Area Element/Examples/Surface of Body

Example of Area Element
An area element $\delta \mathbf S$ is often coincident or approximately coincident with part of the surface of a body in space.

Such a body can be considered to have the whole of $S$ covered by such as $\delta \mathbf S$.

The direction of the normal to such a $\delta \mathbf S$ is conventionally taken to be the outward normal of $B$.

If $B$ is complicated in shape, a redefinition of the term outward normal may be appropriate.