Download Sound - Edublogs

Chapter 21
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All sounds are created by vibrations. A
vibration is the complete back-and-forth
motion of an object or material
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.
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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.
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.
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Your ears are divided into three regions: the
outer ear, the middle ear, and the 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.
Making sound is separate from hearing sound.
Sound can be made and not be heard.
Suppose that a tree falls and and no one is
around to hear it. When the tree falls, the tree and
the ground vibrate. These vibrations create a
sound wave.
So, a sound was made—it just wasn’t heard.
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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.
There are some simple ways to protect your
hearing.
For example, you can wear earplugs to block
out loud sounds. You can listen at a lower
volume when you are using headphones. You
can also move way from sources of loud
sounds.
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The speed of sound depends only on the medium
in which the sound is traveling.
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.
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.
The frequencies of some sounds are out of the range of
human hearing. Sound that have a frequency too high
for people to hear are called ultrasonic.
 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.
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Loudness is a measure of how well a
sound can be heard.
The harder you strike a drum, the louder
the sound. As you strike the drum harder,
you transfer more energy to the drum.
The drum moves with a larger vibration
and transfers more energy to the air
around it.
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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). The softest sounds a human
can hear are at a level of 0 dB.
A device called an oscilloscope can graph
representations of sound waves.
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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.
Reflection is the bouncing back of a wave
after it strikes a barrier. An echo is a reflected
sound wave.
The strength of a reflected sound wave
depends on the reflecting surface. Sound
waves reflect best off smooth, hard surfaces.
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Echolocation is the use of reflected sound
waves to find objects. Animals, such as bats,
use echolocation to hunt food and find objects
in their path.
Animals that use echolocation can tell how far
away something is based on how long it takes
sound waves to echo back to their ears.
People use echoes to locate objects
underwater by using sonar. Sonar is a type of
electronic echolocation.
Sonar can also help navigators on ships
avoid icebergs and can help oceanographers
map the ocean floor.
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Ultrasonography is a medical procedure that uses
echoes to “see” inside a patient’s body without
doing surgery.
Ultrasonography is used to examine kidneys,
gallbladders, and other organs. It is also used to
check the development of an unborn baby in a
mother’s body.
Interference happens when two or more waves
overlap.
As the source of a sound—such as a jet
plane—gets close to the speed of sound, the
sound waves in front of it combine by
constructive interference.
The result of this interference is a highdensity compression called the sound barrier.
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When a jet reaches speeds faster than the speed
of sound, the sound waves trail off behind the jet.
At their outer edges, the sound waves combine by
constructive interference to form a shock wave.
A sonic boom is the explosive sound hear when a
shock wave reaches your ears.
A pattern of vibration that looks like a wave that is
standing still is called a standing wave.
Standing waves form because of interference.
Where you see maximum amplitude, waves are
interfering constructively. Where the wave seems
to be standing still, waves are interfering
destructively.
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The frequencies as which standing waves are
made are called resonant frequencies.
The lowest resonant frequency is called the
fundamental. Higher resonant frequencies are
called overtones.
The difference in sound quality among different
instruments come from their structural
differences.
All instruments produce sound by vibrating. But
instruments vary in the part that vibrates and the
way the vibrations are made.
Three families of instruments are string
instruments, wind instruments, and percussion
instruments.
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String Instruments Violins, guitars, and banjos are
examples of string instruments. String
instruments make sound when their strings
vibrate after being plucked or bowed.
The pitch of a string can be changed by changing
the string’s length. Shorter strings vibrate at
higher frequencies, and thus have higher pitches.
Wind Instruments Saxophones, flutes, French horns,
and tubas are examples of wind instruments. Wind
instruments make sound when a vibration is created at
one end of its air column.
Pitch is changed by changing the length of the air
column. The longer the air column is, the lower the
pitch is.
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Percussion Instruments Drums, bells, and
cymbals are examples of percussion
instruments. Percussion instruments make
sound when struck.
Instruments of different sizes are used to get
different pitches. Usually, the larger the
instrument is, the lower the pitch is.
Most of the sounds you hear are noises. Noise
is any sound that is of a random mix of
frequencies.