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It is a common observation that honey(or any other viscous fluid),tends to overlap/coil/wind up as it reaches the rigid surface. There is this little bend near the pile-up. Why is this so? How does a liquid 'communicate' where it has to start coiling? And why is the coil a sure thing? Can one mathematically determine the pattern formation, and if yes,what would be the factors involved.

Edit: I experimented further, and noticed something interesting . I used honey, and oil as a control. While the oil behaved as expected , the honey was not so.

Up until a certain height,the falling fluid formed uniform patterns(coiling) but soon it became haphazard and criss cross.Further increasing the height caused the pattern to stabilise again. What is going on in this intermediate height?

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  • $\begingroup$ The basic explanation is quite simple: the initial drop of honey creates a bump on the surface (because of it's viscosity), and the honey following it 'rolls off' this bump. This then goes around in a circle. The mathematics are not so straightforward however. Video about the subject - further reading (with mathematics). $\endgroup$
    – Jeff
    Mar 28, 2016 at 14:05
  • $\begingroup$ If one looks closely,the bend appears a few millimeters aboves the spot of actual sliding,doesn't it? $\endgroup$
    – Abhinav
    Mar 28, 2016 at 14:07
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    $\begingroup$ That is again an effect of the viscosity: the displacement is at its maximum at the surface, and this displacement gradually decreases as you go up the stream. $\endgroup$
    – Jeff
    Mar 28, 2016 at 14:30
  • $\begingroup$ This is similar to what happens when you hold a flexible thread vertically from the upper end then move it down to let it pile over a horizontal surface $\endgroup$
    – Tofi
    Mar 28, 2016 at 17:19
  • $\begingroup$ Interesting example, but contrary to a fluid a thread has no viscous forces, then why would it pile sideways to form a loop? $\endgroup$
    – Abhinav
    Mar 28, 2016 at 17:21

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It is possible to determine mathematical conditions for when a given fluid released at a given height will coil. And moreover it is possible to model the shape of the fluid rope! This paper (which hopefully you can access) gives a very neat and accessible explanation of the phenomenon:

Liquid Rope Coiling - Ribe, Habibi, and Bonn - Annual Reviews of Fluid Mechanics. 2012

There are in fact several distinct regimes of liquid rope coiling, but overall a good physical explanation can be found in their summary points:

The coiling of a liquid rope falling onto a surface is an example of a buckling instability, in which a slender object subject to an axial compressive stress becomes unstable to deformation by bending. In general, a coiling liquid rope comprises a long, quasi-vertical tail that deforms mainly by gravity-induced stretching and a helical coil that deforms primarily by bending. Because the differential equations governing bending are of higher order than those describing stretching, the coil can be thought of as a boundary layer in which the bending stresses permit the satisfaction of all the boundary conditions at the surface onto which the rope falls. (emphasis mine)

As to your experiments with honey, the irregular behavior may be due to the fact that honey is a non-Newtonian fluid. The nonlinear dependence of the interior shear stresses on velocity gradients may produce different (even chaotic) behaviors such as the 'haphazard' collapsing of the column you describe (or it could be something else, don't quote me).

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