Goals For Chapter 12
s for Chapter 12
  To describe mechanical waves.
  To study superposition, standing waves and sound.
  To present sound as a standing longitudinal wave.
  To see that waves will interfere (add constructively
and destructively).
  To study sound intensity and beats.
  To solve for frequency shifts (the Doppler Effect).
  To examine applications of acoustics and musical
tones.
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Types of mechanical waves – Figure 12.2
• Transverse – the wave disturbance is perpendicular to the
direction of propagation.
•  Longitudinal – the wave disturbance is parallel to the direction of
propagation.
•  Water waves – a complex mixture of both.
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Waves on Strings and in Air
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Slide 15-13
Snapshot Graphs
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Slide 15-14
Constructing a History Graph
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Slide 15-15
Checking Understanding
The graph below shows a snapshot graph of a wave on a string
that is moving to the right. A point on the string is noted. Which of
the choices is the history graph for the subsequent motion of this
point?
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Slide 15-16
Answer
The graph below shows a snapshot graph of a wave on a string
that is moving to the right. A point on the string is noted. Which of
the choices is the history graph for the subsequent motion of this
point?
(b)
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Slide 15-17
Generating a longitudinal wave – Figure 12.3
•  An object undergoing SHM can cause the disturbance and
the medium can be a string, cord or rope under tension.
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“Time lapse” snapshot of a traveling wave – Figure 12.4
•  If you follow the original set of
markers (3 red dots at top of the
figure), you can see the
movement as time passes going
down from top to bottom.
•  Each fresh sketch as you go
downward elapses 1/8 of the
period.
• Recall 8/8T (all the way from
top to bottom) is one period, the
time for one complete oscillation
to pass.
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Longitudinal and transverse waves
Figures 12.5 and 12.6 help
us to see the sinusoidal
waveform.
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Sinusoidal Waves
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Slide 15-22