Physlet Illustration: A Block Sliding Down a Rough Incline

 

 

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m = Grams  q = ° 
A block slides down a rough incline, as shown. The incline makes an angle q with the horizontal. The speed is given in m/s, and the times shown are in seconds. Adjust the mass (10 g < m < 500 g) and/or the angle (5° < q < 45°), and measure the block's acceleration. How can you determine the coefficient of static friction?  Kinetic friction?

Hints

  1. Remember that the force of static friction is less than or equal to the product of normal force times the coefficient of static friction.  
  2. The force of kinetic friction force is equal to the normal force times the coefficient of kinetic friction.
  3. Can you draw a free-body diagram for the box?
  4. How large does the angle need to be for the block to begin to slide?
  5. When the block accelerates, what force determines the acceleration?

Reference

See Walker, Section 6-1

Illustration written by Steve Mellema and Chuck Niederriter