Transcript properties of sound - Junction Hill C

• Compare the speed of sound
in different media
• Explain how frequency and
pitch are related
• Describe the Doppler effect,
and give examples of it
• Explain how amplitude and
loudness are related
The differences
between the sounds—
how high or low and
how loud or soft they
are—depend on the
properties of the
sound waves
The time it takes for
sounds to reach you
does not depend on
how loud or high the
sound is.
The speed of sound
depends only on the
medium through which
the sound is traveling
I can talk
underwater
The time it takes for
sounds to reach you
does not depend on
how loud or high the
sound is.
The speed of sound
depends only on the
medium through which
the sound is traveling
Speed of Sound in Different
Media at 20 degrees Celsius
Medium
Speed m/s)
Air
343
Helium
1,005
Water
1,482
Sea Water
1,522
Wood (oak)
3,850
Glass
4,540
Steel
5,200
In 1947, American pilot Chuck
Yeager became the first
person to travel faster than
the speed of sound. But he
was flying at a speed of
only 293 m/s. If the speed
of sound in air is 343 m/s,
how did Yeager fly faster
than the speed of sound??
I am traveling
faster than the
speed of sound
In general, the cooler the medium, the
slower the speed of sound
This happens because particles in cool
materials move slower than particles in
warmer materials
When the particles move
slower, they transmit
energy more slowly
Therefore, sound travels
more slowly in cold air than in hot air
Pitch Depends on
Frequency
The pitch of a sound
is determined by the
frequency of the
sound wave
The higher the
frequency the
higher the pitch
Why can’t you hear a dog
whistle??
Because the frequency of the
sound wave is out of the
range of human hearing
A dog hears a very high pitch
from the whistle and comes
running!!
Did you
hear
that??
The average human ear can detect sounds
that have frequencies between 20Hz and
20,000Hz.
Young children can often hear sounds with
frequencies above this range, while
many elderly people have difficulty
hearing sounds higher than 8,000Hz
Range of hearing in Hertz
Ultrasound
Ultrasound is sound of vibrations with frequencies too high
to be audible by the human ear, above approximately 20
kilohertzs or 20,000Hz.
Some sound that is ultrasound to the human ear can be
heard by animals, such as dogs.
Ultrasound has industrial and medical applications. Medical
ultrasonography can visualize muscle and soft tissue,
making them useful for scanning the organs. However,
they will not penetrate bone so they are not a substitute
for conventional X-rays in many cases.
Ultrasonic cleaners, sometimes called supersonic cleaners,
are used at frequencies from 20-40kHz for Jewelry, Lenses,
Optical parts, Watches, Dental instruments, surgical
instruments, and industrial parts.
Heard an ambulance go by recently?
Remember how the siren's pitch
changed as the vehicle raced towards,
then away from you? First the pitch
became higher, then lower.
This change in pitch
results from a
shift in
the
frequency of the
sound waves
Whatever is
coming at me has
a high pitch—it
must have a high
frequency
As an object moves toward
you, this causes the waves to
be closer together and to
have a higher frequency
As an object moves
away from you, this
causes the waves to be
farther apart and to
have a lower frequency
Loudness is Related to Amplitude
If I strike a drum with a large force, I will hear a loud
BOOM!!
Changing the force I strike the drum will change the loudness of
the sound that is created
Loudness is how loud or soft a sound is perceived to be
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 surrounding air
This increase in energy causes air
particles to vibrate farther from their
rest positions.
When you strike a drum harder, you are
increasing the amplitude of the sound waves
being created
The amplitude of a wave is the maximum
An amplifier
distance the particles in
increases the
a wave vibrate from their
amplitude of the
rest positions.
sound generated
by my guitar
The larger the amplitude,
the louder the sound,
and the smaller the
amplitude, the softer
the sound
Some Common Decibel Levels
Sound
Decibel level
The softest sounds you can hear
0
Whisper
20
Purring cat
25
Normal conversation
60
Lawn mower, vacuum cleaner, truck traffic
80
Chain saw, snowmobile
100
Sandblaster, loud rock concert, automobile horn
115
Threshold of pain
120
Jet engine 30 meters away
140
Rocket engine 50 meters away
200
The most common unit used to express loudness is the decibel (dB)
Seeing Sounds
An oscilloscope is used to graph representations of
sound waves
For example, a microscope converts sound waves into
an electric current.
The oscilloscope then converts the electric current into
graphs