Is it possible to run or bike across the surface of a liquid? This demonstration by Kevin Delaney of the Discovery Channel’s Street Science features a 25-foot-long pool and 9 tons of the cornstarch and water mixture known as oobleck, our favorite non-newtonian fluid.
British polymath and Enlightenment hero Isaac Newton studied lots of things: optics, gravity, waves, mathematics, astronomy, history, religion and alchemy and so on. Then in his spare time, he investigated how liquids flow and thus got a whole branch of fluid dynamics named for him. Newton observed how common liquids, such as water, flow the same regardless of how much stress you subject them to. Push a stirring stick into a cup of water and swish it around. The water’s viscosity – how smooth or sticky its consistency is – stays the same.
Pretty simple, yeah? Many liquids that we interact with on a regular basis work this way: things like water, milk, oil, or juice. But there are also a lot of common fluids that don’t. These are non-Newtonian fluids; substances whose viscosity changes based on how much pressure you apply to them.
2022 update: The original video disappeared and was replaced by the similar video above. From the original: