One of the best ways to explore sound is to make music.
Some musical instruments make only one note.
Begin with an empty bottle. With experimentation and practice you can make the bottle sing one note by blowing across its open mouth. But, no matter how you blow you can only make the bottle sing one note.
Add water to the bottle and you can change the one note it will sing.
Poke a small hole in a plastic bottle and the bottle will not sing at all.
A whirly on the other hand will sing several notes. The frequency of the note it sings is proportional to the speed at which the whirly is twirled.
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Scientific Explorations with Paul Doherty
25 May 2000