Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Sound Waves Section 1 Sound Waves.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 The Production of Sound Waves Every sound wave begins with a vibrating object, such as the vibrating prong of a tuning fork. Section 1 Sound Waves

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Section 1 Sound Waves Sound waves are longitudinal. The simplest longitudinal wave produced by a vibrating object can be represented by a sine curve. Amazing water and sound video

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Frequency of Sound Waves As discussed earlier, frequency is defined as the number of cycles per unit of time. Sound waves that the average human ear can hear, called audible sound waves, have frequencies between 20 and 20 000 Hz. Sound waves with frequencies less than 20 Hz are called infrasonic waves. Sound waves with frequencies above 20 000 Hz are called ultrasonic waves. Section 1 Sound Waves

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Frequency and Pitch The frequency of an audible sound wave determines how high or low we perceive the sound to be, which is known as pitch. As the frequency of a sound wave increases, the pitch rises. The frequency of a wave is an objective quantity that can be measured, while pitch refers to how different frequencies are perceived by the human ear. Section 1 Sound Waves

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 The Speed of Sound The speed of sound depends on the medium. –depends on how quickly one particle can transfer its motion to another particle. –For example, sound waves generally travel faster through solids than through gases because the molecules of a solid are closer together than those of a gas are. The speed of sound also depends on the temperature of the medium. This is most noticeable with gases. Section 1 Sound Waves

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Conceptual Challenge Suppose you hear music being played from a trumpet that is across the room from you. Compressions and rarefactions from the sound wave reach your ear, and you interpret these vibrations as sound. Were the air particles that are vibrating near you carried across the room by the sound wave? How do you know? Light waves travel nearly 1 million times faster than sound waves in air. With this in mind, explain how distance to a lighting bolt can be determined by counting the seconds between the flash and the sound of the thunder. Chapter 12 Section 1 Sound Waves

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 The Doppler Effect The Doppler effect is an observed change in frequency when there is relative motion between the source of waves and an observer. Because frequency determines pitch, the Doppler effect affects the pitch heard by each listener. Section 1 Sound Waves

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section Review What is the relationship between frequency and pitch? Dolphins can produce sound waves with frequencies ranging from 0.25 kHz to 220 kHz, but only those at the upper end of this spectrum are used in echolocation. Explain why high frequency waves work better than low-frequency waves. Sound pulse emitted by a dolphin travel through 20 ° C ocean water at a rate of 1450 m/s. In 20 ° C air, these pulses would travel 342.9 m/s. How can you account for this difference in speed? As a dolphin swims towards a fish, the dolphin sends out sound waves to determine the direction the fish is moving. If the frequency of the reflected waves is higher that that of the emitted waves, is the dolphin catching up to the fish or falling behind? Section 1 Sound Waves Chapter 12

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Sound Intensity The rate at which sound energy is transferred through a medium is called the intensity of the wave. Because power (P) is defined as the rate of energy transfer, intensity can also be described in terms of power. Section 2 Sound Intensity and Resonance

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Sound Intensity, continued Intensity has units of watt per square meter (W/m 2 ). The intensity equation shows that the intensity decreases as the distance (r) increases. This occurs because the same amount of energy is spread over a larger area. The intensity of a wave approximately determines its perceived loudness. However, loudness is not directly proportional to intensity but is approximately logarithmic in the human ear which means that if intensity doubles that does not mean that loudness doubles. Section 2 Sound Intensity and Resonance

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Practice: Sound Intensity Calculate the intensity of the sound waves from an electric guitar’s amplifier at a distance of 5.0 m when its power output is equal to each of the following values: –0.25 W –0.50 W –2.0 W If the intensity of a person’s voice is 4.6 e-7 W/m 2 at a distance of 2.0 m, how much sound power does that person generate? The power output of a tuba is 0.35 W. At what distance is the sound intensity of the tuba 1.2 e -3 W/m 2 Chapter 12 Section 2 Sound Intensity and Resonance

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Sound Intensity, continued Human hearing depends on both the frequency and the intensity of sound waves. Section 2 Sound Intensity and Resonance Sounds in the middle of the spectrum of frequencies can be heard more easily (at lower intensities) than those at lower and higher frequencies.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Sound Intensity, continued Relative intensity is the ratio of the intensity of a given sound wave to the intensity at the threshold of hearing. This is referred to as the decibel level. A dimensionless unit called the decibel (dB) is used for values on this scale. Section 2 Sound Intensity and Resonance

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Forced Vibrations and Resonance Each pendulum has a natural frequency (a frequency at which they vibrate more easily) based on its length. If one of the pendulums is set in motion, its vibrations are transferred by the rubber band to the other pendulums, which will also begin vibrating. This is called a forced vibration. Section 2 Sound Intensity and Resonance

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Forced Vibrations and Resonance, continued Resonance is when the frequency of a force applied matches the natural frequency of vibration of the system, resulting in a large amplitude of vibration. If one blue pendulum is set in motion, only the other blue pendulum, whose length is the same, will eventually resonate. Section 2 Sound Intensity and Resonance

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Tacoma Narrows Bridge Collapse "Gallopin' Gertie" Slender, elegant and graceful, the Tacoma Narrows Bridge stretched like a steel ribbon across Puget Sound in 1940. The third longest suspension span in the world opened on July 1st. Only four months later, the great span's short life ended in disaster. "Galloping Gertie," collapsed in a windstorm on November 7,1940. The bridge became famous as "the most dramatic failure in bridge engineering history." Now, it's also "one of the world's largest man- made reefs." The sunken remains of Galloping Gertie were placed on the National Register of Historic Places in 1992 to protect her from salvagers. Section 2 Sound Intensity and Resonance

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 The Human Ear Sound waves travel through the three regions of the ear and are then transmitted to the brain as impulses through nerve endings on the basilar membrane. Section 2 Sound Intensity and Resonance The human ear is divided into three sections—outer, middle, and inner.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Standing Waves on a Vibrating String The vibrations on the string of a musical instrument usually consist of many standing waves, each of which has a different wavelength and frequency. The greatest possible wavelength on a string of length L is = 2L. The fundamental frequency, which corresponds to this wavelength, is the lowest frequency of vibration. Section 3 Harmonics

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Standing Waves on a Vibrating String, continued The harmonic series is a series of frequencies that includes the fundamental frequency and multiples of the fundamental frequency. Section 3 Harmonics

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Practice: What is the fundamental frequency of a guitar string when the speed of waves on the string is 115. m/s and the string length is 70.0 cm? 50.0 cm? 35.0 cm? A violin string that is 50.0 cm long has a fundamental frequency of 440. Hz. What is the speed of the waves on this string? –What controls the speed of the wave on the string? What are the first three harmonics of a note produced on a 31.0 cm long violin string if waves on this string have a speed of 274.4 m/s?

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Harmonic Series of a Pipe Open at Both Ends If both ends of a pipe are open, there is an antinode at each end. In this case, all harmonics are present, and the earlier equation for the harmonic series of a vibrating string can be used. Section 3 Harmonics

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Harmonic Series of a Pipe Closed at One End If one end of a pipe is closed, there is a node at that end. With an antinode at one end and a node at the other end, a different set of standing waves occurs. In this case, only odd harmonics are present. Section 3 Harmonics

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Practice: What are the first three harmonics in a 2.45 m long pipe that is open at both ends? What are the first three harmonics of this pipe when one end of the pipe is closed? Assume the speed of sound in air is 345. m/s. What is the fundamental frequency of a 0.20 m long organ pipe that is closed at one end, when the speed of sound in the pipe is 352. m/s? A flute is essentially a pipe open at both ends. The length of a flute is approximately 66.0 cm. What are the first three harmonics of a flute when all keys are closed, making the vibrating air column approximately equal to the length of the flute? The speed of sound in the flute is 340. m/s.

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Timbre Timbre is the the musical quality of a tone resulting from the combination of harmonics present at different intensities. Differences in timbre cause clarinet to sound different from a viola even when both instruments are sounding the same note at the same volume. The rich harmonics of most instruments provide a much fuller sound than that of a tuning fork. Section 3 Harmonics

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Beats When two waves of slightly different frequencies interfere, the interference pattern causes a listener hears an alternation between loudness and softness. Section 3 Harmonics

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Beats The variation from soft to loud and back to soft is called a beat. The frequency difference between two sounds can be found by the number of beats heard per second. Section 3 Harmonics

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Sound Waves Section 1 Sound Waves.

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Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 12 Sound Waves Section 1 Sound Waves.

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