Technical Glossary Dilatancy

[Dilatancy]

Water mixed with cornstarch at a ratio of 1:1 hardens when gripped strongly, but when placed on a desk, flows like a liquid. This property is called dilatancy, which is a property of a non-Newtonian fluid. In other words, an object with dilatancy responds like a solid to a fast, external force and responds like a liquid to a slow, external force.
Since these fluids harden in response to high-speed external forces, it is expected that they also be resistant against sudden shock. There have been attempts to utilize this property to make bulletproof vests.
Originally, dilatant meant “expanding,” which was chosen to describe the strange expansion which occurs when pressure is applied to a liquid in which powder is dispersed. When walking on a wet sandy beach, it appears as though the area around your foot dries out when stepped on. Actually, the sand is expanding due to the applied pressure; the gap between the sand grains increases, causing the water to drop below the surface of the sand.