NCERT Textbook: Air Around Us | Science & Technology for UPSC CSE PDF Download

 Page 1


11
Air Around us
W
e have learnt in Chapter 6 that
all living things require air.
But, have you ever seen air?
You might not have seen air, but, surely
you must have felt its presence in so
many ways. You notice it when the
leaves of the trees rustle or the clothes
hanging on a clothes-line sway. Pages
of an open book begin fluttering
when the fan is switched on. The moving
air makes it possible for you to fly your
kite. Do you remember Activity 3 in
Chapter 3 in which you separated the
sand and sawdust by winnowing?
Winnowing is more effective in moving
air. You may have noticed that during
storms the wind blows at a very high
speed. It may even uproot trees and blow
off the rooftops.
Have you ever played with a firki
(Fig. 11.1)?
Move it a little, back and
forth. Observe, what happens.
Does the firki rotate? What makes a firki
rotate — moving air, isn’t it?
Have you seen a weather cock
(Fig. 11.3)? It shows the direction in
which the air is moving at that place.
Fig. 11.1 Different types of  firki
Fig. 11.2 Making a simple firki
Fig. 11.3 A weather cock
Activity 1
Let us make a firki of our own, following
the instructions shown in Fig. 11.2.
Hold the stick of the firki and place it
in different directions in an open area.
11.1 IS AIR PRESENT EVERYWHERE
AROUND US?
Close your fist — what do you have in
it? Nothing? Try the following activity
to find out.
Activity 2
Take an empty open bottle. Is it really
empty or does it have something inside?
Turn it, upside down. Is something
inside it, now?
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Page 2


11
Air Around us
W
e have learnt in Chapter 6 that
all living things require air.
But, have you ever seen air?
You might not have seen air, but, surely
you must have felt its presence in so
many ways. You notice it when the
leaves of the trees rustle or the clothes
hanging on a clothes-line sway. Pages
of an open book begin fluttering
when the fan is switched on. The moving
air makes it possible for you to fly your
kite. Do you remember Activity 3 in
Chapter 3 in which you separated the
sand and sawdust by winnowing?
Winnowing is more effective in moving
air. You may have noticed that during
storms the wind blows at a very high
speed. It may even uproot trees and blow
off the rooftops.
Have you ever played with a firki
(Fig. 11.1)?
Move it a little, back and
forth. Observe, what happens.
Does the firki rotate? What makes a firki
rotate — moving air, isn’t it?
Have you seen a weather cock
(Fig. 11.3)? It shows the direction in
which the air is moving at that place.
Fig. 11.1 Different types of  firki
Fig. 11.2 Making a simple firki
Fig. 11.3 A weather cock
Activity 1
Let us make a firki of our own, following
the instructions shown in Fig. 11.2.
Hold the stick of the firki and place it
in different directions in an open area.
11.1 IS AIR PRESENT EVERYWHERE
AROUND US?
Close your fist — what do you have in
it? Nothing? Try the following activity
to find out.
Activity 2
Take an empty open bottle. Is it really
empty or does it have something inside?
Turn it, upside down. Is something
inside it, now?
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116 SCIENCE
Now, dip the open mouth of the bottle
into the bucket filled with water as
shown in Fig. 11.4. Observe the bottle.
Does water enter the bottle? Now tilt the
bottle slightly. Does the water now enter
the bottle? Do you see bubbles coming
out of the bottle or hear any bubbly
sound? Can you now guess what was
in the bottle?
Yes! You are right. It is “air”, that was
present in the bottle. The bottle was not
empty at all. In fact, it was filled
completely with air even when you
turned it upside down. That is why you
notice that water does not enter the
bottle when it is pushed in an inverted
position, as there was no space for air
to escape. When the bottle was tilted,
the air was able to come out in the form
of bubbles, and water filled up the empty
space that the air has occupied.
This activity shows that air occupies
space. It fills all the space in the bottle.
It is present everywhere around us. Air
has no colour and one can see through
it. It is transparent.
Our earth is surrounded by a thin
layer of air. This layer extends up to
many kilometres above the surface of
the earth and is called atmosphere. As
we move higher in the atmosphere, the
air gets rarer.
Fig. 11.4 Experiments with an empty bottle
Fig. 11.5 Mountaineers carry oxygen cylinders
with them
Now can you think, mountaineers
carry oxygen cylinders with them, while
climbing high mountains (Fig. 11.5)?
11.2 WHAT IS AIR MADE UP OF?
Until the eighteenth century, people
thought that air was just one substance.
Experiments have proved that it is really
not so. Air is a mixture of many gases.
What kind of a mixture is it? Let us find
out about some of the major
components of this mixture, one by one.
Water vapour
We have learnt earlier that air contains
water vapour. We also saw that, when
air comes in contact with a cool surface,
it condenses and drops of water appear
on the cooled surfaces. The presence of
water vapour in air is important for the
water cycle in nature.
Oxygen
Activity 3
In the presence of your teacher, fix two
small candles of the same length on a
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Page 3


11
Air Around us
W
e have learnt in Chapter 6 that
all living things require air.
But, have you ever seen air?
You might not have seen air, but, surely
you must have felt its presence in so
many ways. You notice it when the
leaves of the trees rustle or the clothes
hanging on a clothes-line sway. Pages
of an open book begin fluttering
when the fan is switched on. The moving
air makes it possible for you to fly your
kite. Do you remember Activity 3 in
Chapter 3 in which you separated the
sand and sawdust by winnowing?
Winnowing is more effective in moving
air. You may have noticed that during
storms the wind blows at a very high
speed. It may even uproot trees and blow
off the rooftops.
Have you ever played with a firki
(Fig. 11.1)?
Move it a little, back and
forth. Observe, what happens.
Does the firki rotate? What makes a firki
rotate — moving air, isn’t it?
Have you seen a weather cock
(Fig. 11.3)? It shows the direction in
which the air is moving at that place.
Fig. 11.1 Different types of  firki
Fig. 11.2 Making a simple firki
Fig. 11.3 A weather cock
Activity 1
Let us make a firki of our own, following
the instructions shown in Fig. 11.2.
Hold the stick of the firki and place it
in different directions in an open area.
11.1 IS AIR PRESENT EVERYWHERE
AROUND US?
Close your fist — what do you have in
it? Nothing? Try the following activity
to find out.
Activity 2
Take an empty open bottle. Is it really
empty or does it have something inside?
Turn it, upside down. Is something
inside it, now?
Rationalised 2023-24
116 SCIENCE
Now, dip the open mouth of the bottle
into the bucket filled with water as
shown in Fig. 11.4. Observe the bottle.
Does water enter the bottle? Now tilt the
bottle slightly. Does the water now enter
the bottle? Do you see bubbles coming
out of the bottle or hear any bubbly
sound? Can you now guess what was
in the bottle?
Yes! You are right. It is “air”, that was
present in the bottle. The bottle was not
empty at all. In fact, it was filled
completely with air even when you
turned it upside down. That is why you
notice that water does not enter the
bottle when it is pushed in an inverted
position, as there was no space for air
to escape. When the bottle was tilted,
the air was able to come out in the form
of bubbles, and water filled up the empty
space that the air has occupied.
This activity shows that air occupies
space. It fills all the space in the bottle.
It is present everywhere around us. Air
has no colour and one can see through
it. It is transparent.
Our earth is surrounded by a thin
layer of air. This layer extends up to
many kilometres above the surface of
the earth and is called atmosphere. As
we move higher in the atmosphere, the
air gets rarer.
Fig. 11.4 Experiments with an empty bottle
Fig. 11.5 Mountaineers carry oxygen cylinders
with them
Now can you think, mountaineers
carry oxygen cylinders with them, while
climbing high mountains (Fig. 11.5)?
11.2 WHAT IS AIR MADE UP OF?
Until the eighteenth century, people
thought that air was just one substance.
Experiments have proved that it is really
not so. Air is a mixture of many gases.
What kind of a mixture is it? Let us find
out about some of the major
components of this mixture, one by one.
Water vapour
We have learnt earlier that air contains
water vapour. We also saw that, when
air comes in contact with a cool surface,
it condenses and drops of water appear
on the cooled surfaces. The presence of
water vapour in air is important for the
water cycle in nature.
Oxygen
Activity 3
In the presence of your teacher, fix two
small candles of the same length on a
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117 AIR AROUND US
table. Light both the candles. Cover one
of the candles with an inverted glass
tumbler. Observe both the candles
carefully.
Do both the candles continue to burn
or go off?
You must have observed that the
candle covered with glass tumbler got
extinguished after some time, whereas
the other candle continued burning.
What can be the reason for this?
Think about it.
It seems that the candle got
extinguished because the component
inside of the glass tumbler, which
supports burning, is limited. Most of the
component is used up by the burning
candles. However, the other candle is
getting continued supply of air. This
component of air, which supports
burning, is known as oxygen.
Nitrogen
In Activity 3 did you observe that air is
still present in the glass bottle even after
the candle blew out? This indicates the
presence of some component in the air,
which does not support burning. The
major part of air (which does not
support burning candle) is nitrogen.
Carbon dioxide
In a closed room, if there is some
material that is burning, you may
have felt suffocation. This is due to
excess of carbon dioxide that may be
accumulating in the room, as the
burning continues. Carbon dioxide
makes up a small component of the air
around us. Plants and animals consume
oxygen for respiration and produce
carbon dioxide. Plant and animal matter
also consumes oxygen on burning and
produces mainly carbon dioxide and a
few other gases. It is advisable not to
burn dry leaves and discarded remains
of the crop, which pollute our
surroundings.
Dust and smoke
The burning of fuel also produces
smoke. Smoke contains a few gases and
fine dust particles and is often harmful.
That is why you see long chimneys in
factories. This takes the harmful smoke
and gases away from our noses, but,
brings it closer to the birds flying up in
the sky!
Dust particles are always present
in air.
Activity 4
Find a sunny room in your school/
home. Close all the doors and windows
with curtains pulled down to make the
Fig. 15.6 Air has oxygen
Fig. 11.6 Air has oxygen
Candle
Glass tumbler
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Page 4


11
Air Around us
W
e have learnt in Chapter 6 that
all living things require air.
But, have you ever seen air?
You might not have seen air, but, surely
you must have felt its presence in so
many ways. You notice it when the
leaves of the trees rustle or the clothes
hanging on a clothes-line sway. Pages
of an open book begin fluttering
when the fan is switched on. The moving
air makes it possible for you to fly your
kite. Do you remember Activity 3 in
Chapter 3 in which you separated the
sand and sawdust by winnowing?
Winnowing is more effective in moving
air. You may have noticed that during
storms the wind blows at a very high
speed. It may even uproot trees and blow
off the rooftops.
Have you ever played with a firki
(Fig. 11.1)?
Move it a little, back and
forth. Observe, what happens.
Does the firki rotate? What makes a firki
rotate — moving air, isn’t it?
Have you seen a weather cock
(Fig. 11.3)? It shows the direction in
which the air is moving at that place.
Fig. 11.1 Different types of  firki
Fig. 11.2 Making a simple firki
Fig. 11.3 A weather cock
Activity 1
Let us make a firki of our own, following
the instructions shown in Fig. 11.2.
Hold the stick of the firki and place it
in different directions in an open area.
11.1 IS AIR PRESENT EVERYWHERE
AROUND US?
Close your fist — what do you have in
it? Nothing? Try the following activity
to find out.
Activity 2
Take an empty open bottle. Is it really
empty or does it have something inside?
Turn it, upside down. Is something
inside it, now?
Rationalised 2023-24
116 SCIENCE
Now, dip the open mouth of the bottle
into the bucket filled with water as
shown in Fig. 11.4. Observe the bottle.
Does water enter the bottle? Now tilt the
bottle slightly. Does the water now enter
the bottle? Do you see bubbles coming
out of the bottle or hear any bubbly
sound? Can you now guess what was
in the bottle?
Yes! You are right. It is “air”, that was
present in the bottle. The bottle was not
empty at all. In fact, it was filled
completely with air even when you
turned it upside down. That is why you
notice that water does not enter the
bottle when it is pushed in an inverted
position, as there was no space for air
to escape. When the bottle was tilted,
the air was able to come out in the form
of bubbles, and water filled up the empty
space that the air has occupied.
This activity shows that air occupies
space. It fills all the space in the bottle.
It is present everywhere around us. Air
has no colour and one can see through
it. It is transparent.
Our earth is surrounded by a thin
layer of air. This layer extends up to
many kilometres above the surface of
the earth and is called atmosphere. As
we move higher in the atmosphere, the
air gets rarer.
Fig. 11.4 Experiments with an empty bottle
Fig. 11.5 Mountaineers carry oxygen cylinders
with them
Now can you think, mountaineers
carry oxygen cylinders with them, while
climbing high mountains (Fig. 11.5)?
11.2 WHAT IS AIR MADE UP OF?
Until the eighteenth century, people
thought that air was just one substance.
Experiments have proved that it is really
not so. Air is a mixture of many gases.
What kind of a mixture is it? Let us find
out about some of the major
components of this mixture, one by one.
Water vapour
We have learnt earlier that air contains
water vapour. We also saw that, when
air comes in contact with a cool surface,
it condenses and drops of water appear
on the cooled surfaces. The presence of
water vapour in air is important for the
water cycle in nature.
Oxygen
Activity 3
In the presence of your teacher, fix two
small candles of the same length on a
Rationalised 2023-24
117 AIR AROUND US
table. Light both the candles. Cover one
of the candles with an inverted glass
tumbler. Observe both the candles
carefully.
Do both the candles continue to burn
or go off?
You must have observed that the
candle covered with glass tumbler got
extinguished after some time, whereas
the other candle continued burning.
What can be the reason for this?
Think about it.
It seems that the candle got
extinguished because the component
inside of the glass tumbler, which
supports burning, is limited. Most of the
component is used up by the burning
candles. However, the other candle is
getting continued supply of air. This
component of air, which supports
burning, is known as oxygen.
Nitrogen
In Activity 3 did you observe that air is
still present in the glass bottle even after
the candle blew out? This indicates the
presence of some component in the air,
which does not support burning. The
major part of air (which does not
support burning candle) is nitrogen.
Carbon dioxide
In a closed room, if there is some
material that is burning, you may
have felt suffocation. This is due to
excess of carbon dioxide that may be
accumulating in the room, as the
burning continues. Carbon dioxide
makes up a small component of the air
around us. Plants and animals consume
oxygen for respiration and produce
carbon dioxide. Plant and animal matter
also consumes oxygen on burning and
produces mainly carbon dioxide and a
few other gases. It is advisable not to
burn dry leaves and discarded remains
of the crop, which pollute our
surroundings.
Dust and smoke
The burning of fuel also produces
smoke. Smoke contains a few gases and
fine dust particles and is often harmful.
That is why you see long chimneys in
factories. This takes the harmful smoke
and gases away from our noses, but,
brings it closer to the birds flying up in
the sky!
Dust particles are always present
in air.
Activity 4
Find a sunny room in your school/
home. Close all the doors and windows
with curtains pulled down to make the
Fig. 15.6 Air has oxygen
Fig. 11.6 Air has oxygen
Candle
Glass tumbler
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118 SCIENCE
room dark. Now, open the door or a
window facing the sun, just a little, in
such a way that it allows sunlight to
enter the room only through a slit.
Look carefully at the incoming beam
of sunlight.
Do you see some tiny shining
particles moving in the beam of sunlight
(Fig. 11.7)? What are these particles?
During winters you might have
observed similar beam of sunlight filter
through the trees in which dust particles
appear to dance merrily around!
This shows that air also contains
dust particles. The presence of dust
particles in air varies from time to time,
and from place to place.
We inhale air when we breathe
through our nostrils. Fine hair and
mucus are present inside the nose to
Paheli  wants to know, why
the transparent glass of
windows, if not wiped off
regularly, appears hazy?
Fig. 11.7 Observing presence of dust in air with
sunlight
Fig.11.8 Policemen regulating traffic at a crowded
crossing often wear a mask
Boojho wants to know, why
during an incident of
fire, one is advised to
wrap a woollen blanket
over a burning object.
Boojho is asking you, why
do you think, the policeman
in Fig.11.8 is wearing a
mask?
prevent dust particles from getting into
the respiratory system.
Do you recall being scolded by your
parents when you breathe through your
mouth? If you do that, harmful dust
particles may enter your body.
We may conclude, then, that air
contains some gases, water vapour and
dust particles. The gases in air are
mainly nitrogen, oxygen, small amount
of carbon dioxide, and many other
gases. However, there may be some
Rationalised 2023-24
Page 5


11
Air Around us
W
e have learnt in Chapter 6 that
all living things require air.
But, have you ever seen air?
You might not have seen air, but, surely
you must have felt its presence in so
many ways. You notice it when the
leaves of the trees rustle or the clothes
hanging on a clothes-line sway. Pages
of an open book begin fluttering
when the fan is switched on. The moving
air makes it possible for you to fly your
kite. Do you remember Activity 3 in
Chapter 3 in which you separated the
sand and sawdust by winnowing?
Winnowing is more effective in moving
air. You may have noticed that during
storms the wind blows at a very high
speed. It may even uproot trees and blow
off the rooftops.
Have you ever played with a firki
(Fig. 11.1)?
Move it a little, back and
forth. Observe, what happens.
Does the firki rotate? What makes a firki
rotate — moving air, isn’t it?
Have you seen a weather cock
(Fig. 11.3)? It shows the direction in
which the air is moving at that place.
Fig. 11.1 Different types of  firki
Fig. 11.2 Making a simple firki
Fig. 11.3 A weather cock
Activity 1
Let us make a firki of our own, following
the instructions shown in Fig. 11.2.
Hold the stick of the firki and place it
in different directions in an open area.
11.1 IS AIR PRESENT EVERYWHERE
AROUND US?
Close your fist — what do you have in
it? Nothing? Try the following activity
to find out.
Activity 2
Take an empty open bottle. Is it really
empty or does it have something inside?
Turn it, upside down. Is something
inside it, now?
Rationalised 2023-24
116 SCIENCE
Now, dip the open mouth of the bottle
into the bucket filled with water as
shown in Fig. 11.4. Observe the bottle.
Does water enter the bottle? Now tilt the
bottle slightly. Does the water now enter
the bottle? Do you see bubbles coming
out of the bottle or hear any bubbly
sound? Can you now guess what was
in the bottle?
Yes! You are right. It is “air”, that was
present in the bottle. The bottle was not
empty at all. In fact, it was filled
completely with air even when you
turned it upside down. That is why you
notice that water does not enter the
bottle when it is pushed in an inverted
position, as there was no space for air
to escape. When the bottle was tilted,
the air was able to come out in the form
of bubbles, and water filled up the empty
space that the air has occupied.
This activity shows that air occupies
space. It fills all the space in the bottle.
It is present everywhere around us. Air
has no colour and one can see through
it. It is transparent.
Our earth is surrounded by a thin
layer of air. This layer extends up to
many kilometres above the surface of
the earth and is called atmosphere. As
we move higher in the atmosphere, the
air gets rarer.
Fig. 11.4 Experiments with an empty bottle
Fig. 11.5 Mountaineers carry oxygen cylinders
with them
Now can you think, mountaineers
carry oxygen cylinders with them, while
climbing high mountains (Fig. 11.5)?
11.2 WHAT IS AIR MADE UP OF?
Until the eighteenth century, people
thought that air was just one substance.
Experiments have proved that it is really
not so. Air is a mixture of many gases.
What kind of a mixture is it? Let us find
out about some of the major
components of this mixture, one by one.
Water vapour
We have learnt earlier that air contains
water vapour. We also saw that, when
air comes in contact with a cool surface,
it condenses and drops of water appear
on the cooled surfaces. The presence of
water vapour in air is important for the
water cycle in nature.
Oxygen
Activity 3
In the presence of your teacher, fix two
small candles of the same length on a
Rationalised 2023-24
117 AIR AROUND US
table. Light both the candles. Cover one
of the candles with an inverted glass
tumbler. Observe both the candles
carefully.
Do both the candles continue to burn
or go off?
You must have observed that the
candle covered with glass tumbler got
extinguished after some time, whereas
the other candle continued burning.
What can be the reason for this?
Think about it.
It seems that the candle got
extinguished because the component
inside of the glass tumbler, which
supports burning, is limited. Most of the
component is used up by the burning
candles. However, the other candle is
getting continued supply of air. This
component of air, which supports
burning, is known as oxygen.
Nitrogen
In Activity 3 did you observe that air is
still present in the glass bottle even after
the candle blew out? This indicates the
presence of some component in the air,
which does not support burning. The
major part of air (which does not
support burning candle) is nitrogen.
Carbon dioxide
In a closed room, if there is some
material that is burning, you may
have felt suffocation. This is due to
excess of carbon dioxide that may be
accumulating in the room, as the
burning continues. Carbon dioxide
makes up a small component of the air
around us. Plants and animals consume
oxygen for respiration and produce
carbon dioxide. Plant and animal matter
also consumes oxygen on burning and
produces mainly carbon dioxide and a
few other gases. It is advisable not to
burn dry leaves and discarded remains
of the crop, which pollute our
surroundings.
Dust and smoke
The burning of fuel also produces
smoke. Smoke contains a few gases and
fine dust particles and is often harmful.
That is why you see long chimneys in
factories. This takes the harmful smoke
and gases away from our noses, but,
brings it closer to the birds flying up in
the sky!
Dust particles are always present
in air.
Activity 4
Find a sunny room in your school/
home. Close all the doors and windows
with curtains pulled down to make the
Fig. 15.6 Air has oxygen
Fig. 11.6 Air has oxygen
Candle
Glass tumbler
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118 SCIENCE
room dark. Now, open the door or a
window facing the sun, just a little, in
such a way that it allows sunlight to
enter the room only through a slit.
Look carefully at the incoming beam
of sunlight.
Do you see some tiny shining
particles moving in the beam of sunlight
(Fig. 11.7)? What are these particles?
During winters you might have
observed similar beam of sunlight filter
through the trees in which dust particles
appear to dance merrily around!
This shows that air also contains
dust particles. The presence of dust
particles in air varies from time to time,
and from place to place.
We inhale air when we breathe
through our nostrils. Fine hair and
mucus are present inside the nose to
Paheli  wants to know, why
the transparent glass of
windows, if not wiped off
regularly, appears hazy?
Fig. 11.7 Observing presence of dust in air with
sunlight
Fig.11.8 Policemen regulating traffic at a crowded
crossing often wear a mask
Boojho wants to know, why
during an incident of
fire, one is advised to
wrap a woollen blanket
over a burning object.
Boojho is asking you, why
do you think, the policeman
in Fig.11.8 is wearing a
mask?
prevent dust particles from getting into
the respiratory system.
Do you recall being scolded by your
parents when you breathe through your
mouth? If you do that, harmful dust
particles may enter your body.
We may conclude, then, that air
contains some gases, water vapour and
dust particles. The gases in air are
mainly nitrogen, oxygen, small amount
of carbon dioxide, and many other
gases. However, there may be some
Rationalised 2023-24
119 AIR AROUND US
of the container. Do you see tiny bubbles
on the inside (Fig. 11.10)?
These bubbles come from the air
dissolved in water. When you heat the
water, to begin with, the air dissolved in
it escapes. As you continue heating, the
water itself turns into vapour and finally
begins to boil. We learnt in Chapters 5
and 6, that the animals living in water
use the dissolved oxygen in water.
The organisms that live in soil also
need oxygen to respire, isn’t it? How do
they get the air they need, for
respiration?
Activity 6
Take a lump of dry soil in a beaker or a
glass. Add water to it and note what
happens (Fig. 11.11). Do you see
bubbles coming out from soil? These
bubbles indicate the presence of air in
the soil.
When the water is poured on the
lump of soil, it displaces the air which
is seen in the form of bubbles. The
organisms that live inside the soil and
the plant roots respire in this air. A lot Fig. 11.10 Water contains air
variations in the composition of air from
place to place. We see that air contains
mostly nitrogen and oxygen. In fact,
these two gases together make up 99%
of the air. The remaining 1% is
constituted by carbon dioxide and a few
other gases and water vapour (Fig. 11.9).
11.3 HOW DOES OXYGEN BECOME
AVAILABLE TO ANIMALS AND PLANTS
LIVING IN WATER AND SOIL?
Activity 5
Take some water in a glass or metal
container. Heat it slowly on a tripod
stand. Well before the water begins to
boil, look carefully at the inner surface
Here is a question from Paheli, “Will
the tiny air bubbles seen before the
water actually boils, also appear if
we do this activity by reheating
boiled water kept in an air tight
bottle?” If you do not know
the answer you may try doing
it and see for yourself.
Nitrogen
oxygen
carbon dioxide,
water vapour
and other gases
Fig.11.9 Composition of air
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