Chapter 21 Sound

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Chapter 21 Sound
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What is Sound

• All sounds are produced by something that
  vibrates
• A wave carries energy from one place to another
  and without transferring matter
• The vibrating object causes air molecules to move
  back and forth
• As these air molecules collide with those nearby
  , they cause other molecules to move back and
  forth
• A sound wave is a compressional wave, like a wave
  moving through a coiled spring
• In sound waves, air molecules move back and forth
  along the direction of the wave

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Making Sound Waves

• When an object vibrates, it exerts a force on the
  surrounding air
• For example, as the end of the tuning fork moves
  outward into the air, it pushes the air molecules
  together
• As a result, a region where the air molecules are
  closer together, or more dense, is created
• This region of high density is called a
  compression
• When the tuning fork moves back it causes an area
  of low density called rarefaction
• The compression and rarefaction move away from
  the tuning fork as molecules collide with one
  another

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• Sound waves can be described by its wavelengths
  and frequency
• Wavelength is the distance between two
  consecutive compressions or two consecutive
  rarefaction
• Frequency of a sound is the number of
  compressions or rarefactions that pass by a given
  point in one second
• The unit of frequency is the number of
  wavelengths per second, or Hertz (Hz)

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Speed of Sound

• Speed of sound varies because of temperature and
  material it is passing through
• Sound moves faster in solid then liquids or gases
  because the particles that makes solid up are
  closer together
• Sound is slowest in gases because molecules are
  farther apart
• As the temperature heats up its molecules move
  faster, so they collide more frequently
• More frequent the collision the faster sound
  travels
• 0 C sound travels a 331m/s, 20C 343m/s

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Amplitude and Loudness

• Loudness is the human perception of how much
  energy a sound wave is carrying
• The amount of energy a wave carries depends on
  its amplitude
• Higher amplitude- more compressed the particles
  in a compression are and the farther they are
  spread out in a rarefaction
• Higher amplitude means more energy and louder

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Decibel Scale

• Scale used to describe sound waves
• Increase in 10 decibels means that the energy
  carried by the wave has increased 10 times
• Increase in 20 decibels, energy increases 100
  times
• Increase in 30 decibels, energy incresed 1000x
• Hearing Damage begins to occur at 85 dB
• Jet Plane 150 dB
• Whisper 15dB
• Lawn Mower 110

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Frequency and Pitch

• Pitch of a sound is how high or low it sounds
• Pitch corresponds with frequency of the sound
• High the pitch the higher the frequency
• Lower the pitch the lower the frequency
• Human ear can detect sound waves with frequencies
  between about 20Hz and 20,000Hz.
• Dogs can hear frequencies up to almost 50,000 Hz
• Dolphins and Bats can hear frequencies as high as
  150,000 Hz.
• Higher pitch - shorter wavelengths, Lower pitch
  Longer Wavelength
• Length and thickness of your vocal cords help
  determine your pitch
• Short thinner vocal cords vibrate at higher
  frequencies, results in higher voices
• Muscles in throat can stretch the vocal cords
  tighter, letting people vary their pitch

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Wavelength, Frequency, and Pitch
                                                
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posterior lateral                              
                                                  
                                    
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Echoes

• A echoes is a reflected sound wave
• Sound waves reflect off of hard surfaces
• Sonar systems use sound waves to map out objects
  underwater
• The amount of time it takes for echoes to return
  depends on how far away the reflecting surface is
  
• Echolocation the ability to emit high pitched
  squeaks and listen for echoes. Used to navigate
  and hunt
• Bats and dolphins use echolocation

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         Dolphins produce high frequency clicks
that pass through the melon. These sound waves
bounce off objects in the water and return to the
dolphin in the form of an echo.  
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Doppler Effect

• The change in a frequency that occurs when the
  source of the sound is moving relative to a
  listener is the Doppler effect
• Occurs whether the sound source or the listener
  is moving
• As you move closer to the source you encounter
  each sound wave a little earlier
• The closer you get the higher the pitch
• When you move away , each sound wave takes longer
  to reach you, you hear fewer wavelength, which
  results in a lower pitch
• Radar guns used to determine speed of cars and
  baseballs use the Doppler Effect

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Diffraction

• Diffraction means that sound waves can bend
  around obstacles or spread out after passing
  through a narrow opening
• The amount of diffraction depends on the
  wavelength
• If Wavelength is much smaller than the obstacle,
  almost diffraction occurs
• If wavelength is closer or larger then the size
  of the obstacle, the amount of diffraction
  increases

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Using Sound Waves

• Ultrasound using high frequency sound waves as
  an alternative to some surgeries
• Kidney stones and gall stone sometimes can be
  broken up using ultrasound
• Used to exam a developing fetus, and internal
  organs

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The Ear

• The ear is a complex organ that is able to detect
  a wide range of sounds
• Has three parts
• Outer Ear
• Middle Ear
• Inner Ear

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• The Outer Ear
• Collects sound waves and directs them into the
  ear canal
• Shaped like a funnel to collect sound waves
• Animals that rely on hearing to locate predators
  or pry often have large ears and can be adjusted
• Rabbits and Owls

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Ural Owl Ear                                    
                                                  
                                                  
                                                  
                                                  
                                     
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• The Middle Ear
• Sound waves vibrate the Eardrum
• Eardrum is a Thin membrane that stretches across
  the ear canal
• As the eardrum vibrates, it transmits vibrations
  to three small bones
• Hammer
• Anvil
• Stirrup

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• The bones amplify (intensify) the vibrations
• Similar to how a lever can change a small
  movement at one end into a large movement at the
  other end

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• Ruptured Eardrum

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• Inner Ear
• The stirrup vibrates a second membrane called the
  oral window
• Inner ear is filled with fluid
• Vibrations are transferred to hair tipped cells
  in the cochlea
• Different sounds vibrate the hairs differently
• Cells generate signals containing information
  about the frequency, intensity, and duration of
  the sound

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• The nerve impulse travels to the brain along the
  auditory nerve

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How does your ear work ?                       
                              
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Watch the video (Real Player needed) Watch the video (Real Player needed)
                                                                                                                                   
high resolution low resolution

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Hearing Loss

• The ear can be damaged by disease, age, and
  exposure to loud sounds
• Constant exposure to loud sounds can damage the
  hair cells in the cochlea

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• If hair cells die, hearing loss occurs because
  mammals can not produce new hair cells
• Higher frequency hearing is usually the first to
  be lost
• Soft consonants sounds such as s, f, h, sh, ch
  are hard to hear
• People with high frequency hearing loss have
  trouble distinguishing these sound during
  conversation

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