Question

A force scale is attached to a stack of books lying on a flat table.
a) What happens to the size of the static frictional force as you begin to pull on the force scale?
b) What happens to the stack of books if the applied force exceeds the maximum static frictional force?
c) What is the minimum size for the static frictional force, and under what conditions will the minimum static frictional force be observed?
d) What type of friction acts when the books are at rest but a force is exerted?