"The Tornado in the Shower," R&D News section, Discover, October 2001.
David Schmidt (University of Massachusetts) wanted to find out why theshower curtain billows inward when you turn on the water. He used asoftware package to create a virtual shower and after 1.5 trillioncalculations thinks he has found the answer. Drops of water from theshowerhead decelerate due to aerodynamic drag, and the slowdown pulls theair around the droplets into a tornado-like vortex, which creates alow-pressure center that can suck in a lightweight curtain.
--- Annette Emerson