Conservation of Momentum

What is momentum?

The quantity of motion of a moving body, measured as a product of its mass and velocity.
It is calculated by the equation:  P = m x v 

• P = the momentum in kilograms metres per second ( kgm/s)

• m = the mass in kilograms (kg)

• v = the velocity in metres per second (m/s)

The principle of conservation of momentum states that for a system of interacting objects, the total momentum remains constant, provided no external resultant force acts on the system.

If a rail wagon moving constantly along a track collides with a stationary rail wagon and then separates, the result of this collision will mean the momentum of each rail wagon changes. They exert equal and opposite forces when they are in contact.This means the change of momentum of one rail wagon is equal and opposite to the change of momentum of the other rail wagon. In other word, if one object gains momentum, the other object loses an equal amount of momentum. so the total amount of momentum is unchanged ( momentum is conserved).

Uniform circular motion

Uniform circular motion can be said as the motion of an object in a circle at a constant speed. As an object moves in a circle, it is constantly changing its direction. At all time, the object is moving tangent to the circle. Since the object is going in a circle, it's velocity keeps changing and this makes the object accelerate. Even though it's accelerating the speed in a uniform circular motion is constant because the acceleration is due to change in direction.

An object would continue in a straight line, never differing from its direction. Since the centripetal force is present in the circular motion, this force will be perpendicular to the velocity vector; due to this the object is always changing its direction and undergoing an inward acceleration. 

Centripetal force does not exist by its self, but is given by the action of other forces. For example, a fairground ride consists of a number of chairs suspended from wires that swing out as the centre rotates faster and faster. Imagine the ride going around in a circle. The centripetal force is the result of tension within the wire attached to the chairs where the person sits.

Also the fairground ride doesn't have uniform circular motion because it’s speed isn’t constant, it starts of slow and increases as it goes around many times.