Relativistic energy
= Relativistic energy
{title2=$E=\gamma mc^2$}
For a massive free particle with invariant <rest mass> $m$, <speed> $v<c$, and <Lorentz factor> $\gamma=(1-v^2/c^2)^{-1/2}$, its total <energy> is $E=\gamma mc^2$. It includes the rest <energy> $mc^2$ and the <relativistic kinetic energy> $(\gamma-1)mc^2$. Here $c$ is the <speed of light>. At fixed total <energy>, a larger <speed> requires a smaller <rest mass>.