ooblick magick

[nibot]

We all know that cornstarch + water (otherwise known as ooblick) is amazing stuff. However, these guys in texas at the center for nonlinear dynamics have taken it to a new level. If nothing else, you should check out the paper and definitely the movie. I wonder if this could be repeated just using a loudspeaker and function generator? Yet another reason to procrastinate on studying for finals!

[edit: you're too late! I guess the movie was "slashdotted," as it's no longer available from their web page. )-: edit2: nevermind, they fixed it.]

[edit3: here's an experiment with solitons that you can do on the surface of a pool: Falaco Solitons. Check out the paper gr-qc/0101098 in arXiv. "String theorists take note, for the structure consists of a pair of topological 2-dimensional rotational defects in a surface of discontinuity, globally connected and stabilized by a 1 dimensional topological defect or string."]

On another note, I'm curious how much of antenna theory can be co-opted to make antennas for sound. A yagi for sound seems a bit unlikely, but parabolic reflectors certainly work, and it seems that there ought to be some magic with cavity resonators.

Comments

[easwaran.livejournal.com]

You'd most likely have to put the thing directly on the speaker cone to get that magnitude of vibration. I suppose that was always your plan though :-) That makes sense about the audio being overdubbed, explaining why we wouldn't hear anything. But I still have a feeling that would be pretty loud at 120 Hz. (The lowest note I can sing comfortably is somewhere around 95 Hz.)

My wonder about the camera was that if the thing was vibrating, why didn't we see the dish moving? I guess if the vibrations are really small amplitude and the camera wasn't very high resolution, then that vibration wouldn't show up. But I thought the camera might have been vibrating in unison with the dish.

As for the aliasing, let's assume that the dish was vibrating at exactly 120 Hz and the aliasing took 1 second per fade in and out of the waves. This would mean that if the camera recorded at x Hz, then it takes x full cycles of the camera and 120 full cycles of the dish before they are lined up again. So the gcd of x and 120 is 1. This would suggest that the camera is recording actually at 29 or 31 Hz. Or possibly that the camera is exactly 30 Hz and the dish is at 119 or 121, but I suspect they have finer control over their vibrator than their camera. And the aliasing actually seems to be taking a couple seconds, so it's even closer to 30 Hz. Also, the fact that it fades in and out gradually suggests that it's as close to a divisor of 120 as possible, which would suggest 31 or 29 as opposed to 37 or 23.