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About static friction

  1. Dec 1, 2007 #1
    Question
    Can static friction do work? If no, explain why, if yes, give an example.

    Attempts
    What I am thinking is when the car do circular motion , it does not slip off the road because the road provides the static frictional force as the centripetal force.

    However, static friction actually does not move the car for any distance, hence I am not
    sure this is an answer. If yes, why it is? If no, may I know what is the correct answer?
     
  2. jcsd
  3. Dec 1, 2007 #2

    Dick

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    That's the answer. There is no motion of the car in the direction static friction is acting (that's why it's 'static'). If there is no motion along the direction of a force, then the force does no work.
     
  4. Dec 1, 2007 #3
    Do you mean the answer for question is:
    No, static friction cannot do work, because the force does not move the object through any distance?
     
    Last edited: Dec 1, 2007
  5. Dec 1, 2007 #4

    Dick

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    Yes, static friction cannot do work.
     
  6. Dec 1, 2007 #5

    nrqed

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    It is possible for static friction to do work on an object!

    Consider a box inside a speeding train. Imagine that the box is not sliding.
    The kinetic energy of the box is increasing. The normal and gravitational forces do not work on the box (they are perpendicular to the motion). But the static friction force is in the direction of the motion and it does positive work on the box.
     
  7. Dec 1, 2007 #6

    Dick

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    Ummm. Right. I was think about the question much too narrowly. Thanks for the correction.
     
  8. Dec 1, 2007 #7
    How is static friction in the motion direction?
    Is the train accelerating or not?

    I am not so sure about this?

    Casey
     
  9. Dec 1, 2007 #8

    Dick

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    In place of 'speeding train' write 'accelerating train'.
     
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