Re: .Bernoulli and curve balls.

["Richard W. Tarara" <rtarara@saintmarys.edu>]

> From: jmclean@chem.ucsd.edu
>
> Imagine that the Bernoulli effect does tend to curve all spinning balls
in
> the 'correct' direction, but that the magnitude of the effect is many
> orders of magnitude smaller than the Magnus effect.  That is, say that
the
> curve is 99.9% due to Magnus and 0.1% due to Bernoulli.  In that case,
> saying "the ball curves because of Bernoulli" is not a simplification. 
It
> is, at best, a misrepresentation.


I guess I haven't been convinced that this is the case (.1% vrs
99.9%)--certainly haven't for low speed airfoils such as those used in
human-powered planes that Bernoulli is negligible.

Seems that a real curve ball falls in a funny range between dominant
domains and its not so clear what is going on.  

What I really have trouble with on all the Bernoulli bashing is HOW can it
be that we've had several decades of text books that are 'dead-wrong' or
grossly misrepresent the physics.  Aren't these books reviewed by other
physicists before publication? (rhetorical)  Are all of us who see faults
in these texts incapable of writing to authors and publishers to say this
is wrong and that is wrong?  If we've done that, are authors so bull-headed
as to refuse to change?  Sure mistakes do make it into books and do survive
many new additions, but when the majority of texts present air-foils as an
example of Bernoulli (many now do state there are other factors at work)
are we few on this list so sure this is wrong.  To be sure, fewer books use
Bernoulli for curve balls, but many still do.  Every text book I have,
including three separate thermodynamic books, state that Heat IS a form of
energy.  (Sorry Jim)   

If I'm to abandon certain topics or certain explanations that I've gotten
from supposedly reputable sources, I want to be damn sure those sources
were wrong.   I suspect that for many of us it is harder to UNLEARN
something than to learn it, and that is exactly what we're being asked to
do by the 'authorities' on this list.  They may be correct, and I am
convinced that all these phenomenon ARE more complicated than the simple
text-book descriptions, but ultimately the acid-test is whether or not
there is any pedagogical advantage to keeping a simple (even
misrepresentative) description of a phenomenon.  To some that answer is
clear, I'm still struggling with it. 

Rick
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