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Albert Einstein and the Theory of Relativity
Chapter 7
Great Idea:All observers, no matter what their frame of
reference, see the same laws of nature
Chapter Outline
• Frames of Reference• Special Relativity• General Relativity
Frames of Reference
Descriptions in Different Reference Frames
• Coin’s path appears different depending on your frame of reference
The Principle of Relativity
• Baseball vs. Light• Einstein’s solution:
– The laws of nature are not the same in all frames of reference
– Maxwell’s equation could be wrong– Our intuitions about the addition of velocities could be
wrong
• Principle of Relativity– Every observer must experience the same natural laws
• Special relativity• General relativity
• The speed of light, c, is the same in all reference frames
Special Relativity
Time Dilation
• Time Dilation–Moving clock
appears to tick more slowly
The Size of Time Dilation
• Calculation of time dilation– tGG=tMM
– Stationary ground-based observer• tGG=d/c
• Distance traveled by light in 1 tick
Distance and Relativity
• Length Contraction– Moving object
appears shorter
So What About the Train and the Flashlight?
• Addition of velocities–Valid at small velocities–Not valid near speed of light
Mass and Relativity
• Third consequence– Mass is lowest for stationary objects
• Conclusions:– Nothing moving less than speed of light can be
accelerated to or past c– Object above c cannot be decelerated– Objects at c have zero rest mass
Mass and Energy
• Einstein– All objects contain a rest energy
– Mass can be converted to energy and vice versa
2mcE =
General Relativity
The Nature of Forces
• Gravitational forces and acceleration–Frame of reference
The Nature of Forces
• Newton vs. Einstein
Predictions of General Relativity
• The gravitational bending of light
• Planetary orbits
• The gravitational redshift
Who Can Understand Relativity?
Everyone!!