Pendulum Waves (2010) | Hacker News Reader

Pendulum Waves (2010)

sciencedemonstrations.fas.harvard.edu

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I recreated this in CSS/JS a few years ago, inspired by this video.

https://codepen.io/madelinw/details/ocnCl

Same principle, though not a physical simulation: http://wry.me/hacking/moire-eel.html

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

I made it with webgl: http://toplessproductions.com/pendulum/

2D View from above (in GeoGebra)

https://www.geogebra.org/m/yCe42MAX

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!

For this analogy to hold you'd need the 8th ball thread x4 longer than the first, which is very far from the actual ratios used.

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".

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

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

Less the notes and scales themselves, and more polyrhythms and phasing. This reminded me of Steve Reich's Clapping Music, and similar phasing-heavy works (Piano Phase, Drumming, Music for Pieces of Wood, 6 Pianos/Marimbas, and Pendulum Music).

amazing, I need to read that book, any other suggestions ?

also https://news.ycombinator.com/item?id=18696782

Read that book??

The book you listed seems super interesting.

jazz is variable actuators/pendulums

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/

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.

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.

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

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...

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?

Now what happens when you couple the oscillators?

https://www.youtube.com/watch?v=5v5eBf2KwF8

Something like this?

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

it looks like rotating helixes to my eye

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