01.29.2016
Written By: Chris Geach
Today, we followed up last week’s introduction to sound. I talked a little about how a sound wave is different from an ocean wave, for example (transverse vs. longitudinal), but still has the same basic characteristics: frequency, wavelength, amplitude. Then I asked if anyone played a musical instrument, and we talked about how different instruments have different mechanisms for changing the frequency of the note they produce. George provided a sudden and dramatic example, with a trombone solo.
After this introduction, we set them to work designing their own instrument. We provided ~12″ lengths of PVC, which produce a tone by blowing across one end. By lowering the pipe to different levels in the water bottle, they changed the effective length of the pipe, and therefore the tone they produced. They were able to measure the frequency of each note, thanks to guitar tuning apps on our smart phones, then make graphs of frequency vs. length.
Hopefully informed by this exercise, they were then given ~5 ft of PVC to make their own pan flute. They chose the lengths that they wanted the piping to be cut to, then glued pennies over one end of each tube.
I think this experiment was a moderate success. Some of the students were clearly not interested, and many of them had trouble producing a clean note from the pipes. But a lot of them were interested, and eager to design their own pan flute.