DR GARY SETTLES / SCIENCE PHOTO LIBRARY DR GARY SETTLES / SCIENCE PHOTO LIBRARY
Human whistling, schlieren image. Schlieren photography is an imaging technique that is used to show changes in the density of fluids and gases such as air, caused here by the turbulence of the air stream produced when whistling. Whistling involves blowing air through pursed lips, generating a tone that can be changed by moving the lips. This image reveals that the air expelled by whistling forms a turbulent jet that penetrates the surrounding still air. Photographed at Pennsylvania State University, USA.
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