Velocity distribution
= Velocity distribution
{title2=$f(\mathbf v)$}
A function specifying how a particle population is distributed over velocities. If $f$ is a number-density distribution, $f(\mathbf v)d^3v$ counts particles per unit spatial volume in that velocity element and $\int f\,d^3v=n$. A probability-density convention instead has integral one. The normalization must be stated before adding populations or comparing their slopes.