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A capillary wave is a wave travelling along the interface between two fluids, whose dynamics are dominated by the effects of surface tension. Capillary waves are common in nature and the home and are often referred to as ripples. The wavelength of capillary waves is typically less than about a centimeter.
Additional recommended knowledge
The dispersion relation for capillary waves is
The waves with large wavelengths are generally also affected by gravity and are then called gravity-capillary waves. Their dispersion relation reads, for infinite depth of the two fluids,
In water on earth this is observed: Gravity waves have a group velocity half the phase velocity.
Following a single wave in a group one can see the wave appearing at the back of the group, growing and finally disappearing at the front of the group.
Therefore an interesting and common situation occurs when the dispersion caused by gravity cancels out the dispersion due to the capillary effect. At wavelength around 2 cm the capillary effect causes group velocity to equal phase velocity. The dispersion is zero, and a wave ridge can travel for long distances.
Shorter (i.e. 2 mm) ripples do the opposite: the wave appears at the front of the group, growing and finally disappearing at the back of the group.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Capillary_wave". A list of authors is available in Wikipedia.|