27 in the journal Proceedings of the National Academy of Sciences, can be used to simulate oobleck's reaction to various forces, like being squeezed between two plates or hit with a projectile. This variable, which Kamrin jokingly refers to as "clumpiness," allows the model to determine how solid-like or liquid-like the oobleck will be. Most importantly, they added an extra variable to predict how many grains of cornstarch touch one another in a given region of the fluid. Kamrin and his team started with a computer model of wet sand that they'd already developed, making adjustments to better mimic wet cornstarch. But when squeezed together, friction takes over and the particles move like a solid. This repulsive force helps the slurry flow, as the particles prefer a layer of fluid between then. As a result, cornstarch particles in water actually repel each other slightly, held apart by forces too weak to impact something as large as a grain of sand. Cornstarch particles are a micron to 10 microns in size, smaller than the diameter of a human hair.Īt this size, particles are susceptible to the tiniest of thermal and electric forces, Kamrin said. But cornstarch is different, he said, largely because the particles are so tiny. The scientist and his team typically focus on the flow of sand, gravel and other industrial materials. "It really is like a liquid if you move it slowly, but it does everything you expect of a solid if you play with it quickly," Kamrin said.Īfter seeing a scientific talk about oobleck's properties, Kamrin and his colleagues launched a "very healthy" internal debate over how cornstarch and water might differ from other wet, granular materials. When you run your fingers slowly through cornstarch and water, it acts like a liquid, but apply rapid force, and it solidifies, bends and even tears. Oobleck is a non-Newtonian fluid, a term for fluids that change viscosity (how easily they flow) under stress.
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