On Wed, 18 Sep 2002, Dan Kaplan wrote:
> It's a good thing you are so certain of what you know, otherwise you might
> feel compelled to question the conclusions...
That's what I've been trying to do.
> Care to explain away the
> situation I offered where an athlete might alter their drive phase in
> order to minimize wind resistance? If done properly, this could easily
> account for 40% of the race, which I would say is pretty darn significant.
>
I never said my figures are absolute. If you read any of my papers, you'd
see that I am willing to admit limitations. However, I do not toss them
out simply because I didn't account for something which is probably not an
overly-large factor.
The magnitude of the headwind you're discussing would be immense. A
common misconception is that the wind *pushes* the athlete, and that's
why the time is either better or worse. Unless you have a *very* strong
wind, the effects will manifest themselves as drag increase or reduction,
which makes it harder/easier to accelerate. Since we're discussing
pulling figures out of the air, I would be interested in hearing how the
effects you propose will account for 40% of the race.
Remember: the faster they go, the *larger* the drag force, the harder it
is to run! It's rather self-defeating.
> (For anyone wondering, a headwind would actually make it easier to
> maintain a longer drive phase, as it would keep you from falling forward.)
>
The headwind will also make it *harder* to achieve a faster speed. The
drag forces go as (v-w)^2 -- so, a small difference in v results in a
large difference in drag. Headwinds (w < 0) will *increase* the drag
immediately. Also, the velocity in the drive phase is generally much less
than top speed (hence the classification), hence a smaller drag effect.
> On the flip side, a tall and/or wide sprinter might transition earlier and
> run taller in order to take advantage of a tailwind. Someone with good
> knee extension will also be likely to benefit more from the added
> extension to their stride.
>
Look, I don't deny these are interesting questions, and no doubt worth
investigating. My point is that I don't feel the magnitude of the numbers
will result in a 2m/s wind yielding a 0.1s correction for one athlete, and
a 0.001s correction for another. *Maybe* 0.10s and 0.09s, but I've always
conceded that one should expect these kinds of variations (again, in every
paper I've written on the subject).
> > Being a physics professor, I frequently get upset by the argument that
> > "wind affects are different for each sprinter", because this is the same
> > as saying "Some high jumpers excel more than others because they are
> > better at overcoming gravity"...
>
> I hope you don't really see those as being the same???
>
That's what I keep hearing when people say "Wind affects different people
differently", as if they can train to overcome drag forces. The only way
they can do this is to (a) *significantly* reduce their cross-sectional
area, (b) run slower, or (c) reduce their drag coefficient (the aim of
those silly "swift-suits", which are a nice marketing gimmick for Nike,
but otherwise useless). None of the above will produce quality sprint
times.
J.
