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Rolling & slipping

  1. Jan 11, 2013 #1
    hi pf, the more i think i have understood classical rotational mechanics the more it turns out to be clumsy? i am just not able to understand the slipping and rolling of bodies? somewhere friction comes into play and somewhere dont?
    "if a body rolls without slipping such that velocity of COM doesnt change then no frictional force acts on the body" how? why would a body roll if there is no friction?

    please help me out. i am tired of reading so many books. still not able to solve numerical related to it
  2. jcsd
  3. Jan 11, 2013 #2


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    It's not about how it started rolling. Once it is rolling at constant speed no friction is necessary.
  4. Jan 11, 2013 #3


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    What AT said.

    It actually says that in the quote...

    Consider a train that has solid steel wheels (so negligible rolling resistance).... When it accelerates it applies a force on the track in one direction, when it brakes it applies a force in the opposite direction. When it does neither and travels at a constant velocity no frictional forces are acting.

    Aside: In a real train this isn't true because of things like wind resistance and rolling resistance isn't totally zero. So some force (and power from the engine) is required to maintain a constant velocity.
  5. Jan 11, 2013 #4
    ok..if i consider a sphere rolling as well as sliding down an inclined plane? what should i interpret? friction is acting or not?
  6. Jan 11, 2013 #5

    Doc Al

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    If the sphere is rolling without slipping down the incline then there must be a friction force to produce the angular acceleration.
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