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About ScienceNostalgia101

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  1. Despite my background in physics, I've never fully wrapped my head around what weight's supposed to be, other than "not the same thing as mass." It used to hardly even matter, but now I need to know for my students. For instance, if an astronaut is in orbit around the Earth, and the centripetal force is provided by gravity at precisely the right magnitude for the astronaut to feel "weightless" in this non-inertial reference frame, said astronaut would experience "weightlessness," but force of gravity would not be zero. What would be zero is the normal force, as there is no need, until the astronaut encounters an object in spite of weightlessness, for a normal force. So is weight supposed to be the normal force, the gravitational force, or something else?
  2. I ask this as a teacher, not a student... if you have three sets of parallel plates... one of +2a and +a electric potentials, one of of +a and -a electric potentials, and another of +a and 0 which has the higher potential energy? I assume it's +a and -a as it relates to potential difference, I just want to make sure.
  3. This is school related, but I ask it as a teacher, not a student. https://wikimedia.org/api/rest_v1/media/math/render/svg/8c6ee5510ba3c7d6664775c0e76b53e72468303a The above is considered the standard form of the Universal Law Of Gravitation. However, if someone gave the following... https://wikimedia.org/api/rest_v1/media/math/render/svg/ebf0689fbd05781a129e2df24ef5bd8b7edf2f93 ...except without the function notation or r-hat notation, would this count as merely derived from the Universal Law of Gravitation, or as a form of it in and of itself?
  4. One of the advantages to farming in a dry state like California is that with less rain, you have so much more sunlight. One of the disadvantages is that you have to use a hell of a lot of non-salty water just to make it work. What I'm wondering is, what's stopping it from seeping into the groundwater, and gradually shifting toward non-farmland vegetation that could use it too? I look at the fact that California is on fire again; it seems to be an annual thing; and I find it odd that such a supposedly dry state could have naturally built up enough combustible vegetation in the first place to sustain several years' worth of forest fires. I cannot think of any other state as fire-prone as California. Could irrigation have played a role in this, or am I just barking up the wrong tree?
  5. Wouldn't drilling into the side cause the pressure from all the lava at and above that point to force it out of the hole? I get that it's more viscous than water, but still, that's an enormous pressure gradient at the hole. I'm not sure what you'd need to predict... that the volcano won't erupt before installation is complete? If so, why not install the setup remotely?
  6. Subject came to mind again because of post-tropical storm Oscar. How expensive would any materials that can withstand hurricane force winds for the purposes of structures like these be? (For what it's worth, I accept that the "rows of wind turbines to prevent hurricane development" option is out of the question.)
  7. Well, being that particles dissolved in water are known to cause turbidity, I would guess either they collected particulates from the air or bacteria/viruses added impurities. Not sure if saltwater could prevent that... probably not. And being that "convex lens increases converging power focusing light on smaller area" was the point of my idea of using a concave mirror in the first place, I think I might as well abandon that idea. Still though, why can't they make more solar collectors in Australia? There's vast amounts of unused desert out there, and even if they can't use all of the electricity themselves, could they use it to generate hydrogen gas they can then sell to other countries? Surely a boat carrying the gas should be reasonably easy to keep afloat. (Assuming at-sea hydrogen pipelines aren't an option.)
  8. Would the seawater be just as likely to turn green if it were filtered or no? Is it a function of the microbes, the salinity, or just being left out in the open long enough? Interesting concept on Bingham Canyon; would drawing attention to that idea make it more likely to get implemented or less so?
  9. You can't pay them to accept the presence of armed guards protecting the cable? Ok, so maybe North Africa is not the best place. What about other massive deserts, like the aforementioned central Australia? If you constructed a concave mirror there, whether by conventional means or electric repulsion shaping a sheet of metal, and used the electricity to pump seawater out of the ocean and into the concave mirror, would the water then double as a convex lens, increasing its converging power, increasing the amount of water pumped into the concave mirror? Could the excess water then be desalinized and pumped toward neighbouring countries? I ask because for the prior rainwater collection thread I calculated that the estimated sea level rise is by 310 thousand cubic kilometres... however, a half-sphere with a radius of 53 kilometres wide could accommodate all of that without overflowing.
  10. Interesting. All of China? Does that mean I should be able to see it in 2020 if I visit Shanghai? Speaking of the idea of a large concave mirror, here's another thing I was thinking about. The surface area of the Sahara desert is 9.2 x 10^9 square metres. Sunlight's radiant intensity is 1050 watts per square metre. Doesn't that suggest that a solar collector the size of the Sahara could have a power of 9.7 x 10^12 watts? Wouldn't that be several orders of magnitude more power than all the USA's nuclear power plants combined, being that 805 billion kilowatts are 2898000000000000 joules per year, or 91832078 per second? What's the cheapest highly-reflective material with which you could line the Sahara, assuming you could eventually make this pay for itself?
  11. This video showed the construction of a modestly large concave mirror using a fairly meticulous process of carefully placed reflective foil. However, I would presume that, the larger the scale on which it's conducted, the less any wrinkles in the structure matter, at least for the purposes of collecting sunlight. I'm wondering now; is there any cost-effective way to have outer space robotics (Canadarm, etc.) assemble a giant amount of reflective material in outer space? Would electrostatic repulsion and/or magnetic attraction serve to force a giant sheet of reflective material into a concave shape? Could this concave mirror then be used to melt the sands of the Sahara into glass for the purposes of the aforementioned water reservoir idea? Alternatively to mirrors, what about lenses? If one could, using some space elevator or other means, carry a mold impermeable to water into space, and pump a giant amount of seawater into it before it freezes, could this then be used as an outer-space converging lens made of ice, to concentrate sunlight into some massive solar collector? "Geostationary" orbits aside, is there any way to position either's orbit such that it's always at the same angular position relative to the sun? This is not to condone either such project, as I'm guessing there are potential side-effects of which I'm not yet aware, I'm just asking out of curiosity.
  12. So according to this video, flying perpendicular to a magnetic field, including a constant magnetic field at constant velocity, induces emf. Assuming it's right... 1. Would the resulting electric field (in volts per metre) be concentrated in the wingtips, concentrated at the center, or constant from the left tip to the right tip? 2. Would the airplane essentially be functioning as a capacitor as a result? If an airplane were flying through a stronger magnetic field (let's say several teslas) would this in turn cause it to form lightning with surrounding clouds? If it were between two clouds, would it attract electrons in one, repel them in another, and therefore function as part of a complete circuit? 3. In the event an airplane were flying through stronger and stronger magnetic fields, what would become more harmful more quickly? The induced emf or the magnetic field itself? Would the charges being separated have any reason to flow through the bodies of the people on board, whether during or after said charge separation? Would electrons being concentrated on one side of the craft eventually disintegrate the side with fewer electrons in it?
  13. I ask because I keep hearing of groundwater contamination, yet never hear of how quick the process is, vs. how gradual the process is.
  14. Please pardon the crude illustration, this is merely meant to make it clearer where I'm going with this. I'm picturing a power source; I'm not sure whether it's already covered under the "geothermal" umbrella or not; that uses the heat of volcanoes to turn turbines through steam. The idea is that water would be pumped into an active volcano, and a tube would be placed at or near the top to contain the resulting volcanic gases (or at least most of them) and use the force applied by their escaping; or at least from the steam escaping; to turn turbines. This leaves me with a few questions. 1. Would this be a "renewable" resource, wherein heat from the mantle will continuously re-melt the magma frozen by the water, or would too thick a layer of frozen rock eventually block the heat permanently? 2. Either way, would the amount of power required to pump water to the summit of a volcano be greater than or less than the amount of power generated by the escaping gases? 3. If seawater and/or sewer water were used, would the effects thereof on the chemical composition of said magma be carried by the mantle toward other volcanoes?
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