Post date: Feb 11, 2012 2:51:49 AM
The crucial characteristics are elasticity, density and curliness, which essentially tell how springy a piece of hair is, plus the length of the ponytail. The researchers came up with a simple formula that describes the ponytail shape when the hair is bundled together.
They called it the Rapunzel number. “We couldn’t resist,” Dr. Goldstein said.
A short ponytail of springy hair, characterized by a low Rapunzel number, fans outward. A long ponytail with a high Rapunzel number hangs down, as the pull of gravity overwhelms the springiness. “I think we were surprised about the simplicity of this,” Dr. Goldstein said.