Phy107Lect20

# Phy107Lect20 - HW#7: Chapter 11 Concept: 2, 6,14, 20, 32,...

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Fri. Oct 22 Phy107 Lecture 20 • Hour Exam 2 : Wednesday, Oct. 27 • In-class (1300 Sterling Hall) • Twenty multiple-choice questions 10, 11 (Relativity) • You should bring Your student ID 1 page notes, written double sided Calculator Pencil for marking answer sheet HW#7: Chapter 11 Concept: 2, 6,14, 20, 32, 34 Problems: 4, 6

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Fri. Oct 22 Phy107 Lecture 20 General Relativity and Gravity • Special Relativity deals with inertial reference frames , frames moving with a constant relative velocity. • It has some rather unusual predictions – Time dilation – Length contraction – Mass-energy equivalence • These were motivated by thought experiments based on simple postulates. • General Relativity also motivated by some simple thoughts about gravity and free-fall.
Fri. Oct 22 Phy107 Lecture 20 The Equivalence Principle • Led Einstein to postulate the Equivalence Principle. Clip from Einstein Nova special.

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Fri. Oct 22 Phy107 Lecture 20 Equivalence principle Accelerating reference frames are indistinguishable from a gravitational force.
Fri. Oct 22 Phy107 Lecture 20 Try some experiments Constant velocity Cannot do any experiment to distinguish accelerating frame from gravitational field t=0 t=t o t=2t o Floor accelerates upward to meet ball Constant accel. t=0 t=t o t=2t o

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Fri. Oct 22 Phy107 Lecture 20 Light follows the same path Path of light beam in our frame Velocity = v t =0 Velocity = v + at o t = t o Path of light beam in accelerating frame Velocity = v +2 at o t =2 t o
Fri. Oct 22 Phy107 Lecture 20 Is light bent by gravity? • If we can’t distinguish an accelerating reference frame from gravity… • and light bends in an accelerating reference frame… • then light must bend in a gravitational field But light doesn’t have any mass. How can gravity affect light?

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Fri. Oct 22 Phy107 Lecture 20 Light travels in a straight line • In some ways, the path of light defines a straight line. • Surveyors use laser to set heights. • Can use a laser level to put up shelves. • Seems to move in exactly a straight line. Maybe we are confused about what a straight line is
Fri. Oct 22 Phy107 Lecture 20 What is a straight line? • Claim that these are all straight lines

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Fri. Oct 22 Phy107 Lecture 20 Straight is shortest distance • They are the shortest distances determined by wrapping string around a globe. On a globe, they are called ‘great circles’. In general, geodesics. • This can be a general definition of straight,
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## This note was uploaded on 01/05/2012 for the course PHYS 107 taught by Professor N/a during the Spring '08 term at Wisconsin.

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Phy107Lect20 - HW#7: Chapter 11 Concept: 2, 6,14, 20, 32,...

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