Last updated on May 19th, 2023 at 03:17 am
All of you must be familiar with the motion of honey when you pour it, isn’t it? It’s a very common and usual thing we all have observed in our day to day life.
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Whenever we pour honey from its bottle or a spoon it falls of the surface forming alternate sheet-like layers. This is pretty amazing. The faster you make it pour the faster the alternate sheet-like layer formation takes place. However, you must be thinking what’s there in this to be so fascinated about. Its the normal behavior of honey and its due to its high viscosity.
Well, wait let me ask you what will happen if we keep on increasing the speed of the flow and reach high speed? Will the same sheet-like layers fill be formed or something else will happen? This is what happens when we pour honey at high speed-
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Now, that’s fascinating, isn’t it? This is known as the Rope Coiling Effect of Honey.
What is the Rope Coiling Effect?
The tendency for a falling stream of very viscous liquids, like honey, to coil like a rope when it strikes a horizontal surface is known as the Rope Coiling Effect.
Experimental Setup: a) Low Coiling Frequencies b) High Coiling Frequencies
The dynamical regime in which coiling takes place is determined by the strengths per unit rope length of the viscous (abbreviated as FV), gravitational (abbreviated as FG), and inertial (abbreviated as FI) forces within the coil.
Because the rope radius is nearly constant in the coil, the forces depend strongly on the radius, which in turn is determined by the amount of gravity-induced stretching that occurs in the tail. Also, this stretching increases
with height, and the relative magnitudes FV, FG, and FI are themselves
functions of the height. As the height increases, the coiling traverses a series of distinct dynamical
regimes characterized by different force balances in the coil.
As observed the rope’s radius is nearly constant at the lower end of the gravitational regime, weirdly implying that gravitational stretching in the tail can be negligible in “gravitational” coiling. This apparent paradox is resolved by the rationale that for a given strain rate, FV due to the bending and twisting of a slender rope are much smaller than those that accompany stretching. Gravity primarily affects the (bending/twisting) coil initially and has a significant impact, while its influence on the (stretching) tail is minimal and occurs later in the process. Consequently, gravity can be dominant in the former and negligible in the latter simultaneously.
When the height gradually increases ‘inertial’ coiling is observed. Viscous forces in the coil are now nearly completely balanced by inertial forces (i.e. FI ≈ FV ≫ FG), giving rise to what we know as inertial coiling.
This is the #001 article in the article series: “Fluidify – Go With The Flow”. Keep following us to explore more about liquids because it’s all about fluids.
References:
N. M. Ribe, M. Habibi, Daniel Bonn; Stability of liquid rope coiling. Physics of Fluids 1 August 2006; 18 (8): 084102. https://doi.org/10.1063/1.2336803
Mehdi Habibi. Coiling Instability in Liquid and Solid Ropes. Fluid Dynamics [physics.flu-dyn]. Université Pierreet Marie Curie – Paris VI, 2007. English. NNT: . tel-00156591
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