Friction:

           The force that opposes the motion of moving objects is called friction.

 Friction is a force that comes into action as soon as a body is pushed or pulled over a surface.

Factors on which friction depends:

              In the case of solids, the force of friction between two bodies depends upon many factors such as the nature of the two surfaces in contact and the pressing force between them.

Examples:

              Rub your palm over different surfaces such as tables, carpets, polished marble surfaces, brick, etc. You will find smoother the surface, the easier it is to move over the surface. Moreover, the harder you press your palm over the surface, the more difficult would it be to move.