Solid or liquid? - Studying

From What's Next In Science & Technology:

In a simple experiment on a mixture of water, surfactant (soap), and an organic salt, two researchers working in the Pritchard Fluid Mechanics Laboratory at Penn State have shown that a rigid object like a knife passes through the mixture at slow speeds as if it were a liquid, but rips it up as if it were a rubbery solid when the knife moves rapidly. The mixture they study shares properties of many everyday materials -- like toothpaste, saliva, blood, and cell cytoplasm -- which do not fall into the standard textbook cases of solid, liquid, or gas. Instead, these "viscoelastic" materials can have the viscous behavior of a fluid or the elastic behavior of a solid, depending on the situation.

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