The crack-of-the-bat: The acoustics of the bat hitting the ball

Abstract

When a baseball is hit straight at an outfielder he cannot quickly judge the angle of ascent and the distance the ball will travel. If his first step is wrong (in for a long fly ball or back for a short fly ball) the turnaround time reduces his range and he will miss catchable balls. To help his judgment the professional ball player listens to the sound of the wooden bat hitting the ball. If he hears a ‘‘crack’’ he runs out, if he hears a ‘‘clunk’’ he runs in. The crack occurs if the ball is hit near the sweet spot, little collision energy is lost to bat vibration but is returned to the ball which then sails a long distance. The collision time is then near 0.5 ms generating a singular acoustic disturbance of about that time duration—thus a ‘‘crack.’’ If the ball is hit off of the sweet spot, much of the collision energy will be expended in bit vibrations near 170, 560, and 1100 Hz. With that energy diverted to the collision energy, the ball will not go very far and the vibrations generate persistent sound waves that add to a diminished singularity to sound a ‘‘clunk.’’