Transcript 16_LectureOutline sp08

Chapter 16
Sound and Hearing
PowerPoint® Lectures for
University Physics, Twelfth Edition
– Hugh D. Young and Roger A. Freedman
Lectures by James Pazun
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Goals for Chapter 16
• To study many aspects and variations of sound waves
• To relate intensity and sound intensity level
• To consider standing sound waves
• To view interference as it manifests in sound
• To study and calculate beats
• To view the many applications of the Doppler effect
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Introduction
• Listening to an iPod or MP3
files is not different than
listening to cassettes or 8track tapes. The way the
sound is generated changes in
tiny ways, but the method of
hearing has not changed.
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Longitudinal waves show the sinusoidal pattern
• A motion like the pulses of a
speaker cone will create
compressions and
rarefactions in a medium like
air. After the pulse patterns
are seen, a sinusoidal pattern
may be traced.
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Sound waves may be graphed several ways
• See Figure 16.3 for different ways to graph sound
wave information. Refer to Example 16.1.
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Sound waves may be graphed several ways II
• While reading Example 16.2, see Figure 16.4 below.
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Different instruments give the same pitch different “favor”
• The same frequency, say middle c at 256 Hz, played on a
piano, on a trumpet, on a clarinet, on a tuba … they will all be
the same pitch but they will all sound different to the listener.
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Opening values along a coiled tube will change the tone
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Speed of sound in liquids and solids
• The speed of sound will
increase with the density of
the material.
• Refer to Table 16.1 at right
for examples.
• Consider Example 16.3 and
Figure 16.8 below.
• Example 16.4 gives one
more perspective.
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The speed of sound in air
• Sound will travel in air at roughly 340 m/s.
• An exact speed would change slightly with humidity,
temperature, and nature of the atmosphere.
• It still means you need to drive far too fast for our
interstate highways to break the sound barrier in a car.
(It has been done on a very long salt lakebed in Utah
but it’s over 700 miles per hour.)
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Sound intensity
• The in amplitude term in our wave equation can be related to
the sound intensity, but perception of the listener often
complicates the physics (location, weather, voice, or sound)
in question.
• Study Problem-Solving Strategy 16.1.
• Follow Examples 16.6, 16.7, and 16.8.
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The logarithmic decibel scale of loudness
• Table 16.2 shows examples for common sounds.
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The decibel scale for front-row concert seats or for songbirds
• Example 16.9 reflects human reaction to “very” loud music,
explosions, or perhaps walking amidst jet planes on a runway.
• Follow Example 16.10 and consider a much quieter situation.
Figure 16.11 sets this stage.
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Standing sound waves and normal modes
• Experiments often done in a first
physics course laboratory will
use common materials to reveal
standing sound waves in
resonance.
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Sound wave resonance depends on the instrument
• The waveform must match the resonant container (open at both
ends, one end, clamped at both)?
• Conceptual Example 16.11 uses Figure 16.14 to consider
loudspeakers. Figure 16.15 shows how changing the resonator
will change the frequency.
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Cross-sectional views help us visualize the wave
•
Nodes and
antinodes will
line up so that
nodes are
found where
the resonator
is closed and
antinodes at
an open pipe.
•
The crosssectional view
helps to see
the pattern.
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Cross-sectional views reveal harmonic waves II
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Cross-sectional views reveal harmonic waves III
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The speed of sound can be revealed by a resonant pipe
• The frequency, speed of
sound, and wavelength
are all used to measure
normal modes in a pipe
• Follow Example 16.12.
• Figure 16.19 is another
way to consider the sound
in an organ pipe.
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The tone from one instrument can transfer
• Musicians playing near one another often notice
that an organ pipe can cause a guitar string to
resonate.
• Consider Example 16.13.
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Wave interference … destructive or constructive
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Sounds playing on a speaker system can interfere
• Refer to Example 16.4.
• Figure 16.23 illustrates the
situation.
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Slightly mismatched frequencies cause audible “beats”
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The Doppler Effect II—moving listener, moving source
• As the object making the sound moves or as the listener
moves (or as they both move), the velocity of sound is
shifted enough to change the pitch perceptively.
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The Doppler Effect III—Examples to consider
• Problem-Solving Strategy 16.2 will help guide work on
a Doppler problem.
• Consider Example 16.15 and Figure 16.29 to concentrate
on wavelength.
• Consider Example 16.16 and Figure 16.30 to concentrate
on frequencies.
• Consider Example 16.17 and Figure 16.31 to keep the
source at rest and move the listener.
• Consider Example 16.18 and Figure 16.32 to move both
the source and the listener.
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A double Doppler shift
• Consider Example 16.19 and Figure 16.33 below to
guide your work.
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