Synopsis: Ponytail physics

A new theoretical model of hair explains how the curliness and elasticity of hair fibers produce the characteristic shape of a ponytail.

Ponytailed physics professors may now be able to use their coif as a lecture prop. Researchers have for the first time disentangled the factors that determine how hairs hang together, as reported in Physical Review Letters. The analytical model, which was based on a statistical characterization of ponytail shapes, treats the forces on individual hair fibers as continuous quantities inside a hair bundle. The resulting hair “equation of state” could apply to other fibers in biology and industry.

Many scientists (and even more hairdressers) have wondered about the meanderings of hair. Leonardo da Vinci thought hair flowed like water, and this sort of fluid analogy has guided computer animators trying to recreate hair and fur on the movie screen. However, no model has yet addressed one of the most basic hair problems: what shape is a ponytail?

For their part, Raymond Goldstein of the University of Cambridge, UK, and his colleagues obtained human hair switches (a type of commercially available hairpiece) and measured the random curvature (or curliness) of a sample of individual hairs. They then assembled different ponytails—all about 25 centimeters long—and recorded the average shape. This data helped in the formulation of an equation of state that balanced four competing effects: gravity, tension, an elastic restoring force, and a “swelling pressure” coming from the curliness. The model correctly predicted the shape of ponytails as the lengths of the switches were progressively shortened. The authors believe their surprisingly simple equation of state could be used to study other hair “styles,” as well as dynamic problems like a swinging ponytail. – Michael Schirber


Announcements

More Announcements »

Subject Areas

Interdisciplinary Physics

Previous Synopsis

Fluid Dynamics

Floats Like a Pyramid

Read More »

Next Synopsis

Nanophysics

Nanoparticle Sifting

Read More »

Related Articles

Focus: How to Compare Books or Genomes
Complex Systems

Focus: How to Compare Books or Genomes

A mathematical technique for comparing large symbol sets suggests that less frequently used words are mainly responsible for the evolution of the English language over the past two centuries. Read More »

Synopsis: Playing Games with Schrödinger
Interdisciplinary Physics

Synopsis: Playing Games with Schrödinger

Models that treat economic and biological behavior in terms of game-play resemble quantum mechanics. Read More »

Synopsis: A Virtual Physics Classroom
Interdisciplinary Physics

Synopsis: A Virtual Physics Classroom

A classroom simulator with virtual students can provide young teaching assistants a controlled setting for practicing teaching methods.   Read More »

More Articles