An interactive applet and associated web page that demonstrate the the concept of the central angle subtended by an arc. The applet shows an arc and the corresponding central angle. As the arc endpoints are dragged the angle changes. The page gives the formula for the central angle based on the arc length and radius.

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.