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`The statistical physics of fibre bundles and the shape of a ponytail.'

Abstract: There are 100,000 hair fibres on a typical head of hair, hence
calculating perceived properties like 'volume' and compressibility are
problems in statistical physics.  To address this, a density functional theory
for the distribution of hair in a fibre assembly has been developed, treating
individual elements as elastic filaments with random intrinsic curvatures.
This formalism has been applied to the iconic problem of a ponytail, for which
the combined effects of bending elasticity, gravity, and orientational
disorder are recast as a differential equation for the envelope -- the
ponytail shape equation.  Aside from compressibility, this problem is
characterised by a single dimensionless measure of the ponytail length,
christened the Rapunzel number.  From laboratory measurements of model
ponytails, the balance of forces in various regions of the ponytail can be
identified and related to the measured random curvatures of individual hairs.

For this work [R.E. Goldstein, P.B. Warren and R.C. Ball, Phys. Rev. Lett.
108, 078101 (2012)] the authors shared the 2012 Ig Nobel prize in Physics with
Joe Keller of Stanford University, "for calculating the balance of forces that
shape and move the hair in a human ponytail".  Some comments on the award will
also be forthcoming!

SPEAKER: Patrick Warren is a statistical physicist working in industry at
Unilever's R&D facility in Port Sunlight.
See http://sites.google.com/site/patrickbwarren/

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