Does a curve ball really curve?

October 14, 2010

Does a curveball really curve? Really???

For some reason I seem to have done a disproportionate number of baseball-related postings. I guess one of the  benefits of being in the field of design is that I can pretty much turn anything into a design issue. Well either that or it provides me a plausible reason to spend a bit of idle time writing about sports. Ahhh the life.

Someone sent me a very fascinating link recently that probably doesn’t end – but certainly sheds some new and interesting light on the age-old debate of whether a curveball really curves.

For those of you who aren’t fans or fanatics, the curveball is a pitch that was “invented” around the time of the civil war by delightfully named “Candy Cummings” pitcher for the Brookly Excelsiors. Cummings found that by snapping his wrist forward as he released the ball, the trajectory would arc and then suddenly “break” or curve causing batters to lunge and swing comically at the place they thought he ball should – but no longer was. From that moment on the curve ball has bedeviled batters. Those who have seen it often describe it as looking like the ball has rolled off a table. I suspect the difficulty of controlling the pitch properly adds to the allure and baseball aficionados speak of “buckling batters knees” as they alternately swing at a pitch that darts out of the strike zone or watch impotently as a ball seemingly well outside of the zone drops in. Or does it?

As long as pitchers have been throwing curves, players, engineers and physicists have debated whether the ball really curves or it’s an optical illusion.

You see, as long as pitchers have been throwing curves, ball players, engineers and physicists have been debating whether the curve ball really curves or whether it’s all just an optical illusion. Amazingly enough, given the arsenal of brainpower and technological sophistication that’s been brought to bear on the issue – the debate persists to this day.

In 1941, two magazines simultaneously attempted to use stop-action photography to determine if curve balls really curve. Look Magazine concluded they do. Life magazine concluded that they do not.

Both General Motors and the Massachusetts Institute of Technology have been commissioned to investigate the phenomena (Why GM is a matter I can only speculate and I suspect they should have stuck to focusing on their cars).

My father-in-law–a pretty good player in his own right–claims to have faced pitchers who could throw a pitch around the side of an oak tree. Hyperbole? Perhaps... but when you’ve married his oldest daughter are you really going to argue pressure differentials? I think not.

My own baseball career sputtered to a halt sometime in elementary school when the only “curve” pitchers threw was in the vertical plane so I’ve never had the pleasure (or terror) of facing a real curve. Thus my own opinions on the issue are anecdotal at best.

As an engineer I can certainly understand the reasons why a curve ball would (or could) curve. The combination of forward velocity and rotation creates a pressure differential that would serve to “suck” the ball towards the direction of rotation. At the same time, physicist and engineers have struggled to empirically or analytically explain the amount of curve which pitchers and batters perceive.
As near as I can figure – and this is really just an educated guess – curve balls really do curve but (and with full respect and deference) NOT to the extent claimed by pitchers and batters. Sorry. And I can’t think of a reasonable engineering explanation for the real or perceived “drop” that curves seem to take towards the end of flights.

So that brings us to this fascinating study and demonstration by Arthur Shapiro, Zhong-Lin Lu, Emily Knight, & Robert Ennis of American University, University of Southern California, Dartmouth College, SUNY College of Optometry –which incidentally won the 2009 “best illusion of the year contest” from the Vision Sciences Society (I wonder what the trophy looks like… but I digress).
To quite from their entry…

"In baseball, a curveball creates a physical effect and a perceptual puzzle. The physical effect (the curve) arises because the ball’s rotation leads to a deflection in the ball’s path. The perceptual puzzle arises because the deflection is actually gradual but is often perceived as an abrupt change in direction (the break). Our illusions suggest that the perceived “break” may be caused by the transition from the central visual system to the peripheral visual system. Like a curveball, the spinning disks in the illusions appear to abruptly change direction when an observer switches from foveal to peripheral viewing."

Here is the link:

Make sure you follow the instructions and give it a look… it’s pretty amazing.