Here's a really interesting phenomenon that you can explore. And there's no explanation ... at least, we're not telling you what it is. When an ordinary ceramic coffee mug is filled with hot coffee, milk is added, and you give it a stir, something unusual will happen if you immediately tap on the top edge of the cup with your spoon. Of course, you'll hear a sound ... sort of like tonk tonk.
But keep listening. Gradually the sound will raise in pitch ... what was a tonk tonk works its way up the scale through tunk tunk and eventually reaches tink tink, all in the space of a few seconds. The increase in pitch is quite noticeable.
What causes it? Here are some questions you might try to answer, to help you understand the phenomenon:
- Does the liquid have to be hot for this to happen?
- Will it work with any liquid?
- Is the milk necessary?
- Does the speed of stirring have an effect?
- Will it work in other containers? (glass? wood?)
No question this time, just a challenge for you. Design some simple experiments to answer each of the questions above. Repeat them to see if you get the same answer each time. Remember to contol the other variables.
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