Still working with sound, and vibrations, we returned to our failed, straw flute experiment from yesterday, but today followed instructions from Janice VanCleave's 203 Icy, Freezing, Frosty, Cool, & Wild Experiments (a science book for children I can happily recommend).
This experiment is more about making a model of a wind instrument, than the actual instrument itself, but the results are quite striking.
First cut a straw, about an inch down from the top, almost all the way through. Then bend the top section, at a right angle to the lower section (a little more, than in the picture below).
Blow through the top section, so the air passes over the bottom section, vibrating the column of air in it. It doesn't whistle, but it does make a sound you can hear.
Then, dip the bottom end of the straw into a cup of water, and continue to blow, keeping the top section at a right angle to the bottom. As, you lower the straw in the water, you shorten the column of air in the lower section of the straw, and when you blow across it, it vibrates faster, causing the pitch to rise.
The children really enjoyed blowing through the straw, while raising and lowering it the water, and listening to the pitch go up, and down.
It's great to be a homeschooler.