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Moment applied on a circular disc

  1. Oct 14, 2005 #1
    moment on a circular disc(moment applied in the centre)
    A circular disc is hinged in the centre. I am applying a moment at the centre. The result is that the disc will rotate with an angular acceleration "a"

    moment on a circular disc(moment applied not in the centre)
    A circular disc is hinged in the centre. I am applying a moment at some point in the disc but not at the centre. How can i calculate the angular frequency. What is the theory? Will the disc rotate?
  2. jcsd
  3. Oct 14, 2005 #2
    For your moment not applied at the center, it will still rotate about the center. The moment is a free vector, it can act anywhere you put it. It will cuase rotation around the fixed point of the body, if that point allows for rotation in the direction of the moment.

    EDIT: What I said applies for a couple moment, if thats what you mean.
    Last edited: Oct 14, 2005
  4. Oct 20, 2005 #3
    i am not getting. pls elaborate.
  5. Oct 20, 2005 #4
    Because one is incorporating a fixed rotation axis for the disk, it does not matter where on the disk other than its axix that you apply a tangental force to initiate rotation about that axis.
    This would NOT occur if there were no fixed axis. In that case, the disk would rotate around its center of mass, which can be substantially different that the location of a fixed axis.
    With a "fixed axis", centered or not, you are "forcing" rotation to occur around that axis.
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