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vishnun0027

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eli5_dataset

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{ "a_id": [ "h3fkpvn", "h3fjty0", "h3fi7te", "h3g7qu5", "h3gn91k" ], "text": [ "Every blade adds to efficiency but you pretty rapidly enter diminishing returns. A top of the range three blade wind turbine extracts about 80% of the theoretical maximum energy. A two bladed variant is only slightly less efficient, about 5% less. A four bladed turbine only gets you a couple of percent extra efficiency. Each blade is very expensive, so fewer blades allows a return on your capital investment faster which allows you to build more turbines sooner. Ultimately two three blade turbines harvests way more energy than one six blade, and three two blade turbines even more. Two blade turbines have a few issues which results in three being the default choice: 1. They cause \"pulsing\" shadows when the sun is side on which is really disturbing to any houses/cars that end up in the shadow. 2. Aesthetically they aren't as pleasing and people don't like the look of them on the landscape. 3. When one blade passes in front of the tower, the force on it drops due to the tower's wind shadow. This emparts a twisting force onto the assembly that requires special design to adsorb. The twisting force is lesser with three blades because there isn't a blade directly opposite the one in the shadow. 4. Three blade designs are easier to turn to face the wind. With two blades the inertia of the system changes depending whether the blades are pointing up or sideways. This can cause the tower to wobble when rotating to point into the wind. Edit: To add a single blade turbine is actually quite good efficiency wise! It needs a counterweight and looks really weird, and the move to giant turbines has killed them off, but they did use to be a cost effective solution.", "They can have more but it becomes not worth it Three blades are balanced and avoid massive vibrations (unlike 1 or 2 blades). Three blades also do a decent job capturing the energy from the air, adding a 4th blade increases the cost of the rotor by 33% but doesn't capture 33% more energy. Each blade also induces turbulence behind it which means a close follower is significantly less efficient. And probably the most counterintuitive thing of all - you don't want to capture all the energy of the wind. Wind turbines need to operate across a range of wind speeds and survive significantly higher speeds than they can safely operate, adding more blades means more wind resistance when a big storm comes to town. Either you build a bigger/stronger/$$$$ tower to counter the extra load from the additional blades or your tower falls over. The most cost effective way to increase the output of a wind turbine is to make the blades longer so they capture a wider area. A 10% increase in length is a 21% increase in peak power because its about the area of the disc swept", "Cost efficiency. Have you seen any of these blades travelling down the road? I imagine they are more expensive than a sailboat of the same size.", "I heard an explanation a little different than the other answers. The basic idea is that you want to gather the wind without blocking the wind. The moment you block the wind you have diminishing returns. So you want as few thin blades as possible. This video goes over it URL_0", "3 things: & #x200B; The first and most important is balance. If you take a stick and sort of find the halfway point you can balance it fairly easily. If you start spinning it, it spins fairly easily but you can feel your hand wobbling a little. That wobble for your hand isn't much but for a 50 ton arm hung 150m in the air it become a HUGE wobble. if you could have a perfectly matched 3 prong stick that wobble would be almost non existant compared to a 2 sided stick. & #x200B; There is a LOT of heavy math to prove this but let's keep this ELI5. & #x200B; There are a number of other number of prongs that are balanced but then comes point 2: The wind isn't pushing the blades, the air behind the blades is sucking the blades. That means that if I cover the entire disc the blades would cover then nothing comes through, it just bends the disk and potentially breaks the arm (Take an umpbrella out into a high wind and my point will be well made) So there's a balance between covering the circle completely and not at all that will give us the most suck. 5 is actually pretty good BUT its only slightly better then 3 (Again, fairly heavy math). So when you add in the price of each blade 3 makes a LOT more sense financially and structurally (Weight of the blades on the arm). & #x200B; Finally you have to worry about how fast they will go depending on wind speed. and while there isn't that much difference between 3 and 5 the range of safe wind speeds for 3 is better than for 5. (Again heavy math)" ], "score": [ 1562, 29, 11, 10, 5 ], "text_urls": [ [], [], [], [ "https://www.youtube.com/watch?v=WGKIjojADmg" ], [] ] }

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{ "a_id": [ "h3g4gfa", "h3g2e75" ], "text": [ "Most (open source) projects use what is called „semantic versioning“: `major.minor.patch` - changed `patch`: bugfix, minor improvement. No change in functionality or API (API is important for software libraries) - changed `minor`: new functionality, minor changes to existing functionality/API. A `minor` release should not be a /breaking/ change. E.g. a Workflow has changed is ok. The user needs to change all his old works is not ok - changed `major`: substantially changed See [here for a longer explanation ]( URL_0 )", "It is just up to the developer and increasingly up to the marketing departments. There is one standard which is called semver. It say that an increase in the major version (3.27 - > 4.0) signals a massive rewrite of the entire software and you might not even find the same features in the new version as was in the old one. A minor version change (3.27 - > 3.28) signals that there are some major changes and you would expect some new features and some changes in the existing features. However there is no requirement for developers to use semver and they are pretty much free to call their versions anything they want. And this have becoming increasingly common. Some even version their software after the date of the release. So currently release 21.07 would be comming out." ], "score": [ 24, 11 ], "text_urls": [ [ "https://semver.org/" ], [] ] }

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{ "a_id": [ "h3gwx4p", "h3h1daf" ], "text": [ "Weight of oil means who thick it is. The higher the number means thicker the oil. The w means winter / cold. So 5w20 is a 5 weight oil when cold and 20 weight when hot. This is pretty weird, most things get thinner when they heat up, but motor oil has additives that make it thicker when hot. The idea is that when you motor is cold, you want the oil to flow easy so it quickly gets to where it needs to be when the motor starts. Then when the motor gets up to running temperature it's a bit thicker. The issue with thin oils is that they can sneak past all the seals / rings and get into the combustion chamber and get burnt. This is bad for emissions and wastes your oil. But thin oils are also good for mileage since they make less drag on the internal parts of the motor. So whatever oil your car takes, is a trade off between these concerns.", "SAE (Society of Automotive Engineers) has a bunch of different grades of oil that tell you how thick/thin it is, higher numbers are thicker. The winter grades (0W, 5W, 10W, 15W, 20W, and 25W) are tested cold. The non-winter grades (20, 30, 40, 50, and 60) are tested at 100C. A 20W and a 20 aren't the same thickness at their respective temperatures, but they are the same thickness as a standard 20 weight oil would be at those temperatures(but we don't use straight oil anymore, its all got additives) The oil in your car has some additives that change its property over the temperature range. The first \"winter\" grade number tells you how goopy the oil will be when you try to start up the car in the dead of winter. Too thick and its tough to turn the engine over and pump the cold oil everywhere it needs to be. The second number tells you how thin it is once the engine is up to temp, again too thick and its hard to pump which hurts efficiency(wasting power on the oil pump) but too thin and it can sneak through all the seals and then you're burning oil which hurts emissions and tends to gunk stuff up (doesn't burn clean) For the most part, you don't need to worry about the meaning of the numbers. Your car wants a certain grade of oil because that's what all of its hardware was designed for so just feed it what it spec'd and you're good to go" ], "score": [ 10, 7 ], "text_urls": [ [], [] ] }

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{ "a_id": [ "h3lu0cy", "h3lsfq8", "h3lqtcj" ], "text": [ "There are two layers to a mirror. One is very highly polished metal, and the other is glass. Glass in front, metal behind. Light goes through glass and bounces off metal. Find an old mirror and scratch some of the back off, you'll be able to see through the glass.", "For this, it’s important to understand what light is, an electric and magnetic field that changes in strength as it travels as a wave. When it hits a conductor, like a metal, the electrons in the metal move freely, riding the wave up and down like a beach ball on the ocean. But when those electrons move, that motion causes another electromagnetic field to form. The one from the electron ends up canceling the one that is the light going forward, and you’re left with only the one from the electron going backward. Hence, reflection. What’s weirder is that the electrons have a limit on how fast they can move, and if the light is too high a frequency, the electrons are getting pushed from both directions rather than riding the wave, so stay still. So they stop reflecting. The properties of the metal in question change their upper limit on how fast they can move, which causes certain metals to stop reflecting certain colors at different parts of the spectrum. Copper stops reflecting in the red, gold in the greenish-yellow, and silver or aluminum in the UV. This is why metals have different colors.", "So what we consider 'sight' is actually light coming from a source and then bouncing off it. The light that refracts off of surfaces into our eyes is what we see. Opaque substances dont reflect because at a microscopic level, the surface is extremely jagged, not flat in the slightest. The light falls into these cracks, and gets refracted all over the place because the surface is not flat. Mirror surfaces are very very flat, like completely flat. This makes it so that the light that drops onto them, gets refracted away from the surface as there are no jagged edges that the light can bounce off off disappating the light. So light bounces off us, onto the mirror, straight back into our eyes: we see ourselves." ], "score": [ 12, 12, 3 ], "text_urls": [ [], [], [] ] }

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