Visual Calculus?

Just came across a really interesting follow up to my recent Calculus without Limits blog..

To tempt your interest, here is a problem:

A bicycle rider is riding in a perfect circle and his wet tires leave two concentric circles on the pavement. (if that is difficult to visualize, see here) What is the area between the outer circle and the inner circle.(the area of the annulus). You are allowed to ask for one m! easurement (other than the answer) that will allow you to solve the problem. What is that measure.

I came across this little gem following up on some information from a blog at Arjen Dijksman’s Physics Intuitions.
Following up on that and searching around led to a truly interesting MAA article by Tom Apostol about a really interesting approach to a “visual calculus” by Mamikon Mnatsakanian. A really great read for calculus teachers, and students.

Angle of Intersection between Curves Questions