Unit 5, Chapter 15

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Unit 5, Chapter 15
CPO Science Foundations of Physics
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Unit 5 Waves and Sound
Chapter 15 Sound

• 15.1 Properties of Sound
• 15.2 Sound Waves
• 15.3 Sound, Perception, and Music

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Chapter 15 Objectives

• Explain how the pitch, loudness, and speed of
  sound are related to properties of waves.
• Describe how sound is created and recorded.
• Give examples of refraction, diffraction,
  absorption, and reflection of sound waves.
• Explain the Doppler effect.
• Give a practical example of resonance with sound
  waves.
• Explain the relationship between the
  superposition principle and Fouriers theorem.
• Describe how the meaning of sound is related to
  frequency and time.
• Describe the musical scale, consonance,
  dissonance, and beats in terms of sound waves.

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Chapter 15 Vocabulary Terms

• pressure
• frequency
• pitch
• superposition principle
• decibel
• speaker
• acoustics
• microphone
• fundamental
• wavelength
• stereo

• Doppler effect
• supersonic frequency
• spectrum
• shock wave
• resonance
• node
• antinode
• dissonance
• harmonic
• reverberation

• note
• sonogram
• Fouriers theorem
• rhythm
• musical scale
• cochlea
• consonance
• longitudinal wave
• beats
• octave

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15.1 Properties of Sound

• Key Question
• What is sound and how do we hear it?

Students read Section 15.1 AFTER Investigation
15.1
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15.1 Properties of Sound

• If you could see the atoms, the difference
  between high and low pressure is not as great.
  Here, it is exaggerated.

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15.2 The frequency of sound

• We hear frequencies of sound as having different
  pitch.
• A low frequency sound has a low pitch, like the
  rumble of a big truck.
• A high-frequency sound has a high pitch, like a
  whistle or siren.
• In speech, women have higher fundamental
  frequencies than men.

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15.1 Complex sound
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Common Sounds and their Loudness
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15.1 Loudness

• Every increase of 20 dB, means the pressure wave
  is 10 times greater in amplitude.

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15.1 Sensitivity of the ear

• How we hear the loudness of sound is affected by
  the frequency of the sound as well as by the
  amplitude.
• The human ear is most sensitive to sounds between
  300 and 3,000 Hz.
• The ear is less sensitive to sounds outside this
  range.
• Most of the frequencies that make up speech are
  between 300 and 3,000 Hz.

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15.1 How sound is created

• The human voice is a complex sound that starts in
  the larynx, a small structure at the top of your
  windpipe.
• The sound that starts in the larynx is changed by
  passing through openings in the throat and mouth.
  
• Different sounds are made by changing both the
  vibrations in the larynx and the shape of the
  openings.

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15.1 Recording sound

• A common way to record sound starts with a
  microphone. A microphone transforms a sound wave
  into an electrical signal with the same pattern
  of oscillation.

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15.1 Recording sound

• In modern digital recording, a sensitive circuit
  converts analog sounds to digital values between
  0 and 65,536.

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15.1 Recording sound

• Numbers correspond to the amplitude of the signal
  and are recorded as data. One second of
  compact-disk-quality sound is a list of 44,100
  numbers.

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15.1 Recording sound

• To play the sound back, the string of numbers is
  read by a laser and converted into electrical
  signals again by a second circuit which reverses
  the process of the previous circuit.

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15.1 Recording sound

• The electrical signal is amplified until it is
  powerful enough to move the coil in a speaker and
  reproduce the sound.

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15.2 Sound Waves

• Key Question
• Does sound behave like other waves?

Students read Section 15.2 BEFORE Investigation
15.2
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15.2 Sound Waves

• Sound has both frequency (that we hear directly)
  and wavelength (demonstrated by simple
  experiments).
• The speed of sound is frequency times wavelength.
• Resonance happens with sound.
• Sound can be reflected, refracted, and absorbed
  and also shows evidence of interference and
  diffraction.

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15.2 Sound Waves

• A sound wave is a wave of alternating
  high-pressure and low-pressure regions of air.

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15.2 The wavelength of sound
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15.2 The Doppler effect

• The shift in frequency caused by motion is called
  the Doppler effect.
• It occurs when a sound source is moving at speeds
  less than the speed of sound.

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15.2 The speed of sound

• The speed of sound in air is 343 meters per
  second (660 miles per hour) at one atmosphere of
  pressure and room temperature (21C).
• An object is subsonic when it is moving slower
  than sound.

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15.2 The speed of sound

• We use the term supersonic to describe motion at
  speeds faster than the speed of sound.
• A shock wave forms where the wave fronts pile up.
  
• The pressure change across the shock wave is what
  causes a very loud sound known as a sonic boom.

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15.2 Standing waves and resonance

• Spaces enclosed by boundaries can create
  resonance with sound waves.
• The closed end of a pipe is a closed boundary.
• An open boundary makes an antinode in the
  standing wave.
• Sounds of different frequencies are made by
  standing waves.
• A particular sound is selected by designing the
  length of a vibrating system to be resonant at
  the desired frequency.

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15.2 Sound waves and boundaries

• Like other waves, sound waves can be reflected by
  surfaces and refracted as they pass from one
  material to another.
• Sound waves reflect from hard surfaces.
• Soft materials can absorb sound waves.

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15.2 Fourier's theorem

• Fouriers theorem says any complex wave can be
  made from a sum of single frequency waves.

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15.2 Sound spectrum

• A complex wave is really a sum of component
  frequencies.
• A frequency spectrum is a graph that shows the
  amplitude of each component frequency in a
  complex wave.

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15.3 Sound, Perception, and Music

• Key Question
• How is musical sound different than other types
  of sound?

Students read Section 15.3 AFTER Investigation
15.3
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15.3 Sound, Perception, and Music

• A single frequency by itself does not have much
  meaning.
• The meaning comes from patterns in many
  frequencies together.

• A sonogram is a special kind of graph that shows
  how loud sound is at different frequencies.
• Every persons sonogram is different, even when
  saying the same word.

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15.3 Hearing sound

• The eardrum vibrates in response to sound waves
  in the ear canal.
• The three delicate bones of the inner ear
  transmit the vibration of the eardrum to the side
  of the cochlea.
• The fluid in the spiral of the cochlea vibrates
  and creates waves that travel up the spiral.

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15.3 Sound

• The nerves near the beginning see a relatively
  large channel and respond to longer wavelength,
  low frequency sound.

• The nerves at the small end of the channel
  respond to shorter wavelength, higher-frequency
  sound.

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15.3 Music

• The pitch of a sound is how high or low we hear
  its frequency. Though pitch and frequency usually
  mean the same thing, the way we hear a pitch can
  be affected by the sounds we heard before and
  after.
• Rhythm is a regular time pattern in a sound.
• Music is a combination of sound and rhythm that
  we find pleasant.
• Most of the music you listen to is created from a
  pattern of frequencies called a musical scale.

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15.3 Consonance, dissonance, and beats

• Harmony is the study of how sounds work together
  to create effects desired by the composer.
• When we hear more than one frequency of sound and
  the combination sounds good, we call it
  consonance.
• When the combination sounds bad or unsettling, we
  call it dissonance.

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15.3 Consonance, dissonance, and beats

• Consonance and dissonance are related to beats.
• When frequencies are far enough apart that there
  are no beats, we get consonance.
• When frequencies are too close together, we hear
  beats that are the cause of dissonance.
• Beats occur when two frequencies are close, but
  not exactly the same.

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15.3 Harmonics and instruments

• The same note sounds different when played on
  different instruments because the sound from an
  instrument is not a single pure frequency.
• The variation comes from the harmonics, multiples
  of the fundamental note.

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Application Sound from a Guitar