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Tension producing torque on a disk

  1. Jan 3, 2010 #1
    When a string is wrapped around a disk and pulled taut to rotate the disk, such as in a pulley, how can tension be the force producing the torque? Tension would only act upon the string next to the disk. I suppose there would be the normal force of the disk on the string, but that wouldn't produce a torque. Is there some other force involved?
     
  2. jcsd
  3. Jan 3, 2010 #2

    rcgldr

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    The friction force between string and disk (times the radius) generates the torque.
     
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