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Rolling Down Ramp - Question on Friction

  1. Nov 15, 2013 #1
    You have a cylinder rolling down a ramp, without slipping. There is a rope wrapped around it (pulling up) with tension T.

    The direction of friction is always up the ramp. How do I picture this? From the math, I know that it must be true. But I cannot really imagine it.
  2. jcsd
  3. Nov 15, 2013 #2
    Well you know the cylinder rolls down the ramp. What kind of torque would be necessary for the cylinder to roll the correct way? If that was provided by a force at the place of contact between the cylinder and the ramp, where would that force point?
  4. Nov 15, 2013 #3
    You say that I know the cylinder rolls down the ramp. That is not necessarily true--I understand that case (I think). But friction also points up the ramp if the cylinder rolls down it. It's the fact that it's up in both cases that confuses me.
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