Liquid rope coiling
Why does a thin stream of honey or syrup poured onto a surface coil up like a rope instead of falling straight down?
History and references
Settled in 1998 by L. Mahadevan, W. S. Ryu, A. D. T. Samuel (MIT/Princeton).
Barnes and Woodcock gave the first systematic experimental study of coiling honey and syrup streams in 1958, but a predictive theory was lacking for decades. In 1998, Mahadevan, Ryu and Samuel derived a scaling law relating the coiling frequency to the fluid's viscosity, the stream's flow rate, and the fall height, treating the thin viscous jet like an elastic rope (an analogy to the mechanical buckling of a falling rod). Their own group issued a correction in 2000 after realizing multiple distinct coiling regimes exist depending on the dominant balance of forces (viscous, gravitational, or inertial), and later work by others further mapped out the full regime diagram, but the core physical picture -- a buckling instability of a falling viscous thread -- is well established.
A stream of honey coiling into a pile behaves, mathematically, just like a falling elastic rod buckling under its own weight.
Explanations that circulated
- That the coiling frequency simply scales the same way across all pouring heights and viscosities; Mahadevan, Ryu & Samuel's original 1998 scaling law required a correction (published in Nature in 2000) once further regimes (viscous, gravitational, inertial coiling) were identified, showing the simple single scaling law does not hold universally.
References
- Fluid 'rope trick' investigated, L. Mahadevan, W. S. Ryu, A. D. T. Samuel, Nature, 1998
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