Stirring sugar into a cup of coffee

the "hot chocolate effect"

Adding sugar to hot water

Here are some spectrograms (with sound) that show what is happening:

see a spectral movie with sound here (WMV) or sound only here (WAV) or a still image here (JPG)

... and another

Filling a cup with water

see a spectral movie with sound here (WMV) or sound only here (WAV) or a still image here (JPG)

Alkaseltza in cold water

see a spectral movie with sound here (WMV) or sound only here (WAV) or a still image here (JPG)

Explanation:

A fuller explanation can be found under the heading "The hot chocolate effect" in the American Journal of Physics -- May 1982 -- Volume 50, Issue 5, pp. 398-404

and there is a nice acoustic holography image of the vibrating walls of a coffee cup done at the Physics Department, Northern Illinois University

and there's more on the "cheap instant coffee effect" here

Gyroscopes and Boomerangs: go to Hugh Hunt's gyro and boomerang page

Dynamics Videos: go to Hugh Hunt's movies page

and for other stuff: go to Hugh Hunt's Cambridge University home page