Physicists make 'tractor beam' in water

Scientists in Australia have produced a "tractor beam" in a water tank, the BBC reports. 

They can control the movement of a floating ping-pong ball just by making a specific pattern of waves.

By changing the pattern, they moved the ball around the tank in various ways, including pulling it closer like the famous beam from science fiction.

The findings, published in the journal Nature Physics, have the potential to help contain oil spills or control and retrieve other floating debris.

"No one could have guessed this result," said Dr Horst Punzmann, who led the project at the Australian National University in Canberra.

"We have figured out a way of creating waves that can force a floating object to move against the direction of the wave."

Dr Punzmann and his colleagues used a very fast videocamera to record the water movements that resulted from a range of different shapes, plunged in and out of the water at various speeds.

They also covered the surface with floating tracer particles that allowed them to see the direction of currents on the water surface, which are distinct from the patterns of the waves themselves.