1. The Conservation of Momentum Section 9.2
Physics

2. Objectives
Relate Newton’s third law of motion to conservation of momentum in collisions and explosions.
Recognize the conditions under which the momentum of a system is conserved.
Apply conservation of momentum to explain the propulsions of rockets.
Solve conservation of momentum problems in two dimensions by using vector analysis.

3. Two-Particle Collisions
Newton’s Third Law of Motion: For every action there is an equal but opposite reaction.
In this action-reaction pair; momentum is always conserved.
Law of Conservation of Momentum: The momentum remains the same for any closed system upon which there is no net external force.

4. Two-Particle Collisions

5. Law of Conservation of Momentum
pA1 + pB1 = pA2 + pB2
This states that the momentum of the balls is the same before and after the collision.

6. Momentum in a Closed System
Internal forces: are pushing
against the sides of the flask
and the flask is pushing back
with the same force.
Closed system: a system
that doesn’t gain or lose any
mass.

7. Momentum in a Closed System
No system on Earth can be said to be a closed system.
There is always the interaction between the system and the environment.

8. Practice Problems
Pg. 210
7-12
Pg. 214
13-16

9. Two-Dimensional Collisions
The Law of Conservation of Momentum holds true for one-dimensional collisions and two-dimensional collisions.
Think of Pool…
pA1 = pA2 + pB2
There are horizontal and vertical components after the collision.

10. Practice Problems
Pg. 216
17-18