Viral videos of 32 metronomes and 100 metronomes falling into the same tempo while sitting on a moving platform have become popular demonstrations of energy transference. Gizmodo describes it succinctly:
The metronomes are transferring energy to the platform they’re on, which then transfers that energy back to the metronomes—until they all sync up and start hitting the beat in one glorious wavelength.
This Spontaneous Synchronization physics demonstration from the UCLA Physics & Astronomy Instructional Resource Lab demonstrates the same results, but is a bit easier to replicate: Five metronomes sit on a board balancing on two soda cans. From UCLA:
Metronomes of the same frequency and resting on the same base are started randomly. They synchronize after a short period of time. In this case the base is free to move. In 1657, Christian Huygens was the first to observe this phenomenon in the form of clock synchronization. The phenomenon of spontaneous synchronization is found in circadian rhythms, heart & intestinal muscles, insulin secreting cells in the pancreas, menstrual cycles, ambling elephants, marching soldiers, and fireflies, among others.
Would the metronomes behave the same way if the board was not balancing on the cans?
Related demo support from Harvard’s Natural Sciences Lecture Demonstrations.
Related reading: The Kuramoto model “(or Kuramoto–Daido model), first proposed by Yoshiki Kuramoto,… is a mathematical model used to describe synchronization.”
Watch more instructional physics videos from UCLA.
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• How to build your own Wave Machine physics demo
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• Spinning Bike Wheel and Conservation of Angular Momentum
• Homemade marble track demonstrations by science teacher Bruce Yeany
• Demonstrations of the Coanda Effect using Schlieren optics