PDA

View Full Version : Pressure question



EvilEye
2007-Oct-20, 01:11 AM
This will probably sound dumb, but I will ask anyway.

I've watch many deep ocean shows, where they capture animals at great depths in jars along with the water, cap it and bring it to the surface, and all seems normal even when they open it in the reduced pressure.

What would happen if I were in space, and took a jar outside on a spacewalk, then capped it, and brought it back into the pressurized cabin? Would the jar implode?

What would happen if I brought it back to earth under controlled conditions, and then opened it?

Hornblower
2007-Oct-20, 01:18 AM
What would happen if I were in space, and took a jar outside on a spacewalk, then capped it, and brought it back into the pressurized cabin? Would the jar implode?
It would depend on how strong it is.

If you break it with a hammer, it will implode.

What would happen if I brought it back to earth under controlled conditions, and then opened it?
If you could somehow open it without breaking anything, perhaps with a suitable valve, the air would rush in and equalize the pressure.

tdvance
2007-Oct-20, 01:27 AM
The home "canning" process is almost like that--heat the jars up to make the air inside thinner, cap them with rubber-gasketted caps, and let them cool--not exactly a vacuum inside, but reduced pressure. If you take the jars into space, seal them with rubberized canning caps, and brought them back--it would be the same effect multiplied. The cap would be dented in just like with canning--possibly dented too far in so that the seal is broken. If not, you could unscrew the cap, and then--this is the hard part as 14 lbs per square inch is holding the seal onto the jar, and a typical canning jar would have maybe a 7 or 8 square inch-area seal--but if you used a knife or something to pry it off, you'd hear a big pop as so much air goes in all at once and the lid undents--like opening any vacuum-sealed can, but multiplied.

Nick Theodorakis
2007-Oct-20, 02:47 AM
It seems like a pretty contrived and expensive way to pump air out of a jar, which is a common enough procedure in labs on earth.

Nick

Lord Jubjub
2007-Oct-20, 02:58 AM
What is the cheapest way to get the lowest pressure?

loglo
2007-Oct-20, 03:01 AM
As far as the water filled jar is concerned nothing much happens when returning it to the surface as water is nearly incompressible. It is pretty much in the same state at any Earthly depth.

EvilEye
2007-Oct-20, 03:10 AM
Told you it was a dumb question. But thanks for the answers.

It just seemed odd.

Neverfly
2007-Oct-20, 05:34 PM
Told you it was a dumb question. But thanks for the answers.

It just seemed odd.

This proves that there is no deep ocean and it's a hoax.

dhd40
2007-Oct-20, 07:13 PM
What is the cheapest way to get the lowest pressure?

Succeed your boss :whistle: :mad::doh:

JohnD
2007-Oct-20, 10:25 PM
Cheapest is a school experiment I remember.
Take a steel screw-top container - our physics teacher used an empty 5-litre (gallon) oil or syrup tin.
Put a liitle water in it, boil the water over a bunsen and screw up the top.
Either wait, or spray cold water at it.
The tin will collapse, as the almost pure steam inside condenses, and atmospheric pressure crushes the tin.

John

EvilEye
2007-Oct-21, 12:23 AM
I saw that on Beakman's World with a 50 gallon drum!

a1call
2007-Oct-21, 03:34 AM
Note: Link contains popup:
Compressed water table (http://www.engineeringtoolbox.com/compressed-water-d_969.html).

mugaliens
2007-Oct-21, 02:49 PM
If you break it with a hammer, it will implode.


You think?

Dynamite (http://www.youtube.com/watch?v=JR_naKxLEPc)works, too, although it tends to be a bit messier than using a hammer...