Cheerios effect
Pour milk into a bowl, drop in some Cheerios (the breakfast cereal), and notice how they clump together. This attraction is mediated by gravity and surface tension. Each cheerio makes a little depression in the milk-air interface, and the neighbouring one just falls into it.
Publications
He, Nguyen and Mandre. Capillary interactions between nearby interfacial objects. Europhys. Lett. 102, 38001 (2013).PDF Publisher link
Abstract: We develop a general method to study the capillary interactions between objects of arbitrary shape which float close to each other on an interface, a regime in which multipole expansion is not useful. The force is represented as a power series in the small distance between the objects, of which the leading order is finite. For objects with size a much larger than the capillary length lc, the force scales as (a/lc)1/2 and the prefactor depends on the mean radius of curvature R at the closest points. ... (read more)
Fluid Mechanics Capillary Cheerios Effect