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

[squarkz.livejournal.com]

oh, i have such a soft spot in my little heart for fluid dynamics. seeing stuff like this makes me reluctant to leave my current research.

and i'll admit: the first thing i thought when i clicked through the links was, "i should have gone to grad school there!"

i've never made ooblick, but i probably should. and this business of the glass spheres is verrrrry interesting to me right now.

[cdm137.livejournal.com]

ooblick is fun!

[nibot.livejournal.com]

oh, i have such a soft spot in my little heart for fluid dynamics. seeing stuff like this makes me reluctant to leave my current research. and i'll admit: the first thing i thought when i clicked through the links was, "i should have gone to grad school there!"

yeah, I've felt that a few times. Like when reading about spintronics lately... they're working on spintronics at UNC-Chapel Hill but not at Rochester! but that's okay. my 2-week attention span will lock onto just about anything as being the coolest thing in the world, but for only about two weeks.

i've never made ooblick, but i probably should.

that's terrible! of course you should!

my first exposure to ooblick was at defcon iii in las vegas.. afterwards there was cornstarch everywhere in the hotel (the tropicana)! cornstarch footprints. cornstarch on the elevator buttons. it was most excellent!

then i hosted a "festivities" at my house where everyone was instructed to bring along a box of cornstarch:



and it was made into a bunch of ooblick:

(http://splorg.org/people/tobin/pictures/97-sep/)

highly recommended!

[easwaran.livejournal.com]

I got the movie from your link to it!

Pretty fancy stuff...

They said the acceleration was 15g and then 25g at 120 Hz, and it seems unlikely you could get a loudspeaker to do something that powerful. I don't understand why we didn't hear an extremely loud pitch though if there was something vibrating at that frequency. And was the camera moving too, or was it just extremely small vibrations?

[nibot.livejournal.com]

I don't think the acceleration is important.

Suppose the equation for the driven vibrations is sinusoidal, with amplitude A:

  x(t) = A sin ω t

Then we can calculate the velocity and acceleration:

  v(t) = x'(t) = A ω cos ω t
  a(t) = x''(t) = - A ω2 sin ω t

The relationship between angular frequency ω and standard frequency f is ω = 2π f, so 120 Hz is an angular frequency of 754 radians per second. The maximum acceleration is amax = Aω2, acceleration due to gravity is g = 9.8 m/s/s, so 25 g's is about 250 m/s². I compute A = a_max/ω^2 = 0.44 mm. So the amplitude of the vibration is only half a milimeter. I'd say that a loud speaker could do that. (-:

You probably have a better feel for the frequencies than I do, but 60 Hz is the frequency of household AC current, so any time you hear a transformer or power line buzzing, it's most likely at 60 Hz — pretty low. In any case, the audio is probably over-dubbed. Regarding the camera, there are some aliasing effects, since a standard video signal is only 30 frames/second. They said they also used a 2000 frames/second camera for some of the video, but who knows how they transferred that to Windows Media. The fading effect is due to the aliasing, and I'm sure we could figure out exactly what's going on in that respect with a little thought and a re-viewing.

[nibot.livejournal.com]

I don't think the acceleration is important.

whoops -- I mean that the exact value is probably not important. But there are critical values of the acceleration.. the whole thing here is that the fluid is nonlinear, so acc is important.

[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.

[yonked.livejournal.com]

Wow. You're posts always make me feel so... not dumb... but, incurious in comparison. Nice links today. The movie I noticed originally from a mechanical engineering friend. He had a list of several interesting 'weird' fluid movies which he had to analyze for a class.

I wonder how small a body of water you can have in which to demonstrate Falaco solitons. Hmm... conjecturing that the galaxies are Falaco solitons seems pretty wacky, since there is no fluid discontinuity such as the swimming pool surface.

[nibot.livejournal.com]

You're posts always make me feel so... not dumb... but, incurious in comparison.

no! they're supposed to inspire! anyway, i added you because i felt similarly about you (posting cool stuff.. must be a part of it). (-: oh yeah, and because i'm moving to rochester, and, iirc, you're at RPI in Troy? nowhere near rochester, but another netherpart of new york state.

I don't understand this soliton stuff at all. how do the falaco solitons relate to the "solitary waves" we saw i.e. in the manchester channel? i have to do some reading. one of my goals for the next 1-2 years is to be able to understand my friend's masters thesis, "Pions versus Magnons: From QCD to Antiferromagnets and Quantum Hall Ferromagnets (http://www.arxiv.org/PS_cache/cond-mat/pdf/0310/0310353.pdf)" [pdf], on the arXiv as cond-mat/0310353.

hope i'm not just telling you a lot of stuff you've already read

[yonked.livejournal.com]

Well, 'soliton' is a pretty general term. It doesn't have to be a translating wave. It refers to any solution to a nonlinear field equation which has particle-like properties (as I understand it) such as localization, conservation of number, anti-particle pairs, etc.. Sometimes solitons just sit there, like a kink in a twisted rubber band.

See this (http://homepages.tversu.ru/~s000154/collision/main.html) for some maple animations of sine-Gordon solitons, and this (http://math.cofc.edu/faculty/kasman/SOLITONPICS/hmsol.html) for a physical system which those equations actually model.

The coolest thing I've learned about solitons so far is that, even though they are solutions to a nonlinear system, they obey a kind of superposition principle. That's how you can have a swimming pool with lots of Falaco solitons drifting around in it (although apparently always an even number). The graphs above illustrate some superimposed solutions, and some cases where solitons scatter against each other.

The Falaco solitons may have no mathematical relation to the solitons of John Scott Russel... I don't know. I'm pretty sure when you move from 1-d systems (like the 1-d sine gordon) to 2-d and 3-d systems, a lot of wacky things become possible. Such as our wacky friend, angular momentum.

What I would really like to understand is what the Falaco solitons have to do with topology. Kiehn stresses the phrase 'topological discontinuity' over and over again. I'm taking a topology class next semester but it's just introductory...

I think if I keep studying homology, cohomology, exterior algebras, manifolds, general topology, at some point everything will fall into place.

[shamster.livejournal.com]

Why do y'all think it was done using a loudspeaker? The paper says nothing more than "shaker".

btw - any knowledge of where the 'full' paper is published? I recall most phys-rev-lett's as shorter versions of the real deal.

[nibot.livejournal.com]

I'm not saying that they did it with a loudspeaker, but that it might be possible with a loudspeaker.

[shamster.livejournal.com]

Hmmm... maybe. Doubtful. 1 mm displacement is big. A very big load for a loudspeaker. Especially when you're moving a mass of corn starch suspension.

It really doesn't matter, because THIS (http://www.visualprosthesis.com/javoice.htm) is way cooler anyhow!

[nibot.livejournal.com]

A very big load for a loudspeaker.

I suppose you're right. Other suggestions?

Mass-spring suspension system at the resonant frequency? sounds annoying.

I have some old code for producing sound output in linux that might be handy: http://splorg.org/people/tobin/projects/dtmf/

[shamster.livejournal.com]

It is possible to rig up systems with oscillating vibrators (think of a poorly balanced rotating rod) that could drive a platter as if on a cam... of sorts. I'm doubting, but it's possible. Their big paper, if tracked down, will most likely reveal the answer. A very spiffy 'paint-shaker' at 120 Hz seems more likely.