Explain giving two examples each of —

(a) Contact forces, and (b) Non-contact forces.

(a) Contact Forces — The forces which are applied on bodies by making a physical contact with them, are called contact forces.

Examples of contact force:

1. Frictional force — When a body slides (or rolls) over a rough surface, a force starts acting on the body in a direction opposite to the motion of the body, along the surface in contact. This is called frictional force or force of friction.
2. Normal reaction force — When a body is placed on a surface, the body exerts a force downwards, equal to it's weight, on the surface, but the body does not move (or fall) because the surface exerts an equal and opposite force on the body normal to the surface which is called normal reaction force.

(b) Non-Contact forces — The forces experienced by bodies even without being physically in touch, are called non-contact forces or forces at a distance.

Examples of non-contact force:

1. Gravitational force — In the universe, each particle attracts the other particle due to it's mass. This force of attraction between them is called gravitational force.
2. Electrostatic Force — Two like charges repel, while two unlike charges attract each other. The force between the charges is called electrostatic force.