Question

A book placed on a table is at rest. Is the force of friction acting on it or not? Explain?

Answer 1

Consider the forces that can be present between the book and table. While considering the forces between the book and the table, also keep in mind the state of motion (state of rest or state of motion) of the book.

Complete step by step answer:
The force which is present between an object and a surface when the object is just only in contact or sliding over the surface is known as the frictional force.This frictional force depends on smoothness and roughness of the surface.There are two types of frictional forces which are static frictional force and kinetic frictional force.The static frictional force is present between the object and the surface when the object is just in the contact with the surface in a steady state.The kinetic frictional force is present between the object and the surface when the object is sliding over the surface.The book placed on the table is a rest and hence is in the contact with surface of the table.There must be some force holding the book at its position. Otherwise, the book has slipped from the surface of the table.Since the book is at rest and not moving on the surface of the table hence, there is the static frictional force between the book and the surface of the table keeping the book at its position until some force greater than this static frictional force is applied on it.

Note: If the book slides on the surface of the table then there is kinetic frictional force between the book and the surface of the table.Always remember that frictional force act in the opposite direction of the motion and there are mainly two types of friction.One is static friction which act when object is in rest position while other is kinetic friction which act when object is in motion.