What do quicksand, liquid body armor and silly putty have in common? They are all a particular type of non-Newtonian fluid know as dilatants, also called shear thickening fluids. With common Newtonian fluids, temperature is the only factor affecting viscosity. This is a flow property you’re likely familiar with if you’ve ever warmed up thick maple syrup to drizzle over pancakes. The viscosities of non-Newtonian fluids, on the other hand, are dependent also on shear stress or time, resulting in the categories of shear thickening, shear thinning, time thickening and time thinning, along with a couple more variations.
Grant Crilly in the kitchen mixed up a batch of oobleck (cornstarch and water) the other day. Being a shear thickening fluid, the material was runny, and you could easily run your hand through a vat of the stuff as long as you moved slowly. However, a quick jolt will turn the oobleck into a near solid, bringing the mixing hand to a stop. Stress or agitation increases the viscosity. If this stress is applied in a uniform manner, under certain frequencies, otherworldly behavior results. For our demonstration, a subwoofer hooked up to a frequency generator did the trick.