If you're seeing this message, it means we're having trouble loading external resources for Khan Academy.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Flux in 3-D and constructing unit normal vectors to surface

3 videos
Flux can be view as the rate at which "stuff" passes through a surface. Imagine a net placed in a river and imagine the water that is flowing directly across the net in a unit of time--this is flux (and it would depend on the orientation of the net, the shape of the net, and the speed and direction of the current). It is an important idea throughout physics and is key for understanding Stokes' theorem and the divergence theorem.

Conceptual understanding of flux in three dimensions

VIDEO 8:23 minutes
Conceptual understanding of flux across a two-dimensional surface

Constructing a unit normal vector to a surface

VIDEO 6:23 minutes
Deriving a unit normal vector from the surface parametrization

Vector representation of a surface integral

VIDEO 9:35 minutes
Different ways of representing a flux integral