Pressure/physics question

[Reef_Haven]

How does one calculate the pressure that will be produced within a rigid container by a 100ml bubble of air introduced at 20 meters into in a rigid 1000ml container (containing 900ml saltwater) then being brought to the surface?

 

[redacted]

Container filled with air and other not compressible stuff at a depth depth of 20 meters would have a pressure of 3 ATM. Container is rigid so pressure is constant regardless of outside pressure. Wrong?

 

[ianr33]

Its a rigid container. The pressure won't change inside.

Pressure will be 20/10 + 1 = 3AT

Awap types faster than me!

 

[Rhone Man]

So long as it is sealed. Otherwise it will be 300ml of gas at 1 ATA.

 

[idocsteve]

OMG I read this question and I had a flashback to sitting in a classroom in college and glancing down at my feet where I had my notebook open with all the formulas written down that I couldn't bother memorizing..and looking up to make sure the teacher wasn't looking my way as I cheated.

 

[Reef_Haven]

Are you sure?
If the volume of the bubble is only 1 ml in a 1000ml container I don't think there would be much pressure when opened at the surface, but increase that to the full volume of the container the pressure would be much greater near 30 psi ???

 

[ianr33]

Otherwise it will be 300ml of gas at 1 ATA.

Depends.

If the opening is at the top it would be 0ml of gas at 1ATM

 

[Bubbletrubble]

Are you sure?
If the volume of the bubble is only 1 ml in a 1000ml container I don't think there would be much pressure when opened at the surface, but increase that to the full volume of the container the pressure would be much greater near 30 psi ???

@Reef_Haven: Think of the "rigid container" as a scuba tank. When you fill a scuba tank at one ambient pressure and subject it to a different ambient pressure...does this change the pressure inside the tank?

 

[JanK]

Yes, the pressure will be 3ATA no matter what the size of the bubble is, assuming a rigid container. Look at it this way: water is incompressible (well, neglegibly so under these sorts of pressures). So instead of a 1000ml container with 100ml of air and 900ml of water you can just imagine that the 900ml of water is "transmuted" into glass, leaving the container filled completely with air at 3ATA. And if the container is sealed after putting the air in, the pressure inside is constant from that point on, regardless of depth.

Substitute 1ml or 999ml for the air volume and the reasoning (and results) are the same.

 

[cutlass]

Splitting tedious technical hairs, but temperature can also be a factor. Here, the Capt. Obvious assumption is that it's constant.