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Homework Help: Hydrostatics - Why is the pressure force the same?

  1. Feb 6, 2013 #1
    1. The problem statement, all variables and given/known data
    h2bH9c1.png

    3. The attempt at a solution
    So for the cone there is the weight of the liquid (W), the upward force (F_y), and the pressure force acting on the bottom (F_v):
    F_v = W - F_y

    For the cylinder there is only the weight of the liquid and the pressure force acting on the bottom:
    F_v = W

    So how are they the same?
     
  2. jcsd
  3. Feb 7, 2013 #2

    CWatters

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    Science Advisor
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    Gold Member

    Pressure = force/area
    so
    force = pressure * area

    At the bottom of each container the depth of water is the same so the pressure must be the same. The area is the same so the force must be the same.

    If they were placed on scales they would obviously weigh differently yet the force on the bottom is the same, hence the paradox.

    To resolve it remember that pressure acts in all directions.
     
  4. Mar 26, 2013 #3
    sorry,but a doubt of my own from here.

    i know that these 2 containers should weigh different.but shouldn't the contact force be equal to the weight of the body and since the force at the bottom is the same ,shouldn't the weight be same?
    i think that i might be wrong somewhere but can't figure out what.
     
  5. Mar 26, 2013 #4
    In the case of the cone, is there a force acting on the conical surface? What is the direction of this force? Is the conical surface of the cone exerting a force on the water? What is the direction of this force?
     
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