Spherical shell
= Spherical shell
{title2=$r_1<|\boldsymbol x|<r_2$}
A spherical shell is the region between two concentric <spheres>. A thin mass shell at radius $r$, thickness $dr$ and <mass density> $\rho(r)$ has mass $4\pi r^2\rho(r)\,dr$ to first order. Decomposing a spherical body into such shells makes the <spherical shell theorem> applicable to its <gravitational potential energy>.