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Could vacuum based super powers work this way?:
I'm running a play by post RP set in an original world. The basic premise involves people around the world randomly developing super powers during puberty. You only get one power, plus the required secondary super powers needed for the power to work (usually), but only when applied to your primary power. You might have super strength, and this would endow you with the invulnerability needed to punch through steel, but you couldn't stop a bullet just because you have invulnerability as a required secondary super power. No one has been able to figure out just how these super powers work. This is because any scientific experimentation to isolate an underlying operation inherent in all powers always produces massively contradictory results. It would be a slight hyperbole to say that every individual has a unique result on all experiments devised, but only slight. Super powers are a complete enigma. Anyway, that's not really relevant to either the RP or this question. I wanted to create some super power ideas that were somewhat original (I want to avoid resorting to super strength constantly, and especially don't want the main cast my players will interact with almost constantly to have powers like that). One of these powers is the ability to create a vacuum of quality equivalent to space anywhere you can see (but the only matter affected is gas). The idea is that the air is shunted into another plane of reality outside this one almost instantly, only to be pumped back into the area at a later date (determined by how long the user desires it to remain this way, but willpower is necessary to maintain). Now I was wondering if this would have the effect I imagine it would. Assuming this is used outside, the idea is that the air outside the created vacuum will rush in, creating a powerful current of air pulling things towards the center of the vacuum (for simplicity of this model we will assume a spherical vacuum is created, though I haven't decided if that should be an actual limitation yet). The exact strength of this suction would, of course, depend on the volume of this sphere. After this occurs the air originally in the area is shunted back into normal space rapidly, almost instantly. My theory is that this should create a pressure wave similar to an explosive, but without any fire, as the air that moved into the vacuum is pushed violently away. This character is meant to be an extremely powerful fighter, so her normal strategy would probably be to create a vacuum at least a half a mile in size. So this should probably be used as the reference when calculating how powerful any effects are. Now I am not a physicist, I never even took high school physics (physics was more of an elective, in my school at least, and I preferred computer based electives). So my question is do vacuums even come close to working this way? It isn't a very hard science fiction setting, so I think I could get away with just pretending it does, but if I didn't care I obviously wouldn't be asking. And now that I think of it, are there any equations I could run to calculate the force generated by displaced air, so that I can figure out how powerful the suction and "explosion" are? Oh, and other than its affect on visible objects (like if it pulled things into the vacuum, or the destruction of the explosive) this is pretty much invisible right? Probably a stupid question.
Short HairI'm no physicist, so I have to resort to common sense and a little research. The weight of air at room temperature (70 degrees F) is 0.075 lbs/ft^3. The volume of a sphere is 4/3 * pi * radius^3. A 100-ft sphere of air therefore weighs 0.075 * 4/3 * pi * 50^3, or about 32, 950 pounds. If your target were standing on the ground, the sphere would necessarily be a hemisphere, cutting the force in half. At the center, s/he would get the full weight of air rushing in to fill the vacuum, about the same weight as a school bus. Armor wouldn't protect against that damage unless it was sealed. The pressure effect would taper off as you moved towards the edge of the sphere, but then you have to deal with wind. Windows would break. Fires would go out. Any loose debris could become a missile. An already unstable structure might collapse. Finally, the collapsing vacuum would make a sound like a thunderclap, for a similar reason.
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Io vs JupiterThat's not quite right. By that logic, each of us should be crushed to death instantly, since we have millions of pounds of air over our heads all the time. What you would have to look up is stuff about pressure differentials. I'd suggest seeing if you can find any spaceflight-related data. Look up stuff on explosive decompression; if a certain volume is exposed to explosive decompression, how long would it take to decompress completely? How strong would the "wind" be? That sort of thing. Apply it in reverse and you should be good to go. For example, if a 100 cubic foot space at 1 atmosphere of pressure takes 10 seconds of 10 mph winds to completely decompress in vacuum, then a 100 cubic foot space of vacuum would take 10 seconds of 10 mph winds to "recompress" in 1 atmosphere of pressure, and it would take another 10 seconds of 10 mph winds to equalize pressure when the "missing" air bamfed back in later on (actually probably a little less, but close enough for a rule of thumb).
See ALL the stars!The pressure exerted on the unit area by air at 20C is, by definition, 1 atmosphere, or about 101.3 kilopascals. (101.3 kilonewtons per square metre. Imagine 11 alligators biting down on every square metre of surface.) However, the technically correct answer to your question AFAIK requires fluid dynamics, which is a real pain to do even by computer. (The Navier-Stokes equations, which describe how fluids move, are mostly the mathematical equivalent to Riddle for the Ages.) The somewhat-accurate shortcut is to consider what happens the instant you pop the vacuum into existence. If we think about an object sitting on the edge of the vacuum, there's going to be air pressure on one side, and a sudden lack of pressure on the other, which is going to force the object inwards towards the vacuum. The mathematics here are far simpler. Just work out/estimate/guess how much area of the object is exposed to the vacuum, (and call it A) multiply it by 101.3e3. (P=F/A, and we know P=101.3e3. Wolfram can solve equations for you, if you aren't that confident at algebra.) This gives a force, which we can then divide by the object's mass (F=ma) to get the object's acceleration into the vacuum. You can get a speed simply by multiplying that by a small amount of time, say 0.1 seconds. The explosion will cause about the same force, just in the other direction. (Though it will also make a big booming sound.) Or you can abandon the physics entirely and simply have it serve the plot.
edited 9th Mar '11 9:55:35 AM by Yej
Thanks for the input everyone. I think I have the answer to my primary question now, as well as a good way to estimate the force generated.
Banned, selectivelyDoes the evacuation have a point of origin, or does it occur across the volume he concentrates on? How close to instantaneous is the effect? Is the vacuum sustained, or does the surrounding air rush in to fill it? When he puts the air back, is it inserted at a point or across the volume he evacuated? Your gas law, PV=nRT comes into play when he sucks the air out. I think there would be a sharp drop in the ambient temperature so there is a bit of a flash freezing effect. Adding to that is that exposed liquid will boil away. The evaporation of sweat and saliva drops skin and mouth temperature further. If your eyes are open when hit with a vacuum, the moisture in the epithelial layer would vaporize, blurring vision. Blood and other internal bodily fluids aren't as affected as your tissue is elastic and keeps them under pressure. However, gas bubbles in the circulatory and digestive systems would expand and could cause an air embolism that could interrupt blood flow. If the pressure drop is fast enough, your lungs, sinuses and eardrums would rupture causing instant death. If the pressure drop is rapid, but still slow enough for your body to compensate, you still have to worry about hypoxia: unconsciousness occurs in a matter of seconds and death follows in about 4 minutes. The human body is under pressure equal to the air pressure so we don't notice it. A hundred kilopascals is counterintuitive, so think of it in terms of one kilogram per square centimetre (the weight of the vertical column of air from the ground up to space) or 15 pounds per square inch (psi). If the air was reinserted on top of air that rushed in to fill the space, you would temporarily double the air pressure which might damage your ears or sinuses if it happened fast enough, but would otherwise be no more dangerous than being under 30 feet of water. Concentrating the volume of air into a smaller volume will cause higher pressures and an explosive effect. However, the air rushing in to fill the vacuum, or rushing out when it is reinserted could be quite powerful, and would toss people and objects around. A pressure differential of one kilogram per square centimetre translates into ten tonnes per square metre. A human silhourtte is a bit smallee tham thatMy understanding is that air will rush in to fill a hard vacuum at the speed of sound.
edited 10th Mar '11 2:56:21 PM by 66Scorpio
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See ALL the stars!You aren't going to get flash freezing or deep space effects unless the area involved is gigantic (say >10m in diameter), since the air will rush inwards to fill the gap incredibly quickly. (Though you're generally right in that things might get chilly)
edited 10th Mar '11 2:33:25 PM by Yej
Thank you for the wealth of information. To answer some of the questions on how the operation occurs: 1) The point of origin for the evacuation is across the entire volume, but the point of reentry is at the center because I have a feeling that this would be far easier to calculate based off of. And now it has occurred to me that this same principle, ease of calculation, is probably the same for evacuation. Hmmm... 2) The idea is that no, the vacuum is not sustained. A specific volume of gas is removed, and then the air rushes in to fill the pace. Because of the vast amount of gas in the atmosphere compared to the amount removed, the overall conditions of the area should become Earth-like again pretty quickly, I believe (assuming an uncontained, outdoor environment of course), although a force of suction and other effects of rapid pressure change should probably occur. After this, the air is rapidly reintroduced to create an explosive pressure wave. 3) The only guideline I currently have in mind for how quickly the air is removed and replaced is that it happens too quickly for a normal human to notice time passing. Of course, there are any number of speeds at which that could occur. Mathematically speaking, the number is infinite: all speeds greater the lowest speed at which no one could notice with the naked eye. In all point of fact, the ability to cause this change is impossible to the point of supernatural, so any practical limiting factor on speed could probably be ignored, leaving me with an infinite range of speeds a which this all might be occurring. At this phase of development, I haven't decided on a number. Also: I'd heard that one could survive in the vacuum of space for up to 90 seconds and still recover, and if the air rushes in at the speed of sound vacuum conditions should certainly last a far shorter amount of time, correct? Or has Wikipedia lied to me again?
Io vs JupiterYou aren't going to get flash freezing or deep space effects[...] There are no "deep space freezing" effects. See Space Is Cold. You won't explode, either.
edited 11th Mar '11 9:08:53 AM by NativeJovian
See ALL the stars!Yes there are; Liquids exposed to vacuum will quickly boil into cold gas. (Conservation of energy, yo.) You'll die from the resulting biology failures, but only if you're left in the vacuum for long enough.
Io vs JupiterBoiling is not freezing.
See ALL the stars!Expanding gas cools. Without air pressure, nothing bar gravity stops the liquid expanding so diffusely it becomes a vapour. Ergo, it
edited 11th Mar '11 9:32:29 AM by Yej
Io vs JupiterWhich is not freezing. You originally used the term "flash freezing", which calls to mind effects like The Day After Tomorrow, swimming pools instantly turning to ice cubes and such. That would not happen in vacuum. That's all I'm sayin'.
See ALL the stars!Something similar but slower happens on the edge of the vacuum, because the air will rush into the resulting space and cool as it does so.
edited 11th Mar '11 9:44:29 AM by Yej
You know what? With rule of cool in mind, I think I might just go with the flash freezing happening as the air rushes in.
Banned, selectivelyLiquids will boil in low pressure but your blood is in veins and arteries which are elastic and keep the blood under pressure. The sweat would boil away from your skin but the skin itself would freeze. In space, it's hot facing the sun and damn cold in the shade. I can't remember where I read it, but gases put under pressure will heat up, so reducing pressure will lower the temperature. I don't think that s a vacuum created on Earth would make it really cold in the shade.
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