Chapter 15: Air around us (Notes)
Posted on : 12-06-2018 Posted by : Admin

1. We might not have seen air, but we have definitely felt the presence of air in many different ways. For example, when the leaves of the trees rustle or the clothes hanging on a clothes-line sway etc.
2. Moving air is called wind. During wind the air blows at very high speed and it may even uproot trees and blow off the rooftops.
3. The pin wheel or a firki rotates only because of the moving air. Similarly, a weather cock shows the direction in which the air is moving at that particular place.

Is air present everywhere around us?

1. The above experiment shows that Air occupies space and it is present everywhere. Air has no color it is transparent.
2. Earth is surrounded by a thin layer of air extending up to several kilometers above the surface of the earth. This layer of air is known as atmosphere.

What is air made up of? 

Until eighteenth century it was believed that air is just a single substance. But later it was proved that air is a mixture of many component gases. Let us know about a few of them.

• Water vapor: when air comes in contact with a cool surface, it condenses and drops of water appear on the cooled surfaces. The presence of water vapor in air is important for the water cycle in nature.
• Oxygen: Oxygen is one of the components present in the air mixture. It is very important for the survival of the living organisms. It is the component which supports burning.
• Nitrogen: Nitrogen is the component which does not support the burning. It is the major component of air mixture.
• Carbon dioxide: Carbon dioxide makes up the small component of the air. Plants and animals consume oxygen for respiration and release carbon dioxide.
• Dust and smoke: The burning of fuel produces smoke whereas dust particles are always present in the sir. Smoke also contains a few gases and fine dust particles. Smoke and dust particle are often harmful to human beings.

We can observe some tiny shining particles moving in the beam of sunlight. These are the dust particles present in the air. The presence of dust particles in air varies from time to time and also from place to place.

We inhale air when we breathe through our nostrils. Fine hair and mucus are present inside the nose to prevent dust particles from getting into the respiratory system. Sometimes children tend to breathe air through mouth and this may cause harmful dust particles to enter into our body.

Air mostly contains nitrogen and oxygen. They both together make up to 99% of the air. The remaining 1% is constituted by carbon dioxide and a few other gases, water vapor and dust particles.

How does oxygen become available to plants & animals living in water and soil?

1. When we heat water in a vessel, just before the water starts to boil we can observe tiny bubbles on the inner surface of the vessel. These bubbles come from the air dissolved in the water. On further heating the water itself turns into vapour and finally begins to boil. The animals living in water use this dissolved oxygen in water.
2. When the water is poured onto the lump of soil, we can observe bubbles coming out from the soil. These bubbles indicate the presence of air in the soil. The organisms living inside the soil respire in this air.
3. The animals living in the soil make burrows and holes. The air moves in and out of these spaces. During rainy season, these burrows are filled up with water and the animals living in these burrows must come out for respiration.

How is oxygen in the air replaced?

1. During the process of photosynthesis, plants make their own food and oxygen is produced. Plants also consume oxygen for respiration, but they produce more of it than what they consume.
2. It is obvious that animals cannot live without plants. Similarly, plants can not survive for long without animals. They would consume all the carbon dioxide in the atmosphere. We can see that both need each other, as the balance of oxygen and carbon dioxide in the atmosphere is thus maintained. This shows the interdependence of plants and animals.
3. The wind makes the windmill rotate. The windmill is used to draw water from tube wells and to run flour mills. Windmills are also used to generate electricity.
4. Air helps in the movements of sailing yachts, gliders, parachutes and airplanes.
5. Birds, bats and insects can fly only due to the presence of air.
6. Air also helps in the dispersal of seeds and pollen of flowers of several plants.
7. Air plays an important role in water cycle.

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