Re: .Bernoulli and curve balls.

[palmer@sfu.ca (Leigh Palmer)]

[There are deletia in the quotations which follow. I think that they
do not need to be included, but I apologize if they seem to mislead.]

> > > There exists empirical data on this problem taken in wind tunnel
> > > tests which I believe is reported in the Briggs article previously
> > > cited. It confirms a curve opposite to the direction expected from
> > > the Magnus effect and the wind velocity at which this occurs does
> > > correspond to the transition from laminar to turbulent flow.
> > > Evidently, then, there must be some error in the calculation (though
> > > I must confess I didn't catch it).
> >
> > It might confirm a force reversing direction in a steady flow for a
> > mounted spinning ball. We were talking about a curve, however, and
> > my analysis dealt with a pitch, arguing that a reversal of the curve
> > could not occur because the ball does not move with constant speed.
> > I should have made it clearer that the myth I complained about was
> > the suggestion that the ball might actually be made to curve in the
> > opposite direction if the spin and speed were adjusted just right,
> > which is what I thought you were suggesting.
> >
> > Leigh
> It is and it does. A knuckleball, which a slowly spinning pitch, can
> do exactly that and in fact may curve in a variety of directions on
> the way to the plate.

Knuckleball? This argument refers to the pathological behaviour of a
*seamless* ball, I believe. Is a knuckleball seamless? If not it makes
a poor example.

> Adair gives the following argument:

I'm having a copy of Adair brought in. I'll look at it.

> In detail, this is wrong but then in detail the only proper way to
> analyze the problem is by way of the Navier-Stokes equation and that
> is not practical. So:

If Adair's argument is wrong then I see no mitigating value in making
it. I believe the equations of hydrodynamics have been found to be
quite tractable by using supercomputers. This particular problem seems
somewhat simpler than some I've heard have been integrated at NASA's
Ames Laboratory near San Jose. If that is so then it *is* practical to
analyze the problem in the proper manner.

> The important point here is that a curve ball curves not because of
> the Bernoulli effect but because of the Magnus effect. Drag is
> important, as is turbulence.

Well, there it is. We fully agree on this point. The curve ball is not
a manifestation of the Bernoulli effect. I agree that it is properly
ascribed to the Magnus effect, but in that form it amounts to nothing
more than a factoid - there is no teachable physics for the 99% behind
that observation!

> As far as the wind tunnel results go, I don't see how the mount on a
> mounted spinning ball makes a material amount of difference.

Simple. In a wind tunnel the speed of the ball can be maintained
indefinitely and "anomalous" forces due to critical circumstances can
be similarly prolonged. A real curve ball decelerates. That's why I
asked how such a mechanism could be responsible for a reversed curve
ball. I suspect it is not a stable condition over a suitably large
range of velocities.

Leigh