Transcript Chapter 8 Rotational Motion

Chapter 21 Musical Sound
• Noise corresponds to an
irregular vibration of the
eardrum produced by some
irregular vibration.
• The sound of music has a
different character, having
periodic tones-or musical
“tones”.
• Musicians usually speak of
musical tones in terms of
three principal
characteristics: pitch,
loudness, and quality.
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Pitch
• The pitch of a sound relates to its
frequency.
• Rapid vibrations of the sound
source (high frequency) produce a
high note, whereas slow vibrations
(low frequency) produce a low
note.
• Different musical notes are
obtained by changing the frequency
of the vibrating sound source.
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Sound intensity and loudness
• The intensity of sound depends on the
amplitude of pressure variations within
the sound wave.
– Sound intensity is a purely objective and
physical attribute of a sound wave and can
be measured by various acoustic
instrument.
• Loudness is a physiological sensation.
The ear senses some frequencies much
better than others.
– For example, a 3500-Hz sound and a 125Hz sound with the same intensity, the
3500-Hz sound sounds about twice as loud
to most people as the 125-Hz soundhumans are more sensitive to the 3500-Hz
range of frequencies.
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Musical instrument
• Conventional musical
instruments can be grouped into
one of three classes:
– Those in which the sound is
produced by vibrating strings
– Those in which the sound is
produced by vibrating air
columns
– Those in which the sound is
produced by percussion-the
vibrating of a two-dimensional
surface.
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• In a stringed instrument such
as a violin, the vibration of
the strings is transferred to a
sounding board and then to
the air.
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• In a wind instrument,
like a flute, the sound
is produced by a
vibrating air column
in the instrument. The
musician blows air
against the edge of a
hole to produce a
fluttering stream that
sets the air column
into vibration.
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• In percussion
instruments, such as a
drum, a twodimensional
membrane or elastic
surface is struck to
produce sound.
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Homework
• Chapter 21, P. 406-408, Exercises: 8, 26, 27,
30.
• The above problems are assigned from the
10th edition of the textbook by Hewitt.
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