Speed distribution
= Speed distribution
{title2=$f(v),\quad v\geq0$}
A <speed distribution> is the <probability distribution> of the magnitude of <velocity>. When it has a <probability density function> $f$, the fraction of particles with <speeds> between $v$ and $v+dv$ is $f(v)\,dv$, and $\int_0^\infty f(v)\,dv=1$. The <Maxwell speed distribution> describes an equilibrium <ideal gas>; the <effusive beam speed distribution> weights that population by its rate of arrival.