ScienceNostalgia101

I ask because I keep hearing of groundwater contamination, yet never hear of how quick the process is, vs. how gradual the process is.

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?

Indeed, that's why I've since replaced the "over a city" part with "at sea." The "under the ITCZ" qualifier is simply because you get more rain there than at the polar front. However, the key point is the "at sea" one. Here's a quick visual of what I'm talking about, which I probably should've used sooner... Since seawater is 1.02 to 1.03 grams per mL, while water is just 1; and since volume is proportional to r^3; my idea was that the column height for freshwater could be 1.0066 to 1.01 times that of the surrounding seawater, if hull mass is considered negligible. (Depending on necessary thickness, resilience, and lightweight nature of the material.) For a, let's say, 100m seawater column height, this could correspond to a 1 metre water level difference, allowing it to be pumped to a 1 metre tall reservoir with a net zero vertical displacement. (Misinterpreted the definition of siphoned, but the idea is to avoid using more pump power than necessary.) Of course, on further consideration, it's doubtful one could use a large enough (by surface area) region of Earth for 1m to work for the "offset ocean level rise" purpose anyway. Earth's surface is 155 million square km; if it all rose by 2m, (ie. 0.002km) that'd still be 310 thousand cubic km. You'd need a 68km by 68km by 68km reservoir to store that. Highest mountains are less than 9km, so it'd be more like 9km by 204km by 204km. Any geology majors here know of any large valleys surrounded on all sides by material impermeable to water? Or at least of large enough regions of the Earth's surface from which water can't seep into the surface from above to save on floor construction? However, for the "alternative to desalinization" purpose, that still leaves behind the question of whether or not a pump could use electrical power more efficiently than desalinization. . . . For the record, I'm well aware that most uses of desalinized water result in it evaporating and eventually forming rain again.

Gah, I forgot all about the thermal effects of all that air resistance. Anyone know more about air resistance's effects on bullet acceleration?

True, but I was wondering more about convex-mirror-esque reflection than about shape.

The idea is more so that the water would be siphoned off to said reservoirs before it gets beyond that point. I'm not sure why it would need to be an outright boat, though. If it were a simple concave-up structure, wouldn't buoyancy itself act as a restoring force toward equilibrium if it even so much as began to tilt to one side? Also, don't desalinization plants continuously use electricity while desalinating water? Wouldn't constructing a rain collector be an investment in the short run that pays off in the long run through savings on electricity? Or would water siphoning consume even more electricity?

I previously discussed, as part of a broader thread about flood mitigation/adaptation, the notion of concave-up ellipsoids over cities to collect rainwater and prevent flooding. It was noted that they would be weak at the bottom, because of the immense pressure of all the surrounding water. On further consideration, cities are probably not the best place to put them in light of that. However, thinking about this further, I've since come up with another idea; a concave-up rain-collector (whether as ellipsoid or half-cylinder, depending on whichever is more practical) at sea, directly underneath the intertropical convergence zone. This way, rainwater, distillated by nature, could be siphoned off to artificial reservoirs on land. This would kill two birds with one stone; the need for desalinized water, and the rising ocean levels. (Imagine how much by which they could be decreased if a disproportionate chunk of the 100 inches of rainwater that would otherwise annually fall into the ocean were moved to reservoirs on land!) As well, another advantage to making it at sea is that both buoyancy and pressure at a point in space relate to the mass above that point in space. Therefore, even though fresh water is less dense than salt water, this would not matter, as any rate of freshwater-siphoning adequate to keep the rain-collector afloat would be adequate to keep the pressure on the inside of its walls comparable to the pressure on the outside of its walls, hence the forces pointing outward and forces pointing inward being nearly in balance. So why hasn't such a project been pursued?

Is there any mathematical formula (software notwithstanding) into which you could plug the latitude/longitude differences, from said position of direct sunlight, to get the solar angle, not unlike how you can use the pythagorean theorem to find a vector's magnitude from the magnitudes of its components?

Originally I was going to make this a "relative motion" thread, but I think the notion of analyzing movie physics is more interesting overall. In "Rat Race," a mechanic startled by the passing supersonic landspeeder fires a bullet parallel to its path. (At about a minute and a half into the clip.) To the drivers, however, the bullet appears to be suspended in mid-air, as it is moving at approximately the same velocity as the landspeeder. 1. Would the bullet's path be kept horizontal for any non-negligible amount of time by air resistance, or would the vertical component of its motion immediately assume downward acceleration like everything else? 2. How quickly would the horizontal component of its motion be slowed by air resistance? 3. Either way, would it be safe for the drivers of this landspeeder to reach out of the window and grab the bullet, provided they maintained the same velocity as the bullet while it was in contact with their hands?

This isn't meant to endorse such a project, just speculate on whether or not it's possible. Suppose Earth disposed of all its nuclear weapons by firing them at Mars or at craters on the moon. The thermal radiation would presumably be at least partly absorbed. Would there be a layer of molten rock that would then solidify in a semi-spherical shape perpendicular to these planets' gravity, sort of like the almost-flat manner in which ponds freeze over, or would it just sublimate directly into gas? If the former, would this be functionally equivalent to a convex mirror? Would we then have a "virtual image" of the sun at night that would be smaller than the sun and brighter than the moon, and/or contain the same proportion of colours of the sun's spectrum? Or is the moon's absorption of UV rays more a function of its moon rock material than of its diffuse-reflective nature?

I felt reminded of this thread by another thread. I now have another follow-up question; what kind of materials would a town/state/country need in order to make these kinds of solar collectors (relatively) inexpensively? Would used tinfoil be useful for them? Apart from tinfoil, would it be more expensive, or less, to melt down old aluminum cans to make them, or to purchase cast aluminum in bulk for the same purpose? Are maintenance costs comparable to nuclear or lower?

So how would one deduce solar angle from difference in latitude/longitude from "wherever the sun is directly overhead?"

Here's what I've been thinking about lately. If solar collectors can store excess energy as molten salt... ...and electricity can be used to melt metal... ... why can't they use "molten metal storage" and/or "molten salt storage" from excess electricity as a whole to store energy? Or alternatively, what about desalinization of water? California has massive problems with shortages of clean water, and desalinizing water would strain the power grid, so why not use excess energy to store up huge reservoirs of desalinized water so you can shut down desalinization plants when electricity is scarce?

So I was recently thinking about solar angles. A fairly straightforward, everyday example of solar angles. Or so you'd think. However, recently one thing came to mind. Suppose it was 6 hours before or after noon during a fall or spring equinox (for our purposes it wouldn't matter) at the equator. Since it was "halfway" between sun-over-the-horizon and sun-overhead, I presume the solar angle would be 45 degrees, right? Now suppose at the same time someone else was, let's say, at 45 degrees latitude; (north or south for our purposes wouldn't matter) at the same time. How would one determine, then, what the solar angle there would be? Is there some sort of angular equivalent of the "vector components" used in physics and in linear algebra? If so, what would these angular equivalents be, and how would you add them to determine the combined effects of time of day and degrees of latitude on solar angle?

There are a number of factors in whether or not a particular reaction will occur between chemicals, and/or the extent to which it will. An introductory course in chemistry, even at the university level, goes into Gibbs energy, but never goes so far as to say whether or not it's adequate to predict whether or not any given reaction will occur. (If I had my time back, I'd have asked, but as an undergraduate I was only concerned with getting through it.) Does whether or not a spontaneous reaction will occur depend solely upon the Gibbs energy and activation barrier? Is there software out there that can predict for us the reactions between any combinations of chemicals (ie. so a science teacher doesn't have to try them all to decide which looks the most interesting) or is that prohibited for fear of someone misusing it? And what of non-spontaneous reactions? Is there likewise any "formula" and/or software for predicting the products of electrolysis or no?

So it sounds to me like computer programming is the more crucial of engineering-related skills for the modern workplace than engineering physics or engineering chemistry. Why the high school emphasis on physics and chemistry, then?

Thanks!

Okay, being that it's been a month I don't want franco's thread to go to waste... that and I've been thinking lately about this myself too. At 5 and a half minutes in, the narrator talks about the Kola superdeep borehole, which was halted only 1/3 of the way through the Earth's crust because at 180 celsius it was too hot for the drill to operate further. If one were to pour substances that had boiling points, even at high pressure, of less than 180 centigrade, down into that hole, could they have used the expansion due to boiling to generate power and/or bring the temperature down?

Well, for starters, conservative pundit Gavin McInnes insists he's always called everything that isn't STEM "Marxist-Leninist brainwashing school" and blamed parents who sent kids there for them going into student debt. His fandom, which correlates with the large voting blocs of conservatives with whom colleges have to compromise in order to receive voter support for public funding, seems to for the most part agree with this. More broadly, TV news in general from time to time talks about automation and the replacing of old jobs with new jobs maintaining the robots that do the old jobs, but no particular names come to mind.

I'm talking about how the usual reasoning for such bashing of every other degree program (though I more often hear it from conservative pundits than from actual engineers, granted) was about how we'll always need technology, yet now I'm being told using engineering to design robots to do the other jobs is unfeasible.

So I'm reviewing my rules of radicals prior to teaching it to students, and found out I'm a little rusty on them. Suppose you hit an answer that ends with a prime number as your radicand. Provided you used mathematically valid reasoning to get there, does this prime-number radicand now suggest that you arrived at the most simplified form, or are there "dead ends" distinct from the right answer?

So the same question applies. Can there be too many engineers, even if a large enough fraction of them are software engineers hired by a government program designed to make as many other jobs obsolete as possible? (Forgot I even had this thread until now, sorry about that.)

So I was recently thinking about the similarity in formulae between spheres' volume (4*pi*r*r*r/3) and their surface area. (4*pi*r*r) Firstly, I noticed that the surface area looks like it's the derivative of volume with respect to radius... which come to think of it makes sense as the rate of change in volume at a point in time is that outer spherical shell being added times its thickness. But secondly I also noticed that the ratio of the two is r/3. As in, as if the average particle in a sphere were only a 1/3 of the way to the outside. More generally, V/A is in length units. Am I figuring this right? Does V/A represent average distance, root mean square distance, or whatever other measure of central tendency from center to outside? More generally than that, how is this extrapolated to other shapes? Does V/A represent anything in particular more generally or is its dimensionality usually meaningless?

Majoring in engineering's kind of a damned-if-you-do, damned-if-you-don't these days. If you major in engineering, you're told there's an excess of engineers anyway and it's on you if you don't find a job with it. If you DON'T major in engineering in, you're trash-talked on the basis of whatever else you studied supposedly being worthless. What I'm wondering is, how can there be too many engineers in the first place? Surely all those other jobs could eventually be done by robots, and the more engineers we have, the sooner we'll get there. Why isn't the government hiring the "excess" engineers to design robots to do all the other jobs?

https://www.nhc.noaa.gov/gtwo.php?basin=atlc&fdays=2 See, this is the kind of thing I was talking about earlier in the thread. Right now, off the coast of Cancun, Mexico, there's a storm brewing that has a 50-50 chance of developing further, on top of all the other storms the North American continent is about to face in the near future. Cancun is about 200km from the west coast of Cuba, while Key West, Florida, is about 150km north from Havana, Cuba. If we had rows of interconnected floating wind turbines along at least those stretches of ocean, to harvest the wind while it was still gale force, would at least somewhat cut down on hurricane development?