B0mbtrack said:
One last question. Unfortunately my example is from some movie, and maybe this is why I'm getting confused.
I forget the movie, maybe the abyss or the sphere. Someone was trying to escape a submarine that was pretty much at the bottom of the sea. He went in his escape pod and raced to the surface as quickly as possible. On the way the pressure inside the pod changed so much so that blood started coming out of his ears, eyes, and he died. What would have caused pressure difference like that inside a container? I'm thinking the pod walls simply being compressed at first then expanding as it went up but I didnt think there would be that much of a difference in pressure. Anyway, thanks again.
Yeah, that's Hollywood science, not reality. Kind of ridiculous, actually. I'm a scuba diver and I know a lot of the effects of rapid pressure change, and the whole pressure change was just a dumb excuse for that (apparently uninformed) director to make a horrifying scene. I highly, very, very much doubt blood would ever come out from any pressure change.
People have been exposed to vacuum before, though. In one case a pilot ejected at ~50,000 feet, and another was a space suit test failure. Both times they ended up okay. The pilot account says he was bruised all over, and the space suit failure account made no mention of such to my memory.
For some real information on rapid decompression, look up "
decompression sickness", commonly known as DCS.
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The metal container you described - that is a nuclear attack submarine, or a spacecraft . Both can experience rapid and drastic external pressure changes with no effect on the interior.
Pressure is directly proportional to density, if temperature and gas composition are kept the same. i.e, hold the temperature and assuming you keep the same air and don't flood the room with a denser or less dense gas, then pressure will change directly proportionally to density.
There is no reason the pressure would change in a container higher up or lower down. Like you said, the walls might expand or contract slightly under different stresses (contract under pressure, or inflate like a balloon as you ascend), but for a rigid material this will be mostly negligable.
(One picture I'm a bit sorry I can't find is where some submariner hung a clothesline across the width of a submarine (some hallway area was wide enough I guess). The clothesline was tight at the surface, but in another picture at some deep running depth, it had some slack because the walls had compressed.)
Once again, the bathysphere thing, it's a U.S. Navy procedure on submarines:
Here's a clip on the inside:
(begins around 2:20 )
And as for ascent to lower than 1 atm pressure, that's been done plenty of times, also
(Astronauts wear spacesuits during launch for safety reasons in case of rapid depressurization, normally though, the cabin pressure stays the same. For awhile the shuttle astronauts didn't wear a pressure suit on launch, and they were fine, but after Challenger broke apart, they returned to using pressure suits on launch in case of emergency, as it might have saved the lives of the Challenger astronauts had they been wearing them.)
One note: your ears pop in an airliner as you climb because they don't seal the cabin until 8,000 feet. But once they do, then the pressure inside stays the same. (They do this so there isn't as much stress on the aircraft's hull at cruising altitude, giving it a higher service ceiling which means faster and more fuel-efficient flying) If they didn't seal the cabin at all, then everyone inside would die, since there's serious health issues with the low pressures starting as low as 12,000 feet and being rather severe around 25,000 feet (hence the emergency oxygen masks).
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Where'd you get the idea the pressure would change in a hard container?
In the scuba classes I took, they taught it would, which is wrong. They did it to explain how each breath of air takes more air at deeper depths. But the air in the scuba tank doesn't change pressure at any depth. The scuba tank holds a fixed volume at a fixed pressure, and thus has a fixed mass of air.
There's two valves on a set of scuba gear; one reduces the pressure down to 150 psi (10.2 atm), and the second reduces it to ambient pressure. The reason each breath takes more air at deeper depths, is that the outside pressure is higher, and each breath fills the same volume - your lungs, throat, mouth, etc. But at a higher pressure, the same volume holds more mass, so each breath takes more mass out of the scuba tank.
PADI thinks people will get confused, though, so they teach that the air in the tank compresses, when in reality it doesn't. It really bothers me that they do that... I got very confused trusting the instructor when they said that. I don't know how they convince the instructors that pressure can change in a fixed volume without changing the mass or temperature, since it's obviously impossible...
(On a side note, I have a half-sister who is becoming an instructor for pilot's licenses. They teach the Bernoulli effect causes lift, but that's pretty much wrong. Once again, it's simplified/"dumbed down". But she tried to explain the real truth to students in the instructor examination course, and she lost points for it for making it "too complicated".)
