Khan Academy: Calculus: Conceptual Understanding of Flux in Three Dimensions

Video explaining flux through a two-dimensional surface by relating it to line integrals in two dimensions. Sets up a surface integral of the dot product of the product of a mass density function and velocity function with the unit normal vector at each point on surface to see how much mass is traveling through the surface. Gives real-life situations where this concept might be applicable. [8:23]