Sound

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Sound
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The Facts

• Sound
• 1. Is a form of energy produced transmitted by
  vibrating matter
• 2. Travels in waves
• 3. Travels more quickly through solids than
  liquids or gases

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The Ear

• Sound is carried to our ears through vibrating
  air molecules.
• Our ears take in sound waves turn them into
  signals that go to our brains.
• Sound waves move through 3 parts of the ear
  outer ear, middle ear, inner ear.

Middle Ear
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Vibration

• Back and forth movement of molecules of matter
• For example,
• Vibrations are formed through compressions and
  rarefactions.

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Compression

• Where molecules are being pressed together as the
  sound waves move through matter
• For example,
• a wave travels through the springs just like
  sound waves travel through the air
• the places where the springs are close together
  are like compressions in the air.

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Rarefaction

• Rarefaction is when the air particles become less
  crowded as the sound moves through matter.
• For example
• After the compression passes, the springs
  spread out and form rarefactions.

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Sound Waves

• Sound travels as a longitudinal wave
• Sound waves move out in ALL directions from a
  vibrating object
• But, the air does not travel with the sound
  waves. The particles of air only vibrate back
  and forth in place.

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Sound Waves

• - Alternating areas of compressions
  rarefactions in the air
• ALL sound is carried through a medium as sound
  waves
• REMEMBER A medium is a substance through
  which a wave can travel.
• Example air, water

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Properties of Sound

• The speed of sound changes when
• the medium changes.
• Sound travels the slowest through
• gasses and the fastest through solids.
• Why?
• The speed of sound also depends on the
  temperature.
• The cooler the medium, the slower the speed of
  sound. This happens because particles in cool
  materials move slower than particles in warm
  materials. When the particles move slower, they
  transmit energy (or sound) more slowly.

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Wavelength Frequency

• Wavelength is the distance between one part of a
  wave and the same part of the next wave
• Frequency is the number of waves moving past a
  point in one second

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Pitch

• A measure of how high or low a sound is
• Pitch depends on the frequency of a sound wave
• For example,

• Low pitch
• Low frequency
• Longer wavelength

• High pitch
• High frequency
• Shorter wavelength

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Pitch

• So, the higher the frequency, the higher the
  pitch. If the pitch becomes too high, it may
  become difficult to hear.
• The lower the frequency, the lower the pitch.

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Frequency

• Humans can detect sounds that have frequencies
  between 20 Hz and 20,000 Hz.
• EXAMPLES
• Pipe organ 40 Hz
• Screech of a bat 10,000 Hz
• Sounds that have frequencies lower than 20 Hz are
  described as infrasonic.
• Sounds that have frequencies higher than 20,000
  are ultrasonic.

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The Doppler Effect

• Have you ever been passed by an ambulance with
  its siren on? The pitch probably sounded higher
  while it was approaching you and lower after it
  passed. That is because of the Doppler effect.
• The Doppler effect is the apparent change in the
  frequency (or pitch) of a sound caused by the
  motion of either the listener or the source of
  the sound.
• The frequency (or pitch) does not actually
  change, it just sounds like it does.

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Loudness

• Loudness is how loud or soft a sound is perceived
  to be.
• If you strike an object with more force (such as
  a drum), you are increasing the amplitude of the
  sound waves being created. The larger the
  amplitude, the louder the sound, and the smaller
  the amplitude, the softer the sound.
• Loudness is measured in decibels (dB). The chart
  on the next page shows the decibel levels of some
  common sounds.

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Reflection

• Reflection is the bouncing back of a wave after
  it strikes a barrier.
• It is also known as an echo.
• Sound waves will reflect best off smooth, hard
  surfaces (like a gymnasium).
• Some animals use echolocation or they reflect
  sound waves to find objects.

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Reflection

• Humans use echoes to locate objects underwater
  and underground by using sonar (sound navigation
  and ranging).

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Reflection

• Ultrasonography (or an ultrasound) uses echoes to
  see inside a patients body without performing
  surgery.
• It is used to examine kidneys, gallbladders, and
  to check the development of an unborn baby in a
  mothers body.

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Interference

• Interference is the result of two or more waves
  overlapping.
• Interference can be constructive or destructive.

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Constructive Interference

• The compressions of one wave overlap the
  compressions of another wave, and the sound will
  be louder because the amplitude is increased.

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Destructive Interference

• The compressions of one wave overlap the
  rarefactions of another wave, and the sound will
  be softer because the amplitude is decreased.

23
Sound Barrier and Sonic Booms

• A jet plane reaches the sound barrier when it
  goes fast enough that the sound waves in front of
  the plane compress closer and closer together.
• For the jet to travel faster than the speed of
  sound, it must overcome the pressure of the
  compressed sound waves. The sound waves trail
  off behind the jet and combine at their outer
  edges to form a shock wave. A sonic boom is the
  explosive sound heard when a shock wave reaches
  your ears.
• Example on page 548-549.

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Resonance

• Resonance occurs when an object vibrating at or
  near a resonant frequency of a second object
  causes the second object to vibrate.
• For example, a tuning fork can cause a guitar
  string to make a sound without touching it.
• Also, an opera singer can cause glass to break.

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Diffraction

• Diffraction is the bending of waves around
  barriers or through openings.
• This is how sound can travel around the corners
  of buildings and through doorways.
• There would be more diffraction if the size of
  the barrier or opening is the same size or
  smaller than the wavelength of the sound waves.

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Thats all folks!