Third central velocity moment
= Third central velocity moment
{title2=$Q_{ijk}=\int (v_i-u_i)(v_j-u_j)(v_k-u_k)f\,d^3v$}
For unit particle <mass>, this symmetric third-order <tensor> transports the <pressure tensor> in a kinetic fluid description. Its contraction gives the <heat flux> $q_i=Q_{ijj}/2$. It vanishes for a <local Maxwellian>, whose odd central <velocity moments> vanish, but it need not vanish for a general anisotropic or skewed <phase-space distribution function>.