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How to find the coefficient of static friction.

  1. Oct 23, 2012 #1
    1. The problem statement, all variables and given/known data
    In order to hold a book of mass m stationary against a wall, you must push horizontally with a force of at least P.
    a. make a force diagram and find the coefficient of static friction
    b. calculate the coefficient of static friction for the wall and book when at least a 35-N horizontal push is needed to hold a 1.2-kg book steadily at rest against the wall.


    2. Relevant equations
    F=ma
    F_n=mg
    F_f=μF_net
    3. The attempt at a solution
    I find it difficult to grasp the concept that, somehow, there is still friction between the wall and the book even though there is no velocity. My best guess would be:

    F_f = F_net so μ would have to equal 1. help would be greatly appreciated.
     
  2. jcsd
  3. Oct 23, 2012 #2
    If there is no velocity and no acceleration, the system is in equilibrium. Try drawing the force diagram without the static friction and then you'll see how friction plays a role.
     
  4. Oct 23, 2012 #3
    so is friction equal to weight?
     
  5. Oct 23, 2012 #4
    Yes, and knowing that and the basic equation of static friction (f=μ*n), you can now calculate μ.
     
  6. Oct 23, 2012 #5
    great, I see. thank you so much.
     
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