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Vacuum force

  1. Feb 9, 2014 #1
    What is the force associated with a vacuum? If I put a straw in a soda and pinch off the end of the straw, then lift it out of the soda, some soda stays. What force counteracts gravity?
  2. jcsd
  3. Feb 10, 2014 #2
    It is the atmospheric pressure that pushes the liquid up the straw.Since you reduce the pressure inside the straw the downward force on the liquid is only the force of gravity, the upward force due to pressure remains so the fluid goes up. If you try to do this with a very long straw you would reach a point where the weight of the fluid column is greater than the force due to the atmospheric pressure and the fluid would fall.
    prof Walter Lewin did an amazing lecture on this here:
    Last edited by a moderator: Sep 25, 2014
  4. Feb 10, 2014 #3
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