Recoil (source code)
= Recoil
{title2=$E_R\simeq p^2/(2M)$}
Recoil is the motion acquired by a body when it exchanges <momentum> with an emitted, absorbed or scattered particle. For isolated emission from a body initially at rest, <momentum conservation> makes the remaining body acquire the opposite momentum. If its final <mass> is $M$ and the recoil is nonrelativistic, its <kinetic energy> is $E_R\simeq p^2/(2M)$. A <photon> of <energy> $E_\gamma$ has momentum magnitude $E_\gamma/c$, so $E_R\simeq E_\gamma^2/(2Mc^2)$. The transition energy is shared between the photon and the recoiling body; <nuclear recoil> is an important example.
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