MetaFilter: “Ripple Tank Simulation is a delightful, mesmeric java applet simulation of a ripple tank. It demonstrates two dimensional wave phenomena such as interference, diffraction, refraction, resonance, phased arrays, and the Doppler effect (do try the 3D view). From Paul Falstad’s fantastic collection of Math, Physics and Engineering Applets.”
Excellent, I’m adding the ripple tank – and the other applets – to my collection of useful sites for physics lessons.
You might also enjoy my applet Resonata, then – it may not be quite as useful in itself as Paul Falstad’s wonderful collection, but there’s a bunch of accompanying text which should help convey the relevant ideas about waves and particularly resonance…