In physics, kinetic energy is energy possessed by a body by virtue of its motion. In Newtonian mechanics, a body with mass m, moving in a straight line with velocity v, has a translational kinetic energy of
where m is its total mass, m0 is its mass (or rest mass), and c is the speed of light in vacuum. Relativity theory states that the total mass of an object grows towards infinity as its velocity approaches the speed of light, and thus that it is impossible to accelerate an object beyond this boundary.
Where gravity is weak, and objects move at much slower velocities than light (e.g. in everyday phenomena on Earth), Newton's formula is an excellent approximation of relativistic kinetic energy.