This java applet is a simulation of waves in a rectangular membrane (like a drum head, except rectangular), showing its various vibrational modes. To get started, double-click on one of the grid squares to select a mode (the fundamental mode is in the upper left). You can select any mode, or you can click once on multiple squares to combine modes. Also try clicking on the membrane itself and dragging up or down.
Zip archive of this applet.
Version 1.5, posted 3/16/05