SOUND

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SOUND

• Created by Mr. Todd
• Notes provided by Mr. Martonik

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A. NATURE OF SOUND

• Sound Longitudinal Waves
• Sound begins with a vibration
• Sound is a disturbance that travels through a
  medium as a longitudinal wave. (When the
  disturbance reaches your ear, you hear the
  sound.)
• Sound waves carry energy through a medium
  without the particles of the medium traveling
  along. (Medium is air each molecule moves
  back forth)

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LOUD SPEAKER
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• Sound waves must travel through a medium (solids,
  liquids, or gases.)
• (Knock on a door, the particles of the door
  vibrate.)
• Can sound be heard in a vacuum?
• NoNo medium to travel through
• Sound waves bend ( they diffract)

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• 2. Speed of Sound
• The speed of sound depends on the properties of
  the medium through which it is traveling.
• It depends on the elasticity, density
  temperature of the medium.

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• Elasticity-the ability of a substance to bounce
  back. Sound travels faster in elastic mediums.
• Density-how close the particles are to each
  other. Sound travels faster in mediums of the
  same state of matter that are less dense.
  (Ex. Sound travels faster in steel than in lead)
• Temperature-A hot or warm medium will carry sound
  faster than a cold medium. (Room temp. 20 0 C
  sound travels at 342m/s at 0 0 C sound travels
  at 330m/s )

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B. PROPERTIES OF SOUND

• 1. Intensity and Loudness
• Intensity The amount of energy the wave carries
  per second through a unit area. (Watts/meter2)
• When a sound wave carries a large amount of
  energy, the molecules of the medium move a
  greater distance as the wave passes.
• Loudness Measure of the intensity of a sound
  wave.
• The greater the Amplitude of vibration (distance
  particles move from their rest position) the
  greater the intensity and the louder the sound.
• It is measured in decibels (dB)
• Sound waves caused by a shout carry much more
  energy that those of a whisper.

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• 2. Frequency, Pitch and Resonance
• Frequency is the number of vibrations that occur
  per second.
• Measured in Hertz ( 50 Hz 50 vibrations/sec)
•  An increase in vibrations causes the frequency
  to increase.
• People can hear frequencies of 20 Hz to 20,000Hz
• (Ultrasound above normal range)
• (Infrasound below normal range)

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• Pitch-how high or low a sound seems to a person.
  (depends on frequency of the sound wave)
• A tight and/or short guitar or piano string ?
  high frequency?High Pitch
• Resonance- Condition which occurs when the
  frequency of the sound wave and the natural
  frequency of the object are the same.
• If the frequency of a sound wave matches the
  natural frequency of a crystal glass the glass
  may shatter why?
• The sound waves add to the amplitude of the
  natural vibration waves in the glass.

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• 3. Doppler Effect the apparent change in the
  frequency as a sound wave source moves in
  relation to the listener. There will be a change
  in pitch.
• As the sound moves closer the frequency will
  increase and the pitch will be higher.
• As the object moves away the frequency decreases
  and pitch becomes lower.

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As the police car speeds by, the pitch of the
siren seems to change. Ahead of the car, the
sound waves are piling up, so the pitch is
higher. Behind the car the waves spread out, so
the pitch is lower.
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• 4. Sonic Boom Created when a plane flies faster
  than the speed of sound. The plane breaks
  through a pile-up of waves known as the sound
  barrier. As the plane passes through these waves
  the waves smash back together creating the BOOM.

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C. Applications of Sound by Humans

• Sonar Sound Navigation And Ranging
• Sonar machines send out high frequency sound
  waves and then detect the time it takes for those
  waves to reflect back. The machine can then
  calculate the distance to the object.
• Used to find depth of the water, sunken boats,
  schools of fish (fish finder)

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• Ultrasound-high frequency sound above human
  range.
• A. Used to create a sonogram of a fetus.
• B. Used by cameras --autofocus.
• C. Used to clean jewelry by vibrating away dirt
  in hard to reach places.
• D. Used to Inspect BridgesPrines device can
  detect for the frequency of sound given off by
  cracking steel.
• E. Devices placed on fishing nets to keep
  dolphins and whales away.
• F. New technologyUsing sound to assist in
  refrigeration

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C. Applications of Sound by Animals

• EcholocationUse of high frequency sound to
  detect distance or to locate objects
• Bats, dolphins, Whales
• Infrasound-low frequency sound
• Elephantsstomping feet creates a low frequency
  sound that can travel through the ground.