Re: .Bernoulli and curve balls.

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

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> From: Michael Moloney <moloney@nextwork.rose-hulman.edu>
> I would say the top of the ball is travelling through still air faster
that the center of  
> mass, and the bottom of the ball is travelling slower, so that the faster
velocity on  
> top would a la bernoulli create lower pressure. This suggests that
bernoulli would  
> predict that the ball would rise instead of fall.


The standard text-book description is that the rotating ball drags some air
at the surface of the ball in the direction of spin.  If a ball is moving
toward the top of the screen rotating counterclockwise and viewed from
above, then at the right side of the ball the air passing by the ball is
downward (say speed 'V') but the 'drag' air (speed 'u') is up while on the
left side both air flows are downward.  A few texts (e.g. Franklin Miller's
College Physics) then apply Bernoulli by adding these air flow vectors to
get a slower net speed on the right (u-V) and faster on the left
(u+V)--hence a reduced pressure on the left and a curve to the left--with
the spin.  I'm not sure that a 'streamline' analysis gives the same thing,
but let's concentrate on this description--and determine if it is OK or
grossly wrong (IT IS the way I learned it, so if wrong I need to know why).


I don't want to debate whether this is the major effect of not--like in the
airfoil debates, just whether or not this Bernoulli description would cause
an unbalanced force to the left.  

Rick Tarara