197 Relativistic Kinetic Energy Formula Derivation

A derivation of the relativistic kinetic energy formula that is used to obtain \(K_{\mathrm{rel}} = (\gamma - 1)mc^{2}\) from the work done by a force.

The relativistic kinetic energy is

\[ K_{\mathrm{rel}} = (\gamma - 1)mc^{2} \]

with

\[ \gamma = \dfrac{1}{\sqrt{1-\dfrac{u^{2}}{c^{2}}}} \]

where

  • \(K_{\mathrm{rel}}\) is the relativistic kinetic energy.
  • \(\gamma\) is the Lorentz factor.
  • \(m\) is the rest mass.
  • \(c\) is the speed of light in vacuum.
  • \(u\) is the particle speed.