Chapter 9 9-2 Momentum and Its Conservation

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

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.

Figure 9-5 p 181 shows momentum.

Law of Conservation and Momentum Momentum of any closed, isolated system does not change. Fig 9-5 207 pa + pb = pa + p  b mava + mbvb = mava  + mbvb 

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

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.

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.

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

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.