Researchers Solve Ponytail “Mystery”

A team of British physicists have solved a problem pondered by Leonardo da Vinci that could help producers of children’s films and video games.

The problem involves the way hair falls into shape as it grows, a subject mentionned by Da Vinci in his notebooks, where he discussed the way they appeared to act as much like a fluid as a solid.

The researchers, led by Professor Raymond Goldstein of Cambridge University, decided to explore the subject by trying to work out if there was a way to predict the shape of a ponytail based on the person’s hair, the question being how widely the hair would spread out at the base.

The team explored the issue using a selection of human hair ponytails in the lab. and concluded that a “remarkably simple equation”, dubbed the Rapunzel number, was sufficient. It takes into account several forces: the strength and elasticity of human hair, the natural waviness or curliness of the hair, the collisions between the individual hairs (which create an outward pressure on the ponytail as the hairs are pushed apart), and gravity (which pulls hairs down and thus closer together).

Although the research may seem trivial, it could prove useful in understanding how materials work as it gives insight into the interaction between random fibers. It may also make it easier for computer animators to produce more realistic-looking depictions of hair. And anyone who’s ever played a fighting game and seen a proud mullet remain untouched and motionless as a character is thrown about the screen will welcome that news.

The research has been published in Physical Review Letters and will be formally presented to the American Physical Society later this month.