You push a book sitting on a desk with a force of 5 N, but the book does not move. What is the static friction?

The static friction is 5 N acting in the direction opposite to that of the force of push.

Explanation:

Given:

A book lying on a table. Force of push is 5N.

Now, the book is not moving. This clearly means that some resistive force is acting in the opposite direction which has the same magnitude as that of the applied force, thus making the net force acting on the book equal to zero.

This resistive force acting in the opposite direction is called the static frictional force.

Therefore, the static friction acting on the book is equal to 5 N and acts in the direction opposite to that of the force of push.