Glass can shatter when a loud tone matches the frequency at which the glass naturally vibrates.

The longer version

Every rigid object has natural rates at which it prefers to vibrate, set by its shape, stiffness and mass. Drive a glass at one of those rates and each push arrives in step with its own motion, so the flexing builds until the material exceeds its limit.

Sustained loud output is needed because damping in the glass bleeds energy away between pushes, and a flaw or chip gives failure somewhere to start. Thin-walled vessels respond most readily, and tapping one to hear its ring is the usual way to find the rate. Bridges and machine parts fail the same way when a repeated force matches a natural rate.

Where this entry sits

Sound and Music gathers facts about how vibrations move through air and water, how ears turn them into meaning, and how instruments and notation shape what listeners hear. Expect echoes, pitch, volume, acoustics, and the odd silence in between. The full list sits on the Sound and Music page, where every entry is listed in order.