On this page, you will find NCERT Class 7 Geography Chapter 4 Notes Pdf free download. CBSE Class 7 Social Science Notes Geography Chapter 4 SST Air will seemingly help them to revise the important concepts in less time.
Air Class 7 Notes Social Science Geography Chapter 4
CBSE Class 7 Geography Chapter 4 Notes Understanding The Lesson
1. All living beings depend on the atmosphere, use the air for breath and protect us from the harmful effects of the sun’s rays.
2. Air makes the temperature on the earth livable. Without this, during the day time we feel heat and get frozen during night.
3. The air which we breathe is mixture of many gases. The constituents of air are Nitrogen, Oxygen, Argon, Carbon dioxide mainly.
4. Apart from these gases, tiny dust particles are also present in the air.
5. Nitrogen is the most plentiful gas (78%) in the air. In the air, Oxygen, Argon and Carbon dioxide are 21%, 93% and 0.03% respectively.
6. Plants need nitrogen for their survival. They cannot take nitrogen directly from the air. Bacteria that live in the soil and roots of some plant take nitrogen from the air and change its form so that plants can use it.
7. Oxygen that is taken by human and animals as breathe is produced by plants during photosynthesis. In this way oxygen content in the air remains constant. If we cut trees then this balance gets disturbed.
8. Green plants use carbon dioxide to make their food and release oxygen. The amount of carbon dioxide released by humans or animals seems to be equal to the amount used by the plants which make a perfect balance. However, the balance is upset by burning of fuels.
9. Our atmosphere is divided into five layers starting from the earth’s surface.
10. The first layer is the Troposphere whose average height is 13 km.
11. The second layer is the Stratosphere which extends upto the height of 50 km.
12. The third layer is Mesosphere which extends upto the height 80 km.
13. The fourth layer is Thermosphere which extends upto height of 80 to 400km.
14. The fifth and uppermost layer is Exosphere. This layer has very thin air. Light gases like helium and hydrogen float into the space from here.
15. Weather is this hour-to-hour, day to day condition of the atmosphere. A hot or humid weather may make one irritable. A pleasant, breezy weather may make one cheerful and even plan for an outing.
16. The average weather condition of a place for a longer period of time represents the climate of a place.
17. The degree of hotness and coldness of the air is known as temperature. The temperature of the atmosphere changes between day and night and also season to season. Summers are hotter than winters.
18. An important factor that influences the distribution of temperature is insolation. The amount of insolation decreases from the equator towards the poles. Therefore, the temperature decreases in the same manner.
19. Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface.
20. Horizontally, the distribution of air pressure is influenced by temperature of air at a given place. Wherever, pressure of air is low, the air is cold. Likewise, if pressure is high, the air becomes warmer.
21. The air always moves from high-pressure areas to low-pressure areas.
22. Winds can be broadly divided into three types: Permanent winds, Seasonal winds and Local winds.
23. Permanent winds blow constantly throughout the year in a particular direction.
24. Seasonal winds change their direction in different seasons.
25. Local winds blow only during a particular period of the day or year in a small area.
26. When water evaporates from land and different water bodies, it becomes water vapour. Moisture at any time is known as humidity.
27. When the water is full of water vapour we call it a humid day. On a humid day, clothes take longer to dry and sweat from our body does not evaporate easily.
Notes of Geography Class 7 Chapter 4 Important Terms
Atmosphere: Huge blanket of air which surrounds the earth.
Thermometer: An instrument used in measuring temperature.
Barometer: An instrument used in measuring air pressure.
Rain Gauge: An instrument used in measuring the amount of rainfall.
Humidity: Moisture in the air.
Moisture: Water vapour present in the atmosphere.
Temperature: The degree of hotness and coldness of the air.
Climate: The average weather condition of a place.
Global warming: Increased temperature of the earth.