q_id
stringlengths 6
6
| title
stringlengths 3
299
| selftext
stringlengths 0
4.44k
| category
stringclasses 12
values | subreddit
stringclasses 1
value | answers
dict | title_urls
sequencelengths 1
1
| selftext_urls
sequencelengths 1
1
|
|---|---|---|---|---|---|---|---|
85olxj | How do air brakes work? | Engineering | explainlikeimfive | {
"a_id": [
"dvyz7bz"
],
"text": [
"They are not that much different than regular brakes. Reguar brakes use hydraulic fluid. You push the brake pedel, and your master cylinder forces fluid down the brake line, and that squeezes the brake pads against the rotor. Air brakes are the same thing. You have a compressed air tank, and when you press the brake, air pressure is forced down a brake line which forces the brake pads against the rotor. Air brakes can also work the exact opposite way. In a train, the air will keep the brakes open. A reduction in pressure is used to apply the brakes. This has the advantage that if a train car was disconnected or there was a loss of air pressure, the train car or train would come to a stop. It should prevent a runaway train."
],
"score": [
8
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
85qvw4 | How do we manage the massive amount of dead people in large cities like LA or NYC? | Engineering | explainlikeimfive | {
"a_id": [
"dvzjsfe",
"dvzx75g",
"dw092wf"
],
"text": [
"I worked for large funeral care company in the SW UK. I asked during my training what kind of large scale disaster they were prepared to cope with, how many bodies. They (and the government as part of it's disaster planning) have arrangements with several companies with large refrigerated warehouse spaces so they had the capacity for thousands, if not tens of thousands of bodies within a 50 mile radius, in case of a major disaster. I imagine every urban centre and centralised points such as these are in place everywhere.",
"Not a direct answer but I can still chime in. I used to work at a large sports arena that had ice hockey and in the event of an epidemic the ice hockey floor would be used as a morgue",
"According to NYC's website, a person dies about every 9 minutes in NYC. Honestly doesn't sound like very much to me. There are morgues in each borough that can handle many of these. And there's dozens of crematoriums and funeral homes throughout the city for permanent disposition (I lived within 5 minutes of two funeral homes). In short, the simple answer is there really isn't a \"massive amount of dead people\". There's a steady flow of dead with a robust public and private system set up to handle them."
],
"score": [
28,
10,
8
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
85sa27 | What happens when you miss a shift in a manual car? | I watched a drag race on YouTube when one driver lost and said that it was because he missed a shift. Now, I know what gear shifts are for and how they work, but I don't exactly know what happens when you miss a shift. Could the engine shut off because of high load or critical RPM? Or you just lose time? | Engineering | explainlikeimfive | {
"a_id": [
"dvznnsh",
"dvznlu8",
"dvznnsr",
"dvzntj7"
],
"text": [
"Each gear is a compromise between torque and speed. 1st gear gives you maximum torque but super slow speed. 6th gives you speed but very little torque. During initial acceleration from 0 to whatever you want to have perfect timing when switching gears in order to get to the end line as fast as possible. By skipping one he lacked the torque he needed during that phase of the acceleration and was probably left behind by the other car.",
"You lose time attempting to rematch motor rpm to groundspeed to engage the gear you missed.",
"Just a loss of power...gears are meant to keep the engine RPMs in a consistent power band. Gears shift from top of one gear to the bottom of the next. Missing a gear loses that momentum and optimal power isn’t applied. In very high performance driving this can damage the drive train and destabilize the vehicle but it’s rare",
"In a regular car your engine isn't going to shut off. If you miss by accidentally downshifting, your RPMs shoot up and the car will pull forward for a second but then fail to go any faster while the engine red-lines. You *can* damage your engine this way. Realistically, you'd only do real damage if you failed to correct it. If you miss by upshifting, your RPMs drop and you sort of just chug along. During a drag race where milliseconds matter, either one will lose you the race."
],
"score": [
8,
3,
3,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
85sopw | How do power plants know how much electricity to generate? | Are power plants constantly overproducing electricity to be safe? What happens to the excess energy? What happens if there isn't enough energy to supply the grid? | Engineering | explainlikeimfive | {
"a_id": [
"dvzsg7o",
"dw0ll8x"
],
"text": [
"There are many different kinds of power plants with different performance characteristics, and they're used in combination to ensure that the supply of electricity matches the demand as demand changes throughout the day. In one group, you have the \"base load\" power plants. These are typically things like large coal and nuclear plants that produce electricity very cheaply, but need to run at 100% production all the time, and take a long time to turn on or off (on the order of several hours up to several days). These just run at 100% production all the time. Next you have the \"peaking\" power plants. These are typically natural gas plants that produce electricity more expensively, but can be turned on and off quite quickly (sometimes within a few minutes). These are used to handle the times of highest demand, and only run for a few hours a day, if that. Finally, you have \"load following\" power plants. These are plants that can modulate their output to ensure that the right amount of power is available when it's needed. There are a lot of different kinds of plants that can do this, though sometimes they have to have some modifications from the standard design to allow load following operation. These are used to handle the fluctuations in demand outside of peak hours, when they'll be running at full output and the peaking plants will be used to produce the extra supply necessary. The grid is constantly monitoring the amount of load currently connected and feeding that information back to the power producers in order to ensure the correct amount of supply is available. Small fluctuations are handled by the grid itself: the miles and miles of power lines and other infrastructure act as a giant capacitor and can either store up excess energy when there's an oversupply or discharge it if there's an undersupply. The grid changes frequency slightly when that happens, and the grid operator tries to ensure that those frequency changes balance out so that the average frequency of the power system is consistent over the long term. If there's so much load that there isn't enough power generation supply available to satisfy it, the grid will disconnect some customers to bring things under control. The details depend on the specific legal framework and operational systems in place. In some places, large power consumers like factories or office buildings can agree to be the first ones disconnected in exchange for getting a deal on their power bills. In other places, the grid operator will impose rolling blackouts via some specific schedule. There are some other ways to do it as well.",
"The simplest and most correct answer is frequency. For the most part power plants turn physical energy into electricity via a generator or turbine, so lets talk about how that works first. In both cases there is a rotating object inside of a circular case and some wire. Typically the wire is attached to the part that doesn't move and looped in specific patterns, and the rotating part can have magnets or it's own specially placed wires. When rotation happens the changes in magnetic fields cause electricity, or in this case better called current, in the wires. The power that comes to your house is \"AC\" which means Alternating current. That means that unlike a battery the electricity changes direction over time, this happens very fast, about 50 to 60 times every second depending on the country you live in. In order to create electricity that does that the generator or turbine needs to spin at a specific speed, that speed depends on the wires inside but for ease of thinking about it lets imagine that it must rotate once all the way around per full cycle of AC. Now lets think about something else for a second, riding a bike. When you ride your bike on a nice flat road you can go a certain speed, but when you climb a hill you can't go that fast anymore. The demand of trying to climb the hill is too much for you to do at the same speed, so your bike slows down and you need to put in more effort to keep moving. Electrical generators are very similar, when there is more demand (usually called load) it takes more energy to turn the generator at the same speed, so at first the generator starts to slow down. If the power plant can supply more energy to the generator, for example the turbine at a dam could have it's valve opened more allowing more water to turn it, then it will speed back up and everything is good. Now, lets imagine everyone goes to make a cup of tea or hot chocolate all at the same time so a whole bunch of stoves and kettles and microwaves all get turned on. Well now all of the generators start slowing down as they no longer turn as easy (just like a bike going up hill) and the people that run the various power stations can see that the frequency is going down. As a response to this power plants that can react faster either by supplying more energy to their generators, or turning some on that were previously off, start doing that and provide more power to the power grid. As more power is supplied all of the generators start spinning a little faster. It takes less effort to turn so since they are mostly still being turned as hard they go faster, like when you finally get to the top of a hill. Now what happens when everyone is done making a hot drink? All of the generators now turn a little too easily, and the people running the power plants can see the frequency going too high so certain power plants might turn off generators or reduce power going to them. Some modern power stations and solar can be more complicated than that, but they still try to emulate that behavior. As far as how which power stations know when to do what, that comes down to agreements between the various power stations and the types of stations."
],
"score": [
10,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
85swr9 | why are scissors hard to use if you hold them in the wrong hand? | We always give my MIL shit for saying she can't do things because she's left handed (holding playing cards, for example), but I tried to use scissors in my left hand and it just wouldn't cut! Why?? | Engineering | explainlikeimfive | {
"a_id": [
"dvzsf5k",
"dvzshop",
"dvzylry",
"dvzsupb"
],
"text": [
"Your hands aren't symmetrical. When you use scissors, and close them, you're not pushing straight up and down, your thumb is actually also pushing towards you and your fingers are pulling away. With correct handed scissors this helps push the cutting blades together and so they cut properly. With the reversed scissors, you are forcing the cutting blades open slightly, and they don't cut.",
"Your hand naturally produces some lateral pressure from the thumb portion. in your right hand this causes the blades to come together since the thumb is on the outside and torques away from the hand thus pinching the blade more at the cutting edge (pivoting at the pin) . in your left hand it's all backwards so the force from the thumb forces the blade away at the cutting edge.",
"Practice. I'm left-handed and I learned how to use scissors long ago. However, you have to use them differently (pulling with your thumb rather than pushing with it) because your hands mirror each other. You could buy her some left-hand scissors, most fabric shops have them.",
"Scissors, especially if they have loose screws holding the two parts together, require lateral pressure (pushing with the thumb, pulling with the index and middle finger) in order to force the two parts of the scissor to scrape against each other and \"scissor\" (cut the material). When you try with your left hand, the lateral pressure required by the scissors is the same, but now you must accomplish it by pulling with your thumb and pushing with your index finger."
],
"score": [
11,
6,
5,
5
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
860rwq | How are military systems like fighter planes protected from backdooring or other neutralization against their original country of origin? | Let's say a country buys fighter planes from USA or Russia and then later on goes to war against the fighter jet's manufacturing county with the said jets. What prevents the original manufacturer hiding code to disable the jet's electronic warfare suite or critical systems via backdoor in their proprietary code or otherwise leaving vulnerable spots to be exploited in such situations? | Engineering | explainlikeimfive | {
"a_id": [
"dw1ipmh",
"dw1j1b4",
"dw1hja1",
"dw1pcww",
"dw240v6"
],
"text": [
"These days a backdoor would almost certainly be implemented in software and at least some buyers are able to negotiate access to source code as part of the purchase agreement. I believe that the F35 falls in this category because the other countries are considered to be co-developers rather than just buyers and in some cases have unique capabilities built just for them. I suspect that this applies to a fairly small number of contracts but when it does it gives the buyer an extra layer of protection.",
"Often they're not. This has led to significant opposition against Switzerland buying American military jets.",
"Well the fact that they want to remain in business for one thing. The moment something like that is found nobody would ever do business with that company again.",
"1. Complex systems like fighter planes are only sold to allies in the first place. 2. When developed nations buy military hardware of this sort, they generally don't buy the actual hardware but rather the *design* of the hardware - which they then produce themselves. So the only people who would have to worry about the black box nature of the hardware would be the sorts of developing nations that lack the industrial base to produce such equipment anyway. 3. The manufacturing nation doesn't need a 'kill switch' to disable the hardware since the hardware will cease to function in short order without the logistics chain. This happened to Iran after the revolution - their world class air force quickly became scrap metal not from hostile action but simple inaction. The manufacturers stopped supporting their equipment and they ran out of parts. 4. Any such 'kill switch' creates an attack vector that a hostile power could use against the manufacturing nation. The U.S. military would never permit a U.S. manufacturer to include such a device in hardware they were paying for, so it would need to be custom-designed for foreign sale. While not impossible, it would be relatively difficult to hide this sort of mechanism.",
"> Let's say a country buys fighter planes from USA or Russia and then later on goes to war against the fighter jet's manufacturing county with the said jets. First of all, it's unlikely that this will ever happen (at least for the USA). When it comes to weapons systems, the federal government has to approve exports on a nation-by-nation basis. Lockheed can't just say \"I want to sell my plane to China\" and make a deal; they have to go through the state department and get the export deal signed off. If the federal government has any legitimate concerns about the buyer being an adversary during the useful life cycle of the weapon system, they won't authorize a sale. This is particularly true with such an advanced and deadly weapons system as the F-35 or other jet fighters. > What prevents the original manufacturer hiding code to disable the jet's electronic warfare suite or critical systems via backdoor in their proprietary code or otherwise leaving vulnerable spots to be exploited in such situations? While the possibility exists for such a backdoor to be created, it's really not needed. Aside from the fact that we generally sell weapons so that they can be used by our allies, you don't really need a back door to nerf the ability of a foreign country to operate a fighter jet. As an example, we can look at what happened with the Iranian F-14s. Originally sold to an allied government, the F-14's fell into the hands of an adversary government following the revolution (that's an oversimplified description of the governments, but it's all we need to know for the purpose of this question). Suddenly, one of the United State's most advanced weapons at the time was being operated by a government with interests that some perceived as counter to the US interests. Immediately following the revolution, the US pulled all of its mechanics and project leaders (who were employed by Grumman, the manufacturer of the plane) that were stationed in Iran supporting the planes. Because those employees were the most knowledgeable and experienced mechanics, the ability for Iran to keep their planes operational was greatly hindered. To add to that problem, the US stopped exporting parts. As you can imagine, a huge, complicated jet has a lot of moving parts and many of those parts need regular replacement. Even if Iranian ground crews had the technical knowhow to repair the planes, they didn't have the parts they needed. Those two factors made it impossible for Iran to get the most out of their planes. They had to cannibalize certain planes just to use their parts on other planes. They created a blackmarket plan to get naval mechanics to smuggle them parts, but that was slow, expensive, and eventually shut down. Eventually they reverse engineered many of the parts and figured out how to build them, but that was expensive and the parts were of a lower quality. Basically, Iran had to spend a ton of money to keep a limited fleet of planes in the air. As the icing on the cake, the US stopped supplying missiles. It's widely contended that the Phoenix missile is a big part of what made the F-14 a feared plane, and the US cut off their supply of those missiles. So Iran's limited fleet was further limited in the weapons that it could attach to its planes. In a world where combat readiness and operations costs can determine the fate of wars, the US pullout of Iran severely weakened Iran's Air Force. _________ If we look at an export like the F-35, the dependence on US maintenance crews is even more prominent. Stealth planes have tolerances measured in the thousandths of an inch, so the tooling itself is incredibly specialized and hard to reproduce. The avionics are also incredibly complicated and nearly impossible to reverse engineer. If an F-35 had a mechanical issue and a Lockheed team wasn't there to fix it, it probably won't be air ready for a long, long time. It can also be argued that the F-35 is as important as it is because of its networking ability. It's considered a force multiplier because it makes every other asset on the battlefield smarter and more capable. If an exported F-35 falls into the hands of an adversary, it probably won't be able to communicate effectively with an adversary's assets, meaning it has reduced capabilities. Sure it's a stealth plane that can penetrate airspace, but without its armament of missiles/bombs, its networking capability with ground and air based radar, and its network of other F-35s, it's far less lethal."
],
"score": [
16,
11,
10,
4,
3
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
863y48 | What is the purpose of the blue tint/film at the top of windshields? | Engineering | explainlikeimfive | {
"a_id": [
"dw2548b",
"dw25a5x"
],
"text": [
"It helps to shade the sun from blinding you as you drive. Think about how sunglasses work except only for certain angles.",
"The sky is brighter than ground, and the difference in brightness causes eyestrain. so some manufacturers tint that portion of the windshield to balance the brightness between the sky and the ground. It is similar to wearing a baseball hat, or putting down the sun visor."
],
"score": [
6,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
864yih | When you switch a car from modes such as snow, mud, sand, etc., what changes with the car that makes it better suited for the corresponding mode? | Engineering | explainlikeimfive | {
"a_id": [
"dw2dyhi"
],
"text": [
"It changes the behavior of the traction control, stability assist, and ABS system. On some terrain types the wheels are going to spin, that's a fact, so having traction control let that happen instead of throwing on the breaks everytime it detects slip it means you can get out of some tricky situations. On others you need more torque so the computer will put the transmission in a lower gear range to help the car climb out of sticky mud. And on some you don't want ABS at all. If you're trying to stop on gravel then having the wheels lock up can be helpful as it snowplows and builds up a wall in front which helps slow you down rather than relying on the mediocre traction between the tire and the gravel. I'm sure there are dozens of other fine tweaks that the computer does to optimize for it, but those are the broad strokes. You'll usually only find settings like these on off-roading vehicles or Land Rovers"
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
868n1i | Why are pipes under sinks more susceptible to leaks than those under showers or bathtubs? | Engineering | explainlikeimfive | {
"a_id": [
"dw36wtm"
],
"text": [
"Because they are not as well protected. Pipes in floors are almost impossible to bang into or twist. Under the sink lots of stuff goes on. Putting the pipes there makes them more maintainable, but it also causes more need for maintenance."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
869qq3 | How do we know buildings and structures won't collapse? | Also how do we know how much weight, for example, the 49th floor of a skyscraper will be able to hold without being damaged/falling? Sounds like a silly question but I've been reading a few articles about buildings collapsing (especially in developing countries) and just wondered how engineers are sure that structures can handle a certain load at any given time. | Engineering | explainlikeimfive | {
"a_id": [
"dw3h589",
"dw3jjvu",
"dw7cuts"
],
"text": [
"Testing. Extensive testing. If you pour a block of concrete that is 1x1ft, and let that dry properly, how much weight can you put on it before it bursts? That kind of thing can be tested with a machine that crushes things that is also capable of measuring the pressure it applies. Once you have that measured, try it with all the other concrete compounds that are available. So that you know which one you need. The good ones are often awful expensive. Then, you know. Calculate. If you know what you intend to put on a floor, you also know what kind of floor you need. And the other way around. If you know what kind of floor you have, the maximum load can be calculated. But the max load is originally tested. So that the calculations uses numbers with real experience behind them. The trick to it is that if you know that your floor will collapse from exactly a ton and a pound of load, then you can't put a ton on it. That is not how it works. The floor will be built with a safety margin. Say...10% ? So that when you put a ton on it, it's still capable of holding another 10% and thus will manage. Some materials and also some structures have a preferred margin as high as 100% or even 200% because that is how you take wind, rain and snow into account. But that is how it's done. Everything is built for a purpose. And based on the calculated purpose, the building is supposed to be built with a safety margin that allows the intended use. And then some. Buildings that collapse tend to fail there. The margin is poorly calculated (human error). The material is not having the standard expected (ignorance or flat out greed). The wear and tear is higher than estimated (poor research or lack of knowledge. or in the case of a really old building, lack of imagination) when the building was constructed. EDIT: I forgot to add. Sometimes when a structure collapses, it's because someone is using it for a purpose that is very far from it's intended use. Often without asking the owner or designer first. Maybe the newly build boat dock is a pretty bad place to put 200 wedding guests in formal clothing? Especially, you know, since it's probably built for a maximum of ten-twenty people carrying groceries and a toddler?",
"I build these things for a living, residential and office towers. Basic layman’s, columns or walls transfer point loads down to the footings of the building which are designed to accept the total weight of the building along with movement (remember these things in the wind are a giant sail!!). So what makes the point load? The weight that that column is supporting, so the columns are holding the building vertically plus the weight of the horizontal elements. So more columns/walls the weight is distributed more so the columns are holding less loads. Ok so design phase the engineers have a scope to work for, you have design loads, dead loads, live loads. Design load is the building supporting itself in a finished state. Dead load is stuff like aircon units, furniture etc. live loads are people, environment, cars etc. So you have a building being designed to cope with a lot of things in consideration, plus given margins for safety and that’s the design.",
"Good design and engineering, and a lot of testing... We know how strong various material are through testing and practise - so I can tell that a certain mix of concrete will be able to support a certain amount of weight before it starts to crush, and I can calculate how far a steel beam or column of a certain size and grade will deflect under certain load conditions. From here I can then use this information to design a building - we can calculate the weight of the building itself, alongside determining things like the loading for the use it will be put to (there are standard table that tell us the loading required for domestic use, office use, hospitals, etc), what the wind loading on the outside will be or how much snow it will need to be designed to carry. Chase this loading down through a structure and we can determine the loading on a column or other member, and then design it so that we know it is strong enough to support that (with a suitable safety margin included to account for unexpected situations). When a structure collapses something had obviously gone very wrong. This can be for a whole range of reasons, including (but not limited to) things like bad design where the structural engineer had done a poor job and not calculated the loading correctly and under designed it. Where it hasn't been built correctly and concrete has not been reinforced correctly, the wrong size of beams used or other mistakes. Also situations that just were not designed for like an earthquake moving the ground the structure is built on and causing it to fail, or extreme cases like the twin towers where an event has happened that is so unexpected and unlikely that the structure had not been designed to cope."
],
"score": [
11,
3,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
86blg1 | Why can we make machinery with extremely precise movements, but not robots that walk realistically? | Was browsing /r/mechanical_gifs and this occurred to me. Factory line machines seem capable of insanely accurate and exact movements - surely achieving believable and organic looking walking in a robot would simply require the correct combination of well timed movements. | Engineering | explainlikeimfive | {
"a_id": [
"dw3rrry",
"dw3rvj1",
"dw3rfrd",
"dw4a48q",
"dw3ri68",
"dw4h58e",
"dw484ge",
"dw48wow",
"dw4i2lg"
],
"text": [
"The difficult part of walking isn't the precision of the movements, it's knowing what movements to make. Assembly line robots have the advantage of knowing exactly where the thing they are supposed to cut/bend/move/rivet is going to be, exactly where the screw holes are, and so on. Most of them don't even have any sensors, they just know that the work piece is going to be in position X, because the system holds it there. And the ones that DO have sensors (for example, a robot that picks up objects from a moving conveyor belt and puts them in a box) still have it easy because the things they are picking up all look alike, and they are on a background that makes them stand out. In other words, assembly line robots can do what they do with great precision because every part of the process has been designed around them, to make it easy for them. For a robot, walking around in an un-controlled environment is much more difficult. There are a million different floor patterns, and some of them might confuse the robot into thinking that there's an obstacle there. Balancing is hard, because the robot has to figure out exactly how to balance right *in that moment*. An assembly line robot has had its movements planned out for it ahead of time, because those are the only movements it will ever need to make. A walking robot needs to be able to balance itself correctly under a huge variety of different circumstances. The bottom line is that assembly line robots are barely even really robots. Everything they do is planned out carefully by engineers. If you had a team of engineers to plan out a robot's every single step, then sure, it could probably walk great. But figuring out how to do those motions on the fly is WAY harder. Walking may not seem like a challenging task, because you do it without thinking about it, but actually, that's just an indication of how fucking amazing your brain is. Your brain does a lot of work behind the scenes to let you walk without thinking about it.",
"Well, let me pose you a question: how do you think humans walk? Perhaps you could say that the brain tells a bunch muscles to flex or relax at certain points so you can walk. But it’s not that simple. If that was all your brain was doing, no human would ever be able to walk. A good way to look at it is from the perspective of a baby: they are extremely wobbly initially. Their brain is learning what muscles allow the baby to stand and learns how to voluntarily flex/relax them. But this isn’t enough to be able to walk realistically. Then it must learn how much of each muscle they need to flex/relax. When you flex your bicep, you can decide to flex only parts of it or all of it. For every single movement and position in space, your brain must learn how much of each specific muscle to flex/relax. But this is still not enough to be able to walk realistically. Calculating all that is nearly impossible for your brain because of how precise it needs to be. In fact, it doesn’t exactly precisely command all this to happen from the outgo. Your brain tell your body the general layout of the movement. Your body does the planned movement, and then your body sends feedback about its position, its balance, etc back to the brain. Your brain needs this to fine tune the movement. Your brain is getting a continuous stream of feedback from the body during any movement, and it will correct any inaccuracies. Of course, this is again all trial and error by the brain. But.... this is still not enough to be able to walk realistically. Your brain must get information of it’s surroundings and the situation you are in and plan your movements accordingly. You ever wonder why we don’t trip whenever we go uphill? It’s because the brain noticed there was a slight incline, processed the information, and estimated how our body should move to respond appropriately. And your brain does this for everything. Perhaps if you do all this you can walk like a normal person, but I’m sure I am missing something the brain is doing behind the scenes. Now, imagine getting a robot to do all this.",
"Factory line machines generally deal with precise, unchanging patterns of movement. The devices come in in the same way. They're moved in the same way. They leave in the same way. Walking has to deal with terrain, which can vary in elevation, height, traction, slope, all sorts of things. You could undoubtedly make a robot that walks beautifully across a precise, featureless, flat terrain. Making one that can handle any old stretch of ground is much harder.",
"We do not walk in a stable manner, we're constantly falling and catching ourselves. Between muscles, bones, nerves, clothing, and the environment, there's a massive amount of variables in play. Every millisecond matters, as your center of gravity and inertia is constantly changing, requiring different corrections (and those corrections, in turn, change your center of gravity and inertia as well!) Any slight change in speed, angle, ground cover, wind, or loading, requires a compensating change. If a compensating change doesn't occur, something known as a \"compounding error\" occurs. EX: Lean too far forward, but didn't step far enough to compensate, which means you're tipping even further forward the next step and eventually falling. If you watch videos of walking robots, I'm sure you've seen this happen. Point is, you're not repeating a correct and well timed movement, you're creating a unique movement each and every step you take. The hardware to measure it accurately and instantly, the mechanical parts to actually perform the movement, and the software that brings it all together is something that has proven very difficult to bring together.",
"They are making robots that can walk very stable. You can kick them without them falling over.",
"How are you on *reddit* asking this question? [Boston Dynamics]( URL_0 ) my friend Home of the coolest, most unsettling, most human like robots you'll find around!",
"\"Realistic\" walking isn't about well-timed, precise movements. Walking is smooth, fluid, natural, random, and filled with about a thousand unconscious tiny movements, half of which are bits of \"body language\". When we walk, there is always attention paid to the environment and to the people around us. Making eye contact, avoiding eye contact, slumping your shoulders, puffing out your chest, etc.",
"I would say it’s the same reason that it’s easy to get a computer to multiply very very large numbers together but ridiculously hard to get them to have a preference between orange juice and apple juice. Because of how computers are made we have to give them exact inputs and we receive exact outputs. Not really a great explanation but maybe it helps your understanding?",
"Off topic: Is walking on two legs really the most efficient way for robots to maneuver around? Or is it because of the resemblance to humans that has made it the norm to design robots that way?"
],
"score": [
661,
30,
24,
14,
9,
6,
6,
6,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[
"https://www.youtube.com/watch?v=knoOXBLFQ-s"
],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
86cyop | how can jets produce directional thrust | I know how jets work. But in my head, it's a tube with openings both ends. How do we get it ~~directional~~ one way? A rocket makes more sense to me - it's a box with a hole at one end. But a jet, expecially a ramjet, a tube where hot expanding gases can go either way. What am i missing? | Engineering | explainlikeimfive | {
"a_id": [
"dw42hw7",
"dw4fc0d"
],
"text": [
"A jet engine sucks air in through the front, uses that air as part of the chemical reaction that burns fuel and powers the engine, then pushes the hot air and burned fuel out the back, faster than it came in. Wikipedia mentions that a **ramjet** uses the forward motion of the vehicle to intake air, which means it can't work unless the vehicle is already moving. Those vehicles have to get started another way, and then switch to the ramjet once it's moving.",
"Jets and rockets work much the same way, both need to feed fuel and oxidizer into a combustion chamber and then vent the resulting hot gasses out. These are all fluids, so the rules of fluid dynamics apply, one of the simplest of those rules is that fluids flow from high pressure to low pressure. Rockets have crazy powerful pumps to jam the fuel and oxidizer into the combustion chamber at a higher pressure than the exhaust gasses generated by the combustion. Jets have pumps for fuel, but they use a compression section to increase the air pressure to be higher entering the combustion chamber than the exhaust pressure leaving the chamber. I'm sure you're familiar with the narrow then wide shape of rocket engines. Jet engines are designed with a shape that does the same thing, the space between the inner section of the engine and the outer tube gets narrow right after the combustion chamber and then widens out. This is to take advantage of some other laws of fluid dynamics. First, the flow rate of an incompressible fluid is equal to the area of the cross section of the pipe it's flowing through times the velocity of the fluid, therefore the narrower the pipe the faster the fluid flows. At relatively low speeds, gasses act like incompressible fluids, so that narrow section of the engine accelerates the exhaust gasses. However, as a gas starts moving close to *it's* speed of sound, it begins to act as a compressible fluid. So, once the gas is moving faster than mach 1, the velocity can increase as the pipe cross sectional area increases. But then pressure and temperature have to decrease in order to keep the total energy of the system constant. This is what the expanding section of the rocket or jet engine does: It *decreases* the pressure of the flow, ensuring the gasses are traveling out of the combustion chamber instead of trying to push back up the fuel lines. [Here's a video]( URL_0 ) explaining how it works in rockets. The principle is the same in jet engines: Compressed inputs, narrow opening from the combustion chamber to speed up flow, widening exit to reduce pressure and further speed up flow. They're just shaped differently because they have different methods of injecting their oxidizer. Ramjets do the same thing, they just start out moving so fast that the flow *into* the engine is supersonic so they can compress the air to increase pressure first, then ignite it, then compress the exhaust gasses *again* on the way out."
],
"score": [
4,
3
],
"text_urls": [
[],
[
"https://www.youtube.com/watch?v=6JDu7BfVNoY"
]
]
} | [
"url"
] | [
"url"
] |
86jz23 | How do hotels/motels not run out of hot water? | Engineering | explainlikeimfive | {
"a_id": [
"dw5lnb5",
"dw5ltgw",
"dw5lh88"
],
"text": [
"Depends where in the world you are. Here in Australia, a lot of newer hotels use massive instant-hot water heaters. Meaning they don't store tanks of hot water, rather they heat water as needed. Plenty of smaller places (motels) use the same principal, but rather a small instant heater for each room. This is also used a lot in apartment buildings (even large ones).",
"Unlike a home system that uses a tank that can run out and needs to refill and reheat, a hotel has a inline hot water boiler that is always on and ready to be used. Water is circulated through the hotel and tapped into for instant hot water. That's why a home system takes a few seconds to reach desired temps because it has to move from the tank to your bathroom, where as a hotel has a direct hot water line from boiler, always circulating. Heating Tanks vs inline heating. Although every place will be different. Having a bunch of tanks just takes up unnecessary space. So heating the water as it comes in and just constantly pumping it through the building just works better. It removes the chance of running out of hot water during peak hours.",
"Multiple hot water tanks. Recently, they also use compact water heater that take water through a thinner pipe surrounded by a heating element."
],
"score": [
12,
7,
4
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
86ku7s | What is Dielectric loss? | There is a reason I changed from EE | Engineering | explainlikeimfive | {
"a_id": [
"dw5xfck",
"dw5zrpj"
],
"text": [
"A dielectric is a substance that transmits electrical *force* but not electrical *current*: i.e., an insulator. The stuff between the plates of a capacitor is a dielectric. Unfortunately there are no *perfect* dielectrics: they all permit a *small* amount of current to flow. That current is flowing through a high resistance, and since power = I^2 R, it dissipates a measurable amount of energy. That rate of energy dissipation is dielectric loss.",
"Every point in the universe, regardless of whether or not there is matter present, has two properties, which we have defined to be inversely proportional to the speed of light squared: c = 1/sqrt(µε). Permeability, µ, is a measure of how easily we can make a magnetic field in a region, while permittivity, ε, is a measure of how easily an electric field can be set up in the region. A dielectric material has a *relative* permittivity greater than one; this means that the permittivity in a dielectric medium is bigger than it is in empty space, and one consequence of this is that electromagnetic radiation, which moves at the speed of light, actually slows down in this region. Electromagnetic waves are formed from both magnetic and electric fields, which [oscillate against one another as the wave moves along]( URL_0 ). Furthermore, the wave loses energy as it travels through such a material. One way this occurs is by dielectric loss. We normally characterize this through an equation that has real and imaginary parts, and that might be a bit too much for an ELI5, but we can think about it in terms of a (possibly) familiar circuit element: the capacitor. Because the capacitor works by setting up an electric field in the dielectric material used, there is bound to be some loss in setting said field up. In an AC circuit, this happens every time the current (and/or voltage) switches directions. Manufacturers report this property as an \"Equivalent Series Resistance\" or ESR. So if you know the current in the capacitor (i = C dv/dt), then you can approximate the loss in the capacitor due to the dielectric by p = I^2 ESR, where the capital I represents the root-mean-square (RMS) current. This current is the equivalent DC current that would transfer the same energy per cycle (read: per time period of oscillation) as the actual AC current."
],
"score": [
79,
6
],
"text_urls": [
[],
[
"https://upload.wikimedia.org/wikipedia/commons/4/4c/Electromagneticwave3D.gif"
]
]
} | [
"url"
] | [
"url"
] |
86mxp2 | Why can every bus on Schiphol airport be electric, but not all buses in general? | I was recently on Schiphol and I noticed this. | Engineering | explainlikeimfive | {
"a_id": [
"dw69rw6",
"dw6aslj",
"dw69svn"
],
"text": [
"Electric vehicles are more practical when they only have to travel short distances and have easy access to charging facilities. A bus that makes the same 1 mile loop every day fits that description. A bus that travels a couple hundred miles a day, not as much.",
"The problem with most electric vehicles is that, unless they stay on charging rails, they have a pretty limited range; they can only go a few dozen miles, up to a few hundred on the state of the art models, before needing to be plugged in or to swap out their battery. Airports are great for electric buses because, while they may drive around a lot, it's all in a fairly small geographic space. They're never far from a charging station, and can even install charging cables along their routes. Airports also serve the function of being the ambassadors to an entire region; travelers often judge a city by the quality of its airport. Cities are thus willing to chose more expensive, more environmentally friendly options at the airport in order to make a good impression.",
"Electric buses require infrastructure. If they are the trolley type, they get their power from overhead wires. If they are electric vehicles, they need somewhere to plug in and recharge their batteries. Either way it's easiest to roll out an electric bus program on a smaller scale - like an airport - because you either need to build a bunch of overhead wires, or a big depot with lots of charging stations for the whole fleet. There are larger scale electric bus operations in the world, though. Vancouver, British Columbia has overhead wires on most of the major roads for trolley style electric buses."
],
"score": [
14,
4,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
86onkg | the setup and dismantling of cranes in construction. | I'm a grown ass 27-year old man, and I've just realised that I've never really understood cranes. How do we set them up, and how do we get rid of them once we're done? In my ignorance, I always just assumed we had bigger cranes set up the littler cranes, but that just leads to a "cranes all the way down" type scenario... :/ | Engineering | explainlikeimfive | {
"a_id": [
"dw6obrp"
],
"text": [
"So, for the big skyscraper cranes or \"tower\" crane, the center pillar the crane rests on can be jacked up - it grows \"up\" with the building. They'll use a smaller but somewhat portable (or assembled on site) boom crane to assemble the tower crane. Then the tower crane gets jacked up as the building grows. Then, once the building is done, the tower crane will lift up a smaller boom crane to the roof. The boom crane disassembles and lowers the pieces of the tower crane. Remember, the ability of a crane to lift \"up\" from its own level is limited by the length of its own boom and how far it can elevate it. All the smaller crane has to do is reach just above the component of the tower crane, which if they're both on or just above the roof isn't far. But to lower the tower crane components to street level, that's just lots and lots of cable. Sometimes due to practical considerations, there might be a second boom crane halfway down or something. Roof crane lowers tower crane components halfway, 2nd crane lowers to street. [Outside of really tall skyscrapers though, boom cranes at street level are usually tall enough to reach the tower crane.]( URL_0 ) So why not just build with the boom crane on the street? It won't have the lifting capacity of the tower crane. Also it won't be able to hold as much weight out from its center of rotation. The counterweights for the street level boom crane are mounted on the back of the crane itself. The tower crane's counterweights are suspended quite far out. Also, you have to have a lot of bracing for the street crane. The tower crane's stability is anchored by the building itself."
],
"score": [
7
],
"text_urls": [
[
"https://youtu.be/LUQalhFFnOE?t=126"
]
]
} | [
"url"
] | [
"url"
] |
86rwjh | how does a semi-truck/tractor trailer run into an overpass due to height issues? | Engineering | explainlikeimfive | {
"a_id": [
"dw7dvwy"
],
"text": [
"What happens is that each time the road is repaved, the gap between the road and the bridge gets a few inches smaller. But the city/state/whoever in charge of the road rarely replaces the bridge height sign & city maps to reflect the new lower clearance. Semi drivers usually do know the exact height of their truck & load, and they commonly look up the bridge heights along their path to make sure they will clear before they head out. But when the posted height isn’t the actual height, that doesn’t do them any good."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
86sgr1 | How do planes fly upside-down if they generate lift from their wings? | In school we are taught the top edge of a wing is curved, so when air passes over it the air is slown down, this creating higher pressure air on the bottom of the wing to create lift. So with this fact in mind, when fighters or stunt planes flip over and fly for short periods of time, why are they not forced towards the ground and how are they able to keep flying the plane? | Engineering | explainlikeimfive | {
"a_id": [
"dw7h61l",
"dw7hztj"
],
"text": [
"Because the curve actually generates a small portion, often less than 5%, of the lift. Nearly all the lift is generated by the angle at which the wing hits the air. Even planes with completely symmetric wings fly just fine. URL_0",
"The description that a wing need to be curved to provide lift is not true. You can show that at home by folding a paper airplane and throw it. You get lift with flat wings. What you need is a wing that have a angle of attack towards the air ie angled a bit upwards. If you put you hand out the window in a moving car you will notice that the the higher the angle the more life. Why are wings not flat? You what the flow above the top of the wing and and not to separate from it and cause a area with turbulent airflow that increase drag. Increased drag will result in that you need more powerful engines to compensate for it so you get better performance if you shape a wing . Look at URL_1 to see how the flow can separate from the wing. The [airfoil]( URL_2 ) ie shape of a wing can be symmetrical or asymmetrical. The shape that is used will depend on for example what speed is should operate at. A airplane wing is quite symmetric. Look the [airfoil]( URL_0 ) of a Boeing 737 and you notice that it is quite symmetrical. Another thing to compare to that is more familiar to most people is a rudder on a ship. Water behave quite similar to air and you know that you can turn a ship both with a rudder. The force to the side on a rudder is the same same as the lift of a wing but only rotated 90 degrees."
],
"score": [
12,
3
],
"text_urls": [
[
"http://wtamu.edu/~cbaird/sq/2012/12/17/how-do-airplanes-fly-upside-down-if-its-the-shape-of-the-wings-that-make-them-fly/"
],
[
"http://www.rroij.com/articles-images/IJIRSET-350-g003.gif",
"https://youtu.be/6UlsArvbTeo?t=57",
"https://en.wikipedia.org/wiki/Airfoil"
]
]
} | [
"url"
] | [
"url"
] |
86ufrn | why are car cabin fan speeds preset so disproportionately? With 4 settings, the first and second speeds the fan may as well be off- whereas the last speed is relatively extremely fast. I thought it might be an engineering slip up in a few instances but this seems to be the absolute norm. | I figured it was across a few models or one manufacturer but I’ve seen this with countless GM models as well as many by Toyota, Ford, Honda, and Dodge/ Chrysler - new AND old - and even on digital HVAC systems. Sometimes I only want a little air but that never seems to be an option. RPMs across a 4 setting fan might go from 100 RPM to 200 to 900 to 1200 RPM (these examples may be highly over exaggerated). | Engineering | explainlikeimfive | {
"a_id": [
"dw7wxok"
],
"text": [
"The first few fan settings are for people who want some air movement but want it to be silent and unobtrusive. The last setting is for when people want maximum air movement and they don't care what it sounds like. They are disproportionate because the desired application is different. How you want a fan to behave during an 8 hour drive at a comfortable temperature isn't the same as when your car is a million degrees and you want to exchange the air as fast as possible."
],
"score": [
8
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
86xr8q | How does the engine helps braking and increase vehicle control when in transmission? Isn’t moving out of gear supposed to help braking since the engine and the wheels are “disconnected”? | Engineering | explainlikeimfive | {
"a_id": [
"dw8n7jg"
],
"text": [
"If a car is rolling down a hill, the weight of the car gives it potential energy that is converted to kinetic energy as it moves. If the engine is disconnected from the wheels, then all the energy gets used to turn the wheels as the car is pulled down the hill. However if you connect the engine to the wheels via the transmission, there are now lots of heavy metal parts that need to be rotated and moved around. So now some of the potential energy that was going to be used to rotate the wheels, has to get used to rotate parts of the engine as well. This means the car will roll down the hill more slowly because some of the energy is being used to to move the engine parts and not just the wheels. Now I know that you're thinking, \"Doesn't the engine produce its own power?\" and of course the answer is yes. But, depending on which gear the car is in and how much the accelerator is pressed, the engine parts might be turning faster or slower than the weight of the car would make them turn. If the engine's own power is making it spin faster than the weight of the car would make the wheels turn, then the engine causes the car to speed up. However, if the engine's power makes it turn slower than the weight of the car would make it spin, then the engine slows the car down which was call engine braking."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
86yj3c | Why do land vehicles' direction changing parts lie in front while ships have rudders at the back? | Engineering | explainlikeimfive | {
"a_id": [
"dw8txca",
"dw8xmbe"
],
"text": [
"The same reason planes have rudders at the back. Both ships and planes are moving through fluids (air and water), and use the interaction between the fluid and the vehicle itself to change direction. For example, a rudder on a plane or boat tilts one direction, so that the fluid moving past it changes direction, providing a force in the opposite direction. This *reaction* force turns the vehicle. Land vehicles use friction and the interaction between the wheels and the ground, because they are (hopefully) in constant contact. This means that it is more efficient to just turn the wheels instead of trying to use air resistance to change direction. I hope this clarifies your question somewhat, I may have missed a few details.....",
"This has mostly to do with stability of the vehicle--that is, given the normal little deviations that happen, if you don't touch the controls, does the vehicle keep going in the direction you pointed, or veer off to one side? Aircraft and boats keep their direction by reacting with the fluid flow past them, basically by taking a plate and pushing the fluid to one side or the other. in this sense, u/JGass81 is right that it's the reaction force that matters; however, putting a rudder at the front or the back gives you the same reaction force, the important bit is that one makes the ship/airplane keep going in the same direction, and one makes it veer off where you don't want it to go. Now suppose you're in a regular ship, where the rudder is at the back. Suppose also that for whatever reason, the ship is still moving in the same direction, but the bow has turned 5 degrees right. This means the rudder starts pushing water to the left (because the front edge is farther to the right than the back edge), and since pushing on water pushes back, the stern of the boat is pushed to the right, turning the boat back to the left, the direction that it's actually going. If you have the rudder at the front, the reaction force from the rudder in this situation is still to the right, but since it's pushing on the front, it makes the boat turn further and further right, which is bad. So why do cars have steering at the front? It's mostly because convenience--putting the controls at the back gives a \"backwards/delayed\" effect when controlling boats and airplanes (a \"nonminimum phase zero\" in controls terminology) which makes them harder to control precisely. Since you're interacting with the road through wheels, the physics are a bit different, and there's a lot more subtle stuff that you can use to keep the car stable, including [weight distribution]( URL_0 ), [caster angle]( URL_1 ), and similar things. and put the actual steering at the front. **tl;dr: it's mostly to make sure that if you let go of the controls, the vehicle doesn't immediately veer off in a random direction. Subtler points to follow:** Actually, you could *in principle* put a large, fixed stabilizer at the back of the boat/airplane, and then have a much smaller one at the front that is actually connected to the steering wheel for control. In a sense, this is similar to a car--the rear wheels act to stabilize the car, while the front wheels can then steer even though they're in front (take this analogy with a grain of salt--it makes sense to me, but haven't done the math to make sure they're *actually* the same). There's two reasons you don't do this in a boat/airplane: 1) the extra weight/drag are often significant, so you're just wasting fuel to solve a problem that isn't a huge problem, and 2) in a boat/airplane, you can *only* control the vehicle if there's fluid flow moving past the rudder. If you put the rudder behind the propeller, then even when the vehicle itself is moving slowly, you'll always be forcing water/air over the rudder, and still be able to control it for more safety."
],
"score": [
10,
7
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Directional_stability#Example:_road_vehicle",
"https://en.wikipedia.org/wiki/Caster_angle"
]
]
} | [
"url"
] | [
"url"
] |
|
8741bw | Why do level crossings activate so early? | Engineering | explainlikeimfive | {
"a_id": [
"dwa0eb9",
"dwa1u8d",
"dwa0kom"
],
"text": [
"Because they are warning of the approach of a train that has absolutely no possibility of stopping in time to avoid smashing you to tiny pieces. So yeah, some early warning there is pretty cool.",
"The train track has a posted speed limit. Not all trains travel at the speed limit. However, the switch that turns on the crossing arms and lights is positioned so that a train slightly exceeding the speed limit (safety margin) cannot reach the crossing before the arms are completely down. If you happen to be there when a slow moving train trips the switch, it seems early, but a system that measured the speed of the train would be much more expensive and complicated and likely to fail and unsafe - Since it's a safety device, these features are \"bad\" so they don't do it that way.",
"Factor of safety: there is a maximum speed the train should be running at, the detector is keyed to that speed, so if the train is running at half of that speed then it will be activated with more time between when the train approaches and crosses versus at the top rated speed."
],
"score": [
20,
9,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
87crjc | Why do some bricks have purposefully made holes in the middle of them? | That's all, thanks! | Engineering | explainlikeimfive | {
"a_id": [
"dwbvqnx"
],
"text": [
"The holes make for more even drying and firing, which makes for a stronger brick. It also reduces weight and material, meaning they're easier to handle and you can make more with less. Rebar use and bonding properties of the holes are incidental at best."
],
"score": [
28
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
87joe4 | How have the two famous japanese torii's been able to survive such massive disasters such as an atomic bomb and a tsunami? | I understand the ones in the falls pictures aren't the same torii's, but how were they able to survive while everything around them were destroyed to the ground? | Engineering | explainlikeimfive | {
"a_id": [
"dwdc9le"
],
"text": [
"You don't hear about all the structures that *didn't* survive, they're largely famous because they got lucky. They're pretty simple structures that won't catch much wind/debris/water/fire and aren't architecturally complex, so surviving a disaster reasonably intact isn't all that hard to believe. Remember the scorched earth pictures from Hiroshima were taken after fires had burned a lot of damaged-but-not-collapsed buildings to the ground. The bomb itself didn't completely raze the city like that."
],
"score": [
10
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
87tfus | Why do most doors have a two stage locking mechanism instead of one? | If you turn the key to lock the door, you can do so twice most of the time. But what's the point? Why not have it turn once and have the door be completely locked? | Engineering | explainlikeimfive | {
"a_id": [
"dwfkwvm"
],
"text": [
"I would guess that has to do with security from lock-picking. Basically when you lock-pick a simple lock, like the hanging one you can find on barn doors, you have to put all pins up one by one and simultaneously put rotational pressure on the lock to keep pins up, when you've put all the pins up you can fully rotate the lock and open it. But if the lock requires 2 rotations that would mean after first full circle all the pins go down and you have to do the process again. So it doubles the time the locksmith needs to pick your lock."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
88bqzx | Why do bridges cost so much to build today vs 100 years ago? | Was reading about the Royal Gorge Bridge which when adjusted for inflation cost a hair over $5m to build in 1929. The Millau Viaduct a pretty similar bridge cost $460m when it opened in 2001. What accounts for the 100x difference even after adjusting for inflation? | Engineering | explainlikeimfive | {
"a_id": [
"dwjgbz3",
"dwjdtmw",
"dwjgtwe",
"dwjh2lk"
],
"text": [
"Why would you say they are similar? Royal Gorge Bridge has a span of 286m with relative short towers so the ground below and a deep gorge in the middle. It is 5.5 meter wide and has a load limit of 910 ton. The total length is 384m Millau Viaduct has 6x 342 meter bridges and 2 204 m at the end. So a total length of 2460m That is 6.4 times longer. The support of bridge span has to go down to the ground as as it is a multi span bridge so the longest is ~270m. A guess is the average is half that 135m for 7 supports. The bridge is 32 m wide so the total surface area of the bridge is 37 time larger. The road is a 2 lanes per direction highway with a max speed of 110 km/h. I cant find any load limit so it has to survive a highway full of 40 ton trucks on is. I can find any information about the Royal Gorge Bridge in the past but today the speed limit is 10 mph and oversize vehicles, including large trucks, RVs and buses, are not permitted to cross. I would guess that the max weight/axel pressure is quite low and that the speed was not high in the past as it is a wood deck Another complicating factor is that it looks like hard rock in Colorado but is softer limestone in France that complicate how the towers/pylons are build. So the bridges are not the same size at all and the traffic limits are not the same so you can compare the bridges at all. The only comparable face is the clearance below at 291 an 270m. But the depth of the gorge is not relevant if it is a single span bridge on top. The cost would be the same if it was 1000m deep, as long as it it to deep to build a bridge with supports from the ground the depth is not relevant, that if temporary or permanent support are more expensive then the alternative. For a mult-span bridge the clearance bellow is important as Millau Viaduct has 343 m pylons and Royal Gorge Bridge have 46 m towers.",
"A big factor was that labour was dirt cheap in that period. Many other overheads to do with employment nowadays was also fairly well non-existant. So you could have large numbers of cheap workmen where today you would need machinery. Wikipedia suggests an inflation-adjusted figure of $20M rather than 5M though. The Royal Gorge Bridge was constructed as a tourist attraction not a major road connection, so your comparison might not be particularly valid. URL_0",
"I think it would be very inaccurate to compare those two bridges in anything but height above the ground. One was a small project built as a tourist attraction and the other is a gigantic project many, many times in size that is meant to channel extreme amounts of traffic though it. Just for comparison: & nbsp; |Royal Gorge Bridge| Millau Viaduct ---|---|---- Material| Steel with timber deck|Concrete, steel Total Length| 1,260 ft (384 m)|2,460 m (8,070 ft) Width | 18 ft (5.5 m)| 32.05 m (105.2 ft) Longest span |880 ft (268 m)|342 m (1,122 ft) Of course a small partially wooden bridge that does not need to carry much except for the occasional tourist is going to cost less than a modern mega-structures engineering marvel.",
"What do you mean, \"a pretty similar bridge\"? The Millau is six times as long as the Royal Gorge, six times as wide, has seven pylons instead of two, and is rated to carry actual road traffic, not just occasional passenger vehicles. Plus the impressive thing about the Millau viaduct, which is that its pylons reach down two hundred meters to hold it up. No one would *bother* to build the Royal Gorge bridge today– it can't handle modern traffic needs– and no one in the 1920s could have even begun to build the Millau Viaduct. We spend more because we can do more."
],
"score": [
8,
5,
4,
3
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Royal_Gorge_Bridge"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
88c3ee | How are the b52s physically flying with how airline aircraft can only have so many Cabin pressurizations due to micro-fracturing of the metal before they're retired? | Engineering | explainlikeimfive | {
"a_id": [
"dwjh3ao",
"dwjfym5"
],
"text": [
"Actual flying hours isn't as important to aircraft life as take-offs and landing cycles because that's what stresses the airframe. The jolt of landing, and the pressurization and De-presurization of the aircraft. Take a pop bottle and suck out all the air, then fill it again, then bang it against the desk. Notice how it returns to its original shape, but somewhat deformed. The more you do that, the more damage to the bottle. Eventually it will crack and break. This is also why C-47's and WW2 aircraft are still in service today, because they aren't pressurized and therefore don't deal with the same airframe stresses. As for the B-52'2, the B-52 fleet is very large and has very few missions, hours+cycles compared to commercial airliners. Individual bombers aren't doing 2-3 take offs and landings a day. Also the US air force is willing to pay huge sums of money to retrofit, repair and overhaul the fleet to keep them in service. Airliners don't bother because it's too expensive. The reason for this is that if you have a 737 that's past it's life, it's cheaper to just buy a newer 737 because they still make them. B-52's haven't been made in decades so it's cheaper to refurbish them than to develop a new bomber. TLDR: The US air force has a lot of them, and they don't fly that often.",
"Military aircraft get far less cycles (takeoff-presurisation-landing) than civil airliners that spend most of the time airborne."
],
"score": [
6,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
88cind | Why did the NOAA bar SpaceX from showing stage 2 footage during today's Iridium NEXT 5 launch? | SpaceX had a launch today. Just before the launch began, the commentator on the broadcast mentioned that no footage from stage 2 would be shown due to restrictions from the NOAA. Over on the SpaceX sub, there's a [discussion]( URL_0 ) about the NOAA restrictions. [This tweet]( URL_1 ) was also linked as an explanation of the restrictions. However, while I'm an avid astronomer and I watch nearly every launch and I understand much of the ins and outs of spaceflight, this just isn't clicking for me. I need an ELI5 explanation as to why SpaceX can't show footage from the second stage. Why is it a big deal? Also, why was this never an issue before? Some of the other launches have shown suborbital and orbital footage for hours with no problems. Thanks! | Engineering | explainlikeimfive | {
"a_id": [
"dwjjrgz"
],
"text": [
"> Why is it a big deal? It qualifies as a \"remote sensing space system\" which requires a license to operate. Presumably they could have obtained such a license but by the time they understood that one would be needed it was too late. > Also, why was this never an issue before? Perhaps they were in violation of the rule previously but nobody called them on it until now."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
88es4c | Why aren’t houses and buildings built entirely of stone/concrete so that they won’t catch fire or rot as easily? | Engineering | explainlikeimfive | {
"a_id": [
"dwk1pj8",
"dwk22le",
"dwk3fna",
"dwk1xoh"
],
"text": [
"> I understand that wood is cheaper, lighter, easier to cut and easier to work with This answers the question. It's susceptible to fire, damage, termites, etc, but once the sale is completed, that's not the builder's problem. Also buyers tend to not think much about the long term, and they put more value into the local area, schools, comps, etc, than the condition of the house (unless it won't pass inspection or large repairs are imminent). Also some areas it's just not practical to build with stone, especially on alluvial plains like the Gulf Coast and Florida... there's no bedrock to dig down to and no local quarries, and any masonry usually has to be sent a long distance by barge or rail which adds to the price.",
"> I understand that wood is cheaper, lighter, easier to cut and easier to work with This pretty much answers your question. > And look at the structures that have lasted the longest (hundreds and thousands of years): they’re all stone castles and stone walls and stone structures. But not everything needs to last thousands of years.",
"Houses also need to be insulated to prevent heat loss. I believe air is the best insulator. Wood homes have airspace in between the studs(walls) and joists(ceilings). This space is usually insulated with fiberglass batts which are strips of fiberglass wool. This fiberglass must not be squished because that would remove the air gaps inside. Some people think it’s better to squish as much insulation as you can in between the studs. This is worse and you need to use the correct insulation for your depth of wall to have it be fluffy and effective. I believe that this is a good insulator because the fiberglass batts have airspaces in them but they minimize airflow from convection, within the space between the studs. If you just had airspace with no insulation, then heat would rise, moving the air around and contributing to heat loss. As you can see, I know a little about it but I am definitely not an expert by any means. I’m also not sure if this answers your question or if that’s even one of the reasons we build stuff like that. I’m sure we could build out of concrete and stone and still make some sort of nonflammable insulation like a honeycomb design for the inside though. I believe, like the other resources to this post, that the ultimate reason is cost. It’s cheaper and quicker to build houses out of wood.",
"houses may not be made of concrete but most of the largest apartment buildings are made of the steel/concrete combo. that's a lot of dwellings. but even when you go with concrete it doesn't necessarily prevent fires because most people's possessions are made of flammable materials."
],
"score": [
15,
6,
4,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
88hm2e | How does a helicopter land after losing power to the main rotor? | I've read a couple articles about autorotation, but I can't seem to wrap my mind around it. | Engineering | explainlikeimfive | {
"a_id": [
"dwknj70"
],
"text": [
"Basically the air rushing past the rotor blades causes them to spin, and the spinning redirects air, which provides some lift. You're still going down fast, but not nearly as fast as without the rotor. You can also think of it as the rotating blades effectively acting like a parachute."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
88icxu | Why is the falling Chinese space station going to break-up on re-entry but Tesla space rockets do not break up on re-entry? | Engineering | explainlikeimfive | {
"a_id": [
"dwksalt",
"dwkthat",
"dwkuana",
"dwksdo9",
"dwkt3dt"
],
"text": [
"The Chinese space station is going to be falling uncontrollably. It will be tumbling and falling at unpredictable rates, axis, and directions, and has no ability to steer. Air friction will tear it apart. The rocket boosters used for the Space X in the Falcon Heavy are designed to control the descent from a specific altitude, at a specific rate, and in a specific way to minimize friction and prevent damage.",
"SpaceX launch and land rockets not Tesla The first stage of Space X Falcon 9 separate as a speed of 7530 km/h at 72 km with values from the launch yesterday. That is 2100m/s. The orbital speed at low earth orbit is 7800m/s. The reported speed of Tiangong-1 was 7777m/s today. That is 3.7 times faster then the Falcon 9 stage 1 so it is not ripped apart but can come down to the surface and land withoud large heat shield that you would need for orbital speed. The separation speed of the first stage is almost the same as the speed record of the fastest airplane X-15 The second stage of the Falcon 9 provide most of the orbital speed and it is not recovered and is burned up in the atmosphere after it have delivered satellites to orbit. The first stage that is recovered have a empty mass of 25.6 ton and can take 395 ton of fuel and use 9 engines. The second stage have a empty mass of 3.9 ton and can take 92 tons of fuel and have only one engine. You need less engines on the second stage as it is used in almost vacuum and there is almost non air resistance. The first stage have air resistance and need to lift a heavy second stage so you need more engines. It is the engines that are the most expensive part.",
"The rockets are coming in at a certain speed and angle they where also designed with reentry in mind whereas the space station wasn't designed for re entry",
"Because that’s traveling at like +2500ms (don’t know it’s exact velocity) why the rocket boosters are only traveling a fraction of that because they don’t need to leave the atmosphere they just need to push the main rocket and payload into high atmosphere so that main rocket can fire and push the payload where it needs to be at a higher efficiency as a result their speed is much less than an orbiting body, and the slower an object is going the less resistance (friction) is caused by the air and as a result less heat on its return to earth",
"Because the Tesla rockets do not fall. They fly back. Orbital space isn't very high up. It's only 64 miles. But it is very very fast. What destroys things that fall to earth is drag from the air. They are travelling too fast relative to the air. What might be surprising is that it isn't the falling that does it. It's the rotational speed of the earth and orbit. The space station is moving fast. Much faster than you might realize. It orbits the earth once every 90 minutes. That's what keeps it from falling. You can think of it like centripetal force balancing out the force of gravity. Imagine sticking your hand out the window of a car going 100 mph. Now imagine doing that in a car going 17,000 mph. That's what happens as the space station slowly dips into the atmosphere. Rockets don't fire straight up. They start out facing up then curve torward the horizon to use their main engines to get their payload moving fast enough to orbit (17,000 mph or so). They and up on their side. The first stage (the part that lands) only boosts to about 4,000 mph. When Tesla rockets land, the actually have their engines going in the procedure. First, (using little side thrusters) they flip over and point their main engine forward. Then the fire the main engine to slow down from thousands of mph to a few hundred. This causes them to start to fall towards earth. They use their fins to stabilise themselves engine down (how they were oriented at launch) and fire their main engine a few more times to brake and slow their fall. As they touch down, they fire one last time just before touching the ground so they can land lightly. The accuracy is astounding. I've been to the Tesla landing pad in Cape Canaveral. There is the tiniest little scorch mark about 3 feet from the center of the pad."
],
"score": [
14,
6,
3,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
88jw38 | Why are U.S. freeways paved with asphalt in some areas and with concrete in others? Why hasn't one of them established its superiority by now? | Engineering | explainlikeimfive | {
"a_id": [
"dwl42it",
"dwl5gpl",
"dwl604m",
"dwl4bi2",
"dwl3y47",
"dwlpqdq"
],
"text": [
"It’s all about the money. Asphalt is way cheaper than concrete and weather is also a factor if winters are rough concrete for the most part is out of the question due to cracking. Concrete is good due to it’s longer life but other than that asphalt is the cheapest way to go.",
"There's various trade-offs between asphalt and concrete that haven't really changed in many years. And a side street in Florida bears little relation to an interstate highway in Minnesota. * Concrete costs more to initially install. Sometimes there's simply no money to pay for a concrete road instead of asphalt. Sometimes there is * Also costs differ between regions. The difference is less in the Midwest, where most of the oil has to be transported to and there's plenty of raw materials to make concrete. The difference is more in the southeast, which is full of oil refineries to make asphalt, and ports to import oil. * Concrete holds up to better to harsh climate conditions and taking a pounding than asphalt. Putting these points together, the life-cycle cost of concrete is less on a heavily travel led interstate in the harsh Midwestern climate, but is likely to be much more on a side street in Florida. If they have the initial budget agencies like to put down what's going to cost them less over the lifespan of the pavement. In the past, you couldn't use concrete on swampy soil, which the southeast has a lot of and the Midwest has very little of. Asphalt is somewhat flexible which is desirable on poor soils. But there's a new technique to put down a layer of asphalt first, then concrete.",
"Interesting that most of the comments so far say that concrete is better. I guess it makes sense in that it is harder wearing but I always assumed that asphalt is best because the road noise from concrete is awful and I much prefer driving on asphalt. In addition to the points others have made I would add that asphalt is easier to patch or resurface than concrete. Often joins between old and new concrete will fail before those on asphalt. But to answer the question it is really about the different surfaces being best in certain situations. In an area which sees big temperature swings I would imagine asphalt being better as it is more flexible - exposed to freeze-thaw (I could be wrong though). in places that get very hot concrete would be best because it won’t “melt” like asphalt. In places where you are going to have to dig up the road frequently or where food noise might be any issue you want to control then asphalt is likely to win out.",
"Concrete is better, but it is harder to install and maintain, and far more expensive to install or maintain. So it is normally saved for overpasses and the like.",
"Yeah, concrete is better but probably some roads haven't been changed or maybe they went cheaper with asphalt.",
"Asphalt is the default. How it’s usually done. But, asphalt is sometimes inferior. Generally speaking, most roads have a month every year (often when schools are out) when there is a lot less traffic. I.e, you don’t annoy nearly as many people if you close a lane to repave during that month. During a normal working day, you have two periods of rush traffic, one in the morning and one in the afternoon. While during the vacation, the volume is pretty constant during the day. All of this adds up to a pretty obvious maintenance schedule. If you can, you do all the massive road works during the vacation. And definitely not around Christmas. The problem occurs when your road has a traffic volume that wears the road so much that you absolutely must get new pavement on every six months. Because, well. You’ll annoy the hell out of every single person who depend on the road for their commute. Because they will have at least one month of constant annoyance every year. That is, bluntly put, not how you make people keen on paying taxes. And that is where concrete comes to play. It lasts longer. Probably near a decade. Yay, you. If you cough up the extra cost, you’ll annoy people less. Awesome. Let’s do this. But...that doesn’t explain why asphalt is still a thing. Asphalt is not only cheaper. It’s also more flexible. The crews repaving roads are many. And they travel reasonably fast. And they buy a side product from the petroleum industries, so there is plenty of supply. The concrete paving machines are heavy. Kind of slow. And, bluntly put, not nearly as many as the asphalt machines. Asphalt is more widely used in cities. And on the highway it’s literally the exact same machine doing the exact usual job, with another width and thickness setting. The concrete machines don’t often need that flexibility because they are always on a freeway somewhere doing what they are always doing. You have to book them far in advance. Tax funded operations are kind of tricky. Do you want to be the guy who spends the same amount of money on maintenance every year (to make taxation straightforward) or do you want to spend ten years pave budget in one sweep? Can you afford a decades worth of spending in one go for the most expensive road you have in your district? It’s...not obvious how that turns out."
],
"score": [
13,
10,
9,
7,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
88kb7o | How do CPUs switch between the states of 1 and 0? | not what 1 and 0 is, but how CPUs switch between the states of 1 and 0 | Engineering | explainlikeimfive | {
"a_id": [
"dwmsour",
"dwl72pg"
],
"text": [
"You are asking about state, not just signals, so I'll try an explain a latch. Imagine you have water flowing in a pipe. That pipe splits into a bunch of other pipes. There are a few special mechanisms in these pipes that change whether water is flowing in a particular pipe. One of these pipes regularly and precisely switches between sending water and not sending water. We call this a CLOCK. We have some mechanisms that will accept 2 input pipes, and output 1 pipe. One of these will only let water flow if water is flowing in input pipe number 1 AND input pipe number 2, another will only let water flow if water is flowing in input pipe number 1 OR input pipe number 2. There's a mechanism that accepts 1 input pipe and has one output pipe. The output pipe will only have water flowing if the input pipe does NOT have water flowing. With these mechanisms (an AND, an OR, a NOT, and a CLOCK), we can build all sorts of interesting things. The most basic of these is called an SR latch. It's a special combination of AND/OR/NOT/CLOCK mechanisms. Through some very clever feedback structures (where the output pipe is connected to an input pipe), we can have a structure that meets the following properties: 1. It has output pipe called Q. 2. It has input pipes called S and R. 3. It uses an additional feedback input which is the output Q. 4. If S and R are both off, then it outputs whatever the value of Q is. (This is how we hold a value). 5. If R is on, then the output Q is off. 6. If S is on, then the output Q is on. (The CLOCK is used to define \"If S/R is on\". R usually has to on for one full CLOCK cycle for the actions to take effect.) So if we ever decide we want to store a value of 1 in this latch, we turn S on. We can then turn S off, and as long as R is still off, Q will still be on. Anyone can observe Q to know that we are storing a value of 1 here. If we want to change that value to 0 (\"switch between the states of 1 and 0\"), we turn R on and then turn it off. Now anyone can observe Q to know that we are storing a value of 0. One question you might have is \"Who is turning S/R on and off?\". That's a good question. Often, S and R are Q outputs from other latches, maybe with some additional AND/OR/NOT logic manipulating their state. This chain extends all the way until you have some starting state. This state is usually set manually. In a computer, that initial state roughly causes the CPU to start loading data from a place in memory (which would in turn load BIOS and then read from disks, etc...) You might be thinking \"There must be millions of pipes and mechanisms\". Yep. There absolutely are millions of \"gates\" on a CPU. Hundreds of millions, or even billions.",
"1 = on, has power 0=off, does not have power They are literally switches that are either in place and on or popped out and off."
],
"score": [
8,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
88nuo1 | What prevents pipes from building up pressure and bursting when we turn off faucets/water valves | Engineering | explainlikeimfive | {
"a_id": [
"dwm04dc",
"dwm01lb",
"dwm89r1"
],
"text": [
"We pump water up into water towers, and the pressure is the pressure of gravity pulling down on the water. That pressure is fixed. It doesn't increase just because the flow of water is stopped. Just like the pressure in a glass of water doesn't keep increasing until the glass explodes. The scales are different, but the concept is the same.",
"Your pipes are always under constant pressure based on the difference in height from your house to the nearest water tower. The archimedes principle maintains that the pressure is evenly distributed in a non compressible fluid so its all the same. Your pipes and taps are designed to hold back that pressure, it wont build more than that height difference.",
"The others are correct about the water pressure being a function of water tower height. There is another issue that can cause damage to pipes when the flow suddenly stops, it's called water hammer, and it's caused by the momentum of the moving water and generates a pressure spike. Maybe you've heard the 'THUNK' when you rapidly close a faucet? To attenuate this problem, plumbing systems are designed with dead ends that contain air to absorb some of the shock. That's with metal pipes, plastic piping generally uses the ability of the plastic to slightly swell to help with this issue."
],
"score": [
14,
5,
5
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
88pbpt | How do we make things cold? | Engineering | explainlikeimfive | {
"a_id": [
"dwmaogi"
],
"text": [
"By taking away the heat that's already there. In order to cool something down, you have to heat something else up. That's how your refrigerator works. There's a closed circuit with liquid that evaporates before it enters the tubing inside your refrigerator. That proces requires heat which is taken from the inside of your refrigerator. Then the now heated gas is compressed and in liquid from travels thought the black tubing that's usually on the backside of your refrigerator, while releasing heat. Then the process repeats. The liquid evaporates before it enters........"
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
88u96x | What makes a bomb "dirty" | Engineering | explainlikeimfive | {
"a_id": [
"dwn9dtd",
"dwnn8hz"
],
"text": [
"A \"dirty bomb\" is basically an improvised nuclear bomb. It's not a true nuclear bomb- it doesn't actually cause a chain reaction resulting in a nuclear explosion. Instead, it's a regular bomb packed with radioactive materials. So it's \"dirty\" in the context of it spreads radiation, making it dangerous even after it's already exploded.",
"A \"dirty\" bomb is the R in the military acronym CBRN which is decidedly different from the N. R is a radiation threat whereas N is nuclear. Like u/56Subject said a dirty bomb is an explosive device where the builder adds a radioactive element to be spread. In many ways, the explosive is primarily used to spread the radioactive material which causes all sorts of issues with clean-up etc etc Unfortunately, you can also seed a nuclear weapon with a layer of cobalt which will enhance the \"dirty\" aspect of a true nuclear weapon. I'd be happy to answer any more questions in more depth or detail Cheers, ~Q"
],
"score": [
13,
4
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
88x5dz | What is Exergy in terms of Thermodynamics? | Engineering | explainlikeimfive | {
"a_id": [
"dwnw569"
],
"text": [
"Exergy is the energy that an object could transfer to its surroundings. Imagine a warm object in a room. That object has thermomechanical exergy because it is warmer than room temperature. When the object cools, heat transfers from the object into the room until the object is room temperature. Now the object has no exergy from heat, and it is in what is called a dead state. It will never be able to transfer any heat into the room as long as it remains room temperature. While everything has heat and is somewhat warm, exergy is our colloquial definition of hot and cold. When you are cold, you have positive exergy. When you are warm, you have negative exergy. When you are in a comfortable room, you are in a dead state"
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
88xgtw | How does a B-2 Bomber fly and maintain stability without a vertical stabilizer? | Engineering | explainlikeimfive | {
"a_id": [
"dwnxr3z"
],
"text": [
"The B-2 uses what's called a split rudder to maintain yaw stability. [Here]( URL_0 ) you can see the split rudder in operation. Each split-rudder is actually two separate panels that swing out opposite vertically of each other. When the left split-rudder opens it produces drag and causes the B-2 to yaw left into the direction of the opened split-rudders; and this is the same of for the opposing right-side split-rudder. This is all managed but the B-2's sophisticated fly-by-wire system which uses a computer to make minor adjustments to the flight controls faster than a human pilot can, thus keeping the aircraft stable."
],
"score": [
9
],
"text_urls": [
[
"https://qph.fs.quoracdn.net/main-qimg-f163bd832cf0f63e9e4f501072ddf0f4-c"
]
]
} | [
"url"
] | [
"url"
] |
|
895ar3 | Electric smoker | I've googled (and even binged), and there are literally no results for "how do electric smokers work" both intext and intitle. My main questions are: 1. How do they create smoke? Is it actual combustion, or is it closer to vaporization? 2. How do they circulate air? Fan powered vs convection? 3. How does it balance the required heating load between the wood chips and the heating element? 4. Why does it need a water basin? | Engineering | explainlikeimfive | {
"a_id": [
"dwp6udj"
],
"text": [
"1. It is combustion. The wood chips are soaked in water so they solder rather than burn outright. 2. The generally are no fans. There are air vents and the bottom and top that regulate how the smoke gets drawn through the smoker. 3. Cheaper models don't have a regulator on th e burner. It's a simple heating element. Some more expensive models do allow you to regulate the temperature but these are more common on gas smokers. 4. The water pan is two fold. One it can help keep food moist so that like a pork shoulder or ham doesn't just become a desiccated piece of meat. Two when making something like jerky or smoked fish you create alot of steam to basically kill bacteria and allow your food to cure at a lower temperature."
],
"score": [
12
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
896m58 | How is horsepower determined? | Engineering | explainlikeimfive | {
"a_id": [
"dwpbzq2",
"dwpcnrw"
],
"text": [
"It's a very simple calculation. 1 horsepower = 1 foot-pound per second. That's a hyphen in \"foot-pound,\" not a subtraction sign. You take the mass of the car in pounds, multiply by the distance it moved in feet, and divide by how much time it took to move the car that distance in seconds. Mechanical energy can be thought of as the capacity to move something. The amount of energy you need to move something is the mass times the distance you want to move it. Notice that time is missing from this calculation. So you need the same amount of energy to move a car 100 feet in one second as you do to move it 100 feet in one hour. *Power* is a measure of how *fast* you can provide that energy. So it takes more *power* to move a car 100 feet in one second than it does to move the car 100 feet in one hour (3600 seconds). If we assume a 2000 pound car, that's saying that 2000 x 100/1 > 2000 x 100/3600",
"Horsepower is just torque times speed. Torque is just twisting force around a center point ( think removing a jar lid) in foot -pounds. Speed is revolutions per minute (RPM). The formula in English units is HP = t * RPM / 5252 RPM is easy to measure - just count rotations. Measuring torque is a little more difficult. Several ways to do that with strain gages, water brakes, generators, etc."
],
"score": [
5,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
896ujl | How did people figure out precisely which direction to build a railway in before GPS and modern technology? | Engineering | explainlikeimfive | {
"a_id": [
"dwpb453",
"dwpd4tg"
],
"text": [
"You'd be surprised how accurate tools like sextants are. They were around for a while before we started building railroads.",
"Usually the railway as build along an existing feature, like a wagon trail or a river. If you know how to get somewhere by foot or horse, you know how to build rails to it. Also, you can accurately measure your position on earth to well within a mile with a sextant, an accurate clock, a compass, and an almanac. All of those things would be available to a 19th Century rail builder. Finally, straight lines were not always a priority. You build rail where you can, and keeping it as level as possible is often more important than keeping it straight. You might come out 50 miles north because that where the gap in the mountains was."
],
"score": [
6,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
896y0k | Why do electrical plugs with two prongs have a certain orientation for a socket in lieu of making them symmetrical? | I was plugging in my blow dryer this afternoon and I noticed it. | Engineering | explainlikeimfive | {
"a_id": [
"dwpcs3s",
"dwpciri",
"dwpdshx"
],
"text": [
"Electrical outlets are typically set up (in the US) with a “hot” side (carrying the actual voltage) and a neutral side (which is essentially no voltage and the same as ground) The third pin (if present) is also ground and 0 volts. However, the “polarized” plugs you’re referring to won’t have this pin. The blade width difference is to control which wire of the two carries the actual power. (Old-school plugs have blades the same size) It is typical for manufacturers to tie the neutral to the chassis of the device to save on wiring costs (for two-wire devices). The danger is if the chassis is “hot” “ as a result of flipping the plug - you could get a shock just by having your body in between the device and any ground channel (I.e. a plumbing fixture). The narrow blade of the plug is specified to be the “hot” in this case; and allows users and manufacturers to consistently ensure the connection is made without energizing the chassis.",
"The two prongs aren't functionally the same. One is \"hot,\" and does all the work of pushing electrons back and forth in the wire to supply electric power to your devices. The other prong is \"neutral\" and is there to complete the path for the electrons to flow. It's not providing the power, but it is necessary to pick up the slack. Many devices don't care which wire is providing power. But others require power to be supplied by a specific wire. And sometimes devices are designed with extra protection for the hot wire, so that you don't get shocked if something goes horribly wrong.",
"Electrician here. Different outlets have different size slots and orientations depending on the amperage and voltage. This is to stop you from plugging the wrong thing into the oulet and possibly blowing it up. Your average 120v 15 amp outlet will have one larger slot and one smaller one. The smaller is the hot (live) side and the larger is the neutral (return path). If a device is polarity sensitive, one if the prongs will be larger, preventing you from plugging it in the wrong way."
],
"score": [
13,
10,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
89duz2 | How do ATM machines have such a low rate of dispensary error? | I’ve never used an ATM before and had it dispense an inaccurate number of bills. Some bills are new and crisp, others are old and worn. In contrast, a copying / scanning machine seems to make errors all the time even though the medium (paper) typically has a uniform texture. Why is this? | Engineering | explainlikeimfive | {
"a_id": [
"dwq9uvd",
"dwqgbar",
"dwqdvj8"
],
"text": [
"Finally a question I can answer. Former armoured car driver here, my job was to refill and do maintenance on ATM's Short answer is \"Sensors, sensors, and sensors\" Long answer is that the bills are stored in 4 magazines inside, on the back side of each there's an opening and four suction cups. The four suction cups attach to one bill and moves it to one conveyer belt. By this point the bill has been scanned by two different sensors that measure its exact weight and thickness. This process is repeated until you have the desired number of bills in the conveyer belt waiting to go. On its way up the bills passes additional sensors and before they are being delivered to you, all the other sensors in the atm has to report \"all clear\". If something goes wrong at any one step, the bills will go into the \"wreck\" box, which is located under the dispenser itself, and the atm will try again to give you the money. So it may fail without you even knowing. The only way an atm could fail is by human exploit or error, if you somehow hack it to give you money, or if you put the wrong magazine in the wrong spot when filling it (which also requires the magazine to be calibrated for the wrong bills, otherwise it won't give out any bills because the machine knows which currency is supposed to be at each magazine slot). EDIT: This applies for NCR rype ATM's, im sure others are different in form and function.",
"ATM machines are designed to count bills, using speed and thickness sensors. You can have a number of sensors at the cash cassettes, on the path to the presenting module, and on the presenting module itself (the module that ultimately moves the cash to the customer. Any bills that don't fit within the sensors' parameters will go to a 'reject' bin. Taped bills, a bill that has been literally taped back together, will not be read by the senor correctly and will almost always end up in the 'reject' bin. In the event that a cash vendor or bank replenishes cash in an ATM, and brand new unused bills (bricked cash) aren't shuffled beforehand, it's possible that these 'sticky' bills can fool the sensors; hence you get extra bills stuck together. This is still unlikely but possible, I've had it happen to me. And no, I didn't return it. It's also much more likely that the machine will jam with sticky bills. The wheels stripping the bills from the cash cassettes can't always pull these brand new bills apart. Pulling too many bills at one time will cause bills to literally get stuck as they make their way to the exit. This makes for a messy clean up inside the machine once it gets jammed up pretty good. Another way you can get more money than you should is if the bank or cash vendor screws up, loading bills in the incorrect cassettes; putting $50s in a $20 cassette for example. Cash cassettes are 'coded' for a specific bill use. I've seen an ATM run dry when a mistake like this was made. source: was an ATM field tech in a previous life",
"> The only way an atm could fail is by human exploit or error, if you somehow hack it to give you money, or if you put the wrong magazine in the wrong spot when filling it (which also requires the magazine to be calibrated for the wrong bills, otherwise it won't give out any bills because the machine knows which currency is supposed to be at each magazine slot). I wouldn't have any clue how to hack an ATM, but twice I have been given teh wrong number of bills from an ATM. This was several years ago, but I was shorted a $20 bill once and a short time later (less than a month) I was given an extra. Both times it was an ATM attached to a bank, so I just went in and told them what happened. The shorted bill was deposited later into my account and the extra $20 they just took and had me fill out a 2 second form."
],
"score": [
148,
8,
5
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
89gngd | What is the purpose of those rare traffic lights that have "foggy" lights that end up only showing the color of the light when you're about 30 feet away? | Engineering | explainlikeimfive | {
"a_id": [
"dwqsim0",
"dwqtka2",
"dwqz67u",
"dwr9mmc",
"dwrpu10"
],
"text": [
"Generally it's because they are near other lights. They are designed so that you can only see the light from a certain location, which also sometimes limits the distance from which you can see it. If you have a weird 3 way stop it might there's sorta looks like this _\\\\| where all three of those lines are going into an intersection. It could be feasible that someone on that angle street could see regular lights for one of the other streets and assume they are following the correct order. The 'foggy lights' would prevent others from even being able to see the lights of the other lane.",
"They're generally visible from multiple directions. By reducing their visibility until you're near them, you are less likely to mistake it for the proper light of the direction you're travelling. If someone saw a green light there and mistook it for a green light in the direction they're travelling, they may blow through a red light at full speed.",
"In my area these are used in city blocks with multiple intersections in them, like where a major driveway [ex: mall] or an alley has a light, and often where multiple driveways like this dump in the same block. The other common area I see them is where diagonal streets cross a straight-angle street creating a triangle intersection. I think it is to reduce the likelihood that someone will be watching the wrong light and stop or go at a bad time.",
"For us, it's usually intersections that the lights are hard to see because of the sun. I know, sounds illogical but they truly work in those lifting conditions.",
"That foggy light diffusion is caused by a piece called a Fresnel lens installed in front of the light source. Like the other commenters have said, they make the light somewhat directional to help you quickly decipher which light is your light in a complicated intersection. Only drivers in direct line of the beam will be able to see the light clearly."
],
"score": [
80,
19,
10,
4,
3
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
89je1t | In regards to gas and water pipes, what determines the width of a pipe? Why are some large and some incredibly small? | Engineering | explainlikeimfive | {
"a_id": [
"dwrbud8"
],
"text": [
"The wider the pipe, the more material can flow through it per second. Also, water under pressure (your fresh water supply) flows faster than water not under pressure (sewage, drains) so it doesn't need quite as big a pipe."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
89n2rq | Which kills us : Volts or Amps ? | Engineering | explainlikeimfive | {
"a_id": [
"dws7yqm",
"dws3qak",
"dws3rvj",
"dws49lw",
"dws5an8"
],
"text": [
"There is a smarty-pants saying that goes \"It's not the volts that kill you, it's the amps.\" While that is true, it is not useful to people's knowledge of electrical safety. And how to stay alive. To me it's like saying \"It's not the fall that kills you, it's the landing.\", true but useless. Because at the end of the day, the current that flows through a conductor is going to depend both on the applied voltage and the conductor's resistance. We don't know what our body's resistance is at any given time, as it depends on our clothing, skin moisture, body fat content, whether we are wearing shoes, what we're standing on etc. I have accidentally touched live 230VAC with dry fingers more than once, it hurt but only temporarily. I don't think it would be the same story if the same wire touched my face or chest. Meanwhile people have easily died from 110V changing lightbulbs. Its true that your injury is going to be proportional to the current and duration of sustaining that current in your body. But I could easily argue that it is the lack of resistance that kills you. So increase your resistance as much as possible. We **usually always** know what the voltage of a hot wire is going to be. Either 24V for a car battery, 110V for mains if you're in NA/Japan, 415V for industrial equipment, 115kV for overhead lines. Voltage will always be the most useful indicator for electrical safety. You get the gist..it's easier to avoid high V situations than to try to guess your resistance at any given time in order to decide if x amount of amps is going to kill you. Research says 75mA to your heart is enough to disrupt it, 200mA is enough to stop it. Any idea how many volts are needed to put 75 or 200mA through your heart? No you don't. So this isn't useful for the layman.",
"Amps. Volts are just potential. Like standing under a giant rock suspended in air has a lot of potential but it’s the current aka movement of the rock that kills you.",
"The amperage is the main one to worry about. However, a combination of both should be considered. Again the amperage is the trouble maker, but most times our bodies are always at a certain resistance, so something with higher voltage, will have a higher amperage against us. It only takes 100mA to stop your heart.",
"Amps. However, since the resistance in your body is pretty much fixed, a higher voltage, unless it has current limiting circuitry, will give a higher current as well.",
"No one yet has mentioned that the Amps is actually the total amount of electricity there is. And Volts is its pushing power. So if you have only 0.001mA (miliAmp), you wont be killed by the electricity. Even if you have a 300 Volts pushing it through, there is only 0.001mA coming through. Now imagine you have a 9V battery on your tongue, but its only pushing through a a small neglicible amount of Amps. No way that will kill you. 34 9V batteries on your tongue, and you might be feeling a little fuzzy in your head because that tiny amount of Amps is being pushed through with the strength of those 34 batteries. But they just don't have enough electricity in them to hurt you. (Don't try it i'm just guessing the amounts)"
],
"score": [
31,
24,
6,
4,
3
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
89nsgh | How come Apple will switch to ARM processors, while it was always deemed non powerful? | Engineering | explainlikeimfive | {
"a_id": [
"dws8fp5",
"dws99j4"
],
"text": [
"Apple makes their own ARM CPUs, giving them full control over the platform rather than needing to rely on Intel to make improvements. ARM isn't *inherently* less powerful than other CPUs, it's just that most ARM processors to date have been designed around being small, cheap & low power. Apple could easily make some super-fast, 16-core beast of an ARM CPU if they wanted. There's also a lot of work these days around pushing the *really hard* calculations onto the graphics processor. If you're doing all the heavy lifting with a Radeon or Geforce GPU, the CPU doesn't *need* to be as powerful anymore. Finally, there's always just the possibility they're flexing their muscles to get get leverage over Intel and they're *not* moving their systems to in-house designed processors.",
"Apple has been rumored to be switching to ARM for *years*. It's an off again on again rumor that seems to restart once every eight months to two years. They ain't switching any time soon on their desktops. *Maybe* on the laptops, but... I doubt it. Not for a while."
],
"score": [
17,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
89ugzu | The Ford Escape was just rated poor by the IIHS. Don't car manufactures test their cars in crash tests beforehand? Do they not know the parameters or the scoring dynamics for the test beforehand? At this point why are companies still getting poor ratings? | Engineering | explainlikeimfive | {
"a_id": [
"dwtn82y"
],
"text": [
"Probably because engineering always involves tradeoffs and not everyone cares about safety more than other things."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8a2qsu | Why don’t rockets tip over when taking off? | Every try steering a 100m long car with rear wheel drive at high speeds? How is there even any control? | Engineering | explainlikeimfive | {
"a_id": [
"dwvdrxy",
"dwvgs4u"
],
"text": [
"Imagine balancing a pencil on your finger, now imagine you have the speed and accuracy in your reflexes as a high speed computer controlled robotic finger. It helps that the force pushing it along comes from the very bottom end and that generally it gets lighter towards the top end.",
"A rocket has two different rotational centers. The center of mass is the point where the rocket balances. The is the point it would rotate around if it were in a vacuum, and as the fuel burns from the back of a solid fuel motor it moves the center of gravity slightly forward. The center of pressure, on the other hand, is the point where air forces on the rocket are equal. Adding even a tiny fin moves the center of pressure backwards. Think of it like that gaudy rooster wind vane on a rural farmhouse. Air presses on all of the structure if the structure when it isn't pointed into the wind. The center of pressure only depends on the shape, so it doesn't change as the fuel is burned. Small fins are put on the bottom of a rocket so the center of pressure is behind the center of mass. This means that the force of air on the whole of the rocket's shape turns the rocket if it is disturbed to return it to going in the direction it was launched. Solid fuel rockets become more stable as they fly faster."
],
"score": [
3,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
8a46xw | What are the pedals on a piano for? | Engineering | explainlikeimfive | {
"a_id": [
"dwvpek0"
],
"text": [
"Damper pedal, which mutes the strings so they're quieter, hold pedal, that keeps the strings from being damped when you release the key on the keyboard, and \"that other pedal\" which locks the dampers up for any keys currently pressed but doesn't affect the rest."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8a52fr | In some old houses, the light switches are ran through the white wire instead of Black so Why is this and what advantage did it have? | I thought the black wire was the live and juice one too but flipping the switch changed the white. It works but why and what advantage it has? | Engineering | explainlikeimfive | {
"a_id": [
"dww6hdb"
],
"text": [
"Assuming that they didn't just get the color code backwards... When you look at AC power, you've got two wires - \"live\" and \"neutral\". The live wire is the one that has the juice on it & the neutral just exists to give you a path to ground. Normally, you'd put your switch on the \"live\" wire so that, when the switch is off, the light socket has no electricity flowing through it. If the switch is on the neutral wire, the socket is still connected to the live wire, creating the possibility of you shorting it out & creating another path to ground, resulting in electrocution."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
8a5d58 | Do you get electrocuted if you touch overhead electrical wires? Why? | Is this a myth or is it true? Wouldn't the wires be coated in rubber or something similar? | Engineering | explainlikeimfive | {
"a_id": [
"dwvywrd",
"dwvz8rv",
"dwvyz16",
"dwvzcd5",
"dwwglja"
],
"text": [
"> Wouldn't the wires be coated in rubber or something similar? They are not coated. To do so would be prohibitively expensive and would make them much heavier, requiring more structure to support them. Touching power lines absolutely can electrocute you, which I was under the impression was ubiquitously known.",
"You can touch them as long as your not also touching the ground in any manner. Which is why birds can stand on them and not get electrocuted.",
"It depends on what else you're touching. Under controlled circumstances, there are people who can sit/hang from those wires to do maintenance on them, but it's really all about how the electricity is flowing and how you fit into its path.",
"You can get electrocuted if you are touching something else at the same time, which allows the current to flow through you or if the voltage is high enough to arc from you to somewhere else allowing the current to flow. Birds can sit on a wire, because they aren't touching anything else at the same time and don't form an electical circuit.(current doesn't flow)",
"Some power lines are insulated, some are not. If it's mutiple wires hanging from insulators, touching the wire will kill you, a lot. If it's a single wire, usually hanging from poles about the same height as a street light, with not insulator between it and the pole, it's insulated. Still, don't touch it, as the insulation can be damaged, but at least nominally safe."
],
"score": [
22,
9,
5,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
8a8fvy | How does artificial gravity work? | My brother tried to explain it to me that the spinning rooms emulate momentum or something along those lines, dragging the person to the "floor". And I don't quite grasp that. | Engineering | explainlikeimfive | {
"a_id": [
"dwwna5w",
"dwwnlbe",
"dwwm4bo",
"dwx2vzf",
"dwwok42"
],
"text": [
"Get a bucket , fill it half way with water , tip it upside down , it falls out . Get a bucket fill it half way with water , now spin it around from floor to over head to floor quite fast , as if it was connected to the big hand of a clock ,. The force /speed pushers the water to the bottom of the bucket , no matter if it's upsidedown or not ,",
"You know how in a car you're pushed to the opposite side when driving in a curve? Now imaging an eternal curve and more force and you could stand on the side of the car where you're pushed to.",
"Did you ever do that thing when you were a kid where you had an older kid grab your arms and spin you around, which cause your feet to fly up in the air? That is exactly how artificial gravity works. When you are going around in a circle, you are constantly wanting to keep going straight. That creates a force which pushes you away from the center of the circle, making it so the outside of that circle is effectively down.",
"It’s not gravity. When you are revolving in a circle you are constantly being forced out of that circle because of the way you are moving. This pushes you against the whatever surface is outward from the center of the circle.",
"Ok, if you're serious... The reason you are having trouble grasping it is because I don't see anyone describing the required contact with the spinning surface to make it work. If you were in space, and at the center of that spinning thing, nothing would drag you down to the \"floor\". However, if you had contact with the capsule, that's where the force is imparted on you. You need to also be moving in that spin to feel the force being imparted. Size of the spinning room will also matter. Too small and it would feel awkward because the angle of the spin would be too high to feel comfortable. It would also need to be under zero acceleration so that wasn't added as a different angle force. So the real takeaway is, it isn't artificial gravity like the movies. There they flip a switch and you are dragged to the floor. But for this to work, you need contact with whatever is spinning to feel it. And then the other examples make sense."
],
"score": [
213,
34,
12,
6,
6
],
"text_urls": [
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
8aaih1 | Why do above ground pipelines have jogs in them every so often? Every couple hundred of feet they do a 45 degree turn away to a straight section then a 45 degree back to its original position is there a reason for this? | Engineering | explainlikeimfive | {
"a_id": [
"dwx29t3",
"dwxjt7e",
"dwxc8l8",
"dwx8qy3"
],
"text": [
"It's to allow for thermal expansions and contractions. If it was just a straight pipe, it would buckle or break, the kinks give it a little room to move.",
"Best picture of this has to be of TAPS - URL_1 It's avoiding a hill and going at an angle for a while to go down a slope URL_0 There its on sliders and at angles to reduce torque from moving on the sliders during a quake - it made it through a 7.9 in 2002",
"Because they are under direct sunlight and are expected to elongate in the heat. These turns allow the pipes to grow without buckling or breaking their supports/nozzles. In the dessert and really hot regions the pipelines are designed with \"expansion loops\" which serve the same purpose but allow for more thermal expansion.",
"This is to compensate for thermal expansion and contraction, as well as expansion differences in working pressure. Both of these could cause a pipe to expand in length up to several inches over a length of a mile. If the pipe were straight, this would cause extreme compressive stress, causing it to buckle and fail. The same process can be responsible for \"heat kink\" in railroads. URL_0"
],
"score": [
49,
7,
6,
3
],
"text_urls": [
[],
[
"https://en.wikipedia.org/wiki/Trans-Alaska_Pipeline_System#/media/File:Trans_Alaska_Pipeline_Denali_fault_shift.jpg",
"https://en.wikipedia.org/wiki/Trans-Alaska_Pipeline_System#/media/File:Trans-Alaska_Pipeline_System_Luca_Galuzzi_2005.jpg"
],
[],
[
"https://framwormbta.weebly.com/uploads/5/1/0/3/51037529/3622118.jpg?1432760473"
]
]
} | [
"url"
] | [
"url"
] |
|
8adjmn | (Cars) Why can't cylinder deactivation be used at idle? | Engineering | explainlikeimfive | {
"a_id": [
"dwxs6xl",
"dwxt94x"
],
"text": [
"Idle can be defined as the lowest rpm at which an engine will operate. It will turn no slower without stopping. So at that low speed it needs all the cylinders firing smoothly.",
"Imagine you have a merry-go-round with only 1 handle on it, and you have 4 people around it. You push the handle to the next guy, who pushes it to the next guy, and it keeps going around and around. If you were pushing it by yourself and told 3 of those guys to take a break, it might not make it all the way around back to you. A crankshaft for an engine works similar - it needs to be balanced with cylinders each pushing at the right time for the shaft to rotate. It can be set up to work as an 8 or 4 cylinder, but it's difficult to make a balanced 1 or 2 cylinder engine."
],
"score": [
5,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8ai266 | how did we manage to create the machine or whatever that makes transistors with dimensions in nanometers | Engineering | explainlikeimfive | {
"a_id": [
"dwysf2r",
"dwytxco"
],
"text": [
"At such small sizes, transistors are not made individually. Instead, the entire circuitry is 'etched' into the surface of a semi-conductor plate, called the die. Then, that die is subjected to various chemical and physical treatments to create nanometer-sized spots on its surface with different electrical properties, which make up all those millions and millions of transistors. Of course, the real process is *much* more complicated than this, but that's the general idea.",
"Lenses. The “pattern” for the chip is focused and reduced through a lens system to the prepared surface of the silicon. This lets you start with a larger more manageable work space and still create much smaller finished components."
],
"score": [
8,
5
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8albh9 | How does a water pump work? | Engineering | explainlikeimfive | {
"a_id": [
"dwzn5y2"
],
"text": [
"Most of today's pumps are centrifugal, they spin a vane, water enters the middle and spun rapidly, which forces the water to the outside at increased pressure. Positive displacement pumps work like engines, with pistons that suck water into a cylinder through one valve then force it out with another. The pumps that usually keep New Orleans above the water are essentially giant propellors like you'd find on ships, pushing huge quantities of water just a few feet uphill into a canal that runs into the river or lake."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8ao0o9 | Why are the front and back rims of a truck different, but same on a car? | The front rims of a truck are convex, but the back rims are concave. For a car all 4 rims are the same, why is this so? | Engineering | explainlikeimfive | {
"a_id": [
"dx06fh9"
],
"text": [
"They are not different. The front rims are reversed in relation to the rear. All the rims on the truck look the same but the back axle has two rims mounted on it. The inside rim is mounted the same as the front tire with the rim offset going in over the drum or hub and rotor. The outside rim is mounted in the reverse position for clearance and makes it look concave."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
8aq1q7 | How does a High Stall Torque Converter work? | Engineering | explainlikeimfive | {
"a_id": [
"dx0once"
],
"text": [
"A torque converter is a 'fluid coupling' - connecting the spinning force generated by the engine to the rest of the system (transmission, drive shafts, wheels etc). Think of it as two fans inside a container of fluid. The engine is connected to one, and the transmission to the other. At idle speeds the engine is pushing the fluid around slowly enough that the other fan can remain still easily. As you increase the speed of the engine (RPM) it spins the fluid faster which pulls on the other fan more and more, until you reach the 'stall speed' where other fan is forced to move (or there is a problem). By changing things like the angles and numbers of blades on each fan, and the volume of fluid (and a number of other things some of which I don't know about) you can move the 'stall speed' around. A high stall speed torque converter moves the stall RPM up. This would typically be in a performance application where the goal is improved acceleration from a standing start."
],
"score": [
6
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8atnav | why aren't we mining old garbage dumps? There has got to be a higher % of desirable materials in there than in a seam of ore. | Engineering | explainlikeimfive | {
"a_id": [
"dx1tbk8",
"dx1nseo",
"dx1zmpz",
"dx1f2fl"
],
"text": [
"A lot of these answers are edging around the main problem with mining a dump: extracting the goodies (or as we usually call it in the case of a garbage dump, recycling). If you are mining a particular ore there's probably a few other things mixed in with it, but you've got a pretty simple chain of things you need to do to the raw input to get your desired material. For example, maybe you've got too much shale in your iron ore. You can grind everything up fine, and pass a magnet over it to separate the two. Keep the iron ore, throw out the shale. In a garbage dump, it's difficult to even begin to determine all the possible materials you are gathering, and then you have to work out how to keep the valuable stuff and separate it. Our grinding process above put all the valuable gold in with the worthless shale dust to be thrown out, and if there were any batteries that someone carelessly discarded, we've got a significant hazard. So, now we need to work out how remove batteries from our input before we crush, and how to separate gold out either before or after the process. And whoops, it turns out that nickel and cobalt are also magnetic. While they didn't turn up in our shale contaminated iron ore, we're going to find at least some of them in a garbage dump, so we need to find a way to separate them from our iron, preferably in a way that doesn't ruin them, because we'd like to sell them too. And what about silver? Tin? Cadmium? Copper? Aluminium? Zinc? Lithium? Arsenic? Chlorine? Paper? Glass? All the different types of plastics? How do you go about disassembling a broken television for its materials in an efficient, safe, and cost-effective manner? Recycling is slowly solving these problems, but it is still much cheaper to simply get some fresh rock out of the ground and process that.",
"Part of it is that you don’t know what else is down there, and many times what’s down there is hazardous. Sure there might be a shit ton of recoverable gold, silver, whatever you’re after. But if you have to dig up and sift through an even larger amount of asbestos to get to it, you’ve got a bit of a problem on your hands.",
"/u/BillyShears2015 and /u/SparksMurphy have good answers, but just to add to them: > There has got to be a higher % of desirable materials in there than in a seam of ore. This isn't really true. A good aluminum mine produces rock that's about 50% alumina, and alumina (Al2O3) is about 50% aluminum atoms, so the material being mined is about 25% pure. A good iron mine is 60% pure iron. In comparison, the EPA estimates that the material we're dumping into landfills is about 9% \"metals\" of various sorts. I couldn't find information on what the percentage of metals in landfills was 50 or 100 years ago, and looking at raw percentages ignores the fact that recovering pure metal costs less energy than chemically refining ore. But overall, the stuff in landfills is not \"purer\" than a seam of ore. URL_1 URL_0 URL_2",
"I think the answer is as simple as: We should be, but we aren’t. Now in many (controlled) dump sites, things are sometimes vetted for recyclability, but if we really took the time to post-process dump sites, we’d probably manage to supercharge manufacturing with recycled materials. This aside from finding the presumably large amount of discarded valuables such as semi-precious/precious metals, gems, and other such objects. However the whole process of implementing such a thing would require a healthy kickstart of money. So we stand now with the problem of a project like this being funded with the multiple millions, if not billions it would take to install machinery and pay for the man power to get things going. Cost justification would boil down to overcoming a mindset that a majority would have which is: “Why would I want to spend money on literal trash”."
],
"score": [
10,
7,
3,
3
],
"text_urls": [
[],
[],
[
"http://aluminium.org.au/australian-industry/industry-description/australian-bauxite/",
"https://archive.epa.gov/epawaste/nonhaz/municipal/web/html/",
"http://www.australianminesatlas.gov.au/education/fact_sheets/iron.html"
],
[]
]
} | [
"url"
] | [
"url"
] |
|
8awkdk | How do engineers "replace" the code from Voyager's current source code? | I just watched the "The Farthest" movie which is a documentary of Voyager 1 & 2. There's a part there where the Voyager's code needs to be updated to be able to capture a darker environment/image or some sort (you get the idea). I was just wondering what/how do the engineers do it, with just a push of a button, it will rewrite/replace/update the code? Thanks! | Engineering | explainlikeimfive | {
"a_id": [
"dx25yrz"
],
"text": [
"Usually they have an identical binary image on the ground used in a \"hot-bench.\" This is usually a combination of real engineering model hardware, software, and simulation. They make code changes on the ground, test it using the hot-bench, and once it works as expected, they diff the original binary image with the changed image. Each byte difference has a value and an address. The software/hardware supports commands you can send to the vehicle in which you can poke the new values into the known addresses. This is called patching. Of course there is more detail to it than that, but that's the basic gist. The \"push of a button\" is misleading. This button causes the ground software to perform well scripted (and heavily reviewed) sequence of events to perform the patch. The sequence includes such things as sending the commands, receiving telemetry to verify the commands executed as expected, and monitoring other sensors and instruments to make sure everything is still nominal during the whole process."
],
"score": [
21
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
8ax4p3 | What is the purpose of corrugating? | Engineering | explainlikeimfive | {
"a_id": [
"dx297w7"
],
"text": [
"Corrugation provides extra bending strength in one direction of a surface. If a surface (like a sheet of metal or paper) is curved in one direction, it cannot (easily) bend in the perpendicular direction. This is why, if you hold a slice of pizza folded length-wise, it's easier to eat beacuse the tip won't droop downwards like it does it you just hold it at the crust. You've curved it in one direction, so now it resists bending in the other direction. See e.g. [this video]( URL_0 ) for a nice explanation of this geometrical property."
],
"score": [
50
],
"text_urls": [
[
"https://www.youtube.com/watch?v=gi-TBlh44gY"
]
]
} | [
"url"
] | [
"url"
] |
|
8b0wf5 | how do hotel key-fobs work? | Engineering | explainlikeimfive | {
"a_id": [
"dx31nvk",
"dx31voe",
"dx3eu5l"
],
"text": [
"Radio-frequency identification (RFID) uses electromagnetic fields to automatically identify and track tags attached to objects. The hotel key has a chip that is recognized by the room lock as having the adequate credentials to open it within a certain given time.",
"It depends on the hotel. Basic fobs are just RFID tags. Like the badges that companies use to control access. Really fancy ones, like the MagicBand^TM used at Walt Disney World are low power Bluetooth and near field communication devices full of all kinds of tracking technology.",
"Radio-frequency identification sends out a near field radio beam at a specific frequency, that frequency is enough to generate current in the key (if you peel a key apart you'll see a spiral of copper which is used to receive this signal) to send a return signal which is read by the door, if the frequency that is sent back matches the \"code\" the door opens."
],
"score": [
3,
3,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8b1boq | I am living in a building where we are several students with one room each and we share a kitchen. How is it possible that all our keys to our rooms fit the lock to the kitchen, but not the other student's rooms? | Everyone have a key that fit the lock to their own room and the lock to the kitchen, but not to the other student's rooms. | Engineering | explainlikeimfive | {
"a_id": [
"dx35i1p",
"dx42q88",
"dx35izy"
],
"text": [
"A lock has a number of tumblers, which all need to be pushed to a certain height in order for the lock to turn. Each key is unique, and the bumps on the key correspond to the heights of the tumblers within the corresponding lock. Imagine keys and locks as a 6 digit password. Now imagine that your kitchen lock is only a 4 digit password - the kitchen lock only has 4 tumblers, not 6. So your keys can all open the kitchen door if they have the right 4 bumps, but you can't open each other's doors. Imagine the kitchen door is 0134. Imagine your door is 013461 and your roommate's door is 013413. You and your roommate can both open the kitchen because your keys have 0134 (which is all the kitchen needs,) but you can't open each other's doors because your keys don't match the lock.",
"Hopefully, this works with Reddit formatting: This is the kitchen key: O=\\^\\^\\^- > This is your bedroom key O=\\^\\^\\^M > This is your roommates bedrooms key: O=\\^\\^\\^U > And your other roommate: O=\\^\\^\\^S > You all share the first part of the key, which unlocks the kitchen, but the last part of your key is different, and that's the part that unlocks your lock.",
"Physical locks come in varying degrees of security. Your kitchen lock uses the least secure function of the key, which are the widest bumps on your key. Your individual room locks use the exact same wide bump patterns, but the narrower teeth of the keys are all different. Your kitchen lock isn't precise enough to notice the differences in the tips/ridges/bumps on the teeth of your keys, whereas your bedroom locks are."
],
"score": [
1350,
34,
6
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
8b1prw | Would X-Rays work without a transistor? | If yes, why... if no, why? | Engineering | explainlikeimfive | {
"a_id": [
"dx38u1d"
],
"text": [
"Yes, absolutely. The [original x-ray tube]( URL_0 ) was used to create x-rays that reacted with good-old photographic film. No transistors were needed or used for the first 50 years of x-ray photography. As for \"why\" it's not needed. It's because x-rays are \"just\" a form of electromagnetic radiation and can be made using the x-ray tube described above. It's essentially pitching highly energized electrons at a target, and some percentage of the electrons go through the needed reaction to produce and emit x-rays."
],
"score": [
3
],
"text_urls": [
[
"https://en.wikipedia.org/wiki/X-ray_tube"
]
]
} | [
"url"
] | [
"url"
] |
8b52el | What is Brownian Motion and what is their correlation with droplet evaporation? | I wondering why when droplet evaporation happen, the probability of highly energetic liquid molecules going over into a gas phase is higher than that of them being condensating. | Engineering | explainlikeimfive | {
"a_id": [
"dx44eqr"
],
"text": [
"So Brownian motion, is a theory that describes the motion of molecules in a liquid or gas, where they move around and bump into each randomly, and their individual energies (basically speed) can take essentially any value > zero but with differing probabilities for each value, with the frequencies of these energies having Gaussian (I think?) distribution (ie bell shape). This means that what ever the conditions, there will always be some molecules with enough energy to go from the liquid to gaseous phase. In terms of the droplet (ignoring the surrounding environment for now), molecules can either stay within it or escape - so over time, all the molecules will at some point have enough energy to escape, and will escape, so the droplet evaporates. Now consider those molecules which have escaped. They can either remain escaped or return to the droplet. In fact they will move between the droplet and the environment and the system will move toward an equilibrium where these movements are balanced. If the surrounding environment is very large (let’s say it’s effectively infinitely large), because this space is ‘infinitely’ larger those escaped molecules will tend to stay outside the droplet, and it will evaporate. These assumptions don’t consider how much capacity the environment has to hold the escaped molecules but works as long as it’s > zero. So consider also the situation where the space isn’t infinitely larger than the droplet, eg a small closed container, or where the capacity of the environment is < = zero, eg 100% relative humidity. In this situation the equilibrium is shifted, such that the movement of molecules out of the droplet is not always greater than the movement in and the droplet doesn’t evaporate."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
8bd3w7 | When starting to build a new structure, how does the construction crew decided where to start? | I understand that you can't start with the third floor and go from there, and that a foundation (or equivalent) is necessary first, but is there a general rule of thumb on where to start beyond that? I've seen some buildings start with the elevator shaft, but others don't. | Engineering | explainlikeimfive | {
"a_id": [
"dx5rz0k"
],
"text": [
"In most high rise buildings, the majority of the load of the building is supported by the elevator shaft, so that is why they are usually built first. Basically, the architect designs the support structure, and that part will have to be built before anything else."
],
"score": [
4
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
8bemd3 | How does a compensator on an assault rifle actually decrease bullet recoil ? | Engineering | explainlikeimfive | {
"a_id": [
"dx65hx0",
"dx65roo"
],
"text": [
"The pew pew gas is directed upwards, pushing the end of the barrel downwards. This counteracts the normal upwards and backward motion of the barrel due to launch of the projectile. URL_0",
"When a bullet is fired, there is a rush of expanding hot gas. That sudden pressure is mainly used to propel the bullet forward, but it can also have other uses. In an automatic or semi-automatic weapon, some of the gas pressure is diverted to power the steps needed to prepare the next shot -- ejecting the empty cartridge, re-cocking the firing spring, and so on. If you've shot a gun, you probably noticed that the barrel has a tendency to rise a bit after each shot. There are a few reasons for that, but that upward push is really all you need to understand why a compensator helps. The simplest possible recoil compensator is a diagonal cut at the tip of the barrel which allows the expanding gasses to escape in an upward direction; that tends to push the barrel downward, in order to counteract its default tendency to be push upward. More complex compensators take advantage of the gas's velocity to keep the barrel in alignment, by making sure that any change in the barrel's angle would need to push against the gas right as it's expanding forward/outward. In general, though, compensators use the expanding gas to push back against whatever movement the barrel would otherwise be making."
],
"score": [
25,
8
],
"text_urls": [
[
"https://www.youtube.com/watch?v=7pOXunRYJIw&t=140"
],
[]
]
} | [
"url"
] | [
"url"
] |
|
8bpx6w | Why do wind turbines generally have 3 blades? | Engineering | explainlikeimfive | {
"a_id": [
"dx8n9av",
"dx9gc2m",
"dx8u73m"
],
"text": [
"I'll try my best to answer this because I studied this in school. In theory, the most efficient turbine would be with **one blade**, because there are no other blades to create turbulence in front of the blade. However, in practice, this creates an unbalanced rotor, so it doesn't work. Then, the next most efficient blade system would be a **two-bladed system**. However, these tend to vibrate on a third plane, losing lots of energy to friction. To overcome this, some turbines have a teetering hub, but that is more expensive to manufacture. A **three-bladed design** allows for the most efficiency in practice. More blades would create more turbulence, so the costs of making more blades on a turbine would outweigh the benefits of the extra electricity being created.",
"As an interesting aside, one of the main reasons that there are not more wind turbines used to make electricity (other than their immense cost) is that the conditions need to be *just right* in order for them to work and produce electricity for the grid. If they are spinning either too fast or to slow they actually take energy off of the grid and cause a lot of internal stress that is likely to catastrophically damage the internal windings. This is why you see a lot of them not spinning even when it is really windy - it will do a lot more damage to them and the grid they are attached to. (Electrical Engineer)",
"For a given total length of blades, the fewer, the more efficient. However, one blade out be unbalanced and mechanically impossible. Two can also have stability issues, and they also require the tower to be a lot higher. Three is the sweet spot between good efficiency and not having to have too high a tower."
],
"score": [
41,
6,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8btese | how did pre industrial sailing ships move up to or move away from docks in a controlled manner? | Moving in has been covered, but moving away? | Engineering | explainlikeimfive | {
"a_id": [
"dx9h4l1",
"dx9rjyp"
],
"text": [
"If winds were not suitable for sailing right up to the docks, they would run a line (rope) between ship and dock, and then gradually pull it in.",
"To move away, without a favorable wind: send out a boat in the direction you wish to go, and let it tie up or drop anchor. Run a line between the ship and the boat (or the anchor). Use a capstan on board the ship to start hauling on that line, and the ship starts to move toward the boat or anchor. It's a bit of a drag, figuratively and literally."
],
"score": [
11,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
8budj4 | Why do laundry baskets and hampers have holes? | Engineering | explainlikeimfive | {
"a_id": [
"dx9p73j"
],
"text": [
"They're supposed to allow air to flow to the clothes to reduce mildew and mould on damp clothes. Dry clothes also smell better than damp clothes & towels"
],
"score": [
11
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8bvdjk | Why are American semis so much different than European lorries? | Engineering | explainlikeimfive | {
"a_id": [
"dx9ybw3",
"dx9yc09"
],
"text": [
"because different laws and different roads. europe has strict maximum length laws on trucks. so you have to fit your truck in that length at the cost of being super-aerodynamic American semi's go cross country from East Coast to West. the width of the US is from Spain to halfway into Russia. European semi's don't normally cross 10 countries in a trip. you have longer semi's to be more aerodynamic.",
"European trucks usually go for the cab-over-engine layout because they're often used on tighter streets and some nations have length restrictions. This shortens the overall length of the vehicle considerably. American trucks spend their time on the vast open stretches of US highway and generally don't have length consideration, so they go for the simpler front-engined layout."
],
"score": [
5,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8bwww5 | What causes car engines to increase in noise and vibration over time? | New cars are usually silent with little vibration. Over time they become shaky and audible. Why? Is there a way to return them back to what they were? | Engineering | explainlikeimfive | {
"a_id": [
"dxabt0m",
"dxae0c4",
"dxarq4p"
],
"text": [
"Part of why it seems that way is because cars are always getting smoother and quieter. If you bought a new car 10 years ago, it would seem much quieter than an old car at the time, but it was louder than a new car today. The other part is mostly due to breakdown of noise insulating materials (both on the engine, and in the exhaust), and worn down motor mounts. Noticeable vibration in most older cars (assuming the engine is in good shape) is usually caused by bad motor mounts. One other thing is that engines lose compression, and therefore power, as they get older. This usually doesn't happen in every cylinder evenly. Some cylinders will wear more, and some less. This difference in compression will cause a difference in power output in each cylinder, causing vibration. This really shouldn't show up in a relatively modern engine until at least 150k miles or so.",
"The metal surfaces that rub together wear out over time even with proper maintenance and creat larger clearances between them, once that happens the metal surfaces start hitting together instead of smoothly going past one another. Boom, noise increase",
"Engine mounts. Huge difference in old cars. The bushings they use when they are new are well, new. The more the engine wants to move around the more it uses the rubber bushings to hold it in place. They usually never ever get changed on older cars unless they are falling apart or your engine is leaning over. Changing them into a brand new set will be night and day difference over engine vibration."
],
"score": [
21,
5,
5
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
8bxodn | How does a generator turn something spinning into power in a battery? (As in a windmill) | Engineering | explainlikeimfive | {
"a_id": [
"dxazyw9",
"dxah8io"
],
"text": [
"A basic principle of physics is that when you move a magnet through a coil made of conducting material, it will create a current. If you have a short magnet, you can move it through the coil very slowly but it'll still only create a small current for some time. You can move this magnet faster to create a higher current but obviously it'll last a shorter amount of time. Now what you can do is keep increasing the length of the magnet but eventually it will come to an end and you will have to push it through the coil the opposite way, making the current move in the opposite direction. Or what you can do is what generators do, which is taking the coil and spinning it around the magnet, this gets rid of the length problem because you can spin it for as long as you want and keep creating a constant current output. Of course, you need something to spin this mechanism, which is where wind turbines come from. You can power a generator with anything that can create a spinning motion, even a car engine. This electricity goes to a battery for storage because without storage systems, you would have very inconsistent outputs in electricity when lets say the wind speeds are low or too high.",
"They use that spinning motion in the turbine to rotate copper coils in a generator, which generates electricity. It's basically the same way that coal and nuclear power plants work, they spin huge turbines that spin copper coils generating electricity"
],
"score": [
4,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8bzvlt | How are electronics "grounded" on spacecraft? | ...and what happens "electronically" when 2 spacecraft dock? are the isolated from each other? | Engineering | explainlikeimfive | {
"a_id": [
"dxayz87",
"dxb3i4w",
"dxax9gj",
"dxax9oc"
],
"text": [
"\"Grounding\" in electrical circuits just means a reference point, to which everything else can be connected. For example, in a car, one side of the battery is connected to the car's body/chassis. This provides a convenient way to complete an electrical circuit. So, if you want to connect a headlight. You don't need to connect 2 wires - one taking current from the battery to the bulb, and one taking the return current from the bulb to the battery. Instead, you can just use 1 wire to take current from the battery to the bulb, and the return current can go via the car's chassis. The same principle is used in marine craft, aircraft and spacecraft. The metal structure serves as a convenient method of connecting multiple things together to allow circuits to be completed. If two spacecraft need to dock, then the bodies can be electrically connected together to form a single \"ground\" zone covering both craft. Each craft retains its own electrical system, but the two systems share the same reference point. For land based stationary applications (buildings), then the ground itself (which is electrically conductive) can be used as a convenient reference point, and as a failsafe method of carrying current in the case of an electrical fault. The ground itself isn't a very good electrical conductor, so it isn't usually used to carry current under normal conditions for energy efficiency reasons (but this is sometimes used in very rural areas, where a remote house or farm needs a long power line, but only a small amount of power, making it too expensive to run 2 wires on the power poles - in this case, you can just run a single wire, and use the ground as the return path).",
"There was an extensive answer from a guy working as engineer for the ISS: URL_0",
"Electronics aren't truly grounded on a spacecraft (or airplane, or car). They're \"grounded\" to the frame of the vehicle or some other metal components, but not truly grounded. All grounding is, is somewhere for excess electricity to go in case of a short circuit. The best place is the actual ground, but in the case of a car, plane, or spaceship the frame is better than nothing.",
"The docking collars are big chunks of conductive metal bolted securely to the spacecraft structure. That seems like an ideal grounding interface. Isolating the two ships subjects the crew that moves from ship to ship to static electric shocks. That's going to make them unhappy."
],
"score": [
84,
17,
16,
3
],
"text_urls": [
[],
[
"https://www.reddit.com/r/explainlikeimfive/comments/6n1qya/eli5_how_does_electrical_equipment_ground_itself/dk73di4/"
],
[],
[]
]
} | [
"url"
] | [
"url"
] |
8c2s9x | how do some high compression Motors use low octane gas. | 2016 Mazda CX-5. It has a 2.0 skyactive motor with 13.0:1 compression. How does it use 87 octane fuel. I know race cars that have that kind of compression that can't run on fuel less than 100 octane or some form of alcohol (E85). What kind of wizardry is Mazda doing here. | Engineering | explainlikeimfive | {
"a_id": [
"dxbmv0s",
"dxboi9v"
],
"text": [
"From reading this: URL_0 ...it seems like the trick is to use a computer to dynamically change the valve timings.",
"Something else to think about is ignition timing. What many modern engines have is a knock sensor that tells the computer that the ignition timing is too advanced (spark plug firing too early). The computer takes this reading and retards the timing (fires the spark plug later). The octane rating in gas tells you how difficult they are to burn completely. A higher octane gas can be ignited earlier without fully combusting at an inopportune time. What that means is that the engine management computer has a bit easier time playing around with ignition timing, and is more able to tune itself into a more advanced timing setup, which is generally better for performance. With lower octane gas, the engine is forced to put the ignition timing in a spot that the flame front doesn’t interfere with the piston’s travel (that is, it doesn’t ignite and push down on the piston while it is still coming up, which can bend connecting rods and make a big mess if left like that for too long). This is also the reason why many cars don’t benefit from higher octane gas (outside of the added detergents): if they aren’t set up to advance timing enough to take advantage of the higher octane gas, then they won’t perform any better. On the flip side, if your car is designed to utilize higher octane gas and you put in lower octane gas, you will likely see lower performance."
],
"score": [
4,
3
],
"text_urls": [
[
"http://www.enginebuildermag.com/2013/11/the-skys-the-limit-looking-into-mazdas-skyactiv-engine-technology/"
],
[]
]
} | [
"url"
] | [
"url"
] |
8c4a97 | Why do some drinks need foil seals bellow their caps and others don’t? | Engineering | explainlikeimfive | {
"a_id": [
"dxbze81"
],
"text": [
"If you can open the lid/cap and replace it without out someone knowing, it needs a seal underneath. If the lid had a plastic piece that breaks, or you have to rip a wrapping to get to it, it doesn't need a seal underneath. It's all about whether you can detect tampering or not."
],
"score": [
8
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8c7vbx | How can all electrical appliances use the exact same power? | So if you have a voltage X and a current intensity Y. Doesn't that mean all electrical appliances get a power that equals P=X*Y? (before stepping down voltage in their inner transformers where this P will only be decreased by the transformer efficiency). How is that possible that a 40 inch TV screen takes as much power as an electric shaver for example? is that rest of that energy wasted? | Engineering | explainlikeimfive | {
"a_id": [
"dxcrg9s",
"dxcrxqf",
"dxcse5f"
],
"text": [
"They don't use the same power. They operate at the same voltage. Voltage is electrical *potential*. The power that a device actually consumes relies on the reststance the device presents to the grid. Less resistance means more current, which means more power. A washing machine needs more power than a clock radio. The washing machine presents less resistance to the grid, which lets more current flow through it, which the washing machine's motor uses to wash your clothes. The clock radio needs only a little power to run the display and radio. So it presents a lot of resistance to the grid, thus drawing only a little current. Think of voltage like water pressure in your residental water main. The pressure is the same in all the pipes in your house. You can open the tap wide open to water your lawn or fill your bath tub. Or you can open the tap just a little to dribble water onto your toothbrush. An appliance's electrical resistance is the size of the \"hole\" it presents to the electrical \"pressure\" (voltage) in your house's mains. ###more resistance = smaller hole = less current = less power consumed",
"We use a constant voltage system, only the X in your equation is fixed, the Y varies depending on the Resistance Z of the load The current into the load is equal to the voltage across the load (X) divided by the resistance of the load (Z) so Y=X/Z Power still equals X*Y but since YU=X/Z and Z is a parameter of the device then you get P=X*X/Z or the traditional P=V^2/R Items that need more power, like a toaster will have a very low resistance, items that need less power like a new TV will have a higher resistance so the current into them is less You're likely confused because we put devices on circuit breakers, but a 15A breaker doesn't mean that 15A always flows, it means that if more than 15A is flowing the breaker will trip and cut power. Most of the circuits in your house aren't using anywhere close to their breaker rating.",
"All houses in your street also have the same water pressure, it's around 40psi or something like that. Think of that water pressure as the 110v or 230v that is delivered to your home. Every tap and faucet in your house will see that pressure but it doesn't mean you get the same amount of water from each appliance. You have many different taps and faucets in your house that use different amounts of water (current). This depends on their build/requirements and demands. * Your shower might have a water saver restriction, so that's like resistance * Your garden hose allows you to a little or a lot, it almost like a device with a variable resistor (dim-able lights)"
],
"score": [
44,
8,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
8ca7dq | How do oscillators work? | I understand that oscillators turn DC into a sinusiodal signal but I just don't understand how or why. | Engineering | explainlikeimfive | {
"a_id": [
"dxdbty6"
],
"text": [
"It's tough to explain what's going on without a lot of math, but the two basic principles at work here: 1. Inductors/capacitors create time-varying voltages/currents. If you charge up one side of a capacitor, it will quickly reach a steady-state. However, before it does so, it proceeds through an exponential transition phase. This effectively 'smoothes' the signal. 2. Feedback systems create oscillations. Think about taking a shower. If the water is too hot, you turn down the hot water. If the water is too cold, you turn up the hot water. But you never get it quite right - you always overshoot just a little bit and you're constantly adjusting the hot water to get it perfect. That's a feedback system - you set the system to some value, sense the output of the system, then adjust the system settings in response. If you were to graph temperature vs. time for your shower, you'd see that sometimes it was above the desired level, then it was below, then it was back above. If you were to 'smooth' that graph, it would start looking a lot like a sine wave. This won't help you build an electronic oscillator, but hopefully it gives you some intuition about why it works."
],
"score": [
7
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
8cjfxu | Why are practically all canned sodas and beers, even those from different companies, sold in exactly the same can? | Engineering | explainlikeimfive | {
"a_id": [
"dxfgwae",
"dxfj452"
],
"text": [
"The soda can is actually a brilliantly engineered container. The cylindrical shape allows you to fill the most space with the highest structural integrity. They can also be stacked very easily and are cheap to make. Quite simply it's just the best and most efficient way to store beverages. Can you imagine any other way? Edit: this video does a good job at explaining URL_0",
"Standardization is a beautiful thing. If all cans have similar properties, they can be used in interchangeable ways. Like vending machines, which can be branded and distributed easily, without needing to be built specifically for one brand of soda. Just like all usb drives work in all usb ports, which means that you know it'll work with no hassle, cans can work anywhere."
],
"score": [
8,
3
],
"text_urls": [
[
"https://m.youtube.com/watch?v=hUhisi2FBuw"
],
[]
]
} | [
"url"
] | [
"url"
] |
|
8cjqre | In hotels, the bathroom light switch is often on the outside of the bathroom wall. Why not just put the switch on the other side of the wall in the same spot? | Engineering | explainlikeimfive | {
"a_id": [
"dxfh2o4",
"dxfh8z4",
"dxfnu17",
"dxfpwnt"
],
"text": [
"Its an electrical code / safety thing. In your home the light switch is waay the other side of the bathroom so you couldn't - easily - stand in the bathtub and flick it, thereby possibly electrocuting yourself. You could still do it, but you'd have to be pretty determined, and its in your own home. Have at it. Hotels are rather risk averse (insurance things), so by putting the switch outside there's almost NO way you could do something stupid and electrocute yourself in THEIR bathtub.",
"Electrical code defines anything within 36\" of a sink or shower the \"wet zone\" and requires special grounding and such to prevent electrocution. Since most hotels have such small bathrooms, they put the switch outside it instead. Last thing you ever want to do is grab the light switch while washing your hands or in the shower.",
"It so you can prank your brother while he is sitting on the toilet. Still has never forgiven me.",
"1 - So that the electrician does not have to cut the tile wall in the bathroom. Tiles break easily when diamond cutting and the cost is to be worn by the sparky if he breaks it. 2 - Because the electrical device potentially exists in a high risk 'wet zone' depending on the laws of the land. Move to the other side of the wall and it can not get wet."
],
"score": [
45,
13,
4,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8cm47u | How do buildings deteriorate? | If they can withstand the weather when people live in them, why not when they're empty? What starts to deteriorate first once it's abandoned? Do American buildings become ruins faster than European ones, since they are built faster? Is there a point at which it stops degrading, or speeds up? Edit: thanks for your answers! Seems kinda obvious in hindsight... | Engineering | explainlikeimfive | {
"a_id": [
"dxg033t",
"dxg00ou",
"dxg2roe"
],
"text": [
"It depends on what the building is made of, but water is a big factor...metal rusts, roofs leak, wood starts to rot, and from then things start to fall apart. Eventually, the structures that hold a building up fail, and the building then collapses. When a building is occupied, small leaks are usually noticed before they become a major problem, and basic maintenance tasks like clearing gutters helps keep a building watertight.",
"They deteriorate from lack of maintenance. There's typically at least some maintenance if someone lives in it. The rest depends on way too many factors.",
"In addition to the maintenance mentioned in other answers one key part is constant temperature. When a building is occupied it is generally kept at a fairly steady temperature, when it is empty it heats and cools significantly each day which stresses the building."
],
"score": [
5,
4,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
8cpu16 | If I take a typical window fan, and hold the blades, is it using more or less power? | Engineering | explainlikeimfive | {
"a_id": [
"dxgucqn",
"dxgulok",
"dxhlcf1"
],
"text": [
"If a motor is stalled, it is essentially short circuited. It'll heat up very rapidly, and probably blow a thermal fuse to prevent it from bursting into flames. The reason a motor normally does that is that it acts like a generator when rotating, even while you're using electric power to spin it. This current points in the opposite direction however - essentially pushing against the power running into the motor. So on startup, an electric motor typically uses a lot of electricity, which drops rapidly once it starts spinning.",
"For electric motors, the highest currrent draw and greatest torque generation is when the rotor is held in the stalled condition. This is why they often burn out when they get jammed and also why they are good for low speed traction with heavy loads.",
"This is also typically called \"locked rotor\", and the current in that state is sometimes listed on the ratings plaque. It is generally (always?) the highest current possible for a motor."
],
"score": [
8,
6,
3
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8cq1i3 | Why do tin cans have that ribbing around the sides? | Engineering | explainlikeimfive | {
"a_id": [
"dxguoka",
"dxhj1j0",
"dxgusl6",
"dxhnqqo",
"dxgwupq",
"dxhkjd2",
"dxhauro",
"dxhjf1k",
"dxhgr4c",
"dxhs6ym",
"dxhoe8w",
"dxhvot2"
],
"text": [
"The ribs act like tiny beams, reinforcing the side of the can against crushing. A smooth-sided can is much easier to dent.",
"He mentions the ridges on food cans about 8 min in but this is seriously the [most interesting video]( URL_0 ) on the most mundane topic I've ever seen. Just in case you wanted to know more about cans than you ever intended to.",
"It increases the structural integrity of the can. If you have ever seen a water tower you can see a scaled up version of that. They often have ribbing on them too.",
"I talked to someone who works in a can filling factory. The food is often cooked in the can at 121 C, so the ribs allow the cans themselves and the steam produced to expand during said cooking, and then to contract back to regular size after cooking, without damaging the seal. Strength is a secondary concern, usually the crush strength isn't as important as the vertical strength (stacking strength).",
"Corregated materials are a design trick. Imagine a long ribbon laying flat on a surface. Making it curve while still laying flat is quite difficult, it requires either a lot of stretching, or for some of the ribbon to crinkle up. This is because the distance required for the outside of the ribbon to go around the curve is longer than the distance required for the inside, but both parts of the ribbon are the same length. However, if you pick up the ribbon, you can easily curl it up into a spool, because its not very thick. The same rule applies, the inside of the curve is shorter than the outside, but the thin material means the difference is small, and the ribbon is quite capable of stretching that small amount without distortion. When we're building things, we generally want to use as thin a material as possible for weight and cost reasons. But because thin materials are usually easy to bend, we have a problem. One solution is to arrange the thin materials so they're more like the ribbon curving on the flat surface than the picked up ribbon that we can curl easily. The ideal way of doing this actually to curl the material into a cylinder shape. That way, no matter which way you try to bend it, there's always some parts of the material that are far away from each other, and would have to stretch or crinkle up a lot to allow the cylinder to bend. Corrugation is a slightly less ideal way of approximating a series of cylinders, but is easier to manufacture in wide or long sheets. It works the same way though. No matter how you imagine bending the corrugation, some parts of it have to travel much further than others. Tin cans are corrugated for this reason. It makes them less easy to dent, and slightly stronger against crushing. Corrugated cardboard is the same, and is actually stronger in most ways than solid cardboard of the same thickness.",
"Tin cans are hot filled then sealed. When the contents cool it pulls a vaccum in the can. Without the ribbing the can would implode. The reason aluminum cans don't have this feature is because they are pressurized with carbonation that pushes out on the walls giving them strength.",
"Ribbing make can strong. Can stack many can on top of other can. Saves space, easy to ship. Profit.",
"Corrugation geometrically stiffens any thin material. Corrugated core cardboard, for example, and corrugated sheet metal are all much stiffer for having the corrugations compared to the uncorrugated material. Cans that are corrugated are stiffer, and harder to dent. Even steel drums take advantage of this. Usually steel drums will have two to four corrugated ribs spaced out. This is essentially for the same reason. Fewer ribs are needed due to the thickness of the steel drum and the greater depth of the ribs.",
"I own a machine shop and work with a lot of canners and repair seaming chucks, rolls, etc. I thought those ribs were for gripping the sheet metal making it easier to cut. I never asked, I just assumed. Repaired those forming dies a thousand times.",
"Soda cans do not have this ribbing because the internal pressure of the contents keep the can from crushing. The ribbing is on the tin can because the contents lack sufficient pressure to prevent the crushing. TLDR: The ribbing provides structural strength.",
"For several reasons, but most important is the crystal lattice of Tin. The anatomical structure of tin is that of a semi-concerted 9+2 arrangement of protons to neurons. This scales upward (think water crystals packing) allowing for optimal ribbed satisfaction for her pleasure.",
"i used to work at a tin plating line in an integrated steel mill adding the ribs also work hardens the steel, which adds a considerable amount of strength (\"tin\" cans are actually tin plated steel) ELI5 would be when you hurt steel, steel gets stronger another fun fact - consumer tend to think fruit doesnt taste as good when it comes from plastic. that's because they've actually grown accustomed to the flavor of tin-tainted fruit"
],
"score": [
4640,
471,
424,
125,
58,
47,
27,
5,
4,
3,
3,
3
],
"text_urls": [
[],
[
"https://youtu.be/hUhisi2FBuw"
],
[],
[],
[],
[],
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8cqef1 | what’s the difference between 2 stroke and 4 stroke oil, specifically in motorcycles. | Engineering | explainlikeimfive | {
"a_id": [
"dxh14vf"
],
"text": [
"4 stroke oil is meant to be circulated by an oil pump through passages in the engine, and through plain bearings. 2 stroke oil is meant to be mixed with gasoline, which is vaporized, and goes around ball bearings without any sort of pump, then burned in the cylinder."
],
"score": [
8
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8cshol | How does the digital twin concept make manufacturing more efficient? | Engineering | explainlikeimfive | {
"a_id": [
"dxhof5q"
],
"text": [
"You make a model of the system inside a computer. Then you can experiment with the computer simulation in order to find good ideas for improvement — which you then implement in the real one."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8cu5ae | How are skyscrapers in crowded cities like New York built in such a tight space? | Construction in crowded cities seems to happen with minimal disruption to traffic or neighboring buildings. How are cities able to build these huge skyscrapers without spilling over onto nearby streets and taking up a lot of space with equipment and materials? | Engineering | explainlikeimfive | {
"a_id": [
"dxhvne3"
],
"text": [
"Construction management is it's own field. Usually an adjacent area is blocked off for staging, but as you said, as minimal as possible. Remember, it's not usually worth it for anyone, for any project, to bring material and equipment that won't be used for a while, and there is only so much that workers can do at a time, so right there, it's just a truck and small staging space at a time. Easy. Skyscrapers like any project, are built one day at a time, so have materials/eqp. For the one day -at a time. Further, In this case, it basically comes down to that for the first couple of stories, they only bring as needed, so that it doesn't take up too much space, then after that, the have the constructed lower stories themselves to store equipment etc. Finally, very large things that would indeed be brought in at night, or have areas blocked off, but as soon as on the site, open the space back up. The cranes are usually only a few feet wide, and are either on top or more commonly, attached to the side of the building itself, so it's footprint is minimal"
],
"score": [
19
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
8cvzlw | how are tall buildings drained when rain falls at an angle? | When rain falls at an angle and it hits the side of a building, where does the water drain? Given the volume of the rain that falls, is the water somehow drawn into internal drainage via guttering all down the building or does it just sheet down to the ground? | Engineering | explainlikeimfive | {
"a_id": [
"dxi7ka0",
"dxi82bg"
],
"text": [
"It just slides down the outside of the building to ground level, at which point the same drains that cope with the rain that hasn't hit a building first deal with it. Just because it hit a building on its way to the ground doesn't change anything.",
"I think the point of the question is, with such a large surface area, you would think there would be a huge amount of water flowing by the time it got to the bottom."
],
"score": [
16,
6
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
8cx5vs | How did Japan find its huge trove of rare earth metals on Minami-Torishima? | Engineering | explainlikeimfive | {
"a_id": [
"dxinlwe"
],
"text": [
"Despite the name, rare earth metals aren't particularly rare. You can take some random dirt and test it, and it will probably have some rare earth metals in it. On the other hand, it's going to be in absolutely minuscule amounts. Even in areas with high concentrations, rare earth mining has to be done by harvesting absolutely massive amounts of material, and processing it to extract the small amount of useful metals. It sounds like they located this particular type of mud based on research around thermal vents on the ocean floor. At least, that's what some quick reading on my part suggests. Based on that research, it sounds like they looked at several likely sites to find deposits, and they got lucky around this island."
],
"score": [
9
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8d441i | How does narrow ( < 30cm) deep water wells ( > 100m) have such a high flow of water for such a long period of time? | Engineering | explainlikeimfive | {
"a_id": [
"dxk5yec"
],
"text": [
"Most wells are deep enough that they reach what we call the \"water table\" this is where the ground is saturated with water and so if you dig a hole down to this level the hole will fill with water from the surrounding earth. Think of if you are at the beach and you start digging in the sand, you don't have to dig deep for your hole to reach wet sand where the seawater has leeched through the sand below the surface and made it wet too, the same thing happens everywhere, although it is deeper in some parts than others"
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
|
8d68nx | why haven’t we built passengers airplanes with no windows but screen walls on the inside? | Engineering | explainlikeimfive | {
"a_id": [
"dxkp1ry",
"dxktvop",
"dxkqkn5",
"dxkk43l",
"dxkzkiv",
"dxku7g9"
],
"text": [
"The ability for passengers to use natural light from the windows to evacuate in case of an emergency, and for emergency crews to be able to see inside the aircraft, would be lost with screens.",
"Windows are for safety of passengers. Helpers need to look inside an airplane in case of emergency. Also an airplane without windows looks suspicious. It could hide something dangerous. Finally, it's comfortable and healthy to have natural light.",
"Historically, screens were too heavy. Recently they have become thin and light, and now airplane companies are looking at exactly this possibility. Windows are still reliable and well-liked and good for use in an emergency, so they are unlikely to go away completely, though.",
"Screens would cost more money to procure, build into the plane and maintain. They're also heavier (which leads to extra fuel expenses). Unfortunately, airlines are in the business of trying to cut costs and maximize revenue as much as possible. Some are even already taking out those seat-back infotainment screens for passengers on certain flights, so I doubt we'll see this any time soon, unless they can make a cheap screen that's as light as the rest of the plane frame.",
"In addition to the other reasons mentioned, some people (like me 👋) would get pretty airsick if they didn't have any windows to look out of.",
"In case of an accident where there is damage to the aircraft, it's common practice for a member of the flight crew to come out and look out a window at the damage. No windows mean no way to inspect the exterior of the aircraft. Screen walls are still heavy - a Sharp LB-1085 108\" display is 195 kg (429.9 lbs)"
],
"score": [
36,
7,
4,
4,
3,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8d78n1 | How is the combustion moment timed in a diesel engine? | In a gasoline/propane/ethanol (let's call it ND for short non-diesel) engine, the combustion timing is controlled by the spark plug firing and igniting the air-fuel mixture that has been compressed. How is this precise timing accomplished in a diesel engine? | Engineering | explainlikeimfive | {
"a_id": [
"dxl0lux",
"dxl0uzz",
"dxkyr3c"
],
"text": [
"It's not explicitly controlled, but it's anticipated based off of injection timing and boatloads of engine testing. We know that for a given engine, at such and such a speed and load, if we inject at timing A, we'll get combustion at timing B. Fortunately, these timings are pretty repeatable, particularly with modern high-pressure electronically-controlled injection systems.",
"Older diesel engines have an injection pump that delivers a measured squirt of fuel to the cylinder starting right before it reaches top dead center. The pump is driven off of a gear hooked to the crank or off of the timing chain so that each \"squirt\" is synchronized correctly. More modern designs have a high pressure (1500psi) fuel rail with injectors that are computer controlled.",
"It all depends on the timing of fuel injection. In a spark ignited engine, the spark is fired right before the piston reaches the top most portion (TDC) so as to allow the flame to burn through all of the fuel and reach peak pressure just after TDC. It's not so easy in diesel engines. To obtain the correct injection time, a pressure sensor and a crank angle sensor are used. The pressure sensor continuously monitors the pressure inside the combustion chamber, while the crank angle is noted. A graph is drawn to map the variation of pressure with crank angle. In a diesel engine, the duration between the injection of fuel and combustion of all fuel inside is usually longer than that in a gasoline engine, as it takes longer for the diesel to mix with air inside the combustion chamber and attain the temperature necessary for combustion. The injection timing is obtained by trial and error, running the engine at different speed and different load conditions. Basically, the goal is to get complete combustion and maximum pressure just after piston reaches the highest point in the cylinder, so as to exert the maximum downward force. [Sample pressure-crank angle diagram]( URL_0 ) Hope it made sense. Source: Am currently studying automobile engineering."
],
"score": [
10,
7,
3
],
"text_urls": [
[],
[],
[
"https://goo.gl/images/nbEwqb"
]
]
} | [
"url"
] | [
"url"
] |
8dfh8o | Why do kid's toy rockets have fins at the base, but space rockets do not? | Engineering | explainlikeimfive | {
"a_id": [
"dxmoe9l",
"dxmpvnf"
],
"text": [
"The fins at the back of a kid's rocket create drag. Drag slows down the back of the rocket, \"pushing\" it down and maintaining the stability. Full-size rockets achieve this by means of high-precision thrusters that actively orient the craft in the direction it needs to go. Drag would slow them down and cost much more in fuel, so they use an active system. Model rockets COULD use an active orientation system, but for the size, complexity, and cost of it, you may as well just build a full-sized rocket.",
"Historically, space rockets did indeed have such fins to help keep them on course. See them at the bottom of [this moon rocket from the 1960s]( URL_0 ) for example. These days designers prefer to just steer the rocket engine to keep the rocket on course. It requires some expensive tech, but it is more efficient (less weight and drag), and frankly they need something like this anyway for steering."
],
"score": [
23,
5
],
"text_urls": [
[],
[
"http://www.awesomestories.com/images/user/68057635cb.jpg"
]
]
} | [
"url"
] | [
"url"
] |
|
8dgwhb | why does a phone without a battery break when dropped in water? | Engineering | explainlikeimfive | {
"a_id": [
"dxn1e3e",
"dxn1l8l"
],
"text": [
"Electronics guy here. It happens because it isn't the water that breaks the phone - *minerals* ***left behind by the water*** cause short circuits which cause parts of the phone to fry the next time any voltage is applied to them. In theory an electronic device can be restored after getting dunked in water... as long as the minerals are thoroughly washed off beforehand. Edited to add: Professionals use isopropyl alcohol at as close to 100% concentration as they can find - among other things - to rinse away the minerals without leaving anything else behind.",
"If it does, it's because either... 1. The device still has water in it when it's powered back on, creating unintended electrical pathways damaging various sensitive components when the device powers on 2. Conductive residue (Mineral, other) from the evaporation of the water remained on the board, creating unintended electrical pathways damaging various sensitive components when the device powers on This is why it's exceptionally important to make sure a device is THOROUGHLY DRIED OUT, COMPLETELY before attempting to power it back on. While rice might be an extremely mild desiccant (absorbs water), the old 'rice in a bowl/bag' trick is more useful because it gets people to leave their phones alone."
],
"score": [
9,
3
],
"text_urls": [
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8do5de | What causes exhausts to have that rasp-y sound people tend to associate with tuners? (civics, integras, etc) | I've been having trouble trying to understand why this stuff happens. I've done research and it can happen with titanium or stainless steel exhausts, and I know that it also tends to happen more if you have test pipes instead of catalytic converters. Is there a simple way to explain *why*? People on car forums all have their own theories as to why, but it seems like overall it has something to do with the flow of exhaust? | Engineering | explainlikeimfive | {
"a_id": [
"dxorkdj"
],
"text": [
"It has a lot to do with the resonater (muffler) design. Being a resonater, the size volume and pathway makes different tones. Think of how different brass instruments make different sounds. If you are tuning for high rpm horsepower you will likely end up raspy, if you tune towards low end power you will sound more burbley. Things like header design makes a difference too. Like a 4 to 2 to 1 header might sound burbley while a 4 to 1 might sound raspy screamy."
],
"score": [
3
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
8ds78i | Why do jet skis shoot a stream of water straight up when they go forward? | Engineering | explainlikeimfive | {
"a_id": [
"dxpkft6",
"dxpkgyk",
"dxq7q9x"
],
"text": [
"The stream of water makes the jet ski more visible to other boaters; it is entirely for safety. It is typically the water from the coolant circuit through the engine that is sprayed upwards.",
"Those are Yamahas. Almost all engines are water cooled, as in use water to absorb heat from the engine while running. Boats and personal water craft (jet ski is a brand name from Kawasaki) suck up the water from the lake/ocean to cool the engines so they don't need radiators. Yamaha brand just like to point the exit nozzle up and out the rear because it looks cool. Other brands just have it exit parallel to the water out the back. Yamaha does this for brand recognition, serves no better purpose.",
"I've seen the safety answer here, but also found something that mentioned that Yamaha originally created their models for use in oceans as well, and having the plume would allow others to keep track of your location while you're between waves."
],
"score": [
233,
53,
7
],
"text_urls": [
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8dtzlq | How can it be that every lock in the world is different and there are not two of the same? Or isn't this the case? | Engineering | explainlikeimfive | {
"a_id": [
"dxq07t0",
"dxq1ebe",
"dxpzyr4",
"dxq04qu"
],
"text": [
"It isn't the case. It would be theoretical possible to have every lock in the world be different by making them all a different size and shape but it would be highly impractical. Most locks operate with a series of different pins and lengths \\- your standard household lock would have somewhere between 100,000 and 200,000 different possible combinations, which means that once they have cycled through their possible combinations they will start to repeat. But this number is still high enough that it makes the chances of somebody being able to randomly find another lock that matches a key they already have to be small enough to be essentially negligible. A lot of lock manufacturers will further extend the odds by separating batches into different distribution areas \\- so they will sell unique locks only in each individual city.",
"I have two high security Yale door locks I bought 6 years apart. They conform to the highest standards required by an insurance company. The key for each work in either lock.",
"I'm sure the monkeys writing Hamlet thing applies here. Given enough time, and enough locks, two will coincidentally end up identical. But there are so many possible tumbler patterns that it's unlikely.",
"Well with the gigantic increase in technology, there can be almost infinite combinations of the sizes of pins in a tumbler. Not to mention RFID/WIFI/keypad accessibility. While WiFi enabled locks could be potentially hacked the threat isn’t there yet. All tech enabled lock sets sold to the regular consumer have a keyed manual override. Just think about the millions of possible lengths the pins could be set to in a tumbler, and there is your answer. Also locks can be re keyed further complicating the issue. Even if two or multiple lock sets are keyed the same how would you even begin to figure out where to start? Try random doors in you neighborhood?"
],
"score": [
11,
6,
5,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8dwotl | Why do places like Target and Walmart blast you with air when you pass through their sliding doors? | Engineering | explainlikeimfive | {
"a_id": [
"dxqj1oz",
"dxqktah",
"dxqj5ef",
"dxqj4v7",
"dxqnxca",
"dxqofu9"
],
"text": [
"The air blowing when the doors open makes it harder for flies or flying bugs to pass through. The air isn’t for the people it’s to keep the bugs out of the store.",
"Stops bugs from flying through the open door and provides an air curtain to stop heat/AC from escaping the building",
"It's an old trick used by places in warm / cold climates to form an air barrier to keep air conditioning in / heat out or heat in / cold air out.",
"In order to be comfortable when shopping it requires a lot of AC or Heat to regulate the temperature of such a large building. Part of that regulation is to limit how much air escapes when the doors open, and they open a lot. So stores with have a double door entry zone, and air units that put a wall of downward traveling air over the open door.",
"It's an air curtain which helps maintain the internal temperature of the building and prevent drafts coming in.",
"A few people have mentioned bugs. I know at casinos they pump cold air in to keep people awake so they play longer."
],
"score": [
614,
76,
51,
10,
6,
3
],
"text_urls": [
[],
[],
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
|
8dzcr8 | How do 1 phase, 2 phase and 3 phase electrical power work? | And is it possible to have more than 3 phases? | Engineering | explainlikeimfive | {
"a_id": [
"dxr8iu9"
],
"text": [
"An alternator is basically a coil of wire that a magnet rotates past. First the north pole of the magnet, then the south, then the north again, and so on. When one pole swings past, you get a positive voltage, and when the other swings past, you get a negative voltage. If you plot the voltage on a graph, it will be a sine wave. That one sine wave is one phase of electricity. You can improve efficiency by having a second coil of wire on the opposite side of the alternator from the first, so now the second coil of wire also produces electricity, but with the opposite polarity from the first. That one is the second phase of two-phase electricity. (I'm going to take a moment to confess that I've hugely simplified how alternators work, but the principle is sound.) You could also obtain the same effect by running the first signal through a transformer, but that's not important here. To get even *more* efficiency, you place *three* coils of wire around the spinning magnet, spaced 120° apart. This means you now have three phases of electricity. Look up at high-voltage transmission lines, and you'll see three wires running from pole to pole. Those are the three phases. There might be a fourth wire to carry the neutral return, but you usually don't need it. It's an interesting quirk of sine waves that if you were to take the voltage difference between any two of these three phases, the result would still be a sine wave (you'll need to brush off your 11th grade math to prove this to yourself, but it's true.) This means that where the three phases enter your neighborhood, you merely hook a transformer across any two of them, and now you've got your single-phase or even two-phase power going into your house."
],
"score": [
5
],
"text_urls": [
[]
]
} | [
"url"
] | [
"url"
] |
8e2gbi | how is it that the worldest building mia khalifa is able to withstand high winds? does it like sway? | Engineering | explainlikeimfive | {
"a_id": [
"dxruw45",
"dxrurio",
"dxruyrm",
"dxrvkgr"
],
"text": [
"Sometimes I wonder whether r/subredditsimulator is evolving into the rest of reddit when I read things like this",
"Ummmmmm I think you mean BURJ Khalifa.... Mia Khalifa is a porn star..... And it's rounded and build flexible enough to handle winds. Just like all skyscrapers.",
"As mentioned, it’s the Burj Khalifa. The building shape was designed to dissipate incoming winds and not allow vortices to form. In physics, a vortice is like a “whirlpool” of low pressure air. If the other side of the building has normal or high pressure air, it will cause the building to move sideways and damage it.",
"All skyscrapers do sway occasionally up to about a meter. But they have a mechanism in them that are made to counter the sway to keep a building from toppling over. It's like a giant super heavy pendulum in the middle of the towers called a Tuned Mass Dampener. It's a scary thought something like that is required to keep the sky from falling down. Technology is awesome."
],
"score": [
145,
86,
13,
3
],
"text_urls": [
[],
[],
[],
[]
]
} | [
"url"
] | [
"url"
] |
Subsets and Splits
No saved queries yet
Save your SQL queries to embed, download, and access them later. Queries will appear here once saved.