Introduction to Air
Air is present all around us. However, we cannot see it and we can only feel its presence. For example, if we flap a hand fan near our face, we will feel the air and if we ride a bicycle, we will feel the air against our face. A mixture of various gases such as nitrogen, oxygen, carbon dioxide, water vapour, and a few other gases is called air. Air may contain some dust particles and oxygen present in the air to support burning. Air is necessary for the survival of living organisms including plants, animals, and microorganisms. The absence of air can lead to their death.
Class 7th Geography Chapter 4 Air Around Us covers all the concepts related to air and it enhances the knowledge of the students related to the subject. Knowing further, it is important to know that the air we breathe should be clean and fresh which will help us in keeping healthy. Plants are very helpful in keeping the air fresh and clean, therefore, it is necessary to grow more plants and trees. One should try to spend time in open areas such as playgrounds and parks and help their kids also to get fresh air. Homes should also be well ventilated to let in the flow and circulation of air through doors and windows.
Properties of Air
Air is a very unique element of the Earth. It has many characteristics that are its own.
Air is colourless and transparent. This is the factor that allows us to see through the air.
Air lacks smell and taste.
Air occupies the entire space in the atmosphere.
Air has weight.
What Does Air around Us Contain?
Let’s understand some of the terms related to or present in the air around us.
Water Vapour: It is the gas formed as the result of heating up water. The heat of the Sun changes the water into water vapour. The Sun changes the water in the lakes, ponds, rivers, and seas into water vapour. Then, this water vapour mixes with the air and thus air contains water vapour.
Smoke: It is dark-coloured gas that is given out when something is burnt. Factories and vehicles are the major sources of smoke that mixes with the air and makes it dirty. Another example is burning fire crackers that produces smoke; breathing in smoke is harmful to our body.
Dust: It is a dry, powdery form of dirt present in the air. If we want to see the presence of dust in the air, we can do a small experiment. Close all the doors and windows of a room during the day and pull off the curtains, and allow sunlight to enter through a tiny gap. What do we see? We will see tiny things in the air which are movable in the light. It is called dust present in the air around us.
Germs: These are tiny living things growing in dirty places and have the power of making people ill. So, dirty air makes us sick. When a person sneezes, germs from his or her mouth mix with the air. This air may enter another person and make them sick too. So, it is always advised to cover our mouth when we sneeze or cough.
One can easily make small children understand about the air around us in Class 1 chapter by reading and practically showing them some examples and activities related to it. For example, how wet clothes get dried by hanging them outside under the Sun. As the grades are increased, their level of understanding increases and they can get in-depth knowledge about it.
Some Solved Questions
1. What is the main component of air?
Ans: Nitrogen gas is the main component of air.
2. Name the source of oxygen gas in the air.
Ans: Photosynthesis which is the process undergone by green plants is the source of oxygen gas in the air. Photosynthesis helps in giving food to the plants in the form of glucose.
3. How much nitrogen does air contain?
Ans: Air contains around 78.1% of nitrogen.
4. How much oxygen is present in the air?
Ans: The amount of oxygen in the air is 20.9%.
5. Name the source of carbon dioxide in the air.
Ans: Carbon dioxide is released into the air by different means such as when animals and plants respire, they release carbon dioxide or CO2 and burning of fuels also releases CO2 in the air.
6. Name the gases present in the inhaled air and exhaled air.
Ans: Inhaled air by humans contains oxygen and exhaled air contains carbon dioxide whereas plants inhale carbon dioxide and exhale oxygen.
7. How does rusting of iron take place?
Ans: Rusting of iron is due to the presence of moisture in the air. When an iron object is exposed to air, water vapour and air react with each other to form rust.
8. How is oxygen balanced in the air around us?
Ans: Oxygen is balanced in the air around us due to the presence of living organisms living on the Earth. Microscopic organisms and animals living in the air, under water, soil, or on Earth use oxygen present in the air and release carbon dioxide. Green plants use this carbon dioxide during photosynthesis for preparing food and in return, release oxygen gas in the air. This whole cycle resulting in the exchange of gases helps in balancing oxygen in the air around us. Fresh air has more oxygen as compared to polluted air containing more carbon dioxide, smoke, dust, and germs.
9. How does carbon dioxide help in extinguishing fire?
Ans: Since carbon dioxide doesn’t support combustion when sprayed on a burning object, it will stop the supply of oxygen and help in extinguishing the fire.
10. Why is the sky cleaner and clearer after a rainfall?
Ans: The sky gets cleaner and clearer after rainfall because rainfall helps in dropping the dust particles suspended in the air on the ground. This makes the air fresher and dust-free as well as we see the sky clearer as it is free of dust and dirt.
