Force: It is a push or pull on an object that produces acceleration in the body on which it acts.

A force can do 3 things on a body

(a) It can change the speed of a body.

(b) It can change the direction of motion of a body.

(c) It can change the shape of the body.

The S.I. unit of force is Newton.

Newton: A force of one Newton produces an acceleration of 1 m/s² on an object of mass 1 kg.
1N = 1kg m/s²

Types of forces:

1. Balanced force: When the forces acting on a body from the opposite direction do not change the state of rest or of motion of an object, such forces are called balanced forces.
2. Unbalanced force: When two opposite forces acting on a body move a body in the direction of the greater force or change the state of rest, such forces are called as unbalanced force.
3. Frictional force: The force that always opposes the motion of object is called force of friction.