CONTENT NOT ON NOTES PAGE
DEMO: Set up model of Cavendish torsion balance using balanced balls hanging from ceiling, and bowling balls on PVC pipes.
DISCUSSION: Cavendish's motivation was not finding G per se. It was "weighing the Earth." And the rest of the Universe, for that matter.
DISCUSSION: M is the mass inside the sphere of radius r. If we could dig a tunnel to the center of the Earth...