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Announcements. Exam 2 is next time. Will cover Chapters 3 – 6. Sample Questions are posted. Relativity According to Galileo. According to Galileo light should add, too. Speed observed by S` is c (299792458 m / s ) Speed observed by S is c + v If the train is moving at 100 m / s then

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  1. Announcements • Exam 2 is next time. Will cover Chapters 3 – 6. Sample Questions are posted.

  2. Relativity According to Galileo

  3. According to Galileo light should add, too Speed observed by S` is c (299792458 m/s) Speed observed by S is c + v If the train is moving at 100 m/s then c = 299792558 m/s

  4. Moving Reference Frames

  5. An example of moving reference frames using normal addition

  6. Maxwell’s Equations aren’t invariant under Galilean transformation The equations governing the electromagnetic force change when a Galilean transformation is done on them

  7. What is the reference frame of light?

  8. The Michelson-Morley Experiment They were trying to detect the luminiferous aether. They didn’t find it.

  9. In 1889 George FitzGerald proposed another type of transformation Hendrik Lorentz added in a transformation of time as well as space so we now call it a Lorentz transformation

  10. In 1905 Einstein explained why the Lorentz transformations are the correct transformations

  11. Einstein had two basic postulates for Special Relativity • The laws of physics are the same in all inertial reference frames. • The speed of light in a vacuum is the same in all inertial reference frames The “special” of special relativity is that it only applies if the relatives velocities are constants. There must be no acceleration.

  12. The problem of simultaneity Different observers do not see the two events as simultaneous Watch YouTube Simultaneous events video

  13. Time Dilation: Time is not absolute The light travel time is shorter for the observer that is stationary with the light than the outside observer that sees the light moving Watch Time Dilation video

  14. The amount of time dilation depends on the relative speed Note that it is always the other clock that runs slow. Your clock, the one stationary with respect to you, always runs at the right speed. It doesn’t matter who is moving. In fact, you can’t tell who is moving, only relative motions.

  15. Length Contraction Consider a round trip to Alpha Centauri at 99.99% the speed of light. For the person making the trip it takes a few months but for someone left on Earth it takes a little more than 8 years. Since nothing can move faster than the speed of light, the distance to Alpha Centauri to the person making the trip is only a few light months. The distance in the direction of motion shrinks. Play with Cal Tech Space-time applet

  16. Five Minute Essay The Wyle E. Coyote trap a relativistic train caper Tunnel doors courtesy of the Acme Corp.

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