Subject: why can't you break a square sheet of glass with resonance

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Re: What is the frequency that can break glass?

Eric Kramer, post-doc, physics/chemistry, Brandeis University
ID 887071209.Ph 

If you tap a wineglass it produces a high-pitched tone. This is the "natural 
frequency" of the glass. A very steady, very loud sound with this frequency can 
break the glass because of "resonance". 

To understand resonance, consider an adult pushing a child on a swing. If the 
adult stops pushing, the child will swing back and forth with a natural 
frequency of about one swing in 10 seconds. If the adult pushes at exactly this 
frequency the child will swing higher and higher. 

Sound is a periodic wave of air pressure. If the peaks in pressure exactly 
match the natural frequency of the glass, the glass will vibrate more and more 
violently until it shatters. 

The natural frequency of a glass depends on its shape, size, and chemical 
composition. It is typically between 1,000 and 10,000 vibrations per second (1-
10 kHz). Because resonance is difficult to achieve, there is no one frequency 
that would break all glasses. Also, you can't break a square sheet of glass 
with resonance. 

Very loud noises of any frequency can break glass if the sound wave packs 
enough energy. This is why an explosion can shatter windows. 

Re: why can't you break a square sheet of glass with resonance