Why sand on a vibrating plate draws pictures: Chladni figures
30seconds
Sprinkle sand on a thin metal plate, draw a violin bow along its edge, and the sand leaps into sharp, symmetrical lines. Change the pitch and the picture changes.
The sand maps where the plate refuses to move. Grains get thrown off the shaking patches and collect on the still lines between them. In 1787 Ernst Chladni showed these figures, and Napoleon later set a prize for explaining them. Drag across a simulated plate to find the pitches where it rings.
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