The physics of fingernail scrapping and screaming
Stories from Physics for 11-14 14-16
Researchers from Northwestern University, Illinois, have written a paper attempting to determine the cause of the ‘obnoxious’ sound of fingernails on a blackboard. They report that, contrary to expectations, it is not the high frequencies that cause the unpleasant sensation, but elements of the signal at frequencies in the middle of the human auditory range. The authors note that the sound resembles the warning cries of macaque monkeys.
Another team has proposed the theory that the quality that makes screams unpleasant is roughness, the frequency with which loudness varies. Roughness occurs in screams at rates of between 30-150 Hz, much higher than for normal communication (4-5 Hz).