Sand on the the surface of this table skitters in scientifically predictable patterns according to the resonant frequency. I realised halfway through viewing this that my jaw had dropped. It's quite a hypnotic ride.
These patterns you see are called "Chladni figures."
These days, the technique is mostly practised with speakers and a sine wave generator. (electronic oscillator) In this video though, the hands-on, careful rubbing to induce vibration makes the scene more personal I think.
Resonance effect shown for various input frequencies and damping coefficients.
"One of Chladni's best-known achievements was inventing a technique to show the various modes of vibration on a mechanical surface. Chladni repeated the pioneering experiments of Robert Hooke of Oxford University who, on July 8, 1680, had observed the nodal patterns associated with the vibrations of glass plates. Hooke ran a bow along the edge of a plate covered with flour, and saw the nodal patterns emerge."
-Wikipedia entry on Ernst Chladni
Found via Io9
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