Fluid rope trick investigated

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Original entry by Joerg Fritz, AP225 Fall 2009


"Fluid rope trick investigated"

L. Mahadevan, W.S. Ryu, A.D.T. Samuel: Nature, 1998, 392, pp 140 to 141


Buckling, Viscosity, Surface tension, Instability


Fig.1 A slightly more reproducable version of the honey-toast problem: silicon oil filament coiling due to abuckling instability.

This paper studies a very rich problem at the interface between fluid dynamics and classical mechanics that can be observed in thousands of household every morning. If honey is poured from a sufficient height, it approaches the morning toast as a thin filament which twists and whirls steadily even if the pouring hand is completely static. This can be explained by the theory of buckling with very simple scaling laws.

The Math

Fig.2 Plot of normalized coiling frequency over the radius of the falling filament.

What sets the speed with which the honey rotates? We could imagine up to six parameters that could have an influence on the rotation speed. On an intuitive basis it could depend on


working on it