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Force on a body through air pressure

  1. May 7, 2010 #1
    If a body,let's say a big block of steel, has a net downward force of weight of 1000N, would it be possible to lift the block using air pressure? I mean, if you put air in a completely sealed container with a movable piston on top and you pressurized such air to an appropriate pressure, then by formula: pressure=force/area, wouldn't it be possible to achieve a force equal to or more than the weight of the body? And if this could be done and the entire container is attached to the underside of the body, would the body not constantly levitate a little because of the net upward force?
  2. jcsd
  3. May 7, 2010 #2


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    Staff: Mentor

    Welcome to PF.

    Air pressure acts on the top and the bottom of the deviece, so it cancells out. The only way to get air pressure to move something is to use a vacuum pump to remove air from one side.
  4. May 7, 2010 #3
    Yes, its true that air pressure acts in all directions but if, in this container, lets say a cuboid for hypothetical purposes, 5 of the 6 sides are completely sealed and one side is a movable surface, the force would act on all sides but would only have a real effect on the movable surface. I dont think gas pressure will transmit through a solid, immovable surface.
  5. May 7, 2010 #4

    Doc Al

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    Could you pressurize air within some container to lift a piston plus the added weight resting on it? Sure, why not.
  6. May 7, 2010 #5


    Staff: Mentor

    This arrangement is generally called a "piston". Although typically they are made cylindrical rather than cubic.

    Nevermind, I see Doc Al already mentioned that.
  7. May 7, 2010 #6
    Yeah, isn't that how airplanes work?
  8. May 7, 2010 #7
    Good example, the velocity at the top of the wings is faster so the pressure is more under the wings. And an airplane is heavy.

    Air pressure is so strong on earth that if you depressurized your house your lungs would burst and your blood would boil. and then your house would implode.
  9. May 7, 2010 #8


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    A better example would be a pneumatic lift.
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