'Paint Is Probably the Internet’s Second Favorite Non-Newtonian Fluid to Vibrate on a Speaker'

By Alexis C. Madrigal

There are many good media-producing subsubsubcultures on the Internet.

For example, there are people who make slow-motion videos and and there are the people who use the f-word to describe their love for science.

But Internet magic really happens when two groups like this join forces, as in this post on the fluid dynamics of paint vibrating on a speaker from the blog, Fuck Yeah Fluid Dynamics, about a video produced by The Slow Mo Guys.

FYFD tells us precisely what to watch for and why in a video that was already wonderful. It's the science nerd version of Peyton Manning describing how a beautiful play was executed:

It all starts at 1:53 when the less dense green paint starts dimpling due to the Faraday instability. Notice how the dimples and jets of fluid are all roughly equally spaced. When the vibration surpasses the green paint’s critical amplitude, jets sprout all over, ejecting droplets as they bounce. At 3:15, watch as a tiny yellow jet collapses into a cavity before the cavity’s collapse and the vibration combine to propel a jet much further outward. The macro shots are brilliant as well; watch for ligaments of paint breaking into droplets due to the surface-tension-driven Plateau-Rayleigh instability

But two questions remain unresolved.

One, what is a non-Newtonian fluid? There are complex answers, but a simple one is that it's a fluid that does not behave like water. Its viscosity changes in response to the force applied to it. (FYI, the most generally awesome non-Newtonian fluid is quicksand.)

And two, what does FYFD say the number one non-Newtonian fluid to vibrate on a speaker is? That would be Oobleck, a mixture of water and cornstarch. Which looks like this, when it is vibrated on a speaker:

Or if you prefer, which you probably do, here is astronaut Don Pettit vibrating some oobleck on a speaker in space ("Here we don't have to worry about the effects of gravity because we're on space station"):

For what it's worth, Pettit has a remarkably good explanation for what's going on with the oobleck. "What you see here is a balance between surface tension force and the sheer force imparted into the fluid from the speaker oscillating," he says. "You can do this on Earth, I understand."

This article available online at:

http://www.theatlantic.com/technology/archive/2013/12/paint-is-probably-the-internet-s-second-favorite-non-newtonian-fluid-to-vibrate-on-a-speaker/282209/