The drop of water that fails to splash


HERE'S a Zen-like question. If a drop of liquid falls on a flat surface and there is no air around it, does it make a splash?

The answer, which may or may not help you reach nirvana, is no. \"This was to us an incredibly surprising result,\" says Sidney Nagel of the University of Chicago in Illinois. \"If you didn't have the air, you couldn't splash. This means you would never get splashing on the moon.\"

Nagel and fellow physicists Lei Xu and Wendy Zhang were trying to measure the energy of liquid droplets flying away from splashing drops of alcohol. To eliminate any effects of air, they carried out the experiment in a vacuum chamber, where they could reduce the pressure within the chamber from the standard atmospheric pressure of about 1 bar down to 10 millibars. The team found that the lower the air pressure, the less the liquid splattered. And the splash disappeared when the air pressure reached about 0.2 bar.[/b]