Very cool. I don't understand the physics of why they sync up when they are on a rolling surface - is it something to do with the fact that the motion of the metronome moves the platform, and somehow aligns the pendula? I'd try it at home, but I don't have five windup metronomes...
I don't know my physics well enough to tell you...BUT of course I have an uninformed opinion. I think it has to do with systems. Off the cans they are five independent systems. On the cans the board unites them into one system which eventually achieves "balance." I would use the word "stasis" but they are moving and I am weak in physics terminology.
Does anybody remember Le Chatelier's principle? I learned it in chemistry in 11th grade. To paraphrase my memory of it; "All systems adjust to adapt to outside pressure." Maybe this applies. I dunno.
But it is pretty cool!
In theory there is no difference between theory and practice, but in practice there is.