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Homework Help: Forces of 2 dimensional motion w/friction

  1. Mar 6, 2005 #1
    i'm studying for a test and this question came up. i need all the help i can get.

    A small mass m is set on the surface of a sphere. If the coefficient of static friction is (greek letter for coefficient of friction) = .6 at what angle would the mass start sliding?
  2. jcsd
  3. Mar 6, 2005 #2


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    Science Advisor

    it will start to slide when the force parralell to the surface pulling it down is equal to the force of friction.

    parrallell force = mg * sin(angle)
    force of friction = mg * cos(angle) * coefficient of friction

    a nice trick for these types of problems is to know that is you have the coefficient of friction and you want to find the angle at which it wil slide, then use tan^-1(coefficent) = angle,
    if you have the angle and you want the coefficient of friction that will cause it to start to slide at that angle, use tan(angle) = coefficient
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