LASH PROGRAMMING
Whips evolved as herding and cattle-driving
tools. A good whip handler can produce
a cracking sound that bursts from any
location within the whip’s reach. Cattle instinctively
turn away from the loud sound’s source, so the
ability to precisely place these small sonic booms
anywhere in midair lets cattle drivers steer their
herds.
Photograph: Corbis
Crafting a whip that cracks well requires time-tested methods. A well-designed whip is a lesson in
supersonic fluid mechanics. It must taper gradually
from base to end in a specific fashion, and it must
be made of materials that gracefully and easily
transfer the energy and momentum of the moving
internal coil along its length.
Alain Goriely, professor of mathematics at the
University of Arizona, has published several research
papers on the way whips work, and has come up
with several fascinating conclusions about how
waves propagate through these flexible devices. His
research describes how a loop moving down the
length of a whip accelerates as the whip tapers, and
he developed a series of equations that accurately
model the curvature, boundary conditions, tension,
and speed of the whip. Goriely’s computer analysis of whip dynamics confirms that the cracking
sound results from hypersonic movement, and he
has measured tip speeds in well-made whips that
exceed Mach 3 — three times the speed of sound.
Goriely divides the world of whips into two
categories: pain-making whips and noise-making
whips. The pain-makers, such as the infamous
cat-o’-nine-tails, are short, bulky, and made up of
several strands that hang separately. They don’t
crack. Noise-making whips are long and tapered,
consisting of a braided single strand. Despite their
frightening appearance, the noise-making whips
are not used as weapons or torture devices; their
purpose is to produce and aim incredibly high tip
velocities.
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