Hair not a drag... was Re: AAT Theory
J. Moore (j#d#.moore@canrem.com)
Sun, 1 Oct 95 17:34:00 -0500
Ss> David L Burkhead (r3dlb1@dax.cc.uakron.edu) wrote:
Ss> : Again with the streamlined. That's a _claim_, not a "fact."
Ss> : Furthermore, it's a claim that does _not_ fit the conclusion of a
Ss> : "wading ape." In fact, a hairy body would have _less_ drag for that
Ss> : upright wading ape. Go look up turbulent vs laminar flow separation
Ss> : drag in bluff bodies. (This kind of thing is one of the reasons the
Ss> : "obvious" is so often wrong.)
Ss> Just a small note here:
Ss> Last time I checked ALL olympic swimmers shave their legs and body.
Ss> Then they put rubber swimming caps on their heads to cover the hair on
Ss> their heads. It seems to me that if you want to know about moving
Ss> quickly through the water you should ask an olympic swimmer about it. I
Ss> don't think you'd find any that suggest remaining unshaven.
It remains a claim, not a fact. I looked this up a couple of
months back, in literature on sports physiology, and found one
study (and I'm sorry, but I do not have the ref at hand today)
which showed an effect that could help swimming speed. The one
study showed a difference in build-up of lactic acid in the
muscles in athletes who had shaved their bodies.
The reason for this is still unclear, as it could conceivably be a
psychological effect, and the study that showed this result wasn't
designed to differentiate between possible reasons, but just to
show an effect. The study's authors thought it might be due to
the actual shaving of the hair. You see, one problem you have in
checking this is that there's just no way you can do a blind-study,
so there's no way to tell whether any effect you measure is
physiological or psychological.
I am unaware of any study showing an actual decrease in drag due
to shaving a swimmer's body (if you find one, let me know), but I
do know of experiments showing a decrease in drag in seals when
hair is present (see below).
Ss> Turbulent flow may work for wading creatures, but who says that we
Ss> remained wading throughout this entire evolutionary process? Last time
Ss> I checked nobody was suggesting that we are the biological equivalent of
Ss> a golf ball.
David is quite correct to point out that water flow may well be
enhanced by hair. In fact, in *Mammal Skin* (1982) Sokolov
describes experiments which showed this effect: "Experiments on
models covered with the skins of *Phoca vitulina* and *Pusa
sibirica* show a reduction in drag as compared with rough, bare
skin. Hence the damping role of pinniped pelage during swimming
(Mordvinov and Kurbatov, 1972). A hydrodynamic tube experiment
with a dummy having a Baikal sealskin pasted over it reveals that
hair is conducive to an increase in the boundary layer thickness,
to a reduction of the speed pulsation level within 1 to 10 khz,
and to a reduction in drag." (Sokolov 1982: 604).
Ref:
1982 *Mammal Skin* by V.E. Sokolov, University of California
Press: Berkeley.
Jim Moore (j#d#.moore@canrem.com)
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