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# class07 - Announcements Reading for Friday: Chapter 2.1-2.5...

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Announcements • Reading for Friday: Chapter 2.1-2.5 • HW#2 due at beginning of next class Today’s class • Length contraction • Lorentz transformation (relativistic version of Galileo transformation) S x z y S' x' z' y' v (x,y,z,t) (x',y',z',t') Length contraction (Consequence of time dilation and vice versa) Quiz on the reading Proper length of an object is the length of the object measured… A – …in its rest frame. Q1 B – …in any inertial frame. C – …in the inertial frame in which both ends of the object have the same event coordinates. D – …in the frame in which the object is not rotating. E – …by the speed of light. Length of an object ... -3 -2 -1 0 1 2 3 ... This stick is 3m long. I measure both ends at the same time in my frame of reference. “Same time” or not doesn’t actually matter here, because the stick isn’t going anywhere. This length, measured in the stick’s rest frame, is its proper length . ‘Proper length’ Proper length: Length of object measured at rest / object measured in the frame where it is at rest (use a ruler) ... -3 -2 -1 0 1 2 3 ...

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Remember ‘proper time’ Proper time: Time interval Δt = t 2 – t 1 between two events measured in the frame, in which the two events occur at the same spatial coordinate, i.e. time interval that can be measured with one clock . v Length of an object ... -3 -2 -1 0 1 2 3 ... Observer in S measures the proper length L of the blue object. Another observer comes whizzing by at speed v. S v S’ This observer measures the length of the stick, and keeps track of time . Event 1 – Origin of S’ passes left end of stick. 0 Length of an object ... -3 -2 -1 0 1 2 3 ... S v S’ 0 Event 1 – Origin of S’ passes left end of stick. Event 2 – Origin of S’ passes right end of stick.
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## This note was uploaded on 08/24/2010 for the course PHYS 2130 taught by Professor Staff during the Spring '08 term at Colorado.

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class07 - Announcements Reading for Friday: Chapter 2.1-2.5...

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