https://en.m.wikipedia.org/wiki/Cymatics
Cymatics (from
Ancient Greek: κῦμα,
romanized:
kŷma,
lit. 'wave') is a subset of
modal vibrational phenomena. The term was coined by Swiss physician
Hans Jenny (1904–1972). Typically the surface of a plate, diaphragm, or membrane is vibrated, and regions of maximum and minimum displacement are made visible in a thin coating of particles, paste, or liquid.
[1] Different patterns emerge in the excitatory medium depending on the geometry of the plate and the driving frequency.

Resonance made visible with black seeds on a harpsichord soundboard

Cornstarch and water solution under the influence of sine wave vibrationA demonstration of sand forming cymatic patterns on a metal plate.
The apparatus employed can be simple, such as the Chinese
spouting bowl, in which copper handles are rubbed and cause the copper bottom elements to vibrate. Other examples include the
Chladni plate[2] and the so-called cymascope.