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A Ball on a Massless Rod

  1. Feb 5, 2013 #1
    1. The problem statement, all variables and given/known data

    A ball of mass m is attached to a massless rod and is suspended from a frictionless pivot. It is moving in a vertical circle or Radius R such that it has speed v1 at the bottom. The ball is in a vacuum.


    Find an expression for the force exerted by the rod at the top of the loop as a function of m, v1, g, and R.


    This is more of a general question. Not looking for an answer to the entire problem. I'm just wondering if the rod exerts a normal force if it is massless. If so, at the top there is a Normal force acting upward and gravity and tension acting downward, correct?
     
  2. jcsd
  3. Feb 5, 2013 #2

    ehild

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    As the mass is attached to the rod, the rod can either push or pull the ball, but there is only one force it exerts on the ball. This force and the weight of the ball keeps it moving along the vertical circle.

    ehild
     
  4. Feb 5, 2013 #3
    So at the top, we have a normal force pushing the ball up, and at the bottom, a tension force pulling the ball?
     
  5. Feb 5, 2013 #4

    ehild

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    At the top you can have both a pushing force or a pulling one, it depends on the speed which determines the centripetal force needed.

    At the bottom, the rod pulls the ball upward.

    ehild
     
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