An interactive applet and associated web page that demonstrate the radius of a circle. The applet shows a circle with a radius line. The radius endpoints are draggable and the figure changes to ensure the line is always a radius of the circle. Demonstrates the radius is always a constant length for a given circle. See also the entries for circumference and diameter.

Applet can be enlarged to full screen size for use with a classroom projector. After use in the classroom, student can access it again from any web browser at home or in the library with no login required.

This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.