# Question #26c7f

Dec 31, 2014

Relativity .

This part of Physics deals with movement at very high speed, i.e., near or comparable to the speed of light (indicated by $c$).
It covers, mainly, the work of Albert Einstein that divided it in two parts:
- Special Relativity: it is an extension of the laws of cinematic to include the effect of moving at high speed;
- General Relativity: it is an extension of Newtonian Mechanics (and Gravitation).

In Relativity it is considered the fact that the speed of light cannot be exceeded; even if the source of light is moving with a certain speed, light itself, will always move at $c = 3 \cdot {10}^{8} \frac{m}{s}$. This fact introduces the need to consider TIME as relative. Basically, time can change according to the reference frame in which is measured.
A person moving with high speed will measure a certain time between two events. Another person moving at different speed relative to the first will measure a different time!!!