Winds, Storms and Cyclones Class 7 Notes CBSE Science Chapter 8 (Free PDF Download) (Not in the Current Syllabus)

• The invisible gaseous material that surrounds the earth is known as air.

• Air is composed of 78.09 per cent nitrogen, 20.95 per cent oxygen, 0.93 per cent argon, 0.04 per cent carbon dioxide, and trace amounts of other gases by volume. Water vapour is also present in the air, with an average concentration of roughly 1% at sea level and 0.4 per cent throughout the atmosphere. 

• Air has the Following Properties: 

1. It exerts pressure on us.

2. When air is heated, it expands and contracts.

3. Warm air rises, while cooler air sinks towards the earth's surface.

4. As warm air rises, air pressure drops at that location, allowing cooler air to move in.

• The term "wind" refers to the movement of air. Air travels from a high-pressure region to a low-pressure zone.

• Air Pressure:

Air goes from a place with high air pressure to one with low air pressure. The faster the air moves, the larger the pressure differential. Air pressure is the force exerted by the air on all bodies in all directions at all times. A low-pressure area is created when air travels at high speeds.

A balloon's air exerts pressure in all directions, causing it to inflate. The motion of a moving object is opposed by air. This is referred to as air resistance. That is why, when riding a bicycle, you must push yourself and pedal hard.

• Air expands on heating:

Cool air is heavier than warm or hot air. Warm air rises like smoke, while cool air descends. When heated air rises, it causes a drop in pressure in the area, causing cooler air from higher pressure to rush in to take its place.

• Wind Types Include:

1. Wind Currents: Wind currents are created when the earth's surface heats up unevenly. 

The non-uniform heating of the Earth causes wind currents to arise. This means that heating is unequal at the equator and at the poles. This heated air rises and colder air from the 0-30 degree latitude band on each side of the equator moves in to replace it. Wind currents are created in this manner.

2. Thunderstorms: A storm that includes thunder, lightning, and rain. Lightning and sound are created by the rapid movement of falling water droplets combined with rising air. This is what we refer to as a thunderstorm.

• Rain is brought by winds carrying water vapour.

• Cyclones are formed by strong winds and a difference in air pressure. The use of advanced technology such as satellites and radars has made it easier to monitor cyclones. The finest help is self-help. As a result, it is preferable to plan ahead of time and be prepared to defend against any approaching cyclone.

• Tornadoes do not occur frequently in our nation. Tornadoes are dark funnel-shaped clouds that form from the sky and descend to the ground. The majority of tornadoes are weak. Tornadoes may move at rates of up to 300 kilometres per hour. Within cyclones, tornadoes can form.

• The flowchart below will assist you in comprehending the phenomena that cause clouds to form, rain to fall, and storms and cyclones to form.

• A Cyclone notice or Cyclone watch is issued 48 hours ahead of any forecast cyclone, while a Cyclone warning is issued 24 hours ahead, thanks to satellites and radars. When a cyclone is approaching the coast, the message is aired every hour or half-hour. Several national and international organisations work together to monitor disasters caused by cyclones.

CBSE Class 7 Science Chapter 8 Notes PDF

Understanding Winds

Let’s start the class 7 science chapter 8 notes with the topic of air pressure. According to experts, the air is always around us and is exerting constant pressure.  And wind can be defined as the natural motion of air. This motion occurs due to the presence of a current in any particular direction.

It should also be noted in this NCERT class 7 science chapter 8 notes that increased wind speed is always accompanied by reduced air pressure. Also, the air tends to move from regions with high pressure to regions that have low pressure.

If you want to know more about winds than what is mentioned in this class 7th science chapter 8 notes, then it is suggested that you should read some other academic articles. You can find those articles on the internet.

Wind currents can be caused due to uneven heating or water and land. This happens because we know that land gains and loses heat faster in comparison to water. During the summer months, we know that winds move from the cooler seas towards the land that is hotter. These winds carry moisture, and that results in the monsoon season.

When it comes to the winter months, then the direction of the wind is reversed. This means that the wind moves from land towards the oceans. Rains are caused when winds from the seas and oceans flow towards the land. These winds carry moisture. The moisture that is present in the clouds gets so saturated after a point that it pours down as rain or a shower. This also results in the monsoon season.

Looking at Cyclones

According to the guidelines set by authorities, a cyclone can be defined as a large mass of air. This mass of air rotates in a violent manner of about 1015 km high in the air. Surprisingly, the center of a cyclone is nothing but a calm area, which is also known as the eye of the storm.

The diameter of the eye of a storm can range from 10 to 30 km. There is also a region of clouds of about 150 km around the eye of the storm. This region also has winds that have speeds of about 150 to 250 km per hour. Eventually, the speed of the wind will decrease as it moves from the center of the cyclone.

It is advised that you should go through the image that is attached below. This image depicts the structure of a cyclone. And it will help readers to get a better idea regarding the structure of a cyclone.

(Image to be added soon)

Fun Facts about Winds and Storms

According to many popular science class 7 chapter 8 notes, wind currents are also caused due to the uneven heating that occurs between the poles and the equator. Do you know how that happens? If you don’t, then let’s look at the explanation that is mentioned below.

The entire process begins when the regions that are in proximity to the equator receive a higher amount of heat from the sun. After that, the warm air rises up into the atmosphere. The air from the latitudes 0 to 30 degrees moves in from the north direction and south to take its place.

In a similar manner, the air at the poles is far cooler than the air that is present around the latitudes of 60 degrees. The latter is comparatively warmer. This means that the warm air will rise while the cool air, which is present around the poles, will move towards the inside to occupy the space.

Hence, it can be said that the wind currents move from the poles to places with a warmer latitude. And as we have already seen, this happens because of the uneven heating of the surface of the earth.

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