sy12_oct15_07hc

# sy12_oct15_07hc - Physics 207 Lecture 12 Oct 15 Physics...

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Physics 207: Lecture 12, Pg 1 Physics 207, Physics 207, Lecture 12, Oct. 15 Lecture 12, Oct. 15 Agenda: Finish Chapter 9, start Chapter 10 Agenda: Finish Chapter 9, start Chapter 10 Assignment: Assignment: HW5 due Wednesday HW5 due Wednesday HW6 posted soon HW6 posted soon Collisions Momentum conservation in 2D Impulse

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Physics 207: Lecture 12, Pg 2 Transition from forces to conservation laws Transition from forces to conservation laws Newton’s Laws Conservation Laws Conservation Laws Newton’s Laws They are different faces of the same physics phenomenon for special “cases”
Physics 207: Lecture 12, Pg 3 Lecture 12, Lecture 12, Exercise 1 Exercise 1 Momentum Conservation Momentum Conservation A. Box 1 B. Box 2 C. Same Two balls of equal mass are thrown horizontally with the same initial velocity . They hit identical stationary boxes resting on a frictionless horizontal surface. The ball hitting box 1 bounces elastically back, while the ball hitting box 2 sticks. In which case does the box ends up moving fastest ? No external force then, vectorially, COM 1 2

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Physics 207: Lecture 12, Pg 4 Lecture 12, Lecture 12, Exercise 1 Exercise 1 Momentum Conservation Momentum Conservation Which box ends up moving fastest ? Examine the change in the momentum of the ball. In the case of box 1 the balls momentum changes sign and so its net change is largest . Since momentum is conserved the box must have the largest velocity to compensate. (A) (A) Box 1 (B) (B) Box 2 (C) (C) same 1 2
Physics 207: Lecture 12, Pg 5 A perfectly inelastic collision in 2-D A perfectly inelastic collision in 2-D Consider a collision in 2-D (cars crashing at a slippery intersection. ..no friction). v v 1 v v 2 V V before after m 1 m 2 m 1 + m 2 If no external force momentum is conserved. Momentum is a vector so p x , p y and p z

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Elastic Collisions Elastic Collisions Elastic means that the objects do not stick. There are many more possible outcomes but, if no
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sy12_oct15_07hc - Physics 207 Lecture 12 Oct 15 Physics...

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