The video is of an effect known in fluid dynamics as the coalescence cascade, which can be observed (provided you have access to a video camera with a sufficiently high frame rate) when a drop of liquid is deposited very gently onto the surface of a layer of the same liquid. Fuck Yeah Fluid Dynamics explains:

When a droplet impacts a pool at low speed, a layer of air trapped beneath the droplet can often prevent it from immediately coalescing into the pool. As that air layer drains away, surface tension pulls some of the droplet's mass into the pool while a smaller droplet is ejected. When it bounces off the surface of the water, the process is repeated and the droplet grows smaller and smaller until surface tension is able to completely absorb it into the pool.


Pretty awesome, right? In the video shown up top, the effect manages to repeat itself four times (in what scientists who study fluid mechanics call "events") before the viscous properties of the resting pool become too strong for the smallest drops to withstand coalescing completely.

And while the highest number of events I've been able to find anywhere else is five (see the video above), MIT's John Bush claims to have observed as many as seven such events in a row. I just wish he'd included a video of it...


[Spotted on Fuck Yeah Fluid Dynamics]