Lect03-Phys172s11-(2.1-2.4-Relativity,Momentum_principle)

# Lect03-Phys172s11-(2.1-2.4-Relativity,Momentum_principle) -...

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Spring 2011 PHYS 172: Modern Mechanics Lecture 3 – Relativity, The Momentum Principle Read 2.1-2.4 Average rate of change of momentum The stronger the interaction, the faster is the change in the momentum f i f i p p p t t t - Δ = Δ - Average rate of change of momentum: Instantaneous rate of change of momentum: 0 lim t dp p dt t Δ → Δ = Δ Units: 2 kg m s

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The principle of relativity Physical laws work in the same way for observers in uniform motion as for observer at rest Inertial reference frame Inertial frame: a frame in which Newton’s first law of motion is valid ? Is the Earth’s surface an inertial reference frame? Physical laws work in the same way in any inertial frame
Special theory of relativity Published in 1905. Based on the principle of relativity and on experimental fact that c =const in all inertial reference frames Time dilation: time runs slower in moving reference frames Length contraction: object length becomes shorter in moving reference frame Light photon frame: time does not exist, the universe has zero length! 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 = + - avg v (=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
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## This note was uploaded on 04/23/2011 for the course PHYS 172 taught by Professor ? during the Spring '08 term at Purdue.

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Lect03-Phys172s11-(2.1-2.4-Relativity,Momentum_principle) -...

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