What's your idea of the perfect ponytail?

The Ponytail Shape Equation explains the physics behind the ponytail. (istockphoto)A new study has created an equation that tries to answer, in its own words, the "iconic problem of the ponytail."

The study, posted in the Physical Review Letters Journal, presents the Ponytail Shape Equation, a figure that takes into account the stiffness of a person's hair, the randomness of its curvature, and the effect of gravity.

Raymond Goldstein, a professor at the University of Cambridge and one of the study's authors, spoke with CBC Radio's As It Happens about the science behind the scrunchie.

He said that there's a "characteristic length" of two inches, "beyond which gravity affects the hair." A single hair held horizontally, for example, won't start to bend downward until it's longer than about two inches.

The resulting equation measures the ratio between the "characteristic length" of two inches to a person's actual hair length. The researchers called the resulting ratio the Rapunzel number.

If your Rapunzel number is low, then your ponytail will fan out, "like a paintbrush." If it's larger, you'll likely see what Goldstein calls "a characteristic arc that straightens out near the bottom."

Goldstein says the equation could be used to explain the physics of other filamentary fibers including wool or fur, objects whose physical properties aren't completely understood to this day.

It might also help the makers of hair products - co-author Patrick Warren also works for consumer products corporation Unilever.

Do you have a ponytail, or have you had one in the past? How might the Rapunzel number help you keep it under control? Share your thoughts in the comments section below.


(This survey is not scientific. Results are based on readers' responses.)