The Nature of Sound

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The Nature of Sound

• Students will describe how sound is caused by
  vibrations, how it is transmitted through a
  medium.
• Students will also compare the speed of sound in
  different media, explore the doppler effect, and
  explain how echoes are produced.
• Students will discuss the range of hearing for
  humans, and the threshold of pain.

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Sound is caused by vibrations

• The medium is vibrating and particles are
  compressed and decompressed.

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Another view of the particles vibrating back and
forth
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A cross section of a sound wave
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(No Transcript)
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Tuning Fork notice how the sound spreads out in
all directions. You can also see the reflection
of some of the sound waves, as well.
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Tuning Fork Sound WavesTime-lapse showing the
compressions moving through the medium
First second Second2 Third second Fourth
second Fifth second Sixth second Seventh second
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Sound Spreads Out in All Directions
Can you name the compressions and the
rarefactions?
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Amplitude of Sounds
Both waves have the same frequency, but the top
one has a much greater amplitude. This means that
they have the same pitch (or note on a musical
scale), but the top one is louder than the bottom
one.
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Sound vs Light
Light travels at 3x108 m/s, whereas sound only
travels at about 340 m/s That is 880,000 times
faster!!!! So the music you hear out of your
radio was transmitted through the air from radio
towers as a form of light (radio waves) not sound
waves
3x108 300000000
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The speed of sound
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Alsothe speed of sound depends on temperature!

• The cooler the media, the slower the speed of
  sound.
• Remember, the particles are moving slower when it
  is cooler, so they also transfer sound energy at
  a slower rate!

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How much can the teacher really hear in class???
Gum being chewed is about 5 Hz

• The average human can detect frequencies of 20 Hz
  to 20,000 Hz. (Augustyn can detect 2 Hz to
  200,000,000 Hz)
• Sounds that are lower than 20 Hz are called
  infrasonic
• Sounds that are higher than 20,000 Hz are called
  ultrasonic

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Doppler Effect

• The Doppler Effect (for sound waves) is the
  apparent change in pitch as a sound approaches
  and then passes by
• Example Train whistles at you while your
  standing by the tracks it seems to be higher in
  pitch as it approaches, and lower after it passes
  by.
• The frequency (pitch) does not really change, it
  only appears to change.

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Loudness is related to Amplitude

• The higher the amplitude, the louder the sound
• Loudness of sound is measured in decibels (db)
• Near total silence - 0 dB
• A whisper - 15 dB
• Normal conversation - 60 dB
• A lawnmower 80-90 dB
• A car horn 110-115 dB
• A rock concert or a jet engine - 120 dB
• Threshold of pain - 120 dB
• A gunshot or firecracker - 140 dB
• Jet engine 15 miles away 140 dB
• Instant perforation of the ear drum 160 dB

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EchoesEchoesEchoesEchoesEchoesEchoes

• Sound waves bouncing off a surface.
• Best when sound bounces off smooth surfaces.
• Which provides a better echo? An empty house, or
  a house full of furniture and carpeting?

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Students will describe how sound is caused by
vibrations, how it is transmitted through a
medium. Students will also compare the speed of
sound in different media, explore the doppler
effect, and explain how echoes are
produced. Students will discuss the range of
hearing for humans, and the threshold of pain.