You will need:
enough milk to fill the mug
enough granulated instant coffee to at least partially fill the teaspoon
a microwave oven, with a connection to mains electricity
at least one hand
at least one ear
To investigate what happens acoustically when you stir granulated coffee into a mug of hot milk
Fill mug with milk.
Place milk filled mug into microwave oven.
Heat on full power for 2 minutes (750 watt oven) or until milk is hot enough to make what you'd describe as a "hot" drink.
Add granulated coffee to mug of hot milk using teaspoon. (Any brand of coffee will do here. Caffeinated or decaffeinated are both fine. When I did this experiment, I used Kenco de-caff, but ethical experimenters should find that fair trade organic instant coffee will work just as well)
Stir. Vigorously enough for the spoon to repeatedly tap the internal sides of the mug.
Well you can hear it can't you? The note generated by the spoon's contact with the mug changes. It becomes lower. Perhaps by as much as an octave.
The process of homogenising hot milk and granulated instant coffee in a mug causes a change in the acoustic properties of the medium.
Suggested further research:
The three main factors here appear to be the solvent, the solute and the noise generating media.
So, other soluble materials, such as chocolate powder, andrews liver salts and sugar could be added to hot milk, and stirred so that their acoustic properties can be analysed. Insoluble materials, eg, sand, and woodchips could also be added to the hot milk.
A different solvent, such as water, vinegar, molten lead or sulphuric acid (H2SO4) could be used with coffee, or with other solutes as mentioned above.
Finally, different media could be used. A plastic spoon and a snare drum full of hot milk/cofee solution may generate a different dataset for example.
The possibilities are endless with this one, kids! do try this at home!