NCERT Textbook: Exploring Forces | Science Curiosity Class 8 - New NCERT PDF Download

 Page 1


62
Curiosity — Textbook of Science for Grade 8
Exploring Forces
5
Probe and ponder
 
 z Why does it feel harder to pedal a bicycle when going uphill 
than on flat ground?
 z Why is it easier to slip on a wet surface?
 z Why do we feel ‘light’ or like we are ‘floating’ just after our 
swing reaches its highest point and begins to come down? 
 z Share your questions 
  ?
Chapter 5.indd   62 Chapter 5.indd   62 6/28/2025   3:08:44 PM 6/28/2025   3:08:44 PM
Page 2


62
Curiosity — Textbook of Science for Grade 8
Exploring Forces
5
Probe and ponder
 
 z Why does it feel harder to pedal a bicycle when going uphill 
than on flat ground?
 z Why is it easier to slip on a wet surface?
 z Why do we feel ‘light’ or like we are ‘floating’ just after our 
swing reaches its highest point and begins to come down? 
 z Share your questions 
  ?
Chapter 5.indd   62 Chapter 5.indd   62 6/28/2025   3:08:44 PM 6/28/2025   3:08:44 PM
Chapter 5?—?Exploring Forces
63
It was a windy day. Sonali and Ragini were excited to go 
cycling. Their summer vacation had just begun, and they wanted 
to explore the beautiful landscapes around their village. After 
pumping air into their bicycle tyres, they set off. As they rode 
through the village, the wind rushed past them. “Oh no! The 
wind is pushing me hard!” said Ragini. Smiling, Sonali replied, 
“We are riding against the wind. We must push our pedals harder 
to move faster.”
Their ride took them up a long path to a hilltop. Some parts 
of the road were rough where they found it hard to pedal, while 
other parts were smoother. When they reached the top and were 
enjoying the view, they heard thunder and saw flashes of lightning 
at a distance. Even though it looked beautiful, they decided to 
head back immediately. On the way back, while passing a herd of 
sheep, they pressed their bicycle bells and turned the handles to 
change direction.
As they were coming down the slope of the hill, they realised 
that their bicycles were moving down at a great speed even 
though they were not pedalling! Sonali yelled, “It’s thrilling! It 
seems something is pulling us downhill, what could it be?”
5.1 What Is a Force?
Let us try to experience the push and the pull.
Activity 5.1: Let us explore
 z Take a large cardboard box. 
 z Try moving the box in as many different ways as you can 
think of.
Did you move the box in any other way than shown in Fig. 5.1? 
In all the ways that you might have used to move the box, you 
had to apply a push or pull to the box. Generally, the push or pull 
applied on an object is called force in science.
Fig. 5.1: Moving a box in different ways (a) Pushing; (b) Pulling;  
(c) Lifting (pulling up), and carrying
(a) (b) (c)
Chapter 5.indd   63 Chapter 5.indd   63 6/28/2025   3:08:45 PM 6/28/2025   3:08:45 PM
Page 3


62
Curiosity — Textbook of Science for Grade 8
Exploring Forces
5
Probe and ponder
 
 z Why does it feel harder to pedal a bicycle when going uphill 
than on flat ground?
 z Why is it easier to slip on a wet surface?
 z Why do we feel ‘light’ or like we are ‘floating’ just after our 
swing reaches its highest point and begins to come down? 
 z Share your questions 
  ?
Chapter 5.indd   62 Chapter 5.indd   62 6/28/2025   3:08:44 PM 6/28/2025   3:08:44 PM
Chapter 5?—?Exploring Forces
63
It was a windy day. Sonali and Ragini were excited to go 
cycling. Their summer vacation had just begun, and they wanted 
to explore the beautiful landscapes around their village. After 
pumping air into their bicycle tyres, they set off. As they rode 
through the village, the wind rushed past them. “Oh no! The 
wind is pushing me hard!” said Ragini. Smiling, Sonali replied, 
“We are riding against the wind. We must push our pedals harder 
to move faster.”
Their ride took them up a long path to a hilltop. Some parts 
of the road were rough where they found it hard to pedal, while 
other parts were smoother. When they reached the top and were 
enjoying the view, they heard thunder and saw flashes of lightning 
at a distance. Even though it looked beautiful, they decided to 
head back immediately. On the way back, while passing a herd of 
sheep, they pressed their bicycle bells and turned the handles to 
change direction.
As they were coming down the slope of the hill, they realised 
that their bicycles were moving down at a great speed even 
though they were not pedalling! Sonali yelled, “It’s thrilling! It 
seems something is pulling us downhill, what could it be?”
5.1 What Is a Force?
Let us try to experience the push and the pull.
Activity 5.1: Let us explore
 z Take a large cardboard box. 
 z Try moving the box in as many different ways as you can 
think of.
Did you move the box in any other way than shown in Fig. 5.1? 
In all the ways that you might have used to move the box, you 
had to apply a push or pull to the box. Generally, the push or pull 
applied on an object is called force in science.
Fig. 5.1: Moving a box in different ways (a) Pushing; (b) Pulling;  
(c) Lifting (pulling up), and carrying
(a) (b) (c)
Chapter 5.indd   63 Chapter 5.indd   63 6/28/2025   3:08:45 PM 6/28/2025   3:08:45 PM
64
Curiosity — Textbook of Science for Grade 8
5.2  What Can a Force Do to the Bodies on 
Which It Is Applied?
We experience push or pull in our daily lives all the time, often 
without even realising it. Let us recall some of these experiences 
and analyse them.
Activity 5.2: Let us analyse
 z Think of situations where a force (push or pull) is applied 
and list them in Table 5.1.
 z Analyse each situation and write the effect of the force 
in Table 5.1. Some situations and their effects are already 
listed for you.
S.No. Action Push/Pull Effect 
1. Your friend holding 
your moving bicycle 
from behind to stop 
it
Pull Stopping or decreasing  
the speed of the bicycle
2. Hitting a moving ball 
with a bat
Push Changing the direction  
of a moving ball
3. Pressing an inflated 
balloon
Push Change in shape of  
the balloon
………………… ………………… …………………
Table 5.1: Different actions and their effects
What do you conclude from these examples? Does a force 
cause a moving object to stop? Can it change speed, or direction 
of motion, or change the shape of an object?
Fig. 5.2: Applying force on objects
Chapter 5.indd   64 Chapter 5.indd   64 6/28/2025   3:08:48 PM 6/28/2025   3:08:48 PM
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62
Curiosity — Textbook of Science for Grade 8
Exploring Forces
5
Probe and ponder
 
 z Why does it feel harder to pedal a bicycle when going uphill 
than on flat ground?
 z Why is it easier to slip on a wet surface?
 z Why do we feel ‘light’ or like we are ‘floating’ just after our 
swing reaches its highest point and begins to come down? 
 z Share your questions 
  ?
Chapter 5.indd   62 Chapter 5.indd   62 6/28/2025   3:08:44 PM 6/28/2025   3:08:44 PM
Chapter 5?—?Exploring Forces
63
It was a windy day. Sonali and Ragini were excited to go 
cycling. Their summer vacation had just begun, and they wanted 
to explore the beautiful landscapes around their village. After 
pumping air into their bicycle tyres, they set off. As they rode 
through the village, the wind rushed past them. “Oh no! The 
wind is pushing me hard!” said Ragini. Smiling, Sonali replied, 
“We are riding against the wind. We must push our pedals harder 
to move faster.”
Their ride took them up a long path to a hilltop. Some parts 
of the road were rough where they found it hard to pedal, while 
other parts were smoother. When they reached the top and were 
enjoying the view, they heard thunder and saw flashes of lightning 
at a distance. Even though it looked beautiful, they decided to 
head back immediately. On the way back, while passing a herd of 
sheep, they pressed their bicycle bells and turned the handles to 
change direction.
As they were coming down the slope of the hill, they realised 
that their bicycles were moving down at a great speed even 
though they were not pedalling! Sonali yelled, “It’s thrilling! It 
seems something is pulling us downhill, what could it be?”
5.1 What Is a Force?
Let us try to experience the push and the pull.
Activity 5.1: Let us explore
 z Take a large cardboard box. 
 z Try moving the box in as many different ways as you can 
think of.
Did you move the box in any other way than shown in Fig. 5.1? 
In all the ways that you might have used to move the box, you 
had to apply a push or pull to the box. Generally, the push or pull 
applied on an object is called force in science.
Fig. 5.1: Moving a box in different ways (a) Pushing; (b) Pulling;  
(c) Lifting (pulling up), and carrying
(a) (b) (c)
Chapter 5.indd   63 Chapter 5.indd   63 6/28/2025   3:08:45 PM 6/28/2025   3:08:45 PM
64
Curiosity — Textbook of Science for Grade 8
5.2  What Can a Force Do to the Bodies on 
Which It Is Applied?
We experience push or pull in our daily lives all the time, often 
without even realising it. Let us recall some of these experiences 
and analyse them.
Activity 5.2: Let us analyse
 z Think of situations where a force (push or pull) is applied 
and list them in Table 5.1.
 z Analyse each situation and write the effect of the force 
in Table 5.1. Some situations and their effects are already 
listed for you.
S.No. Action Push/Pull Effect 
1. Your friend holding 
your moving bicycle 
from behind to stop 
it
Pull Stopping or decreasing  
the speed of the bicycle
2. Hitting a moving ball 
with a bat
Push Changing the direction  
of a moving ball
3. Pressing an inflated 
balloon
Push Change in shape of  
the balloon
………………… ………………… …………………
Table 5.1: Different actions and their effects
What do you conclude from these examples? Does a force 
cause a moving object to stop? Can it change speed, or direction 
of motion, or change the shape of an object?
Fig. 5.2: Applying force on objects
Chapter 5.indd   64 Chapter 5.indd   64 6/28/2025   3:08:48 PM 6/28/2025   3:08:48 PM
Chapter 5?—?Exploring Forces
65
In everyday life, we come across many situations where a force 
is applied, for example, opening a drawer, stretching a rubber 
band, a fielder stopping a ball, kicking a football, applying brakes 
on a moving bicycle, rolling a chapati, or turning the steering 
handle of an autorickshaw. What effect can the application of 
force have on objects?
The force applied on an object may
 z make an object move from rest.
 z change the speed of an object if it is moving.
 z change the direction of motion of an object.
 z bring about a change in the shape of an object.
 z cause some or all of these effects.
5.3  Are Forces an Interaction Between Two 
or More Objects?
When you push a table, your hand is one object applying force 
on another object — the table. Here, we say that your hand and 
the table are two objects interacting with each other. 
Think of all the actions listed in Table 5.1. How many objects 
are involved in each of the actions? Do you notice that forces 
result only when two objects are interacting in some way or 
the other? From these examples, we can infer that at least two 
objects must interact for a force to come into play.
A force is a push or pull on an object resulting from the 
object’s interaction with another object. The SI unit of force is 
newton (written with a small ‘n’) and its symbol is N.
A step further
Suppose an object is at rest. Does it mean that no force is acting 
on this object? It means that the forces acting on the object are 
balancing one another. You will learn about balanced forces in 
higher grades.
Does this mean that 
whenever there is a change 
in speed or direction, or 
change in shape, a force is 
acting on the object?
Yes, none of these take 
place without the action 
of force.
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Page 5


62
Curiosity — Textbook of Science for Grade 8
Exploring Forces
5
Probe and ponder
 
 z Why does it feel harder to pedal a bicycle when going uphill 
than on flat ground?
 z Why is it easier to slip on a wet surface?
 z Why do we feel ‘light’ or like we are ‘floating’ just after our 
swing reaches its highest point and begins to come down? 
 z Share your questions 
  ?
Chapter 5.indd   62 Chapter 5.indd   62 6/28/2025   3:08:44 PM 6/28/2025   3:08:44 PM
Chapter 5?—?Exploring Forces
63
It was a windy day. Sonali and Ragini were excited to go 
cycling. Their summer vacation had just begun, and they wanted 
to explore the beautiful landscapes around their village. After 
pumping air into their bicycle tyres, they set off. As they rode 
through the village, the wind rushed past them. “Oh no! The 
wind is pushing me hard!” said Ragini. Smiling, Sonali replied, 
“We are riding against the wind. We must push our pedals harder 
to move faster.”
Their ride took them up a long path to a hilltop. Some parts 
of the road were rough where they found it hard to pedal, while 
other parts were smoother. When they reached the top and were 
enjoying the view, they heard thunder and saw flashes of lightning 
at a distance. Even though it looked beautiful, they decided to 
head back immediately. On the way back, while passing a herd of 
sheep, they pressed their bicycle bells and turned the handles to 
change direction.
As they were coming down the slope of the hill, they realised 
that their bicycles were moving down at a great speed even 
though they were not pedalling! Sonali yelled, “It’s thrilling! It 
seems something is pulling us downhill, what could it be?”
5.1 What Is a Force?
Let us try to experience the push and the pull.
Activity 5.1: Let us explore
 z Take a large cardboard box. 
 z Try moving the box in as many different ways as you can 
think of.
Did you move the box in any other way than shown in Fig. 5.1? 
In all the ways that you might have used to move the box, you 
had to apply a push or pull to the box. Generally, the push or pull 
applied on an object is called force in science.
Fig. 5.1: Moving a box in different ways (a) Pushing; (b) Pulling;  
(c) Lifting (pulling up), and carrying
(a) (b) (c)
Chapter 5.indd   63 Chapter 5.indd   63 6/28/2025   3:08:45 PM 6/28/2025   3:08:45 PM
64
Curiosity — Textbook of Science for Grade 8
5.2  What Can a Force Do to the Bodies on 
Which It Is Applied?
We experience push or pull in our daily lives all the time, often 
without even realising it. Let us recall some of these experiences 
and analyse them.
Activity 5.2: Let us analyse
 z Think of situations where a force (push or pull) is applied 
and list them in Table 5.1.
 z Analyse each situation and write the effect of the force 
in Table 5.1. Some situations and their effects are already 
listed for you.
S.No. Action Push/Pull Effect 
1. Your friend holding 
your moving bicycle 
from behind to stop 
it
Pull Stopping or decreasing  
the speed of the bicycle
2. Hitting a moving ball 
with a bat
Push Changing the direction  
of a moving ball
3. Pressing an inflated 
balloon
Push Change in shape of  
the balloon
………………… ………………… …………………
Table 5.1: Different actions and their effects
What do you conclude from these examples? Does a force 
cause a moving object to stop? Can it change speed, or direction 
of motion, or change the shape of an object?
Fig. 5.2: Applying force on objects
Chapter 5.indd   64 Chapter 5.indd   64 6/28/2025   3:08:48 PM 6/28/2025   3:08:48 PM
Chapter 5?—?Exploring Forces
65
In everyday life, we come across many situations where a force 
is applied, for example, opening a drawer, stretching a rubber 
band, a fielder stopping a ball, kicking a football, applying brakes 
on a moving bicycle, rolling a chapati, or turning the steering 
handle of an autorickshaw. What effect can the application of 
force have on objects?
The force applied on an object may
 z make an object move from rest.
 z change the speed of an object if it is moving.
 z change the direction of motion of an object.
 z bring about a change in the shape of an object.
 z cause some or all of these effects.
5.3  Are Forces an Interaction Between Two 
or More Objects?
When you push a table, your hand is one object applying force 
on another object — the table. Here, we say that your hand and 
the table are two objects interacting with each other. 
Think of all the actions listed in Table 5.1. How many objects 
are involved in each of the actions? Do you notice that forces 
result only when two objects are interacting in some way or 
the other? From these examples, we can infer that at least two 
objects must interact for a force to come into play.
A force is a push or pull on an object resulting from the 
object’s interaction with another object. The SI unit of force is 
newton (written with a small ‘n’) and its symbol is N.
A step further
Suppose an object is at rest. Does it mean that no force is acting 
on this object? It means that the forces acting on the object are 
balancing one another. You will learn about balanced forces in 
higher grades.
Does this mean that 
whenever there is a change 
in speed or direction, or 
change in shape, a force is 
acting on the object?
Yes, none of these take 
place without the action 
of force.
Chapter 5.indd   65 Chapter 5.indd   65 6/28/2025   3:08:52 PM 6/28/2025   3:08:52 PM
66
Curiosity — Textbook of Science for Grade 8
Fig. 5.3: Use of muscular force by living beings
A step further
When you pushed the table with your hand, did you feel a force 
on your hand too? The moment you stopped pushing, the force on 
your hand disappeared. Whenever two objects interact, each object 
experiences a force from the other. As soon as the interaction 
ceases, the two objects no longer experience the force. 
5.4 What Are the Different Types of Forces?
5.4.1 Contact forces
In many situations, we find that to apply a force on an object, 
physical contact is necessary between our body and the object. 
This contact can be direct, such as using our hands or other body 
parts, or indirect, such as using a stick or rope. Forces of this 
type which act only when there is physical contact between the 
objects are called contact forces.
Muscular force
An example of contact force is muscular force. When we perform 
any physical activity, such as walking, running, lifting, pushing, 
jumping, or stretching, the force is caused by the action of muscles 
in our body. The force resulting due to the action of muscles is 
known as muscular force. Muscular force occurs when muscles 
contract and elongate while doing any activity. 
Animals, birds, fish, and insects use muscular forces for 
movement and survival.
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