From: American Institute of Physics

When ball meets bat, the hands no longer matter: Physicist shows that grip does not make a difference during contact

College Park, MD --In this World Series week, the sharp-eyed viewer will notice that some batters--such as David Justice of the Yankees and Mike Bordick of the Mets--sometimes remove one of their hands during their swing. A physicist is about to publish new research findings that would reassure the hitting coaches of both teams.

In a paper about to appear in the American Journal of Physics, a University of Illinois researcher says the grip on the bat during contact with the baseball does nothing to affect the power delivered to the ball. Even if the hitters were to let go of the bat right before contact, the batted ball would have the same speed and trajectory, he says.

"Just prior to the collision with the ball, the bat is already at its maximum speed," says Alan Nathan, the author of the paper and a professor of physics at the University of Illinois at Urbana-Champaign. "There's nothing that the hands can do to affect the ball at this point."

Many coaches are instinctively aware of this, as they typically ask batters to relax their grip on the bat during their swing. But these results, demonstrated in theory and experiment, would correct the advice of other coaches who suggest to their players that they use their hands to "muscle" the ball during the brief period the ball and bat are in contact.

The hands do play an important role during the actual swing prior to the actual contact, as they help transfer energy generated in the large muscles of the body to the baseball bat. This muscle power propels the bat to the high velocity needed to transfer a lot of momentum to the ball and send it on its way. But during the bat-ball contact time, the grip does nothing to affect the ball's final velocity or trajectory.

There are several reasons for this, Nathan explains. First of all, the bat exerts a force on the ball that can easily reach eight or nine thousand pounds and that compresses the ball to perhaps half its radius. This force is so large--many times the weight of the batter--because the ball is in contact with the bat for such a short time--about one thousandth of a second. During that contact time, Nathan says, the hands would add little to the amount of force exerted on the ball.

Second, the collision between bat and ball creates a vibrational wave in the bat. The wave originates at the collision point and ripples down to the hand. The wave itself, since it absorbs energy from the baseball, can affect the exit speed of the ball. But by the time the wave hits the hand, the ball is already separated from the bat, and there's nothing that the hands can do to alter this vibrational wave, assuming of course that the impact occurs in the barrel of the bat, far from the hands.

The same reasoning suggests that, for impacts far from the handle, the thickness and size of the bat handle do nothing to affect the final speed and trajectory of the batted ball. According to Nathan, the ball doesn't even "know" that the far end of the bat is there.

Can these studies lead to a better design for a bat? For major league baseball, where the bats are made of wood and the specifications on the bat are already highly constrained, the answer is probably "no." But they may offer helpful insights for college baseball, which use aluminum bats made of many highly modified designs. The handle is one more red herring in the quest for the perfect bat, Nathan says.

Dynamics of the baseball-bat collision
Alan M. Nathan, American Journal of Physics, November 2000.

Alan Nathan
Professor of Physics
University of Illinois at Urbana-Champaign

This article comes from Science Blog. Copyright 2004