The singing coffee cup - Detective work

You might have noticed that if you make a cup of coffee or cocoa (instant cup-soup is a good one as well) and stir it to get it mixed, the tone of the clinking of the spoon against the sides of the cup changes. Why is this?

1. To list the various hypotheses you can think of such as dissolving the sugar, denaturing the milk, heating the cup, getting bubbles out of the fluid and so on.
2. To devise a plan for eliminating each of these hypotheses. Eg try with and without sugar.
3. Try to eliminate as many as possible using some test procedure.
4. Come to a conclusion about the causes of this phenomenon.

You now have the CAUSES identified but not the MECHANISM. If you are still on speaking terms with your local physicist, explain the story so far then ask for:

1. The mechanism
2. Proof (A demonstration.)

The fun of this experiment is:

• Answering a question that may have occurred to you but never bothered to investigate.
• Making up, eliminating and refining hypotheses. (The classical scientific method.)
• Pushing the all-knowing physicist to demonstrate the mechanism not on a blackboard but in the workshop.

This problem has been taken up by various people and even prompted New Scientist to try their own experiments. So far (after 5 years) the lack of scientific result has been astounding. This is one of those problems that 'Scientists' know they don't know the answer to but strangely can't be bothered to do the simple work that any school child could do. Never mind: It's never too late to start enjoying being inquisitive start today... ...put the kettle on to become an expert!

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