Cornstarch Physics Is Shear Nonsense

Published in Science, 11 Jul 2012

Filling a small swimming pool with cornstarch and water has long been a physicist’s party trick. Step onto it slowly and you’ll sink but run across quickly and the oozy mixture will support your weight—almost as though it has turned from liquid to solid. Several reasons have been offered for the phenomenon, but now researchers believe they have the real answer.

Mixtures of cornstarch, water, and other suspensions have been known as “shear-thickening” materials. Shear is the type of stress that exists when particles slide over one another, and scientists thought that if the shear stress in a cornstarch suspension exceeded a certain threshold, the thickness or viscosity would increase massively—enough to support a person’s weight. […]

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