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Dial-a-splash: thin air quells liquid splatter.


In a classic image of high-speed photography, a drop of milk landing on a surface explodes into an ornate crown with beads of fluid leaping from its rim. Now, a study of other splashes finds that the air in which such bursts unfold is a previously overlooked actor in that performance.

"I don't think anyone ever thought poor little old air could do anything to the splash," says physicist Sidney R. Nagel, who led the investigation. Yet he, Lei Xu, and Wendy W. Zhang, all of the University of Chicago, have discovered that even modestly reducing the air pressure completely quells the rococo (jargon, abuse) rococo - Baroque in the extreme. Used to imply that a program has become so encrusted with the software equivalent of gold leaf and curlicues that they have completely swamped the underlying design. Called after the later and more extreme forms of Baroque architecture and decoration prevalent during the mid-1700s in Europe. Alan Perlis said: "Every program eventually becomes rococo, and then rubble."

Compare critical mass.
 exuberance of crashing drops.

"Flabbergasting," comments Detlef Lohse of the University of Twente in Enschede Enschede (ĕnskhədā`), city (1994 pop. 147,624), Overijssel prov., E Netherlands, near the German border. It is a rail junction with textile, rubber, and machinery manufacturing. Enschede was rebuilt after a fire largely destroyed it in 1862. De Kogge, a Dutch, Flemish, and German writers group, meets in the city triennially., the Netherlands.

Nagel, Xu, and Zhang made their unexpected observations while releasing alcohol drops onto glass slides in a sealed chamber with adjustable air pressure. To monitor the impacts, the team filmed them at 47,000 video frames per second.

The experimenters also found that replacing air with lighter gases, such as helium, diminished splashing and that heavier gases, such as krypton
krypton 81m  an unstable radioactive isotope of krypton having a half-life of 13 seconds and emitting gamma rays (0.19 MeV); used in pulmonary ventilation studies.


kryp·ton (krp
, enhanced it.

To explain their results, the Chicago researchers posit that the leading edge of a fallen, squashed drop rushes outward, compressing a thin layer of gas next to the glass surface. At normal pressure, as the gas resists this compression, it forces up the film's edge, which then breaks up. The result: a splash.

But at reduced pressures--or if the gas is light--the compressed gas resists less vigorously, generating a weaker splash or none at all. The splash is "very tunable," Xu says.

The team details its findings in a report on the Internet site called ArXiv, where physicists often post new results (www.arxiv.org/abs/physics/0501149).

Splashing occurs, for better or worse, in many industrial processes, such as fuel combustion, ink-jet printing, and the coating and washing of various products. The Chicago findings could have practical importance, comments David Quere of College de France in Paris, because they have revealed "a new and very efficient way to prevent the splash."
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Title Annotation:This Week; Air pressure effects on fluid drips
Author:Weiss, P.
Publication:Science News
Date:Feb 12, 2005
Words:344
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