The Weissenberg Effect and Other Amazing Things About Non-Newtonian FluidsRead Now
When a spinning rod is inserted into a normal fluid like water, the spinning of the rod will introduce a rotation into the liquid that will push it outwards. When you step on water, you will sink. When you subject water to sound waves, it will cause ripples in the water surface and maybe even make it splash, but the water will remain liquid. This is because water and other such liquids are what are called Newtonian fluids. These are fluids whose viscosity always remains constant. But there are other types of liquids that are called non-Newtonian fluids which have some rather amazing properties due to the fact that they can change their viscosity in response to stresses or forces applied to them.
One property of non-Newtonian fluids is shown in the video below. When a spinning rod is inserted into the fluid, the shear stress of the spinning rod will cause the fluid to thicken and be drawn to the rod creating an inward force that will push the fluid in contact with the rod upwards. This is called the Weissenberg effect after the Austrian physicist Karl Weissenberg who studied it.
When you suddenly apply pressure to a non-Newtonian fluid such as cornstarch, the stress induced on the liquid will turn it momentarily into a solid. This property allows you to walk on the liquid or even ride a bike on it as shown in the video below.
Sound waves can also introduce shear stress into cornstarch leading to some interesting effects as shown in the video below.