Chapters 15 and 16 - Special Relativity

Terms and Objectives

New terms in Chapters 15 and 16:

special relativity	postulate	space-time	time dilation
Correspondence Principle	rest mass	rest energy	relativistic velocity

Indiana Physics Standards relating to Chapters 15 and 16:

P.1.4 Employ correct units in describing common physical quantities.

P.2.4 Describe how the Scottish physicist James Clerk Maxwell used ... to predict the existence of electromagnetic waves and predict that light was just such a wave.

P.2.5 Describe how among the surprising ideas of Albert Einstein's Special Relativity is that nothing can travel faster than the speed of light, which is the same for all observers no matter how they or the light source happen to be moving, and that the length of time interval is not the same for observers in relative motion.

P.2.6 Explain that the special theory of relativity (E = mc²) is best known for stating that any form of energy has mass and that matter itself is a form of energy. (BHS Physics "Power Standard")

P.2.7 Describe how General Relativity theory pictures Newton's gravitational force as a distortion of space and time.

Core Ideas in Chapters 15 and 16:

The core ideas in Chapter 15 and 16 include:

The Special Theory of Relativity
- was created by Albert Einstein in 1905.
- deals with objects that move at constant velocity only.
- has two postulates (foundation ideas).
  - Everyone measures the same speed of light (in a vacuum). The speed of light is not a relative quantity.
  - The speed of light, c, is approximately 3 x 10⁸ m/s = 300,000 km/s = 186,000 miles/s
  - The laws of physics operate the same way for everyone.
- Implications:
  - Space and time are not separate concepts, but are combined into the concept of space-time.
  - Time slows down for objects moving at high speeds.
  - The mass of moving objects increase as their speed increases.
  - The length of moving objects decreases (in the direction of motion) as their speed increases.
  - These effects are too small to measure at "human" velocities, but become apparent for sub-atomic particles moving with speeds that are a large fraction of the speed of light.
  - The speed of light, c, is the "ultimate speed limit of the universe."
- E=mc²
  - gives the energy equivalent, E, of an object of mass m at rest.
  - says that mass is a very condensed and organized form of energy.
The Correspondence Principle
- Two physical theories must agree where ever they overlap.
- The theory of relativity must produce the same results as classical physics for "human scale" motions.
The General Theory of Relativity
- was created by Albert Einstein in 1915.
- deals with motion in general, including accelerated motion.
- is also a theory of gravity, since Einstein showed that accelerated motion and the action of a gravitational field are equivalent (Equivalence Principle).
- replaces the concept of force with the notion of "curvature of space-time."

Chapters 15 and 16 Learning Targets:

When you complete Chapters 15 and 16, you should be able to:

... describe the conflict between Maxwell's and Newton's predictions of the speed of light.
... identify the scientist responsible for the theories of Special and General Relativity.
... state the two postulates of special relativity.
... describe, in general terms, what happens to the passage of time for objects moving with relativistic velocities.
... describe, in general terms, what happens to the length of objects moving with relativistic velocities.
... describe, in general terms, what happens to the mass of objects moving with relativistic velocities.
... explain the meaning of the equation E = mc².
... discuss the Correspondence Principle in terms of the results of special relativity and classical mechanics.
... describe how General Relativity theory pictures Newton's gravitational force as a distortion of space and time.

last update April 27, 2009 by JL Stanbrough