Inspection of an instrument such as a harp or piano shows that it contains a number of stretched strings which vary in length and thickness. Harp strings (Fig. 29.5) are caused to vibrate by plucking them, while piano strings are struck by felt hammers. In contrast, the violin has only four strings of different thickness but the same length. The effective length of the strings is, however, altered by fingering. All stringed instruments are periodically tuned to correct pitch by adjusting the tensions of the strings.
In the following sections we shall discuss the factors which determine the pitch of the note emitted by a stretched string.