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Phy107Lect18

# Phy107Lect18 - From Last Time Events observed to be...

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Mon. Oct 18 Phy107 Lecture 18 From Last Time… •Events observed to be simultaneous in one frame may not be simultaneous in another. •Measured interval between events different for different observers. — Time dilation. Proper time is that measured in frame where events occur at same spatial location — All other measured times are longer by factor γ •Measured distance between events different for different observers. — Length contraction. Proper length is that measured in frame where events are simultaneous. — All other lengths are shorter by factor γ

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Mon. Oct 18 Phy107 Lecture 18 Hour Exam 2 • Wednesday, Oct. 27 • In-class (1300 Sterling Hall) • Twenty multiple-choice questions • Will cover 8.1-8.6 (Light and E&M) 9.1-9.5 (E&M waves and color) 10, 11 (Relativity) • You should bring – 1 page notes, written double sided – Calculator – Pencil for marking answer sheet
Mon. Oct 18 Phy107 Lecture 18 Time dilation I am on jet traveling at 500 mph and throw a ball up and catch it in my hand. You are on the ground and watch me. How do the time intervals compare for you and I? A. t jet = t Earth B. t jet > t Earth C. t jet < t Earth Proper time is measured in the jet frame (events occur at same spatial location). Times measured in other frames are longer (time dilation).

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Mon. Oct 18 Phy107 Lecture 18 Geometrical space-time diagrams • We came to these conclusions via particular thought experiments. • Were able to make quantitative determinations, using sequential logical arguments. (e.g. to get from time dilation to length contraction) • Shortly after relativity, Minkowski developed the space-time diagram. • A geometrical way to display observations in different reference frames.
Mon. Oct 18 Phy107 Lecture 18 Events and relativity • In relativity, it is helpful to think of ‘events’ – E.g. a lightning strike, – a flashbulb going off, – a spaceship arriving at a planet • Describe event by spatial position and time as ( x , t ) • Can think of this as a point in two-dimensional space, but axes would have different units ( meters, sec) • Use event ‘coordinates’ of ( x , ct ).

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Phy107Lect18 - From Last Time Events observed to be...

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