Newtons Laws of Motion.

Sir Issac Newton made the three laws of motion we know of today. His first law was the law of inertia. He said every object was in a state of rest ,or not moving, and would remain so until acted upon. The example you see at http://science.discovery.com/interactives/literacy/newton/newton.html is you hitting an apple with a worm in it. However, if you suddenly stop the apple, the worm will continue moving. Its like when you suddenly slam on the brakes of a car, you hit the seat belt hard. You were moving at the same rate as the car until you suddenly stopped the cars movement. You, were still going until you hit the seat belt. His second law states that if the forces acting upon an object were balanced, the object wouldn't move. If two people were exerting an equal amount of force on say a rope, it wouldn't move. His third law is the most well known. It states every action have an equal and opposite reaction. If I threw a ball on the floor, it would bounce back, with the height it bounces upward with is equal to the force I applied throwing it.  http://www.physics4kids.com/files/motion_laws.html