Question: What is the name of the curve formed by a point on the circumference of a circle that rolls on the outside of a fixed circle? This curve is used in the study of gears.

Hi Sharon,

It's called an epicycloid. You can find a beautiful page about epicycloids on the mathworld site. If the circle rolls inside another circle then the curve is called a hypocycloid.

You can generate your own epicycloids, hypocycloids and related curves by using a spirograph.

Stephen and Penny