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Direction of Static Friction on an incline plane

  1. Jul 1, 2008 #1
    An object of a mass "m" is held stationary on an incline plane at an angle "theta" by means of a rope attached to it. The rope is parallel to the incline. The coefficient of static friction between the mass and the incline is "mu_s". I assume the static friction force is up the plane to oppose the mgsin(theta) component of the weight and the tension therefore must provide the additional upward force to balance the "down the plane component of the weight". Is this correct?

    Could the static friction force point down the plane and the tension (up the plane) be used to balance the combined downward force of the static friction and mgsin(theta) component of the weight?

    thanks in advance

  2. jcsd
  3. Jul 1, 2008 #2

    Doc Al

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    Staff: Mentor

    You don't have enough information to determine the direction of the friction force. Depending upon the tension in the rope, the friction can point in either direction.

    All you can say is that the sum of forces along the incline (rope tension, mgsin(theta), and static friction) must add to zero.
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