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Water Pressure and Internal (Air) Pressure

  1. Jun 12, 2015 #1
    If you have, say, two tubes of different internal pressures submerged to a given depth (for sake of the example, let's just say 1,000M underwater or 100 ATM), will the smaller internal air pressure tube experience a greater relative force from the water pressure? The water pressure on both tubes should be the same from the outside, but is there an additional effect where water tries to equalize the pressure at a greater magnitude of force on the tube with less internal air pressure? I guess an extreme, clearer hypothetical comparison would be between a tube with a vacuum on the inside compared with a tube with air pressure equal to 99.99% of the water pressure on the inside. I'm also assuming that the tube's microstructure is impermeable to water, and that the tube is strong enough to withstand the water pressure at the given depth.

    Thanks in advance!
    Last edited: Jun 12, 2015
  2. jcsd
  3. Jun 12, 2015 #2


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    Yes. The net force is proportional to the pressure difference.

    If the tube distorts in any way that changes the volume then the pressure inside can change meaning the pressure differential and the net force will also change.
  4. Jun 12, 2015 #3
    Is this force derived from the water and air pressure combo, or something else?
  5. Jun 12, 2015 #4


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    What else could it be?
  6. Jun 12, 2015 #5


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    The pressure on the outside surface of the tube is the water pressure. If the tube is flexible, the pressure on the inside surface is also the water pressure.
  7. Jun 12, 2015 #6
    The tension or compression stress in the circumferential direction (i.e., the so called hoop stress) supports the difference in pressure between the inside and the outside of the tube. So the tube itself is part of what is happening.

  8. Jun 13, 2015 #7
    Thanks for the answers. :)

    I was wondering if there were other forces, maybe even buoyant forces that would be significant.

    But from what I can tell, it seems like the major ones are water and air pressure.
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