Lect08

# Lect08 - PHYS 172 Modern Mechanics Fall 2011 Lect 8&9 Rate...

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Fall 2011 PHYS 172: Modern Mechanics Lect. 8&9 - Rate of Change of Momentum Read 5.1-5.7 1

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TODAY Forces on a System Changing Momentum Circular Motion 2
Rules for Identifying Forces on a System Choose "The System" Draw arrows for all forces due to objects in the surroundings that interact with The System. – Objects that touch The System – Objects that interact from a distance Label each force with the name of the object in the surroundings 3

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Example – Hanging Ball System: Ball Surroundings: Earth, Wire Free-body diagram ! F net = d ! p dt 4
Equilibrium with two strings net dp F dt = ! ! m Static equilibrium mg ! ! F 2 ! F 1 Know mass. Need to know the force F 2 required to achieve θ x y 0 dp dt = ! ! ! F 1 + ! F 2 + m ! g = ! 0 Geometrical: mg ! ! F 2 ! F 1 ! F 2 = mg tan ! ! F 2 = mg tan ,0,0 5

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Perpendicular component (to trajectory) Parallel component (Along trajectory) Changing momentum ! p
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## This note was uploaded on 12/07/2011 for the course PHYS 172 taught by Professor ? during the Fall '08 term at Purdue.

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Lect08 - PHYS 172 Modern Mechanics Fall 2011 Lect 8&9 Rate...

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