Figure 1: Using round boxes to determine the curl.

In § {Activity: Using Technology to Visualize the Curl} you were asked to apply the geometric definition of curl. It is important to realize that the divergence is a vector field; it is not enough to examine the behavior near a single point, such as the origin.

It is helpful when trying to apply the geometric definition of curl as directed circulation per unit areaa to draw a box of the appropriate shape. If the vector field is round, use round boxes! An example is shown in Figure 1.