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Why is ketchup so hard to pour? - George Zaidan

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Ever go to pour ketchup on your fries…and nothing comes out? Or the opposite happens, and your plate is suddenly swimming in a sea of red? George Zaidan describes the physics behind this frustrating phenomenon, explaining how ketchup and other non-Newtonian fluids can suddenly transition from solid to liquid and back again.

We say that a non-Newtonian fluid’s thickness (“apparent viscosity”) depends on how hard, how long, or how fast you apply a force. But aren’t a force’s magnitude, time, and speed related somehow? Do you think applying a strong quick force would have the same effect as a weak long force? Why or why not?

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