Bouncing Indefinitely

On the surface of a gently vibrating liquid, a droplet can bounce indefinitely without coalescing, kept aloft by an air film too small to see. As long as the droplet lifts off before the air layer drains out from under it, the droplet won’t contact the water below. Now scientists have shown that this is possible with a solid surface, too.

Using an atomically smooth mica plate, researchers were able to bounce a droplet indefinitely without wetting the surface. At higher vibration rates (below), the droplet essentially hovers in place, bouncing so quickly that we simply see its shape vibrating in response to the surface. (Image and research credit: L. Molefe et al.; via APS)