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Sound Waves
Chapter 11 Section 1
Sound Waves
• Sound waves are compressional waves
• Sound waves require a medium
• The medium can be a solid, liquid, gas, or
another combination of the three
• In general, sound waves travel slowest in
gases and fastest in solids
• Sound waves also travel faster at higher
temperatures
– Why?
• Because the molecules and atoms are already colliding
more frequently
The Speed of Sound
• When a tuning form
makes sounds
waves
– The wave forms a
compression when
the tuning fork tine
moves inward (c)
– The wave forms a
rarefaction when the
tuning fork tine
moves outward (b)
Amplitude and Energy
• The amount of energy carried by a wave is
directly related to the amplitude of the
wave.
• As amplitude increase, energy increases
• In a compression wave, denser
compressions and more disperse
rarefactions are associated with high
amplitude
Amplitude and Energy
• The amount of energy transferred by a
sound wave through a medium each
second is the intensity.
• High amplitude = high intensity = high
energy
• Intensity decreases as the waves travel
away from the source
– Intensity decreases as sound waves spreads
out
Amplitude and Loudness
• Your ears and brains can detect changes
in intensity
• Loudness is the human perception of
sound intensity
• As intensity increases, loudness increases
A Scale For Sound Intensity
• There is a scale for sound intensity
• Each unit on the scale is a decibel (dB)
– 0 dB is the faintest sound that most people
can hear
– Sounds above 120 dB may cause pain and
permanent hearing loss
A Scale for Sound Intensity
•
There is no cure for noise induced hearing loss; therefore, prevention is important
Pitch and Frequency
• Pitch is the human perception of the
frequency of sound waves
• Pitch increase as frequency increases
– Frequency is the measure of how many
compressions pass a fixed point in one second
• The human ear can usually hear frequencies
between 20 Hz and 20,000 Hz
– The ear is most sensitive to sounds between 440
Hz and 7000 Hz
Pitch and Frequency
Ultrasonic Waves
• Waves about 20,000 Hz are called
ultrasonic waves
– Can’t typically be heard by the human ear
– Dogs can usually hear up to 35,000 Hz
– Bats can hear more than 10,000 Hz
– Used in medicine for diagnostics and
treatment
– Also used in depth detectors
Infrasonic Waves
• Waves with frequency below 20 Hz
• The frequency of these waves vibrate very
slowly
– Earthquakes, wind, heavy machinery
• Even when they can’t be heard, you can
often feel them
Doppler Effect
• When an object
making sound is at
rest, sound waves
radiate out from
the object with
equal wavelength
in all directions.
• A person in front of
the object will “see”
the same
wavelength as a
person behind the
object
Doppler Effect
• Now lets consider a
object in motion
• The moving object
begins to catch up to the
waves in front of it
causing them to bunch
up.
• The observer in front will
experience the bunched
up waves (high
frequency)
• The observer behind the
object will experience
less dense waves (lower
frequency
Supersonic
• When the object is
moving faster than
the speed of sound,
the observer will
hear the sound after
the object has
passed
• The sound that
results is a sonic
boom
• Supersonic Flight
Using Sound
• Curing Cancer
• Boiling Water
• Healing Wounds
• Growing Food
• Revealing Natural Geometry
• Stabilizing Braining Waves
• Cancelling Sound
• Levitation
• Echolocation
• Ultrasound
10 Amazing Uses of Sound