The Kaye Effect
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A Liquid That Jumps
There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy.
While philosophers may indeed not have dreamed of certain phenomena, physicists strive to explore and understand them. There are many phenomena that may seem unbelievable at first, yet upon deeper examination, their mechanisms turn out to be quite natural.
One such fascinating phenomenon is the Kaye Effect, first described by British engineer Alan Kaye in 1963. He observed that when a liquid flows downward in a stream, it behaves in a highly unusual way: instead of merging with the rest of the liquid, the stream periodically "bounces" off its surface and shoots upward! You can see this effect in the animation below:
The Kaye Effect can be reproduced using materials readily available in any home.
What Do We Need?
The Kaye Effect occurs with shear-thinning non-Newtonian fluids. Where can we get such a liquid? It’s actually quite easy, as most shampoos, dishwashing liquids, and liquid soaps are shear-thinning fluids. You can use any of these liquids, but it’s best to try a few different types and select the one that works best.
Now, we need to set up a system that allows us to observe the effect. The chosen liquid must flow as a small, uniform stream without any turbulence. The easiest way to achieve this is by using a small valve and a thin tube that delivers the liquid from a container placed above. The drop height, i.e., the length of the stream, must also be adjustable.
If the liquid flows directly into a regular container, the liquid level will continuously rise, causing the stream length to change and making it harder to adjust. This can be solved by using a small overflow dish as shown in the diagram:
The liquid in the overflow dish maintains a constant level.
Before the experiment, fill the overflow dish. Then open the valve so that the liquid flows steadily and set the stream length to about 20 cm (8 inches). You should see a result similar to the one below:
Now all that’s left is to fine-tune the stream’s length and flow rate to achieve the Kaye Effect! You’ll notice it easily because the liquid will begin to behave very unusually: instead of immediately merging with the surface of the liquid, the stream will bounce off and shoot upward:
The entire experiment is also illustrated in my video below.
It's not uncommon to observe a multiple effect: the stream may bounce several times off the surface of the liquid, as shown in the photo below:
The points where the stream bends are marked with arrows.
Explanation
Non-Newtonian fluids exhibit many unusual properties, some of which I have also written about here. In general, a non-Newtonian fluid is any fluid that does not obey Newton’s law of viscosity. Unlike Newtonian fluids, the viscosity of non-Newtonian fluids is not constant and changes over time. As a result, the flow curve of such a fluid is nonlinear. When the shear stress increases less than proportionally to the increase in shear rate, the fluid is classified as shear-thinning. Conversely, when the shear stress increases more than proportionally to the increase in shear rate, the fluid is classified as shear-thickening.
The Kaye Effect is one of the viscoelastic phenomena that occur in non-Newtonian fluids. A single event lasts about 300 milliseconds, as the upward jet eventually collides with the downward stream. However, Dr. Devaraj van der Meer from the University of Twente in the Netherlands managed to produce a stable Kaye Effect on an inclined surface continuously wetted with a fluid solution. The photo below is from his website:
The phenomenon is not yet fully explained, but it is suspected that at the point where the stream hits the liquid surface, intense shear causes the liquid to thin, acting locally as a lubricant or an insulating layer that reduces surface friction. This prevents the stream from merging with the liquid, causing it to bounce or slide along the surface. Mathematical models of the phenomenon have been developed, and they accurately reproduce the behavior observed in reality.
Enjoy your experiments!
Further readings:
- Ball P., Puzzle of leaping liquid solved, Nature, opublikowano on-line: 6.04.2006
- Kaye A., A Bouncing Liquid Stream, Nature, 1963, 197, pp. 1001-1002
- Versluis M., Blom C., van der Meer D., van der Weele K., Lohse D., Leaping shampoo and the stable Kaye effect, Journal of Statistical Mechanics: Theory and Experiment, Vol. 2006
Marek Ples