Sometimes on television a high pitched noise breaks the windows in a house. I know that tubular objects such as wine glasses will break when the frequency corresponds to the natural frequencies of the glass, but does flat sheet glass such as windows experience this same effect? — RF, Jackson, Michigan
In real life, only explosive sounds will break normal glass. That’s because normal glass vibrates poorly and has no strong natural frequencies. You can see this by tapping a glass window or cup—all you hear is a dull “thunk” sound.
For an object to vibrate strongly in response to a tone, that object must exhibit a strong natural resonance and the tone’s pitch must be perfectly matched to the frequency of that resonance. A crystal wineglass vibrates well and emits a clear tone when you tap it. If you listen to the pitch of that tone and then sing it loudly, you can make the wineglass vibrate. A crystal windowpane would also have natural resonances and would vibrate in response to the right tones. But it would take very loud sound at exactly the right pitch to break this windowpane. A few extraordinary voices have been able to break crystal wineglasses unassisted (i.e., without amplification) and it would take such a voice to break the crystal windowpane.