All sound is just a series of vibrations in
the air. That's why there's no such thing as
sound in outer space (no air), and that's why
sound travels faster through solids or liquids
(there's more stuff there to vibrate).
Our outer ears, the part you can see,
collect and focus those vibrations. In the
middle ear, the eardrum is a tight membrane
that moves with those vibrations.
The eardrum is connected to three little bones
called the malleus, the incus, and the
stapes. They move as the eardrum
moves,transmitting the vibrations to a
fluid-filled chamber in the inner ear. As
the inner ear fluid vibrates, little hairs
called cilia move in the current. Each hair
or cilium is connected to a nerve that goes to the
part of the brain devoted to hearing. Our
brains translate the nerve impulses into what we
perceive as sound.
We can detect the direction of the sound source
if the sound arrives at different ears at slightly
different times. We perceive loudness and
pitch in sounds based on characteristics of
the vibrations. "Bigger" vibrations,or sound waves
with greater amplitude, are perceived as louder
"Faster" vibrations, or sound waves that
occur with greater frequency, are perceived as
higher in pitch.
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