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Re: .Bernoulli and curve balls.



First: The main audience for Bernoulli descriptions of curve balls,
airfoils, etc. are those 99% who are in an Intro course and won't be going
on. Bernoulli is accessible to these students as a 'reasonably good'
description whereas laminar flow, vortices, Reynolds numbers, and the like
are not as accessible to them.
For the 1% that goes one, 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.

I take the 'common sense' meaning of the direction of spin. Look at the
ball from above (for left/right curvature). Look at the leading edge of
the ball along its direction of motion. In what direction is that leading
edge turning? If the ball is moving up the screen then counter-clockwise
rotation is a 'leftward' rotation and the ball should curve to the left.
Clockwise rotation the opposite.

Rick Tarara
----------
From: Jim Riley <jriley@lib.drury.edu>

Some of the confusion in the discussion may be the result of different
responders having different definitions of that direction. Part of the
problems we have with our students is that we have certain definitions or
meanings in mind for a particular quantity and they have a different one.