Scalar second mass moment
= Scalar second mass moment
{title2=$I=\int r^2\,dm$}
The scalar second mass moment is the <trace> of the <second mass moment tensor>. The <moment of inertia> about a specified axis instead integrates squared distance from that axis. For an isotropic distribution each axial <moment of inertia> is $2I/3$; the sum over three orthogonal axes is $2I$.