What happens when you fill a pool with a non-Newtonian fluid? Well, for one, you can hold races across the surface! In this video, the pool is filled with a mixture of cornstarch and water, a shear-thickening fluid known as oobleck.
Category: Phenomena
Dripping into Droplets
The Plateau-Rayleigh instability is one that just about everyone has witnessed. It describes how a liquid jet breaks up into droplets. Notice the waviness in the jet before breakdown. The tiniest curvature in the jet causes an imbalance in the liquid’s pressure due to surface tension. Because the system is unstable, any small changes will become larger, ultimately resulting in the jet breaking into droplets.
Un-mixing a Flow
Laminar flow (as opposed to turbulence) has the interesting property of reversibility. In this video, physicists demonstrate how flow between concentric cylinders can be reversed such that the initial fluid state is obtained (to within the limits of molecular diffusion, of course!)
For more examples, see the first half of this video.
Floating on an Invisible Sea
Many gases may be invisible to the human eye, but that doesn’t make them the same. Sulfur hexafluoride is more than 5 times as dense as air at standard conditions, which lends itself to some fun demonstrations.
The Weissenberg Effect
Non-Newtonian fluids exhibit all kinds of odd behaviors, even climbing up a spinning rod! This is known as the Weissenberg effect and is associated with polymers in the fluid.
Bouncing into a Pool
Here is another take on what happens when a drop of water falls into a larger pool.
Automotive Wind Tunnels
Wind tunnels have been a staple of aerodynamics since the Wright brothers built one to help them test wing shapes for their gliders and airplanes. The GM Aerodynamics Laboratory’s much larger wind tunnel, pictured above, tests full-sized vehicles’ aerodynamics. It is the largest automotive wind tunnel and has been in operation since August 1980. GM estimates that it has cut the coefficient of drag on vehicles by approximately 25% in that time. The tunnel can reach speeds near 125 mph, as one hapless reporter discovered firsthand. (Submitted by @Vinnchan)
Fizziness in Space
Removing gravity has interesting effects on fluids. Here an astronaut aboard the ISS demonstrates what happens when Alka-Seltzer is added to water in microgravity.
Can a Squid Fly?
Evidence is mounting that several kinds of squid will use jets of water to propel themselves into the air where they can actively fly some 50 times their body length.
Turbulent Mixing in the Gulf
Sediments carried by rivers and stirred from the shallows meet the Gulf of Mexico in a vivid display of turbulent mixing. Although turbulence is not well-understood, it is a process vital to our lives. Without turbulence, it would take days for molecular diffusion to mix milk into your coffee! #
