1. Chapter 9 9-2 Momentum and Its Conservation

2. 9.2 Conservation of Momentum
System is a defined collection of obj
ects.

3. Newton’s 3rd Law & Momentum
Impulse-Momentum Theorem is another way of stating Newton’s 3rd Law.
A system is isolated if no net external forces acts on it.
The momentum is conserved.

4. Figure 9-5 p 181 shows momentum.

5. Law of Conservation and Momentum
Momentum of any closed, isolated system does not change.
Fig
pa + pb = pa + p  b
mava + mbvb =
mava  + mbvb 

6. This fig. shows that when cars A & B collide, p is conserved.
Example Problem 209
Practice Problems 210

7. Internal and External Forces
Internal forces cannot change total momentum.
External forces the system is not closed and momentum is not conserved.
It’s important to define a system carefully.
The total momentum of an isolated system is constant.

8. Conservation of Momentum in Two Dimensions
Ex Pr Recoil 212 Prac Pr 213
Conservation of Momentum in Two Dimensions
Total momentum is the vector sum of the momenta of all the parts of the system.

9. Figure 9-10 p 214
Ex Problem 215-6
Prac Pr 216

10. 9.2 The Conservation of Momentum
Newton’s 3rd law is another statement of the law of conservation of momentum.
The law of conservation of momentum states: In a closed, isolated system, the total momentum of the system does not change.
The momentum of a system changes when it is not isolated, that is, when a net external force acts on it.