Water tractor beam can control flow patterns

In a first, Australian physicists have created a tractor beam on water - a radical new technique that could confine oil spills or manipulate floating objects.

They found that water flow patterns can be controlled 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 Horst Punzmann from school of physics and engineering at Australian National University (ANU).

The new technique gives scientists a way of controlling things adrift on water in a way they have never had before, resembling sci-fi tractor beams that draw in objects.

Using a ping-pong ball in a wave tank, the team worked out the size and frequency of the waves required to move the ball in whichever direction they want.

Advanced particle tracking tools, developed by team members Nicolas Francois and Hua Xia, revealed that 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. The tractor beam is just one of the patterns, they can be inward flows, outward flows or vortices," explained professor Michael Shats.

The team also experimented with different shaped plungers to generate different swirling flow patterns.

"It is one of the great unresolved problems yet anyone in the bathtub can reproduce it. We were very surprised no one had described it before," Shats said.