The
Science Notebook
Gilbert Sound - Chapter II
NOTE: This book was published around 1920 as a
manual to accompany the Gilbert Sound set. The
set and manual were part of the "Boy Engineering" series,
While some of the experiments and activities here may be
safely done as written, some of them may be considered
hazardous in today's world. In addition, some of
the information contained in this book is either outdated
or inaccurate. Therefore, this book is probably
best appreciated for its historical value rather than as a
source of current information and good experiments. If
you try anything here, please understand that you do
so at your own risk. See our Terms of
Use.
Pages 16-24
[16]
Chapter II
ORIGIN OF SOUND
Now we are ready for experiments and scientific research into the
questions we asked in the earlier pages of this book. What is
sound? What is it that comes from our throats when we
talk? How does it travel to our ears?
There are three things concerning sound that are necessary before
there can be any sound in the proper sense of the word. (1)
Sound must begins somewhere; (2) it must travel to us; and (3) it
must be heard by the ear. First let us see where sound begins.
Take a cork hammer (see Figure 5) and lightly strike the edge of a
wine glass. It gives a strong clinking sound. Now put
your finger on the edge of the glass. Two things should
happen. First, you feel a slight tremble or vibration on your
finger
(16)
GILBERT
SOUND EXPERIMENTS 17
and, second, the sound ceases. It should be plain to you then
that the glass was vibrating and when you stopped this vibration you
stopped the sound. Now let us figure out what this vibration
is.
Special Note. As many
of the following experiments require a tuning fork to be vibrated,
we will explain different methods of accomplishing this. Each
method has its advantages for certain experiments.
1st. Hold a tuning fork by the base and strike one of the
prongs sharply against the heel of your shoe or any solid object,
such as a table top. You will not be able to hear much of a
sound from the fork as you hold it in your hand, but if you bring it
close to your ear or place it with the base firmly against a table
top or box cover (See Figure 6) you will hear a clear, even tone.
2nd. Force the base of a tuning fork into a hole bored in a
block of wood. Hold the block firm with the left hand and with the
right, take a wood or cork hammer and strike one prong of the fork
with a sharp blow. (See Figure 7.)
18 GILBERT BOY ENGINEERING
3rd. Proceed as in the second method, except that instead of
striking the fork with a hammer you take a violin bow, well resined,
and draw it across the face of the tuning fork. (See Figure
8.) This will set the fork into violent vibration, and is
GILBERT
SOUND EXPERIMENTS 19
the method which you will find most satisfactory for a majority of
your experiments.
Experiment No. 6.
Attach a tuning fork to a block in place on a table or box and
strike one of the prongs of the tuning fork with a cork
hammer. Now hold a shoe button by means of a thread (see
Figure 9) against one side of the tuning fork. The resulting
action of the button will prove that the tuning fork is a vibrating
body in that it is moving with a "to and fro" motion like the
pendulum. As the sound grows fainter the button does not
rebound so far, because like the "to and fro" motion of the pendulum
the vibrations or oscillations are growing smaller. This
proves the theory that a sound-producing
body is a vibrating body.
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GILBERT BOY ENGINEERING
Experiment No. 7. Pick up a
vibrating tuning fork and place the base of it between your teeth
and feel the vibration. (See Figure 10.) Now take the
tuning fork and set it in vibration by hitting it with a cork hammer
and then bring it in contact with the surface of the water.
(See Figure 11.) To make the experiment more effective,
scatter some lycopodium powder on the surface of the water.
The action of the fork will then produce beautiful waves.
Experiment No. 8.
Strike a bell with a cork hammer. (See Figure 12.) See
if you can observe the vibration or motion of
GILBERT
SOUND EXPERIMENTS 21
the bell, and notice that the sound grows less as the vibration
diminishes. We are certainly convinced by this time that
sounds are produced by vibrations, and it should be conclusively
proved to you that the motion which we studied in connection With
the pendulum is the same kind of motion that is producing these
sounds - that is, "to and fro" motion.
HOW
WE MAKE SOUNDS WITH OUR THROATS
The apparatus that nature has provided for making sounds with our
throats is very simple and easily understood.
In our throats are two cords, known as the vocal cords, and when we
talk air waves from the lungs throw these cords into vibration,
producing the different sounds. The wonderful part
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GILBERT BOY ENGINEERING
of the mechanism is that we can produce so many sounds with only two
cords, the human throat being so constructed that the cords can be
lengthened or shortened by means of muscles. Tubes leading
from these cords, in conjunction with the lips, enable us to produce
almost any sound.
VIBRATION
OF AIR COLUMNS
We have discovered now that sound is produced by vibrating
bodies. You should know that it is also produced by the
vibrations of columns of air contained in tubes and pipes, as in
many musical instruments. There are three classes of air
instruments or mouth-piece instruments by means of which
columns of air are vibrated in the instruments themselves.
1st. We have the
instruments in which the air is blown
GILBERT
SOUND EXPERIMENTS 23
across the sharp edge of the opening, such as the whistle, the flute
and pipe organ. (See Figure 13.)
2nd. We have air
instruments in which the sound is produced by blowing air past a
thin tongue, known as a reed. (See Figure 14.) The
reed opens and closes the air column.
3rd. There is that
air instrument used in all bands, known as the cornet, where sound
is produced by vibration of the lips on the mouthpiece. (See
Figure 15.)
MUSICAL
FLAMES
There are probably no prettier experiments in the study of sound
than those in which tones are obtained from tubes by means of a
flame.
Procure of glass tube about 1/4 of an inch in diameter and 6 inches
long. Bend this tube at right angles and, by means of a
staple, fasten it to a small board under a tripod covered with wire
gauze. (See Figure 16.) Connect the bent glass tube into
a gas jet and make a light,
24
GILBERT BOY ENGINEERING
holding a match a over the wire gauze. Adjust the
pressure of the gas and the position of the bent glass tube until a
blue flickering flame is obtained. Now place another tube,
about 2 inches in diameter and of almost any length, over the flame
and you will at once here loud musical tones. By trying tubes
of different lengths, you will get many fascinating results.
As you may have concluded already, the sounds are produced by
vibrations of the air within the large glass tube.
"The Science Notebook"
Copyright 2008-2018 - Norman Young
