Newton's Laws of Motion

How forces are related to motion was first discovered by Sir Isaac Newton (1642-1727),who also stated three important laws of motion known as Newton's Laws of Motion.


Laws of Motion
1. Newton's first law of motion- idea of inertia: The first law States that every object continues in its state of rest or of uniform motion in a straight line unless acted upon by an external force.
This tendency of bodies to remain in their state of rest or of uniform linear motion in the absence of applied forces is known as Inertia. Newton's first law shows that inertia is inherent in a body at rest or the one moving with a constant velocity. Inertia is a property of matter. Mass is a measure of inertia, the more massive an object is, the more inertia it has.
Newton's first law explains why passenger in a fast moving vehicle tend to move forward when the car suddenly stops, or to be pushed backwards when the vehicle suddenly speeds off, since there is little or no force to restrain them. Hence safety belts are used to provide this restraining force.

Newton's Second Law of Motion : The second law of motion States that the rate of change of momentum is proportional to the impressed force and takes place in the direction of that force.
Newton's second law enables us to define an absolute unit of force which remains constant under all conditions. In symbols the law states that
F=change in momentum /time taken for the change
F=mv-mu/t
F=m(v-u) /t
but v-u/t = acceleration
F=ma.

Newton Third law of motion: It states that action and reaction are equal and opposite, or to every action there is an equal and opposite reaction.
For example, when you push down on your desk with your fingers, the desk pushes your fingers up with an equal force.