The resonance square
 

This is one of the coolest things I've ever seen...

I don't have perfect pitch, but can someone who does confirm (or disprove) my suspicion that when the sand seems to "snap" to a pattern, it's when it hits a natural pitch?

http://thatvideosite.com/view/2289.html

Thats pretty awesome.

There is no such thing as a "natural pitch" however. :\
The patterns snap in at the specific resonant frequencies, which would be (theoretically) integer multiples of the length and width of the square plate.

I wonder what the setup was for this display.

oh fuck - I should've known that - the frequencies are multiples of the natural frequency of the plate?

i remember seeing a setup like this in high school physics. it was smaller but the effect was the same. so wait, i forget.... is the sand settling where the plate's not moving (the nodes of the waves, so to speak)? or am i just pulling that logic from nowhere?

still pretty cool.

Yeah, you are right, its at the nodes. Everywhere else, the vibrations of the plate are moving the sand away.

the resonance of the tones hurt my head.

Couldn't they have toned that down a little?

whoo, i was right for once.

speaking of physics class and frequencies, another demonstration was a simple speaker set up where the teacher kept increasing the frequency until you could no longer hear the sound. the whole point was to demonstrate that different people have different ranges of hearing. sadly i found out i was one of the lower ranges and was one of the first to no longer hear the tone. ah well, at least i've got my 20/20 vision.

Thats amazing! In all the theoretical stuff, nothing convinces more than seeing it happen in real life.

I remember a visual demonstration on discrete sampling once. It was done simply with an OHP and two pieces of acetate. One had the pattern of a 2D sinc function (looks like concentric circles) and the other is the 'sampler' of fine black bands. Put them on top of the other and you see their convolution! you see most of the original circles plus copies of them either side along the sampled direction. Exchange the bands with more widely spaced thicker bands has the same effect as reducing the sampling frequency. Flop it back on and you see the effects of aliasing where the circles overlap! Pretty neat stuff. And I'd always thought of this sampling malarkey as an audio sound wave thing...

Does anyone know what governs the patterns at a given frequency?