Friction idiophone#Friction plaques (132)

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| image1 = ThomasBlochHandsGlassharmonica low notes on left and high notes on right.jpg

| caption1 = Glass harmonica; sound produced by friction of the fingers against the rotating glass

| image2 = Koncert na szklanej harfie. GLASS DUO w Filharmonii Warmińsko-Mazurskiej w Olsztynie.jpg

| caption2 = Glass harp; sound produced by friction of the fingers rotating against the wine glass rims

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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.

According to musicologist Curt Sachs:Sachs, Curt (1940). The History of Musical Instruments, p.456-7. W. W. Nortan & Company, Inc. {{ISBN|0-393-02068-1}}

{{quote|... 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.}}