Image credit: Joe Wolfe; image source; larger image
PhysicsCentral: Fiddle Physics
These patterns, known as Chladni patterns, show modes of vibration on a guitar faceplate (left) and a metal plate (right). The motion of the plates shakes sand into lines where the surface is still--these lines are called nodes. Read more about Chladni patterns here, and see the larger image for more Chladni patterns on a guitar.
Check out PhysicsCentral: Fiddle Physics to see how a fiddle works and how Chladni patterns form on a violin faceplate. You can watch Chladni patterns form in this YouTube video, Chladni Patterns on a Square Plate.
This feature was updated March 9, 2010.
Breaking Glass with Sound
You don't have to be an opera singer to break a glass with sound. Watch Breaking Glass with Sound from MIT TechTV, and be sure to watch the strobe light camera imagery at the end.
For more sound demonstration videos, see this Physics Demonstration Video page from Wake Forest University.