Important Terms

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

The body's momentum is the quantity of motion possessed by the body. The momentum of a body is equal to the product of its mass and velocity.

The force that opposes the motion of a body is called friction. 

Newton's first law of motion states that a body continues its state of rest or uniform motion in a straight line provided no net force acts on it.

Newton's first law of motion states that a body continues its state of rest or uniform motion in a straight line provided no net force acts on it.

SI unit of force is newton (N). It is defined as the force which produces an acceleration of 1 $ms^{-2}$  in a body of mass 1 kg

The mass of a body is the quantity of matter possessed by it. It is a scalar quantity. SI unit of mass is the kilogram (kg). 

The weight of a body is the force of gravity acting on it. It is a vector quantity. SI unit of weight is Newton (N). 

Newton's third law of motion states that to every action there is always an equal and opposite reaction. 

The Law of conservation of momentum states that the momentum of an isolated system of two or more two interacting bodies remains constant.

Rolling friction is the force of friction between a rolling body and a surface over which it rolls. Rolling friction is lesser than the sliding friction.

The motion of a body moving along a circular path is called circular motion. 

The force which keeps the body moving in a circular path is called the centripetal force and is given by:

$F_{c}=\frac{mv^{2}}{r}$

According to Newton's third law of motion, there exists a   reaction to the centripetal force. The centripetal reaction that pulls the string outward is sometimes called the centrifugal force.