IF YOU’VE seen a whirling dervish, you may have been reminded of a hurricane. It turns out that the skirts of these dancers are buffeted by the same physical force.
Dervishes are Sufi Muslims whose whirling, ritual dance has become a tourist attraction in places such as Istanbul in Turkey. James Hanna at Virginia Tech in Blacksburg and his colleagues wanted to understand the science behind the dervishes’ mesmerising skirts.
In particular, a skirt can take on the shape of a triangular-based pyramid with its apex near the dancer’s midriff. The material forms three gently concave faces, separated by three remarkably sharp ridges.
The team ignored complexities such as gravity, and built a model that considered only the inertia and tension of the material. Despite this, they found they could recreate the pyramidal shapes – but only if their simple model took into account the Coriolis force.
This force affects objects moving on the surface of a rotating body, for example generating hurricanes in Earth’s atmosphere as it moves over our spinning planet. The researchers say that a Coriolis force occurs when the skirt flows over the slowly rotating pyramid, even though the pyramid is merely a shape and not a solid object (New Journal of Physics, doi.org/p8n). The model may be useful for calculating the stresses experienced by rotating components in machinery, says Hanna.
This article appeared in print under the headline “Hypnotic whirling dervishes rely on hurricane physics”