There are lots of interesting interactive wave demonstrations on the web. The particularly interesting ones are the ones that show interference. Some of them make your eyes water. Others make your ears hurt. These simple animations show superposition (constructive and destructive interference) very nicely, but the language is a little advanced.
What I like about Dan Russell’s 2d animations is that they show the wave motion using particles. If you track a single particle with your eye you can see that while the wave moves from one side of the area to the other, the particles just move back and forth in the same general region.
I like this demo because you easily control the wave amplitude and lengths of two waves and it shows how they superimpose.
This animation of wave interference is nice because when you click on the 2d animation it shows the two waves’ effects at the point you’ve chosen as curves. You can choose points to show both constructive and destructive interference.
This elegant but somewhat complex video shows the two dimensional sine waves generated by a rotating wheel.
