Re: .Bernoulli and curve balls.

[jmclean@chem.ucsd.edu]

Jim Riley says:
> James McLean says:
>
> > Do I read this correctly to say that the baseball curves in the direction
> > opposite to it's spin?
>
> There have been several comments about balls curving opposite or in the same
> "direction as its spin".  My question is, what is meant by direction of
> spin?  Obviously not the standard mathematical definition given by a right
> hand rule.  

Look at the ball along the axis of the spin.  Say the ball is spinning
counter-clockwise.  Now I'll draw the spinning ball (with little arrows)
and the trajectory (moving towards the top of the screen).  Then we have:

  Ball curving in          Ball curving opposite
direction of spin:	   the direction of spin:
       \          	            /
        \         	           /
        |         	           |
         \        	          /
         |        	          |
         |        	          |

         <        	          <
       v O ^      	        v O ^
         >        	          >

This can, actually, be well described in terms of the right-hand rule.  In
both cases omega (w) of the spin is pointing out of the screen.  In the
first case, the Omega (W) of the curve is also pointing out of the screen
(with a varying magnitude);  W is 'in the direction of' w.  In the second
case, W is into the screen, in the opposite direction of w.

-- 
--James McLean
jmclean@chem.ucsd.edu
post doc
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