Non-Newtonian fluid

From Wikipedia:

A non-Newtonian fluid is a fluid in which the viscosity changes with the applied strain rate. As a result, non-Newtonian fluids may not have a well-defined viscosity.

This video demonstrates the principle nicely; it shows a big pool filled with a mixture of corn starch and water (which is a non-Newtonian fluid), and how people can run across the surface quickly (acts as a solid) but if they move slowly they sink into it (acts as a liquid). Pretty cool!

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