How a voice is capable of breaking glass?

Question

I mean, I understand that it’s difficult and has to be a very certain key at a specific volume, but I still don’t understand how that alone is capable of breaking a solid object. And why just glass? What about glass? Surely we can break other stuff too? I’m confused.

In: 2

Answer 1

It’s a two part scenario.

The first part is something called “resonance” and if you’ve ever been on a swing set you can understand it. A wave is like a person going back and forth on a swing, if you add energy to wave in the just the right way (pushing someone on their way down) you can increase the energy (make them swing higher). Compare this to pushing someone when they are swinging *up*. You’ll reduce their height. You need to apply the energy input in just the right way. In a resonant system the energy inputs are all coming together in just the right way that the wave gets bigger and bigger and bigger. It’s sort of like not just any shape can be come a saxophone. The form of a saxophone is designing in just the right way that a small input (someone buzzing on a tiny reed) becomes a massive output, a loud saxophone you can hear across the orchestra pit.

In our example, the human voice is the small buzzing reed, the glass cavity is the saxophone and the the human voice hitting “the right pitch” is like fingering a note on the saxophone keys. The three qualities all come together in just the right way to create acoustic resonance inside the glass cavity.

The acoustic energy hits the glass and makes the glass start to vibrate back and forth. With a proper resonance the pushing and pulling all lines up in a way that makes the vibration significant. When I say “vibration” what I’m saying is if you imagine a slice of a ring of the glass, that ring is getting wider and narrower back and forth. That widening is literally similar to taking your fingers on the inside of the glass and pulling them apart, creating tension in the glass material. Glass is extremely weak to tension forces and will shatter violently.

So to answer your final question, that’s why glass specifically shatters like this, glass is extremely weak to tension. Other materials like wood or metal are pretty strong in tension and won’t fail due to such small forces.