Particles defy gravity, float upstream

Inspired by tea leaves’ reverse route, physicists demonstrate that water’s surface tension allows unexpected movement

By Andrew Grant, 11:15 AM July 11, 2013

Rogue tea leaves have led physicists to the discovery of a counterintuitive phenomenon: Particles can float upstream in moving water.

“It’s interesting and very cool,” says Eva Kanso, a physicist at the University of Southern California. “I’m going to have my students do an experiment like this.”

Any kayaker, plumber or physicist would probably say that things always flow downstream. But that conventional wisdom started to unravel for Sebastian Bianchini one night in 2008 when he prepared some ...

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