Monday, December 18, 2006

Coffee music

Does anybody know why the sound of my spoon against my coffee mug increases in pitch as I stir? Can you check this with your mug of coffee?

Pour instant coffee into mug. (Yes, I'm lazy.)
Pour boiled water into mug and stir.
Listen to pitch of the coffee music.

I think this also happens when I make hot chocolate, and Orange pekoe tea with sugar.

I assume it has something to do with substances dissolving into the water. I initially thought it was the speed of the water turning in the mug. But I slowed the water down (even reversed it) but the pitch stayed constant.

Any chemists out there care to explain?


Sean O'Hagan said...

I suppose I should have Googled this first. There's a little discussion here which suggests that as microbubbles dissipate while stirring, the speed of sound varies, thereby affecting pitch.

Anonymous said...

Wow! I am so pleased to know the answer to this mystery. Thank you so much!

Sean O'Hagan said...

You are very welcome anonymous!