An interactive applet and associated web page that demonstrate the concept of 'perpendicular'. The applet presents two intersecting line segments, one initially at right angles to the other. As you drag the end points of the line segments a message and the right-angle mark at the intersection tell if it is currently perpendicular. The goal is to show what a right angle 'looks like'.

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.