Re: [Phys-l] football orientation in flight

["Jeffrey Schnick" <JSchnick@Anselm.Edu>]

Does this work?  (Discussed as viewed by the thrower.)  The ball is
spinning clockwise meaning it has forward directed angular momentum.  As
it arrives at the top of its flight it has a positive angle of attack.
This results in some circulation which means the air acquires some
rightward angular momentum.  This means the ball gains some leftward
angular moment which, with its big roughly forward angular momentum,
means it yaws left.  This results in some leftward lift and its
associated circulation which means the air acquires some upward angular
momentum.  This means the ball gains some downward angular momentum
which, with its big roughly forward angular momentum means it pitches
downward.

> -----Original Message-----
> From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-
> bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker
> Sent: Thursday, May 22, 2008 3:13 AM
> To: Forum for Physics Educators
> Subject: Re: [Phys-l] football orientation in flight ERRATUM
>
> On 05/21/2008 10:19 PM, I wrote:
>
> > Disclaimer: This is probably quite a complicated phenomenon.  It is
> very,
> > very easy to get the wrong answer in situations like this.
>
> I got that part right.  I should have quit while I was ahead.
>
> > Having said that, here's the first hypothesis that occurs to me, and
> it seems
> > to fit the facts.
>
> Actually my hypothesis does *not* fit the facts.  I got the direction
> wrong on the Magnus force, and therefore (unless I made ANOTHER
> mistake)
> my previous conclusion was diametrically wrong.
>
> When correctly analyzed, the effect I identified makes a _negative_
> contribution to the angle-of-attack stability.
>
> I have no idea how to explain the observed stability.  It is easy to
> guess that some other effect makes a larger contribution in the
> direction
> of positive stability ... but I have no idea what effect that would
> be.
>
> Sorry for causing confusion.
>
> ============
>
> The following reference is not much help, either:
>   http://www.blackwell-synergy.com/doi/abs/10.1046/j.1460-
> 2687.2002.00106.x
>
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