In the Special Theory of Relativity, the concepts of momentum and energy undergo significant changes compared to classical physics. One of the fundamental ideas introduced by Einstein is the concept of relativistic mass, which takes into account the increase in mass as an object's velocity approaches the speed of light.

The formula for calculating relativistic mass is given by:

m = m0 / √(1 - v²/c²)

Where m is the relativistic mass, m0 is the rest mass, v is the velocity, and c is the speed of light. This equation highlights that as the velocity of an object increases, its mass also increases.

An important consequence of relativistic mass is that as the velocity of an object approaches the speed of light, its mass approaches infinity. This suggests that it would require an infinite amount of energy to accelerate an object with mass to the speed of light.