I hesitate to show these. They are made from my lecture transparencies.
Our technician won't mess with color when he puts them up, so "You had
to be there" for these transparencies to make complete sense. They seem
to be used by the students (the counter has only been running for a
little over a week). I will apologize for the penmanship. I have a
shoulder problem that renders my usually difficult holography illegible
when writing on an overhead. Still, many students seem to follow, and
they come right along with me when I depart from the textbook.
See the beginning of Lecture 10 for the weight development. I show the
motion of a person standing on a bathroom scale located in Vancouver as
circular with constant speed. The free body diagram shows that the only
forces acting on him are the gravitational force and a reaction force
with which the scale pushes upward on him. The sum of these two forces
is the net external force acting on him, as shown below the diagram.
Students seem to understand this picture. I know it looks a little bit
unfamiliar to some of you, but try it; you'll like it.