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What causes gas particles to accelerate so that P = F / A

  1. Dec 15, 2012 #1
    Dear Physics Forums,

    Pressure is force / area, and force is mass * acceleration. When you have a gas in a container, it's said to exert a pressure on its container. Therefore, the particles are accelerating toward the container's walls. What's causing these gas particles to accelerate toward the container? Why can't pressure be momentum / area? Momentum, like force, has a tendency to transfer energy as well to a stationary object (the container's walls).

    Thank you for addressing my confusion,

    Vanmaiden
     
  2. jcsd
  3. Dec 15, 2012 #2
    You are nearly there.

    Force = rate of change of momentum.

    When a gas particle collides with a container wall it is deflected, suffering a change of momentum (vector change).

    This is experienced as a force and a reaction.

    The pressure is the aggregate of many such collisions, taken over area and time.
     
  4. Dec 19, 2012 #3

    Philip Wood

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    Gold Member

    Studiot has it. Where you were getting confused is in demanding that the molecule must be accelerating towards the wall. [For an ideal gas we ignore any such effect.] The acceleration occurs when the molecule hits the wall and changes its direction, and therefore its velocity.
     
  5. Dec 19, 2012 #4
    Excellent point.
     
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