2010 PHYSICS 002C Lecture 19

2010 PHYSICS 002C Lecture 19 - HYSICS 002C Lecture 19 May...

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HYSICS 002C Lecture 19 May 12, 2010 Serway and Jewett Chapter 9.4-6 – Relativity Clicker Q1: Lorentz contraction is when the length of a rapidly moving object measured by an observer at rest is a) more than; b) less than; c) the same as; d) irrelevant compared to; e) pixilated after the length determined by a commoving observer. Clicker Q2: Time dilation is when a time interval occurring on a rapidly moving object measured by an observer at rest is a) more than; b) less than; c) the same as; d) irrelevant compared to; e) proxibated during the time interval determined by a commoving observer. Clicker Q3: The 1887 Michelson-Morley experiment to detect the motion of the earth through the ether a) was too crude to give a meaningful answer; b) has been overturned by modern versions of the experiment; c) found no evidence for an ether; d) showed that the earth’s orbital speed around the sun is about 30 km/s; e) was a pointless endeavor which wasted millions of taxpayers’ dollars. Chap 9.3 Einstein’s principle of relativity All the laws of physics are the same in any local inertial reference frame (coordinate system). In the absence of an ether, this means that the speed of light is the same in any inertial reference frame. This principle is reasonable but its consequence is totally incomprehensible. It means that space and time are not separate as they would be in a Newtonian or Galilean world. Newton said: “Absolute time flows without relation to anything external” This is not correct when we have things moving very fast. We now work out the amazing consequences of special relativity, but don’t be disturbed by the heckler whose comments you will recognize by the blue writing mostly in upper case. SURE, SURE! 1
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2 Chap 9.4 Amazing consequences of Special Relativity: “The speed of light is the same for all inertial observers”. YEAH, YEAH – AMAZING, SHLAMAZING! Then think about Fig 9.4 A. The Relativity of Time. The boxcar experiment. Lightning strikes both ends of a speeding boxcar. O sees light from both ends at the same time and concludes that events and are simultaneous. O sees O’ is moving toward B so the light from event has a shorter distance to travel till it reaches O’, than the light from A. Thus O knows that O’ does not receive the signals simultaneously. O’ must agree, since the order of events occurring at the same point cannot be reversed or we could do time travel! A more quantitative analysis is as follows. Let and be the length of the car and track interval AB as observed by O and likewise for and except is not going to equal .
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This note was uploaded on 09/23/2010 for the course PH 02c taught by Professor Mile during the Spring '04 term at Riverside Community College.

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2010 PHYSICS 002C Lecture 19 - HYSICS 002C Lecture 19 May...

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