Question

give reason that why frictional force is contact force​

Answer 1

Friction is caused due to contact of two or more than two object, so frictional force is often called contact force Frictional force comes into play only when two surfaces are in contact.  If you push a book on the table in the forward direction the frictional force will act in the backward direction.

Example : when you take a matchstick and slide it to the side of the matchbox, fire is produced, as know friction produces heat, and so the matchstick and the side of the matchbox are in contact , it's contact force