Relativistic mechanics is a framework of physics that extends classical mechanics by incorporating principles derived from the theory of special relativity. It is necessary when dealing with objects moving at speeds that are a significant fraction of the speed of light, as classical Newtonian predictions fail to accurately describe the behavior of matter and energy under these conditions. The theory fundamentally revises concepts such as time and space, positing that measurements of time intervals and distances are relative to the motion and gravitational environment of the observer. This approach ensures that the laws of physics remain consistent across all inertial reference frames and is crucial for understanding high-energy particle interactions and cosmology.