Newton’s second law of motion:

Newton’s second law of motion: The rate of change in momentum of a body is directly proportional to the applied force on the body and takes place in the direction of force.

If F = force applied, a= acceleration produced and

M= mass of body the nF = ma.

Newton’s second law gives the magnitude of force.

Newton’s first law is contained in the second law.

Newton’s Third Law of Motion: To every action, there is an equal and opposite reaction.

Examples of third law- (i) Recoil of a gun (ii) Motion of rocket (iii) swimming (iv) While drawing water from the well, if the string breaks up the man drawing water falls back.

Principle of conservation of linear momentum: If no external force acts on system of bodies, the total linear momentum of the system of bodies remains constant.

As a consequence, the total momentum of bodies before and after collision remains the same.

Impulse: When a large force acts on a body for very small time, then force is called impulsive force. Impulse is defined as the product of force and time.

Impulse = force x time = change in momentum.

It is a vector quantity and its direction is the direction of force. It SI unit is Newton second (Ns).

Centripetal Force: When a body travels along a circular path, its velocity changes continuously. naturally in external force always acts on the body towards the centre of the path.

The external force required to maintain the circular motion of the boy is called centripetal force.

If a body of mass m is moving on a circular path of radius R with uniform speed v  then the required centripetal force, F  = mv²/ R

Centrifugal Force: In applying the Newton’s laws of motion, we have to consider some forces which cannot be assigned to any object in the surrounding. These forces are called pseudo force or inertial force.

Centrifugal force is such a pseudo force. It is equal and opposite to centripetal force.

Cream separator, centrifugal drier work on the principle of centrifugal force.

Centrifugal force should not be confused as the reaction to centripetal force because forces of action and reaction act on different bodies.