Friction idiophones is designation 13 in the Hornbostel-Sachs system of musical instrument classification. These idiophones produce sound by being rubbed either against each other or by means of a non-sounding object. Instruments of this type are not very common; possibly the best known examples are the musical saw and the nail violin.

Glass harmonica; sound produced by friction of the fingers against the rotating glass

Glass harp; sound produced by friction of the fingers rotating against the wine glass rims

According to musicologist Curt Sachs:^[1]

... It is essential to distinguish between rubbing and scraping. The latter results in a series of beats cause by passing a stick over a notched surface; [whereas] friction is based on adhesion....On a higher level we find...the glass harmonica.