BRISTOL, England, Oct. 8 British scientists have shown liquid drops can travel uphill when the surface they are on is vigorously shaken up and down.
Everyone is familiar with raindrops on a window. The small ones stay in place while the big ones roll down the window. That occurs because surface tension holds the small drops onto the screen until they grow to a size where the force of gravity is greater than the surface tension.
University of Bristol mathematicians have shown such small drops can defy gravity and travel uphill -- even on an incline as steep as 85 degrees -- if the surface vibrates up and down sufficiently strongly.
Mathematics Professors Jens Eggers and Philippe Brunet said the drops become compressed as the shaking plate rises, and it bulges upward as the plate falls.
"If the shaking is vigorous enough to overcome surface tension experienced as the drop is compressed, the drop will tend to lean forward, producing a net force which drives the drop uphill," said Eggers.
The scientists said their research, which appears in the online issue of the journal Physical Review Letters, might prove useful in understanding the small-scale manipulation of fluids.
Copyright 2007 by UPI
