This video demonstrates the principle of Chladni figures and vibrating plates.

Brass plates of different shapes are fixed centrally at the top of wooden columns. Sand is spread on a circular plate. The plate vibrates and emits a sound when its rim is rubbed by a bow. The nodal lines of the vibration mode are displayed by the figures formed by the sand that accumulates along them (Chladni figures). The same experiment is repeated with a circular plate of smaller diameter. The different figures obtained with a square plate depend on where and how it is rubbed by the collector. The vibrations of the plate can also excite the oscillation of a thin paper membrane.