LORD Rayleigh, modern fluid dynamicists, and readers of New
Scientist all have something in common: they’ve all been wrong about how
flags flap.
Ever since the 18th century people have believed that a flag must flap even
in the softest breeze, because the slightest imperfections in the flag’s surface
creates swirling vortices in the passing air. These vortices make the flag
billow out, creating more vortices and even more billows. This was how readers
of Â鶹´«Ã½’s The Last Word answered the question “What makes a
flag flutter?”
(18 December 1999).
But physicists Jun Zhang and Michael Shelley of…
