Non-Newtonian fluids are usually liquid, but when force is applied they can change to be more solid or more liquid. Oobleck (a mixture of cornstarch and water) looks and behaves like a liquid, but you can walk over it as if you were walking on water.(Ketchup is also non-Newtonian, except that it gets runnier when you apply pressure. That’s why you have to hit the bottom of the bottle to get it out.)
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