Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley PowerPoint ® Lectures for University Physics, Twelfth Edition – Hugh D. Young and Roger A. Freedman Lectures by James Pazun Chapter 16 Sound and Hearing

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Amplitude of sound wave in air A sound wave with maximum pressure of 3 x Pa above atmospheric pressure has a frequency of 1000 Hz. The speed of sound is 344 m/s and the bulk modulus is 1.42 x 10 5 Pa. What is the maximum displacement of air for this sound wave? What is the maximum pressure at 5000 Hz?

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Sound waves may be graphed several ways See Figure 16.3 for different ways to graph sound wave information. Refer to Example 16.1.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Sound waves may be graphed several ways II While reading Example 16.2, see Figure 16.4 below.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley At a compression in a sound wave, A. particles are displaced by the maximum distance in the same direction as the wave is moving. B. particles are displaced by the maximum distance in the direction opposite to the direction the wave is moving. C. particles are displaced by the maximum distance in the direction perpendicular to the direction the wave is moving. D. the particle displacement is zero. Q16.1

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley At a compression in a sound wave, A. particles are displaced by the maximum distance in the same direction as the wave is moving. B. particles are displaced by the maximum distance in the direction opposite to the direction the wave is moving. C. particles are displaced by the maximum distance in the direction perpendicular to the direction the wave is moving. D. the particle displacement is zero. A16.1

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Velocity of sound depends on medium Speed in a fluid Speed in a solid

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Speed of sound in liquids and solids The speed of sound will decrease with the density of the material. But sound generally travels faster in solids

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Wavelength of sonar waves A ship uses a sonar system to detect underwater objects. The system emits underwater sound waves and measures the time interval for the reflected wave to return to the detector. Find the wavelength of a 262 Hz wave. How long does it take before the ship hears the reflection off of a ship on the bottom of the ocean 1000 m away?

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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.)

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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. The Who

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Increasing the pressure amplitude of a sound wave by a factor of 4 (while leaving the frequency unchanged) A. causes the intensity to increase by a factor of 16. B. causes the intensity to increase by a factor of 4. C. causes the intensity to increase by a factor of 2. D. has no effect on the wave intensity. E. The answer depends on the frequency of the sound wave. Q16.2

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Increasing the pressure amplitude of a sound wave by a factor of 4 (while leaving the frequency unchanged) A. causes the intensity to increase by a factor of 16. B. causes the intensity to increase by a factor of 4. C. causes the intensity to increase by a factor of 2. D. has no effect on the wave intensity. E. The answer depends on the frequency of the sound wave. A16.2

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Increasing the frequency of a sound wave by a factor of 4 (while leaving the pressure amplitude unchanged) A. causes the intensity to increase by a factor of 16. B. causes the intensity to increase by a factor of 4. C. causes the intensity to increase by a factor of 2. D. has no effect on the wave intensity. E. The answer depends on the frequency of the sound wave. Q16.3

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Increasing the frequency of a sound wave by a factor of 4 (while leaving the pressure amplitude unchanged) A. causes the intensity to increase by a factor of 16. B. causes the intensity to increase by a factor of 4. C. causes the intensity to increase by a factor of 2. D. has no effect on the wave intensity. E. The answer depends on the frequency of the sound wave. A16.3

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The logarithmic decibel scale of loudness Table 16.2 shows examples for common sounds.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Thumping bass Your friend has fixed the problem with their subwoofer and is now pumping 800W of obnoxiously loud, bass-heavy music through their subwoofer-equipped car, causing the entire car to rattle. If the bass note is vibrating at 40 Hz, what is the maximum displacement of air at 1 m away from the subwoofer? How many dB’s is this? Why does your friend have an 800W subwoofer instead of an 800W amplifier for all sound frequencies?

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Sound wave resonance depends on the instrument The waveform must match the resonant container (open at both ends, one end, clamped at both)?

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The air in an organ pipe is replaced by helium (which has a lower molar mass than air) at the same temperature. How does this affect the normal-mode wavelengths of the pipe? A. The normal-mode wavelengths are unaffected. B. The normal-mode wavelengths increase. C. The normal-mode wavelengths decrease. D. The answer depends on whether the pipe is open or closed. Q16.4

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The air in an organ pipe is replaced by helium (which has a lower molar mass than air) at the same temperature. How does this affect the normal-mode wavelengths of the pipe? A. The normal-mode wavelengths are unaffected. B. The normal-mode wavelengths increase. C. The normal-mode wavelengths decrease. D. The answer depends on whether the pipe is open or closed. A16.4

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The air in an organ pipe is replaced by helium (which has a lower molar mass than air) at the same temperature. How does this affect the normal-mode frequencies of the pipe? A. The normal-mode frequencies are unaffected. B. The normal-mode frequencies increase. C. The normal-mode frequencies decrease. D. The answer depends on whether the pipe is open or closed. Q16.5

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley The air in an organ pipe is replaced by helium (which has a lower molar mass than air) at the same temperature. How does this affect the normal-mode frequencies of the pipe? A. The normal-mode frequencies are unaffected. B. The normal-mode frequencies increase. C. The normal-mode frequencies decrease. D. The answer depends on whether the pipe is open or closed. A16.5

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Different instruments give the same pitch different “flavor” 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.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Cross-sectional views reveal harmonic waves II

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Cross-sectional views reveal harmonic waves III

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley A. 110 Hz. B. 220 Hz. C. 440 Hz. D. 880 Hz. E Hz. Q16.6 When you blow air into an open organ pipe, it produces a sound with a fundamental frequency of 440 Hz. If you close one end of this pipe, the new fundamental frequency of the sound that emerges from the pipe is

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley When you blow air into an open organ pipe, it produces a sound with a fundamental frequency of 440 Hz. If you close one end of this pipe, the new fundamental frequency of the sound that emerges from the pipe is A. 110 Hz. B. 220 Hz. C. 440 Hz. D. 880 Hz. E Hz. A16.6

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Wave interference … destructive or constructive

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Sounds playing on a speaker system can interfere Refer to Example Figure illustrates the situation.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley Slightly mismatched frequencies cause audible “beats”

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley You hear a sound with a frequency of 256 Hz. The amplitude of the sound increases and decreases periodically: it takes 2 seconds for the sound to go from loud to soft and back to loud. This sound can be thought of as a sum of two waves with frequencies A. 256 Hz and 2 Hz. B. 254 Hz and 258 Hz. C. 255 Hz and 257 Hz. D Hz and Hz. E Hz and Hz. Q16.7

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley You hear a sound with a frequency of 256 Hz. The amplitude of the sound increases and decreases periodically: it takes 2 seconds for the sound to go from loud to soft and back to loud. This sound can be thought of as a sum of two waves with frequencies A. 256 Hz and 2 Hz. B. 254 Hz and 258 Hz. C. 255 Hz and 257 Hz. D Hz and Hz. E Hz and Hz. A16.7

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley A. a higher frequency and a shorter wavelength. B. the same frequency and a shorter wavelength. C. a higher frequency and the same wavelength. D. the same frequency and the same wavelength. Q16.8 On a day when there is no wind, you are moving toward a stationary source of sound waves. Compared to what you would hear if you were not moving, the sound that you hear has

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley A. a higher frequency and a shorter wavelength. B. the same frequency and a shorter wavelength. C. a higher frequency and the same wavelength. D. the same frequency and the same wavelength. A16.8 On a day when there is no wind, you are moving toward a stationary source of sound waves. Compared to what you would hear if you were not moving, the sound that you hear has

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley On a day when there is no wind, you are at rest and a source of sound waves is moving toward you. Compared to what you would hear if the source were not moving, the sound that you hear has A. a higher frequency and a shorter wavelength. B. the same frequency and a shorter wavelength. C. a higher frequency and the same wavelength. D. the same frequency and the same wavelength. Q16.9

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley On a day when there is no wind, you are at rest and a source of sound waves is moving toward you. Compared to what you would hear if the source were not moving, the sound that you hear has A. a higher frequency and a shorter wavelength. B. the same frequency and a shorter wavelength. C. a higher frequency and the same wavelength. D. the same frequency and the same wavelength. A16.9

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley A double Doppler shift Consider Example and Figure below to guide your work.

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley 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