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Unformatted text preview: CHAPTER 26: RELAT IV I TY I. Galilean Relativity a. To describe a physical event, a frame of reference is necessary. b. Principle of Galilean relativity: the laws of mechanics must be the same in all inertial frames of reference. NOT accelerated! i. Inertial frames of reference: Netwon’s laws are valid and objects move in straight lines at constant speed unless acted on by a non-zero net force. c. There is no preferred frame of reference for describing the laws of mechanics. I I. The Speed of Light a. Galilean relativity (ex: throwing a ball in a plane, observer sees parabolic path and source sees up/down) in mechanics does not apply to electricity, magnetism, optics, or other areas. i. Inconsistent with Maxwell’s theory. Electromagnetic theory states speed of light is 3 × 10 6 m/s, but Galilean relativity states the speed of the pulse relative to the stationary observer is c+v. b. Electromagnetic theory predicts that light waves must propagate through free space at the speed of light, but did not account for the medium. i. Such a medium was called luminiferous ether. Present everywhere, even in empty space, and waves ere ether oscillations. Massless, but rigid medium. Have no effect on the motion of planets 1. Laws of electricity and magnetism would exist in the absolute frame at rest with respect to the ether. Would have to be modified in other cases. c. Earth was thought to be in motion through the ether, from the view of an experimenter on Earth. Ether wind was detected to measure the wind’s influence on the speed of light. d. The M ichelson-Morley Experiment : study designed to detect small changes in the speed of light by determining the Earth’s velocity relative to the hypothetical ether....
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