The shattering of a drinking glass by an opera singer's voice can be explained by the phenomenon of resonance. Every glass has a natural resonant frequency-a specific frequency at which it vibrates most easily when disturbed. When the opera singer produces a sound wave at this exact frequency, the sound waves cause the air molecules around the glass to vibrate at the glass's resonant frequency, making the glass itself vibrate
. If the singer sustains the note loudly and precisely at this resonant frequency, the vibrations in the glass amplify progressively, increasing the amplitude of the glass's oscillations. Because the glass is brittle and has microscopic flaws or cracks, these vibrations put stress on the glass structure. Eventually, the vibrations become so intense that the glass can no longer withstand the stress and shatters
. Key factors for this to happen include:
- Matching the exact resonant frequency of the glass with the sung note.
- Producing a sufficiently loud sound (often above 100 decibels) to drive strong vibrations.
- The glass being fragile, thin-walled, and free from damping effects (such as sitting on a soft surface or being embossed)
Thus, the opera singer’s voice causes resonance in the glass, amplifying vibrations until the glass breaks. This is a real physical effect, not just a cartoon myth, although it requires skill, the right glass, and loudness to achieve
