These DAV Class 7 SST Notes and DAV Class 7 SST Chapter 4 Notes – Air Around Us hold significant importance as study material for students.
Air Around Us Class 7 DAV Notes
→ We cannot survive without air. Air is very important for all living organisms. Our earth is surrounded by a thick layer of air which is called the atmosphere.
→ The atmosphere is divided into four layers starting from the earth’s surface. These are- Troposphere, Stratosphere, Mesosphere and Thermosphere.
→ Troposphere is the densest layer of the atmosphere. This is the portion we live in. All weather phenomena take place in this layer.
→ Stratosphere lies above the troposphere. This layer is almost free from clouds and associated weather phenomena. It is ideal for flying aeroplanes.
→ Mesosphere lies above the stratosphere. This layer acts as a shield over the earth’s surface.
→ Thermosphere lies above the mesosphere. Air is very thin in this layer of atmosphere. In the lower layer of thermosphere, ion-particles are present in concentration. These ion-particles are electrically charged and play an important role in our wireless communication.
→ The air without which we cannot survive, is a mixture of a number of gases such as nitrogen (78%), oxygen (21 %), carbon dioxide (0.03%), helium, ozone, argon and hydrogen. A part from these gases, the air also contains some amount of dust particles and water vapours.
→ Nitrogen is the most plentiful gas in the air. When we inhale air, a major amount of nitrogen is not utilised inside our body system. But plants absorb nitrogen through the soil.
→ Oxygen is needed for all living organisms. It is the second most plentiful gas in the air. Green plants produce oxygen during photosynthesis. Thus, oxygen content in the air remains constant. Here it is worth mentioning that we must give due importance to afforestation.
→ Carbon dioxide, though constitutes a very small percentage of the air, it is a very important gas in maintaining the life cycle of plants over the earth.
→ Our atmosphere is continuously receiving man-made substances of both solid and gaseous nature largely due to multiple human activities. As a result of the air we inhale, gets polluted. We must take steps to avert this situation.
→ We are constantly under the pressure of air. This pressure or weight of air is measured by means of barometer. The unit of air pressure is known as millibar.
→ Wind always blows from high pressure area to low pressure area. Monsoon that brings rain, is a type of seasonal wind. Our agricultural activities largely depend on the monsoonal rainfall.
→ When the water vapour rises, it starts cooling. The water vapour condenses causing formation of droplets of water. When these droplets of water become too heavy to float in the air, they start falling down in the form of rain. The rainfall is measured with the help of rain gauge. The unit of measuring rainfall is cm or mm.
→ Weather keeps on changing while climate does not. We should know the daily temperature and pressure conditions of the place where we live. It is equally important to know the weather reports which are given daily in the newspapers, radio and television.
→ Atmosphere : The thickest layer of air that surrounds the earth.
→ Troposphere : The densest layer of the atmosphere we live in.
→ Stratosphere : Above the layer of troposphere lies a calm and clear air called stratosphere.
→ Tropopause : The zone which demarcates line of separation between troposphere and stratosphere.
→ Smog : Smoke particies when combined with fog form smog.
→ Atmospheric pressure : The pressure exerted by the weight of air on the earth’s surface.
→ Wind : The swift horizontal movement of air.
→ Barometer: Instrument to measure atmospheric pressure.
→ Millibar: The unit of air pressure.
→ Rain gauge : The instrument to measure rainfall.
→ Weather: Hour-to-hour, day-to-day condition of the atmosphere.
→ Climate : The date of atmospheric condition that includes temperature rainfall, pressure over a long period of time and covers a larger area.
→ Global warming : A gradual increase in the overall temperature of the earth’s atmosphere.
→ Humidity : Amount of water vapours in the atmosphere.
→ Monsoons : Seasonal reversal of the wind direction according to the change in season.
→ Photosynthesis : Plants absorb carbon dioxide in the presence of sunlight and turn that energy into food.