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science question: why do coffee mugs "sing"??

updated sat 19 apr 08


Teresa Wooden on fri 18 apr 08

This question has perplexed me for years...I have asked the kids' physics
and chemistry teachers and they can't really provide me with an answer, so
I figured some of the MFA's on the list could easily enlighten me...

You fill a mug with coffee or tea (it's hot). You stir in the sugar and
then tap the spoon on the rim. Keep tapping, and the mug keeps "tinking"
in ever higher notes, reaching a couple octaves higher than the original
tap in some cases.

Filling a mug with cold water does not produce the same effects. Also, if
you tap a hot mug once, then tap in five minutes, it has not reached the
ultimate note that it would have reached after several taps. So, it is a
result of heating the molecules in the clay body, combined with the effect
of vibrating the body. Can anyone tell me what exactly is happening that
causes the clay to resound in higher and higher notes as it is tapped?

I just want to impress the kids' teachers at the next parents'
conference. :)

Teresa Wooden