5Law of Conservation and Momentum Momentum of any closed, isolated system does not change.Figpa + pb = pa + p bmava + mbvb =mava + mbvb
6This fig. shows that when cars A & B collide, p is conserved. Example Problem 209Practice Problems 210
7Internal 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.
8Conservation of Momentum in Two Dimensions Ex Pr Recoil 212 Prac Pr 213Conservation of Momentum in Two DimensionsTotal momentum is the vector sum of the momenta of all the parts of the system.
109.2 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.