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Calculating the weight of an object required to overcome grease seal

  1. Jul 2, 2013 #1

    I am trying to work out a problem with a piece of equipment:

    imagine a container that has grease injected into it at say 3,000 Psi

    The container has a piece of wire running though the middle vertically with a 100lbs weight attached to bottom. Only the wire is in contact with the grease and the mass is outside of the container.

    I'm trying to work out what weight you would require to overcome the frictional force/drag associated with the grease acting on the wire.

    My first though was F=uN where N is the F=PA, P= 3,000 and A = cross sectional area.

    But is this oversimplified? Should I be introducing the navier stokes equation?

    This is a real problem not a piece of homework :)

    Any suggestions would be most welcome.

  2. jcsd
  3. Jul 4, 2013 #2


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    Gold Member

    F= uN would work as long as you could find a way to obtain u, which though would be a function of the velocity of the wire, temperature of the grease, and its pressure.

    The grease will act as a fluid and I think Navier-Stokes would be the way to go.
    Does 3000psi make the grease act more solid-like, which is something you will have to determine.
    You may want to investigate skin friction.
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