Physics 101- Introduction to Mechanics
February 18- Applications of Newton's Laws

Friction

Consider a 1 kg book at rest on a table.  The book-table surface has a coefficient of static friction of 0.5.  What is the static frictional force on the book?

Our model says that-

• Friction is independent of surface area.
• The frictional force is only dependent on the normal force.

Why do new cars come equipped with antilock braking systems?

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 phillips@lmu.edu Loyola Marymount University Spring 2002