physics notes

Conservation of Momentum

1. The term conservation is derived from the root word “conserve” which means constant.
2. The principle of conservation of momentum states that in the absence of an external force, the total momentum of a system remains unchanged.
3. An example of external force is friction and this can be contact friction or air friction.
4. An isolated or closed system the sum of external forces is zero, thus, the principle of conservation of momentum is true for a closed system.

Collisions

1. There are two types of collision:
(a) Elastic collision
(b) Inelastic collisions

2. In Elastic collision: Two objects collide and move apart again after a collision. Momentum is conserved. Total energy is conserved. Kinetic energy is conserved.
Formula: m1u1+m2u2 = m1v1+m2v2

3. In Inelastic collision: Two objects combine and stop or move together with a same velocity after a collision. Momentum is conserved. Total energy is conserved. Kinetic energy is not conserved (the total kinetic energy after the collision is less than the total kinetic energy before collision, excess energy is released as heat, sound energy etc).
Formula: m1u1+m2u2 = (m1+m2)v