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A simple question in regards to Gravitys effect over compressed gas

  1. Jul 10, 2006 #1
    This is a question which im sure i already know the answer to.
    Its purpose is simpley to clear up a dispute between my self
    and someone i know.

    In a canister where gas is compressed into a state of liquid.
    Is the liquid suspended toword the top side of the can held
    up by some non-liquid pressure system?Is it held down toword the
    bottom of the canister by gravitation and having some non-liquid pressure
    system above?Or is the liquid equally distributed throughout the canister
    with only negligible difference produced by gravity?
  2. jcsd
  3. Jul 10, 2006 #2


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    What are the densities of the gas and liquid phases? Do rocks float on water?
  4. Jul 10, 2006 #3
    If this point could be further illustrated i would greatly appresieate it.
    Gas suspending liquid is without question one of,if not THE,most silly thing you've ever heard.
    But,it brought me to think about something that im hoping you can explain.
    If we have a tank containing,say,compressed oxigen,and its half empty.
    Is the other half then filled with pure empty pressure,like an anti-vacuum
    without substance.
    Last edited: Jul 10, 2006
  5. Jul 10, 2006 #4


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    Grab a bottle of propane and slosh it around. You'll find it is not top-heavy...
  6. Jul 10, 2006 #5


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    A fluid such as oxygen which is at least partially in a liquid state inside a tank is also going to have that fluid in a gasseous state. Take water for example, boiling in a pot. If you have a lid on the pot that is not sealed tight, the boiling water vapor soon pushes all the air out and all that's left is the boiling liquid water on the bottom of the pot and the water vapor above the liquid.

    In a sealed tank, the same holds true. All cryogenic fluids such as liquid nitrogen, oxygen, hydrogen, etc... are typically boiling liquids which have that gas above the liquid. The gas and liquid are typically very close in temperature, and of course at the same pressure. That pressure and temperature is call the "saturation" pressure/temperature.
  7. Jul 11, 2006 #6


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    Actually it's not at the same pressure if gravity is invovled. The pressure decreases relatively rapidly with altitude within a tank. If the tank has sides that are perpendicular to the pull of gravity, then the net force due to the total pressure differential between the top and the bottom of the tank will exactly equal the weight of the fluid/gas inside the tank.

    For example, force 80 cubic feet of air which is about 6 pound mass into a scuba tank, and the tank increases in weight by about 6 pounds due to the addition of the air. As I just mentioned, the air exerts it's "weight" on the tank via a pressure differential that changes with altitude within the tank. Pressure is lower at the "top" (relative to the direction of pull of gravity) of the tank, and higher at the "bottom" of the tank.
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