Newton's Third law is probably the most famous of his laws. In laymen terms, it is:

These actions are forces, so you can remember this law as being every force has an equal and opposite force. Remember that these are two seperate forces, wich act upon two seperate objects, and so they do not cancel each other out.

The Third Law at first seems simple, but is a very important law. Everytime we interact with our surroundings we feel the Third Law. When you punch someone in the face, your hand not only applies a force to the person's face; the person's face applies a force to your hand. Since the person's face is softer than your hand it suffers more from the interaction. The Third Law is very important for space travel. In the cold void of space their is no air for jets to suck or for propellers to churn, and yet space ships can manouver in a vacuum. How do they do it? The engines propel gas particles out the back of the space ship. Since every force has an equal and opposite reaction force, the space ship will be propelled forwards. Because of the First Law space ships do not need very much fuel -- once they are moving they will stay in motion

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BOB (who isn't very bright) is tired of pushing his van to the gas station. He gets an idea -- "Hey! I go much faster when I am roller-blading than when I am walking. Why don't I wear my roller-blades!" So BOB gets his roller blades from the back of his van, and starts pushing.

Since every action has an equal and opposite reaction, when BOB pushes the van, the van pushes BOB. BOB weighs 50 kg, and the van weighs 2,000 kg. Thanks to the Second Law, you can compute how much BOB and the van will move after 1 second (hint: use A=f/m). Okay, now that you are done (you did do the problem, didn't you?), check your answer