Well, how many of you love to play or experiment with shampoos and soaps? If you are one of them then this article is like a treat to you all.
We often hear that science is all around us in our day to day life and it is also very true. But, it is surprising to know that the small things we happen to ignore demonstrate basic laws of science in a practical way. In today’s article, we are going to discuss something that’s very common yet we fail to observe it.
Try it out
Pour a steady flow of shampoo from a height of 30cm about the surface. Make sure that you try to pour it at a single point itself. What is expected to be observed? A heap of shampoo on the surface, true but, it is also accompanied by something strange as well. Have a look-
Did you observe the mysterious and bizarre jet like steam coming out of the heap of shampoo? This is called Kaye Effect and is observed thin shear-thining fluids. By far in practical life, it has been observed in shampoos only, but other shear-thinning fluids may also show Kaye Effect under suitable conditions.
What is the Kaye Effect?
The Kaye effect was first reported in 1963 by British engineer Alan Kaye, who noticed this unusual behavior when working with complex organic liquids. A complete explanation for this phenomenon remained uncertain until 2006 when Dutch researchers did some clever work to elucidate the effect.
What is Shear-Thining?
In reality, most fluids are non-Newtonian, which means that their viscosity is dependent on shear rate (Shear Thinning or Thickening). In contrast to Newtonian fluids, non-Newtonian fluids display either a non-linear relation between shear stress and shear rate.
Fluids are shear thinning if the viscosity decreases as the shear rate increases. Shear thinning fluids, also known as pseudo-plastic, are ubiquitous in industrial and biological processes. Common examples include ketchup, paints, and shampoo.
Most of the time, the shampoo just forms a heap on the bottom of the surface, something like this:
Occasionally, however, a dimple forms at the top of the pile. This is due to the fact that the jet of the falling shampoo has some momentum and exerts a force on the heap. Then a thin layer of shear-thinned fluid forms in the dimple, making a slippery barrier between the heap and the descending stream, preventing their merging. The stream gets a ramp-like structure to get deflected and launches from the dimple like a ski jumper: This in accordance with conservation of momentum as extra in coming shampoo is ejected out.
Why there is a time lapse between the jets?
Once the stream of extra incoming shampoo is ejected the dimple begins to fill up again. They form a heap and the cycle continues. Therefore there is a time lapse between the outgoing jets of the shampoo.
Video Courtesy – ” Steve Mould “