Astroid Applet

The Astroid

The astroid is a famous curve that arises in an interesting way. Suppose that a ball of radius a/2 is rolling inside a ball of radius a. The astroid is the curve traced out by a point on the inner circle. You can find a java applet demonstrating this at Here is that applet. You can see the curve being swept out by either dragging the red ball around or by starting the animation using the "Start" button.