Example 1:

Consider a car is moving in a straight line. When a brake(external force)

is applied the car comes to rest position.

Example 2:

When a ball in the rest position is hit(external force), it begins to move along the

direction of force.

Newton's Second law

A car rides on a horizontal track with very little friction.

On the car place weights of various size.

The car and its weights are drawn along the track with a known constant force, and the acceleration is measured.

Result:

1. A constant force produces constant acceleration.

2. For the car loaded in a particular way, its acceleration is proportional

to the force applied.

i.e. F = ma

Newto's Third Law

Example 1:

A nail pulls a magnet with a force equal & opposite to that of the magnet on the nail.

Example 2:

An alpha particle and a nucleus repel one another with equal magnitude of force.