Lorentz factor

Summary

The Lorentz factor of a speed $v$ below the speed of light $c$ is $\gamma = 1/\sqrt{1 - v^2/c^2}$. It is the factor by which moving clocks run slow and moving rods shrink. It appears in the Lorentz transformation and in relativistic energy and momentum. It equals $1$ at rest and grows without bound as $v$ approaches $c$.