Figure 2.

Helices Unwind When They Are Stretched.

A cylinder, whose wall has a right-handed (Z) helical construction, unwinds in the opposite direction as it is stretched. Although the stretched helix maintains its right-handed construction (albeit with a steeper pitch), markers on its surface (vertical dashed line) are rotated to the left by the unwinding to form a contrary, left-handed S-shaped helix. (Figure courtesy of Tracey Cross.)