Chapter 13: Sound

Section 1 (Sounds Waves)

Compressions: areas of high pressure
Rarefactions: areas of low pressure
Pitch: the frequency a sounds wave is percieved to have
Infrasonic: frequencies below 20 Hz
Ultrasonic: frequencies above 20,000 Hz
Doppler Efect: sound source and the detector are moving relative to one another

Humans can hear sounds from about 20 Hz to 20,000 Hz
Speed of sound is approximately 343 m/s

v= speed

f' = pitch
f= frequency

Section 2 (Sound Intensity and Resonance)


Intensity: the rate at which energy is transferred from one molecule to the next
Perceived intensity: dependent on the logarithm of the intensity and is measured in decibels.
Resonance: response at certain frequencies
Resonant frequency: the amplitude of its vibrations

Threshold of hearing:

Threshold of pain:

Intensity: is the intensity of the sound being measured.

An increase of 10 decibels will be perceived as being twice as loud, and intensity will be increased by a factor of 10
Section 3 (Standing Waves)


The lowest frequency able to form a standing wave

Harmonics: frequencies above the lowest frequency
Harmonic series: the frequency of each harmonic frequency is equal to the fundamental frequency multiplied by the harmonic number (n)
Timbre: sound quality of the resulting sound
Beat: two sources that admit sound waves close to each other but are not exactly the same

Fun review problems that YOU SHOULD TRY:
(Section 1)
1. A ambulance passes a stationary listener at 25 m/s. If the frequency of the ambulance's siren is 530 Hz what frequency will the listener hear s the ambulance is approaching and moving away?

(Section 2):
1. If the intensity of a person's voice is 4.6x10 -7 W/m2 at a distance of 2.0 m, how much sound power does this person generate?
2. The power output of a piccolo is 0.35 W. At what distance is the sound intensity of the piccolo 1.2 x 10 -3 W/m2?

(Section 3)
1. What is the fundamental frequency of a .20 m long wine bottle that is closed at one end, when the speed of sound in the pipe is 352 m/s?
2. Mr. Strong uses a 392 Hz tuning fork (when at his side job as a piano tuner) to tune the wire for G natural hears 4 beats per second. What are the two possible frequencies of vibration of this piano wire?

Faughn, Jerry S., and Raymond A. Serway. Physics. Austin: Harcourt Classroom Education Company, 2002.