In response to what Jeffrey Schnick wrote on 05/26/2008 08:04 AM ...
In case it wasn't obvious, I reckon that in the main place where
his analysis diverges from mine, his is better.
In particular, I think I was implicitly imagining the Reynolds
number to be higher than it really is. I should have known
better. This is one of the standard reasons why the analysis
of sports balls is much more difficult than (say) the analysis
of aircraft, which are larger and faster and therefore have a
much higher Reynolds number.
Moving on:
*) I don't know what to make of the observation that the ball does
not exhibit any pronounced hook or slice. It's something of a
catch-22. If we have a strong mechanism to keep the orientation
vector nearly parallel to the velocity vector, then there is almost
no angle of attack, and no opportunity for much Magnus force to
arise.
I think we need to account for the "spin-rate to velocity ratio"
before we can make sense of the "hook to reorientation ratio".
*) Before we "explain" "why" the ball keeps its angle of attack close
to zero, we should look at the data again. What I see is
-- The ball is nose-high during the first part of the flight.
So far so good.
-- The ball is nose-low during the final part of the flight.
All well and good.
-- However, in the middle part of the flight, it looks like
there is some nasty tumbling.
Does the final nose-down attitude arise because of the tumbling? In
spite of the tumbling? I have no idea.
In any case, we'd better be careful, or we might wind up "explaining"
a phenomenon that does not actually occur (angle of attack remaining
close to zero).