CBSE Class 8 Science Revision Notes Chapter 6 Pressure, Winds, Storms, and Cyclones

Pressure depends on the force applied and the area over which that force acts. Differences in air pressure produce winds and support the formation of storms, thunderstorms and cyclones.

Wind can lift dry leaves, bend trees, rattle windows and even damage weak structures. These effects occur because moving air applies force and creates pressure.

These CBSE Class 8 Science Revision Notes Chapter 6 explain pressure in solids, liquids and air. They also cover wind formation, lightning, thunderstorms and cyclones according to the current 2026–27 textbook.

Key Takeaways

• Pressure: Force acting per unit area.
• Pascal: The SI unit of pressure, written as Pa.
• Wind: Air moving from a high-pressure region towards a low-pressure region.
• Cyclone: A rotating system of clouds, strong winds and rain around a very low-pressure centre.

Revise Class 8 Science Chapter 6 in 30 Minutes

Use this order for quick revision:

First 10 minutes: Pressure formula, effect of area and liquid pressure
Next 10 minutes: Atmospheric pressure, formation of wind, sea breeze and land breeze
Final 10 minutes: Thunderstorms, lightning, cyclones and safety measures

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Pressure in Class 8 Science Chapter 6 Notes

Pressure tells us how much force acts on a given area.

A force may produce different effects depending on whether it acts over a large area or a small area. This is the basic idea covered in these pressure Class 8 notes.

Definition of Pressure

Pressure is defined as the force acting per unit area.

The pressure formula Class 8 students need to remember is:

Pressure = Force/Area

At this stage, we consider the force acting perpendicular to the surface.

SI Unit of Pressure

The SI unit of force is newton.

The SI unit of area is square metre.

Therefore:

Unit of pressure = N/m²

This unit is called pascal.

Its symbol is:

Pa

So:

1 Pa = 1 N/m²

Example

Force = 100 N
Area = 2 m²

Pressure = 100/2

= 50 N/m²

= 50 Pa

Difference Between Force and Pressure

Force and pressure are related, but they are different quantities.

The same force can create different pressure when the area changes.

Effect of Area on Pressure

For the same force:

• Smaller area produces greater pressure.
• Larger area produces smaller pressure.

Narrow and Broad Bag Straps

A narrow strap acts on a smaller area of the shoulder.

Therefore, it produces greater pressure and may hurt.

A broad strap spreads the same weight over a larger area. This lowers the pressure and makes the bag more comfortable to carry.

Sharp Knife

The sharp edge of a knife has a very small area.

When force is applied:

• Pressure becomes high.
• Cutting becomes easier.

A blunt edge has a larger area and produces less pressure.

Pointed Nail

The pointed end of a nail has a small area.

Therefore, it creates greater pressure and enters wood more easily.

Cloth Under a Load

People carrying loads on their heads often place a folded cloth underneath.

The cloth increases the contact area and reduces pressure on the head.

Daily-Life Examples of Pressure

Liquid Pressure in Class 8 Science

Liquids exert pressure because of the weight of the liquid above a point.

These liquid pressure Class 8 concepts explain why water pushes on the bottom and walls of a container.

Liquid Pressure and Height

The pressure exerted by a liquid depends on the height of its liquid column.

A taller liquid column produces greater pressure at the bottom.

A shorter liquid column produces lower pressure.

Pipe-and-Balloon Activity

Suppose two pipes have different widths but contain water up to the same height.

Balloons attached at the bottom bulge by almost the same amount.

This shows that the pressure depends mainly on the height of the water column, rather than the width of the pipe.

When more water is added:

• The height of the water column increases.
• Pressure at the bottom increases.
• The balloon bulges more.

Why Are Water Tanks Placed at a Height?

An overhead water tank provides a tall water column.

The greater height produces greater water pressure in the pipes.

This gives a stronger stream of water from the taps.

A tap on a lower floor usually receives stronger water pressure than a tap closer to the tank because the water column above it is taller.

Liquids Exert Pressure in All Directions

Water does not exert pressure only downwards.

It also pushes on the sides of its container.

Bottle Activity

If holes are made at the same height around a bottle filled with water, water flows out from all the holes.

This shows that liquid pressure acts sideways as well.

Therefore, liquids exert pressure:

• At the bottom
• On the walls
• In all directions

Why Is the Base of a Dam Broad?

Water pressure increases with depth.

The lower part of a dam experiences greater pressure than the upper part.

Therefore, the base of a dam is made broader and stronger so that it can withstand the greater water pressure.

Atmospheric Pressure in Class 8 Science

The layer of air surrounding Earth is called the atmosphere.

Air has mass and exerts force on objects.

The pressure exerted by the air around us is called atmospheric pressure. This is the main idea covered under atmospheric pressure Class 8.

Air Exerts Pressure

Air exerts pressure in all directions.

Examples include:

• A balloon expands when air is blown into it.
• Air escapes from an open inflated balloon.
• A rubber sucker sticks to a smooth wall.
• Air pressure acts on roofs, windows and doors.

Why Does a Balloon Expand?

Air filled inside a balloon pushes against its inner walls.

This pressure acts in all directions.

Therefore, the balloon expands.

If the mouth remains open, air moves out because the pressure inside the balloon is greater than the pressure outside.

Rubber Sucker and Atmospheric Pressure

When a rubber sucker is pressed against a smooth surface:

• Most of the air trapped below it is pushed out.
• Pressure inside the sucker becomes low.
• Atmospheric pressure outside remains higher.
• The higher outside pressure pushes the sucker against the surface.

This makes the sucker difficult to remove.

A sucker does not stick properly to a rough surface because air can enter through small gaps.

Why Does Atmospheric Pressure Not Crush Us?

Atmospheric pressure is very large.

The air column over an area of about 15 cm × 15 cm may exert a force close to 2250 N.

We are not crushed because the fluids and gases inside our body exert pressure outwards.

The pressure inside and outside the body remains balanced.

Units of Air Pressure

The SI unit of pressure is pascal.

Practical units of air pressure include:

• Millibar
• Hectopascal

1 millibar = 100 Pa

1 hectopascal = 100 Pa

Formation of Wind in Class 8 Science

Wind is moving air.

The formation of wind Class 8 concept is based on differences in air pressure.

Direction of Air Movement

Air moves from:

High pressure → Low pressure

The movement continues until the pressure difference becomes smaller.

Pressure Difference and Wind Speed

A greater pressure difference usually produces faster-moving air.

A smaller pressure difference produces gentler winds.

This is why the wind is stronger on some days and lighter on others.

Sea Breeze and Land Breeze Class 8

The difference in heating between land and water produces local winds.

The sea breeze and land breeze Class 8 topic shows how air pressure changes during the day and night.

Sea Breeze

During the day:

1. Land heats faster than water.
2. Air above the land becomes warm.
3. Warm air expands, becomes lighter and rises.
4. A low-pressure region develops above the land.
5. Cooler air above the sea remains at higher pressure.
6. Air moves from the sea towards the land.

This movement of air is called sea breeze.

Land Breeze

At night:

1. Land cools faster than water.
2. Water remains warmer.
3. Air above the sea becomes warm and rises.
4. A low-pressure region develops above the sea.
5. Air above the land remains at higher pressure.
6. Air moves from the land towards the sea.

This movement is called land breeze.

Sea Breeze and Land Breeze Comparison

High-Speed Winds Class 8

High-speed winds are accompanied by lower air pressure.

This relationship helps explain why roofs may be lifted during storms and why two balloons move towards each other when air is blown between them.

Balloon Activity

When air is blown between two hanging balloons:

• Air speed increases between them.
• Pressure between them decreases.
• Higher pressure outside pushes the balloons inwards.
• The balloons move towards each other.

This shows that fast-moving air produces a region of reduced pressure.

Why Can Strong Winds Blow Off Roofs?

When high-speed winds pass over a roof:

• Pressure above the roof becomes low.
• Pressure inside the house may remain higher.
• The higher inside pressure pushes the roof upwards.
• A weak roof may be lifted or blown away.

The pressure difference between the inside and outside of a building can therefore become dangerous during a storm.

Storms in Class 8 Science Chapter 6 Notes

A storm is formed when strong winds are accompanied by rain, hail or snow.

Formation of a Storm

1. Land becomes heated.
2. Warm and moist air rises.
3. A low-pressure region develops.
4. Cooler air moves in from nearby high-pressure regions.
5. The incoming air also becomes warm and rises.
6. Rising air expands and cools.
7. Water vapour condenses into droplets.
8. Clouds form.
9. Droplets combine and fall as rain, hail or snow.
10. Strong winds with precipitation form a storm.

Storms are common in hot and humid regions.

Thunderstorm Class 8 Notes

A thunderstorm is a storm accompanied by thunder and lightning.

These thunderstorm Class 8 notes explain how moisture, strong winds, water droplets and ice particles help create electric charges inside clouds.

Formation of Electric Charges in Clouds

At high altitudes, water droplets may freeze into ice particles.

Strong upward and downward winds cause water droplets and ice particles to rub against one another.

This produces static electric charges.

Generally:

• Lighter, positively charged particles move upwards.
• Heavier, negatively charged droplets stay in the lower part of the cloud.

This causes separation of charges inside the cloud.

The negatively charged lower part of the cloud may also cause positive charges to gather on the ground, trees and buildings.

Formation of Lightning

Air normally acts as an electrical insulator.

When the build-up of charge becomes very large:

1. Air loses its insulating ability.
2. Charges suddenly flow.
3. A bright flash appears.

This bright flash is called lightning.

Lightning may occur:

• Within the same cloud
• Between two clouds
• Between a cloud and the ground

Formation of Thunder

Lightning heats the surrounding air very quickly.

The heated air expands suddenly.

This rapid expansion produces a loud sound called thunder.

Light travels faster than sound. Therefore, lightning is seen before thunder is heard.

Lightning Safety Class 8

Lightning can cause fires, burns, injuries and death.

The following lightning safety Class 8 points are important for students.

Safe Actions During Lightning

• Move indoors when possible.
• Stay away from tall isolated trees.
• Move away from metal poles and fences.
• Get out of water immediately.
• Avoid open fields when a safer place is nearby.
• Stay inside a closed vehicle if caught outdoors.
• Follow official weather warnings.

If No Shelter Is Available

• Find a low-lying place.
• Crouch down.
• Keep contact with the ground as small as possible.
• Do not lie flat.
• Avoid using an umbrella with a metal rod.

Lightning Conductor

A lightning conductor is a metallic rod fixed along a building.

One end is placed above the highest part of the building.

The other end is buried deep in the ground.

It provides an easier path for electric charge to move safely into the ground.

This protects the building from lightning damage.

Local Thunderstorms in India

Local thunderstorms have different regional names.

Examples mentioned in the chapter include:

• Kalboishakhi: West Bengal, Bihar and Jharkhand
• Bordoisila: Assam
• Mango showers: Kerala, Karnataka and Tamil Nadu

Some pre-monsoon thunderstorms help crops and fruit development.

Cyclone Class 8 Notes

A cyclone is a large rotating storm that develops over warm ocean water.

These cyclone Class 8 notes explain how warm moist air, low pressure and Earth’s rotation create a spinning system of clouds, winds and rain.

Main Features of a Cyclone

A cyclone contains:

• Strong rotating winds
• Thick clouds
• Heavy rainfall
• A very low-pressure centre

Formation of a Cyclone

Cyclone formation can be understood step by step.

1. Ocean water becomes warm.
2. Warm, moist air rises above the ocean.
3. A low-pressure region develops near the surface.
4. Water vapour cools and condenses.
5. Condensation releases heat into the atmosphere.
6. The released heat warms the rising air further.
7. More air rises and pressure falls further.
8. Surrounding air rushes into the low-pressure region.
9. Earth’s rotation makes the moving air spin.
10. The cycle continues and forms a rotating storm system.

This rotating system of clouds, winds and rain is called a cyclone.

Role of Earth’s Rotation

Earth’s rotation causes the inward-moving air to turn and spin.

Without this rotation, the moving air would not form the same organised rotating cyclone structure.

Eye of Cyclone Class 8

The centre of a cyclone is called its eye.

The eye of cyclone Class 8 topic is important because the eye behaves differently from the surrounding storm.

It is the region of lowest pressure.

Inside the Eye

• Winds may be comparatively calm.
• Rain may reduce for a short time.

Around the Eye

• Winds are extremely strong.
• Rainfall is heavy.
• Damage may be severe.

The calm eye should not be taken as the end of the cyclone because dangerous winds can return.

Why Does a Cyclone Weaken Over Land?

A cyclone gains energy from warm, moist ocean air.

When it moves over land:

• Its moisture supply reduces.
• Friction with the land slows the winds.
• The cyclone gradually becomes weaker.

Even after landfall, it may continue to cause heavy rainfall and flooding.

Effects of Cyclones

Cyclones can cause:

• Destructive winds
• Heavy rainfall
• Coastal flooding
• River overflow
• Landslides
• Damage to homes
• Fallen trees
• Blocked roads
• Power cuts
• Contamination of drinking water
• Damage to farmland
• Loss of life and property

Storm Surge

Strong cyclone winds may push seawater towards the coast.

This creates a raised wall of water called a storm surge.

Storm surges may flood coastal areas and places located farther inland.

Salt water may:

• Contaminate fresh water.
• Damage crops.
• Reduce soil fertility.
• Enter homes and fields.

Cyclone Safety and Preparedness

People in cyclone-prone areas should follow official warnings.

Important precautions include:

• Listen to alerts issued by the India Meteorological Department.
• Keep an emergency kit ready.
• Store safe drinking water and basic medicines.
• Protect important documents.
• Charge communication devices.
• Move to a designated cyclone shelter when instructed.
• Stay away from coastal areas and flooded roads.
• Do not touch fallen electric wires.
• Return home only after authorities say it is safe.

Role of the India Meteorological Department

The India Meteorological Department monitors:

• Weather systems
• Thunderstorms
• Cyclones
• Wind speeds
• Rainfall
• Likely storm paths

Weather satellites help track cyclones and provide early warnings.

This can reduce damage to life and property.

Storm, Thunderstorm and Cyclone

Important Formulas in Class 8 Science Chapter 6

Solved Examples

Example 1: Calculate Pressure

Force = 200 N
Area = 4 m²

Pressure = 200/4

= 50 Pa

Example 2: Elephant Standing on Four Feet

Weight of elephant = 20,000 N

Area of one foot = 0.25 m²

Total area of four feet:

4 × 0.25 = 1 m²

Pressure:

20,000/1 = 20,000 Pa

Example 3: Pressure Exerted by Two Boats

Boat A:

• Base area = 7 m²
• Number of people = 5
• Weight per person = 700 N

Total force:

5 × 700 = 3500 N

Pressure:

3500/7 = 500 Pa

Boat B:

• Base area = 3.5 m²
• Number of people = 3

Total force:

3 × 700 = 2100 N

Pressure:

2100/3.5 = 600 Pa

Boat B experiences greater pressure by:

600 − 500 = 100 Pa

Important Terms in Pressure Winds Storms and Cyclones Notes

These Pressure Winds Storms and Cyclones notes include several terms that students should revise carefully.

Quick Revision of CBSE Class 8 Science Chapter 6 Notes

Use these CBSE Class 8 Science Chapter 6 notes for a final recap:

• Pressure is force divided by area.
• The SI unit of pressure is pascal.
• Smaller area produces greater pressure for the same force.
• Liquids exert pressure in all directions.
• Liquid pressure increases with the height of the liquid column.
• Overhead tanks increase water pressure.
• Air exerts atmospheric pressure.
• Air moves from high pressure to low pressure.
• A greater pressure difference can produce faster winds.
• Sea breeze moves from sea to land during the day.
• Land breeze moves from land to sea at night.
• High-speed winds are accompanied by lower pressure.
• Storms form when warm, moist air rises and condenses.
• Charge separation inside clouds produces lightning.
• Thunder is caused by rapid expansion of heated air.
• A lightning conductor transfers charge into the ground.
• Cyclones form over warm ocean water.
• The eye is the low-pressure centre of a cyclone.
• Cyclones weaken after moving over land.
• Official alerts and cyclone shelters reduce risk.

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