Sound & Hearing

Humming Plates

HUMMING PLATES consists of two metal plates, round and square, each supported in the middle, with fine sand on their surfaces. A taut bow is rubbed on the edge of the plate, sending out a wave, a vibration that travels along the surface of the plate. The waves spread out in all direction and reflect from the edge of the plate. The reflected waves meet new waves produced by the bow. Where these waves meet, they can add together and make the plate vibrate a lot, or cancel out so that the plate is hardly vibrating at all. The sand bounces away from places where the plate vibrates a lot, and collects in relatively still areas.