Sound

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Sound
Name ________________ Class _________________
Index ________________
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Objectives -- describe the production of sound by
vibrating sources. -- describe the longitudinal
nature of sound waves and describe compression
and rarefaction and deduce that a medium is
required in order to transmit these waves. -- the
speed of sound differs in air, liquids and
solids. -- describe a direct method for the
determination of the speed of sound in air and
make necessary calculation. -- explain how the
loudness and pitch of sound waves to amplitude
and frequency. -- explain why different
instruments produce sounds of different
quality. -- describe how the reflection of sound
may produce an echo, and how this may be used for
measuring distances. -- define ultrasound and
describe one use of ultrasound, e.g. cleaning,
quality control and pre-natal scanning.
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WAVE NATURE OF SOUND

• SOUND IS A FORM OF ENERGY THAT COMES IN THE FORM
  OF LONGITUDINAL WAVES.
• SOUND IS PRODUCED BY ANY VIBRATING SOURCE PLACED
  IN A MEDIUM.

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LONGITUDINAL SOUND WAVES CONSISTS OF COMPRESSIONS
AND RAREFACTIONS. THE DISTANCE BETWEEN TWO
CONSECUTIVE COMPRESSIONS AND RAREFACTIONS IS THE
WAVELENGTH OF THE SOUND WAVES.
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Compression and Rarefactions
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A tuning fork has a pure frequency
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THE TRANSMISSION OF SOUND.
THE MECHANICAL NATURE OF SOUND.

• SOUND WAVES REQUIRE A MEDIUM FOR TRANSMISSION.
• THE SPEED OF SOUND WAVES VARIES FROM ONE MEDIUM
  TO ANOTHER. IT IS FASTEST IN SOLIDS, NEXT IN
  LIQUIDS, AND SLOWEST IN GASES.

MEDIUM APPROXIMATE SPEED / m/s
AIR 300 WATER 1500 IRON 5000
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Changes in Effect of sound in air
Temperature As temperature increases, speed increases.
Humidity As humidity increases, speed increases
Pressure Change in pressure has NO effect on speed
An F/A-18F Super Hornet hits the speed of sound.
As the plane pushes air away, the temperature
drops and water vapor in the air forms a ring
cloud around it.
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THE HUMAN EAR.
AUDIBILITY

• THE RANGE OF FREQUENCIES WHICH A LISTENER CAN
  HEAR IS KNOWN AS THE RANGE OF AUDIBILITY.

• FOR THE HUMAN EAR, THE LOWER LIMIT IS
  APPROXIMATELY 20 HZ AND THE UPPER LIMIT 20 000HZ.
• OUR EARS CANNOT HEAR SOUND OF VERY HIGH
  FREQUENCIES (ULTRASOUND) OR VERY LOW FREQUENCIES
  (INFRASOUND).

Infrasound Below 20 Hz Range of audibility 20 Hz 20 000Hz Ultrasound Above 20 kHz
Detectable by Dogs, Bats Used in detection of
mines in the sea and foetuses in the womb.
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Ultrasound travels freely through fluid and soft
tissues. However, ultrasound is reflected back
(it bounces back as 'echoes') when it hits a more
solid (dense) surface. For example, the
ultrasound will travel freely though blood in a
heart chamber. But, when it hits a solid valve, a
lot of the ultrasound echoes back. Another
example is that when ultrasound travels though
bile in a gallbladder it will echo back strongly
if it hits a solid gallstone.
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The unit for sound is the decibel.
Sound Level Meter
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THE REFLECTION OF SOUND

• SOUND WAVES UNDERGO REFLECTION.

• AN ECHO IS A REFLECTION OF SOUND.
• USES OF ECHOES INCLUDE
• 1. FINDING THE DEPTH OF THE SEA OR THE LOCATIONS
  OF SHOALS OF FISH.
• 2. DETECTION OF MINES.
• 3. DETECTION OF OBSTACLES BY BATS.

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Reflection of Sound
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Multiple echoes are a nuisance
REVERBERATION IS THE EFFECT OF PROLONGED SOUND
DUE TO THE MERGING OF MANY ECHOS.
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Sonar (originally an acronym for SOund Navigation
And Ranging) is a technique that uses sound
propagation (usually underwater, as in Submarine
navigation) to navigate, communicate with or
detect other vessels. Two types of technology
share the name "sonar" passive sonar is
essentially listening for the sound made by
vessels active sonar is emitting pulses of
sounds and listening for echoes.
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Sonar may be used as a means of acoustic location
and of measurement of the echo characteristics of
"targets" in the water (i.e. fishes).
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Example A sound signal from the sonar on a ship
is sent underwater into the sea. It takes 1.35 s
for the signal to return to the ship. If sound
travels at 1500 m/s, how deep is the
sea? Solution Depth 1500 m/s x (1.35/2) s
1012.5 m 1.01 x 103 m (3
s.f.)
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MEASURING THE SPEED OF SOUND
Direct Method
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MEASURING THE SPEED OF SOUND
Echo Method
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• MUSICAL NOTES CAN BE DESCRIBED BY
• 1. PITCH
• 2. LOUDNESS
• 3. QUALITY.

• WHEN WE DESCRIBE A MUSICAL NOTE OR SOUND AS
  HIGH OR LOW, WE ARE COMMENTING ON THE PITCH
  OF THE SOUND.
• PITCH IS RELATED TO THE QUANTITY CALLED
  FREQUENCY.
• THE HIGHER THE FREQUENCY, THE HIGHER THE PITCH.

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Pitch is related to the frequency of sound
High pitch
Low pitch
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• LOUDNESS IS RELATED TO THE QUANTITY OF AMPLITUDE.

louder
softer
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Question

• How do you change the pitch in the guitar?
• 1. length of string
• 2. tension of string
• 3. cross-section of string
• How do you change the loudness in the guitar?
• 1. By plucking it harder.

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Quality
THE SAME NOTE PLAYED ON DIFFERENT MUSICAL
INSTRUMENTS SOUNDS DIFFERENT ALTHOUGH THE
FREQUENCY AND AMPLITUDE ARE THE SAME.
i.e. Middle C on PIANO Middle C on VIOLIN Do
they sound the same?
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Differences in Quality of Sound
Stringed instruments sound different for many
reasons. What you hear depends on how and of what
the string is made, how the string is vibrating,
how long it vibrates, and how long you can hear
it vibrate.
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overtones
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References http//www.privateline.com/TelephoneHis
tory/soundwaves.html http//www.worldculturepictor
ial.com/blog/comment/reply/574 http//en.wikipedia
.org/wiki/Sonar http//visual.merriam-webster.com/
arts-architecture/music/traditional-musical-instru
ments_7.php http//www.hps.cam.ac.uk/whipple/explo
re/acoustics/historicalnotes/ http//www.webweaver
.nu/clipart/music/piano.shtml