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making sound waves visible

On Sun, 12 Sep 1999, Cliff Parker wrote:

I went to a concert at Soldiers field in Chicago a couple of years ago. The
crowd of 65,000 was clapping with the beat of the music. I was sitting at one
end of the field and noted a shimmering wave pass from one end of the stadium
to the other. Suddenly I realized I was watching sound! Goosebumps!


Holy cow! Cooooool!

That's a much better method of setting up the visual patterns than relying
on human reaction time (while hoping that the spread in reaction times
doesn't blur the resulting wave into indetectability)

No loud gunshots are needed. Just set up a loudspeaker at one end of a
long row of students outdoors, and have them flap their arms in time with
the beat of the music they hear. Even better, fill a 2-D grid with
students (on the soccer field) and place the loudspeaker at one end.

William Beaty wrote:
Fill the football field with several hundred students. Instruct them to
hold their arms outwards, but to suddenly drop their arms when they hear
the crack of the starter pistol. Stand in the end zone of the field, and
fire the pistol. An overhead observer will see a circular green wave
radiate from the pistol at the speed of sound. The "wave" is composed of
students' arms which suddenly turn vertical and so expose the green grass
beneath. (I've never tried this. No teaching job, no students.)


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William J. Beaty SCIENCE HOBBYIST website
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