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Homework Help: Need Help with rotational dynamics

  1. Oct 27, 2015 #1
    Refer to https://www.physicsforums.com/threads/rolling-motion-of-plank-and-cylinders.93329/

    I am able to understand all the points until the point v_roller+rω=v_plank.
    I have a tough time understanding this part.

    My attempt at the question:
    I think that the static friction at the top and bottom of the roller will provide the external torque. This external torque will provide the rotating motion.

    V_roller is the velocity due to the friction between the ground and the roller?
    rω is due to the friction between the roller and the plank?

    And one more question
    I know what is pure rolling but i am wondering how does non pure rolling looks like, is it rolling or not ?
    Last edited: Oct 27, 2015
  2. jcsd
  3. Oct 27, 2015 #2


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    "non-pure" rolling usually indicates rolling with slipping.
  4. Oct 27, 2015 #3
    Is it true that when an object is rolling, it may or may not be pure rolling?
  5. Oct 27, 2015 #4


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    Pure rolling is an idealization of what happens to real, physical objects.

    It's like analyzing objects in free-fall, but neglecting air resistance, for example.
  6. Oct 27, 2015 #5
    From what I know, it is possible for an object that is not rolling without slipping to achieve rolling without slipping even though it have an initial angular velocity and velocity as long as they fulfill the equation v=rω
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