The science of whistling — and annoying your co-workers

I’m not so sure that whistling while you work is such a good idea. I used to whistle “Cherry Pink and Apple Blossom White” all the time in the biology lab. I liked the way the fourth note hung out there for as long as I wanted before I staggered it down. Then, one day, a delegation of graduate students held an intervention. They thought I whistled fine, but the inconsistency in the length of that fourth note was driving them crazy.

My sister taught me how to whistle while we were swinging on some park swings. That was way before I knew anything about sound vibrations and air waves. Now it seems strange to me that a seemingly smooth flow of air would generate oscillating sound waves.

People are like that, I think. Once we learn how to do something, we don’t give much thought to how we learned it or how we do it anymore. Most of the time we can’t remember when, where or how we learn many things. When did you learn to read? I bet you don’t even know how you swallow.  (Note to self: future column on swallowing.)

Did you know that there are two holes on a standard whistle-kettle cap? It’s true, and I had to look long and hard to find a tea kettle with an intact lid to verify that fact. The two holes are crucial to whistling, according to recent research done at Cambridge by Ross Henrywood and Anurag Agarwal. 

They explain that when the water in the kettle is heated to steam, it is pushed out of the kettle by internal heat pressure. This creates a stream of moisture laden air that escapes through the first hole. This stream quickly becomes unstable because, as soon as the pressure is released, the steam begins to coalesce back into droplets. It’s like water from the nozzle of a hose goes from being a stream to being droplets again after traveling a short distance. 

Then the unstable stream is immediately forced through the second hole. Because the stream of air is now unstable, it arrives at the second opening in an irregular series of pressure pulses that cause the stream to exit the second hole in a series of vortices, or spirals. These spirals of air pressure create sound pulses of air waves that are very close together. It’s these that create the high-pitched whistle. 

All that sounds perfectly plausible and interesting, if perhaps a little useless. I was doubtful of their theory at first because I didn’t see how it explained “Cherry Pink and Apple Blossom White” as whistled with the traditional pucker-whistle humans use for melodic whistling. I therefore conducted a series of dangerous, and sometimes painful, experiments to discover the mechanisms behind pucker-whistling. 

The pucker-whistle is produced by placing the tip of the tongue behind the front bottom teeth, puckering the lips, and blowing. This appears to be a single opening with no opportunity for the flow of air to be turned into pressure pulses. However, careful and painful analysis indicates that the tone is changed by altering the position of the back of the tongue. The back of the tongue forms a restricted opening through which the air must first pass before leaving the second opening created by the tongue and pursed lips. 

So melodic whistling has some characteristics in common with tea kettle whistling after all. Why didn’t they just say so? Now that’s important!  Ironically, it was Hermann Ludwig Ferdinand von Helmholtz, an early pioneer in acoustic research, who once observed, “Whoever, in the pursuit of science, seeks after immediate practical utility may rest assured that he seeks in vain.” 

I, building on the shoulders of Henrywood and Agarwal, suggest that by altering the shape of the tongue, the fourth note of “Cherry Pink and Apple Blossom White” can be sustained for a variable duration which drives other people crazy.

Gary McCallister, .(JavaScript must be enabled to view this email address), is a professor of biology at Colorado Mesa University.


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