lecture 14

lecture 14 - Lecture 14 Momentum Impulse Conservation of...

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1 Lecture 14 Momentum Impulse Conservation of momentum Center of mass Motion of the center of mass

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2 Consider two interacting bodies: F 21 F 12 If we know the net force on each body then t m t = = net F a v The velocity change for each mass will be different if the masses are different.
3 t m = 21 1 1 F v Rewrite the previous result for each body as t t m - = = 21 12 2 2 F F v Combine the two results: ( 29 ( 29 i f i f m m m m 2 2 2 1 1 1 2 2 1 1 v v v v v v - - = - - =

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4 The quantity (m v ) is called momentum ( p ). p = m v and is a vector. The unit of momentum is kg m/s; there is no derived unit for momentum.
5 From slide (3): 2 1 2 2 1 1 p p v v - = - = m m The change in momentum of the two bodies is “equal and opposite”. Total momentum is conserved during the interaction; the momentum lost by one body is gained by the other.

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6 Definition of impulse: ( 29 p F J = = t t dt t 0 Note: dt d t p F p F = = net av Limit as t 0 Both expressions refer to the external forces acing on the system.
7 Example: Shown are three different time dependent forces, compute the impulse on an object of mass m due to each force. t

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This note was uploaded on 07/04/2011 for the course PHYS 121 taught by Professor Staff during the Spring '11 term at ASU.

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lecture 14 - Lecture 14 Momentum Impulse Conservation of...

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