From Leonardo da Vinci to the Brothers Grimm, the properties of hair have been of enduring interest in science and art. Now, a University of Cambridge physicist and collaborators have quantified the curliness of human hair and developed a mathematical theory that explains the shape of a ponytail.
Research published this week in Physical Review Letters provides the first quantitative understanding of the distribution of hairs in a ponytail. To derive the Ponytail Shape Equation, the scientists took account of the stiffness of the hairs, the effects of gravity and the presence of the random curliness or waviness that is ubiquitous in human hair. Together with a new quantity described in the article – the Rapunzel Number – the equation can, they say, be used to predict the shape of any ponytail.
Image: Suvi's ponytail Credit: Nick Saffell
Reproduced courtesy of the University of Cambridge