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Horizontal Circular Motion FBD Diagram Help

  1. Feb 24, 2007 #1
    1. The problem statement, all variables and given/known data
    Draw and FBD of a rubber stopper (mass) in circular horizontal motion. Be realistic here: Is the tension force on the stopper truly horizontal?

    This question is from an experiment where a rubber stopper is tied to a string and swung horizontally. When the question says "Be realistic here," it means that the rubber stopper is being swung horizontally but at a slight angle (such as 10 degrees) below the horizontal.

    2. Relevant equations

    3. The attempt at a solution

    I know that there's going to be a Fg downwards on the stopper, and a Force of tension going from the stopper to the centre of rotation, but I'm not sure about other forces such as Fc and which direction it would be going.
  2. jcsd
  3. Feb 24, 2007 #2


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    You've got them all. When drawing a FBD, generally you look for two types of forces: gravity and contact. Here, you have correctly identified the gravity force (the objects weight) and the contact force (the tension in the cord).
    The centripetal force is not an additional force; it is the horizontal component of the tension force that provides the inward centripetal acceleration necessary to keep the object moving in a horizonatal circle.
  4. Feb 25, 2007 #3
    So Ftx and Fc are equivelant. That's good, I'm done that part then.
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