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Homework Help: Required tension of rope around a cylinder to hold a object.

  1. Dec 15, 2011 #1
    please see attached drawing. I am trying to understand how this would work.

    Imagine a vertical cylinder of diameter "D". I would like to tie a mass M to it, using a rope. what is the tension "T" that is required on the rope?

    I assume the force required will depend on the coefficient of friction between the cylinder and the mass, let us assume that to be "mu".

    but in this case, friction force = mu * force perpendicular to the cylinder surface

    how to calculate this perpendicular force? is it just equal to the tension T? I am confused because when a rope goes though a pully we always assume tension to be tangential to the pully at any given point...

    any clarifications of my understanding is welcome!

    Attached Files:

    Last edited: Dec 15, 2011
  2. jcsd
  3. Dec 15, 2011 #2
    I have redrawn the problem a bit, I think the physics remains the same. Hope this helps.

    Attached Files:

  4. Dec 15, 2011 #3
    You wrote,

    is it just equal to the tension T?

    No in general. I think you would have to accurate dimensions of the mass M to calculate what fraction of T presses mass M against the cylinder. My sketch above takes liberty with the dimensions as none were given.
  5. Dec 16, 2011 #4
    That clarified my doubt..thanks.
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