PURPOSE: To demonstrate the relationship of musical pitch and musical intervals to mechanical vibration frequency.

DESCRIPTION: A set of four toothed wheels is mounted on a fast rotator, where the ratio of number of teeth on the four wheels is 4:5:6:8. Tones are produced by holding a piece of cardboard or plastic against the spinning teeth. The resulting notes are the harmonics 4, 5, 6, and 8 of the overtone series, which form a major triad with the octave. A second set of wheels contains a different set of tooth ratios and therefore creates a different (minor) chord.

SUGGESTIONS: Be careful! This thing can trim your fingernails REAL fast.

See Question of the Week #236 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA 3C20.40)

EQUIPMENT: Savart's Disk apparatus with two sets of toothed wheels.

SETUP TIME: None.