Friction

Determine the Coefficient of Static Friction

Place your book (level) on the table.

Place a quarter on the book in the center of the front cover.

Tilt the front cover until the quarter begins to slip.

Measure angle q.

Mass of quarter = 5.0 g


 
The motion of the quarter does not occur immediately when the book cover is raised slightly.  The slide is impeded by the strong attractive intermolecular forces between the quarter's surface and the cover's surface.  This type of friction is known as static friction, acting as a force opposing motion.  The magnitude of the static frictional force is proportional to the normal force and is given by the equation 

            fs = m sN

where ms is the coefficient of static friction. 
 

 

Friction Questions
  1. Draw a force diagram for the quarter, resolving all the forces into components along the axes.
  2. Since the quarter on the cover is motionless in two dimensions, the equilibrium conditions are expressed by 
    3. (a) S Fx= 0  and   (b)  S Fy= 0
    Substituting the forces in this experiment leads to 

    for    (a)   w sin q - fs = 0 
    and   (b)  N - w cos q = 0 

    Solve these equations for fs and N. 
     

  3. What is the value of ms?


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