Sympathetic Vibration
Definition
When one vibrating object sets another tuned object singing without touching it — strike one tuning fork and its twin across the room hums.
Technical definition
Energy transfers via acoustic coupling between oscillators sharing a resonant frequency; the driven twin's amplitude grows at resonance.
Example
Press a piano's sustain pedal, sing a note into the strings, and the matching strings ring back on their own.
Common confusion
Sympathetic vibration is not action at a distance — sound waves in the air carry the energy. In a vacuum the twin fork stays silent.