Now Dave answers Sheri's question and offers to send her an e-mail copy of the figure he uses with his students.

Subj: two curves for rolling balls
From: Dave

Sheri - I use an 8.5 x 11 sheet of paper. The two curves are arcs (about 120 degrees) from concentric circles, inner circle radius about 2.5 inches, outer circle about 5.5 inches. (These are all approximate numbers - you may need to play around with the curves a little to be sure there's a straight line path between them.)

If you're on a Mac, I could mail you the figure I use...

next message >>