NCERT Textbook: Changes Around us | Science & Technology for UPSC CSE PDF Download

 Page 1


46 SCIENCE
6 Changes Around us
W
hat a fun would it be if you
suddenly get some magical
powers to change things
around you. What are the things you
would want to change?
Can some of the changes be grouped
together?
How can we group various changes?
It might help, if we find some similarities
between them.
6.1 CAN ALL CHANGES ALWAYS BE
REVERSED?
Activity 1
Take a balloon and blow it. Take care
that it does not burst. The shape and
size of the balloon have changed
(Fig. 6.1). Now, let the air escape the
balloon.
Fig 6.1 A balloon changes its size and shape on
blowing air into it
Activity 2
Take a piece of paper and fold it as
shown in Fig.6.2. You have changed the
sheet of paper  into a toy aeroplane. You
may have lots of fun in flying this plane.
Once you are tired of it, unfold the
paper again.
We do not have magical powers, of
course. But, we can still change a few
things around us, perhaps many things.
Can you list a few things you can
change around you, with no magic
involved?
Many changes are taking place
around us on their own. In the fields,
the crops change from time to time.
Sometimes, leaves fall from trees, change
colour and dry out. The flowers bloom
and then wither away. Are any changes
happening in your body? Your nails
grow, your hair grows, you grow taller
and your weight increases as you grow.
Did you realise earlier that so many
changes are taking place around you all
the time?
2022-23
Page 2


46 SCIENCE
6 Changes Around us
W
hat a fun would it be if you
suddenly get some magical
powers to change things
around you. What are the things you
would want to change?
Can some of the changes be grouped
together?
How can we group various changes?
It might help, if we find some similarities
between them.
6.1 CAN ALL CHANGES ALWAYS BE
REVERSED?
Activity 1
Take a balloon and blow it. Take care
that it does not burst. The shape and
size of the balloon have changed
(Fig. 6.1). Now, let the air escape the
balloon.
Fig 6.1 A balloon changes its size and shape on
blowing air into it
Activity 2
Take a piece of paper and fold it as
shown in Fig.6.2. You have changed the
sheet of paper  into a toy aeroplane. You
may have lots of fun in flying this plane.
Once you are tired of it, unfold the
paper again.
We do not have magical powers, of
course. But, we can still change a few
things around us, perhaps many things.
Can you list a few things you can
change around you, with no magic
involved?
Many changes are taking place
around us on their own. In the fields,
the crops change from time to time.
Sometimes, leaves fall from trees, change
colour and dry out. The flowers bloom
and then wither away. Are any changes
happening in your body? Your nails
grow, your hair grows, you grow taller
and your weight increases as you grow.
Did you realise earlier that so many
changes are taking place around you all
the time?
2022-23
47 CHANGES AROUND US
Activity 4
Take the same balloon, which you used
in Activity 1. Blow it to its full size and
tie its mouth with a string tightly. Prick
it with the pointed tip of your pencil.
Oops! It burst.
Activity 5
Take the same piece of paper, which you
used in Activity 2.  Draw an aeroplane
on it and cut along its outline (Fig.6.4).
Activity 3
Take some dough and make a ball. Try
to roll out a roti (Fig. 6.3). May be you
are not happy with its shape and
wish to change it back into a ball of
dough again.
Fig 6.2 A toy aeroplane made by folding paper
Fig 6.3 A ball of dough and a rolled out roti
Now, think about the three changes
you observed in Activity 1, 2 and 3.
What do they have in common?
Was it possible to get the balloon back
to its original shape and size?
Was the size of the paper same as
before and after making an aeroplane?
Was it possible to get back the ball of
dough again?
What do you conclude? In each of
the three activities, is it possible to get
back to the material with which we
started our activity? If the answer is yes,
it means that the changes occurring in
these activities can be reversed. Now, let
us repeat the same activities with
a difference.
Fig. 6.4 An aeroplane cut out of paper
Activity 6
Roll out a roti from the ball of dough
again and bake it on a tawa (Fig.6.5).
Suppose, you are asked the same
three questions which you answered
after Activity 3. What would your
answers be, now?
We see that, the changes which have
occurred in the Activity 4, 5 and 6 can
not be reversed.
You use a pencil and an eraser. With
repeated use, their shape and size
change. Can we reverse this change?
Fig 6.5 A roti
2022-23
Page 3


46 SCIENCE
6 Changes Around us
W
hat a fun would it be if you
suddenly get some magical
powers to change things
around you. What are the things you
would want to change?
Can some of the changes be grouped
together?
How can we group various changes?
It might help, if we find some similarities
between them.
6.1 CAN ALL CHANGES ALWAYS BE
REVERSED?
Activity 1
Take a balloon and blow it. Take care
that it does not burst. The shape and
size of the balloon have changed
(Fig. 6.1). Now, let the air escape the
balloon.
Fig 6.1 A balloon changes its size and shape on
blowing air into it
Activity 2
Take a piece of paper and fold it as
shown in Fig.6.2. You have changed the
sheet of paper  into a toy aeroplane. You
may have lots of fun in flying this plane.
Once you are tired of it, unfold the
paper again.
We do not have magical powers, of
course. But, we can still change a few
things around us, perhaps many things.
Can you list a few things you can
change around you, with no magic
involved?
Many changes are taking place
around us on their own. In the fields,
the crops change from time to time.
Sometimes, leaves fall from trees, change
colour and dry out. The flowers bloom
and then wither away. Are any changes
happening in your body? Your nails
grow, your hair grows, you grow taller
and your weight increases as you grow.
Did you realise earlier that so many
changes are taking place around you all
the time?
2022-23
47 CHANGES AROUND US
Activity 4
Take the same balloon, which you used
in Activity 1. Blow it to its full size and
tie its mouth with a string tightly. Prick
it with the pointed tip of your pencil.
Oops! It burst.
Activity 5
Take the same piece of paper, which you
used in Activity 2.  Draw an aeroplane
on it and cut along its outline (Fig.6.4).
Activity 3
Take some dough and make a ball. Try
to roll out a roti (Fig. 6.3). May be you
are not happy with its shape and
wish to change it back into a ball of
dough again.
Fig 6.2 A toy aeroplane made by folding paper
Fig 6.3 A ball of dough and a rolled out roti
Now, think about the three changes
you observed in Activity 1, 2 and 3.
What do they have in common?
Was it possible to get the balloon back
to its original shape and size?
Was the size of the paper same as
before and after making an aeroplane?
Was it possible to get back the ball of
dough again?
What do you conclude? In each of
the three activities, is it possible to get
back to the material with which we
started our activity? If the answer is yes,
it means that the changes occurring in
these activities can be reversed. Now, let
us repeat the same activities with
a difference.
Fig. 6.4 An aeroplane cut out of paper
Activity 6
Roll out a roti from the ball of dough
again and bake it on a tawa (Fig.6.5).
Suppose, you are asked the same
three questions which you answered
after Activity 3. What would your
answers be, now?
We see that, the changes which have
occurred in the Activity 4, 5 and 6 can
not be reversed.
You use a pencil and an eraser. With
repeated use, their shape and size
change. Can we reverse this change?
Fig 6.5 A roti
2022-23
48 SCIENCE
You must have seen a potter working
on his wheel. He shapes a lump of clay
into a pot. Can this change be reversed?
He then bakes the pot in an oven. Now,
can this change be reversed?
Some common changes are given in
Table 6.1. Which of these changes, do
you think can be reversed?
We find that one way we can group
changes is to see if they can be
reversed.
6.2 COULD THERE BE OTHER WAYS
TO BRING A CHANGE?
We all have seen the tools which are used
to dig the soil (Fig. 6.6 ). Have you ever
seen how the iron blade in these tools
is fixed to the wooden handle?
The iron blade of these tools has a
ring in which the wooden handle is
fixed. Normally, the ring is slightly
smaller in size than the wooden handle.
To fix the handle, the ring is heated and
it becomes slightly larger in size
(expands). Now, the handle easily fits
into the ring. When the ring cools down
it contracts and fits tightly on to
the handle.
Table 6.1  Some common changes
Fig. 6.6 Tools are often heated before fixing
wooden handles
Such a change is also used for fixing
the metal rim on a wooden wheel of a
cart as shown in Fig.6.7. Again the
metal rim is made slightly smaller than
the wooden wheel. On heating, the rim
expands and fits onto the wheel. Cold
water is then poured over the rim, which
contracts and fits tightly onto the wheel.
2022-23
Page 4


46 SCIENCE
6 Changes Around us
W
hat a fun would it be if you
suddenly get some magical
powers to change things
around you. What are the things you
would want to change?
Can some of the changes be grouped
together?
How can we group various changes?
It might help, if we find some similarities
between them.
6.1 CAN ALL CHANGES ALWAYS BE
REVERSED?
Activity 1
Take a balloon and blow it. Take care
that it does not burst. The shape and
size of the balloon have changed
(Fig. 6.1). Now, let the air escape the
balloon.
Fig 6.1 A balloon changes its size and shape on
blowing air into it
Activity 2
Take a piece of paper and fold it as
shown in Fig.6.2. You have changed the
sheet of paper  into a toy aeroplane. You
may have lots of fun in flying this plane.
Once you are tired of it, unfold the
paper again.
We do not have magical powers, of
course. But, we can still change a few
things around us, perhaps many things.
Can you list a few things you can
change around you, with no magic
involved?
Many changes are taking place
around us on their own. In the fields,
the crops change from time to time.
Sometimes, leaves fall from trees, change
colour and dry out. The flowers bloom
and then wither away. Are any changes
happening in your body? Your nails
grow, your hair grows, you grow taller
and your weight increases as you grow.
Did you realise earlier that so many
changes are taking place around you all
the time?
2022-23
47 CHANGES AROUND US
Activity 4
Take the same balloon, which you used
in Activity 1. Blow it to its full size and
tie its mouth with a string tightly. Prick
it with the pointed tip of your pencil.
Oops! It burst.
Activity 5
Take the same piece of paper, which you
used in Activity 2.  Draw an aeroplane
on it and cut along its outline (Fig.6.4).
Activity 3
Take some dough and make a ball. Try
to roll out a roti (Fig. 6.3). May be you
are not happy with its shape and
wish to change it back into a ball of
dough again.
Fig 6.2 A toy aeroplane made by folding paper
Fig 6.3 A ball of dough and a rolled out roti
Now, think about the three changes
you observed in Activity 1, 2 and 3.
What do they have in common?
Was it possible to get the balloon back
to its original shape and size?
Was the size of the paper same as
before and after making an aeroplane?
Was it possible to get back the ball of
dough again?
What do you conclude? In each of
the three activities, is it possible to get
back to the material with which we
started our activity? If the answer is yes,
it means that the changes occurring in
these activities can be reversed. Now, let
us repeat the same activities with
a difference.
Fig. 6.4 An aeroplane cut out of paper
Activity 6
Roll out a roti from the ball of dough
again and bake it on a tawa (Fig.6.5).
Suppose, you are asked the same
three questions which you answered
after Activity 3. What would your
answers be, now?
We see that, the changes which have
occurred in the Activity 4, 5 and 6 can
not be reversed.
You use a pencil and an eraser. With
repeated use, their shape and size
change. Can we reverse this change?
Fig 6.5 A roti
2022-23
48 SCIENCE
You must have seen a potter working
on his wheel. He shapes a lump of clay
into a pot. Can this change be reversed?
He then bakes the pot in an oven. Now,
can this change be reversed?
Some common changes are given in
Table 6.1. Which of these changes, do
you think can be reversed?
We find that one way we can group
changes is to see if they can be
reversed.
6.2 COULD THERE BE OTHER WAYS
TO BRING A CHANGE?
We all have seen the tools which are used
to dig the soil (Fig. 6.6 ). Have you ever
seen how the iron blade in these tools
is fixed to the wooden handle?
The iron blade of these tools has a
ring in which the wooden handle is
fixed. Normally, the ring is slightly
smaller in size than the wooden handle.
To fix the handle, the ring is heated and
it becomes slightly larger in size
(expands). Now, the handle easily fits
into the ring. When the ring cools down
it contracts and fits tightly on to
the handle.
Table 6.1  Some common changes
Fig. 6.6 Tools are often heated before fixing
wooden handles
Such a change is also used for fixing
the metal rim on a wooden wheel of a
cart as shown in Fig.6.7. Again the
metal rim is made slightly smaller than
the wooden wheel. On heating, the rim
expands and fits onto the wheel. Cold
water is then poured over the rim, which
contracts and fits tightly onto the wheel.
2022-23
49 CHANGES AROUND US
Activity 7
Take a small candle and measure its
length with a scale. Now, fix it at a
suitable place and light it. Let it burn
for some time. Now blow out the candle
and measure its length again (Fig.6.8).
Can the change in the length of the
candle be reversed? If we were to take
some wax in a pan and heat it, can this
change be reversed (Fig. 6.9)?
Fig. 6.7  Cart wheel with metal rim fixed to it
Boojho has often noticed that road
construction workers heat a black
material (tar) for repairing a road.
He wants to know whether the
change caused in tar, by
heating, can be reversed?
Paheli wants to know if
you have ever seen a
blacksmith making some
tools. How does a
blacksmith change a
piece of iron into different tools? A
piece of iron is heated till it becomes
red-hot. It then becomes soft and is
beaten into a desired shape. What
change has taken place in iron, on
being heated?
When we heat water in a pan, it
begins to boil after some time. If we
continue to heat further, the quantity
of water in the pan begins to decrease.
The water changes into its vapour.
In Activity 7, Chapter 5 you have
observed that water vapour gets changed
into liquid water when it is cooled. We
all have noticed melting of ice. Ice melts
when it is heated. What does it change
into? Is it possible to change this water
back into ice?
Let us observe some more changes.
Fig.6.8 Burning of a
candle
Fig.6.9  Heating wax
2022-23
Page 5


46 SCIENCE
6 Changes Around us
W
hat a fun would it be if you
suddenly get some magical
powers to change things
around you. What are the things you
would want to change?
Can some of the changes be grouped
together?
How can we group various changes?
It might help, if we find some similarities
between them.
6.1 CAN ALL CHANGES ALWAYS BE
REVERSED?
Activity 1
Take a balloon and blow it. Take care
that it does not burst. The shape and
size of the balloon have changed
(Fig. 6.1). Now, let the air escape the
balloon.
Fig 6.1 A balloon changes its size and shape on
blowing air into it
Activity 2
Take a piece of paper and fold it as
shown in Fig.6.2. You have changed the
sheet of paper  into a toy aeroplane. You
may have lots of fun in flying this plane.
Once you are tired of it, unfold the
paper again.
We do not have magical powers, of
course. But, we can still change a few
things around us, perhaps many things.
Can you list a few things you can
change around you, with no magic
involved?
Many changes are taking place
around us on their own. In the fields,
the crops change from time to time.
Sometimes, leaves fall from trees, change
colour and dry out. The flowers bloom
and then wither away. Are any changes
happening in your body? Your nails
grow, your hair grows, you grow taller
and your weight increases as you grow.
Did you realise earlier that so many
changes are taking place around you all
the time?
2022-23
47 CHANGES AROUND US
Activity 4
Take the same balloon, which you used
in Activity 1. Blow it to its full size and
tie its mouth with a string tightly. Prick
it with the pointed tip of your pencil.
Oops! It burst.
Activity 5
Take the same piece of paper, which you
used in Activity 2.  Draw an aeroplane
on it and cut along its outline (Fig.6.4).
Activity 3
Take some dough and make a ball. Try
to roll out a roti (Fig. 6.3). May be you
are not happy with its shape and
wish to change it back into a ball of
dough again.
Fig 6.2 A toy aeroplane made by folding paper
Fig 6.3 A ball of dough and a rolled out roti
Now, think about the three changes
you observed in Activity 1, 2 and 3.
What do they have in common?
Was it possible to get the balloon back
to its original shape and size?
Was the size of the paper same as
before and after making an aeroplane?
Was it possible to get back the ball of
dough again?
What do you conclude? In each of
the three activities, is it possible to get
back to the material with which we
started our activity? If the answer is yes,
it means that the changes occurring in
these activities can be reversed. Now, let
us repeat the same activities with
a difference.
Fig. 6.4 An aeroplane cut out of paper
Activity 6
Roll out a roti from the ball of dough
again and bake it on a tawa (Fig.6.5).
Suppose, you are asked the same
three questions which you answered
after Activity 3. What would your
answers be, now?
We see that, the changes which have
occurred in the Activity 4, 5 and 6 can
not be reversed.
You use a pencil and an eraser. With
repeated use, their shape and size
change. Can we reverse this change?
Fig 6.5 A roti
2022-23
48 SCIENCE
You must have seen a potter working
on his wheel. He shapes a lump of clay
into a pot. Can this change be reversed?
He then bakes the pot in an oven. Now,
can this change be reversed?
Some common changes are given in
Table 6.1. Which of these changes, do
you think can be reversed?
We find that one way we can group
changes is to see if they can be
reversed.
6.2 COULD THERE BE OTHER WAYS
TO BRING A CHANGE?
We all have seen the tools which are used
to dig the soil (Fig. 6.6 ). Have you ever
seen how the iron blade in these tools
is fixed to the wooden handle?
The iron blade of these tools has a
ring in which the wooden handle is
fixed. Normally, the ring is slightly
smaller in size than the wooden handle.
To fix the handle, the ring is heated and
it becomes slightly larger in size
(expands). Now, the handle easily fits
into the ring. When the ring cools down
it contracts and fits tightly on to
the handle.
Table 6.1  Some common changes
Fig. 6.6 Tools are often heated before fixing
wooden handles
Such a change is also used for fixing
the metal rim on a wooden wheel of a
cart as shown in Fig.6.7. Again the
metal rim is made slightly smaller than
the wooden wheel. On heating, the rim
expands and fits onto the wheel. Cold
water is then poured over the rim, which
contracts and fits tightly onto the wheel.
2022-23
49 CHANGES AROUND US
Activity 7
Take a small candle and measure its
length with a scale. Now, fix it at a
suitable place and light it. Let it burn
for some time. Now blow out the candle
and measure its length again (Fig.6.8).
Can the change in the length of the
candle be reversed? If we were to take
some wax in a pan and heat it, can this
change be reversed (Fig. 6.9)?
Fig. 6.7  Cart wheel with metal rim fixed to it
Boojho has often noticed that road
construction workers heat a black
material (tar) for repairing a road.
He wants to know whether the
change caused in tar, by
heating, can be reversed?
Paheli wants to know if
you have ever seen a
blacksmith making some
tools. How does a
blacksmith change a
piece of iron into different tools? A
piece of iron is heated till it becomes
red-hot. It then becomes soft and is
beaten into a desired shape. What
change has taken place in iron, on
being heated?
When we heat water in a pan, it
begins to boil after some time. If we
continue to heat further, the quantity
of water in the pan begins to decrease.
The water changes into its vapour.
In Activity 7, Chapter 5 you have
observed that water vapour gets changed
into liquid water when it is cooled. We
all have noticed melting of ice. Ice melts
when it is heated. What does it change
into? Is it possible to change this water
back into ice?
Let us observe some more changes.
Fig.6.8 Burning of a
candle
Fig.6.9  Heating wax
2022-23
50 SCIENCE
Repeat Activity 7 with an incense
stick. Wait till it burns away completely.
What are the changes that occur in the
incense stick? The stick burns to
produce some new material. These are
ash and some gases. We cannot see
these gases but can sense them due to
their pleasant smell. Can this change
be reversed? And what about the
change, which occurred in the
matchstick you used for lighting the
candle or incense stick?
So far we have discussed the changes
occurring in a given object or its
material. What about the changes
that occur when two substances are
mixed together?
In Chapter 4, we dissolved salt in
water. Do you think a change occured
in salt or in water?  Is it possible to
reverse this change? Wait, in Chapter
5, we learnt how to separate salt from
its solution in water. So, can we say that
the change due to dissolving salt in
water be reversed?
Paheli asks if you have ever seen curd
being set. A small quantity of curd is
added to warm milk. The milk is stirred
and is set aside for a few hours at a warm
place. In a few hours, the milk changes
into curd. Can this change be reversed?
We find that a few ways to bring about
a change in a substance could be, by
heating it or by mixing it with some
other substance. We also find that some
changes can be reversed, while some
others cannot be reversed. There must
be many other ways of changing things
around us. It is possible that some of
them could be reversed. Thus, changes
around us could be grouped as those
that can be reversed or cannot be
reversed. In higher classes, you will
learn more about the ways in which
changes can be made and the way these
can be grouped.
s e g n a h C
n o i t c a r t n o C
n o i t a r o p a v E
n o i s n a p x E
g n i t l e M
n Some changes can be reversed and some cannot be reversed.
n A change may occur by heating a substance or by mixing it with some
other.
2022-23