
Pendulum Waves (2010) - kp25
https://sciencedemonstrations.fas.harvard.edu/presentations/pendulum-waves
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madelinw
I recreated this in CSS/JS a few years ago, inspired by this video.

[https://codepen.io/madelinw/details/ocnCl](https://codepen.io/madelinw/details/ocnCl)

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abecedarius
Same principle, though not a physical simulation:
[http://wry.me/hacking/moire-eel.html](http://wry.me/hacking/moire-eel.html)

By moving the mouse you can amuse yourself with various Moiré effects.

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aethr
Without analyzing it too much this seems to be a perfect visualization of the
mathematics of music theory. The lengths of string become quite a direct
metaphor for the wavelengths of notes on the music scale, and seeing them move
together in progressively different "groups" of notes I imagine closely
matches traditional chord structures in different keys.

Quite mesmerizing, and mathematically satisfying at the same time!

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mrob
It's a closer analogy to the "beat frequencies" you get with constructive and
destructive interference of waves of similar frequency. The envelope of the
total amplitude of the pendulums oscillates with lower frequency than the
amplitude of any individual pendulum.

I used Audacity to mix sine waves of the frequencies of the pendulums
(51/60Hz, 52/60Hz, ..., 65/60Hz), multiplied by 440 to get them to audio
frequency, and it sounds a lot like the UFO sound effect from the 1970s TV
series "UFO".

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hrayr
I'm very curious how that sounds, would you mind posting it somwhere?

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mrob
Posting on first Google result for "share short sound clip". I can put it
somewhere else if you have a better suggestion.

[https://clyp.it/rfu2x1kb](https://clyp.it/rfu2x1kb)

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aardvark291
If you enjoy demos like this and live in or visit San Francisco, check out the
Exploratorium, which is full of amazing physical demos like this.

[https://www.exploratorium.edu/](https://www.exploratorium.edu/)

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kaycebasques
They have “adult swim” on Thursday nights. I.e. adults only, and alcohol for
sale. Classic first date spot. But to really make the most of it you’ve got to
go by yourself and spend a day there, taking the time to appreciate and think
about each exhibit.

I have fond memories of field trips to the Exploratorium back when it was at
the Palace of Fine Arts.

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todd8
I’ve seen this demonstration at least a couple of times, once as an undergrad
around 1971. I always remembered it and a few years later I was working with a
minicomputer with limited I/O so I decided to blink the row of front panel
lights just to show that the program was running. I blinked each on and off
with a slightly different frequency and got a similar, interesting effect.

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inutard
Great to see this come up again! Here's a simulator I wrote for it a looooong
(almost 8 years!) ago:
[https://cs.stanford.edu/people/paulliu/webapps/pendulum.html](https://cs.stanford.edu/people/paulliu/webapps/pendulum.html)

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ms013
Interesting to see this come up again. Here’s a small model for this system
written in Haskell from a few years back:

[http://syntacticsalt.com/blog/2011-08-27-harmonic-
motion.htm...](http://syntacticsalt.com/blog/2011-08-27-harmonic-motion.html)

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kaycebasques
It seems like the pendulums fall into a few repeating patterns. E.g. for a
second it looks like a snake, for another second it looks like a double helix,
and so on. The whole set cycles through each pattern and then begins again.
How many patterns are there?

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dest
Now what happens when you couple the oscillators?

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kaffeemitsahne
[https://www.youtube.com/watch?v=5v5eBf2KwF8](https://www.youtube.com/watch?v=5v5eBf2KwF8)

Something like this?

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dest
yes, but I am looking for coupling between oscillators of different
fundamental frequencies.

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the_cat_kittles
it looks like rotating helixes to my eye

