In the Special Theory of Relativity, relativistic kinematics refers to the study of motion in the presence of high velocities. It introduces a new set of equations that describe the behavior of objects traveling close to the speed of light.

One of the fundamental concepts in relativistic kinematics is time dilation. According to this phenomenon, time appears to pass more slowly for objects that are moving relative to an observer. For instance, if a spaceship travels at a significant fraction of the speed of light, time on board will flow at a slower rate compared to time measured on Earth. This effect has been experimentally confirmed and has practical implications for space travel.

Another important concept is the relativistic mass. As an object's velocity approaches the speed of light, its mass increases. This is distinct from the concept of rest mass, which is the mass of an object at rest. The increase in relativistic mass leads to changes in the object's inertia and affects its motion.