Theory of glass shattering


In one of the episodes of everyone's favourite comic, Tintin, the professor demonstrates his devastating invention - a speaker system that destroys any glass objects in a certain vicinity. It worked due to resonance, but what on earth is resonance anyway?

Image courtesy of

Image courtesy of

Resonance is the state of an object when the frequency of applied external oscillations matches exactly with its natural frequency of vibration. Natural frequencies of vibrations can be observed in simple examples like:

  • The 'ping' sound when you tap a wineglass
  • The 'ooong' sound when you blow across an empty glass/metal tube or bottle (like in a xylophone)
  • Waves crashing on the seashore
  • The up and down movement of a bridge
  • The sounds of a guitar/piano string when plucked
  • The 'hummm' from a tuning fork

When resonance occurs, the crests of the applied vibrations match the natural reactions of the object, and thus there is constructive interference - the crests become larger. Each vibration after this adds to the crest until something critical happens... like a bridge toppling over (the Tacoma Narrows bridge is one hell of a good example of this).

Now onto the first experiment!

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