"Any sufficiently advanced technology is indistinguishable from magic", truly said by Sir Arthur C. Clarke. See the image in your left and you'll find a group of 15 uncoupled simple pendulums organized in their increasing lengths.

Each one is designed to oscillate one time less than the last. They dance together to produce visual traveling waves, standing waves, beating, and random motion. The choreography of the pendulums is just outstanding and will leave you hypnotized until they finish dancing.

Check it out in the video below:




Let's understand how it works:

"The period of one complete cycle of the dance is 60 seconds. The length of the longest pendulum has been adjusted so that it executes 51 oscillations in this 60 second period. The length of each successive shorter pendulum is carefully adjusted so that it executes one additional oscillation in this period. Thus, the 15th pendulum (shortest) undergoes 65 oscillations. When all 15 pendulums are started together, they quickly fall out of sync—their relative phases continuously change because of their different periods of oscillation. However, after 60 seconds they will all have executed an integral number of oscillations and be back in sync again at that instant, ready to repeat the dance." 

Some brilliant people at Harvard University have set this apparatus and get it working.