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Sound
and
Communication
Sound is caused when
vibrations make air move and
vibrate.
This causes sound waves
which are picked up by your
eardrum causing it to vibrate.
This is translated by your brain
into a recognized sound.
• Sound needs a medium to
travel on such as gas, solid or
liquid.
• Sound travels in air at about
1,224 km per hour. It travels
much faster in water at about
5,400 km per hour.
• An echo occurs when a sound
bounces off a surface and
comes back to you.
A large vibration causes a large
sound and a small vibration
causes a small sound.
Sound can also be caused by
energy.
Energy causes vibration which
causes sound.
• Vibrations were used by North
American Indians to track
buffalo. They would put their
ears to the ground to try and
hear the buffalo.
• Soft materials such as cotton
wool absorb sound, this is why
you cannot hear anything when
you drop them
An Ancient Greek Philosopher
called Aristotle believed that
sound and light were carried
through air like waves.
He believed that they couldn’t
travel through a vacuum.
Many centuries later scientists
could create a vacuum to test
Aristotle’s theory.
An Irish scientist called Robert
Boyle created an experiment in
1658.
He pumped air from a jar that held a
ticking watch. This created a
vacuum.
As there was no air left in the jar, he
could not hear ticking at all. This
proved Aristotle’s theory correct
Sound Intensity
• Decibels are used to
measure the intensity
of sound (how
powerful a sound is)
• If something is 0
decibels it is not
powerful enough to
be heard.
Whispering
10 decibels.
Wind and leaves
rustling
20 decibels.
Waves on the
seashore
40 decibels.
A shouted
conversation
70 decibels.
A vacuum cleaner
80 decibels.
Rock music
100 decibels.
A jet engine
110 decibels
The threshold of
pain
120 decibels!
The Ear
Anatomy of the Ear
Your Voice Box – the Larynx
The larynx is another name for the voice box. The
larynx is made up of nine parts of cartilage and it
has two main parts.
When you are swallowing the epiglottis which is
the upper cartilage covers the voice box to stop
food going down into the lungs.
Whenever you aren’t swallowing food the epiglottis
opens and the larynx opens as well.
The larynx plays an important part in voice
production.
Sound is produced when the vocal cords vibrate
as air flows out of the lungs.
The adam’s apple is in front of the larynx. When
boys reach their teenage years the larynx grows
and that causes their voice to deepen.
Sound Waves
• Sound Waves: A vibrating object gives off sound waves
and different vibrating objects can give off different
amounts of sound waves.
• Ultrasonics is the study of high-frequency sound waves.
• Frequency: Frequency is the number of sound waves
given off by a vibrating object.
• Measuring Sound Waves: Frequency is measured in
Hertz (Hz for short) which is the number of sound waves
given off by a vibrating object per second.
• An echo happens when a sound bounces
off a surface and bounces back to you.
• A large vibration causes a large sound and
a small vibration causes a small sound.
• Soft materials such as cotton wool absorb
sound.
• Indians used vibrations to track buffalo.
They would put their ears to the ground to
try and hear the buffalo.
Sound in Water
Sound travels faster through water than
through air. This helps animals such as
whales to communicate or talk with each
other over very long distances. Whales
also use sound waves to help them travel
through dark water. They send and receive
sound waves in the same kind of way as
the sonar on a ship or submarine.
Animal Sounds
• Dolphins use echolocation to communicate, to
locate fish and to detect underwater obstacles.
• Echolocation is a loud clicking sound produced
by dolphins.
• The clicking sound bounces off objects which
causes an echo.
• Dolphins can communicate to each other over
hundreds of kilometres. Dolphins produce
clicking sounds from an organ called a melon on
their head.
• Humans can hear millions of sounds, from
screams to the hissing of a cat, but there are
some sounds that are far too high-pitched for
humans to hear.
• Some animals including dogs can hear these
high-pitched signals.
• Whales use this method to see, by sending the
signal against the sea-floor. It then bounces
back to them, telling them where they are
located.
• Some whales sing songs which can be heard
throughout the oceans.
• A male humpback whale has it’s own song
which will last for 35 minutes.
• Fishermen have copied this method. If it
was a foggy night and they couldn’t see
and they knew there were cliffs ahead they
would shout out.
• An echo would come back to them. They
would start counting after they shouted
out.
• If it took 5 seconds they were one mile
away, 10 seconds if they were two miles
away etc.
Animal Hearing
• Bats can fly in total darkness.
They can do this by screeching
out a very high pitched note.
Humans cannot hear this high
pitched sound and ultrasonic
sound.
• Bats can hear up to 120,000
hertz. A young person can hear
up to 20,000 hertz. Some
notes and sounds are just too
high for humans to hear.
• Many animals can hear a lot
better than humans
Bats
Up to 120 000
Hertz
Mice
Up to 100 000
Hertz
Dogs
Up to 35 000
Hertz
Cats
Up to 25 000
Hertz
People
Up to 20 000
Hertz
Animal Hearing
An
im
al
H
ea
rin
g
Ba
ts
M
ic
e
D
og
s
C
at
Pe s
op
le
140000
120000
100000
80000
60000
40000
20000
0
Animal Hearing
Bats
Mice
Dogs
Cats
People
Ultrasound
• Hospitals use ultrasound to see babies in
a mother’s womb.
• They send the signal into the mother’s
womb. It bounces off the baby and goes
back out.
• The hospital then puts this picture on a
special camera, allowing the family to see
the baby
• Sound waves make their way through the
ear canal. The waves then go into the ear
drum. The ear drum is very thin.
• The Ear drums vibrate when the sound
waves arrive.
• The sound waves go through three small
bones, the hammer, anvil and stirrup. They
are called the ‘ear ossicles’. They bring the
sound waves through a small space of air.
It is called the ‘Middle Ear Cavity’.
• The sound waves then travel through the oval
window to fluid in the inner ear. This fluid is
called the endolymph. The sound waves make
the endolymph fluid move. This causes tiny hair
cells and the cochlea to vibrate.
• The hair cells are called hair cells because they
look like tiny little hairs. The vibrations of the hair
cells and the cochlea send messages to the
auditory nerve.
• The auditory nerve brings the message to the
brain. The brain understands the message as a
type of sound.
The Sound Barrier.
The sound barrier is a speed barrier that judges an airplane’s
actions by the speed its going. To break the sound barrier
you have to travel faster than the speed of sound. The shock
wave that is made by an airplane moving at a supersonic
speed makes a shocking change in air pressure.
The fastest plane ever is the SR-7I blackbird.
Going through the sound barrier is very difficult because the
high-speed flight makes heat through friction.
(eg. Rub your hands together really hard you will feel that they
are getting hotter. That is friction)
Because of that, the surface of the plane’s temperature gets
higher then the safety limit for the structure of the aircraft.
Concorde was the only passenger plane to go faster than
the speed of sound
Silent Space!
• In space, there are no solids, gases or
liquids to travel through meaning sound
can’t exist.
• Spacemen use radios to communicate
with each other in space.
• So “In space no one can hear you
scream”.
•
•
•
•
How Sound Travels
Sound is actually moving waves of molecules
and that molecules are found in matter. So how
do different types of matter influence how sound
travels?
The medium has a direct effect on how fast
sound travels. If the molecules that make up the
substance are loosely packed, sound will travel
slowly.
If the molecules are tightly packed, sound will
travel faster.
Where there is no medium, no sound can be
transmitted. Other factors that may affect the
transmission of sound include temperature,
humidity, and altitude.
Sound: High & Low
• Have you ever played a piano? Keys to the right side of
a piano keyboard play notes that are higher than keys to
the left
• The term pitch is used to talk about the "highness" or
"lowness" of a sound.
• We say that the notes to the right of a piano keyboard
have a higher pitch than the ones on the left.
• The pitch of a sound is directly related to the frequency
of the sound wave.
• Higher frequency means higher pitch.
• Lower frequency sound waves create sounds with lower
pitch.
• Changing the frequency of a sound wave changes the
pitch of the sound.
Understanding Sound
To understand sound, you first need to understand
matter. Everything is made up of matter. Matter
is the general term we use to describe the "stuff"
that is all around us. "What makes up matter?"
you ask . . . molecules.
Molecules are small particles that you cannot see
with your naked eye that join together to form
everything around you: the table you are leaning
on, the chair you are sitting in, the computer
screen you are looking at. All these objects are
made up of molecules, thousands and
thousands of molecules.
Molecules in Motion
• "What is Sound?" Sound is created when something
vibrates back and forth. The vibration pushes into
molecules and creates a wave of sound.
• The sound wave starts at whatever is making the sound
(by vibrating) and travels all the way to your ears, where
you hear it.
• Molecules are so small that it is difficult to actually see
them.
• As the string of a guitat makes sound waves, the
molecules themselves don't move very far - it is the wave
that travels as the molecules bump into each other.
Bouncing Sound
When a sound wave meets an obstacle, a portion of the
wave is reflected from the obstacle, and the other portion
is transmitted through the obstacle. Hard obstacles like
concrete reflect almost all the sound, while soft materials
like cloth allow the sound to be transmitted.
Other Sound Facts
• Sound waves eventually stop because all the energy in
the wave is used as the molecules in the medium move.
• As sound travels, its energy is used up, causing it to
become less intense (softer) the farther it travels from its
source.
Sound Vocabulary – A Wave
• What is a Wave? Before we talk about sound waves, let's find out a
little more about waves that you already know something about . . .
ocean waves! You can think of any kind of wave as energy in motion
or energy moving from point to point.
• Crest: the highest point on the wave
•
Trough: the lowest point on the wave
•
Wavelength: the distance from one crest to the next crest
•
Amplitude: the distance between a wave's crest and trough
•
• Frequency: the number of waves passing a point in a given amount
of time
The Voice