1. Chapter 16
Sound and Hearing

2. 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
To contemplate sound shock waves

3. Introduction
Listening to an iPod or MP3 files is not different than listening to cassettes or 8-track tapes. The way the sound is generated changes in tiny ways, but the method of hearing has not changed.

4. 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.

5. Sound waves may be graphed several ways
See Figure 16.3 for different ways to graph sound wave information. Refer to Example 16.1.

6. Sound waves may be graphed several ways II
While reading Example 16.2, see Figure 16.4 below.

7. 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.

8. Opening values along a coiled tube will change the tone

9. 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 gives one more perspective.

10. 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.)

11. 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.

12. The logarithmic decibel scale of loudness
Table 16.2 shows examples for common sounds.

13. 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 and consider a much quieter situation. Figure sets this stage.

14. 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.

15. 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 uses Figure to consider loudspeakers. Figure shows how changing the resonator will change the frequency.

16. 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 cross-sectional view helps to see the pattern.

17. Cross-sectional views reveal harmonic waves II

18. Cross-sectional views reveal harmonic waves III

19. 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
Figure is another way to consider the sound in an organ pipe.

20. 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

21. Wave interference … destructive or constructive

22. Sounds playing on a speaker system can interfere
Refer to Example 16.4.
Figure illustrates the situation.

23. Slightly mismatched frequencies cause audible “beats”

24. 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.

25. The Doppler Effect III—Examples to consider
Problem-Solving Strategy 16.2 will help guide work on a Doppler problem.
Consider Example and Figure to concentrate on wavelength.
Consider Example and Figure to concentrate on frequencies.
Consider Example and Figure to keep the source at rest and move the listener.
Consider Example and Figure to move both the source and the listener.

26. A double Doppler shift
Consider Example and Figure below to guide your work.

27. Very fast aircraft can outrun the sound they generate
A “sonic boom” can be heard when an aircraft’s speed overcomes the sound it generates.
Before Chuck Yeager’s flight, designers were not sure the plane would survive.
See Figure and Example