Now that we have proper definitions of the curl and the methods of evaluating it, we must return to the physical meaning
of the curl. First, we note the following properties of the curl:
(1) The curl of a vector field is a vector field.
(2) The magnitude of the curl gives the maximum circulation of the vector per unit area at a point.
(3) The direction of the curl is along the normal to the area of maximum circulation at a point.
(4) The curl has the general properties of the vector product: it is distributive but not associative