3.5.2 Collisions

The principle of conservation of momentum states that for a closed system the total momentum in a specified direction remains constant as long as no external forces act on the system.

It is important to recognise that both momentum and total energy are conserved when objects collide. There are two types of collision:

• perfectly elastic:
• momentum is conserved, total kinetic energy is conserved.
• inelastic:
• momentum is conserved, total kinetic energy is not conserved.

As we know, linear momentum must always be conserved. We can resolve the different directions of momenta into 'x' 9horizontal) and 'y' (vertical) directions and ensure that each is constant.