Phenomena

The Dangerous Clatter of Dishes

3 plates in a dishwasher

Have you ever noticed how loud dishes are when you’re handling them? Under the right (or, perhaps more accurately, wrong) circumstances, the clatter of ceramics like porcelain can be dangerously loud, as engineer Phil Metzger discovered when repairing his toilet. At one point the lid to his tank slipped from his hands and fell about 20 centimeters to strike the edge of the toilet. The lid did not break, but Metzger stumbled away stunned from the loud noise. He immediately noticed that his hearing was distorted – he described his own voice as sounding “like talking through a kazoo”. Upon further experiment, he found that the distortion occurred at specific, regularly-spaced frequencies. Like any engineer, therefore, he turned to physics to analyze the accident.

Since the lid didn’t break, he knew that the energy from the lid’s fall went into two places: the sound he heard and a small amount of dissipated heat. Using the speed of sound in a ceramic and the dimensions of the lid, he was able to calculate the frequency of sound produced by the impact, and with a little more work, he could estimate that the sound, as transmitted to his nearby ear, had been about 138 dB. Permanent damage from brief sounds can occur at 140 dB, so this was well inside the danger zone. The pressure from sounds this loud is enough to severely bend the tiny hairs in your cochlea that are responsible for sensing these vibrations. Luckily for Metzger, his hearing did recover after a few days, but it’s a good reminder to be careful. Sometimes everyday physics can be surprisingly dangerous! (”Research” credit: P. Metzger; image credit: comedynose/Flickr; via Motherboard via J. Ouellette)

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