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I have seen in Ripleys believe it or not that an opera singer generates a very high frequency of sound and breaks a glass window.How do they do it?

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  • $\begingroup$ Acoustic Resonance. Read this: en.wikipedia.org/wiki/… ;) $\endgroup$ – cinico Aug 5 '13 at 10:18
  • $\begingroup$ What about avalanche? Ice breaks at more lower frequencies. Is that resonance too? Because the ice block is much bigger than a glass? $\endgroup$ – huseyin tugrul buyukisik Aug 5 '13 at 11:02
  • $\begingroup$ The sharp sound breaks crystal the same way kids make their swing swinging higher and higher. I suspect it is much harder with normal glass, for the same reason that crystal gives a very pure sound when hit, whereas the average glass does not. $\endgroup$ – babou Aug 5 '13 at 11:54
  • $\begingroup$ Indeed. Resonance happens at a specific frequency, the resonance frequency, which has virtually no dampening. The pure sound given off by a crystal glass is that same frequency. The other frequencies die out quickly (are converted by friction into heat). Avalanches would not have a resonance frequency. They're not homogeneous enough. $\endgroup$ – MSalters Aug 5 '13 at 15:41
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Essentially, the glass breaks because the sound is at the right frequency. Every object has a natural frequency (vibrations per second), at which it prefers to vibrate. This is called the "resonant frequency". If you tap a quality wineglass next to your ear, you'll hear it sing at that frequency. If you stimulate the glass with a sound at that frequency, the vibrations in the glass will be much more intense than at any other frequency. If they are intense enough, the glass will break. It does not need to be a very high frequency, just the right, resonant, frequency for that glass.

This webpage has a very good explanation, along with some videos (including Mythbusters).

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  • $\begingroup$ I am curious: could things other than glass theoretically break if they were exposed to the right sound at the right frequency? For example, could one shatter wood or stone if they had the right sound at an intense enough level? $\endgroup$ – Thomas Reinstate Monica Myron Nov 9 '17 at 23:34
  • $\begingroup$ Yes it's possible. Materials with a low "Q factor", which they do not "ring" when struck, are generally safe. Wood is like that - but wooden structures may not be. Soldiers are told to break step when marching across bridges to prevent problems, and some bridges have collapsed because strong wind made them vibrate at their resonant frequency. See en.wikipedia.org/wiki/Angers_Bridge $\endgroup$ – hdhondt Nov 10 '17 at 3:25
  • $\begingroup$ @Thomas Myron Also see sciencemag.org/news/2017/11/… $\endgroup$ – hdhondt Nov 10 '17 at 23:20
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It is very difficult to break a glass in this manner. Not only one must emit sound at exactly the resonant frequency of the object, but this sound should also be very strong.

You got a bunch of very interesting links from @hdhondt, but this one is my favorite (by Prof Walter Lewin from MIT). It explains everything about resonance, and there is a glass break experiment at the end.

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