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information into something your brain can understand. To understand how your ears hear sound, you
first need to understand just what sound is.
What is Sound?
An object makes sound when it vibrates in something. This could be in a solid, like earth, a
liquid, like water, or a gas, like air. Most of the time, we hear sounds traveling through the air in our
atmosphere.
When something vibrates in the atmosphere, it moves the air particles around it. Those air
particles then move the air particles around them, which carry vibrations through the air.
To see how this works, let's look at a simple object: a bell. When you hit a bell, the metal
vibrates, or moves in and out. When it moves out to one side, it pushes on the air particles on that
side. These air particles then collide with the particles in front of them, which collide with the
particles in front of them, and so on.
When the bell moves away, it pulls in the nearby air particles. This pulls in more air particles, and
those pull in particles even farther out. In this way, a vibrating object sends a wave of pressure
changes through the atmosphere.
We hear different sounds from different vibrating objects because of differences in the sound
wave frequency. Frequency is how fast the air pressure switches back and forth. A higher wave
frequency means that the air pressure switches back and forth very quickly. We hear this as a
higher pitch, or sound. When there are fewer changes in pressure in a period of time, the pitch is
lower. The level of air pressure in each switch determines how loud the sound is.
Sound and the Human Ear
To hear sound, your ear has to do three basic things. It has to:
Direct the sound waves into the hearing part of the ear
Feel the changes in air pressure
Convert the changes into a signal that your brain can understand
The outer part of the ear, called the pinna, "catches" the sound waves. Your outer ear is pointed
forward, and it has many curves. This structure helps you figure out the direction of a sound. If a
sound is coming from behind you or above you, it will bounce off the ear in a different way than if it
is coming from in front of you or below you. Your brain recognizes certain patterns and decides
whether the sound is in front of you, behind you, above you, or below you. If the sound is to your
left, it will come to your left ear a little bit sooner than it comes to your right ear. It will also be a little
bit louder in your left ear than your right ear.
Since the pinnae face forward, you can hear sounds in front of you better than you can hear
sounds behind you. Many animals, like dogs, have large, movable ears that let them focus on
sounds from a specific direction. Human ears are not as good at focusing on sound. They lay pretty
flat against the head and don't have the muscles needed for a lot of movement. But you can easily
improve your natural hearing by cupping your hands behind your ears.
adapted from http://science.howstuffworks.com/hearing.htm
Read the following passage about animals who did not think. Then answer the questions
that follow.
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They Didn't Think
By Phoebe Cary
Once a trap was baited
With a piece of cheese;
It tickled so a little mouse,
It almost made him sneeze.
An old rat said, "There's a danger,
Be careful where you go!
"Nonsense!" said the other,
"I don't think you know!"
So he walked in boldly—
Nobody in sight—
First he took a nibble,
Then he took a bite;
Close the trap together
Snapped as quick as wink,
Catching mousey fast there,
'Cause he didn't think.
Once there was a robin,
Lived outside the door,
Who wanted to go inside
And hop upon the floor.
"No, no," said the mother,
"You must stay with me;
Little birds are safest
Sitting in a tree."
"I don't care," said Robin,
And gave his tail a fling,
"I don't think the old folks
Know quite everything."
Down he flew, and kitty seized him
Before he'd time to blink;
"Oh," he cried, "I'm sorry,
But I just didn't think."
Read the following passage about a song for the Earth. Then answer the questions that
follow.
Earth Song
By D. A. Tony Ciango
One Star was painting the story on a buffalo hide when I met him. He was an old man now, and
he wanted to record the tale while his memory was still sharp.
He invited me to sit beside him, and I watched and listened as the old man told me about the
Earth Song.
One Star had been a young chief when the owl and the wolf came to him in a dream, and the
song they had sung was a sad one.
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The owl was the first to appear. He sang of a time when the skies were clear and the air was
pure. A time when his kind could nest in the tall pines of the great forests that stretched for as far as
the eye could see. A time when food was plentiful and his family could soar and hunt above the
wide open plains forever.
The owl sang of a beautiful land where cool clean water glided from magnificent mountains into
lush green valleys. The creatures of the air had prospered in this land. Generation after generation
had raised their young and thanked the Creator for this place.
But all that had changed.
The new people had come, and they had cleared the dense forests for materials to build their
own wooden nests, which now covered the flowing plains. Their machines polluted the air, and their
waste was thrown into the once clean rivers and streams.
The new people hunted for food, which the owl understood. But they also hunted for sport, which
the owl did not understand. As the new people grew in number, the number of owls shrank. They
were forced to look for new homes in unfamiliar lands. Nesting places were scarce, and food was
harder to find. Some could not adapt to the changing ways and were never to be seen flying on the
earth again.
Then the wolf appeared and his song echoed the owl's. His clan had also been forced to retreat
from the new people. They went into the foothills of the mountains and had to roam far from their
dens in search of food. They were feared, misunderstood, and hunted. The wolves that were once
called the protectors of women were cast away from their homelands by the new people.
The owl and the wolf ended their song by asking One Star what they might have done that had
upset the Creator and caused him to treat them so. The young chief had no answer for them. He
knew their troubles, because his tribe had walked a similar path. One Star had listened to the elders
of the tribe speak of times of freedom and plenty. When man and beast shared the earth in
harmony, and were caretakers of the land, not raiders of it.
One Star could not give the owl and the wolf an answer, but he did make them a promise. He
swore to sing their song to all he met. To tell everyone of the importance of keeping nature's
balance, and try to bring man and beast and earth together again in one caring family, as it was
meant to be. One Star is gone now. But his message, the Earth Song, is still in the air for all to hear
and notice.
Reprinted by permission of the author.
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