Tractor Beam Created Using Water Waves� — The Physics arXiv Blog — Medium

Tractor Beam Created Using Water Waves� — The Physics arXiv Blog — Medium: This fluid jet carries any floating particles along with the waves...

But as the waves get bigger, they become unstable and their behaviour changes dramatically...

Punzmann and co say the interaction between the waves in this non-linear regime changes the direction of the jet at the centre of the wave maker. “It now pushes floaters inward, towards the wave maker and against the wave propagation,” they say. Any floaters caught in this jet, are therefore pulled.

To test this idea, Punzmann and co have recreated exactly this situation in a wave tank with an elongated wave maker. They place a ping-pong ball on the water and then measure its movement as well as the shape of the water surface and the fluid flow on the surface.

Sure enough, when the amplitude of the waves is small, the ping-pong ball moves in the same direction as the waves. But as the waves become larger, the ping-pong ball reverses direction and moves back towards the wave maker...