MIT engineers were able to develop how the cornstarch-water mixture, a non-Newtonian fluid, can behave like a solid or liquid, depending on how fast it’s deformed. The mixture acts as a liquid when it’s swirled slowly. But it can behave as a rubbery solid, forming a glue-like string when deformed quickly.
It’s a phenomenon many preschoolers know well: When you mix cornstarch and water, weird things happen. Swish it gently in a bowl, and the mixture sloshes around like a liquid. Squeeze it, and it starts to feel like paste. Roll it between your hands, and it solidifies into a rubbery ball. Try to hold that ball in the palm of your hand, and it will dribble away as a liquid.
Most of us who have played with this stuff know it as “oobleck,” named after a sticky green goo in Dr. Seuss’ “Bartholomew and the Oobleck.” Scientists, on the other hand, refer to cornstarch and water as a “non-Newtonian fluid” — a material that appears thicker or thinner depending on how it is physically manipulated.
Using the mathematical model, MIT engineers were able to accurately simulated how oobleck turns from a liquid to a solid and back again, under different conditions.
“As long as you squish slowly, the grains will repel, keeping a layer of fluid between them, and just slide past each other, like a fluid,” Kamrin says. “But if you do anything too fast, you’ll overcome that little repulsion, the particles will touch, there will be friction, and it’ll act as a solid.”
Here’s a video of how the cornstarch-water mixture behaves when applied with various forces.
Image Credit: A. Baumgarten, K. Kamrin, and J. Bales
neat yo
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