On the Mechanical Properties of Oobleck

Abstract

The effect of velocity on the drag force acting on a sphere moving through varying concentrations of oobleck, a suspension of cornstarch in water, was studied. A ball was pulled horizontally through the oobleck with different forces and the resulting velocity of the ball was measured. For the lowest concentration of oobleck tested, 50%, the drag force remained proportional to velocity, indicating that it acted like a Newtonian fluid. However, as concentration increased the behavior deviated from this. For the higher concentrations, 54-56%, the velocity stayed constant no matter how great the force with which the ball was pulled through the oobleck, indicating that it had transitioned to a non-Newtonian fluid. It was also shown that drag force increases with increasing depth for the highest concentrations, likely due to the properties of the oobleck being sensitive to a small increase in pressure.

Keywords

• oobleck
• non-newtonian fluid
• drag force
• velocity