High notes and low notes, soft notes and shrill notes, all travel at
the same rate. If bass notes traveled faster or slower than soprano
notes, or if the delicate tones of the violin traveled faster or
slower than the tones of a drum, music would be practically
impossible, because at a distance from the source of sound the various
tones which should be in unison would be out of time--some arriving
late, some early.
255. Sound Waves. Practically everyone knows that a hammock hung
with long ropes swings or vibrates more slowly than one hung with
short ropes, and that a stone suspended by a long string swings more
slowly than one suspended by a short string. No two rocking chairs
vibrate in the same way unless they are exactly alike in shape, size,
and material. An object when disturbed vibrates in a manner peculiar
to itself, the vibration being slow, as in the case of the long-roped
swing, or quick, as in the case of the short-roped swing. The time
required for a single swing or vibration is called the _period_ of the
body, and everything that can vibrate has a characteristic period.
Size and shape determine to a large degree the period of a body; for
example, a short, thick tuning fork vibrates more rapidly than a tall
slender fork.
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