1. Momentum – Key Ideas

2. Review – If a force F x is applied to a body over a displacement  x, the product F x  x = (Fcos  )  x = Work

3. Review – If a force F x is applied to a body over a displacement  x, the product F x  x = (Fcos  )  x = Work If the friction force is less than F x, the work increases the object’s Kinetic Energy

4. NOW ask: What is the effect of applying a force over a time interval? Vocabulary: events in which objects apply forces to each other are called INTERACTIONS

5. NOW ask: What is the effect of applying a force over a time interval? Vocabulary: events in which objects apply forces to each other are called INTERACTIONS You predicted the outcomes of some interactions.. How did you do?

6. You predicted the outcomes of some interactions.. How did you do? A general rule about interaction forces:

7. Forces come in

8. A general rule about interaction forces: Forces come in This is Newton’s 3 rd Law.

10. Impulse = Change of momentum

12. The impulse is the area under the force vs. time curve. The average force gives the same impulse to the object in the time interval Δt as the real time-varying force.

13. Conservation of Momentum The principle of conservation of momentum states when no external forces act on a system consisting of two objects that collide with each other, the total momentum of the system remains constant in time. Specifically, the total momentum before the collision will equal the total momentum after the collision.

14. Conservation of Momentum Mathematically: Momentum is conserved for the system of objects. The system includes all the objects interacting with each other. Assumes only internal forces are acting during the collision. Can be generalized to any number of objects.

15. Force as a function of time for the two colliding particles.

16. In all collisions, total momentum is conserved. We consider two types of collisions in one dimension: 1. Totally elastic 2. Totally inelastic

17. Perfectly Inelastic Collisions When two objects stick together after the collision, they have undergone a perfectly inelastic collision. Conservation of momentum becomes

18. Elastic Collisions Both momentum and kinetic energy are conserved.