David G. Browning
Browning Biotech, 139 Old North Rd., Kingston, RI 02881
Robert H. Mellen
Kildare Corp., New London, CT 06320
Robert J. Schneck
Univ. of Rhode Island, Kingston, RI 02881
The analyses of the sound from a hand-struck or ``spiked'' volleyball, a ``dribbled'' basketball, and a place-kicked football show that in each case the fundamental ``breathing'' vibrational mode is excited in these inflated sport balls. Under regulation conditions the resonant frequency of a volleyball was found to be approximately 150 Hz; a basketball, which is larger but has a higher inflation pressure, was found to have a slightly higher frequency. Due to the shell material these vibrations are quickly damped. The results support the theoretical work [P. M. Morse and H. Feshbach, Methods of Theoretical Physics (McGraw-Hill, New York, 1953), p. 1469] for a hollow, flexible sphere. It was found that ``good'' hits strongly excite this mode, ``poor'' ones do not. Acoustic analysis may be an important tool in determining optimum performance.