Lect03-Phys172s10-(2.1-2.6-momentum_principle)

# Lect03-Phys172s10-(2.1-2.6-momentum_principle) - PHYS 172:...

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Spring 2009 PHYS 172: Modern Mechanics Lecture 3 - The Momentum Principle Read 2.1-2.6 RELATIVITY “Physical laws work in the same way for observers in uniform motion as for observers at rest.” The position update formula ( ) f i avg f i r r v t t = + - h h h avg v h (=in all inertial reference frames)

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RELATIVITY “Physical laws work in the same way for observers in uniform motion as for observers at rest.” The position update formula ( ) f i avg f i r r v t t = + - h h h avg v h avg v h (=in all inertial reference frames) Note: all parameters must be measured in respect to the selected reference frame to predict motion in respect to that reference frame The Momentum Principle p mv γ = a a 2 1 1 v c = - a An object moves in a straight line and at constant speed except to the extent that it interacts with other objects The Momentum Principle net p F t Δ = Δ a a Change of momentum is equal to the net force acting on an object times the duration of the interaction • Assume that F does not change during Δ t What is “force” F ? • measure of interaction. • defined by the momentum principle. 2 F units: N m kg/s (Newton)
The principle of superposition net p F t Δ = Δ a a push F a gravity F a earth F a Net force The Superposition Principle: The net force on an object is the vector sum of all the individual forces exerted on it by all other objects Each individual interaction is unaffected by the presence of other interacting objects Misconception: need constant force to maintain motion ? Why planets move ? Ignored

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## This note was uploaded on 02/07/2010 for the course PHYS 17200 taught by Professor Gaboracsathy during the Spring '09 term at Purdue.

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Lect03-Phys172s10-(2.1-2.6-momentum_principle) - PHYS 172:...

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