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I read about this demonstration where all this guy did was put a balloon to his ear and somehow he could hear what he couldnt before. Why is this? I was told it had something to do with the effect of air pressure on accoustic refracrion.
I didn't see this demonstration, but have seen something rather similar
at a science museum, the Exploratorium in San Francisco (there may be
others). The idea is that a gigantic rubber ball with thin walls -- a
big balloon, essentially, is filled with carbon dioxide. Because sound
waves travel more slowly in this gas than in air (carbon dioxide is
more dense than nitrogen), this ball has the same effect as as lens has
for light, for essentially the same reason.
Here is our description
of how light travels in different situations.
Because the balloon is round and the speed of sound is slower than
that in air, it focuses sound waves like a convex lens. In the
demonstration, it is important that the speed of sound in the gas in
the balloon is less than it is in the surrounding air.
(republished on 07/29/06)
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