Lamina

$\begin{figure}\begin{center}\BoxedEPSF{Lamina.epsf}\end{center}\end{figure}$

A 2-D planar closed surface which has a mass and a surface density $\sigma(x,y)$ (in units of mass per areas squared) such that

$\begin{displaymath} M=\int_L \sigma(x,y)\,dx\,dy. \end{displaymath}$

The Center of Mass of a lamina is called its Centroid.