When Liquids Rebel
For a bit of science today, I’d like to mention non-Newtonian fluids. Normally when you stir a fluid, it doesn’t change its viscosity based on how fast you stir it. Custard stays viscous (or thick,) and water stays relatively easy to stir. This is because they’re Newtonian fluids, which means they move as Isaac Newton’s equation predicted.
More interesting fluids, though, act in strange ways. If you’ve ever played with Silly Putty, you’re somewhat familiar with this. Move it slowly, and it will behave like a non-sticky molasses. Hit it with a hammer, and it will shatter. There are some liquids that are even cooler, though. Oobleck, which is a mixture of two parts corn starch to one part water, can behave like nothing we’re used to when you vibrate it regularly.
When you apply stress to the oobleck, the stress causes it to thicken—this is why it acts more like a solid when the speaker is on, but more like a liquid when it’s on the lip or the speaker is off. Specifically, oobleck is a shear-thickening liquid. When you apply shear stress to it, the viscosity increases and the liquid thickens.
Other liquids, though, are shear-thinning, and this is often quite handy in our lives. Latex paint is an excellent example: when you spread it on the wall with a brush, it flows evenly. But when you stop applying stress to it with the paint brush, it doesn’t drip and run off of the wall. Shear-thinning liquids can behave strangely too, and I would like to leave you with an example of jetting liquids, known as the Kaye Effect.
Posted by carneywilson on Jun. 08, 2010