Ch07 lecture

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!!