The Nature of Sound, Chapter 21
Word
Sound Wave
Mechanical Wave
Sound Wave Velocity (m/s)
Approx. 343 m/s in air
Pitch
KEY
Explanation
Produced by a VIBRATION which is a
complete back and forth motion that
moves the energy
Have crowded areas called
COMPRESSIONS and less crowded
areas called RAREFACTIONS
Drawing/Examples
Ex: Tuning fork in water – moves
energy!
Sound requires a MEDIUM in order to
travel
The wave vibrations form a repeating
pattern of COMPRESSIONS and
RAREFACTIONS, making them called
COMPRESSION waves
Must have a medium –
solid/liquid/gas
Think domino effect
Velocity is determined by the
MEDIUM & TEMPERATURE.
Sound travels fastest through SOLIDS
and slowest through GAS. (why?)
Cooler temperatures make sound
travel SLOWER.
Solid – particles close together, so
bump faster
Liquid – particles further apart,
longer to bump
Gas – furthest apart
high temp – particles move faster
lower temp – move slower
Soprano vs bass
How HIGH or LOW you perceive a
sound to be
Determined by the FREQUENCY of the
wave
Higher frequency = higher PITCH
Sound Wave Frequency (Hz)
Pitch and frequency have direct
relationship
Frequencies below 20Hz
Animals with high frequency range
BATS, DOLPHINS, some WHALES
Animals with low frequency range
CATS, DOGS, some WHALES
Human frequency range = 20 to
20,000Hz (range shrinks as we age)
infra means “below” – we can’t hear!
Frequencies above 20,000 Hz
ultra means “above” – we can’t hear!
When an object making noise
approaching you makes you perceive
a HIGHER pitch than when it passes
you
Ex: fire truck passing you – sounds
higher pitch coming at you vs after
passing by (picture in textbook of
waves closer together coming &
spread out after passing)
Drawing of small vs larger amplitude
Higher frequency = SHORTER
wavelength (inverse relationship!)
Infrasonic (Frequency)
Ultrasonic (Frequency)
Doppler Effect
Sound Wave Amplitude
Decibels (dB)
As amplitude increases, the sound
energy INCREASES and it sounds
LOUDER
Loudness of sound
Threshold of pain for human ear is
ABOUT 120 dB
Measurement for sound
Word
Sound Interaction – Reflection
Sound Interference – Constructive
Sound Interference – Destructive
Sound Interference - Resonance
Noise
Sound Interaction - Diffraction
Explanation
Called an ECHO
Drawing/Examples
Bats/Whales/Dolphins use
ECHOLOCATION
Ships use SONAR
Ultrasounds used for MEDICAL
DIAGNOSIS
Compressions overlapping result in
sound being LOUDER
Compressions overlapping
rarefactions result in the sound being
SOFTER / CANCELING
Soloist vs choir
(higher amplitude)
Noise canceling headphones
(lower amplitude)
The tendency of an object to vibrate
at maximum amplitude at certain
frequencies…. One vibrating object
causes the other object to VIBRATE at
the same resonant frequency
Instruments –
Undesired sound due to mix of
random FREQUENCIES of sound
Sound can travel around BARRIERS or
through OPENINGS in order for you to
hear it
Tacoma Narrows Bridge –
Ex: glass breaking w/ high soprano
note (high pitch)
CAFETERIA OR AUDITORIUM
Why you hear students in the locker
area in our classroom