Final answer:
Einstein's theory of special relativity is named 'special' because it deals with motion at speeds significantly less than the speed of light. It explains how time, length, and mass are affected as objects approach the speed of light.
Step-by-step explanation:
Einstein's theory of special relativity carries the name 'special' because it deals only with motion at speeds significantly less than the speed of light. According to the theory, the speed of light in a vacuum is constant and is the fastest speed that anything can travel in the universe. As objects approach the speed of light, the theory predicts that time slows down, lengths contract, and mass increases.
For example, if an object is moving near the speed of light relative to another object at rest, the moving object's time will appear to pass slower and its length will appear shorter when observed by the stationary object.
Therefore, the name 'special' refers to the theory's focus on the relationship between motion, time, length, and mass at speeds significantly less than the speed of light.