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Why does my coffee mug give off a rising pitch when stirred/tapped with a spoon once full?
I noticed years ago that when I filled my ceramic coffee mug with hot coffee and stirred it, the pitch of the sound given off by the spoon scraping or tapping against the mug rises from a low pitch to a higher pitch with every tap. Try it, take a mug, fill it with boiling water and gently start tapping the bottom of the mug with a metal spoon, listen as the pitch rises steadily with each tap...
3 Answers
- Mr. CuriousLv 62 decades agoFavorite Answer
When the coffee is first poured in the molecules in the ceramic are further apart, because cold things shrink (just ask George Costanza) thus causing more room between molucules and creating a lower pitch, but as the coffee heats the mug the molecules expand, reducing the distance between each molecule and raising the pitch.
- QuerierLv 42 decades ago
The mug behaves like an open ended resonating pipe, and hence when you begin filling up the cup, the resonance keeps changing coz the wavelength of the lowest resonance modes keep decreasing. Now, its a known fact that as wavelength decreases, frequency increases. Hence, the increased shrillness of the sound generated.
- 2 decades ago
Hey, I've noticed that too! I thought I was crazy, but I guess I'm not the only one. Don't have an answer for you, but good question! I'll keep checking back for the answer...
