London, Oct. 6: British scientists have managed to make drops of water defy gravity by flowing uphill.
Researchers achieved the unlikely feat by vigorously vibrating the droplets. The force created when they bulged upwards as the surface they were dropped on was enough to make them trickle up a steep slope.
Small raindrops on windscreens can remain in place due to surface tension, until they grow to a size where this force is overcome by gravity.
Mathematicians have now demonstrated small drops of various different liquids can be made to move up gradients as steep as 85 degrees.
Jens Eggers, from the University of Bristol, said: “This is totally new. It’s never been done before, and we’re still not totally sure exactly what’s happening.
“As the shaking surface rises the drop is compressed, while it bulges upward as the plate falls.
“If the shaking is vigorous enough to overcome the surface tension experienced as the drop is compressed, the drop will tend to lean forward, producing a net force which drives the drop uphill.
“We don’t completely understand why this is happening. It means there is a lot of interesting physics and maths to discover.”
The basic mechanism is that the drop has greater freedom to bulge upwards when the surface falls than it has to compress when the surface rises — creating a force which pushes it uphill.
Eggers and colleague Philippe Brunet discovered the phenomenon accidentally while investigating the properties of corn flour.