The following applet simulated a famous pendulum wave.
The length of each pendulum is different so that the frequency of each pendulum is different by a fixed amount.
The frequency of the first one f1 and the difference between near by pendulum can be adjusted by slider.
Because the frequency is too faster to be observed by our eye, so the simulation show slow motion of the real wave by a factor of 100. (You can change time scale,too. Drag the slider to the right to make it faster.)