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Is the force given by pressure infinite?

  1. Jan 14, 2014 #1
    If you have a container that contains pressurized gas such as hydrogen, the hydrogen would be pressing against the walls of the container, correct? Now if you had some sort of shape on an axle that somehow allowed the pressure to spin it around, would it spin it perpetually? I know such a shape cannot be created, as the force would be distributed along all the surface area on that shape, and thus it would remain motionless. But theoretically, would this work?
     
  2. jcsd
  3. Jan 14, 2014 #2

    berkeman

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    Staff: Mentor

    No. You cannot extract cyclic (continuing) energy from a static force field.
     
  4. Jan 14, 2014 #3
    Berkeman is correct, the answer is no. If the gas molecules strike a paddle, for instance, causing the axle to turn, they do work and rebound from the paddle with less momentum than when they arrived. This momentum loss would be reflected in less molecular kinetic energy of translation and hence lower gas temperature. Over time, the gas would cool to the point where the resulting pressure would be insufficient to turn the axle (P=nkT).
     
  5. Jan 15, 2014 #4

    berkeman

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    Staff: Mentor

    Thanks klimatos.

    @ ageattack -- this thread will now be locked. We don't discuss over-unity or perpetual-motion machine (PMM) mechanisms here on the PF. From the PF Rules link (at the top of the page under Site Info):

     
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