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Air Compression vs Water Depth

  1. Sep 30, 2009 #1
    Hey ya,

    Well, I have been having a difficult time finding the answer to this question, probobly because I dont know the specific terminology. So here I am. I did not know exactly which forum category to put this in so...

    I am building a small diving bell with a remote controlled camer inside. Nothing more than a hobby project..

    The Bell is actually nothing more than a 1 liter Pickle Jar.

    What I am wondering is, how much compression of air can I expect at lets say a max of 10 meter depth. meaning if I have 1 liter of air in the jar, how far will that compress per meter fresh water depth.

    I would like to know this because I need to know how much room in the jar I have that I can use, or even how deep I should limit myself before water would reach my gear in the jar.

    is there a simple equasion which states X cc/ml of air compression per meter depth?

    Attached Files:

  2. jcsd
  3. Sep 30, 2009 #2


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    Staff: Mentor

    pV=nRT is all you need. Or even pV=const will do.

    In general - look for ideal gas equation.

  4. Sep 30, 2009 #3

    Thanks for your quick response... But what does it all mean...? I am basically an idiot in this :bugeye:
  5. Sep 30, 2009 #4


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    Gold Member

    Yes, you can calculate exactly what the water pressure will be. If you are interested it is simple. If not, then you can use a diving rule of thumb of 1 atmosphere per every 10 meters of depth (it's within about .5 psi depending on a few things). At 10 meters you'll basically be doubling your pressure, therefore halving your volume which sounds like more than accurate enough for what you want to do.
  6. Sep 30, 2009 #5
    sorry about my delayed responses, I believe there is an anti spammer thingy.. as a newbie my posts have to get approved first. all good..

    SH. Ouch.. so, given the ballpark figure, Im filling half my jar at 10m.. looks like Im going to need a larger jar.. otherwise Im going to run out of useable dry space...
  7. Sep 30, 2009 #6
    ok... one last question. (Promise I'll come back and show what I built)

    Would the integrity of the glass (where the air is trapped) be acted upon in the same respect or would it only be effected by the same boyancy as when on the surface.. meaning, is the pressure of the water going to press on the glass or just where the water meets the air inside?

    Oh.. and I Wiki'd the pV=nRT.. now it makes sense to me!! Thanks B.
  8. Sep 30, 2009 #7


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    Staff: Mentor

    Pressure will be identical everywhere - which means you don't have to worry about it.

    I feel like you will benefit from some reading about pressure and basic physics in general.
  9. Sep 30, 2009 #8
    I do agree that I have a bit of reading to do. the only problem has been that most reading in physics as well as other scientific arenas, the authors asume you know so much already which I dont. I understand alot and am quick to pick up things, I am often times at a loss for the starting info.. yaknow?

    appreciate your help.
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