NCERT Textbook: Exploring the Investigative World of Science | Science Curiosity Class 8 - New NCERT PDF Download

 Page 1


Chapter 1?—?Exploring the Investigative World of Science
1
Exploring the 
Investigative 
World of Science
1
Dear Young Scientists, 
Welcome back! On the first page of each chapter, you will find a set of questions. 
These are not meant for any exam— they are unique invitations to spark your 
curiosity to explore the world of science!
Why is one side of a puri thinner than the other?
Are there more grains of sand on all the beaches and deserts of the world, or more 
stars in our galaxy?
Right from Grade 6, we’ve observed the incredible diversity of plants and animals 
around us. From the different shapes of leaves to the many kinds of insects — why 
has nature created such a vast variety?
Is there such a question that makes you curious about the 
world? 
Write it here! _________________________________  
Probe and ponder
Chapter 1.indd   1 Chapter 1.indd   1 6/28/2025   11:38:53 AM 6/28/2025   11:38:53 AM
Page 2


Chapter 1?—?Exploring the Investigative World of Science
1
Exploring the 
Investigative 
World of Science
1
Dear Young Scientists, 
Welcome back! On the first page of each chapter, you will find a set of questions. 
These are not meant for any exam— they are unique invitations to spark your 
curiosity to explore the world of science!
Why is one side of a puri thinner than the other?
Are there more grains of sand on all the beaches and deserts of the world, or more 
stars in our galaxy?
Right from Grade 6, we’ve observed the incredible diversity of plants and animals 
around us. From the different shapes of leaves to the many kinds of insects — why 
has nature created such a vast variety?
Is there such a question that makes you curious about the 
world? 
Write it here! _________________________________  
Probe and ponder
Chapter 1.indd   1 Chapter 1.indd   1 6/28/2025   11:38:53 AM 6/28/2025   11:38:53 AM
2
Curiosity — Textbook of Science for Grade 8
Our journey with Curiosity, into the world of science continues 
in Grade 8. We hope you bring along the spirit of adventure and 
exploration that has guided us so far. In Grade 6, we discovered 
how science begins with wonder, with simple “Why?” and 
“How?” questions about the world around us.
In Grade 7, we learnt that science is always evolving — that 
each answer opens new questions, and how our ideas can slowly 
change as we explore deeper. Now, in Grade 8, we take the next 
step: entering the Investigative World of Science, where wonder 
and evolution come together to form the heart of how science 
works.
We don’t want you to just learn new facts, we want you to 
learn how to find new facts. Investigation in science means more 
than just looking at something and asking only simple questions. 
Now you can ask more focused questions, and design ways to 
perhaps do simple experiments to answer those questions, and 
then use your observations to improve your understanding.
Step by step, we will learn how to use questions as starting 
points to try to observe carefully, experiment thoughtfully, and 
explain clearly what we see. In doing so, each of you won’t just 
be learners but also investigators, young scientists, exploring 
real-world puzzles. These may range from everyday life — like 
why does dough rise? — to the bigger mysteries of Earth and 
beyond like is the world getting warmer?
As you turn each page of this book, we hope you notice the 
interesting design of our page numbers once again. On the 
left-hand pages, at the bottom, you’ll find the image of a root, 
symbolising the deep, solid foundation of knowledge that keeps 
us connected to our environment, traditions, and our cultural 
and natural heritage.
On the right-hand pages, in the top corner, you’ll find a 
kite soaring in the sky, reminding us that curiosity must take 
flight if we are to explore the unknown. Together, these two 
symbols — the root and the kite — invite you to stay grounded in 
real observations, while allowing your ideas to soar towards new 
horizons. Remember, investigation in science works best only 
when we balance the solid ground of careful observation with 
the freedom of creative thinking.
You will also notice some patterns in the lines at the bottom 
of the page. There are some hidden scientific thoughts in these as 
well. But don’t worry, they are mainly to make the page a little 
less boring. Let us now take a brief look at the various stops on 
our journey this year, and see where our curiosity, supported by 
strong roots and lifted by soaring ideas, might take us!
Chapter 1.indd   2 Chapter 1.indd   2 6/28/2025   11:38:53 AM 6/28/2025   11:38:53 AM
Page 3


Chapter 1?—?Exploring the Investigative World of Science
1
Exploring the 
Investigative 
World of Science
1
Dear Young Scientists, 
Welcome back! On the first page of each chapter, you will find a set of questions. 
These are not meant for any exam— they are unique invitations to spark your 
curiosity to explore the world of science!
Why is one side of a puri thinner than the other?
Are there more grains of sand on all the beaches and deserts of the world, or more 
stars in our galaxy?
Right from Grade 6, we’ve observed the incredible diversity of plants and animals 
around us. From the different shapes of leaves to the many kinds of insects — why 
has nature created such a vast variety?
Is there such a question that makes you curious about the 
world? 
Write it here! _________________________________  
Probe and ponder
Chapter 1.indd   1 Chapter 1.indd   1 6/28/2025   11:38:53 AM 6/28/2025   11:38:53 AM
2
Curiosity — Textbook of Science for Grade 8
Our journey with Curiosity, into the world of science continues 
in Grade 8. We hope you bring along the spirit of adventure and 
exploration that has guided us so far. In Grade 6, we discovered 
how science begins with wonder, with simple “Why?” and 
“How?” questions about the world around us.
In Grade 7, we learnt that science is always evolving — that 
each answer opens new questions, and how our ideas can slowly 
change as we explore deeper. Now, in Grade 8, we take the next 
step: entering the Investigative World of Science, where wonder 
and evolution come together to form the heart of how science 
works.
We don’t want you to just learn new facts, we want you to 
learn how to find new facts. Investigation in science means more 
than just looking at something and asking only simple questions. 
Now you can ask more focused questions, and design ways to 
perhaps do simple experiments to answer those questions, and 
then use your observations to improve your understanding.
Step by step, we will learn how to use questions as starting 
points to try to observe carefully, experiment thoughtfully, and 
explain clearly what we see. In doing so, each of you won’t just 
be learners but also investigators, young scientists, exploring 
real-world puzzles. These may range from everyday life — like 
why does dough rise? — to the bigger mysteries of Earth and 
beyond like is the world getting warmer?
As you turn each page of this book, we hope you notice the 
interesting design of our page numbers once again. On the 
left-hand pages, at the bottom, you’ll find the image of a root, 
symbolising the deep, solid foundation of knowledge that keeps 
us connected to our environment, traditions, and our cultural 
and natural heritage.
On the right-hand pages, in the top corner, you’ll find a 
kite soaring in the sky, reminding us that curiosity must take 
flight if we are to explore the unknown. Together, these two 
symbols — the root and the kite — invite you to stay grounded in 
real observations, while allowing your ideas to soar towards new 
horizons. Remember, investigation in science works best only 
when we balance the solid ground of careful observation with 
the freedom of creative thinking.
You will also notice some patterns in the lines at the bottom 
of the page. There are some hidden scientific thoughts in these as 
well. But don’t worry, they are mainly to make the page a little 
less boring. Let us now take a brief look at the various stops on 
our journey this year, and see where our curiosity, supported by 
strong roots and lifted by soaring ideas, might take us!
Chapter 1.indd   2 Chapter 1.indd   2 6/28/2025   11:38:53 AM 6/28/2025   11:38:53 AM
Chapter 1?—?Exploring the Investigative World of Science
3
This year, our investigative adventure will take 
us on a journey from the tiny microbes we can’t 
see to planet-wide challenges we can’t ignore.
We will start by examining something as small 
as a single drop of water, and uncover a hidden 
world of tiny organisms, unseen but deeply 
linked to us. Some of these are invisible helpers, 
that help us digest our food or produce medicines, 
while others can be harmful, causing infections.
But what does our body need to stay healthy? How do we fight 
these infections? We’ll find out how nutritious food, exercise, 
medicines, and vaccines help us stay healthy and fight infections.  
But that’s just the beginning. In today’s world, science does play 
a major role in improving our lives.
For example, we use electric current in many 
ways to help make our lives easier. We depend 
on the heating effect of electric current to keep 
us warm, while the magnetic effect helps motors 
run and machines function.
These phenomena depend on fundamental forces. So after 
watching electricity do work, we move on to study these forces 
themselves, starting with those that make objects speed up, slow 
down, or change direction.
Understanding forces helps explain why a ball thrown up 
in the air falls back to the ground, or why a car stops when 
the brakes are applied.
This also leads us to the idea of pressure — how the force 
is distributed over an object. The same concepts of force 
and pressure also decide how air moves. A small difference 
in pressure can result in a gentle breeze while a stronger 
pressure difference can lead to strong winds, and sometimes 
even cyclones.
Chapter 1.indd   3 Chapter 1.indd   3 6/28/2025   11:39:02 AM 6/28/2025   11:39:02 AM
Page 4


Chapter 1?—?Exploring the Investigative World of Science
1
Exploring the 
Investigative 
World of Science
1
Dear Young Scientists, 
Welcome back! On the first page of each chapter, you will find a set of questions. 
These are not meant for any exam— they are unique invitations to spark your 
curiosity to explore the world of science!
Why is one side of a puri thinner than the other?
Are there more grains of sand on all the beaches and deserts of the world, or more 
stars in our galaxy?
Right from Grade 6, we’ve observed the incredible diversity of plants and animals 
around us. From the different shapes of leaves to the many kinds of insects — why 
has nature created such a vast variety?
Is there such a question that makes you curious about the 
world? 
Write it here! _________________________________  
Probe and ponder
Chapter 1.indd   1 Chapter 1.indd   1 6/28/2025   11:38:53 AM 6/28/2025   11:38:53 AM
2
Curiosity — Textbook of Science for Grade 8
Our journey with Curiosity, into the world of science continues 
in Grade 8. We hope you bring along the spirit of adventure and 
exploration that has guided us so far. In Grade 6, we discovered 
how science begins with wonder, with simple “Why?” and 
“How?” questions about the world around us.
In Grade 7, we learnt that science is always evolving — that 
each answer opens new questions, and how our ideas can slowly 
change as we explore deeper. Now, in Grade 8, we take the next 
step: entering the Investigative World of Science, where wonder 
and evolution come together to form the heart of how science 
works.
We don’t want you to just learn new facts, we want you to 
learn how to find new facts. Investigation in science means more 
than just looking at something and asking only simple questions. 
Now you can ask more focused questions, and design ways to 
perhaps do simple experiments to answer those questions, and 
then use your observations to improve your understanding.
Step by step, we will learn how to use questions as starting 
points to try to observe carefully, experiment thoughtfully, and 
explain clearly what we see. In doing so, each of you won’t just 
be learners but also investigators, young scientists, exploring 
real-world puzzles. These may range from everyday life — like 
why does dough rise? — to the bigger mysteries of Earth and 
beyond like is the world getting warmer?
As you turn each page of this book, we hope you notice the 
interesting design of our page numbers once again. On the 
left-hand pages, at the bottom, you’ll find the image of a root, 
symbolising the deep, solid foundation of knowledge that keeps 
us connected to our environment, traditions, and our cultural 
and natural heritage.
On the right-hand pages, in the top corner, you’ll find a 
kite soaring in the sky, reminding us that curiosity must take 
flight if we are to explore the unknown. Together, these two 
symbols — the root and the kite — invite you to stay grounded in 
real observations, while allowing your ideas to soar towards new 
horizons. Remember, investigation in science works best only 
when we balance the solid ground of careful observation with 
the freedom of creative thinking.
You will also notice some patterns in the lines at the bottom 
of the page. There are some hidden scientific thoughts in these as 
well. But don’t worry, they are mainly to make the page a little 
less boring. Let us now take a brief look at the various stops on 
our journey this year, and see where our curiosity, supported by 
strong roots and lifted by soaring ideas, might take us!
Chapter 1.indd   2 Chapter 1.indd   2 6/28/2025   11:38:53 AM 6/28/2025   11:38:53 AM
Chapter 1?—?Exploring the Investigative World of Science
3
This year, our investigative adventure will take 
us on a journey from the tiny microbes we can’t 
see to planet-wide challenges we can’t ignore.
We will start by examining something as small 
as a single drop of water, and uncover a hidden 
world of tiny organisms, unseen but deeply 
linked to us. Some of these are invisible helpers, 
that help us digest our food or produce medicines, 
while others can be harmful, causing infections.
But what does our body need to stay healthy? How do we fight 
these infections? We’ll find out how nutritious food, exercise, 
medicines, and vaccines help us stay healthy and fight infections.  
But that’s just the beginning. In today’s world, science does play 
a major role in improving our lives.
For example, we use electric current in many 
ways to help make our lives easier. We depend 
on the heating effect of electric current to keep 
us warm, while the magnetic effect helps motors 
run and machines function.
These phenomena depend on fundamental forces. So after 
watching electricity do work, we move on to study these forces 
themselves, starting with those that make objects speed up, slow 
down, or change direction.
Understanding forces helps explain why a ball thrown up 
in the air falls back to the ground, or why a car stops when 
the brakes are applied.
This also leads us to the idea of pressure — how the force 
is distributed over an object. The same concepts of force 
and pressure also decide how air moves. A small difference 
in pressure can result in a gentle breeze while a stronger 
pressure difference can lead to strong winds, and sometimes 
even cyclones.
Chapter 1.indd   3 Chapter 1.indd   3 6/28/2025   11:39:02 AM 6/28/2025   11:39:02 AM
4
Curiosity — Textbook of Science for Grade 8
So, these forces are connected to powerful weather 
events—like storms and cyclones—that affect our daily 
lives, agriculture, and even our safety.
To truly understand how air can exert pressure or 
why water boils at a certain temperature we need to 
zoom into these materials and see what kind of particles 
they are made up of, and how they move around.
Everything around us is made of tiny particles. 
In materials that are solid these particles cannot move 
much, while in gases they can move around freely.
Classifying things around us is an important feature 
of science. We can also classify materials around us 
into elements (pure substances), compounds (two 
or more elements bonded together), and mixtures 
(combinations that can be separated physically).
Once we know how particles combine or mix, we can then 
understand solutions — for example, how sugar dissolves in tea 
to make it sweet.
From the world of particles and 
mixtures, we then move into the world 
of light. We’ll study how light rays reflect 
off flat and curved mirrors, and bends 
when passing through lenses and helps 
us understand the working of many 
objects around us. The bending of light 
explains what happens when we see an image in a shiny 
metal spoon or how corrective glasses help many of us 
see clearly.
It’s not just a polished mirror that reflects light, 
rough surfaces reflect light as well, and so does the 
Moon. Depending on the relative positions of the Earth, 
Moon and Sun, a slightly different part of the Moon is 
illuminated each night, giving rise to the beautiful phases 
of the Moon that we see in the sky.
Watching the periodic cycles of the Moon’s phases allowed 
humans to come up with the first calendars. By combining careful 
observations of sunrises, sunsets, and lunar cycles, various 
calendars came into being. Isn’t it fascinating that the calendars 
which determine our routines on Earth are linked to the motions 
of objects  far beyond our planet?
Chapter 1.indd   4 Chapter 1.indd   4 6/28/2025   11:39:12 AM 6/28/2025   11:39:12 AM
Page 5


Chapter 1?—?Exploring the Investigative World of Science
1
Exploring the 
Investigative 
World of Science
1
Dear Young Scientists, 
Welcome back! On the first page of each chapter, you will find a set of questions. 
These are not meant for any exam— they are unique invitations to spark your 
curiosity to explore the world of science!
Why is one side of a puri thinner than the other?
Are there more grains of sand on all the beaches and deserts of the world, or more 
stars in our galaxy?
Right from Grade 6, we’ve observed the incredible diversity of plants and animals 
around us. From the different shapes of leaves to the many kinds of insects — why 
has nature created such a vast variety?
Is there such a question that makes you curious about the 
world? 
Write it here! _________________________________  
Probe and ponder
Chapter 1.indd   1 Chapter 1.indd   1 6/28/2025   11:38:53 AM 6/28/2025   11:38:53 AM
2
Curiosity — Textbook of Science for Grade 8
Our journey with Curiosity, into the world of science continues 
in Grade 8. We hope you bring along the spirit of adventure and 
exploration that has guided us so far. In Grade 6, we discovered 
how science begins with wonder, with simple “Why?” and 
“How?” questions about the world around us.
In Grade 7, we learnt that science is always evolving — that 
each answer opens new questions, and how our ideas can slowly 
change as we explore deeper. Now, in Grade 8, we take the next 
step: entering the Investigative World of Science, where wonder 
and evolution come together to form the heart of how science 
works.
We don’t want you to just learn new facts, we want you to 
learn how to find new facts. Investigation in science means more 
than just looking at something and asking only simple questions. 
Now you can ask more focused questions, and design ways to 
perhaps do simple experiments to answer those questions, and 
then use your observations to improve your understanding.
Step by step, we will learn how to use questions as starting 
points to try to observe carefully, experiment thoughtfully, and 
explain clearly what we see. In doing so, each of you won’t just 
be learners but also investigators, young scientists, exploring 
real-world puzzles. These may range from everyday life — like 
why does dough rise? — to the bigger mysteries of Earth and 
beyond like is the world getting warmer?
As you turn each page of this book, we hope you notice the 
interesting design of our page numbers once again. On the 
left-hand pages, at the bottom, you’ll find the image of a root, 
symbolising the deep, solid foundation of knowledge that keeps 
us connected to our environment, traditions, and our cultural 
and natural heritage.
On the right-hand pages, in the top corner, you’ll find a 
kite soaring in the sky, reminding us that curiosity must take 
flight if we are to explore the unknown. Together, these two 
symbols — the root and the kite — invite you to stay grounded in 
real observations, while allowing your ideas to soar towards new 
horizons. Remember, investigation in science works best only 
when we balance the solid ground of careful observation with 
the freedom of creative thinking.
You will also notice some patterns in the lines at the bottom 
of the page. There are some hidden scientific thoughts in these as 
well. But don’t worry, they are mainly to make the page a little 
less boring. Let us now take a brief look at the various stops on 
our journey this year, and see where our curiosity, supported by 
strong roots and lifted by soaring ideas, might take us!
Chapter 1.indd   2 Chapter 1.indd   2 6/28/2025   11:38:53 AM 6/28/2025   11:38:53 AM
Chapter 1?—?Exploring the Investigative World of Science
3
This year, our investigative adventure will take 
us on a journey from the tiny microbes we can’t 
see to planet-wide challenges we can’t ignore.
We will start by examining something as small 
as a single drop of water, and uncover a hidden 
world of tiny organisms, unseen but deeply 
linked to us. Some of these are invisible helpers, 
that help us digest our food or produce medicines, 
while others can be harmful, causing infections.
But what does our body need to stay healthy? How do we fight 
these infections? We’ll find out how nutritious food, exercise, 
medicines, and vaccines help us stay healthy and fight infections.  
But that’s just the beginning. In today’s world, science does play 
a major role in improving our lives.
For example, we use electric current in many 
ways to help make our lives easier. We depend 
on the heating effect of electric current to keep 
us warm, while the magnetic effect helps motors 
run and machines function.
These phenomena depend on fundamental forces. So after 
watching electricity do work, we move on to study these forces 
themselves, starting with those that make objects speed up, slow 
down, or change direction.
Understanding forces helps explain why a ball thrown up 
in the air falls back to the ground, or why a car stops when 
the brakes are applied.
This also leads us to the idea of pressure — how the force 
is distributed over an object. The same concepts of force 
and pressure also decide how air moves. A small difference 
in pressure can result in a gentle breeze while a stronger 
pressure difference can lead to strong winds, and sometimes 
even cyclones.
Chapter 1.indd   3 Chapter 1.indd   3 6/28/2025   11:39:02 AM 6/28/2025   11:39:02 AM
4
Curiosity — Textbook of Science for Grade 8
So, these forces are connected to powerful weather 
events—like storms and cyclones—that affect our daily 
lives, agriculture, and even our safety.
To truly understand how air can exert pressure or 
why water boils at a certain temperature we need to 
zoom into these materials and see what kind of particles 
they are made up of, and how they move around.
Everything around us is made of tiny particles. 
In materials that are solid these particles cannot move 
much, while in gases they can move around freely.
Classifying things around us is an important feature 
of science. We can also classify materials around us 
into elements (pure substances), compounds (two 
or more elements bonded together), and mixtures 
(combinations that can be separated physically).
Once we know how particles combine or mix, we can then 
understand solutions — for example, how sugar dissolves in tea 
to make it sweet.
From the world of particles and 
mixtures, we then move into the world 
of light. We’ll study how light rays reflect 
off flat and curved mirrors, and bends 
when passing through lenses and helps 
us understand the working of many 
objects around us. The bending of light 
explains what happens when we see an image in a shiny 
metal spoon or how corrective glasses help many of us 
see clearly.
It’s not just a polished mirror that reflects light, 
rough surfaces reflect light as well, and so does the 
Moon. Depending on the relative positions of the Earth, 
Moon and Sun, a slightly different part of the Moon is 
illuminated each night, giving rise to the beautiful phases 
of the Moon that we see in the sky.
Watching the periodic cycles of the Moon’s phases allowed 
humans to come up with the first calendars. By combining careful 
observations of sunrises, sunsets, and lunar cycles, various 
calendars came into being. Isn’t it fascinating that the calendars 
which determine our routines on Earth are linked to the motions 
of objects  far beyond our planet?
Chapter 1.indd   4 Chapter 1.indd   4 6/28/2025   11:39:12 AM 6/28/2025   11:39:12 AM
Chapter 1?—?Exploring the Investigative World of Science
5
But it’s not just calendars or the movements 
of the Sun and Moon that are linked. Right here 
on Earth, there are marvellous and complex 
patterns of relationships between living 
organisms and their environments. Every living 
being — from tiniest insect to the largest whale, 
from blades of grasses to tall trees — depends 
on and responds to the air, water, sunlight, 
and other organisms around them forming the 
ecosystems that support life on our planet.
In the final chapter of this book, we can put 
it all together and try to understand what makes 
Earth ‘just right’ for life and to recognise the urgent challenges 
that our planet now faces.
Most importantly, the Earth lies at the perfect distance from 
the Sun, where water remains liquid, and it has an atmosphere 
that provides the oxygen we breathe while shielding us from 
harmful ultraviolet rays. But human activities on the planet can 
cause small changes in the temperature of the Earth, disrupting 
climate patterns, with dangerous consequences.
Shaka Era 1947
March 22, 2025 - March 21, 2026
Chaitra
22
MAR
APR
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30 1 31 23 45
6 7 89 10 11 12
13 14 15 16 17 18 19
1
2 4 35 67 8
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23 25 24 26 27 28 29
30
20
(March 22 - April 20, 2025)
MON TUE WED THU FRISAT SUN MON TUE WED THU FRISAT SUN MON TUE WED THU FRISAT SUN
APR
MAY
22 21 23 24 25 26
27 29 28 30 12 3
4 6 57 89 10
11 13 12 14 15 16 17
2 13 45 6
7 9 810111213
14 16 15 17 18 19 20
21 23 22 24
20 19 21
30 29 31
25 26 27
28
18
Vaisakha
(April 21 - May 21, 2025)
Jyestha 
(May 22 - June 21, 2025)
24
MAY
JUN
25 27 26 28 29 30 31
1 3 24 56 7
8 10 911121314
15 17 16 18 19 20 21
3
4 6 57 89
22 23
12
10
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18 20 19 21 22 23 24
25 27 26 28 29 30 31
At the heart of both the problem — and any possible 
solution — is us. We are the ones influencing Earth’s climate. 
But we are also the ones who can — and must — use science to 
understand these changes and guide our actions.
The same scientific principles that we have guided our 
journey through the middle stages — observing, measuring, 
experimenting — will be key in helping us protect the delicate 
balance on which life depends. The challenges ahead won’t 
always be easy. We hope some of you will try to solve these 
difficult problems with Curiosity as your guide.
Chapter 1.indd   5 Chapter 1.indd   5 6/28/2025   11:39:19 AM 6/28/2025   11:39:19 AM