# Synching Up: Another Cool Physics Video

Last week I stumbled upon that beautiful pendulum video. In comments, Max shared another cool video from the same people (Harvard Natural Sciences Lecture Demonstrations) – about synchronizing metronomes: (Thanks Max!)

The audio effect is important; watching the metronomes isn’t as powerful as hearing them get in a rhythm.

Any variation between the metronomes results in energy “swaying” the system, leading them to synchronize over time. After all, you wouldn’t expect a metronome to keep perfect time if you were shaking it – the setup just makes the shaking work against metronomes going against the consensus. I’m sure our friends at Ask a Mathematician/Ask a Physicist could give a more thorough answer.

What surprised me is that they got OUT of synch after being removed from the soda cans. I thought that, once in a rhythm, they would stay that way. I guess that by picking the system up and putting it back on the table was enough to break that. Or am I missing something?

### 7 Responses to Synching Up: Another Cool Physics Video

1. Max says:

I think the metronomes go out of sync because they have a slightly different frequency, but the difference goes away when they’re coupled.
If I didn’t know any better, I’d think it was paranormal đź™‚

It sounds like Eastern European applause. Listen to it going in and out of sync.

2. <>

The system is sensitive to initial conditions.

The interesting part is that the 1 degree of freedom provided by the cans somehow synchs the pendulums. Look up “coupled oscillator”.

3. Physicist says:

Not much more.

4. Barry says:

Also, possibly, “driven harmonic oscillator” — even if the individual metronomes have slightly different periods, if they’re subject to a driving force with a period and phase that’s close to the average of all of them, my hunch is that they’ll converge on that average.

You might also try checking into “metrognomes,” which are presumably much more citified than your garden-variety gnome.

5. Lauren says:

here’s my guess. The kinetic energy of their initial phases are stored by the spring inside (as potential energy) while they sync and remain in sync. The energy It is released once the metronmes stop being effected by each other….now a joke…Musicians call that rubato.

6. Lauren says:

that “It” shouldn’t be there in the second line.

7. Paul Schmidt says:

I believe this has to do with what I’ll call “kinetic damping” and the friction that removes freedom of side-to-side movement of the base. The net kinetic energy of the metronomes is largely being transmitted to the base on which they are mounted, which, when on the table, is dampened in a way that prevents (or mostly prevents) a harmonic oscillation in the movement of the base. That kinetic energy is lost via friction. When placed on the cans, the kinetic energy is not lost (it is translated into positional movement) and the base is free to allow the kinetic oscillation of the metronomes into new position. As the base moves back and forth on the cans, the disagreement of each of the metronomes fight each other and act as positive and negative corrections to the rate at which each metronome oscillates as a result of the changing positions. The net result of these corrections one each metronome puts each metronome in sync – essentially, the change in position of the base acts as a factor that exactly averages all of the frequencies. (This is my uneducated guess – clearly based on system 1 [intuitive] thinking rather than system 2 thinking; thank you Julia Galef for pointing this out to my face. đź™‚ )

I suspect that if one were to put the entire table on something that gives it similar freedom of side-to-side motion (and very low friction), the same effect would be seen, but it would likely take more time to happen as the mass of the table is much larger than the base on which the metronomes are mounted (or than the cans have.) Similarly, if the cans were replaced by smooth steel weights, I suspect it would increase the amount of time it takes to synchronize the metronomes. (Yet, I don’t know.)

If this is correct about the table, then, in theory, the entire planet should have the same effect. However, I suspect that the friction caused by all of the liquids and gasses on the planet would cause so much friction that the result wouldn’t be perceptible in any reasonable amount of time.

I have no training in physics. I derived the above conclusion before the video was over. I’m kinda curious if I’m correct.

So…what was I doing again? Oh yeah…procrastinating.