Name
CHAPTER 21
Class
Date
The Nature of Sound
SECTION
2 Properties of Sound
National Science
Education Standards
BEFORE YOU READ
After you read this section, you should be able to answer
these questions:
PS 3a
• How fast does sound travel?
• How are frequency and pitch related?
• How are loudness and amplitude related?
How Fast Does Sound Travel?
Suppose you are standing at the one end of a pool. You
hear two people from the opposite end of the pool yell
at the same time. You hear their voices at the same time
because the speed of sound depends only on the medium
in which the sound travels. So, you hear them at the same
time even if one person yelled louder.
The speed of sound depends on the state of the medium.
Sound travels faster through solids than through liquids or
gases. The speed of sound also depends on the temperature of the medium. Particles of cool materials move more
slowly than particles in a warmer material. They also transmit energy more slowly than particles in a warmer medium.
Therefore, the speed of sound is slower in cooler media.
Medium
Speed of Sound
Air at 0°C
331 m/s
Air at 20°C
343 m/s
Air at 100°C
366 m/s
Water at 20°C
1,482 m/s
Steel at 20°C
5,200 m/s
STUDY TIP
Compare Discuss with a
partner experiences you have
had with the properties of
sound discussed in this section.
READING CHECK
1. Identify The speed of
sound is faster in what two
media states?
It is possible to move faster than the speed of sound.
In 1947, pilot Chuck Yeager was the first person to fly an
airplane faster than the speed of sound. He flew high in
the atmosphere, where the temperature of air is very low.
How Are Pitch and Frequency Related?
The pitch of a sound is how high or low the sound
seems to be. The pitch of a sound depends on the frequency of the sound wave. The frequency of a sound
wave is the number of compressions or rarefactions
produced in a certain amount of time. Frequency is often
expressed in hertz (Hz). A frequency of 1 Hz is equal to
1 compression or rarefaction per second.
Math Focus
2. Describe What does a
frequency of 10 Hz equal?
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The Nature of Sound
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SECTION 2
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Properties of Sound continued
high frequency high pitch
low frequency low pitch
FREQUENCY AND HEARING
READING CHECK
3. Identify What are sounds
with frequency too high for
people to hear called?
READING CHECK
4. Describe What causes the
Doppler effect?
Humans, like all animals, can only hear sounds with
certain frequencies. For example, a dog whistle produces
a sound with a higher frequency than humans can hear.
Therefore, dogs will respond to the sound of a dog whistle. Sounds with frequencies too high for people to hear
are called ultrasonic sounds.
THE DOPPLER EFFECT
You have probably heard the pitch of a police car’s
siren change as the car passed by you. When the car is
moving toward you, the siren seems to have a high pitch.
When the car moves past and away from you, the pitch
seems to drop. The change in pitch is caused by the
Doppler effect.
The Doppler effect is a change in the pitch of a
sound you hear that is caused by motion. If the source of
the sound is moving compared to the listener, the pitch
seems to change.
Think again about the police car. When the car is
behind you, both the sound waves and the car are moving
toward you. Therefore, the compressions and rarefactions of these sound waves are pushed closer together.
The frequency (pitch) of the sound seems to go up.
After the car passes, it is moving in the opposite
direction from the sound waves. Therefore, the compressions and rarefactions of the sound wave are farther apart. The frequency (pitch) of the sound seems to
go down. The figure on the next page shows how the
Doppler effect works.
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The Nature of Sound
Name
Class
SECTION 2
Date
Properties of Sound continued
c
a
b
TAKE A LOOK
a The car is moving toward the
sound waves that are traveling in the same direction.
The sound waves are pushed
closer together. A person in
front of the car hears a sound
with a high pitch.
b The car is moving away from
the sound waves that are traveling in the opposite direction.
The sound waves are farther
apart. A person behind the car
hears a sound with a low pitch.
5. Explain Why do the
people at the rear of the
car hear a sound of lower
frequency than those at the
front of the car?
c The person in the car is moving at the same speed and direction as the
sound waves. Therefore, the person in the car always hears the same
pitch of sound.
How Are Loudness and Amplitude Related?
The loudness of a sound is a measure of how well the
sound can be heard. A sound’s loudness depends on the
amplitude of the sound wave. The amplitude of a wave
is a measure of how far particles move when the wave
passes them. The larger the amplitude of a sound wave,
the louder the sound. The smaller the amplitude of a
sound wave, the softer the sound.
The amplitude (and loudness) of a sound wave is
determined by the wave’s energy. Waves with a lot of energy
have larger amplitudes than waves with little energy.
Imagine hitting a drum. When you hit the drum, you
transfer energy to it. The energy causes the drum to
vibrate. These vibrations produce a sound wave that
travels through the air. If you hit the drum harder, more
energy is transferred to the drum. The drum’s vibrations
are larger, so the sound wave has larger amplitude. The
drum produces a louder sound.
When energy...
Amplitude...
...increases
...decreases
Loudness...
...increases
STANDARDS CHECK
PS 3a Energy is a property of
many substances and is associated with heat, light, electricity,
mechanical motion, sound,
nuclei, and the nature of a
chemical. Energy is transferred
in many ways.
6. Complete Fill in the
missing boxes in the table.
...decreases
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The Nature of Sound
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Properties of Sound continued
MEASURING LOUDNESS
READING CHECK
7. Identify What is the unit
used to measure loudness?
Scientists usually use the unit decibel (dB) to
measure loudness. Soft sounds have low decibel levels.
Loud sounds have high decibel levels. The table below
shows the decibel levels of some common sounds.
Decibel level
Sound
0
the softest sounds an
average person can hear
20
whisper
25
purring cat
60
loudness of a normal
speaking voice
80
lawn mover, vacuum
cleaner, loud traffic
100
chain saw, snowmobile
115
sandblaster, loud music
concert, car horn
120
sound that is loud enough
to cause pain
140
jet engine 30 m away
200
rocket engine 50 m away
How Can You “See” Amplitude and Frequency?
Sound waves are invisible. However, you can use
a tool called an oscilloscope to “see” sound waves.
An oscilloscope is a device that can produce graphs to
represent sound waves.
HOW AN OSCILLOSCOPE WORKS
READING CHECK
The figures on the next page show examples of oscilloscope graphs of sound waves. Notice that these graphs
look like transverse waves instead of longitudinal waves.
It is easier to see the amplitude and frequency of the
sound wave when it is graphed as a transverse wave. The
crests of the transverse wave represent compressions.
The troughs represent rarefactions.
8. Describe On an oscilloscope graph, what do the wave
crests represent? What do the
wave troughs represent?
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The Nature of Sound
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Properties of Sound continued
A receiver on an oscilloscope
converts a sound wave
into an electrical signal. The
signal travels to a computer
in the oscilloscope. The
computer interprets and
graphs the sound wave as a
transverse wave.
INTERPRETING AN OSCILLOSCOPE GRAPH
You can use an oscilloscope to learn the pitch (frequency) and loudness (amplitude) of a sound wave. The
figures below show how to interpret the graph produced
by an oscilloscope.
TAKE A LOOK
9. Compare What is the amplitude of the graph on the
right compared to the
amplitude of the graph
on the left? What is the
wavelength of the graph on
the right compared to the
wavelength of the graph on
the left?
Image A
The wave in the graph on the right has a larger amplitude
than the one on the left. Therefore, the sound represented
by the right-hand graph is louder than the one represented
by the left-hand graph.
Image B
10. Compare What is the
frequency of the graph on
the left compared to the
frequency of the graph
on the right? What is the
wavelength of the graph on
the right compared to the
wavelength of the graph on
the left?
The wave in the graph on the right has a lower frequency
than the one on the left. Therefore, the sound represented
by the right-hand graph has a lower pitch than the one
represented on the left.
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Section 2 Review
NSES
PS 3a
SECTION VOCABULARY
decibel the most common unit used to measure
loudness (symbol, dB)
Doppler effect an observed change in the frequency
of a wave when the source or observer is moving
pitch a measure of how high or low a sound is
perceived to be, depending on the frequency
of the sound wave
loudness the extent to which a sound can be heard
1. Explain In your own words, explain why the sound made by an object moving at
you has a higher pitch.
2. Compare The table below lists several different media sound waves can pass
through. Indicate whether a sound wave passing through the media would be
expected to travel faster or slower than air at room temperature.
Medium
Relative speed
A glass window
A glass of lemonade
Air on a cold winter day
3. Applying Concepts A drum is struck first with little energy. The drum is then
struck with a lot of energy. Which sound will be louder? Why?
4. Identify Below are three screens showing sound waves detected by an
oscilloscope. Label the wave that has the loudest sound, and label the wave that
has the highest pitch.
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The Nature of Sound
Physical Science Answer Key continued
3.
Wave situation
Wave interaction
The image of an object is seen
in a mirror.
reflection
A straight pencil appears to bend
when the bottom half is placed
in a glass of water.
refraction
Two rocks dropped in the
water a meter apart produce a
large wave centered between
them.
interference
A radio turned on in one
classroom can be heard down
the hall in a second classroom.
diffraction
3. They can damage the hair cells in the
cochlea. Damaged hair cells do not grow
back, so damage can result in permanent
hearing loss.
4. The compressions are regions where
particles are packed more closely. The
rarefactions are regions where particles
are spread farther apart.
5. a medium
6. Small vibrations may not be increased
enough to be heard.
SECTION 2 PROPERTIES OF SOUND
Chapter 21 The Nature of
Sound
1. solids and liquids
2. equal to 10 compressions or rarefactions per
second
3. ultrasonic sounds
4. The source of the sound is moving relative
to the listener.
5. The waves at the rear of the car are farther
apart; they have lower frequency than sound
waves at the front of the car.
6. When energy... Amplitude...
Loudness...
SECTION 1 WHAT IS SOUND?
1. the complete back-and-forth motion of an
2.
3.
4.
5.
6.
7.
8.
9.
10.
object
Two areas where particles are clustered
close together should be circled.
The paths are the same.
any substance that a wave can travel
through; yes
tiny hair cells
The eardrum makes the hammer vibrate. This
makes the anvil vibrate and the stirrup vibrate.
Sound is made by making an object vibrate;
detecting a sound means hearing the sound.
ringing or buzzing in the ear
They can damage the inner ear and cause
permanent hearing loss.
Stay away from loud sounds; use earplugs
when needed; lower the volume when using
headphones.
Work done by the organ
Stirrup
It vibrates the oval window in
the entrance to the inner ear.
Cochlea
Vibrations of the liquid inside it
cause hair cells to bend.
Hair cells
When they bend, nerves are
stimulated to send electrical
signals to the brain.
Ear canal
It funnels sound waves into the
middle ear.
Eardrum
Membrane stretched over the
opening to the middle ear
vibrates with the sound waves.
...increases
...decreases
...decreases
...decreases
represent rarefactions.
9. The graph on the left has lower amplitude
than the graph on the right, but the wavelengths are the same.
10. The graph on the left has higher frequency
and shorter wavelength than the graph on
the right.
Review
1. The compressions and rarefactions of the
sound wave are pushed closer together. This
makes the frequency higher. Therefore, the
pitch is higher.
forth. They do not move through space but
vibrate around a resting position.
Organ in ear
...increases
7. decibel
8. Crests represent compressions, and troughs
Review
1. The particles in the air vibrate back and
2.
...increases
2.
Medium
Relative speed
A glass window
faster
A glass of lemonade
faster
Air on a cold winter day
slower
3. The drum struck with a lot of energy will
be louder. The more energy added to the
vibration, the farther the particles in the
medium move from their rest position. The
amplitude of the wave is larger, and the
sound is louder.
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Physical Science
Physical Science Answer Key continued
SECTION 4 SOUND QUALITY
4. The screen in the middle has the loudest
sound. The screen to the far right has the
highest pitch.
1. Each instrument produces different over2.
3.
SECTION 3 INTERACTIONS OF
SOUND WAVES
4.
5.
6.
7.
8.
9.
1. A wave bounces off a barrier.
2. soft, uneven surfaces
3. the use of reflected sound waves to find
objects
4. ultrasonic
5. damage to organs and the development of
6.
7.
8.
9.
10.
11.
12.
13.
14.
unborn babies
when two or more waves overlap or combine
A point where two bright curves overlap
should be circled; a point midway between
a bright curve and a dark area should be
circled.
sound waves that overlap making an area of
high air pressure in front of a jet
a sonic boom
a pattern of vibrations that look like a wave
that is standing still
fundamental frequency
six
The person pushing the swing is transferring
energy into mechanical energy of the swing.
It is amplified.
Review
1. Each instrument produces different over-
tones along with the fundamental frequencies of the notes.
2. It’s a musical note because it has a repeating
pattern.
3. Strings of longer length produce lower-pitched
notes. The larger cello has longer strings than
the violin. Therefore, we would expect the
pitch of the cello to be lower than that of the
violin. (Some students may realize that the
strings of a cello are thicker than the strings of
a violin. This is also correct.)
4. Instrument description Type of instrument
Review
1. The bat creates ultrasonic waves and listens
for their return. The time it takes for the
sound wave to return indicates the distance
between the bat and the food. A change in
frequency of the sound wave indicates the
direction the food is moving.
2. Each of the nodes represents destructive
interference. The peaks represent
constructive interference.
The fourth overtone is five times the
fundamental.
3. Sound wave
Wave interaction
A jet produces a shock
wave.
Music is produced when
air vibrates in a column.
wind instrument
Music is produced when
the instrument is struck.
percussion instrument
Music is produced by
plucking or bowing to
create vibrations.
string instrument
Chapter 22 The Nature of
Light
SECTION 1 WHAT IS LIGHT?
1. There should be two perpendicular lines
2.
3.
4.
5.
6.
7.
8.
constructive interference
Ultrasonography can “see” reflection
a patient’s heart.
Sonar locates fish
underwater.
tones along with the fundamental pitch.
interference of sound waves
longer strings
changes the pitch
trumpet player’s lips
clarinet player’s lips
It must be struck.
a random mix of frequencies
There is a repeating pattern for the piano
note but not for the clap.
reflection
4. Without resonance in musical instruments,
drawn.
negative
attract each other
moves/vibrates
magnetic field
EM waves
light waves
plants, animals, fossil fuels
the sounds the instruments make would not
be amplified.
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Physical Science