How does mass change theoretically in relation to speed and relativity?

The concept of mass in relation to speed, particularly in the framework of relativity, is rooted in the principles established by Albert Einstein. As an object moves faster and approaches the speed of light, its relativistic mass increases. This increase in mass is not due to the addition of physical matter but rather a consequence of the object's energy increasing with velocity. According to the theory of relativity, as an object's speed approaches the speed of light, the energy required to continue accelerating it increases significantly, making it more "massive" in terms of relativistic mass.

At lower speeds, where common physics operates, mass can be treated as constant; however, as velocities get closer to the speed of light, the implications of relativistic physics must be considered, leading to the conclusion that mass effectively increases. This understanding is fundamental in explaining many phenomena in particle physics and cosmic dynamics, where the velocity of particles often approaches relativistic speeds.

In summary, the correct response reflects the relationship between mass and speed in a relativistic context, indicating that mass increases as one approaches the speed of light.