NCERT Textbook: Pressure, Winds, Storms, and Cyclones | Science Curiosity Class 8 - New NCERT PDF Download

 Page 1


80
Curiosity — Textbook of Science for Grade 8
Pressure, Winds, 
Storms, and Cyclones
6
 
 z Why are winds stronger on some days than on others?
 z Why are water tanks usually placed at a height?
 z Can air pressure really crush us? 
 z What causes storms and cyclones? If the Earth stopped rotating, 
would cyclones still form?
 z Share your questions  
 ?
Probe and ponder
Chapter 6.indd   80 Chapter 6.indd   80 6/28/2025   3:59:54 PM 6/28/2025   3:59:54 PM
Page 2


80
Curiosity — Textbook of Science for Grade 8
Pressure, Winds, 
Storms, and Cyclones
6
 
 z Why are winds stronger on some days than on others?
 z Why are water tanks usually placed at a height?
 z Can air pressure really crush us? 
 z What causes storms and cyclones? If the Earth stopped rotating, 
would cyclones still form?
 z Share your questions  
 ?
Probe and ponder
Chapter 6.indd   80 Chapter 6.indd   80 6/28/2025   3:59:54 PM 6/28/2025   3:59:54 PM
Chapter 6?—?Pressure, Winds, Storms, and Cyclones
81
You must have observed fallen leaves on the ground swirling 
in the air or being swept away, and trees swaying or even 
bending when a strong wind blows. Have you ever wondered 
why fallen leaves rise in the air or trees sway or bend? Does the 
wind exert force on fallen leaves to make them rise or on trees 
to bend? Recall other similar effects of the force exerted by wind 
like slamming of doors or rattling of windows, or fluttering of 
clothes? How does the force exerted by wind make this happen? 
The force exerted by wind creates wind pressure which causes 
these effects. In this chapter, we will explore the relationship 
between force and pressure, and understand how they shape 
powerful natural events like thunderstorms and cyclones.
6.1 Pressure
 
Megha and her brother Pawan are going on a picnic. They walk 
to the picnic spot, carrying identical items in their bags (Fig. 6.1). 
On the way, Pawan keeps adjusting his bag, and looks 
uncomfortable. Megha asks, “Is there a problem with 
your bag?” Pawan responds, “Yes, it is hurting my 
shoulders.” Megha says, “Both our bags are equally 
heavy. Why does your bag hurt, and mine doesn’t?” 
Pawan reflects for a minute and says, “Perhaps, it is 
because of the difference in the straps of our bags. 
My bag has narrow straps while your bag has broad 
straps.”
Can the shape or size of the straps really make a 
difference? Let us try to find out.
When we carry a bag, we feel its weight because 
of the force of gravity acting on our shoulders. The 
weight of the bag with narrow straps acts on a 
smaller area of our shoulders, whereas the weight of 
the bag with broad straps is spread out over a larger 
area of our shoulders. It is due to this reason that we feel 
more comfortable carrying a bag with broader straps than one 
with narrow straps, although both bags have the same weight. 
Since the area over which the force acts is involved, we define 
a quantity called pressure, which is the force per unit area. 
So,   Pressure =
Force
Area
At this stage, we will consider only those forces which act 
perpendicular to the surface on which the pressure is to be computed.
Fig. 6.1: Megha and Pawan  
carrying their bags
Chapter 6.indd   81 Chapter 6.indd   81 6/28/2025   3:59:56 PM 6/28/2025   3:59:56 PM
Page 3


80
Curiosity — Textbook of Science for Grade 8
Pressure, Winds, 
Storms, and Cyclones
6
 
 z Why are winds stronger on some days than on others?
 z Why are water tanks usually placed at a height?
 z Can air pressure really crush us? 
 z What causes storms and cyclones? If the Earth stopped rotating, 
would cyclones still form?
 z Share your questions  
 ?
Probe and ponder
Chapter 6.indd   80 Chapter 6.indd   80 6/28/2025   3:59:54 PM 6/28/2025   3:59:54 PM
Chapter 6?—?Pressure, Winds, Storms, and Cyclones
81
You must have observed fallen leaves on the ground swirling 
in the air or being swept away, and trees swaying or even 
bending when a strong wind blows. Have you ever wondered 
why fallen leaves rise in the air or trees sway or bend? Does the 
wind exert force on fallen leaves to make them rise or on trees 
to bend? Recall other similar effects of the force exerted by wind 
like slamming of doors or rattling of windows, or fluttering of 
clothes? How does the force exerted by wind make this happen? 
The force exerted by wind creates wind pressure which causes 
these effects. In this chapter, we will explore the relationship 
between force and pressure, and understand how they shape 
powerful natural events like thunderstorms and cyclones.
6.1 Pressure
 
Megha and her brother Pawan are going on a picnic. They walk 
to the picnic spot, carrying identical items in their bags (Fig. 6.1). 
On the way, Pawan keeps adjusting his bag, and looks 
uncomfortable. Megha asks, “Is there a problem with 
your bag?” Pawan responds, “Yes, it is hurting my 
shoulders.” Megha says, “Both our bags are equally 
heavy. Why does your bag hurt, and mine doesn’t?” 
Pawan reflects for a minute and says, “Perhaps, it is 
because of the difference in the straps of our bags. 
My bag has narrow straps while your bag has broad 
straps.”
Can the shape or size of the straps really make a 
difference? Let us try to find out.
When we carry a bag, we feel its weight because 
of the force of gravity acting on our shoulders. The 
weight of the bag with narrow straps acts on a 
smaller area of our shoulders, whereas the weight of 
the bag with broad straps is spread out over a larger 
area of our shoulders. It is due to this reason that we feel 
more comfortable carrying a bag with broader straps than one 
with narrow straps, although both bags have the same weight. 
Since the area over which the force acts is involved, we define 
a quantity called pressure, which is the force per unit area. 
So,   Pressure =
Force
Area
At this stage, we will consider only those forces which act 
perpendicular to the surface on which the pressure is to be computed.
Fig. 6.1: Megha and Pawan  
carrying their bags
Chapter 6.indd   81 Chapter 6.indd   81 6/28/2025   3:59:56 PM 6/28/2025   3:59:56 PM
82
Curiosity — Textbook of Science for Grade 8
Broad straps reduce the pressure exerted by the bag on 
our shoulders as compared to narrow straps. Therefore, we 
feel more comfortable carrying a bag with broad straps. 
Can you now understand why it feels easier to lift a 
water-filled bucket with a broad handle than with a narrow 
handle (Fig. 6.2)? Similarly, we have seen that when people 
carry loads like pots or vegetable baskets on their heads, they 
often place a round piece of cloth under the loads (Fig. 6.3). In 
both cases, the objective is to reduce pressure by increasing 
the area over which the weight acts. 
Pressure is defined as the force per unit area. The SI unit 
of force is newton and that of area is metre
2
. Therefore, the 
SI unit of pressure is newton/metre
2
 (N/m
2
). This unit is also 
called a pascal, denoted by Pa.
If a force of 100 N is applied on a cardboard of area 2 m
2
, 
then the pressure applied on the cardboard will be:
Pressure = = 50 N/m
2
= 
Force
Area
100 N
2 m
2
 
There are many situations in daily life where pressure plays 
a role. Conduct the activities given in Table 6.1 and record your 
observations. Explain how pressure influences the mode of 
action undertaken for each activity.
Fig. 6.3: Persons 
carrying loads  
Fig. 6.2: Buckets with broad  
and narrow handles
Broad Narrow
Safety first
The activities listed in Table 6.1 should be conducted under the 
supervision of an adult.
Activity Modes of action
Easy or difficult to 
perform? Give reasons.
Driving an 
iron nail
By the head of 
the nail
By the pointed 
end of the nail
Cutting an 
apple with 
a knife
Using the sharp 
edge of the knife
Using the blunt 
edge of the knife
Table 6.1: Record your observations
Chapter 6.indd   82 Chapter 6.indd   82 6/28/2025   4:00:00 PM 6/28/2025   4:00:00 PM
Page 4


80
Curiosity — Textbook of Science for Grade 8
Pressure, Winds, 
Storms, and Cyclones
6
 
 z Why are winds stronger on some days than on others?
 z Why are water tanks usually placed at a height?
 z Can air pressure really crush us? 
 z What causes storms and cyclones? If the Earth stopped rotating, 
would cyclones still form?
 z Share your questions  
 ?
Probe and ponder
Chapter 6.indd   80 Chapter 6.indd   80 6/28/2025   3:59:54 PM 6/28/2025   3:59:54 PM
Chapter 6?—?Pressure, Winds, Storms, and Cyclones
81
You must have observed fallen leaves on the ground swirling 
in the air or being swept away, and trees swaying or even 
bending when a strong wind blows. Have you ever wondered 
why fallen leaves rise in the air or trees sway or bend? Does the 
wind exert force on fallen leaves to make them rise or on trees 
to bend? Recall other similar effects of the force exerted by wind 
like slamming of doors or rattling of windows, or fluttering of 
clothes? How does the force exerted by wind make this happen? 
The force exerted by wind creates wind pressure which causes 
these effects. In this chapter, we will explore the relationship 
between force and pressure, and understand how they shape 
powerful natural events like thunderstorms and cyclones.
6.1 Pressure
 
Megha and her brother Pawan are going on a picnic. They walk 
to the picnic spot, carrying identical items in their bags (Fig. 6.1). 
On the way, Pawan keeps adjusting his bag, and looks 
uncomfortable. Megha asks, “Is there a problem with 
your bag?” Pawan responds, “Yes, it is hurting my 
shoulders.” Megha says, “Both our bags are equally 
heavy. Why does your bag hurt, and mine doesn’t?” 
Pawan reflects for a minute and says, “Perhaps, it is 
because of the difference in the straps of our bags. 
My bag has narrow straps while your bag has broad 
straps.”
Can the shape or size of the straps really make a 
difference? Let us try to find out.
When we carry a bag, we feel its weight because 
of the force of gravity acting on our shoulders. The 
weight of the bag with narrow straps acts on a 
smaller area of our shoulders, whereas the weight of 
the bag with broad straps is spread out over a larger 
area of our shoulders. It is due to this reason that we feel 
more comfortable carrying a bag with broader straps than one 
with narrow straps, although both bags have the same weight. 
Since the area over which the force acts is involved, we define 
a quantity called pressure, which is the force per unit area. 
So,   Pressure =
Force
Area
At this stage, we will consider only those forces which act 
perpendicular to the surface on which the pressure is to be computed.
Fig. 6.1: Megha and Pawan  
carrying their bags
Chapter 6.indd   81 Chapter 6.indd   81 6/28/2025   3:59:56 PM 6/28/2025   3:59:56 PM
82
Curiosity — Textbook of Science for Grade 8
Broad straps reduce the pressure exerted by the bag on 
our shoulders as compared to narrow straps. Therefore, we 
feel more comfortable carrying a bag with broad straps. 
Can you now understand why it feels easier to lift a 
water-filled bucket with a broad handle than with a narrow 
handle (Fig. 6.2)? Similarly, we have seen that when people 
carry loads like pots or vegetable baskets on their heads, they 
often place a round piece of cloth under the loads (Fig. 6.3). In 
both cases, the objective is to reduce pressure by increasing 
the area over which the weight acts. 
Pressure is defined as the force per unit area. The SI unit 
of force is newton and that of area is metre
2
. Therefore, the 
SI unit of pressure is newton/metre
2
 (N/m
2
). This unit is also 
called a pascal, denoted by Pa.
If a force of 100 N is applied on a cardboard of area 2 m
2
, 
then the pressure applied on the cardboard will be:
Pressure = = 50 N/m
2
= 
Force
Area
100 N
2 m
2
 
There are many situations in daily life where pressure plays 
a role. Conduct the activities given in Table 6.1 and record your 
observations. Explain how pressure influences the mode of 
action undertaken for each activity.
Fig. 6.3: Persons 
carrying loads  
Fig. 6.2: Buckets with broad  
and narrow handles
Broad Narrow
Safety first
The activities listed in Table 6.1 should be conducted under the 
supervision of an adult.
Activity Modes of action
Easy or difficult to 
perform? Give reasons.
Driving an 
iron nail
By the head of 
the nail
By the pointed 
end of the nail
Cutting an 
apple with 
a knife
Using the sharp 
edge of the knife
Using the blunt 
edge of the knife
Table 6.1: Record your observations
Chapter 6.indd   82 Chapter 6.indd   82 6/28/2025   4:00:00 PM 6/28/2025   4:00:00 PM
Chapter 6?—?Pressure, Winds, Storms, and Cyclones
83
What can you conclude from your observations in Table 6.1?
We conclude that when the area over which a 
force applied is smaller, the resulting pressure is 
higher, making it easier to do certain tasks. This is 
why it is easier to drive a nail using its pointed end, 
and it is easier to cut an apple with the sharp edge 
of a knife.
You must have seen overhead water tanks 
(Fig. 6.4) in your locality, or on the rooftops of houses 
used for water supply. Why are these tanks always 
placed at a height?
Do liquids also exert pressure?
Let us find out by conducting the following activity.
Activity 6.1: Let us try and find out
 z Take two transparent glass or plastic pipes of the same 
length (about 25 cm), but of different diameters, as shown 
in Fig. 6.5. 
 z Take two good-quality rubber balloons. Attach 
them to one end of each pipe. 
 z Clamp the pipes on a stand as shown in Fig. 6.5.
 z Now, fill both the pipes with water up to the 
same level about halfway.
 z Observe what happens to the balloons.
 z Do both balloons bulge? Do they bulge to the 
same extent?
What can you infer from this activity? You must 
have observed that the two balloons bulge to the 
same extent. Why is it so? Notice that because of the 
different diameters, the weight of water in the two 
pipes is different. However, the bulge in both the 
balloons is the same. This means that the weight of 
water in the pipes could not be responsible for the 
extent of the bulge of the balloons. 
Could it be that the water column is exerting pressure? Yes, it 
is the pressure exerted by the water column which is responsible 
for the bulge. That is why equal water column heights produce 
equal bulges in the balloons, despite their different diameters.
Fig. 6.4: Overhead tank
Fig. 6.5: Equal heights of water columns 
produce same bulge in balloons
Broad 
pipe
Balloons
Water
Narrow 
pipe
Stand
Chapter 6.indd   83 Chapter 6.indd   83 6/28/2025   4:00:02 PM 6/28/2025   4:00:02 PM
Page 5


80
Curiosity — Textbook of Science for Grade 8
Pressure, Winds, 
Storms, and Cyclones
6
 
 z Why are winds stronger on some days than on others?
 z Why are water tanks usually placed at a height?
 z Can air pressure really crush us? 
 z What causes storms and cyclones? If the Earth stopped rotating, 
would cyclones still form?
 z Share your questions  
 ?
Probe and ponder
Chapter 6.indd   80 Chapter 6.indd   80 6/28/2025   3:59:54 PM 6/28/2025   3:59:54 PM
Chapter 6?—?Pressure, Winds, Storms, and Cyclones
81
You must have observed fallen leaves on the ground swirling 
in the air or being swept away, and trees swaying or even 
bending when a strong wind blows. Have you ever wondered 
why fallen leaves rise in the air or trees sway or bend? Does the 
wind exert force on fallen leaves to make them rise or on trees 
to bend? Recall other similar effects of the force exerted by wind 
like slamming of doors or rattling of windows, or fluttering of 
clothes? How does the force exerted by wind make this happen? 
The force exerted by wind creates wind pressure which causes 
these effects. In this chapter, we will explore the relationship 
between force and pressure, and understand how they shape 
powerful natural events like thunderstorms and cyclones.
6.1 Pressure
 
Megha and her brother Pawan are going on a picnic. They walk 
to the picnic spot, carrying identical items in their bags (Fig. 6.1). 
On the way, Pawan keeps adjusting his bag, and looks 
uncomfortable. Megha asks, “Is there a problem with 
your bag?” Pawan responds, “Yes, it is hurting my 
shoulders.” Megha says, “Both our bags are equally 
heavy. Why does your bag hurt, and mine doesn’t?” 
Pawan reflects for a minute and says, “Perhaps, it is 
because of the difference in the straps of our bags. 
My bag has narrow straps while your bag has broad 
straps.”
Can the shape or size of the straps really make a 
difference? Let us try to find out.
When we carry a bag, we feel its weight because 
of the force of gravity acting on our shoulders. The 
weight of the bag with narrow straps acts on a 
smaller area of our shoulders, whereas the weight of 
the bag with broad straps is spread out over a larger 
area of our shoulders. It is due to this reason that we feel 
more comfortable carrying a bag with broader straps than one 
with narrow straps, although both bags have the same weight. 
Since the area over which the force acts is involved, we define 
a quantity called pressure, which is the force per unit area. 
So,   Pressure =
Force
Area
At this stage, we will consider only those forces which act 
perpendicular to the surface on which the pressure is to be computed.
Fig. 6.1: Megha and Pawan  
carrying their bags
Chapter 6.indd   81 Chapter 6.indd   81 6/28/2025   3:59:56 PM 6/28/2025   3:59:56 PM
82
Curiosity — Textbook of Science for Grade 8
Broad straps reduce the pressure exerted by the bag on 
our shoulders as compared to narrow straps. Therefore, we 
feel more comfortable carrying a bag with broad straps. 
Can you now understand why it feels easier to lift a 
water-filled bucket with a broad handle than with a narrow 
handle (Fig. 6.2)? Similarly, we have seen that when people 
carry loads like pots or vegetable baskets on their heads, they 
often place a round piece of cloth under the loads (Fig. 6.3). In 
both cases, the objective is to reduce pressure by increasing 
the area over which the weight acts. 
Pressure is defined as the force per unit area. The SI unit 
of force is newton and that of area is metre
2
. Therefore, the 
SI unit of pressure is newton/metre
2
 (N/m
2
). This unit is also 
called a pascal, denoted by Pa.
If a force of 100 N is applied on a cardboard of area 2 m
2
, 
then the pressure applied on the cardboard will be:
Pressure = = 50 N/m
2
= 
Force
Area
100 N
2 m
2
 
There are many situations in daily life where pressure plays 
a role. Conduct the activities given in Table 6.1 and record your 
observations. Explain how pressure influences the mode of 
action undertaken for each activity.
Fig. 6.3: Persons 
carrying loads  
Fig. 6.2: Buckets with broad  
and narrow handles
Broad Narrow
Safety first
The activities listed in Table 6.1 should be conducted under the 
supervision of an adult.
Activity Modes of action
Easy or difficult to 
perform? Give reasons.
Driving an 
iron nail
By the head of 
the nail
By the pointed 
end of the nail
Cutting an 
apple with 
a knife
Using the sharp 
edge of the knife
Using the blunt 
edge of the knife
Table 6.1: Record your observations
Chapter 6.indd   82 Chapter 6.indd   82 6/28/2025   4:00:00 PM 6/28/2025   4:00:00 PM
Chapter 6?—?Pressure, Winds, Storms, and Cyclones
83
What can you conclude from your observations in Table 6.1?
We conclude that when the area over which a 
force applied is smaller, the resulting pressure is 
higher, making it easier to do certain tasks. This is 
why it is easier to drive a nail using its pointed end, 
and it is easier to cut an apple with the sharp edge 
of a knife.
You must have seen overhead water tanks 
(Fig. 6.4) in your locality, or on the rooftops of houses 
used for water supply. Why are these tanks always 
placed at a height?
Do liquids also exert pressure?
Let us find out by conducting the following activity.
Activity 6.1: Let us try and find out
 z Take two transparent glass or plastic pipes of the same 
length (about 25 cm), but of different diameters, as shown 
in Fig. 6.5. 
 z Take two good-quality rubber balloons. Attach 
them to one end of each pipe. 
 z Clamp the pipes on a stand as shown in Fig. 6.5.
 z Now, fill both the pipes with water up to the 
same level about halfway.
 z Observe what happens to the balloons.
 z Do both balloons bulge? Do they bulge to the 
same extent?
What can you infer from this activity? You must 
have observed that the two balloons bulge to the 
same extent. Why is it so? Notice that because of the 
different diameters, the weight of water in the two 
pipes is different. However, the bulge in both the 
balloons is the same. This means that the weight of 
water in the pipes could not be responsible for the 
extent of the bulge of the balloons. 
Could it be that the water column is exerting pressure? Yes, it 
is the pressure exerted by the water column which is responsible 
for the bulge. That is why equal water column heights produce 
equal bulges in the balloons, despite their different diameters.
Fig. 6.4: Overhead tank
Fig. 6.5: Equal heights of water columns 
produce same bulge in balloons
Broad 
pipe
Balloons
Water
Narrow 
pipe
Stand
Chapter 6.indd   83 Chapter 6.indd   83 6/28/2025   4:00:02 PM 6/28/2025   4:00:02 PM
84
Curiosity — Textbook of Science for Grade 8
Pour some more water in any one of the pipes 
used in Fig. 6.5. Observe the bulge of the balloon. 
Repeat this process a few times, adding more 
water each time and noting the extent of bulge as 
shown in Fig. 6.6. 
Do you see any relation between the amount 
of bulge of the rubber balloon and the height of 
the water column in the pipe? You must have 
observed that the bulge of the balloon increases 
as the height of the water column increases.
Thus, as the height of the water column in the pipe increases, 
the pressure at the bottom of the pipe also increases, which causes 
the balloon to bulge more. So, we can say that the pressure exerted 
by a liquid in a vessel depends on the height of its column. This 
is the reason why overhead tanks are placed at a height so that 
the pressure in the taps is increased, resulting in a good stream of 
water from the taps. 
Suppose you are living on the second floor of a three-storeyed 
building and an overhead water tank is placed on the top floor. 
Will you or your friend on the first floor receive a more powerful 
stream of tap water? Give reasons.
....................................................................................................................
Do liquids also exert pressure on the walls of the container? 
Let us find out by conducting the following activity.
Activity 6.2: Let us find out
 z Take a used plastic bottle and remove its cap. Make 
four small holes near the bottom around the sides 
using a needle or a nail. Make sure that the holes are at 
the same height from the bottom as shown in Fig. 6.7. 
(If you find it difficult to make a hole, you can slightly 
heat the needle and poke it to make holes.) 
 z Seal the holes with a tape and fill the bottle with water. 
 z Now, remove the tape from all holes at the same time. 
 z What do you observe? 
Water
More 
water
Balloon 
bulges 
out more
Balloon 
bulges 
out
Fig. 6.6: Higher heights of water column 
produce bigger bulge of the balloon
Bottle
Water
Holes
Fig. 6.7: Liquid exerts pressure 
on the wall of the container
What will happen to the 
bulge of the balloon if we 
increase the height of the 
water column? 
Chapter 6.indd   84 Chapter 6.indd   84 6/28/2025   4:00:03 PM 6/28/2025   4:00:03 PM