 Capillary wave

A capillary wave is a wave along a fluid interface whose restoring stress is predominantly supplied by surface tension. A curved free surface requires a pressure jump by the Young–Laplace equation; increasing its corrugation also costs surface energy. In the ideal limit, inertia carries the interface through its flat position and the resulting oscillation propagates. When gravity also contributes appreciably, use the combined gravity-capillary wave model. Within the capillary wave regime, shortening a ripple makes it travel faster. ^[ref]

The laser-diffraction measurement of capillary waves below turns this mechanism into a test: set the frequency, measure the wavelength independently with light, and ask whether the dispersion relation follows. The theory is useful both for predicting how ripple wave packets separate and for inferring surface tension from their motion.

Capillary waves are small surface waves that occur on the interface of a fluid, primarily driven by surface tension. They are typically generated when a disturbance, such as wind or a small object, disturbs the surface of a liquid, leading to oscillations. The wavelength of capillary waves is generally short, typically on the order of a few centimeters, and they have periods that range from a fraction of a second to several seconds.