Chapter 7 Relativity

n Special Theory of Relativity – Einstein 1905 – space contraction and time dilation n General Theory of Relativity – Einstein 1916 – theory of gravitation

7.1 Special Relativity n Problems with Electromagnetic Radiation – Sound requires a medium? – Shouldn’t electromagnetic waves also need a medium? – Physicist postulated a medium called ether.

Thought Experiments n What is the relative speed between you and the other car? n Answer: 35m/s - 25 m/s = 10 m/s Car You 35m/s 25m/s

Thought Experiments n What is the relative speed between you and the beam of light? n Answer: 300,000,000m/s - 25 m/s n = 299,999,975 m/s ? n No, no, no! Real Answer: 300,000,000 m/s Flashlight at rest You 300,000,000m/s 25m/s

Conclusion n Experiments show that “the speed of light in a vacuum is the same for all observers, independent of their motion”. n This suggests that something is wrong with the concept of ether. n Michelson and Moley in 1887 showed with an experiment that the speed of light did not depend of the motion of the observer.

Problems with Simultaneity Explosions in a Train Example At Rest

n There is no experiment we can perform to tell us which inertial from is moving and which is at rest. n There is no ‘preferred’ inertial frame.

7.2 Time Dilation MIRROR Light Clock at Rest L Tick-Tock Time for the Clock at Rest

Light Clock in Motion MIRROR Tick-Tock Time for the Clock in Motion MIRROR v v

End of Chapter 7