Sound Nature
Very simply, sound is the vibration of any
substance. The substance can
be air, water, wood, or any other material, and
in fact the only place in which
sound cannot travel is a vacuum. When these
substances vibrate, or rapidly move
back and forth, they produce sound. As
described in the How We Perceive Sound:
The Ear section, our ears gather
these vibrations and allow us to interpret
them. To be a little more accurate
in our definition of sound, however, we must
realize that the vibrations that
produce sound are not the result of an entire
volume moving back and forth at
once. If that were the case, the entire
atmosphere would need to shift for
any sound to be made at all! Instead, the
vibrations occur among the
individual molecules of the substance, and the
vibrations move through the
substance in sound waves. As sound waves travel
through the material, each
molecule hits another and returns to its original
position. The result is
that regions of the medium become alternately more
dense, when they are
called condensations, and less dense, when they are called
rarefactions.