CPO Science
Foundations of Physics
Unit 5, Chapter 15
Unit 5: Waves and Sound
Chapter 15 Sound
 15.1 Properties of Sound
 15.2 Sound Waves
 15.3 Sound, Perception, and Music
Chapter 15 Objectives
1.
Explain how the pitch, loudness, and speed of sound are
related to properties of waves.
2.
Describe how sound is created and recorded.
3.
Give examples of refraction, diffraction, absorption, and
reflection of sound waves.
4.
Explain the Doppler effect.
5.
Give a practical example of resonance with sound waves.
6.
Explain the relationship between the superposition
principle and Fourier’s theorem.
7.
Describe how the meaning of sound is related to
frequency and time.
8.
Describe the musical scale, consonance, dissonance, and
beats in terms of sound waves.
Chapter 15 Vocabulary Terms
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
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
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pressure
frequency
pitch
superposition
principle
decibel
speaker
acoustics
microphone
fundamental
wavelength
stereo
 Doppler effect
 supersonic
frequency
 spectrum
 shock wave
 resonance
 node
 antinode
 dissonance
 harmonic
 reverberation
 note
 sonogram
 Fourier’s
theorem
 rhythm
 musical scale
 cochlea
 consonance
 longitudinal
wave
 beats
 octave
15.1 Properties of Sound
Key Question:
What is sound and how
do we hear it?
*Students read Section 15.1
AFTER Investigation 15.1
15.1 Properties of Sound
 If you could see the
atoms, the difference
between high and low
pressure is not as great.
Here, it is exaggerated.
15.2 The frequency of sound
 We hear frequencies of sound as
having different pitch.
 A low frequency sound has a low
pitch, like the rumble of a big
truck.
 A high-frequency sound has a
high pitch, like a whistle or siren.
 In speech, women have higher
fundamental frequencies than
men.
15.1 Complex sound
Common Sounds and their Loudness
15.1 Loudness
Every increase of 20 dB,
means the pressure
wave is 10 times
greater in amplitude.
Logarithmic
scale
Linear
scale
Decibels (dB)
Amplitude
0
1
20
10
40
100
60
1,000
80
10,000
100
100,000
120
1,000,000
15.1 Sensitivity of the ear
 How we hear the loudness
of sound is affected by the
frequency of the sound as
well as by the amplitude.
 The human ear is most
sensitive to sounds between
300 and 3,000 Hz.
 The ear is less sensitive to
sounds outside this range.
 Most of the frequencies that
make up speech are
between 300 and 3,000 Hz.
15.1 How sound is created
 The human voice is a complex
sound that starts in the larynx, a
small structure at the top of your
windpipe.
 The sound that starts in the
larynx is changed by passing
through openings in the throat
and mouth.
 Different sounds are made by
changing both the vibrations in
the larynx and the shape of the
openings.
15.1 Recording sound
1. A common way to record sound starts with a
microphone. A microphone transforms a sound
wave into an electrical signal with the same pattern
of oscillation.
15.1 Recording sound
2. In modern digital recording, a sensitive circuit
converts analog sounds to digital values between 0
and 65,536.
15.1 Recording sound
3. Numbers correspond to the amplitude of the signal
and are recorded as data. One second of compactdisk-quality sound is a list of 44,100 numbers.
15.1 Recording sound
4. To play the sound back, the string of numbers is
read by a laser and converted into electrical signals
again by a second circuit which reverses the
process of the previous circuit.
15.1 Recording sound
5. The electrical signal is amplified until it is powerful
enough to move the coil in a speaker and reproduce
the sound.
15.2 Sound Waves
Key Question:
Does sound behave like
other waves?
*Students read Section 15.2
BEFORE Investigation 15.2
15.2 Sound Waves
1. Sound has both frequency (that we hear
directly) and wavelength (demonstrated by
simple experiments).
2. The speed of sound is frequency times
wavelength.
3. Resonance happens with sound.
4. Sound can be reflected, refracted, and
absorbed and also shows evidence of
interference and diffraction.
15.2 Sound Waves
A sound wave is a wave of alternating high-pressure
and low-pressure regions of air.
15.2 The wavelength of sound
15.2 The Doppler effect
 The shift in frequency caused by motion is called the
Doppler effect.
 It occurs when a sound source is moving at speeds
less than the speed of sound.
15.2 The speed of sound
 The speed of sound in air is 343 meters per
second (660 miles per hour) at one atmosphere
of pressure and room temperature (21°C).
 An object is subsonic when it is moving slower
than sound.
15.2 The speed of sound
 We use the term supersonic to describe motion at
speeds faster than the speed of sound.
 A shock wave forms where the wave fronts pile up.
 The pressure change across the shock wave is what
causes a very loud sound known as a sonic boom.
15.2 Standing waves and resonance
 Spaces enclosed by boundaries can create
resonance with sound waves.
 The closed end of a pipe is a closed boundary.
 An open boundary makes an antinode in the
standing wave.
 Sounds of different frequencies are made by
standing waves.
 A particular sound is selected by designing the
length of a vibrating system to be resonant at the
desired frequency.
15.2 Sound waves and boundaries
 Like other waves, sound
waves can be reflected
by surfaces and
refracted as they pass
from one material to
another.
 Sound waves reflect
from hard surfaces.
 Soft materials can
absorb sound waves.
15.2 Fourier's theorem
 Fourier’s theorem says any complex wave can
be made from a sum of single frequency waves.
15.2 Sound spectrum
 A complex wave is really a sum of component
frequencies.
 A frequency spectrum is a graph that shows the
amplitude of each component frequency in a complex
wave.
15.3 Sound, Perception, and Music
Key Question:
How is musical sound
different than other
types of sound?
*Students read Section 15.3
AFTER Investigation 15.3
15.3 Sound, Perception, and Music
 A single frequency by itself does not have much
meaning.
 The meaning comes from patterns in many frequencies
together.
 A sonogram is a special
kind of graph that shows
how loud sound is at
different frequencies.
 Every person’s sonogram
is different, even when
saying the same word.
15.3 Hearing sound
 The eardrum vibrates in
response to sound
waves in the ear canal.
 The three delicate
bones of the inner ear
transmit the vibration of
the eardrum to the side
of the cochlea.
 The fluid in the spiral of
the cochlea vibrates
and creates waves that
travel up the spiral.
15.3 Sound
 The nerves near the
beginning see a
relatively large
channel and respond
to longer wavelength,
low frequency sound.
 The nerves at the small end of the channel respond
to shorter wavelength, higher-frequency sound.
15.3 Music
 The pitch of a sound is how high or low we
hear its frequency. Though pitch and frequency
usually mean the same thing, the way we hear
a pitch can be affected by the sounds we heard
before and after.
 Rhythm is a regular time pattern in a sound.
 Music is a combination of sound and rhythm
that we find pleasant.
 Most of the music you listen to is created from
a pattern of frequencies called a musical scale.
15.3 Consonance, dissonance, and
beats
 Harmony is the study of how sounds work together to
create effects desired by the composer.
 When we hear more than one frequency of sound and
the combination sounds good, we call it consonance.
 When the combination sounds bad or unsettling, we
call it dissonance.
15.3 Consonance, dissonance, and
beats
 Consonance and dissonance are related to beats.
 When frequencies are far enough apart that there are
no beats, we get consonance.
 When frequencies are too close together, we hear
beats that are the cause of dissonance.
 Beats occur when two frequencies are close, but not
exactly the same.
15.3 Harmonics and instruments
 The same note sounds different when played on
different instruments because the sound from an
instrument is not a single pure frequency.
 The variation comes from the harmonics, multiples of
the fundamental note.
Application: Sound from a Guitar