July 2003 (Volume 12, Number 7)

# Physicists Tell Batting Coaches To Get a Grip on Grip Advice

Some good news for players and batting coaches: physicists say they shouldn't worry about a player's grip on the bat as it connects with the ball. The sharp-eyed baseball fan will notice that some batters, like David Justice, remove one of their hands during their swing-sometimes against the advice of batting coaches. But now physicists are telling coaches and players alike to rest easy. New research shows that the released hand has nothing to do with how fast the ball leaves the bat.

In research published recently in the American Journal of Physics, University of Illinois professor of physics Alan Nathan says the grip on the bat during contact with the baseball does nothing to affect the power delivered to the ball. Nathan says that even if the hitters were to let go of the bat right before contact, the batted ball would have the same speed and trajectory. "Just prior to the collision with the ball, the bat is already at its maximum speed," says Nathan, "There's nothing that the hands can do to affect the ball at this point."

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, the bat exerts a force on the ball that can easily reach eight or nine thousand pounds. The force can be so large, many times the weight of the batter, because the ball is in contact with the bat for only about one thousandth of a second.

Nathan also points out that 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.

-From Inside Science News Service, a joint effort
of the American Institute of Physics and the APS
.

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