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Average torque of a rotational freefall

  1. Jan 24, 2012 #1
    Hi all, this is not actually homework or similar but the board seemed as the appropriate place for the question.

    I have an arm of 1m length pointing upwards from a rotation axis, on the end of the arm is a mass of 1kg, upon release the arm starts rotating downwards due to gravity (no other forces).
    What is the average torque produced from the topmost to the bottommost position.

    I haven't been doing physics calculations for like 10 years now so am pretty rusty. I can calculate the torque for a force acting in the direction of rotation, but since the force vector and the arm vector angle changes I'm stuck.
  2. jcsd
  3. Jan 24, 2012 #2


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    Staff: Mentor

    Welcome to the PF.

    Well, you have very little torque at the top and bottom of the swing, and maximum torque when the weight and arm are out in the horizontal position (if I understand your problem definition correctly). Can you sketch a graph of the torque as a function of the angle? What does that function look like? Is it a function that is easy to integrate and find the average of?
  4. Jan 25, 2012 #3
    It is normal circular rotation. I am sure it is very simple but i haven't been doing this a long time so i can't even start.
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