PHY213_Chapter26_Sec1to4

PHY213_Chapter26_Sec1to4 - Chapter 26 Relativity Relativity...

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Chapter 26 Relativity
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General Physics Relativity I Sections 1–4
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General Physics Basic Problems The speed of every particle of matter in the universe always remains less than the speed of light Newtonian Mechanics is a limited theory It places no upper limit on speed It breaks down at speeds greater than about 10% of the speed of light (v > .1c) Newtonian Mechanics becomes a specialized case of Einstein’s Theory of Special Relativity When speeds are much less than the speed of light v<<c
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General Physics Galilean Relativity Choose a frame of reference Necessary to describe a physical event According to Galilean Relativity, the laws of mechanics are the same in all inertial frames of reference An inertial frame of reference is one in which Newton’s Laws are valid Objects subjected to no forces will move in straight lines
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General Physics Galilean Relativity, cont. A passenger in an airplane throws a ball straight up It appears to move in a vertical path This is the same motion as when the ball is thrown while standing at rest on the Earth The law of gravity and equations of motion under uniform acceleration are obeyed 2 0 2 1 0 gt t v y x y = =
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General Physics Galilean Relativity, cont There is a stationary observer on the ground Views the path of the ball thrown to be a parabola The ball has a velocity to the right equal to the velocity of the plane The law of gravity and equations of motion under uniform acceleration are still obeyed 2 0 2 1 gt t v y vt x y = =
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General Physics Galilean Relativity, final The two observers disagree on the shape of the ball’s path Both agree that the motion obeys the law of gravity and Newton’s laws of motion Both agree on how long the ball was in the air Conclusion : There is no preferred frame of reference for describing the laws of mechanics
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General Physics Galilean Relativity – Limitations Galilean Relativity does not apply to experiments in electricity, magnetism, optics, and other areas Results do not agree with experiments According to Galilean relativity, the observer S should measure the speed of the light pulse as v+c Actually observer S measures the speed as c
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General Physics Luminiferous Ether Classical physicists (Maxwell, Hertz, etc.) compared electromagnetic waves to mechanical waves Mechanical waves need a medium to support the disturbance (air, water, string, etc.) The luminiferous ether was proposed as the medium required (and present) for light waves to propagate Present everywhere, even in empty space Massless, but rigid medium Could have no effect on the motion of planets or other objects
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General Physics Verifying the Luminiferous Ether Associated with the ether was an absolute frame of reference in which light travels with speed c The Earth moves through the ether, so there should be an “ether wind” blowing
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This note was uploaded on 08/25/2009 for the course PHY 213 taught by Professor Cao during the Summer '08 term at Kentucky.

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PHY213_Chapter26_Sec1to4 - Chapter 26 Relativity Relativity...

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