In 1638 Galileo Galilei remarked that “a glass of water may be made to emit a tone merely by the friction of the finger-tip upon the rim of the glass”. In 1761 Benjamin Franklin designed an “armonica”, where sound was radiated due to vibration of rotating glass bowls in frictional contact with the moistened fingers of a performer. Shortly after Rayleigh qualitatively described the onset of bending waves in the singing wine glass by the friction, applied in the circumferential direction, and pointed out the proximity of the main audible frequency of the glass to the one of the spectrum of its free vibrations, a disk brake had been invented. Nowadays, the automotive car brake squeal due to vibrations of a rotating annular plate in contact with the friction pads (in general, a sound with one dominant frequency) is one of the primary subjects of investigations in the acoustics of friction because its reliable reproduction or even prediction is still not possible. The attempts to designa silent brake are still extensively based on the ‘trial-and-error’ method. Among other examples of such audible friction-induced oscillations is high-frequency self-excitation in paper calenders that yields emission of sound and a wear pattern known as the calender barring and squeaking occurring in ceramic-on-ceramic hip arthroplasty.
Dr. Oleg N. Kirillov 