Transcript Chapter 21

Chapter 21
The Nature of Sound
Section 1: Objectives
•
Describe how vibrations cause sound.
•
Explain how sound is transmitted
through a medium.
•
Explain how the human ear works,
and identify its parts.
•
Identify ways to protect your hearing.
Components of Sound
•
All sounds are created by vibrations.
•
A vibration is the complete back-andforth motion of an object or material.
•
The next slide shows how a stereo
speaker produces sound.
Components of Sound: Figure 1
Components of Sound
•
Sound Waves are longitudinal waves
that are caused by vibrations, which are
then carried through a substance and
transfers energy.
•
The particles of the substance vibrate
back and forth along the path that the
sound waves travel.
•
Sound is transmitted through the
vibrations and collisions of the particles.
Components of Sound
•
Sound waves travel in all directions
away from their source.
•
However, the air or other matter
through which the wave is traveling
does not travel with the sound waves.
•
The particles of air only vibrate back
and forth.
Components of Sound
•
All sound waves require a medium
(plural, media).
•
A medium is a substance through which
a wave can travel by vibrating particles in
the material.
• Air is the most common medium of sound
waves.
•
There are no particles to vibrate in a
vacuum.
• So, no sound can be made in a vacuum.
Components of Sound
•
•
•
Your ears are divided into three regions:
the outer, middle, and inner ear.
The outer ear collects sound waves.
Then, organs in the middle ear increase
the size of the sound wave’s vibrations.
• The inner ear changes the vibrations into
electrical signals that your brain interprets as
sound.
Components of Sound: Figure 2
Components of Sound
•
The parts of the ear must work together
for you to hear.
• If any part of the ear is damaged or does not
work properly, hearing loss or deafness may
result.
•
Loud sounds can cause damage the
cochlea.
•
Damage to the cochlea or any other part
of the inner ear usually results in
permanent hearing loss.
Ch. 21 Sec. 1 Recap
1) What is a vibration?
 2) Explain how sound is transmitted
through particles.
 3) When sound travels through a
medium, does the medium travel with the
sound? Explain your answer.
 4) What is the most common medium of
sound?
 5) Explain how there can be no sound in a
vacuum.

Ch. 21 Sec. 1 Recap
6) List and describe the function of the 3
parts of the ear.
 7) From Figure 2, what is the function of
the pinna?
 8) From Figure 2, list the 3 bones that act
as levers to increase the size of
vibrations.
 9) From Figure 2, what is the eardrum?
 10) From Figure 2, what is the oval
window?

Ch. 21 Sec. 1 Recap
11) What is the function of the liquid in
the cochlea?
 12) What 2 things may be caused if part
or parts of the ear do not work properly?
 13) What can loud sounds cause damage
to?
 14) What does damage to the cochlea
result in?
 15) From Figure 1, what is the difference
between a compression and rarefaction?

Section 2: Objectives
•
Compare the speed of sound in different media.
•
Explain how frequency and pitch are related.
•
Describe the Doppler effect, and give examples.
•
Explain how amplitude and loudness are
related.
•
Describe how amplitude and frequency can be
“seen” on an oscilloscope.
Properties of Sound
•
The speed of sound depends only on the
medium in which the sound is traveling.
•
How the Speed of Sound Can Change
Sound travels quickly through air, but it
travels even faster in liquids and even
faster in solids.
•
Temperature also affects the speed of
sound. The cooler the medium is, the
slower the speed of sound.
Properties of Sound
•
How low or high a sound seems to be
is the pitch of that sound. The pitch of
a sound is related to the frequency of
the sound wave.
•
Frequency and Hearing The
frequencies of some sounds are out of
the range of human hearing. Sounds
that have a frequency too high for
people to hear are called ultrasonic.
Properties of Sound: Figure 1
Properties of Sound
The Doppler Effect is the apparent
change in the frequency of a sound
caused by the motion of either the
listener or the source of the sound.
 In other words, the sound source of
the listener is moving causing the
frequency to change.
 Changing the frequency affects the
properties of the sound.

Properties of Sound: Figure 2
Properties of Sound

The amplitude of a wave is the largest
distance the particles in a wave
vibrate from their rest positions.

The larger the amplitude, the louder
the sound.

The most common unit to express
loudness is the decibel (dB).
Properties of Sound

A device called an oscilloscope can
graph representations of sound
waves, as shown below. Notice that
the graphs look like transverse waves
rather than longitudinal waves.
Properties of Sound
•
A microphone attached to an
oscilloscope changes a sound wave
into an electrical signal.
• The electrical signal is graphed on the
screen in the form of a wave.
•
The graph shows the sound as if it
were a transverse wave.
• So, the sound’s amplitude and frequency
are easier to see.
Chapter 21 Sec. 2 Recap
1)What does the speed of sound depend
on?
 2)Rank the speed at which sound travels
from 1-3 in solids, liquids, and gases.
 3) What can also affect the speed of
sound?
 4) How do cooler temperatures affect
the speed of sound?
 5)What property of sound is pitch related
to?

Chapter 21 Sec. 2 Recap
6) What are ultrasonic sounds?
 7) T/F Some sounds have a frequency out
of the range of human hearing.
 8) From Figure 1, how do the closeness of
air particles relate to high frequency?
 9) From Figure 1, how do the closeness of
air particles relate to low frequency?
 10) From Figure 1, how do frequency and
pitch relate?

Chapter 21 Sec. 2 Recap
11) For the Doppler Effect to occur, what
changes when the sound source changes
locations?
 12) What does altering frequency change?
 13) From Figure 2, what is the sound source?
 14) From Figure 2, what is/are the listeners?
 15) From Figure 2, which listener will hear
waves at a higher frequency?
 16) From Figure 2, which listener will hear
waves at a lower frequency?

Chapter 21 Sec. 2 Recap
17) What is amplitude and how does it
affect sound?
 18) What is “loudness” expressed in?
 19) What changes a sound wave into an
electrical signal on an oscilloscope?
 20) What is the importance of changing
the sound wave into an electrical signal
and then a visible transverse wave?

Section 3: Objectives
•
Explain how echoes are made, and
describe their use in locating objects.
•
List examples of constructive and
destructive interference of sound
waves.
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Explain what resonance is.