Re: .Bernoulli and curve balls.

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

----------
> From: Leigh Palmer <palmer@sfu.ca>
> If the explanation had
> any socially redeeming quality other than that it unasks the question
> I might go for it, but as it stands it looks like a *counterexample*
> to the "Bernoulli effect", since one gets the incorrect direction for
> the lateral force with straightforward application of the principle.

But  my original question was 'does Bernoulli give the wrong direction'.  I
really can't believe that generations of texts (including many still used)
REALLY have this wrong.  But my question still holds--for a ball moving
towards the top of the screen, spinning counter-clockwise as viewed from
above, which way does it curve?  Bernoulli (at least the presentations I've
seen) says TO THE LEFT.  To my mind that is IN THE DIRECTION OF THE SPIN. 
IS THAT WRONG?  My sense of most responses is that it is NOT!

 
> > For the 1% that goes on, they will recognize later that Bernoulli was a
> > gross simplification of the 'real' situation--just as they eventually
learn
> > that massless strings, frictionless pulleys, air resistance free
movement
> > and the like are all simplifications to the real world.
>
> Nonsense. 99% of my students know that those are idealizations, not 1%.
> That knowledge is not arcane.

THE 1% THAT GO ON will understand that Bernoulli was a gross
simplification--THIS STATEMENT DOES NOT SAY THAT the other 99% DON'T see
massless strings etc as simplifications.  Your response IS NONESENSE--AND
RUDE!

> We already have a perfectly good way of specifying the direction of
> spin. It is specified with respect to an axis, and there is no
> "common sense" direction ascribable to any direction perpendicular
> to that axis. In fact the axial direction of the spin is only
> ascribable by convention; but the axis is defined in both technical
> and "common sense" terms.

Again the majority of physics students don't define direction of spin the
way PhD physicists do in the midst of an introductory course.  They WOULD
view a ball with backspin as spinning 'up', overspin as spinning 'down' and
right and left spin as I've described.  


> When you've all figured out how to explain all natural phenomena in
> terms of high school physics, I would like some help on a problem
> I've been wondering about for some time. Why does a spinning
> curling stone curl the way it does? Every simple explanation I can
> think of has it curling the opposite way. I know it curves in the
> "common sense" direction, but I'm unsatisfied by that explanation.
 
Part and parcel of teaching introductory courses to non-physics majors is
to make the subject interesting and relevant to their lives.  It is also
necessary to draw on their experience and familiarity with phenomenon. 
FLUIDS, for those of us who still deal with this area, offers MANY such
examples.  Bernoulli offers a bridge to fluid phenomenon using Energy
Conservation principles along with Mass conservation--continuity
equation--topics that are usually central to this level course.  The fact
that almost all the TEXTS do present phenomenon such as curve balls,
airfoils, and the like with these simplified explanations is reason enough
to cover them--UNLESS one is telling  students NOT TO READ the books--or is
so great a lecturer that a book is unnecessary.  

Its Friday, I'm getting more annoyed by this thread than educated--so I'm
'out of here' for the weekend!

Rick