Physicists at the Australian National University (ANU) have created a tractor beam on water, providing a radical new technique which could confine oil spills, manipulate floating objects or explain rips at the beach.
The group, led by Professor Michael Shats, discovered they can control water flow patterns with simple wave generators, enabling them to move floating objects at will.
“We have figured out a way of creating waves that can force a floating object to move against the direction of the wave,” said Dr Horst Punzmann, from the Research School of Physics and Engineering.
“No one could have guessed this result,” he said.
The new technique gives scientists a way of controlling things adrift on water in a way they have never had before, resembling science fiction tractor beams which draw in objects.
Using a ping-pong ball in a wave tank, the group worked out the size and frequency of the waves required to move the ball in any direction they want.
Advanced particle tracking tools, developed by team members Dr Nicolas Francois and Dr Hua Xia, show the waves generate currents on the surface of the water.
“We found that above a certain height, these complex three-dimensional waves generate flow patterns on the surface of the water,” Professor Shats said.
“The tractor beam is just one of the patterns, they can be inward flows, outward flows or vortices.”
The team also experimented with different shaped plungers to generate different swirling flow patterns.
As yet no mathematical theory can explain these experiments, Dr Punzmann said.
“It’s one of the great unresolved problems, yet anyone in the bathtub can reproduce it,” he says. “We were very surprised no one had described it before.”
In theory this can be done at home but in a practical sense it’s more difficult.
Professor Shats told Business Insider a vertically oscillating plunger is needed to produce periodic waves on the wave surface. It is important to control the wave heights and their frequency (8-14 oscillations per second).
“In our experiments we used a computer controlled electrodynamic shaker which oscillated the plungers,” he says. “Apart from this, anyone can create surface flows by generating waves in a sufficiently large water container.”
The research is published in the journal Nature Physics.
Watch the tractor beam at work:
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