1. Notes: Chapter 11.3 Newton’s Third Law of Motion and Momentum

2. Newton’s Third Law of Motion For every action force there is an equal and opposite reaction force. Called force pairs or action/reaction pairs Force pairs do not act on the same object, and thus don’t always have the same effect! Movie: Newton's third

3. Newton’s Third Law of Motion The equal forces don’t always have the same effect, though. According to the second law, F=ma. You will have different results depending on their masses.

4. Momentum An extension of Newton’s Third Law…tells what will happen from the action/reaction Is equal to mass x velocity p = mv units have no name, just kg. m/s

5. Momentum & Collisions In collisions, momentum is conserved for the system (both balls), that is, it is the same for all the objects before and after the collision. Called The Law of Conservation of Momentum

6. Law of Conservation of Momentum The system is both of the pool balls. If they have the same mass: – the total momentum before is mv + m0 = mv – the total momentum after is m0 + mv = mv

7. Law of Conservation of Momentum What if the red ball has twice the mass of the white one? How fast will it move? What if the white ball has twice the mass of the red one? How fast will it move?

8. Momentum & Collisions Elastic collision : objects hit each other and don’t stick together (bounce off) Inelastic collision : objects hit each other and stick together Momentum and Collisions Conservation of Momentum