# Newton's Laws of Motion

Sir Isaac Newton given the three laws of motions. They describe the relationship between a body and the forces acting upon it

## First Law of Motion

A body at rest will remain at rest, and a body in motion will continue to remain in motion in a straight line with a uniform speed, until and unless an external force is applied on it. Newton's first law of motion is also known as the Law of Intertia.

Inertia is the property due to which a body resists to changes its state of rest or state of motion.

## Second Law of Motion

The force acting on a body is directly proportional to the mass of the body and the 'acceleration' produced in the body by the line of the force applied.

Force = mass × acceleration
F = m × a
So, a = f/m

Units of Force: The unit of force is 'newton' which is denoted by N. A 'newton' is that force which when acting on a body of mass 1 kg produces an acceleration of 1m/s2 in it.

## Third Law of Motion

Every action has equal and opposite reaction. It means whenever an object pushes another object it gets pushed back in the opposite direction equally hard eg:

1. The rocket's action is to push down on the ground with the force of its powerful engines, and the reaction is that the ground pushes the rocket upwards with an equal force.

2. In swimming races, while starting the swimmer uses his feet to push off the wall. The more force he applies on the wall, the faster will be his movement in water. The reason being the wall exerts the same force on the swimmer as he applies on the wall, but in the opposite direction.

## Momentum

The momentum of a body is defined as the product of its mass and velocity
Momentum = mass × velocity
P = m × v, where P = momentum, m = mass of body and v = velocity(speed) of the body.

## Law of Conservation of Momentum

When two bodies act upon one another, their total momentum remais constant provided no external forces age acting. The law of conservation of momentum means that whenever one body gains momentum then some other body must lose an equal amount of momentum. This also states that momentum can neither be created nor be destroyed