NCERT Textbook - Sound Class 8 Notes | EduRev

General Science for UPSC (Civil Services) Prelims

Created by: Divey Sethi

Class 8 : NCERT Textbook - Sound Class 8 Notes | EduRev

 Page 1


SOUND
SOUND
H
ow do you come to know that a
‘period’ is over in your school?
You come to know easily that
someone is at your door when he knocks
or you hear the sound of the doorbell.
Most of the time you can make out that
someone is approaching you by just
hearing the foot steps.
You might have played a game called
hide and seek. In this game a person is
blind-folded and has to catch the
remaining players. How is the blind-
folded person able to guess which player
is closest to her?
Sound plays an important role in our
life. It helps us to communicate with one
another. We hear a variety of sounds in
our surroundings.
Make a list of sounds you hear in
your surroundings.
In the music room of your school you
hear the sounds made by musical
instruments like flute, tabla,
harmonium etc. (Fig 13.1).
How is sound produced? How does it
travel from one place to another? How
do we hear sound? Why are some sounds
louder than others? We shall discuss
such questions in this chapter.
Fig. 13.1 : Some musical instruments
Tabla
Harmonium
Sitar
Flute
© NCERT
not to be republished
Page 2


SOUND
SOUND
H
ow do you come to know that a
‘period’ is over in your school?
You come to know easily that
someone is at your door when he knocks
or you hear the sound of the doorbell.
Most of the time you can make out that
someone is approaching you by just
hearing the foot steps.
You might have played a game called
hide and seek. In this game a person is
blind-folded and has to catch the
remaining players. How is the blind-
folded person able to guess which player
is closest to her?
Sound plays an important role in our
life. It helps us to communicate with one
another. We hear a variety of sounds in
our surroundings.
Make a list of sounds you hear in
your surroundings.
In the music room of your school you
hear the sounds made by musical
instruments like flute, tabla,
harmonium etc. (Fig 13.1).
How is sound produced? How does it
travel from one place to another? How
do we hear sound? Why are some sounds
louder than others? We shall discuss
such questions in this chapter.
Fig. 13.1 : Some musical instruments
Tabla
Harmonium
Sitar
Flute
© NCERT
not to be republished
SCIENCE 160
13.1 Sound is Produced by a
Vibrating Body
Touch the school bell when not in use.
What do you feel? Again touch it when
producing sound. Can you feel it
vibrating?
Activity 13.1
Take a metal plate (or a shallow
frying pan). Hang it at a convenient
place in such a way that it does not
touch any wall. Now strike it with a
stick (Fig.13.2). Touch the plate or
pan gently with your finger. Do you
feel the vibrations?
Fig. 13.2 : Striking a frying pan
Again strike the plate with the stick
and hold it tightly with your hands
immediately after striking. Do you
still hear the sound? Touch the
plate after it stops producing sound.
Can you feel the vibrations now?
The to and fro or back and forth
motion of an object is termed as
vibration as you learnt in Class VII.
When a tightly stretched band is
plucked, it vibrates and produces
sound. When it stops vibrating, it does
not produce any sound.
Activity 13.3
Take a metal dish. Pour water in it.
Strike it at its edge by a spoon (Fig.
13.4). Do you hear a sound? Again
strike the plate and then touch it.
Can you feel the dish vibrating?
Strike the dish again. Look at the
surface of water. Do you see any
waves there? Now hold the dish.
What change do you observe on the
surface of water? Can you explain
the change? Is there a hint to
connect sound with the vibrations
of a body?
Activity 13.2
Take a rubber band. Put it around
the longer side of a pencil box
(Fig. 13.3). Insert two pencils
between the box and the stretched
rubber. Now, pluck the rubber band
somewhere in the middle. Do you
hear any sound? Does the band
vibrate?
Fig. 13.3 : Plucking the rubber band
© NCERT
not to be republished
Page 3


SOUND
SOUND
H
ow do you come to know that a
‘period’ is over in your school?
You come to know easily that
someone is at your door when he knocks
or you hear the sound of the doorbell.
Most of the time you can make out that
someone is approaching you by just
hearing the foot steps.
You might have played a game called
hide and seek. In this game a person is
blind-folded and has to catch the
remaining players. How is the blind-
folded person able to guess which player
is closest to her?
Sound plays an important role in our
life. It helps us to communicate with one
another. We hear a variety of sounds in
our surroundings.
Make a list of sounds you hear in
your surroundings.
In the music room of your school you
hear the sounds made by musical
instruments like flute, tabla,
harmonium etc. (Fig 13.1).
How is sound produced? How does it
travel from one place to another? How
do we hear sound? Why are some sounds
louder than others? We shall discuss
such questions in this chapter.
Fig. 13.1 : Some musical instruments
Tabla
Harmonium
Sitar
Flute
© NCERT
not to be republished
SCIENCE 160
13.1 Sound is Produced by a
Vibrating Body
Touch the school bell when not in use.
What do you feel? Again touch it when
producing sound. Can you feel it
vibrating?
Activity 13.1
Take a metal plate (or a shallow
frying pan). Hang it at a convenient
place in such a way that it does not
touch any wall. Now strike it with a
stick (Fig.13.2). Touch the plate or
pan gently with your finger. Do you
feel the vibrations?
Fig. 13.2 : Striking a frying pan
Again strike the plate with the stick
and hold it tightly with your hands
immediately after striking. Do you
still hear the sound? Touch the
plate after it stops producing sound.
Can you feel the vibrations now?
The to and fro or back and forth
motion of an object is termed as
vibration as you learnt in Class VII.
When a tightly stretched band is
plucked, it vibrates and produces
sound. When it stops vibrating, it does
not produce any sound.
Activity 13.3
Take a metal dish. Pour water in it.
Strike it at its edge by a spoon (Fig.
13.4). Do you hear a sound? Again
strike the plate and then touch it.
Can you feel the dish vibrating?
Strike the dish again. Look at the
surface of water. Do you see any
waves there? Now hold the dish.
What change do you observe on the
surface of water? Can you explain
the change? Is there a hint to
connect sound with the vibrations
of a body?
Activity 13.2
Take a rubber band. Put it around
the longer side of a pencil box
(Fig. 13.3). Insert two pencils
between the box and the stretched
rubber. Now, pluck the rubber band
somewhere in the middle. Do you
hear any sound? Does the band
vibrate?
Fig. 13.3 : Plucking the rubber band
© NCERT
not to be republished
SOUND 161
We see that a vibrating object
produces sound. In some cases, the
vibrations are easily visible to us. But
in most cases, their amplitude is so small
that we cannot see them. However, we
can feel them.
Activity 13.4
Take a hollow coconut shell and
make a musical instrument Ektara.
You can also make it with the help
of an earthen pot (Fig. 13.5). Play
this instrument and identify its
vibrating part.
Table 13.1 : Musical instruments and
their Vibrating Parts.
S.No. Musical Vibrating part
Instrument producing sound
1. Veena Stretched string
2. Tabla Stretched
 membrane
3. Flute Air-column
4. _________ _________
5. _________ _________
6. _________ _________
7. _________ _________
Many of you might have seen the
manjira (cymbals), the ghatam, and the
noot  (mudpots) and the kartal. These
instruments are commonly used in
many parts of our country. These
musical instruments are simply beaten
or struck. Can you name a few other
musical instruments of this type?
You, too can make a musical
instrument.
Fig. 13.4 : Vibrating plate produces waves
in water
Fig. 13.6 : A few more musical instruments
Ghatam
Make a list of familiar musical
instruments and identify their vibrating
parts. A few examples are given in Table
13.1. Complete the rest of the Table.
Fig. 13.5 : Ektara
Manjira
© NCERT
not to be republished
Page 4


SOUND
SOUND
H
ow do you come to know that a
‘period’ is over in your school?
You come to know easily that
someone is at your door when he knocks
or you hear the sound of the doorbell.
Most of the time you can make out that
someone is approaching you by just
hearing the foot steps.
You might have played a game called
hide and seek. In this game a person is
blind-folded and has to catch the
remaining players. How is the blind-
folded person able to guess which player
is closest to her?
Sound plays an important role in our
life. It helps us to communicate with one
another. We hear a variety of sounds in
our surroundings.
Make a list of sounds you hear in
your surroundings.
In the music room of your school you
hear the sounds made by musical
instruments like flute, tabla,
harmonium etc. (Fig 13.1).
How is sound produced? How does it
travel from one place to another? How
do we hear sound? Why are some sounds
louder than others? We shall discuss
such questions in this chapter.
Fig. 13.1 : Some musical instruments
Tabla
Harmonium
Sitar
Flute
© NCERT
not to be republished
SCIENCE 160
13.1 Sound is Produced by a
Vibrating Body
Touch the school bell when not in use.
What do you feel? Again touch it when
producing sound. Can you feel it
vibrating?
Activity 13.1
Take a metal plate (or a shallow
frying pan). Hang it at a convenient
place in such a way that it does not
touch any wall. Now strike it with a
stick (Fig.13.2). Touch the plate or
pan gently with your finger. Do you
feel the vibrations?
Fig. 13.2 : Striking a frying pan
Again strike the plate with the stick
and hold it tightly with your hands
immediately after striking. Do you
still hear the sound? Touch the
plate after it stops producing sound.
Can you feel the vibrations now?
The to and fro or back and forth
motion of an object is termed as
vibration as you learnt in Class VII.
When a tightly stretched band is
plucked, it vibrates and produces
sound. When it stops vibrating, it does
not produce any sound.
Activity 13.3
Take a metal dish. Pour water in it.
Strike it at its edge by a spoon (Fig.
13.4). Do you hear a sound? Again
strike the plate and then touch it.
Can you feel the dish vibrating?
Strike the dish again. Look at the
surface of water. Do you see any
waves there? Now hold the dish.
What change do you observe on the
surface of water? Can you explain
the change? Is there a hint to
connect sound with the vibrations
of a body?
Activity 13.2
Take a rubber band. Put it around
the longer side of a pencil box
(Fig. 13.3). Insert two pencils
between the box and the stretched
rubber. Now, pluck the rubber band
somewhere in the middle. Do you
hear any sound? Does the band
vibrate?
Fig. 13.3 : Plucking the rubber band
© NCERT
not to be republished
SOUND 161
We see that a vibrating object
produces sound. In some cases, the
vibrations are easily visible to us. But
in most cases, their amplitude is so small
that we cannot see them. However, we
can feel them.
Activity 13.4
Take a hollow coconut shell and
make a musical instrument Ektara.
You can also make it with the help
of an earthen pot (Fig. 13.5). Play
this instrument and identify its
vibrating part.
Table 13.1 : Musical instruments and
their Vibrating Parts.
S.No. Musical Vibrating part
Instrument producing sound
1. Veena Stretched string
2. Tabla Stretched
 membrane
3. Flute Air-column
4. _________ _________
5. _________ _________
6. _________ _________
7. _________ _________
Many of you might have seen the
manjira (cymbals), the ghatam, and the
noot  (mudpots) and the kartal. These
instruments are commonly used in
many parts of our country. These
musical instruments are simply beaten
or struck. Can you name a few other
musical instruments of this type?
You, too can make a musical
instrument.
Fig. 13.4 : Vibrating plate produces waves
in water
Fig. 13.6 : A few more musical instruments
Ghatam
Make a list of familiar musical
instruments and identify their vibrating
parts. A few examples are given in Table
13.1. Complete the rest of the Table.
Fig. 13.5 : Ektara
Manjira
© NCERT
not to be republished
SCIENCE 162
13.2 Sound Produced by
Humans
Speak loudly for a while or sing a song,
or buzz like a bee. Put your hand on
your throat as shown in Fig. 13.8. Do
you feel any vibrations?
In humans, the sound is produced
by the voice box or the larynx. Put your
fingers on the throat and find a hard
bump that seems to move when you
swallow. This part of the body is known
as the voice box. It is at the upper end
of the windpipe. Two vocal cords, are
stretched across the voice box or larynx
in such a way that it leaves a narrow
slit between them for the passage of air
(Fig.13.8).
Fig. 13.7 : Jaltrang
When we pluck the string of an
instrument, like the sitar, the sound
that we hear is not only that of the
string. The whole instrument is forced
to vibrate, and it is the sound of the
vibration of the instrument that we
hear. Similarly, when we strike the
membrane of a mridangam, the sound
that we hear is not only that of the
membrane but of the whole body of
the instrument.
When we speak, does
any part of our body
vibrate?
Fig.13.8 : Voice box in humans
When the lungs force air through the
slit, the vocal cords vibrate, producing
sound. Muscles attached to the vocal
cords can make the cords tight or loose.
When the vocal cords are tight and thin,
the type or quality of voice is different
Activity 13.5
Take 6-8 metal bowls or tumblers.
Fill them with water up to  different
levels, increasing gradually from
one end to the other. Now take
a  pencil and strike the bowls gently.
Strike all of them in succession. You
will hear a pleasant sound. This is
your Jaltrang (Fig.13.7).
© NCERT
not to be republished
Page 5


SOUND
SOUND
H
ow do you come to know that a
‘period’ is over in your school?
You come to know easily that
someone is at your door when he knocks
or you hear the sound of the doorbell.
Most of the time you can make out that
someone is approaching you by just
hearing the foot steps.
You might have played a game called
hide and seek. In this game a person is
blind-folded and has to catch the
remaining players. How is the blind-
folded person able to guess which player
is closest to her?
Sound plays an important role in our
life. It helps us to communicate with one
another. We hear a variety of sounds in
our surroundings.
Make a list of sounds you hear in
your surroundings.
In the music room of your school you
hear the sounds made by musical
instruments like flute, tabla,
harmonium etc. (Fig 13.1).
How is sound produced? How does it
travel from one place to another? How
do we hear sound? Why are some sounds
louder than others? We shall discuss
such questions in this chapter.
Fig. 13.1 : Some musical instruments
Tabla
Harmonium
Sitar
Flute
© NCERT
not to be republished
SCIENCE 160
13.1 Sound is Produced by a
Vibrating Body
Touch the school bell when not in use.
What do you feel? Again touch it when
producing sound. Can you feel it
vibrating?
Activity 13.1
Take a metal plate (or a shallow
frying pan). Hang it at a convenient
place in such a way that it does not
touch any wall. Now strike it with a
stick (Fig.13.2). Touch the plate or
pan gently with your finger. Do you
feel the vibrations?
Fig. 13.2 : Striking a frying pan
Again strike the plate with the stick
and hold it tightly with your hands
immediately after striking. Do you
still hear the sound? Touch the
plate after it stops producing sound.
Can you feel the vibrations now?
The to and fro or back and forth
motion of an object is termed as
vibration as you learnt in Class VII.
When a tightly stretched band is
plucked, it vibrates and produces
sound. When it stops vibrating, it does
not produce any sound.
Activity 13.3
Take a metal dish. Pour water in it.
Strike it at its edge by a spoon (Fig.
13.4). Do you hear a sound? Again
strike the plate and then touch it.
Can you feel the dish vibrating?
Strike the dish again. Look at the
surface of water. Do you see any
waves there? Now hold the dish.
What change do you observe on the
surface of water? Can you explain
the change? Is there a hint to
connect sound with the vibrations
of a body?
Activity 13.2
Take a rubber band. Put it around
the longer side of a pencil box
(Fig. 13.3). Insert two pencils
between the box and the stretched
rubber. Now, pluck the rubber band
somewhere in the middle. Do you
hear any sound? Does the band
vibrate?
Fig. 13.3 : Plucking the rubber band
© NCERT
not to be republished
SOUND 161
We see that a vibrating object
produces sound. In some cases, the
vibrations are easily visible to us. But
in most cases, their amplitude is so small
that we cannot see them. However, we
can feel them.
Activity 13.4
Take a hollow coconut shell and
make a musical instrument Ektara.
You can also make it with the help
of an earthen pot (Fig. 13.5). Play
this instrument and identify its
vibrating part.
Table 13.1 : Musical instruments and
their Vibrating Parts.
S.No. Musical Vibrating part
Instrument producing sound
1. Veena Stretched string
2. Tabla Stretched
 membrane
3. Flute Air-column
4. _________ _________
5. _________ _________
6. _________ _________
7. _________ _________
Many of you might have seen the
manjira (cymbals), the ghatam, and the
noot  (mudpots) and the kartal. These
instruments are commonly used in
many parts of our country. These
musical instruments are simply beaten
or struck. Can you name a few other
musical instruments of this type?
You, too can make a musical
instrument.
Fig. 13.4 : Vibrating plate produces waves
in water
Fig. 13.6 : A few more musical instruments
Ghatam
Make a list of familiar musical
instruments and identify their vibrating
parts. A few examples are given in Table
13.1. Complete the rest of the Table.
Fig. 13.5 : Ektara
Manjira
© NCERT
not to be republished
SCIENCE 162
13.2 Sound Produced by
Humans
Speak loudly for a while or sing a song,
or buzz like a bee. Put your hand on
your throat as shown in Fig. 13.8. Do
you feel any vibrations?
In humans, the sound is produced
by the voice box or the larynx. Put your
fingers on the throat and find a hard
bump that seems to move when you
swallow. This part of the body is known
as the voice box. It is at the upper end
of the windpipe. Two vocal cords, are
stretched across the voice box or larynx
in such a way that it leaves a narrow
slit between them for the passage of air
(Fig.13.8).
Fig. 13.7 : Jaltrang
When we pluck the string of an
instrument, like the sitar, the sound
that we hear is not only that of the
string. The whole instrument is forced
to vibrate, and it is the sound of the
vibration of the instrument that we
hear. Similarly, when we strike the
membrane of a mridangam, the sound
that we hear is not only that of the
membrane but of the whole body of
the instrument.
When we speak, does
any part of our body
vibrate?
Fig.13.8 : Voice box in humans
When the lungs force air through the
slit, the vocal cords vibrate, producing
sound. Muscles attached to the vocal
cords can make the cords tight or loose.
When the vocal cords are tight and thin,
the type or quality of voice is different
Activity 13.5
Take 6-8 metal bowls or tumblers.
Fill them with water up to  different
levels, increasing gradually from
one end to the other. Now take
a  pencil and strike the bowls gently.
Strike all of them in succession. You
will hear a pleasant sound. This is
your Jaltrang (Fig.13.7).
© NCERT
not to be republished
SOUND 163
from that when they are loose and
thick. Let us see how the vocal cords
function.
Activity 13.6
Take two rubber strips of the same
size. Place these two pieces one
above the other and stretch them
tight. Now blow air through the gap
between them [Fig. 13.9(a)]. As the
air blows through the stretched
rubber strips, a sound is produced.
You can also take a piece of paper
with a narrow slit and hold it
between your fingers as shown in
Fig. 13.9 (b). Now blow through the
slit and listen to the sound. Our
vocal cords produce sound in a
similar manner.
(a)
(b)
Fig. 13.9 (a), (b) : Working of vocal cords
The vocal cords in men are about
20mm long. In women these are about
5mm shorter. Children have very
short vocal cords. This is the reason
why the voices of men, women and
children are different.
13.3 Sound Needs a Medium
for Propagation
When you call up your friend who is
standing at a distance, your friend is
able to hear your voice. How does the
sound travel to her?
Activity 13.7
Take a metal glass tumbler. Make
sure that it is dry. Place a cell phone
in it. (Remember that the cell phone
must not be kept in water .) Ask your
friend to give a ring on this cell
phone from another cell phone.
Listen to the ring carefully.
Now, surround the rim of the
tumbler with your hands (Fig.
13.10). Put your mouth on the
Fig. 13.10 : Sound needs a medium to travel
© NCERT
not to be republished
Read More

< Previous

Complete Syllabus of Class 8

Dynamic Test

Content Category

Related Searches

study material

,

video lectures

,

Exam

,

MCQs

,

Semester Notes

,

Extra Questions

,

Viva Questions

,

Free

,

NCERT Textbook - Sound Class 8 Notes | EduRev

,

NCERT Textbook - Sound Class 8 Notes | EduRev

,

pdf

,

Previous Year Questions with Solutions

,

Summary

,

Objective type Questions

,

ppt

,

practice quizzes

,

NCERT Textbook - Sound Class 8 Notes | EduRev

,

past year papers

,

shortcuts and tricks

,

Sample Paper

,

Important questions

,

mock tests for examination

;