Comments on Lesson VC.06

• The concept of measuring the flow out of a singularity by drawing (small) circles of radius r around it and taking the limit as r goes to 0 needs explanation. Students are confused as to what is going on in practice when confronted with this problem.
• Students are frequently curious how about the situation where divField is always positive. They know intellectually that this is supposed to mean that there is always a net flow out of any curve, but this conflicts with their practical expectations. It seems that if water is flowing out of one curve, you ought to be able to draw another curve that absorbs that flow and gets net flow towards the inside. Try having them do some picture experiments and explain how this works.
• See also the hints section.
• I consider the instructions that you do not have to explain you "agree" answer in G.3 to be a bug.