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Possible Duplicate:
Why does the sound pitch increase on every consecutive tick at the bottom of a filled cup of coffee?

A colleague suggested this experiment this morning :

  • Get a cup of coffee
  • Spin the coffee in the cup using a spoon
  • Tap the bottom of the cup with the spoon

Observations : As the coffee slows down, the sound produced by the tapping gets higher in frequency.

I'm very curious about this, does anyone have an explanation ?

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    $\begingroup$ See this: physics.stackexchange.com/questions/23038/… $\endgroup$ – tmac Jun 6 '12 at 8:30
  • $\begingroup$ The situation described is not identical to the the one in the proposed duplicate, but I think that the explanation is. I'm going to close this as a duplicate, but would be willing to re-open if anyone expresses a desire to write an answer about the quantitative differences. Just flag. $\endgroup$ – dmckee --- ex-moderator kitten Jun 6 '12 at 14:08