Exploring
Sound
From
The Basics of Physics Series
Unit of Study
INSTRUCTOR’S GUIDE
EXPLORING SOUND
From
The Basics of Physics Series
A Unit of Study
Instructor’s Guide
Produced by
Colgren Communications
Written by
John Colgren
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EXPLORING SOUND
From The Basics of Physics Series
Introduction......................................................................... 1
Instructional Notes ........................................................... 1
Links to Curriculum Standards ........................................ 2
Student Objectives............................................................ 3
Assessment Tools ............................................................... 3
Teacher Preparation .......................................................... 4
Introducing the Program .................................................. 4
View the Program................................................................ 4
Discussion Questions ......................................................... 4
Blackline Master Descriptions......................................... 5
Enrichment Activities........................................................ 6
Answer Key........................................................................... 7
Internet Resources............................................................ 11
Script of Presentation....................................................... 11
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EXPLORING SOUND
From The Basics of Physics Series
Grade Levels: 5-8
INTRODUCTION
This live-action program is designed for use with the intermediate
grade levels (5-8).
This program is about sound. Sound is all around us. Sometimes we
have to stop and quietly listen to really appreciate all the various
sounds that we come in contact with everyday. But humans can only
appreciate a small range of sounds. Sounds are made up of
vibrations. Humans can only hear sounds within the frequencies of
20 and 20,000 vibrations per second. There are animals that can
detect sounds with much higher frequencies. The whale for instance
can hear up to 200,000 vibrations per second.
INSTRUCTIONAL NOTES
Before presenting this lesson to your students, we suggest that you
preview the program and review this guide and the accompanying
blackline master activities in order to familiarize yourself with their
content.
As you review the materials presented in this guide, you may find it
necessary to make some changes, additions, or deletions to meet the
specific needs of your class. We encourage you to do so, for only by
tailoring this program to your class will they obtain the maximum
instructional benefits afforded by the materials.
It is also suggested that the program presentation take place before
the entire group under your supervision. The lesson activities grow
out of the context of the program; therefore, the presentation
should be a common experience for all students.
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LINKS TO CURRICULUM STANDARDS
This Unit of Study addresses the following National Science
Education Standards for grades 5-8:
Science as Inquiry
Content Standard A:
• Abilities necessary to do scientific inquiry
Plan and conduct simple investigations.
Employ simple equipment and tools to gather data.
Use data to construct a reasonable explanation.
Communicate investigations and explanations.
• Understanding about scientific inquiry
Physical Science
Content Standard B:
• Energy is a property of many substances and is associated with
heat, light, electricity, mechanical motion, sound, nuclei, and the
nature of a chemical. Energy is transferred in many ways.
Science and Technology
Content Standard E:
• Abilities of technological design
• Understanding about science and technology
People have always had questions about their world. Science is
one way of answering questions and explaining the natural world.
People have always had problems and invented tools and
techniques to solve problems.
Scientists and engineers often work in teams.
Tools help scientists make better observations, measurements,
and equipment for investigations.
History and Nature of Science
Content Standard G:
• Science as a human endeavor
Science and technology have been practiced for a long time.
Men and women have made a variety of contributions throughout
the history of science and technology.
Although men and women using scientific inquiry have learned
much about the objects, events, and phenomena in nature, much
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more remains to be understood. Science will never be finished.
Many people choose science as a career and devote their entire
lives to studying it.
STUDENT OBJECTIVES
After viewing the video and participating in the lesson activities,
the students should be able to do the following:
• Describe how the human ear works.
• Describe how some animals such as bats use echo location to
find their way and capture food.
• Describe why there is no sound in outer space.
• Explain how the Doppler effect works.
• Define terms such as wavelength, frequency, crest, trough,
and pitch.
• Recognize that sound travels slower than light.
• Describe how sound is produced by vibration.
• Recognize that sounds travel at different speeds through
different substances.
• Compare the hearing ability of different animals.
ASSESSMENT TOOLS
This lesson provides you with three different assessment tools.
Together they make it possible to follow closely the progress of
your students and to judge their mastery of the subject matter.
The Pre-Test (Blackline Master 1) can be used to get some idea
of students’ understanding of the topic before the program is
presented.
The Post-Test (Blackline Master 15) can be used as a final test
for the lesson.
The Program Quiz and its accompanying answer sheet (Blackline
Master 2) can be used either as a way to introduce the topic
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prior to showing the program or to judge student mastery once
the program has been presented.
TEACHER PREPARATION
View the program and review the accompanying activities.
Duplicate any blackline masters you wish to distribute. If you
plan to use the Program Quiz, which immediately follows the
program presentation, you may wish to have copies of the quiz
ready to distribute at the completion of the program. Also, plan
to pause the tape between questions if students require more
time.
INTRODUCING THE PROGRAM
Ask the students to close their eyes and quietly listen to the
sounds all around them. After a minute or so ask students to
describe and identify some of the sounds they heard. Maybe
there was the sound of the ventilation system or the hum of a
computer fan. Today’s program is about sound. How sounds are
produced and how they travel.
VIEW THE PROGRAM
Viewing time for this program is 15 minutes. The program quiz
that follows the presentation will take about three minutes when
you build in pauses for recording answers.
DISCUSSION QUESTIONS
You may wish to conduct a discussion after viewing the program
based on the following:
1. Discuss how some animals such as bats and dolphins use echo
location to hunt for food? How has that idea been used by
humans to help map the ocean floor?
2. How have television shows and movies misled audiences to
believe that there are sounds in outer space?
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BLACKLINE MASTER DESCRIPTIONS
This program contains fifteen blackline masters that can be used
to reinforce ideas and information presented in the program.
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Blackline Master 1, Pre-test, provides a way of finding out
how much students know about the material covered in this
lesson before you present it. Student scores on the PreTest can be compared with their scores on the final PostTest (Blackline Master 15).
Blackline Master 2, Program Quiz, is to be used at the end
of the program. At the completion of the program, there is a
short quiz. The narrator will read the questions which are
displayed on the screen. Students can use Blackline Master
2 to record their answers. Answers to the questions are
provided in the Answer Key section of this instructor’s guide.
Blackline Master 3, Vocabulary, contains the twenty
important words and their definitions associated with a study
of sound. Students are to match the definitions in column B
with the terms in column A.
Blackline Master 4, Vibrating Ruler, is an experiment about
vibrating rulers and it explores ideas associated with the
length of the vibrating ruler as well as the transfer of sound
through some different substances.
Blackline Master 5, Things That Vibrate, is an experiment
for examining the behavior of various vibrating objects.
Blackline Master 6, Dixie Cup Telephone, is an experiment
for building a homemade string telephone.
Blackline Master 7, Reflected Sound, is an experiment to
demonstrate how sound can bounce or reflect off of objects.
Blackline Master 8, Sound Reflection,is an experiment for
determining how different substances can be used to soften
or deaden sounds.
Blackline Master 9, Noisemaker, provides the directions
for building a paper noisemaker.
Blackline Master 10, The Human Ear, is an information
sheet about the workings of the human ear.
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Blackline Master 11, Animal Comparison, provides
information about the hearing ranges of some animals. There
are three questions for students to respond to with short
answers. Question three asks students to design a chart or
graph that represents the information on this page. Have
the students consider various ways to display this
information.
Blackline Master 12, Two Ears Help Find the Source of a
Sound, is an experiment for testing a person’s ability to
distinguish between slight differences in perceiving the
tapping sound that travels through the hose to each ear.
Students should work in teams of three and take turns with
each job.
Blackline Master 13, Resonance, is an experiment to
determine how various sounds in the room can be separated
into different frequencies.
Blackline Master 14, Decibels, is an information sheet that
lists the decibel levels of common sounds. This sheet can
lead to a good discussion about how sounds above 90 decibels
can be harmful if we are exposed to them for extended
periods of time.
Blackline Master 15, Quiz,is an evaluation tool for this unit.
ENRICHMENT ACTIVITIES
1.
Buy a decibel meter at Radio Shack and have students take
turns investigating different areas of the school or home
where sounds are present. Have them keep a record of the
location, the type of sound and the decibel reading. Think
about places like the boiler room, playground, gym class,
cafeteria, etc.
2. Have students build homemade instruments.
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ANSWER KEY
•
Blackline Master 1, Pre-Test
A. Matching
1. e
2. b
3. c
4. a
5. d
6. g
7. f
B. Short Answer
1. Sound travels faster in solids such as metals because the
atoms and molecules are closely packed.
2. Bats and dolphins use echo location to navigate and find their
food. They emit an ultrasonic sound that bounces against
objects or prey and then reflects or bounces back to the
animal. This provides a picture of what is around them.
3. There is no sound is space because there are no gases for
the sound to travel through. Without a medium to travel
through sound is impossible.
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Blackline Master 2, Program Quiz
1. Light travels faster. You see the fireworks before you hear
the explosion.
2. Sound travels faster in solids because the atoms and
molecules of the solid are packed closer together.
3. The animal produces an ultrasonic sound that radiates away
from the animal. The sound bounces off of surrounding
objects and bounces back to the animal allowing the bat or
porpoise to create an image of their surroundings.
4. There is no sound in space because there is no medium for
the sound waves to travel through.
5. It means the sound is created by 150 vibrations per second.
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6. An echo is possible if a sound bounces off a smooth surface
and is reflected.
7. Musical instruments can be divided into three groups;
percussion, string, and wind.
8. A decibel is the unit of measurement used to represent the
loudness of a sound.
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Blackline Master 3, Vocabulary
1. E
2. K
3. R
6. S
7. B
8. C
11. Q
12. F
13. L
16. T
17. P
18. M
4.
9.
14.
19.
O
J
N
I
5. D
10. G
15. A
20. H
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Blackline Master 4, Vibrating Ruler
Observations:
1. The sound of the ruler depends on the surface the ruler is
resting on.
2. The sound will have a greater frequency.
3. A short section will give a high pitched sound and a long
section will give a low pitched sound.
4. The pin should sound loud when tapped on the meter stick.
5. The metal bar will have a different quality to the sound.
Conclusions:
These demonstrations show how sound is created when objects
vibrate. The ruler will cause different sounds depending on what
it is made, how it is twanged, and how much of it is extended
over the edge of what it is resting on.
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Blackline Master 5, Things That Vibrate
Observations:
1. The tuning fork produces a repeating sound and vibrates.
2. The aluminum ball will bounce away from the fork if they are
brought near each other.
3. The water splashes around as the vibrating prongs are
brought near it.
4. The rubber band gives off a sound and vibrates.
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5. Stretched across the width of the shoebox the sound will be
lower than across the length of the shoebox.
6. The sound can be changed based on the way the neck of the
balloon is held.
Conclusion: These experiments deal with the ability to change
the pitch of a sound.
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Blackline Master 6, Dixie Cup Telephone
Conclusion:
The sound vibrates the string and the sound is transferred to
the other cup.
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Blackline Master 7, Reflected Sound
Conclusion:
The individual results depend on the materials that are used.
Smooth surfaces reflect sounds well. Materials made of cork or
cloth will soften the reflection of the sound.
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Blackline Master 8, Sound Reflection
Results depend on the materials selected by the individuals.
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Blackline Master 9, Noisemaker
Answers will vary.
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Blackline Master 10, The Human Ear
This is an information sheet.
Blackline Master 11, Animal Comparison
1. Bats and dolphins depend on echo location to find their way in
murky water or to find food. They use the ultrasonic sounds
because these sounds are above the hearing ability of their
prey.
2. Dogs and cats can hear sounds above the human range. They
could be hearing a sound from a refrigerator or other
appliance that we can’t hear.
3. Answers will vary.
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Blackline Master 12, Two Ears Help Find the Source of a
Sound
We have two ears so that we can determine where sounds are
coming from.
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Blackline Master 13, Resonance
Observations:
1. Answers will vary
2. The longer tubes
3. The shortest tubes
4. The shortest tubes
5. The longest tubes
It is the vibrating air column in the tube that we hear. The
longer the column of air the slower it tends to vibrate. So long
tubes pick up low frequency sounds and short tubes pick up high
pitched sounds.
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Blackline Master 14, Decibels
This is an information sheet that can lead to a good discussion
about harmful decibel levels and what people can do to avoid
hearing loss or damage.
•
1.
Blackline Master 15, Post Test
Light is faster than sound. We see the lightning before hearing
the thunder.
We see the fireworks before hearing the
explosion.
Bats and dolphins use echo location to find food and to identify
what their surroundings are like.
The three primary types of instruments are percussion, winds,
and string.
A decibel is the unit of measurement for the loudness of sound.
An echo can occur when a sound reflects off a smooth surface.
There is no sound in outer space because there is nothing for the
sound waves to travel through. The vacuum of space means there
are no gases present.
2.
3.
4.
5.
6.
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7. The Doppler effect happens when a sound is moving towards or
away from you. The sound sounds high pitched if it is coming
near you and it is low pitched as it moves away.
8. An oscilloscope is an electronic device capable of showing what
sound waves look like.
9. Sound travels faster in liquids and solids because the atoms and
molecules of liquids and solids are closer together than the
atoms and molecules of air.
10. A kilohertz is one thousand hertz and a megahertz is one million
hertz.
INTERNET RESOURCES
The following websites may be valuable sources of additional
information to reinforce the objectives of this lesson:
1. http://library.thinkquest.org/19537/physics.html
A
site
designed by high school students. Worth a visit.
2. http://www.sci.mus.mn.us/sound/nocss/top.html Site sponsored
by the Science Museum of Minnesota and the Minnesota
Orchestra. Good activities, discussions, performances, etc.
3. http://www.silcom.com/~aludwig/musicand.htm Music and sound
waves is the title for these pages. Intended for a sophisticated
vocabulary it does contain some nice animations.
Script of Program Narration
EXPLORING SOUND
INTRODUCTION TO SOUND WAVES
Sounds are everywhere. Close your eyes and just listen. Think of
familiar sounds. What comes to mind? Birds chirping, lawn mowers
in the morning, fire engines racing to a fire, rockets lifting off the
ground. Could you picture those things? But what if we take away
the sound?
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Sound is important to our daily lives. It helps us to experience the
world around us. Without sound, things just don’t seem right.
Sound is possible because of vibrations. Something has to be
vibrating, moving back and forth. Sound travels as longitudinal
waves. We can demonstrate this idea with a slinky. The slinky is
stretched and one end is given a push. A wave is set in motion and it
travels the length of the slinky. Sound can only travel when there is
something through which the vibrations can travel. Air is the most
common substance through which sound travels, but actually, sound
can travel through many things other than air. In some substances,
sound even travels faster than it does in air. So how fast is sound?
In air it travels 343 meters per second or 750 miles per hour. This
is a little more than 1,000 feet per second. For comparison, a
sprinter can run about 11 meters per second or about 36 feet per
second. Traffic on the highway travels about 30 meters per second
or about 98 feet per second.
Here is a comparison of the speed of sound in different materials. In
water, sound travels about four times faster than in air, and in steel,
sound travels almost 15 times faster. Can you guess why sound
travels faster in liquids and solids? Well, think about the atoms and
molecules contained in gases, liquids, and solids. The particles are
closer together in liquids and solids, so sound can travel faster
because the particles can hit each other more easily.
When you watch a fireworks display, you see the explosions before
you hear them. Which travels faster, sound or light? Well, think
about another situation, like a thunderstorm. We see the lightning
and then hear the thunder. Light is actually much faster than sound.
Light travels 300,000 kilometers 186,000 miles, per second. That
would be like traveling from New York to San Francisco sixty two
times in one second. Sound compared to light is barely moving.
When an object vibrates, it disturbs the air molecules around it.
The molecules carry the energy of the sound in all directions. The
sound travels out as waves. Think of a wave in water. If we drop a
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pebble into a pond, the waves move out along the surface from where
the pebble hit the water. Sound travels in longitudinal waves like
these, but in all directions. The vibrations of the sound disturb the
air molecules.
In outer space, where there are no gases, sound would be impossible.
The emptiness of space is called a vacuum. There are no molecules
of matter for sounds to move through, so, in outer space, there are
no sounds. Two things are needed for making sounds: vibrating
matter to create the waves and a medium or something to carry the
sound waves.
We can receive sounds over great distances when we use a telephone
or when we dial up a radio station. When you use the telephone, a
small microphone in the telephone changes the sound of your voice
into electrical signals. This signal travels to the person with whom
you are speaking, and is changed back into sound when it goes into a
small loudspeaker in that person’s phone. Along the way between the
two people, the electric signal may be carried through wires, changed
to radio signals and sent through the air, or even changed to light to
travel through fiber optic cable.
This flashlight has been altered so it can show how light can be used
to transmit sound. This solar cell picks up the rapid fluctuations and
the brightness of the flashlight bulb and turns it back to electrical
pulses.
THE DOPPLER EFFECT AND RAREFACTION
You may have noticed that sirens sound high-pitched when coming
towards you, and then when moving away, the sound is lower-pitched.
This effect is called the Doppler Effect. It is explained that, as the
sound approaches, the waves are pushed closer together, causing a
high-pitched sound. When the sound is moving away from you, the
waves are further apart and the sound is lower.
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Here is a tuning fork. When we strike it, it gives off a certain tone.
If we could see what is happening, it might look like this: the tuning
fork is vibrating. As the prongs move out, they push against the air
molecules around them. The molecules push together, which is called
compression. Then, there are places where the molecules are spread
out between the compressions. This spread out section is called
rarefaction. The whole sound wave travels as a longitudinal wave.
So, compressing some molecules and leaving areas between the
compressions with fewer molecules carries the sound.
The slinky is pulled and held across the floor. We pull together some
of the slinky sections and then let it go. Notice that it travels the
length of the slinky with areas of compression and rarefaction.
Remember that sound needs a material to travel through.
FREQUENCY
The rate of vibration is called the frequency of the sound.
Frequency is how many times the sound vibrates in a certain amount
of time. Frequency is measured in a unit called the hertz, after
Heinrich Hertz, who demonstrated the existence of radio waves in
1886. One vibration per second is one hertz, two vibrations per
second is two hertz and so on. Humans can hear sounds that range
from 20 to 20,000 hertz. That means we can’t hear sounds that
have frequencies less than 20 vibrations per second, or greater than
20,000 vibrations per second.
Sounds below 20 hertz are called infrasonic, and those above 20,000
hertz are called ultrasonic. Even though we can’t hear above 20,000
hertz, there are other animals that can. For instance, we can’t hear
a dog whistle because the sound is so high, but dogs certainly can
hear it. The dog whistle produces a sound at 30,000 hertz. Here is a
chart of the frequencies some animals can hear and produce. Notice
that the bat and porpoise have huge ranges of sounds that they can
make and hear. That’s because they use their ability to produce and
hear ultrasonic sounds to help them find things.
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You can tune in radio stations because each station is given a certain
frequency that they can use for transmission. The station sends its
signal as a radio wave that corresponds to a certain number of
vibrations per second.
On the AM dial, the frequencies are
measured in kilohertz. This means that if you dial to 940 kHz on
your radio dial, then the frequency of that situation is 940,000
vibrations per second. On the FM dial, everything is measured in
megahertz, so the frequencies are even higher. Remember, humans
can only hear up to 20,000 hertz, so these signals are well above
what we can hear. The signals are out there all the time, all we need
is something to convert them to sounds we can hear.
ECHOS AND ECHOLOCATION
The bat hunts by sending out an ultrasonic signal that bounces off an
insect and returns to the bat’s big ears. The bat can determine the
exact location of the insect and catch it in complete darkness. He
doesn’t use his eyes; he uses echo location. The high-pitched sound
he makes bounce off things and return to his ears, creating a picture
of what is around him.
Porpoises and dolphins use echo location to swim in murky water or to
locate objects in the water.
The best conditions for an echo are when a sound strikes a hard,
smooth surface. The sound is reflected, or bounces, off the surface
and we hear it again. Echoes and sound reflection can cause
problems in certain situations, such as at a movie or in a concert hall.
To cut down on reflected sound, materials are used that help absorb
the sound. In a movie theater they have carpeting and drapes and
padded seats to help soundproof. In this recording booth, the walls
have soundproofing tiles that are made of cushioned material with
many tiny holes to deaden the sound. Sometimes we need to get the
sound reflected out to a large area, so curved surfaces are used to
bounce the sound out to the audience.
REVERBERATION
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Reverberation is the repeated reflection of sound waves against
smooth surfaces. That’s why sounds in a gym seem to echo and sound
strange. Another problem is called interference. This is where two
sounds come together. If they come together at the same time, and
their compressions and rarefactions match up, the sound is
strengthened and becomes louder. However, if the compression of
one wave hits the rarefaction of the other, they cancel, or wipe each
other out, and there is silence. That’s why when people design
concert halls, they try to consider the reflection of the sound and
how it will produce reverberation or interference.
DECIBELS
Sound can be measured in terms of loudness. To do that, we use an
instrument that measures the loudness of sounds in units called
decibels, which are abbreviated dB. A soft sound is rated as one and
a loud sound is 120 decibels. This meter is used to measure the
loudness of sounds in decibels. Here are some examples of common
sounds and their decibel readings. Breathing is rated at about 10
decibels. Talking is 30 to 60 decibels. A vacuum cleaner is 60 to 80
decibels. Motorcycles and subway trains are from 70 to 90 decibels.
Thunder is 95 to 115 decibels. A rock band is about 110 decibels.
And a jet taking off ranges from 120 to 140 decibels. Humans will
experience pain when decibels reach 140. Exposure to loud sounds
can cause hearing damage, and even loss. People who work around
loud machinery need to wear protective ear gear.
THE EAR
We hear sound waves passing through the air with our ears. The
outer ear helps to collect and direct the sound waves to the tube
leading to the middle ear. In the middle ear is called the eardrum,
which is a membrane that vibrates with the pressure changes caused
by the sound waves. The eardrum is attached to several tiny bones.
They are called the hammer, the anvil, and the stirrup. They amplify,
or increase, the sound. The bones are attached to the cochlea in the
inner ear. The cochlea is filled with a liquid that changes the signal
to an electrical message. This message is then sent to the auditory
nerve, which goes to the brain. The brain then interprets the sound.
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MUSIC
Music is an important and enjoyable part of our lives. Music is
different from noise because music is made up of regular patterns.
Music has pitch, rhythm, and quality. Pitch has to do with the
frequency of vibrations. Close vibrations produce high notes, and
spread-out vibrations produce low notes.
Rhythm is a regular pattern of tones. The quality of music is made
up of the different tones. We can use this oscilloscope to look at an
electrical representation of sounds. This electronic keyboard is
connected to the oscilloscope. When we hit a key on the keyboard,
we can see a picture of the wave pattern. The high points are called
crests, and the low points are troughs. The distance between one
crest and the next crest, or from one trough to the next trough, is
called wavelength. If we play a low note and then a high note, you
can see how the frequency changes. Low notes have a frequency that
is spread out and the wavelength is greater. A high note has
wavelengths and a frequency that are closer together. Notice that
if we change to a different instrument sound, the result is a wave
pattern that is different in shape. The piano and the trumpet
keyboard sound have different wave patterns. The oscilloscope is
helpful when analyzing and studying sounds.
There are three categories for musical instruments called strings,
wind, and percussion. Each type of instrument must be able to set
particles of air into motion. Again, vibration is the key to sound.
With stringed instruments, the string is plucked or stroked and
begins to vibrate. The hollow part of the instrument helps to
increase the volume of this vibration. Here is an example with a
tuning fork. We strike the fork and the sound given off is faint,
until we touch the fork to the sounding box, which increases the
volume, or amplitude, of the tuning fork.
Wind instruments rely on vibrating air inside the instrument to
create the tones of instrument. Sometimes, the tones are changed
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by covering and uncovering holes that make the column of air shorter
or longer. Sometimes the instrument creates the sound by changing
the length of the air column, such as sliding the u-shaped tube in and
out on a trombone.
Percussion instruments can make music when a stretched membrane
is struck with a hand, stick, or mallet. The stretched membrane is
tightly attached to one end of a frame. When the membrane is hit,
it set the air to vibrating in the frame. Different sized frames
produce different sounds.
Of course you don’t need expensive musical instruments to make your
own interesting sounds. Things from around the house can be used.
Here are some examples: This first one is made from a section of
plastic tubing. Twirl this around your head and notice the strange
sound. Whirl it faster and faster to hear the sound change. You can
get a wine glass to sing by pouring about an inch of water into the
glass. Then wet your finger and rub it slowly and gently around the
rim of the glass. Be sure to hold the glass with your other hand so
that it doesn’t tip over. Try different amounts of water in the glass
to see how the sound changes. Make a guitar from the materials
shown. The eye screws are used to tighten the fishing line so that
you can get the air vibrating. Make different notes. Move your
finger up and down the neck of the guitar and hold the fishing line
down to make it shorter or longer. Short line is high-pitched and
long line is low-pitched. Stretching materials, such as plastic, paper,
or rubber from a balloon over different containers can make drums.
Try large bowls and even cardboard boxes and tubes. For a wind
instrument, try different lengths of an old hose.
DIGITAL SOUND
We get great sound from laser discs, such as CDs and DVDs. Laser
discs carry digital information. That means the information is
represented by the ones and zeros of the binary code. Any number
can be represented in the binary code. For instance, the number one
is represented as 1, the number 2 is zero one, and the number 3 is
one, one. Laser discs are made up of microscopic pits. The pits
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represent a zero and the spaces that don’t have a pit represent a
one.
A laser beam is directed to the reflective side of the disc and
responds to the pits or pit less areas. So the laser beam is focused
on a very small part of the disc. If it hits a flat pit less area the
laser beam is reflected back to the detector and is registered as a
one. If it hits a pit then very little of the light is reflected back to
the detector and it is registered as a zero. The laser beam never
touches the disc and because it has a clear protective coating the
disc will not wear out.
A SOUND REVIEW
Sound is an important part of our lives. We collect information
about things around us by listening. We are relaxed and entertained
by music. Or we rely on sound to get our ideas from one place to
another through the use of telephones. Sounds are important in the
animal world also. Some animals use ultrasonic sound to catch their
food or find their way. Others use sound to send out warnings of
danger. Some use sound to call to each other or to signal that this is
their territory. However it may be used, sound is a major part of our
daily routines.
Now it is time for the program Quiz. There are eight short answer
questions.
Question number one: Which travels faster, sound or light?
Question number two:
Sound travels at different speeds in
different substances. Why does it travel faster in metal than in air?
Question number three: How do animals, like bats or porpoises, use
ultrasonic sounds to find their way or to catch food?
Question number four: In outer space there are no sounds. Why?
Question number five: The hertz is used to measure the frequency
of sound. If something is rated at 150 hertz, what does that mean?
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Question number six: What is an echo?
Question number seven:
musical instruments?
What are the three primary types of
Question number eight: What is a decibel?
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