A Moment of Science

Bang!

There’s nothing that sends the stomach up into the throat quite as effectively as a sudden, unexpected loud noise at close range. Counted in this category of shocking sounds are the accidental popping of a balloon and the forceful smashing of an air-filled paper bag. But why are these things so loud? It makes sense that the metal-on-metal clash of banging cymbals creates a racket, but air, paper, and latex? What gives?

As most of us know from elementary school science class, sound travels in waves. More specifically, sound consists of waves of pressure transmitted through the air to the ears. When a sound wave hits the ear it signals a change in pressure to the inner ear. A sensitive instrument, the inner ear can detect minute changes in pressure and interprets these changes as sounds. So logically, the higher the change in pressure, the louder the sound.

If we think about the air inside a balloon or paper bag as a large, contained pressure wave, then the puzzle begins to make sense. Both balloon and paper bag contain pressurized air pushing out against the sides. When the balloon pops or the bag is compressed, the pressurized air rushes out all at once in a powerful wave. Think of an ocean wave. The larger the wave, the more powerfully it crashes into the surf. When the highly pressurized wave from a popped balloon or bag hits the ear, the inner ear translates the sudden increase in pressure as a loud, ringing pop.

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