Splish, Splash
There's a lot of physics in the "margins;" namely, the areas where no one has checked because things are "obvious." If you throw a ball into water, you expect a splash. After all, there's the sudden displacement of water, and it's easier for the water to penetrate air than to displace another volume of water. You would expect that the material of the ball would have very little effect on the size of the splash, if any at all. A team of French scientists decided to investigate whether the surface condition of the ball really mattered, and they were able to explicate this previously unexplored margin of physics.
Cyril Duez, Christophe Ybert, and Lydéic Bocquet of the Université, Lyon, along with Christophe Clanet of CNRS, Marseille, dropped spheres of aluminum, steel and glass with diameters between 7 mm and one inch from a 1.25 meter height into water [1]. The spheres were chemically treated to produce a range between extremely hydrophilic and hydrophobic. The most hydrophilic surface was obtained by treatment of glass in a hydrogen peroxide/sulfuric acid mixture ("piranha solution"), followed by a deionized water rinse and heating to 110oC. Hydrophobic surfaces were obtained by producing silane chains at the surface by various treatments, depending on the ball material.
Duez, et al., found that the hydrophobic surfaces generate a larger splash. Their theory is that a hydrophobic surface creates an air cavity at the ball-water interface that allows extra movement of water to create a splash. Hydrophilic surfaces allow the water to flow smoothly around the ball so the air space does not form. There is an historical reference to their work. More than a hundred years ago, A. M. Worthington and R. S. Cole used high-speed photography to study impact of solid spheres on water [2]. They observed a range of splashing depending on whether the ball surface was "rough" or "smooth," but they didn't speculate on a cause. Of course, laboratory instrumentation was not well developed a hundred years ago, so they can be excused for publishing only qualitative information. Duez, et al., used high-speed photography, as did Worthington and Cole, but they recorded the sound, also. Hydrophilic surfaces gave a weak "plop," but the hydrophobic surfaces gave loud splashes.
Bobby Darin (Walden Robert Cassotto, 1936-1973) recorded the song, Splish Splash in 1958. Darin was said to have had a genius IQ, and he attended the Bronx High School of Science. Perhaps you can see the interplay between genius and madness in these lyrics [3].
Splish splash, I was takin' a bath
Long about a Saturday night
A rub-a-dub, just relaxin' in the tub
Thinking everything was all right
References:
1. Cyril Duez, et al., "Making a splash with water repellency," Nature Physics vol. 3 (March 2007) pp. 180-183. Available as a PDF file here.
2. A. M. Worthington and R. S. Cole, "Impact with a liquid surface
studied by the aid of instantaneous photography II," Phil. Trans., vol.
A 194 (R. Soc., London, 1900), pp. 175-199.
3. Splish Splash (Darin-Murray, Atco 6117, 1958),
4. Katharine Sanderson, "Small plops, big splashes," (Nature Online - Subscription Required).
5. Gaia Vince, "Nano-coating makes for an awesome splash" (New Scientist, 25 February 2007).