Physics 101- Introduction to Mechanics
February 20- Applications of Newton's Laws







Our model says that-

  • Friction is independent of surface area.
  • The frictional force is only dependent on the normal force.
  • The maximum static frictional force is given by FSF= ms FN
  • The kinetic frictional force is given by FKF= mK FN


You push horizontally on a 35 kg crate with a 110 N force.  The coefficient of static friction between the crate and the floor is 0.37.

  • Does the crate move?
  • What is the frictional force exerted on the crate by the floor?
  • What is the maximum magnitude of the static frictional force under the circumstances?
  • Suppose, that a classmate pulls directly upward on the crate to help out.  What is the least pull that they can exert that will allow the your push to move the crate?
  • If, instead, your friend pulls horizontally to help out, what is the least pull they can exert to get the crate moving?


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Jeff Phillips
Loyola Marymount University
Spring 2002