1. Newton’s Third Law

2. Objective At the end of today, you will be able to: Demonstrate that whenever one object exerts a force on another, an equal amount of force is exerted back on the first object. PS D-24

3. 3rd Law - Action and Reaction Newton's third law of motion states that when an object exerts a force on a second object, the second object exerts a force on the first that is equal in strength and opposite in direction. Simplified = for every force there is an equal and opposite force. We can call one force the action force, and the other the reaction force These forces are = in strength and opposite in direction

4. 3rd Law - Action and Reaction Concept Check Question - When a heavy football player and a light one run into each other, does the light player really exert as much force on the heavy player as the heavy player exerts on the light one? Answer - Yes. The forces each exert on the other have equal strengths.

5. 3rd Law - Action and Reaction Since the forces are equal, is the effect of the force on the heavy player the same as the effect of the force on the light one? No. Although the forces are =, the effects of these equal forces are unequal. The mass of each player plays a role in the effect of the force applied. There is a difference between the force and the effect of force.

6. Identifying Action and Reaction A simple way to ID action and reaction forces: 1. ID the interaction: Object A interacts w/ Object B 2. Then action and reaction forces can be stated in this form: Action: Object A exerts a force on object B Reaction: Object B exerts a force on object A

7. Identifying Action and Reaction This is easy to remember - If the action is A on B, the reaction is B on A Ex - Hand on Wall The action is your hand (object A) exerting a force on the wall (object B) Then, the reaction is the wall (B) exerting a force on your hand (A).