12. 4 applications of double integrals notes: sterling. Provide a generalization to each of the key terms listed in this section. A lamina is a 2d planar closed surface that has both a mass and surface density (which is measured in "units of mass per areas squared"). (x, y) (a continuous function"s point) with being used as an continuous function on a region. Now, if you add all of the various masses, then the following will be an approximation for a total mass: k l m . If you can increase the given number of rij (subrectangles), then the following is m (the total mass) of the lamina while its limiting value to m (the total mass): m = lim k,l k l. When it comes to physicists, using various types of density can actually be used in the exact same concept.