Wonderful example of Ernst Chladni plates, to see the sounds:

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.

Chladni’s technique, first published in 1787 in his book, Entdeckungen ├╝ber die Theorie des Klanges (“Discoveries in the Theory of Sound”), consisted of drawing a bow over a piece of metal whose surface was lightly covered with sand. The plate was bowed until it reached resonance and the sand formed a pattern showing the nodal regions. Since the 20th century it has become more common to place a loudspeaker driven by an electronic signal generator over or under the plate to achieve a more accurate adjustable frequency.

Variations of this technique are commonly used in the design and construction of acoustic instruments such as violins, guitars, and cellos.

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