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Friction and rolling

  1. Dec 22, 2011 #1
    when a roller is rolling on a flat surface with a constant speed, how is about the friction force?
    is there any friction forces or not?
     
  2. jcsd
  3. Dec 22, 2011 #2

    berkeman

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    Staff: Mentor

    What are your thoughts? The term "constant speed" is a key in this question...
     
  4. Dec 22, 2011 #3
    constant speed doesn't say much - it could be a forced motion.

    if the roller is rolling without slipping, there is static friction with does no work.
     
  5. Dec 22, 2011 #4

    berkeman

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    Staff: Mentor

    Ah, good point. Didn't think of that possibility.
     
  6. Dec 23, 2011 #5
    thanks all
    let me clarify my question:
    consider a roller without slipping(a disk) which it's center has a constant speed.
    if there were any friction force on a roller during rolling then the disk can't have a constant speed(due to friction the velocity is decreasing). on the other hand the torque(due to friction) should increase it's angular velocity.
    so i think there is a discrepancy here.
     
  7. Dec 23, 2011 #6

    Doc Al

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    If something is just rolling without slipping along a horizontal surface, the static friction will be zero. Static friction would be non-zero if it were accelerating.

    (This ignores losses due to deformation and rolling friction, of course.)
     
  8. Dec 23, 2011 #7
    ok
    thanks
     
  9. Dec 23, 2011 #8

    NascentOxygen

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    Have you rolled a marble along a flat surface? What about trying different flat surfaces?
     
  10. Dec 23, 2011 #9

    rcgldr

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    Homework Helper

    I'm guessing your thinking of rolling resistance, as opposed to static friction. Wiki article about rolling resistance:

    http://en.wikipedia.org/wiki/Rolling_resistance
     
  11. Dec 23, 2011 #10
    There is pretty much always friction.
     
  12. Dec 23, 2011 #11
    When the disk is freely rolling without slipping at constant velocity, the friction is zero. If your disk rolls onto a frictionless surface, there will be no difference in how it moves - it will still appear to be rolling without slipping because rw=v i.e. they are matched perfectly.

    Friction only comes into play if there is any acceleration.
     
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