(i) Inertia:

The inertia of a body is its property due to which it any change in its state of rest or motion.

Galileo related the inertia of a body with its mass; the greater is the mass of a body greater its inertia.

Inertia $\propto$ mass of the body

 

(ii) Momentum:

The momentum of a body is the quantity of motion it possesses due to its mass and velocity.

The momentum P of a body is given by the product of its mass m and velocity v. Thus

P = mv

Momentum is a vector quantity. Its SI unit is $kgms^{-1}$

The momentum of a system depends on its mass and velocity.

 

(iii) Force:

A force moves or tends to move stops or tends to stop the motion of a body. The force can also change the direction of motion of a body.

F = ma

Si unit of a force in the newton.

Note:  A force can also change the shape or size of a body on which It acts.

 

(iv) Force of friction:

Friction:

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

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

Factor 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.

 

(v) Centripetal force:

Centripetal force is a force that keeps a body moving in a circle.

The centre-seeking force is called the centripetal force. It keeps the body moving in a circle. Centripetal force always acts perpendicular to the motion of the body

$Fc =\frac{mv^2}{r}$