Oobleck Explained by Physicists

July 15, 2012 • Commentary • by
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You may have discovered the mysterious substance known as “oobleck” in your third grade science unit, but do you really know how it works? Now you may finally find out. A team of rubber-suited physicists at the University of Chicago are getting their hands, lasers, sensors, and high-speed cameras dirty with the deceptively simple concoction trying to discover the causes of and potential applications for its unusual properties.

Oobleck is a simple mixture of cornstarch and water, combined at about a 2:1 ratio. When sitting still, it looks like an ordinary milky liquid. However, when disturbed by forces like a sudden strike, pulling, or vibrating, oobleck defies Newtonian physics and becomes a solid strong enough for adults to walk across. The substance gets its name from the Dr. Seuss book Bartholomew And The Oobleck, in which green ooze falls from the sky instead of rain. To go along with the story, oobleck is often dyed green with food coloring for effect.

Now a staple of grade school science curricula, oobleck begs the question of its observer: liquid or solid? Because the substance has characteristics of both at different times, it perplexes people of all ages. And that’s for good reason: oobleck actually defies Newtonian physics (in which the same substance cannot simultaneously behave as a liquid and a solid) and is classified as a non-Newtonian fluid alongside flubber and silly putty. In an attempt to understand its properties, these physicists put oobleck to the test of high-speed cameras and force sensors and feature their findings in this video:

As fun and frivolous as the experiment sounds, a press release cited several practical applications for suspension substances like oobleck:

Handling suspensions is important to a broad range of industries, from construction to biomedicine. Some engineers are even investigating these suspensions as the basis for a new type of body armor.

“It would be liquid, so it would conform to a particular shape, and when it gets hit hard it knows it needs to become hard,” Waitukaitis said. It’s a smart material, one that increases resistance with the amount of force applied against it.
 

The scientists behind the experiment, physicists Scott Waitukaitis and Heinrich Jaeger from the University of Chicago, reported their findings in Nature last week in an article titled “Impact-activated solidification of dense suspensions via dynamic jamming fronts” that’s worth checking out if you’re the physics type. As for me, I’m content to gape in astonishment at the goo like my third-grade self.

Attritbution

Messy experiment cleans up physics mystery of cornstarch, UChicago News
Impact-activated solidification of dense suspensions via dynamic jamming fronts, Nature

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