This Har­vard-pro­duced video has gone viral, and then some, hav­ing clocked more than 3,000,000 views. We’ve watched the pen­du­lum balls swirl, mov­ing almost impos­si­bly from pat­tern to pat­tern, and we’ve remained daz­zled all along. But the mechan­ics behind this chore­o­graphed action haven’t real­ly been brought to the fore. So let’s turn to Har­vard’s web site to under­stand how this kinet­ic art 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.

We’re adding this clip to our col­lec­tion of 125 Great Sci­ence Videos. You’ll also find a good num­ber of Physics cours­es in our big col­lec­tion of Free Online Cours­es.