
Researchers prove Huygens was right about pendulum synchronization - dnetesn
http://phys.org/news/2016-03-huygens-pendulum-synchronization.html
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roywiggins
"Another new discovery is that pendulum clocks are not only synchronous but
also move more slowly over time and thus are not very reliable timekeepers."

Wait, what? That's surely not a "discovery"...

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grahamburger
Not sure if this is what you mean, but pendulum clocks work because the
pendulum "... swings back and forth in a precise time interval dependent on
its length, and resists swinging at other rates."[0]

[0]
[https://en.wikipedia.org/wiki/Pendulum_clock](https://en.wikipedia.org/wiki/Pendulum_clock)

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jessaustin
The fact that a particular mechanism _resists_ the effects of friction doesn't
mean it's _unaffected_ by them.

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wlesieutre
But (approximating at small angles), the pendulum's period is _constant_.
Friction will have the effect of reducing the distance that it swings, but the
amount of time it takes to swing it doesn't change.

That's a simplified model of a pendulum and isn't completely accurate, but
even if your pendulum has a 30° swing its true period is only 1.7% off of the
approximation.

And pendulum clocks don't just let the pendulum lose energy to friction until
they swing down and stop. Take a look at this deadbeat escapement:
[https://en.wikipedia.org/wiki/Anchor_escapement#/media/File:...](https://en.wikipedia.org/wiki/Anchor_escapement#/media/File:Scappamento.gif)
(one of several pendulum mechanisms)

There are three main actions going on here. 1) A weight is hung so that its
downward force is trying to drive the escape wheel's rotation. 2) The side
face of the anchor (swinging part w/ pendulum attached) moves in front of the
escape wheel tooth and stops it. This locks the motion of the clock mechanism
to one tooth per swing (and is the reason the weight doesn't just drop
immediately). 3) As the anchor swings off the dead face, the tooth applies a
slight push to the sloped impulse face at the end of the anchor. That repeated
nudge transfers potential energy from the weight to the pendulum swing, and
keeps its swing distance consistent against friction losses.

Mechanical clocks are actually pretty clever.

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krastanov
See my response to grahamburger. Friction does not only cause decay of the
amplitude, it also changes the frequency.

edit: But you are right, the mechanical clocks are still pretty amazing and
quite precise given the limitations of the technology.

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julien-c
Relevant video:
[https://www.youtube.com/watch?v=5v5eBf2KwF8](https://www.youtube.com/watch?v=5v5eBf2KwF8)

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nkurz
More than relevant, it's a fantastic video of 32 out-of-phase metronomes
sitting on a shared surface "magically" coming into (seemingly) perfect sync
over several minutes. Thanks!

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mchahn
I have observed crystals and oscillation circuits syncing up on PC boards
because of tiny noise on the power supply. This is a direct analogy of the
Huygens observation.

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effie
Were those crystals and oscillations circuits independently driven by the
power supply, or were they mutually connected?

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mchahn
The only thing connected was the power line. I have heard of oscillation
circuits with no common power syncing up because of RF from coils.

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smaddox
Such effects have been pretty thoroughly studied in the quantum mechanics of
Bosons. Bosons are particles or quasi-particles that follow Bose-Einstein
statistics, including photons and phonons, i.e. quantised electromagnetic and
acoustic vibrations, respectively. This phenomenon of pendulum synchronization
on a shared acoustic surface is not completely unlike that of photon
synchronization in a laser cavity.

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amelius
Of course, the clocks need to have compatible internal time constants
(pendulum length) for this to work.

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tgb
How close do the natural frequencies need for this to happen? There must be
some relation between how tightly coupled they are and how close their
frequencies must be. Is it a sharp cut-off? What happens near the breaking
point?

Easier to explore in electronic systems than kinetic ones, as we did in a lab
in college. You get some fun phenomena, with chaos and fractals arising:
[https://en.wikipedia.org/wiki/Arnold_tongue](https://en.wikipedia.org/wiki/Arnold_tongue)

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amelius
Good points. This would certainly be interesting to figure out.

