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# Chapter 7: Momentum

Difficulty Level: At Grade Created by: CK-12

Credit: CK-12 Foundation

[Figure1]

Momentum is another way of looking at how objects affect each others' motion.  Rather than looking at how forces change over the time of the interaction, we can look at how objects are moving before they interact and then after they interact.

## Chapter Outline

### Chapter Summary

1. Momentum is a vector quantity; $\vec p$ defined as the product of mass and velocity: $\vec p = m \vec v$
2. The impulse $F \Delta t$ is equal to the change in momentum $\Delta p : F \Delta t = \Delta p$
3. Momentum is a conserved quantity. For any isolated system the change in momentum of the system is zero: $\Delta p=0$
4. The center of mass of an isolated system always moves with constant velocity.
5. The kinetic energy of a system is conserved in elastic collisions.
6. The kinetic energy of a system is not conserved in inelastic collisions; however, momentum is still conserved!
7. In solving for momentum in two dimensions, the momentum must be conserved in each direction.

1. [1]^ Credit: CK-12 Foundation; License: CC BY-NC 3.0

Jun 27, 2013