Wanna make a water droplet dance? Turns out all you need is a pair of opposing ultrasonic speakers. Called acoustic levitation, this technique holds droplets of water against gravity using ultrasonic waves. While this process has been done before, a team of scientists took the experiment a step further and influenced the shape of the water drops. Typically, when a drop of water is levitated within an acoustic field it creates a flat sphere. The shape of the droplet is detrmined by the combination of acoustic pressure trying to flatten the drop and surface tension, which tries to pull the drop into a sphere. By manipulating the strength and frequency of the acoustic field, researchers were able to make the droplet change shape and appear to dance as seen in this mesmerizing video.
Source: "Shape oscillation of a levitated drop in an acoustic ﬁeld," by W. Ran & S. Fredericks at Clemson University, Department of Mechanical Engineering