Question #7f383

1 Answer
Jan 11, 2015

The definition of a fluid is a substance which can sustain no shear stress. If you try to impose a shear, the fluid will flow to eliminate the shear.

For example, if you have a plastic bottle half full of water, squeezing the middle will momentarily impose a shear stress. After a brief time (limited by the viscosity and mass of the water) the water will assume a new shape and return to being stationary.

If you filled the bottle instead with some solid latex, squeezing the center would cause the material to change shape. However, the material in the middle would be under much more stress than the material at the edges. And the latex would exert forces on the bottle differently at different points depending on how much shear stress is being exerted.