Newton's Third Law of Motion
- for every action there is an equal and opposite reaction
any time a force is applied to an object there is an equal force that pushes back in the opposite direction
When a bullet is propelled from the chamber of a gun an equal force is applied in a backward motion often felt by the shooter and is called "recoil".
[youtube=http://www.youtube.com/watch?v=7y7KjanpWOk]
This is best visually illustrated through the "Newton's Cradle". Here you can see that as one ball is pulled back and released it applies that force equally on the remaining balls. While the original force propels a single ball from the other side of the cradle causing it to mirror the original action taken on the first ball. The opposite force stops the original ball. The cycle continues until momentum is lost.
[youtube=http://www.youtube.com/watch?v=_UxYnWpqwbY]