The Nature of
Sound
Physical Science
What is Sound?
• Sound comes from vibrations that
move in a series of compressions and
rarefactions (longitudinal waves).
• A tree falls in the woods when no one is
around. Did it make a sound?
• There is a difference between creating a
sound and detecting a sound.
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The Human Ear
Outer ear: Funnel for sound waves – directs
vibrations to ear canal.
• Middle ear: 3 bones act as levers to increase
(amplify) the vibrations (Where eardrum is
located).
• Inner ear: Vibrations turn into electrical
signals for the brain to interpret. Vibrations
cause waves in liquid inside the cochlea,
which sends the electric signals to the brain.
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How the Ear Works
• http://www.youtube.com/watch?v=r1P6I
Q5Wr_I
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Causes of Hearing
Loss/Deafness
• Tinnitus – hearing loss due to longterm exposure to loud sounds
(“ringing” in ears).
• Deafness can occur from serious
tinnitus or any damage to any of the
parts of the ear. (How safe are Q-tips?)
• Ear protection is important when
exposed to unusually loud noises.
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How Does Medium Affect the
Speed of Sound?
• The closer the particles, the faster the
vibrations, the faster the sound waves
travel.
• Sound travels fastest in solids, then
liquids, and slowest in gases.
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Sound Speed and
Temperature
• Cooler temperatures slow down the
speed of sound (air particles move
slower).
• Since cooler temperatures lower the
speed of sound, why is it easier for
pilots to break the sound barrier while
flying?
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Changing the Speed: How the
Hindenburg disaster really sounded
• http://www.youtube.com/watch?v=pUV
DmXvXcbk&safety_mode=true&persist
_safety_mode=1&safe=active
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Properties of Sound
• Speed – Since sound requires a
medium, then speed can
increase/decrease, depending on
resistance of the medium.
• Sound can speed up or slow down
(travels 3 times faster in helium)
• Sound waves travel faster through
many solid objects (i.e., wood, glass,
steel, etc.)
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Pitch and Frequency of
Sound
• The “highness” or “lowness” of sound
is the pitch.
• Pitch depends on the frequency of the
sound waves (1 Hz = 1 wave per sec.)
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Frequency and Human
Hearing
• Humans can hear frequencies between
20 Hz and 20,000 Hz (depends on age).
• Just like any machinery, parts become
worn with age. As humans mature,
they may need more amplification of
sound vibrations (hearing aids)
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Pitch and Frequency of
Sound
• Infrasonic – Sounds with frequencies
lower than 20 Hz (outside of range of
human hearing)
• Ultrasonic – Sounds with frequencies
greater than 20,000 Hz (Too high for
hearing, can be used for cleaning
jewelry.)
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Vocal Cord Vibration Changes
Causes Pitch Changes
• Helium and Sulfur hexafluoride:
• http://www.youtube.com/watch?v=ALD
3cB4YJg&safety_mode=true&persist_s
afety_mode=1&safe=active
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Ultrasound
Hear the reaction of a couple
who find out they are having
twins!
http://www.youtube.com/watch?v
=1EStMIHpFow&safety_mode=tru
e&persist_safety_mode=1
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Amplitude in Sound =
Loudness
• In sound, when you increase the
amplitude of a wave, you increase the
loudness of that wave.
• Loudness is measured in decibels.
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How Loud Can You Hear?
• Human ears hear at an average of 0 db70 db. 120 db is called the “pain
threshold”. Continued exposure to
sounds above 85 db can cause gradual
but permanent hearing loss.
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Common Noises and Their
Decibel Levels
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Aircraft at take-off (180)
Fireworks (140)
Snowmobile (120)
Chain saw (110)
Amplified music (110)
Lawn mower (90)
Noisy office (90)
Vacuum cleaner (80)
City traffic (80)
Normal conversation (60)
Refrigerator humming (40)
Whisper (20)
Noise levels of 130 decibels or
over will be painful and is very
likely to cause immediate hearing
damage.
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The Doppler Effect
• The Doppler Effect is a change in
sound caused by either the motion of
the listener or the source of the sound.
• Imagine a car, honking its horn, as it
comes towards you, getting louder and
louder. What does it sound like after it
passes you?
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Transferring Sound to Paper
• Sound waves can be received and then
graphed on paper. The instrument that
can do this is called an oscilloscope.
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Interactions of Sound Waves
• Echolocation – When sound is sent out
and reflects back to find an object or
location.
- Sonar – Type of electronic echolocation
Uses short ultrasonic wavelengths
(often used on ships)
- Ultrasongraphy – Ultrasound uses sound
waves (not xrays) to bounce off organs and
create a “picture” of them.
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Dolphin Using Echolocation
• http://www.youtube.com/watch?v=51G8
3jaeNC4&safety_mode=true&persist_sa
fety_mode=1
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Can Humans Use Echo
Location?
• http://www.youtube.com/watch?v=r9mv
RRwu5Gw
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The Sound Barrier
• Since the source of sound, like a jet
plane, accelerates to the speed of
sound, the sound waves in front
compress together. If the jet
accelerates pass the speed of sound, a
tremendous shock wave results.
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Sonic Boom!
• When the shock waves reach your ears,
you hear a large explosive sound.
Sonic booms are large enough to cause
ear damage and some minor damage.
• http://www.youtube.com/watch?v=XZMK7pCtVNk&fe
ature=related&safety_mode=true&persist_safety_mo
de=1&safe=active
• http://www.youtube.com/watch?v=6o0zmafxTmE&fe
ature=related&safety_mode=true&persist_safety_mo
de=1&safe=active
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Light and Sound: The Russian Meteor of February,
2013
Once a meteor enters our atmosphere,
the amount of friction causes both
intense light and heat. The momentum of
the meteor is faster than the speed of
sound.
http://www.youtube.com/watch?v=Rp5eg
_lk8zA
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