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How to use friction equations

  1. Dec 13, 2012 #1
    1. The problem statement, all variables and given/known data
    The coefficient of sliding friction between two materials is 0.35. A 5.0 kg object made of one material is being pulled along a table made of another material. What is the force of friction?

    I'm fairly certain I solved the problem correctly, the thing is, I should be getting a negative force as the answer (because I defined forward as positive), and I'm getting a positive force. Could someone please point out which part of my solution is incorrect.

    2. Relevant equations
    F1 is force of sliding friction, F2 is normal force, and μ is the coefficient of sliding friction:
    F1=μF2

    3. The attempt at a solution
    F1=μF2
    =0.35(mg)
    =17.15N
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Dec 13, 2012 #2

    SammyS

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    The equation F1=μF2 only gives the magnitude of the frictional force. The force of friction, F1, is in a direction perpendicular to the normal force, F2 , so that equation cannot be true in a vector sense.

    The force of friction is in such a direction as to oppose the relative motion of the two objects.
     
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