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Homework Help: Two Friction Questions

  1. Mar 2, 2009 #1
    1. Why do we use static friction instead of kinetic friction for a rolling object?

    2. Why do we ignore the effects of friction in the conservation of energy?
    Last edited by a moderator: Mar 3, 2009
  2. jcsd
  3. Mar 2, 2009 #2
    Because, even though a rolling object is moving, it isn't sliding across the surface.

    We don't. Friction turns kinetic energy into heat energy.

    Need me to clarify or give examples of either answer?
  4. Mar 2, 2009 #3


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    Science Advisor

    1. The bottom of the wheel is not moving with respect to the ground at contact.
    2. Since bottom of the wheel is not moving, the force does not move through a distance.
  5. Mar 6, 2009 #4
    Right, I should clarify my second answer. Kinetic friction turns kinetic energy into heat energy. Static friction does not. sorry.
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