Phy107Lect19

Phy107Lect19 - HW#7: Chapter 11 Concept: 2, 6,14, 20, 32,...

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Wed. Oct 20 Phy107 Lecture 19 • 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 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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Wed. Oct 20 Phy107 Lecture 19 From Last Time… • World line : path of particle through space-time. • World line is made up of sequence of events, plotted as points in space-time. • Different inertial reference frames represented as ‘tilted’ coordinate axes on space-time diagram. • Event has different coordinates (space & time) measured on these coordinate axes. • But the combination x 2 - c 2 t 2 is ‘universal’ in that it is measured to be the same for all observers. • Suggests that space & time are ‘components’ of space- time, a conceptually new quantity.
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Wed. Oct 20 Phy107 Lecture 19 Today: Forces, Work, and Energy in Relativity or, What about Newton’s laws? • Relativity dramatically altered our perspective. – But clearly objects still move, spaceships are accelerated by thrust, work is done, energy is converted. • All the things we studied in the first six weeks. • But some things are different in relativity.
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Wed. Oct 20 Phy107 Lecture 19 • As motorcycle velocity approaches c , V ball also gets closer and closer to c • End result: nothing exceeds the speed of light. V ball = v ball + v motorcyle 1 + v ball v motorcycle c 2 v motorcycle Observes ball to have velocity V ball =0.96c motorcycle v ball ball
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Wed. Oct 20 Phy107 Lecture 19 Newton again • Fundamental relations of Newtonian physics acceleration = Force / mass acceleration = (change in velocity)/(change in time) Work = Force x distance Kinetic Energy = (1/2) (mass ) x ( velocity ) 2 Change in Kinetic Energy = net work done • Newton predicts that a constant force gives – Constant acceleration – Velocity proportional to time – Kinetic energy proportional to (velocity) 2
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Wed. Oct 20 Phy107 Lecture 19 Momentum • Newton’s laws become simpler when we use the momentum of a particle.
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Phy107Lect19 - HW#7: Chapter 11 Concept: 2, 6,14, 20, 32,...

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