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Homework Help: Rotational conceptual problem?

  1. Sep 29, 2011 #1
    1. The problem statement, all variables and given/known data
    a disk is rolling on a flat horizontal surface.only rolling friction will act on the body.(true/false).ans false WHY?a body rolls.therefore sliding friction can't act on body.(true/false).ans. false WHY?

    2. Relevant equations

    3. The attempt at a solution
    since the point of contact is at rest with respect to the surface (rolling condition) therefore no sliding friction must be there.
  2. jcsd
  3. Sep 29, 2011 #2


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    Staff: Mentor

    The question seems to be relying on vagueness and technicalities to trick you :frown:

    Technically, a rolling disk may also be sliding if it has an initial rotational speed that differs from the linear tangential speed; The speeds would eventually match as friction worked to equalize them.

    Technically, a rolling disk may also be sliding perpendicularly to the rolling motion (think of a car tire negotiating a curve when the car is traveling to fast -- lateral road friction is too small to impart sufficient centripetal force and the rolling tire slides sideways).

    Technically, air friction will also operate on the moving disk...
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