1. A body at rest will remain at rest and one in motion will remain in motion, until and unless acted upon by an external force. (Law of inertia)

2. The rate of change of momentum of a body is proportional to the resultant force acting on the body in the same direction as its motion. (F = ma)

3. For every action there is an equal an opposite reaction.

Note: These laws apply only at speeds not approaching the speed of light and do not apply to sub-atomic particles.