Physics Puzzle: Woodwinds in the Willows
June 1st, 2009
| Categories: Music and Audio, Physics Puzzles
Level of difficulty: highschool
Take a recorder’s head and blow through it - you’ll get a sound with a particular frequency.
Next, take your hand and cover the head’s end. Will the head emit a sound when blown through? If so, how will it be related to the sound in the unblocked case (for example, what could you say about its pitch)?
EDITED, 2/June/2009: the puzzle has been solved, and quite quickly, by our faithful reader jbrydle. You can read his solution in the comments section. However, as an added bonus, you can also view my presentation on Youtube explaining everything in detail, complete with narration and all:
I believe all that is needed for sound is air flowing over the fipple (the notch) at the head of the recorder. The pitch is determined by the way way waves resonate in the tube. An open end is associated with a freely moving wave crest, like an unsecured end of a rope. A closed end is associated with a node, like a rope tied to a point.
Uncovered, the wavelength of the fundamental wave will be 2X the distance between fipple and end - crest at fipple, crest at end = half a wave. A closed end, it seems would double the fundamental wavelength - crest at fipple and node at end = quarter wave. That would mean the tone gets one octave lower when you cover the end of the recorder.
I’ve made a lot of assumptions based on half-remembered concepts though. I may be dead wrong!
Arrrgh, solved so quickly :).
I love the video! I hope you do more of those. My solution wasn’t very good in terms of explaining concepts, but now I know