Pressure Winds Storms and Cyclones Class 8 Notes Science Chapter 6

Students can rely on these Class 8 Science Notes Chapter 6 Pressure Winds Storms and Cyclones Class 8 Notes for complete exam preparation.

Class 8 Science Chapter 6 Pressure Winds Storms and Cyclones Notes

Class 8 Science Curiosity Chapter 6 Notes

Class 8 Science Chapter 6 Notes – Pressure Winds Storms and Cyclones Notes Class 8

→ Pressure is a force applied per unit area.

→ Atmospheric pressure is the force per unit area exerted on a surface by the weight of the air (the atmosphere) above it.

→ Liquid and gas pressure Liquids and gases exert pressure on the walls of their containers.

→ Lightning conductor is a device that protects buildings from lightning by safely conducting electric charges into the ground.

→ Cyclone is a large-scale rotating storm system characterised by a low-pressure centre and inward spiraling winds.

→ IMD (India Meteorological Department) The official agency that monitors cyclones and thunderstorms in India.

→ A sharp knife cuts better than a blunt one. What could be the reason?

→ Breathing becomes harder as we climb a mountain. What explains this change?

→ A porter uses a round cloth pad while carrying load on the head. What is the benefit of doing this?

→ Despite huge atmospheric pressure around us, we feel normal. What balances this pressure?

→ A moving fan pushes air around the room. What does this show about the nature of air?

→ Two hanging balloons move towards each other when air is blown between them. What does this show?

→ Air moves from coastal areas to land during daytime. What condition makes this possible?

→ A coastal village experienced sudden seawater flooding even before the cyclone fully arrived. What might be the reason?

→ Two cities were hit by the same cyclone. One had fewer casualties. What factor could explain the difference?

→ A bird finds it difficult to fly during a thunderstorm. What does this indicate about the air pressure and wind condition?

→ Two metal towers were struck by lightning, but only one caught fire. What design feature might the safer one have had?

→ Fishermen are advised not to go to sea during low-pressure conditions. What might be developing over the sea?

Pressure

• Pressure is the force acting on one unit of area.
• Pressure = \(\frac{\text { Force }}{\text { Area }}\)
• The SI unit of force is newton (N) and of area is metre² (m²), so the SI unit of pressure is newton per square metre (N/m²) or pascal (Pa).
• Things with a small surface area like pointed nails or sharp knives apply more pressure, which makes them easier to use for cutting or piercing.

Pressure Exerted by Air

1. Air is present all around us and occupies space.
2. The air surrounding the Earth is called the atmosphere.
3. Air is made up of gases like nitrogen, oxygen, argon, carbon dioxide, etc.
4. We may not feel it, but air exerts pressure on everything.
5. In daily life, this can be observed through activities such as
   • Blowing up a balloon the balloon inflates as air pushes outwards.
   • Covering a plate with a large sheet becomes harder to lift because air presses down on it.
6. As the area increases, the force applied by air also increases.
7. This shows that air applies pressure in all directions.

Atmospheric Pressure

1. The pressure exerted by air on all objects is called atmospheric pressure.
2. When we inflate a balloon, the air pushes on its walls from inside, causing it to expand. This proves that air exerts pressure equally in all directions.

Some Facts about Atmospheric Pressure

1. Atmospheric pressure is the pressure exerted by the weight of air present in the atmosphere.
2. It is highest at sea level and decreases with height (altitude).
3. The standard atmospheric pressure at sea level is 1 atmosphere (atm) = 101325 pascal (Pa).
4. Atmospheric pressure is measured using an instrument called a barometer.
5. Mountaineers and pilots carry oxygen cylinders because low atmospheric pressure at high altitudes makes breathing difficult.
6. Our body balances atmospheric pressure with internal body pressure, so we don’t feel its effect.

The bottom part of a dam is made broader because water pressure is highest at the bottom.
This pressure pushes both sideways and downwards. A strong and broad base helps the dam to bear this pressure and remain stable.

Formation of Winds

• Wind is caused by differences in air pressure. Air always moves from a region of high pressure to low pressure. This movement of air is called wind.
• For example, when an inflated balloon is left open, air escapes quickly. Similarly, in a punctured bicycle tube, air rushes out. These show that air moves due to pressure difference.

High Speed Winds and Air Pressure

• When air moves very fast, it creates a low-pressure area around it. This can be seen when two balloons tied to a stick move closer if air is blown between them the space between them becomes low pressure. See fig (a)

• High-speed winds reduce air pressure. That is why during a storm, roofs may blow off, because pressure below the roof is more than the low pressure above it, pushing the roof upward. See fig (b)

Storms, Thunderstorms and Lightning

• When the land becomes hot, the air above it also heats up. This warm air becomes light and rises, creating a low-pressure area. The cooler air from nearby areas moves in to take its place. This movement of air is called wind.
• As the warm air rises higher, it cools down, and the water vapour in it condenses to form clouds. When the water droplets become heavy, they fall as rain, hail or snow. The fast movement of air with rain is called a storm.
• If the storm is also followed by lightning and thunder, it is called a thunderstorm. Thunderstorms often happen in hot, humid areas, especially in the summer season.

How do Lightning and Thunder Occur?
Inside the storm cloud, water droplets and ice particles rub against each other because of strong upward and downward winds. This rubbing creates static electric charges.

• The lighter ice particles become positively charged and move to the top of the cloud.
• The heavier water droplets become negatively charged and gather at the bottom.

Accumulation of charges leading to lightning
This creates a difference in charges inside the cloud. Sometimes, the negative charge at the bottom of the cloud also makes the ground or buildings positively charged.

When this charge difference becomes large, a discharge happens in the form of a bright flash of lightning. The air gets very hot suddenly and expands fast, which causes the sound of thunder.

Safety During Lightning

Lightning can be very dangerous. It can cause fires, injuries, and even death. To stay safe

• Avoid standing under trees or near poles during lightning.

• Do not lie flat on the ground-instead, crouch down with your head low.
• Do not use umbrellas with metal rods.
• If you are in water, come out immediately.
• It is safer to sit inside a car or bus than to stand outside.

Cyclone

A cyclone is a large, spinning storm that forms over warm ocean waters. It consists of strong winds, clouds, and heavy rainfall, revolving around a low-pressure centre.

How Does a Cyclone Form?

• When the sun heats up the ocean, the air just above the warm water also gets heated. This warm air becomes light and starts rising. As it goes higher, the water vapour in the air cools down and turns into clouds.
• While forming clouds, it gives off heat, which makes the air even warmer. This causes more air to rise quickly, and the air pressure in that area becomes even lower.
• Now, the cooler air from around that area rushes in to fill the space left by the rising air, because the Earth is spinning, this rushing air doesn’t go straight-it starts spinning too. This whole spinning system of clouds and wind becomes a cyclone.

Eye of the Cyclone

• The eye is the centre of a cyclone and has the lowest air pressure. Surprisingly, it is calm and quiet inside the eye there is hardly any wind or rain. But around the eye, there are very strong winds and heavy rainfall.
• When a cyclone moves from the sea towards land, the wind becomes even stronger. But once it reaches the land, it starts to slow down because it no longer gets moisture from the ocean.

What Can a Cyclone Do?

• Cyclones can be very harmful. The fast winds can break trees, electric poles, houses, and roads. The cyclone also pushes a huge amount of seawater onto the land. This is called a storm surge, and it can flood coastal areas with water that is 3 to 12 metres high.
• Cyclones can also cause floods, landslides, and damage to crops. Salt water can mix with drinking water and spoil it. Power lines may break, causing electricity cuts for many days.

How Can We Stay Safe from Cyclones?

• We can stay safe by getting early warnings.
• The India Meteorological Department (IMD) uses weather satellites to watch cyclones and sends alerts before they arrive. People who live in cyclone-prone areas should listen to these warnings, keep emergency supplies ready, and go to a safe cyclone shelter if needed.

A lightning conductor is a metal rod installed on tall buildings to protect them from lightning strikes. Its top end is pointed and placed above the building, while the bottom end is buried in the ground. When lightning strikes, the conductor safely transfers the electric charge into the Earth, preventing damage to the building.