1. Newton’s Third Law of Motion: Action and Reaction

2. Newton’s Third Law: Whenever one body exerts a force on a second body, the second body exerts an equal and opposite force on the first. “to every action there is always opposed and equal reaction” One force is called the action force and the other is called the reaction force. They are equal forces; neither force exists without the other. Forces occur in pairs. Ex. When you walk, you push against the floor and the floor in turn pushes against you. YouTube - conceptual physics action and reaction

3. Identifying action and reaction Make a statement about one of the forces in the pair, say the action force, in this form: Body A exerts a force on body B. Then the statement about the reaction force is simply: Body B exerts a force on body A. Ex. Action: tire pushes road Reaction: Road pushes tire Action: earth pulls ballReaction: ball pulls earth

4. Action: rocket pushes gas Reaction: gas pushes rocket YouTube - Space Shuttle Discovery 2006 Launch

5. Action and Reaction on bodies of different masses If a ball is falling, the Earth pulls the ball with the same force the ball pulls the Earth, but do to the massiveness of the Earth, we do not sense the Earth’s acceleration. This also can be explained considering a bullet in a rifle: The force the rifle exerts on the bullet is the same and opposite to the force the bullet exerts on the rifle; the bullet flies away, the rifle kicks. They experience different accelerations because they have different masses. For the bullet:For the rifle: a =F a = F m

6. Why action and reaction forces don’t cancel: Action and reaction forces act on different bodies, they never act on the same object. Hence, action and reaction forces never cancel one another. Read pg 58-61. You cannot have an action force unless there can be a reaction force. Ex. You can not hit a piece of a paper with a great action force, because the paper cannot exert a great reaction force.

7. Roller Coaster Physics Roller_Coaster_Physics_256k.asf

8. Newton’s Third Law of Motion: Action and Reaction