Why do some drops of water bounce and others do not?

Study the dynamics of water drops may seem futile. But it is not. Water droplets constantly collide in the clouds. And better understanding their behavior would also help develop techniques like3D printing sure metal. Today, precisely, physicists from the University of Warwick (UK) explain why some drops bounce and others do not.

When colliding with a surface, drops can either form a splash, spread over the surface, or even rebound. And it would seem that the fate of the drops is determined by the formation of an end air cushion. With a thickness of a few nanometers only. Kind of like the Moon came to bounce on the children's trampoline in the garden.

An illustration of what happens when a drop of water spreads over a surface with a zoom on the air cushion that forms between the two. © University of Warwick

Fall at the right speed

In general, an affinity, known to physicists under the name ofvan der waals attraction, is created between molecules of the drop and the molecules making up the surface. So, gout is like trapped. It does not rebound.

Through numerical simulations detailed, the researchers show, however, that the falling speed is capital. If it is too high, the drop crashes without a cushion ofair could have formed and prevented it. If it is too low, the Van der Waals strengths take over. It's only good speed that the drop simply bounces off the air cushion that forms between it and the surface.