If you've ever tried to retrieve an object that's floating away in a lake or the ocean, then you'll know how frustrating it can be, trying to draw that item towards you. According to research recently conducted at The Australian National University (ANU), however, it's possible to move such objects in whichever direction you wish – as long as you can generate the right type of waves.
The research team experimented with a table tennis ball floating in a wave tank. By precisely manipulating the size and frequency of three-dimensional waves created by a wave generator, they were able to keep the ball in place, move it away from the generator, or even towards it – in the case of the latter, the ball was actually moving against the waves that were traveling out from the generator.
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Although the scientists did establish that the waves generate flow patterns along the surface layer of the water, the actual mathematics behind the phenomenon are still not understood. "It's one of the great unresolved problems, yet anyone in the bathtub can reproduce it," said project leader Dr. Horst Punzmann. "We were very surprised no one had described it before."
It is hoped that if scaled up, their findings could be used in applications such as containing oil spills, retrieving drifting watercraft, or better understanding rip tides, in which swimmers are drawn away from the shore even though the waves are moving towards it.
A paper on the research was published today in the journal Nature Physics. The wave tank experiments can be seen in the video below.
Source: Australian National University