Waves in a ripple tank

The slinky, the tank and the waves are simulated. The slinky waves have a frequency of 1 Hz and travel at 0.35 m/s, so each wave is 35 cm long. On a real slinky a wave bounces back from the fixed end; here the far end soaks it up, so you see each wave only once.

The water waves travel at 0.20 m/s at every frequency, and at 0.12 m/s over the glass plate; real ripples also change speed a little with frequency. The waves are shown three times slower than they really move, and the cork’s bobbing is drawn larger than it would be. In a real ripple tank the lamp makes the pattern on the screen bigger than the waves themselves; here the screen shows them at their real size.

The barrier is met by a short burst of three waves, so that the reflected waves don’t get mixed up with the waves still arriving. A real plate would also reflect a little of each wave at its edge, and that is left out. Beyond a gap or an edge, the waves are worked out by adding up small waves spreading from every point of the opening; the waves reflected back from the front of the barriers are left out.

With reduced motion each step happens at once: the slinky’s wave and the waves in the tank appear straight away as they are at the end of the run, the picture of the water stands still, and the camera cuts between the slinky and the tank.