Point mass
= Point mass
{title2=$\rho=m\delta^{(3)}(\mathbf x-\mathbf z)$}
A point mass idealizes a localized body's mass density as $\rho(\mathbf x,t)=m\delta^{(3)}(\mathbf x-\mathbf z(t))$, using the <Dirac delta function>. Its <second mass moment tensor> is $I_{ij}=mz_i z_j$. The approximation ignores its internal size and structure.