of screws in the section of the hardware store- what are some basics to know what you need? | Engineering | explainlikeimfive | {
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"Know what you are fastening to what and why. Wood screws don’t work well on metal, for example. Washers are sometimes needed to keep the screws from pulling through. If you are looking for a bolt or nut to match something you already have, bring that to the store with you. There’s a box that will let you match the size and thread pattern."
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k4po85 | How do planes get tested whether they can be used and sold | Engineering | explainlikeimfive | {
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"Certified aircraft in development undergo extremely rigorous flight testing in order to determine key characteristics such as the minimum and maximum airspeed the airframe can safely handle, its behavior in abnormal conditions like stalls and spins, simulated emergencies and other scenarios that test the capabilities of the engine and airframe. Basically, test pilots take those planes flying and try to break them under carefully controlled conditions. They might overload them, perform aggressive maneuvers, and otherwise explore the limits of the airframe in order to find out what those limits are. Then, the manufacturer takes that data and publishes the operating envelope for the aircraft that makes this data available to pilots who will later fly the plane. When pilots prepare to fly an aircraft, we review the operating manual in order to get critical information about the aircraft that was determined by this testing such as: What is my stall speed? What is the minimum speed I need to maintain if one of my engines fails after takeoff? How will my passenger's 40lb suitcase affect my aircraft's center of gravity? How will that affect my ability to recover from a stall? How much fuel will I burn during this trip? How far can I glide if my engine goes out? What airspeed do I need to maintain? All of this is critical information to a pilot that has to be determined by a manufacturer before an aircraft can be certified and sold in the US"
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k536zr | My lamp has flickered a few times tonight, then flipped the whole houses power when the bulb blew, despite being turned off. Instantly all the houses on and around my street have their house alarms going off! How did my bulb break the whole area?! It's 5:28am. I just pissed off a whole postcode | Engineering | explainlikeimfive | {
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"There's no way your light bulb caused any kind of damage to anything else in your house, much less the neighbor's. Are you sure there wasn't a neighborhood-wide power surge?",
"Yeah, as others said, it wasn't the bulb blowing that took out the neighborhood, it was the neighborhood going out, or I should say the fluctuation in power that pushed a near-failure bulb over the proverbial edge."
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k5gcbj | Why do we have no signal on our mobile phones in elevators? | Engineering | explainlikeimfive | {
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"text": [
"Because most elevators are made with a metal framework that blocks radio signals. This is an unwanted side effect of making the elevator safe enough to carry enough weight. This effect is also used in laboratories to study radio interference It is called a Faraday Cage.",
"In an elevator you are basically surrounded by metal, some metals can reflect and absorb radio frequencies preventing you from receiving or sending a signal.",
"Phones work by sending and receiving signals. Signals get blocked by metal. Elevators a metal boxes"
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k5khxy | what exactly do engineers do as a profession? | Engineering | explainlikeimfive | {
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"In theory the job of an engineer is to take scientific information and use it to design a functional and practical thing. An engineer may design a car, or a bridge, or a screw. They get requirements for what the thing is supposed to do and limitations for it - how big it can be, environmental restrictions, and cost. They then design a thing that will do what is required within the constraints - if possible.",
"Engineers use scientific concepts to plan and test new ways of doing things. We first think of ideas, make a drawing, build a prototype, test, redraw, rebuild, test, redraw, rebuild test..... Until one day we decide our creation does it's job without killing anyone.",
"There are completely different possibilities, some do experiments, some only act as decision makers with an engineering background. Tbh an engineering degree most of the time is only certificate that shows that you can teach yourself new things in a short amount of time.",
"Engineer is just a very broad term. You better look at these SEVEN completely different types of engineer jobs: 1. Inventor. One that tries to create new mechanisms and solutions. (tesla electricar car designing, programmers) 2. Designer. One that uses known solutions that Inventor made and combine them to find the perfect one. (civil engineering, technical writing, documentation, projecting) 3. Implementer/builder. One that comes to put things in necessary physical order that Designer intended to (actual construction site workers) 4. Installator/tuner. One that comes to tune/install things in some necessary programm/tuning way (fire alarm engineer, SCADA engineer) 5. User/executive. A member of some organization that is responsible for a installed thing to perform well. (chief engineer on electrical station) 6. Repairman/warranty provider. By request of user he comes to fix a thing. 7. Supervisor. Some sort of people who check how users perform their duties according to current professional standards (technical safety engineer, quality engineer)",
"Why doesn't your car explode when you turn on the ignition? Why doesn't a bridge fall down when you walk over it? Why doesn't your oven burst into flames when you cook? Engineers. More than any other profession engineers let you interact with hundreds of potentially dangerous machines and systems every day and do so safely.",
"Solve problems - big ones and little ones and involving many different things or a few very tricky things. Sometimes the problem requires a lot of thinking and others require more trying but both are required to find a solution. And then that solution is checked to see if it was the best. After that the process is repeated.",
"depends upon the type of engineer. some, like chemical engineers, have to create chemicals within a specific set of parameters with lots of research. others, like electrical engineers, need to fix things having to do with electrics and possibly create new electrical systems. so basically, Google is right when it says the definition of engineering is \"the branch of science and technology concerned with the design, building, and use of engines, machines, and structures.\"",
"That varies a huge amount depending on the particular engineering discipline, and even within disciplines and particular jobs. For example, some electrical engineers may work on power systems. Some may work on designing power generation equipment, or distribution networks. Others may work on actually building those things, or on maintaining those things, or making sure that they are safe and meet regulatory requirements. Other electrical engineers may know very little about such things, and work on something like integrated circuits (\"microchips\"). And within that area, there is also a huge variety of different specialties and job functions. Or an EE might work on designing circuit boards to go into electronic devices like cellphones or PCs. Or on toasters. And that's just a hint of the variety among EE jobs. There are a lot of other engineering disciplines, also with great variety."
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k5z99o | Why do they not make regular clothes that are waterproof? | Engineering | explainlikeimfive | {
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"Some combo of price/comfort, I’m assuming. Cheap waterproof materials don’t breath and can be horribly uncomfortable to wear, and breathable waterproof materials can be very expensive, not to mention the waterproof functionality usually wears off after a certain amount of use. I feel like it would either be too expensive or too uncomfortable if every day clothes were waterproof",
"Waterproof also means sweatproof. I dunno about you, but when I wear latex or other rubber gloves in a warm environment, it's really unpleasant how sweat just builds up in there.",
"Many/most/all washing machines recommend not washing waterproof clothing in them. So there’s one reason."
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k601wh | Why are giant telescopes radio telescopes? | Engineering | explainlikeimfive | {
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"1. ~~Building optical telescopes on Earth generally doesn't get you very good results; the atmosphere distorts the image and isn't fully transparent (hence why the Hubble is on a satellite)~~ My information was true in the past, but not so much these days. See replies below ↓ 2. It's simply not feasible or practical to build a lens that's 100m+ across. The largest is 10m ( URL_0 ). 3. The reason we have such large dishes is to resolve the much lower frequencies of radio waves - generally, when building a parabolic reflector, the larger the aperture, the lower the frequencies you can resolve. Light is electromagnetic radiation in the order of THz (i.e. trillions of cycles per second), but radio waves are KHz (thousands) or MHz (millions).",
"In order to make a good reflector you need to make sure that any flaws/imperfections in your reflector are smaller than the wavelength of the radiation you're trying to reflect, otherwise the flaws in your reflector will screw up your image. Radio waves have wavelengths that are measured in meters. Building something to that degree of precision is fairly easy to achieve on a REALLY large scale. Visible light has a wavelength measured in nanometers, which ends up limiting the practical size of visible light optics to maybe a few meters. There is also a secondary concern - how much does the atmosphere mess up your observations? You mention IR in your post. A lot of the IR wavelengths are absorbed by earths atmosphere, and may of the ones that are not tend to be wavelengths that are emitted by the earths atmosphere."
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k6dyjn | What happens at the atomic level when a steel cable snaps? | Engineering | explainlikeimfive | {
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"It's not really in the spirit of the sub to just send a video, so I'll add some supplementary explanation. [Here's the animation.]( URL_0 ) Atoms in a crystalline material are not arranged in a perfect pattern, but rather in small chunks of patterned atoms which haphazardly stick together at the boundaries. Under high strain, these boundaries begin to slip, allowing the material to slowly thin if under tension or bend if under compression."
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k6m41s | In a parallel hybrid electric vehicle (HEV), how do both the engine and the motor engage the drive axle at the same time? | I'm a mechanical engineering student and I know generally how HEVs operate, but I can't seem to find anywhere that explicitly explains how torques are "added together" to increase overall torque of the vehicle. Is there a particular device that allows two shafts to drive one (thus adding their torques), and does that mean that both these shafts would need to have the same rotational velocity to avoid excess torsion on the driven shaft? Any explanation would be greatly appreciated! | Engineering | explainlikeimfive | {
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"You use something called an overrun clutch. This is already a really common part in automatic transmissions so they’re easy to come by. An overrun clutch is like a diode or check valve but for rotary motion... it transmits torque in one direction but spins freely in the other. So you put two gears on the driveshaft, each with an overrun clutch between the gear and the shaft (the clutch is a cylinder). Each motor drives one gear. If they try to drive the gear faster than the driveshaft the clutch engages and they transmit torque to the shaft. If they try to go slower (that motor is off) the clutch disengages and the gear just free wheels. It’s a mechanism for summing torques. If they’re engaged, driven shafts have to go the same speed as the driveshaft. There’s an alternate way to do it with fluid couplings (“torque converters”) where they don’t have to go the same speed, this is how the main “clutch” of an automatic transmission works."
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k72uc1 | . How some modified cars make firecrackers noises and create a lot of flames from their exhausts ? | Engineering | explainlikeimfive | {
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"text": [
"I believe it has to do with engine timing. Usually all the fuel in the cylinders is burned up and only exhaust gas exits through the muffler. If you adjust the timing you can cause the fuel and spark to happen when the engine is in the exhaust stroke so the flames exit the muffler. I’m no mechanic but that makes logical sense to me."
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k75esn | Could artificial gravity exist or is it just something made up for convenience in science fiction. | Engineering | explainlikeimfive | {
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"text": [
"You can make a rotating space station: URL_0 which had been considered, and possibly built in the near future. The idea is simple enough: acceleration is indistinguishable from gravity (without, you know, looking outside).",
"The main problems with artificial gravity as we see in SciFi is that it creates a big problem for the idea of a ship with multiple decks. If you're on deck 1, you have some source of artificial gravity below you. If you're on deck 15, you have some source of artificial gravity *above* you. It's impossible to perfectly balance all the artificial gravity so that every deck feels correct. The other problem is that gravitational forces dissipate based on the square of the radius between the objects pulling. If your gravity source is really close, then it's going to dissipate very quickly as you get away from it. The difference in gravity between your feet and your head would be pretty extreme."
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k76pi0 | How do step down transformers "increase" amps? | Sorry if this is a very specific question, but here goes: I've been thinking about those projects where people salvage microwave transformers and rewind them to have fewer secondary turns, and hence lower voltage on the secondary side. When you do this, the output will be able to push out massive current that can melt metals such as spanners and whatnot. So my question, let's say the transformer is hooked into mains (220V, rated 2200W). When loaded with such low resistance, the current rises and the voltage dips to a point where P=2200W. Having the exact same load resistance, why would a stepped down voltage through the transformer cause higher current through the load, when the voltage difference through the resistance is lower? | Engineering | explainlikeimfive | {
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"Rewinding with a smaller turn number secondary also means you can fit thicker wire into the same space, which means lower resistance in the secondary. The original secondary wire in a MOT is razor thin - it is only good for carrying 1A or so. For welding, you want to be able to supply hundreds of amps (because heating power is P=I^2 x R so want a big current and *all* the R in the circuit to be the workpiece you are heating), so you must use big chunky wires. Effectively you *do* in fact reduce your load resistance significantly."
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k7cu4h | How the pieces of equipment in a large foundry or forge get made originally? | I can understand using a metal with a higher melting point to make make brass,(like steel, for example), but how do the steel forging pieces get made, and then what is in turn used to make those pieces? To me its like an arms race | Engineering | explainlikeimfive | {
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"You don't need a huge bucket to cast a huge bucket, if I get your drift. You make a mold, heat metal, and let the metal fall in. Your mold can be made of something like sand, which is easy to shape and produce even in large amounts without requiring a larger container. Alternatively, cold working of blocks of metal produces things like sheet metal which can be welded to make a bucket. This probably wouldn't be used for making smeltery crucibles but still applies to a broader version of your question.",
"this is called a bootstrapping problem. the answer is ceramics, mostly. ceramics can be formed similar to mud or concrete, but sport melting points well beyond most metals. a primitive furnace made of mud and charcoal can create crude cast iron. at the highest end is tungsten, which you just don't melt at-all. which is refined through chemical, rather than thermal, processes. it's formed into useful products using *sintering*, a process that fuses material with a combination of heat and pressure that doesn't actually melt it. even so, the relevant machinery actually has parts that are consumed in the process. rather than trying to keep the parts in contact form melting, you just work fast so they don't melt completely and then replace them. what's why all those tungsten, cobalt, etc. tools at the hardware store are so much more expensive."
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k7dwww | [BOAT- Break Out Another Thousand] Why are boats so prone to failure, or why do they need so much maintenance? | Engineering | explainlikeimfive | {
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"Water is a very aggressive substance. It can dissolve, infiltrate, or oxidize a huge variety of materials. Add salt and it can also corrode most metals. And boats, by their nature, are constantly exposed to it all the time. This is a very different operating environment than anything else and it’s *really* hard to keep everything protected all the time. You’re basically fighting a constant rear-guard action against slow rotting and decay.",
"It's not so much that boats are prone to failure. Modern boating engines are extremely reliable. But there are a lot of expenses to operate a boat. On the low end you have trailers and storage and slip space. On a high end for commercial boating, for safety purposes you have to have all kinds of redundant systems and there are regulations requiring all kinds of equipment and inspections for safety. Recreational boats are also not a necessary item, so prices reflect the income level of those who have them.",
"Being in water (especially salt water), being out in the elements 24/7, being designed for lightweight, all contribute. But some is lack of economies of scale, too. There are far fewer boats and they are more custom so there aren’t the benefits from standardized parts and repair techniques. It’s also harder to get a boat someplace to fix it. And then there is simply the deep pockets of the owner... boats are luxury goods, so those catering go to boat maintenance and repair aren’t going to work extra hard to cut costs to pass on."
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k7mkl3 | Why does it always look like rocket ships take off in slow motion? | Engineering | explainlikeimfive | {
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"Because they are taking off slowly. It takes up to 20 min for the rocket to reach the 11km/s. At first it's only going a few cm per second but builds more speed as the thrusters burn. If it went from zero to escape velocity instantly, the folks inside would be jelly.",
"1. **Rockets are huge.** Think of a twenty-storey building: that's how tall a rocket is. So some of the \"slow motion\" effect is that you're watching from far away, and both the rocket, and the distance it has traveled so far, look a lot smaller. 2. **Rockets start off literally clamped or bolted down to the launch pad.** Especially for liquid-fueled rockets, after they ignite, they remain attached to the ground until they are sure everything is working properly, and then it is released. So, even after ignition, it usually takes a few seconds before it gets released from the pad. This is why you hear someone say \"Ignition\" (when the rocket engines are lit) followed by \"Liftoff\" a few seconds later; the time between the two is while they're waiting for the rocket to be released from the pad. 3. **When the rocket is on the ground is when you need to push the hardest to even move it.** Even though a rocket is being pushed really hard off the ground, a lot of what is in the rocket being pushed is the propellant (rocket fuel and oxygen) to make it go up. The more of that rocket fuel it burns, the easier it is to push. So, when it's on the ground, the rocket is its very heaviest, and the rocket engines need to push their very hardest just to get it off the ground, so they can't make it go very fast right away. As it gets higher, because there's less fuel in the tanks, the rocket engines can push just as hard and add more speed to the rocket than they can right off the ground, because it's easier to push lighter things. 4. **It's starting from a complete stop, and not going that fast until it reaches space.** When you're in a car that's stopped at a stop light, and then the light turns green, you don't immediately start going 50km/h (30 mph) as soon as your foot touches the gas pedal. Instead, you accelerate slowly until you reach the speed you want to be at. For a car, it could take ten seconds or longer to be going full speed, starting from a full stop. For rockets, it generally takes them several minutes to get up to orbital speed (the ISS orbits at ~27,500 km/h or 7.66 km/s, and it took 9 minutes for SpaceX's Crew-1 mission to reach that speed). By the time it clears the launch tower, it may be only going 50 km/h. Which is still a lot: it's how fast a car moves on a side street, not very fast compared to how fast it goes when it reaches orbit.",
"I assume you're considering cars the baseline. Cars, and anything propelled by spinning a wheel, have a lot of acceleration at low speeds, and it drops off as speed increases. Rockets don't behave like this. They essentially have constant acceleration regardless of speed. So at low speeds, the acceleration may be lower than expected, but at high speeds, it just keeps going. This is how they get to incredibly high speeds, it just takes a while.",
"Because it takes a lot of thrust to overcome the inertia of the mass of the rockets and their payload.",
"Newton's second law. Force is proportional to mass and acceleration. Rockets are massive so it takes a lot of force to accelerate them. A slower acceleration means less force is needed and there's only so much oomph a rocket engine can output. I guess theoretically they could design rocket engines with more oomph. But it would use a LOT more fuel ( weight is always very expensive in space launches. thousands of dollars per kilo) and since too much force would squish the astronauts they do need to keep the acceleration within certain safe limits.",
"They're very big and the square-cube law says that big rockets will take off proportionately slower than small ones. For example, watch some videos of model rocket take-offs to see how amazingly fast they are. An orbital booster would rip itself apart trying that scaled speed. Have a look at pictures of the orbital rockets with, say, a person standing next to it for scale. Then their take-off acceleration and speed become more believable."
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k7x6p2 | How do windows on the ISS and other spacecraft not fog up? | Since it is extremely cold in outer space, moisture in the air inside a spacecraft should condensate on the inside of the windows. How is this prevented? | Engineering | explainlikeimfive | {
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"Condensation on your windows occurs because the heat from inside transfers to the outside through the glass, thus creating cold air right on the glass layer which causes the water to condensate out. It's cold in space (when in shadows, otherwise it's actually really hot), but there is a very limited ability for heat to transfer in space. Heat transfers through conduction (touching something that has a lot of heat), convection (fluid currents carrying heat), or radiation. Heat from inside the ISS can only transfer to space outside via radiation. And radiative heat transfer tends to be very small unless the absolute temperatures involved are very large.",
"On earth windows are cooled by conduction with the cold air outside. Heat is microscopic movements, and the moving glass gets slowed down when it touches slower moving air molecules. In space there are almost no gasses on the outside, so the window can stay warm, which means water won't condense on it. ISS windows also have four layers of glass, so the inner layer is also well insulated and again should not be particularly cold.",
"> Since it is extremely cold in outer space It is extremely *nothing* in outer space. There is no air outside to carry away heat from the window's outer side like on Earth, it only radiates heat via infrared light. That is, as long as it is in a shadow. In space sunlit surfaces heat up *quite a bit* because the Sun is bombarding them with more IR than they can themselves let off. For this reason the space suits are white and have an internal A/C and the space station has enormous IR heatsinks to let off heat produced by stuff inside, or else they would cook themselves. However, the more significant factor in the windows staying dry that is that there isn't much humidity to begin with, since they can't risk condensation cropping up in electronics or causing corrosion/mold, so the A/C dries the air out (and collects the moisture for drinking and other uses!)."
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k7zfvc | Why covering half of the back wheels of a car improve its efficiency? | Will it work if I cover my car's back wheels? Can it cause some crazy vibration? Is it dangerous in any way? | Engineering | explainlikeimfive | {
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"Because it provides for an overall more streamlined vehicle. Air resistance is a big contributor to efficiency losses. It's also the reason for why some semi trailers have those wing skirts under them now to streamline it. Dangerous? Probably not, providing a professional and secure design and installation of the covers. Though it may complicate changing a flat tire, and snow buildup may or may not cause a little trouble.",
"Spinning wheels generates all manner of turbulent air. This turbulence can cause drag and reduce efficiency of the vehicle. Often road cars don't have covers mostly because people find them hideously ugly. You might be interested in the Aerocivic. This is some guy's project car. I believe it's an 86 or 87 Honda Civic that he covered with sheet metal from a disused shed. He made the car shaped like a wing to minimize drag, which included covering the wheels. Even though he added weight to the car, the stock carbureted engine still managed to get him 70 mpg. Once the original engine wore out, he got an aftermarket high efficiency engine that raised vehicle efficiency I believe into the 110s per gallon. You should look at modern aerodynamics they use in racing. Just look at an F1 car, for example. All those fins and angles all shape the air around the vehicle. It's common as a sports car aftermarket mod to apply ground effect body kits on a car; these are skirts that keep air out from entering under the car from the sides, and even old F1 cars did this I think into the 90s. Now days, they generate vortexes of air that act as a dam, producing the same effect. They can even change the length of the car, essentially, by changing the aerodynamics, and thus the length and shape of the vortex that trails the car, and this changes the amount of drag and downforce on the car. So with a little ingenuity, you can probably muck with the aerodynamics of your car and improve the efficiency with essentially primitive tools, by todays standards. I think most manufacturers pay only enough attention to aero on any given vehicle to try to avoid disturbances to the passengers and hopefully obvious dangers. The only problem I have with my GTI is Volkswagen gave no consideration to air pressures or oscillation in the cabin if the rear windows are down, and I'll never drive another fucking Nissan Versa again - the fucking thing had so much lift at highway speeds you felt like you were floating, like the car was going to blow over at any moment. You could feel it. Terrifying. So, the manufacturers have oversights and mistakes, and there is obvious room for improvement. They're going to sell the car based on its styling, and aerodynamics aren't an impressive talking or selling point when you're buying, say, an SUV. The aerodynamics I would approach with caution would be on *some* sports cars."
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k84r9d | How did Neil Armstrong's jet aircraft altitude keep rising in the early part of movie "First Man"? | Fyi, it's on netflix Neil was going above the atmosphere using this aircraft, but he can't get back, and instead was rising in altitude. How is this happening? Can jet aircraft leave the atmosphere? | Engineering | explainlikeimfive | {
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"If you go high enough, the air gets too thin for airplane control surfaces to do anything to control your plane and you need to have a [Reaction Control System]( URL_0 ) which is a bunch of tiny gas thrusters all over your craft that helps you rotate. Jets don't really get up to such altitudes because they need air to run. Armstrong flied the X-15 which was a rocket powered aircraft, not a jet."
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k88m6y | If watts equals volts*amps, why do products such as UPSs have different W and VA ratings? | Engineering | explainlikeimfive | {
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"Watts do indeed equal volts × amps. This is true in all cases. However, you'll note with AC, voltage and current change over time, they well, alternate. Current and voltage go negative at some point. They go zero at some point. And this is fine. It just means the power is also an alternating wave. How do devices have a power rating if it's always changing? Simple. It's an average. So are the volts and amps, they are just averages too. If voltage and current line up perfectly, power is always positive. +volts × +amps = +watts. -volts × -amps = +watts. But what if they were opposite? +volts × -amps = -watts. Well, you'll get negative power the whole time. That's fine. Just means it's a power source rather than power consuming device, assuming you defined your current a certain way. But what if they were mostly line up, but not completely. Like say the current was part of a cycle behind the voltage. Not a half a cycle where they are opposite, just a little. When voltage goes negative, current is still positive for a little but. Well, you'd have mostly positive power, but you'd have a small period of negative power. What does this mean? The load most of the time is consuming power, but for a small period of time it is returning power to the source. So going back to averages, we have two types of power. The power the load throws back at the source, and then absords back, and then throws back, and so on. Capacitors and inductors do this, as they can store energy really quickly, and then throw it back. They are fast enough to do this 60 timers per second. We call this reactive power. We measure it in VAR, or volt-amps reactive. This is power cycling back and forth, never doing anything. Then there is the real power. We measure this in watts. This is power the load absords, and never gives back. Finally there is apparent power, this is just multiplying the volts and amps, with no consideration of how they are lined up. We measure this in VA, volt-amps. Apparent power^2 = real power^2 + reactive power^2. Yes, that's Pythagoras' theorem for a triangle. Apparent power matters. Power being thrown back and forth means actual current is flowing. Power supplies, UPS, wires, they all need to handle this pointless power moving back and forth. As I'm calling it pointless, you can imagine it's not a good thing. It stresses the electrical grid, while doing nothing. or stresses your UPS while doing nothing. Ideally we want as little of it as possible, but often times it's hard to avoid. A UPS may be rated say 1250 VA, 1000 W. This means it can handle 1000 W of real power being used and 750 watts of power, or more commonly called VAR, being thrown back and forth between the load and the UPS. This totals 1250 VA (remember, Pythagoras, not addition), or say 10 A at 125 V. The power factor is real power over apparent power, so 1000/1250, 0.8. Now, this tells you how far behind the voltage the current is. If you take arc-cosine of 0.8, you get 37°. That's how far behind the voltage the current is, 37°. Or 37/360 of a full cycle. More triangles and trig, or more accurately triangles formed within a circle representing 1 cycle. There's 60 cycles in a second on the North American power grid, so this means the current is 37/360 × 1/60 = 1.71ms delayed behind the voltage. Middle school trigonometry math to the rescue. You can also do this all with some imaginary numbers with basic arithmetic too, but that's a little beyond most people's math knowledge. It's why I keep calling it real power, it's represented with a real number. Reactive power gets an imaginary number, and apparent power because complex power with a complex number that serves as a vector. And imaginary numbers can help you solve a lot more complex problems than a steady state AC circuit.",
"Watts only equals volts x amps if the product is purely resistive, such as an incandescent light bulb, a toaster, or a space heater. For most products (we will call them loads) the load is a combination of the wattage and the magnetic component. This is called apparent power and is VA, volts x amps. For example, take an average motor. Not only does it need power to turn a shaft, but it takes energy to maintain the magnetic field that does this work. Those two components create the VA. You can think of it this way. The watts does the work and the what is left over helps facilitate the work to get done.",
"Because of things like Capacitors and Inductors (coils of wires), the peak voltages don't always occur at the same time as the peak currents. If you viewed both as waves, the voltage can \"lead\" the current, or \"lag\" behind the current rather than line up exactly. W=VA in the case that Voltage peaks act at the exact same time as current peaks, otherwise, it will be less than VA. Power Factor is a number less than 1 that gets multiplied by VA to tell you the wattage, so the real equation in AC circuits is W=VA X Pf. VA numbers are good for sizing wiring and circuit breakers. Watt numbers are good for determining how much power you are buying and the heat generated. If you've ever wondered what \"imaginary\" numbers are good for, they can be used to help calculate the difference in phases between the Voltage peaks and Current peaks."
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k8eo3s | How is my water, gas and electricity meter work? | So basically how water, elecetricty and gas are measured in a meter, aka what's the mechanism behind the meter readers in gas, water, electricty etc? | Engineering | explainlikeimfive | {
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"They literally measure the flow into your system. A water meter measures water following through a pipe, the gas meter measures how much gas flows through the gas pipe and the electricity meter measures how much current (electrons) flow through its main cable. For gas and water if you know the diameter of the pipe and flow rate you know the volume of fluid that’s moved through the pipe in a given time, in both a turbine can be used to measure flow rate for use in the volume calculation. In analogue meters the turbine would drive a series of wheels to give the readings. For electricity the voltage is analogous to the pipe diameter and the electric current is the ‘fluid’ flowing through the cable. So by monitoring the current and voltage you have the Power. For example if a device pulled 4 amps at 250 volts for an hour that would cost whatever your energy company charges per kWh since you were using 250x4=1000W=1kW of power for one hour. Current can be measured by the magnetic field it generates."
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k8gvrp | Why are people acting like it’s impossible to build a new Arecibo telescope when the rebuild cost Would only be the same as a Boeing 747 (350 million dollars) | Engineering | explainlikeimfive | {
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"From the one and only, /u/Andromeda321 > **Why don't we just build a bigger telescope? One on the far side of the moon sounds great!** I agree! But good Lord, Arecibo has been struggling for years because the NSF couldn't scratch together a few million dollars to keep it running, which probably led to the literal dish falling apart. Do you really think a nation that can't find money to perform basic maintenance is going to cough up to build a radio telescope on the far side of the moon anytime soon?! Radio astronomy funding has been disastrous in recent years, with our flagship observatories literally falling apart, and the best future instruments are now being constructed abroad (FAST in China, SKA in South Africa/Australia). Chalk this up as a symbol for American investment in science as a whole, really... URL_0",
"$350M to build it isn't that bad, but the $10M per year to keep it up and running is where you hit the snag. A $350M 747 pays for itself in a few years, a $350M telescope gobbles money for decades. Arecibo had been struggling for a few decades, only getting about a quarter of the funding that it needed from NASA and the NSF. While a big ass radio telescope is great to have when you need it, it turns out you don't need it often and something like the Very Large Array is easier to maintain and more useful for general research. Arecibo had very specific uses that it was good for, but that meant that it wasn't being used all the time and funding just wasn't there. I also suspect $350M is a very low ball figure for something that will require helicopter support to be built and most of the roads leading to it will have to be rebuilt to support the heavy truck traffic as they're all beat to hell too.",
"Well, simple question: where is that money coming from? They apparently haven't been able to afford a few million dollars to maintain the existing telescope for the last few years, finding $350 million down the back of the sofa seems unlikely at this stage.",
"Bear in mind that the nation is the USA. The same nation that can find $400 million for the president's personal debt fund can't find the money to feed it's starving, house its homeless, or educate its poorest. It's not a matter of can't. It's a matter of won't.",
"The collapse of the telescope were in large part due to a lack of maintainence over the last decade and a half induced by a lack of funding. And because keeping up with maintainence would have been cheaper then building a new one when it collapsed it is a bit of a stretch to expect that the US scientific sociaty will be able to collect the funds for a new telescope. This is something like expecting someone to buy a new car because they did not have money for an oil change which ended up ruining their old one."
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k8tgh2 | How can machine code actually create electric signals to turn transistors on and off? | I’m a junior EE student, but I’m still genuinely confused about this, and other answers still haven’t cleared my confusion. How can voltages be manipulated by code in a digital circuit without someone physically closing and opening circuit connections? | Engineering | explainlikeimfive | {
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"Ben Eater has a fantastic series on building a breadboard computer from scratch: URL_0 To answer your question, the first part of each instruction is called the \"op code.\" This code goes into a decoder which translates the binary value into several control lines. E.g. code 100 (4) turns on the memory address lines, turns on the adder input buffer, and turns off the display input buffer. Think of it like a lookup table of different \"recipes\" which trigger different actions inside the computer.",
"You might find it interesting to read a bit about computer architecture, von Neumann and Harvard Architecture. These building blocks are made out of logic gates, which in turn are made out of transistors. Group the various building blocks together and now you've got a primitive ripple carry adder. Group many of these together and you've got an arithmetic logic unit. Group those together... Etc etc. To understand what the actual voltage does it makes sense to just go one abstraction level higher. Keep going until you get to your keyboard. There is a very handy Java applet that I used to play with as an EE. URL_0 Have a look at the sequential logic examples."
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k8xi0y | Why do helicopters make a chopping noise instead of a smooth spinning noise? | Engineering | explainlikeimfive | {
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"Because you’re hearing the sound of each blade as it goes by. Listen to different helicopters with different numbers of blades. The UH-1 Huey has 2 blades and makes a very distinctive whip whup sound but a 4 bladed copter has more of a buzz to it.",
"Helicopter rotors operate a low RPM, usually around 600. That's much much slower than things like fans, and not fast enough to produce a continuous noise: Each blade create a pressure wave as it passes by, and the time between one wave and the next is long enough that they stay distinct."
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k8yale | How does a fire on a gas stove stay only on the stovetop and not travel down into the stove? | Engineering | explainlikeimfive | {
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"I believe it’s because the concentration of gas is too high, in other words not enough oxygen to ignite in a closed environment"
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k8yd74 | Why are car roofs not made as hard and stable as possible so that you are no longer killed by trees or light poles? | Engineering | explainlikeimfive | {
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"Because the chance for that to happen is *really* low and making the roofs much stronger will add weight to the car, decreasing fuel efficiency, increasing required stopping distance, adding more potential energy (due to higher weight *presumably* moving at the same speed) to auto accidents, etc.",
"Because that would make the roof a lot heavier, raising the center of gravity and perhaps making the car more prone to flip. The data shows that the roof not being strong enough is not a huge cause of death in car crashes, therefore it’s cheaper and lighter to make the way it is now.",
"Being killed by trees or light poles due to the roof caving in by being hit by one is so rare that the added cost in materials and weight reducing fuel efficiency that a reinforce roof would have is not worth it at all for car makers to design. Such as design would also raise the center of gravity of the car making it far more likely to roll and thus more dangerous over all."
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k9cedm | why is it that when driving down some highways the sound from the road or smooth, and sometimes it goes “ DUGA DUGA DUGA DUGA”. For reference: it all looks like blacktop. | Engineering | explainlikeimfive | {
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"I know at least where I live. There are some small black lines that run perpendicular to the roads surface. This is for a speed/red light camera There are similar kinds that also measure traffic flow/density and number of cars etc. They use this data to plan how to improve, fix roads and give more money to transurban because the government is corrupt."
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k9f424 | Why do CT scanners need to spin so fast? | Engineering | explainlikeimfive | {
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"text": [
"They don't. But the speed they can make the image, and hence how quickly they can get results, how many machines you need to buy for a particular patient load, how much each CT scan costs, etc. all scale with how fast it spins. A faster spinning machine is more productive, more efficient, and produces results faster (can be important for some conditions). It's like asking \"why do cars need to go so fast?\" They don't, but we're all happier with faster cars up to the point that safety starts to get compromised."
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ka29c1 | Is working on small engines (thinking like, go-cart or pocket rocket as opposed to lawn mowers, unless they're the same idk) similar at all to working on regular, car engines? Are there even the same types of parts, "under the hood"? | So I know a little bit about cars, can replace a few things/do a few jobs myself (starter, brakes, anything in the serpentine belt area), and was wondering if small engine repair is similar whatsoever? I realize saying "engine repair" and then listing things that AREN'T engines might not make sense, and that's kinda my question also...do small engines HAVE the same kind of starters, or serpentine belts, or alternators? Could my general knowledge of working on cars translate to small engine repair, whatsoever, or would it be learning a 100% different thing? | Engineering | explainlikeimfive | {
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"text": [
"Small engines are usually pull-start, and usually caurberated instead of fuel injected. Much simpler than a car engine, but the very basics are the same, you need fuel, air, compression, and spark.",
"The basic aspects of the engines will be the same. Where a car engine will differ from a smaller, off highway, engine will will be around the complex variable components modern cars need to meet emissions and the wider range of operating conditions. A modern car engine will probably have some form of variable valve timing. They may have variable intake geometry, variable displacement (cylinder deactivation), some cars can even vary piston stroke. Also every car these days will have fuel injection. Cheaper engines will not have any of that variable stuff and may still be carbureted. If the off highway engine does use fuel injection the system is likely to be simpler and the ECU will be much simpler and monitor fewer aspects of engine operation. There will also be fewer and more simplified accessories. No AC compressor, perhaps no power steering, no water pump if the engine is air cooled, simplified alternator as electrical demands will be smaller.",
"Small engines are significantly simpler than car engines. It depends on the engine. But they are probably lacking all emissions controls like catalytic converters and O2 sensors. The engines probably aren't computer controlled, that means you still need to know how to 'tune' an engine, something you haven't had to do with a modern car in 30+ years. Fuel injection is making its way down to smaller engines, but you'll still need to know your way around a carburetor. Starters: maybe, or pull start. Serpentine belts: likely not, there's a lot less accessories attached to the engine, probably no power steering, A/C, water pump. Alternators: maybe It'll be 80% the same stuff, and learning a bunch of stuff that is obsolete in modern cars. Like 2 stroke engines."
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kad5ai | Why do cars sound different in reverse? | Engineering | explainlikeimfive | {
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"text": [
"Reverse gears often are straight-cut instead of cross-cut because they get used far less and are cheaper to make. In this image the straight cut gears are on the bottom: URL_1 The gears on the top are cross-cut and make far less noise and last a lot longer. Straight cut makes more noise because the teeth sort of slap against each other as the gears mesh. Cross cut are quiet because the more gently mesh with each other over a diagonal. edit: If you want to hear some REAL \"reverse\" noise (warning - it's loud): URL_0",
"It’s called a “lay shaft” in manual gearboxes. In the gearbox, you put an extra cog in there, so that it spins the gearbox and wheels backwards. The extra cog is only small, so it spins like crazy while you reverse, and you can hear it. Usually you only have first gear backwards, so it’s also hella noisy if you try to go backwards fast. It’s all about the extra cog in the gearbox. The engine itself will make the same noise.",
"If you have ever played around with something that uses cogs and gears you have noticed that they tend to make a bit of noise. This is because there is some slack between the teeth and as one tooth slips off there is a tiny bit of slack before the next tooth slams into the tooth opposite. This makes noise and also cause the gears to wear out over time. So for a car gearbox this is no good. Instead they use helical gears. These have teeth that mash in a different way so that there is always one tooth in contact with the next and there is never any sudden changes. This means that normally a cars gearbox is quiet. However the reverse gear is not like the rest of the gears. In order to change the direction of motion it requires an odd number of cogs which means there are other challanges when designing the reverse gear then the other gears. Because of the issues that helical gears can have with regards to shifting and space constrains in addition to the costs most reverse gears use regular noisy straight gears instead. The gear is not use that much anyway and when it is used it tends to be at low speeds. So most people will not have an issue with wear on their reverse gear. The noise even have an additional benefit of notifying anyone near you that you are reversing and therefore might not have good visibility. The last part have become so important that even if car manufacturers get the option to use helical gears in the reverse gear they prefer not to do so or even add devices to mimic the sound. In some legislation cars are even required to make noises like this for safety reasons."
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kafrtc | How is a "fast charging" battery charger different from a regular one? | How can a charger change how fast electricity is charging a battery? | Engineering | explainlikeimfive | {
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"Actually it's the phone who asks charger nicely for a quick or slow charge and the charger responds with what it's capable of. After that quick handshake it's just a matter of how quickly phone can gulp the stream of electricity provided by the charger. Picture drinking from a hose when someone is controlling how much the valve is opened. You have to tell them how much you can handle first.",
"It just has the ability to \"negotiate\" with the phone to provide a higher wattage. To really simplify it and ignore some of the nuances of charging, if 5W down the wire charges in 6 hours, 10W charges in 3.",
"The charging speed of your phone is limited by a few different things and the speed of charge is restricted to the lowest value. Obviously the battery can't charge any faster than the battery can charge safely, but it also can't charge with more power than the charger can provide, and it can't pull more current than the cable can support. A basic little USB cable and Micro USB connector is really restricted to about 2 amps. If your charger runs at 5V (USB standard) then your phone has no more than 10 watts of power to charge with regardless of how much the charger could provide or the battery could use. Fast charging or QuickCharge have the phone and charger negotiate the voltage that the charger will send. If your charger outputs 25V then you can get up to 50W down the cable which will charge the phone up to 5x faster. Running at the higher voltage with a high capacity charger means that you've removed bottlenecks 2 and 3 and are only limited by how fast the battery can safely charge. Fast charging requires that the phone talk to the charger though because not all devices are ready for 25V on their USB cable, and it would make a device that wasn't expecting it very sad. This results in more expensive chargers and some minimum level of compatibility/trust between the phone and charger. Most Lithium Ion powered items are built with a charge controller and the assumption that all chargers are garbage until they prove otherwise to keep the charging process safe."
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kawmga | Why can’t I cut easily with scissors when I’m using my left hand? | Engineering | explainlikeimfive | {
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"text": [
"You are using right-hand scissors. Scissors are designed so when you use them you press the blades togherer. Using them on the other hand result in you pressing the blades apart. So right and left-handed scissors are a mirror of each other just like the left and right hang. You can see both [in this image]( URL_0 ). Notice that which blade is on top is different. If you try to move your thumb towards the hand and not away from it when it is in the other hand the work better The difference is larger in bad scissors where the blade is not held together with good enough. This is all in addition to the difference in using a non-dominant hand."
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kb5xdq | is there a difference in tunnels underground versus under water (underground) | In basic terms I was wondering if a tunnel that goes underground has any more pressure or possibility of collapsing if it goes under a river or ocean versus just going under land. Thanks. | Engineering | explainlikeimfive | {
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"There isn't a huge difference. The top of the tunnel has to be able to support the mass of what's above it, without collapsing. Soil is heavier than water, but not much heavier - e.g., a cubic metre of sand weighs around 1.7 to 1.8 times as much as a cubic metre of water."
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kb6bwc | Why do we not use aircraft/balloons as launch platforms for rockets? | I did search but the last responses didn't address the reasons why this might be useful in an error with reusable rockets, a plane or balloon launch would be a reusable primary booster. | Engineering | explainlikeimfive | {
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"Rockets need all that fuel to go *sideways* and reach orbital velocity of 17,000 mph. The fuel spent going up 100 miles is comparatively small. Adding more complexity to the system to shave off a dozen miles from the initial launch isn’t worth the trouble.",
"Airplanes are used - it's called air-launch-to-orbit, and it's been used for satellite delivery in lower orbits. URL_0 Balloons aren't as practical, they won't have the lift capacity necessary to raise a heavy object up high enough.",
"The aircraft+rocket is how Virgin Galactic intends to reach space, see SpaceShip Two. It just adds extra complexity in general."
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kbf6h1 | Why haven’t airplane windows gotten larger or generally changed much in 50yrs? | Engineering | explainlikeimfive | {
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"text": [
"They have, look at the 787 and A380, they are significantly bigger than previous planes. The reason it doesn't seem like it's true is those are the only really new planes released in the last 30-40 years or so. The workhorse planes you mostly see on domestic trips in the US are probably the A320 and 737, released in 1987 and 1967 respectively.",
"Why not go windowless and put a lightweight screen and stream live camera feed from multiple angles around the plane. Probably lighter than the windows and supporting structure."
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kbf7r0 | Why is the acceleration of cars controlled via a foot pedal and not by hand? | Why isn't there some sort of button you can press and hold on the steering wheel instead to control acceleration, à la Mario Kart (but obviously way more sophisticated than that)? | Engineering | explainlikeimfive | {
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"Three major reasons: 1) Almost all steering mechanisms on all vehicles, with the exception of boat tillers, work by turning a wheel. This means you will occasionally have to let go of the wheel to reposition your hands as you turn. This would make any continuously-held button difficult to keep held while doing large turns. 2) When we tense, we instinctively grab tight to whatever we're holding. This means, in a panic situation, we'd mash the accelerator button. That's generally bad. With feet you have a much larger gross foot motion to go to the pedal (and we don't instinctively smash our foot down quite the same way we death grip the wheel). This is still an issue with people mistaking the gas pedal for the brake and mashing the accelerator anyway, but it's not as bad as if acceleration was done by hand grip. 3) At this point, \"everyone\" assumes that the right pedal is the accelerator. There'd be a huge retraining burden for no obvious value. Like QWERTY keyboards, we long ago past the point that the value of a better interface can overcome the inertia of the installed base. For acceleration that doesn't require fast reaction (cruise control) we \\*do\\* typically use a hand button."
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kbfglb | how car rear-view mirrors tint went you hit the switch? | At night when the person behind you is driving too close you flip the switch and instant relief! It looks like it angles the mirror up, and it doesn't work in the daytime. So how does it actually work? | Engineering | explainlikeimfive | {
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"There are actually two mirrors, both partially reflective. You see both all of the time, however one of them is significantly less reflective (or receives less light being blocked by the other) and so you can't usually see its image unless the lighting is weird. If your mirror is adjusted properly, one of these two mirrors will point out the back window and the other will point at the chair or ceiling. In a dark car, the chair or ceiling is significantly less illuminated than the back window and see you only see the back window. Depending on which mirror is 'selected' it may be bright or dimmer. If you look very carefully, you can often see the dim image in the second mirror. Especially if you flip it to the 'dim' side during daytime. Bloody brilliant, this system is.",
"It's a clever trick that's, somewhat, similar to the design of a teleprompter, First, let's break down the construction of the mirror. It's not a single surface. It's a sheet of glass with a piece of mirrored glass behind it. There are two layers (and this part is important for how it functions). In \"day\" mode, the surface glass is parallel with your eyes as you look up at it and the mirror is *nearly* parallel with your eye from its position behind the surface glass. What you see in the mirror is more or less directly reflected into your eye which is why the stuff in the mirror looks about as bright as you would expect it. In \"night\" mode, you reach up and move the little lever on the back. It feels pretty stiff and firm because it's not like a lightswitch toggle, you're actually tilting the entire mirror assembly inside the rearview mirror. When you make that adjustment the actual mirror surface is tilted back away from you. Some of the light that shines into the mirror bounces back out and refracts on the glass surface of the outer layer of the rearview mirror assembly, but a lot of it shines straight ahead (above the level of your eye). This is a lot how the reflection in a window at night looks less bright than the actual object--a window isn't a mirror (even if nighttime makes it semi-function like one) and a lot of light is lost out the window and not reflected back at you. So the manual-adjustment rearview mirror is essentially a nifty little optical trick. Automatic mirrors, which are a lot more common these days, work on a totally different principle. Rather than automatically making a mechanical adjustment to the angle of the mirror, the mirror is in a fixed position but between the glass and the mirror layer, there is a layer that is, more or less, like the e-ink screen of a Kindle. When the sensor in the mirror assemblyy detects it is dark out, it switches to \"night\" mode by putting an electric current through that middle layer that applies a semi-opaque \"sunglasses\" effect to the mirror that dims the brightness of the lights you see behind you by actually reducing the amount of light the mirror can reflect back at you."
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kbj1wp | How do “detangle hair brushes” work so effectively on hair that wont accept a regular hairbrush. | The ones that look similar to a normal hair brush but have that curve. What makes them special? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"Because it is so flexible. A stiff bristle will get to a knot and just push through. That works for straight hair, but with curly, kinky, or just very thick hair, you can't just push through because the tension needed to push through will rip out the hair at the scalp first. You have to slowly work out what hair you can little by little. A flexible brush will pull the loosest strands out, making the overall knot looser, eventually working out the whole tangle."
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kbspuk | How do companies that make measuring tools like rulers make sure the product is accurate? Is there a universally ruler that is used to check? How do they make sure the measurements are exact? | Engineering | explainlikeimfive | {
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"There are primary standards locked away from which secondary standards (copies) are made and certified. Those copies are sent around and used to make calibration standards. All standards are traced everytime they are copied, and become a little less accurate with each copy. 1. Company makes ruler. 2. Company checks ruler against their calibration standard and passes or fails ruler. 3. Company calibration standard is sent to a Metrologist every so often. Metrologist checks company standard against their standard. 4. The metrologist standardis checked against a secondary standard. 5. The secondary standard is traced to the primary. There could be more copies than listed in my example above but that is the general idea. The unit of length is no longer based on a physical object but rather the speed of light in a vacuum. NIST is responsible for maintaining this system. Edit: adding a great video that is easy to follow. URL_0",
"Rulers, in particular, are \"accurate enough\" for their use. Many wooden rulers are stamped with the lines and numbers, so a few careful measurements are copied over and over. The piece of wood is \"about a foot\". Plastic rulers, again are measured when their extruder template is made and the metal form is \"accurate enough\" when used to make the final product. Tl;dr - most every day measuring devices are not exact, but they are good enough.",
"If you have a laser, a detector and a good clock you can measure the distance of an object to a very precise degree. A meter is exactly defined as the distance light travels in 1/299,792,458 of a second. There was at points in history actual physical objects which defined units like the meter, for example the International prototype metre bar but now they are defined in terms of universal constants.",
"When a ruler is made, you check it against a ruler that you know is more accurate than the ruler you're making. In turn, when that ruler was made it was checked against another ruler that was known to be more accurate. ... repeat a bunch of times ... So, where does this end? Well, there are a handful of laboratories around the world that have the ability to make a very accurate ruler. This is done with a science experiment. The official definition of a meter is: \"The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.\" (Note that other units of length, such as inches, are now defined based on the length of a meter, so it always ends up with that definition of a meter). But, to do that the laboratory needs to be able to time a fraction of a second very accurately. Just like rulers, clocks are compared against more and more accurate clocks. And, just like the meter, the official definition of a second is based on a science experiment: The second is \"the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom\" (at a temperature of 0 K) Translating that into ELI5: If you take this material and do complicated stuff to it, it gives off microwaves. You can measure the frequency of those microwaves - i.e. how many waves there are per second. This is exactly 9,192,631,770, so if you get a different number then your clock is wrong and you need to adjust your clock until you get the right number.",
"I’ve wondered this same thing except for time. Almost a billion people in the world use their iPhone to tell the time (and reference it to set their other clocks). So where does Apple get their time from? Is there a universal clock that all clocks are based on?"
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kc2og9 | Why do you need to add air to your tires when it gets cold, but you don’t have to release air from your tires when it warms up? | Engineering | explainlikeimfive | {
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"Technically you should, if you want to maintain the same PSI. After a long drive on a hot day, your air pressure will have increased, just as it decreases on a cold day",
"Recommended tire pressure ratings take a few different factors into account, including but not limited to fuel economy, towing and hauling capacity, and the health of the tire itself. Your tire's performance and health is at greater risk when it's pressure goes down versus when it goes up. An under inflated tire even at rest risks damage to the sidewall from the crushing force of the car's weight. On the other hand, most tires have a recommended inflation pressure that is actually much lower than its burst pressure. If you check your tire sidewall on a typical stock sedan, it probably has a max rating of around 80 psi or so, but the vehicle user manual probably recommends only 35 to 40 psi. If your tire pressure goes up slightly in hot weather, it isn't likely to put your tires at any sort of risk.",
"Sudden cold snaps will actually cause the rubber to contract. Air will leak out between the rim and bead when the tire deforms. This is more apparent with cheap tires. Source: I asked my best friends dad who has operated a tire store for 30+ years."
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kcopxj | How come hot water “runs out” | Warm water will go out until you turn the dial to make it warmer, instead of just staying warm, why is that? | Engineering | explainlikeimfive | {
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"text": [
"Most of the time in a residential setting, the hot water is coming from a tank of heated water somewhere in the building. This water doesn't replenish continuously- after the hot water is exhausted, it refills with cold water and heats back up over a period of time. Warm water from the tap is just a blend of hot and cold water, so the hot water is going to be exhausted much slower than if you turned it on full bore hot.",
"Your house has a big box called a boiler that heats water. Big box stores a little bit of hot water in it, along with heating more. If you use hot water faster than big box can make it, then big box runs out of hot water and it becomes colder.",
"The heater in your water heater can't heat water from the tap temp to the hot temp as fast as you can draw water. Once you start drawing hot water, it's replaced in the heater by cold water. That cold water takes heat from the hot water already in there and drops the temperature. The heater will kick on and try to maintain temperature which is why a 25 gallon tank is good for around 35 gallons of hotter water. The heater is fighting a losing battle and can't keep up though. That's why after you run out of hot water you need to wait to use it. The tank has to build up the water in the heater to the hot temperature. There are tankless water heaters. They're simply a big, beefy heating element that can put out enough heat to have hot water forever."
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kcu3qp | How do phone screens register my finger clicks? How do phone styluses manage to recreate this? | Engineering | explainlikeimfive | {
"a_id": [
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"text": [
"There is a little electricity in your body. The screen reacts to that electricy. A stylus uses a conductive rubber that transfers your electricity from you to the stylus to the screen. Phone screens are not pressure sensitive at all, ignore the people saying that."
],
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kcuk0l | when you turn your left right indicator on in your car, and it makes a ticking noise, what actually makes this noise? | Is there like a small speaker that plays the ticking sound that is pre recorded? Is it due to some metal clunking together in the car? | Engineering | explainlikeimfive | {
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"gfsq12r",
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"text": [
"In older cars, there is a small electrical switch, and you can hear the switch clacking. It's basically a switch which turns itself off, and then a spring pulls it back on. It's a simple and robust system for switching the signals on and off. Newer cars just have a speaker.",
"Originally the sound was caused by a component called a relay - this is a type of magnetic switch that allows you to interface low power electronics (like a cars dashboard) with high power electronics (like the headlights). So the click you hear is a small magnetic switch turning on and off (exactly like a house light switch clicks when you switch it). A lot of modern cars however no longer use this system - modern led indicators for example don't need to use relays in the same way, so the sound is often played by a small speaker in the car - it isn't necessary, but a lot of people rely on it as a sign that the indicators are active (the same as watching the blinking light in the dash), so it is recreated in modern cars that don't make the sound naturally."
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kcvkqe | How is using an inefficient filament light bulb different than using a space heater to heat a room? | I obviously know that the magnitude of heat output is not the same, but does the ‘wasted’ energy from the lightbulb just go directly to heat energy? | Engineering | explainlikeimfive | {
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"text": [
"Yes heat in that sense can be classified as wasted energy, since the purpose of a light bulb is to produce light and not heat. Any heat that is produced, is essentially energy not transferred into a form that is intended to be used. A space heater is a little different. Since the obvious purpose is to produce heat, then the effect that would be inefficient in a light bulb would be more efficient in this case. It is essentially the reverse of what is true for the bulb.",
"Yeah basically. A filament is just a tiny electrical heater. A very small fraction of the energy will be lost as light escaping through windows and heating the outside, but that is really a minor amount."
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kd37m9 | How do car wheels automatically realign themselves after we let go of the steering wheel? | Engineering | explainlikeimfive | {
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"text": [
"The front wheels have a built-in caster angle. The geometry is hard to explain in words, pictures are much easier. But the basic concept works the same way as the wheels on an office chair or the front wheels on a grocery shopping cart. No matter which way they are turned, if you push the chair or cart the wheels will align themselves in that direction. In your car, the steering wheel is attached to the front wheels, so it follows what they are doing."
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Subsets and Splits