In music, the physical phenomenon whereby one vibrating object, such as a string or a bell, can induce another that is initially unmoving to vibrate also, without any physical contact. For example, strings that are related to others within a harmonic series are subject to sympathetic resonance. A string will cause another, such as one that is an octave higher, to vibrate by sympathetic resonance because the latter is an overtone of the former, meaning its frequency is in a harmonic ratio with that of the principal string.