A non-Newtonian fluid (NNF) is a fascinating substance that defies the standard behavior of liquids, acting sometimes like a fluid and sometimes like a solid. Unlike common liquids, which have constant viscosity regardless of applied force, non-Newtonian materials change their viscosity based on the stress or “shear” they experience. The most famous example is Oobleck, a simple mixture of cornstarch and water made easily at home. This unique material allows for a hands-on exploration of complex physics.
Materials and Mixing Instructions
Creating this unique fluid requires cornstarch, water, and a mixing bowl. Use a wide bowl for easy mixing and play. While a spoon or spatula helps with initial combining, final mixing is best done by hand to feel the changing consistency.
The targeted proportion is roughly two parts cornstarch to one part water, but achieving the correct consistency requires adding the water gradually. Start by pouring the cornstarch into your bowl, then slowly introduce the water, stirring continuously with your fingers. If the mixture feels too dry and crumbly, add a few more drops of water; if it is too soupy and splashes easily, incorporate a little more cornstarch.
The ideal mixture is achieved when you can easily stir it slowly, but attempting to tap or strike the surface results in a feeling of firm resistance. You should be able to quickly scoop up a handful and roll it into a ball, only to have it instantly relax and flow through your fingers the moment you stop applying pressure. This responsiveness demonstrates that you have successfully created a shear-thickening fluid.
The Science Behind the Behavior
The strange dual nature of this fluid stems from the fact that it is a concentrated suspension, not a solution. The microscopic cornstarch particles do not dissolve but remain suspended within the liquid, packed densely together and separated only by a thin layer of water.
When moved slowly, the water acts as a lubricant, allowing the cornstarch particles to easily slide past one another. This low-speed movement applies minimal shear stress, resulting in low viscosity and easy flow, much like a normal liquid.
However, when a sudden, high-force impact (high shear stress) is applied, the behavior changes dramatically. The rapid movement forces the water out from between the particles. This removal of the lubricating water causes the cornstarch particles to jam or “lock up” against each other, forming a rigid, solid-like structure that resists the force. This phenomenon is known as shear-thickening, where viscosity increases dramatically with the rate of force applied. Once the stress is removed, the water flows back in, and the substance returns to its liquid state.
Tips for Handling and Cleanup
To maximize enjoyment, try experimenting with different ways to interact with the fluid, like pouring it slowly versus slapping it quickly, or even vibrating it on a speaker cone. If you wish to save the mixture, you can store it in a sealed container for about a day or two, though it will likely separate. If it dries out, simply mix in a splash of water to restore the consistency.
The most important rule for disposal is to never pour the fluid down any household drain. As the water evaporates or is washed away, the cornstarch residue will dry and solidify inside the pipes, creating a stubborn clog. Instead, scrape the bulk of the material into your regular trash bin using a spatula or paper towels.
For any residue left in the bowl or on surfaces, allow it to dry out completely. It will turn into a powder or a brittle crust that can be easily scraped off and thrown away. Alternatively, small amounts are biodegradable and can often be safely added to a compost pile.