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Waves on a String, one of the exhibits in the Science
Museum of Minnesota's Experiment Gallery.
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By J. Shipley Newlin
J. Newlin is director of physical sciences and technology at
the Science Museum of Minnesota in St. Paul, where he led development
of the Experiment Gallery and has worked on exhibitions about
a range of topics from time to calculus.
My favorite exhibits are those that offer insight into a phenomenon
– insight that, like science itself, has an aesthetic dimension.
The effect may be visual, as in a sheet of soap film swirling
with colors. It may be kinesthetic, as when we try to turn the
"wrong" end of a large gear-reduction mechanism. It also may be
aural.
One example is our exhibit Waves on a String, which helps us see
the difference we can hear between a plucked and a bowed
cello string. The exhibit displays the waveform of a vibrating
cello string in much the same way as an oscilloscope displays
the waveform of an electrical signal.
The exhibit consists of a three-quarters size cello mounted on
its side. A light shows through a hole cut into the cello body
and shines onto a single string. A lens projects the silhouette
of a segment of the cello string onto a curved screen via a rotating
faceted mirror. As the mirror rotates, the shadow of the projected
point is swept rapidly and repeatedly across the screen, where
it appears to form a continuous line. Visitors can move the string
up and down, pluck or bow it, and control the speed of the mirror.
They can also change the frequency by pressing the string against
the fingerboard.
Waves on a String is wonderful visually, and it makes wonderful
sounds. After you've seen it, if you go into a classroom and study
waves, you can say, "I know that, I've seen it,
I've heard it."
J. Shipley Newlin is author of Experiment Bench: A Workbook
for Building Experimental Physics Exhibits, which is available
from ASTC Publications. The drawing of Waves on a String is reproduced
from that book.
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