**General relativity:**

Theory dealing with how massive object bend or warp space and time around themselves.

**Special relativity:**

Theory dealing with the effects of motion at near light speeds.

**Postulates of Special Relativity: **

Two fundamental assumptions that form the basis of the theory of special relativity.

**Classical/Newtonian Physics:**

Physics based upon Newton’s laws. These laws work very well for motion that is not near the speed of light. This physics is inaccurate for near light speed motion.

**Relativistic Physics:**

Physics that describes the behavior of object that move at nearly the speed of light. At low speeds, it simplifies to agree with Newtonian physics.

**Correspondence principle:**

Any new theory must agree with an old theory when the old theory gives a correct result.

**Time dilation:**

The slowing down of time in a frame of reference moving at relativistic speeds.

**Twin paradox:**

An apparent contradiction where one twin takes a high speed trip and returns with a different age compared to the other twin.

**Muon:**

A subatomic particle with a very short life span. When moving at very high speeds, it seems to exist for a longer period of time. This is one experimental piece of evidence that supports the theory of special relativity.

**Length contraction:**

The shrinking of a distance or length due to motion at relativistic speeds.

**Rest energy:**

The energy of mass itself, as given by the equation E=mc2

**Frame of Reference:**

A viewpoint or set of coordinate axes to which position and motion can be described.