Physical Science
Chapter 11: Sound
Sound
 Sound Waves
waves are a type of
compressional wave which require a
medium to travel.
 The
study of sound is called acoustics.
• Sound waves travel at about 750 mi/hr.
This speed is effected slightly by the
type of medium, temperature of medium
(directly proportional), and elevation.
Ok, quick review:
• Frequency is a property of a wave, not
a part of one.
• Frequency is the number of waves
which pass a given point in 1 second.
• Hertz (Hz) is the SI unit for frequency.
1 Hz = 1 wave passing a given point in
1 second
Compressional Waves

A compressional wave vibrates in the
direction that the wave is travelling.
Examples: slinky, sound waves
• The 2 main parts of a compressional wave
are:
A. Compression- area of higher density
within the wave
B. Rarefaction- area of lower density
within the wave
pg. 464
• When an object such as a jet travels at a
speed greater than 750 mi/hr it is said to
be supersonic.
• What happens when an object travels at
supersonic speeds?
Pitch
• Pitch is how high or how low a sound is to
the human ear.
This is determined by the sound frequency,
which is directly proportional to the sounds
pitch.
pitch h h frequency
pitch i
i frequency

Humans can only hear sounds which are
within a certain range. For the average
person this range is from approximately 20
Hz to 20,000 Hz (vibrations per second).
• Frequencies above 20,000 Hz, and beyond
the normal range of human hearing are
called ultrasonic.
• Very high frequency
sound waves can be
used in the medical
field.
• Ultrasonic waves can
be used to break up
kidney stones and gall
stones.
• Ultrasound imaging uses the reflections
produced by ultrasonic sound waves to
produce images from inside the body.
• What advantages do you think
ultrasonic sound waves would have
over x-rays or MRI’s?
• Sounds below the normal range of human
hearing (20 Hz) are called subsonic, or
infrasonic.

Music is a combination of specific
sounds used in a regular pattern.

Musical notes are produced by
sound vibrations at a certain
frequency.

However, even though certain
notes correspond to certain
frequencies, different people may
perceive these notes differently.
• Natural frequencies are the frequencies at
which an object or material will vibrate
when it is disturbed.
• The right frequency
combined with enough
energy (loudness) in a
sound wave could
cause a wine glass to
vibrate at it’s natural
frequency (resonance)
and eventually break
due to constructive
interference.
• Other examples of resonance
Loudness

Loudness is human perception of sound
intensity (the amount of energy in the
wave), and is measured on the decibel
scale (dB).
 Loudness
is subjective to the
individual. However, the decibel
scale still assigns numeric values to
different levels of loudness.
• What is the lowest
value on the
decibel scale, and
what does it
represent? and
the highest?
• Strong shock waves could produce a condition
called lethal over-pressure shock. This is
caused by a large increase in air-pressure (100
p.s.i.+) and can actually result in death. Large
explosions in the area of 200 dB’s or more can
produce such a condition.
Doppler Effect
• The Doppler effect is a change in
wave frequency due to a moving
wave source.
• The frequency is higher in the
direction that the wave source is
moving and lower in the opposite
direction.
A bug swimming in a pool of water produces
waves which exhibit the doppler effect.
• Other examples of the
Doppler effect include radar
guns, sounds produced by
a racecar or an ambulance,
and Doppler radar.

Doppler radar uses radio waves to detect
winds, clouds, and precipitation in order to
identify and forecast weather.
• Doppler radar can identify a tornado and
issue a warning without having an actual
eye-witness to the event.
• Sounds can also
bounce off of
objects or surfaces.
• When a sound
wave bounces off
and returns to the
wave source, it is
called an echo.
• When an area produces
multiple echoes, this is
called reverberation, or
reverb.
• Echolocation is the process of locating and
identifying objects by interpreting sound
waves which are reflected back.
• Bats will used high pitched squeaks,
echolocation, and the Doppler effect to
locate food.
• Echolocation can also be used under
water. It is called SONAR when it is used
underwater.
SOund
Navigation
And
Ranging
• Humans and animals alike will use
SONAR to detect and identify underwater
objects and structures.
• Fish finders and depth finders are common
uses for SONAR.
White Noise
• White noise is a combination of sounds at
different audible frequencies, used to
mask out annoying background noises.
• Say you're listening to 2 people talking at
the same time. You would be able to pick
out one of the 2 voices.
If 3 were talking, their speech would be
more inter-mixed, but you could still
probably pick out 1 person's voice.
How about if 50 were talking at the same
time and same volume, could you pick out 1
individual voice?
• That's kind of how white noise works.
It has a combination of different sounds at
different frequencies within the range of
20-20,000 Hz. Any background sounds
will blend into this, and be masked over.
The resulting sound is similar to static you
may hear from your t.v.
• Think of it like a Where’s Waldo cartoon.
Waldo is in there somewhere, it’s just hard to
pick him out of the crowd. White noise does
that to the annoying background noises that
you’d prefer not to be distracted by.
• So what exactly does white noise
sound like?
• Could you say that white noise blocks
out background noises?
• Why do you think it's called
white noise?
• What are some places where white
noise might be used?
A bored scientist decided to see what would happen
if he let a bat loose in a sound proof chamber like
the one pictured. He also let a few moths loose in
the chamber as well, for food. Describe how the bat
most likely behaved inside the chamber.
Jared loads luggage into planes at KCI. The
headphones he was issued for hearing protection
from the noise were very uncomfortable, so he
bought his own pair of “noise canceling” Bose
headphones. Will these work about the same, better,
or worse than his original headphones? Explain.
• James is going to the Gulf Coast for vacation
to do some fishing. He takes his boat and
his fish finder. Will the fish finder which he
normally uses in fresh water work well in salt
water? Explain your answer.
• Is it possible for a sound which is not
audible to our ears to cause hearing
damage? Explain.
• Fish finders use frequencies in the 50-200 kHz
range. Why do you think this is so? (give 2
reasons)
• What sound wave property does the
intensity of the wave determine, pitch or
loudness? Is this always true? Explain.
• Why do you think radio waves
are used for radar (through
the air), but not for SONAR?
• Meredith heard a
noise in her backyard.
So she went out back
out shined a flashlight
around, and found a
raccoon messing
around. So you could
say that she used
Lidar.
What?!?
• As the teacher was writing on the chalk
board, the chalk suddenly screeched and
caused several students to jump. Why did
they respond this way?
• Todd noticed that when he had a head cold
and was all stopped up, every sound that he
heard sounded muffled. Why do you think this
happened?
• When Angela, Pam,
and Kelly were
swinging at the park,
Kelly was able to go
much higher than the
other two. “What’s
you’re secret for
swinging so high”,
asked Pam.
“Resonance my friend,
resonance”. What did
Kelly mean?
• The B-2 stealth bomber is designed to make it
nearly invisible to most radar systems. What are
some ways that an aircraft such as the stealth
could decrease it’s visibility to radar?