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are interference patterns of two sound waves of slightly different 5.7
frequencies. _
power
Every elastic object or medium in nature has a characteristic natu- intensity = area
ral frequency (or frequencies) of vibration. Resonance is a phenomenon P _

where the energy transfer from one object (or medium) to another I =
A
happens at natural frequencies of the object (or medium) that receives 5.8
the energy. At resonance, the energy transfer is most effi cient and the
number × velocity on string
amplitude of vibrations grow very fast. resonant frequency = ___

Sounds are compared by pitch, loudness, and quality. Th e qual- 2 × length of string
ity is determined by the instrument sounding the note. Each instru- where number 1 = fundamental frequency, and numbers 2, 3, 4, and
ment has its own characteristic quality because of the resonant so on = overtones.
frequencies that it produces. Th e basic or fundamental frequency
nv _
is the longest standing wave that it can make. Th e fundamental f n =
2L
frequency determines the basic note being sounded, and other resonant
frequencies, or standing waves called overtones or harmonics, combine
with the fundamental to give the instrument its characteristic quality. KEY TERMS
A moving source of sound or a moving observer experiences an

apparent shift of frequency called the Doppler eff ect. If the source is
amplitude (p. 117)
moving as fast as or faster than the speed of sound, the sound waves
beat (p. 126)
pile up into a shock wave called a sonic boom. A sonic boom sounds
cycle (p. 117)
very much like the pressure wave from an explosion.
decibel scale (p. 128)
Doppler eff ect (p. 131)
SUMMARY OF EQUATIONS echo (p. 125)
frequency (p. 117)
5.1
fundamental frequency (p. 130)
_
1

period = hertz (p. 117)
frequency
infrasonic (p. 122)
1 _
T = longitudinal wave (p. 119)

f
period (p. 117)
5.2 pitch (p. 122)
_ refl ection (p. 124)
1

frequency =

period refraction (p. 124)
1 _ resonance (p. 128)
f =
T reverberation (p. 125)
5.3 shock wave (p. 131)
sonic boom (p. 131)
velocity = (wavelength) (frequency)
standing waves (p. 129)
v = λf
transverse wave (p. 119)
5.4 ultrasonic (p. 122)
vibration (p. 116)
velocity of velocity 0.600 m/s present
sound (m/s) = of sound + increase per × temperature wavelength (p. 121)
waves (p. 119)
at present at 0°C degree Celsius in °C
temperature
)
0.600 m∙s
(
v T (m/s) = v 0 + _ T p )

(

p °C APPLYING THE CONCEPTS
5.5
1. A back-and-forth motion that repeats itself is a
velocity of velocity 2.00 ft /s present a. spring.
sound (ft /s) = of sound + increase per × temperature b. vibration.
at present at 0°C degree Celsius in °C c. wave.
temperature d. pulse.
2.00 ft∙s
(

)

(

v T (ft /s) = v 0 + _ T p ) 2. The number of vibrations that occur in 1 s is called

p °C a. a period.
b. frequency.
5.6
c. amplitude.
beat frequency = one frequency – other frequency d. sinusoidal.
f b = f 2 – f 1
134 CHAPTER 5 Wave Motions and Sound 5-20