Air is present everywhere. What is air? Air is transparent and colorless, therefore it can never be seen. When we see things around us, we always see them through the air. Though air cannot be seen, its presence can be felt in many ways. The presence of air may be felt like the wind.

When we ride on a bicycle or a motorcycle, we feel our shirt or muffler being pulled backward. Table cloth, curtains start fluttering when the fan is switched on. The moving air makes the leaves of the trees rustle, and clothes hanging on the clothesline sway. Winnowing is more effective in moving pairs.

How strong is the wind?

We can get a good idea of the speed of the wind by looking at the movement of smoke and the bending of trees. High-speed wind may even uproot trees and blow off the rooftops. High winds can even destroy suspension bridges.

Small kids enjoy playing with paper firkin. The firki rotates when moving air strikes the front of the firki. To make the firki rotate faster children often run holding the stick of the firki. The faster they run, the faster the firkin rotates. Have you seen a weathercock? It shows the direction in which the air is moving at that place. Air is matter and it is present everywhere.

An empty glass is not empty even if it is turned upside down. It is always full of air. If a glass is half filled with water, its upper half is filled with air. When you are pouring any liquid in a vessel, you are also removing air from inside the vessel.

What is air made up of?

Air is not just one substance. Like seawater which is a mixture of many substances, the air is also a mixture of gases. The air around us contains four major gases, namely nitrogen, oxygen, carbon dioxide, and argon. Another major component of air is water vapor. In addition to gases air also contains traces of dust particles, pollen, plant grains, and other solid particles.

 

Let us learn about the different components of air one by one.

Water Vapor

Water keeps evaporating from the surface of oceans, lakes, rivers, and ponds. Plants also release water in the form of vapor through the process of transpiration. Water vapor, thus gets continuously added to air When air comes in contact with a cold surface, it condenses and drops of water appear on the cold surface.

Oxygen

Oxygen supports burning. When wood or coal or LPG is burnt, some quantity of oxygen gas present in the air is used up.

Where does oxygen in the air come from?

Oxygen is produced by plants and trees during photosynthesis. The Amazon rainforest has been described as the "Lungs of our planet". About 20% of Earth's oxygen is produced by the Amazon rainforest.

Nitrogen

We observe that a major part of the air is still left inside both the inverted glasses even after the flames went out. This indicates the presence of other components of air that obviously do not support burning. A major part of the air which does not support burning is nitrogen gas.

Carbon Dioxide

Activity:- Take some freshly prepared lime water in a beaker and keep it inside a room, having cross-ventilation, for a day or two and observe. A white thin layer appears on the surface of the lime water. This is because lime water reacts with carbon dioxide to form insoluble calcium carbonate. Burning of wood coal or LPG consumes oxygen and produces carbon dioxide.

Composition of the air we breathe:

Inhaled air: - 78% nitrogen, 21% oxygen, 04% carbon dioxide, and little water vapor.

Exhaled air: - 78% nitrogen, 17% oxygen, 4 % carbon dioxide, and saturated water vapor.

Dust and Smoke

We know that the burning of fuel produces carbon dioxide. Fuels burning produces smoke when their incomplete combustion occurs due to an insufficient supply of air. Smoke contains some gases and fine dust particles. Heavy particles settle down after some time. Fine dust particles are always present in the air.

You must have seen long chimneys in factories. These chimneys keep harmful gases and smoke away from our noses. We feel suffocated if the air, we breathe in, contains lot of smoke particles.

Dust Particles in the air

When sunlight enters a dark room through a crack or small opening. It appears in the form of a beam. We see many tiny shining particles moving randomly in the beam of sunlight. These tiny particles are nothing but dust particles that reflect the light and make the path of the light visible. The presence of dust particles in air varies from time to time and from place to place

You might have observed similar beams of sunlight passing through the canopy of trees. Headlight beams are visible on foggy nights. We see that air contains mostly nitrogen and oxygen. These two gases together make up 99% of air.

The remaining 1% consists of carbon dioxide, argon, and few other gases, water vapor, and dust particles.

 

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

Air in Water

Take some water in a glass vessel. Heat it slowly on a gas burner. Watch carefully the inner surface of the vessel. Tiny bubbles are produced at the bottom of the vessel. These bubbles come from the air dissolved in water; they rise from the bottom and break free at the top. Air becomes less soluble in water as the temperature goes up. Cold water holds more dissolved air than warm water. Animals living in water use the oxygen dissolved in water to perform various activities.

Air in Soil

Take a lump of dry soil in a beaker. Add water to it and observe. You see bubbles coming out of the soil. These bubbles show that air is present in the soil. The organisms that live inside the soil use this air for their respiration. Animals living in the soil make burrows and holes for air to move in and out of the soil. During rainy season, when all the spaces occupied by the air are filled up with water, animals living in the soil have to coming out for respiration. You must have seen earthworms coming out of the soil during heavy rains.

Oxygen Cycle

Almost all living beings use oxygen during the process of respiration. Plants use carbon dioxide to make their food during photosynthesis. Plants breathe in carbon dioxide and breathe out oxygen during photosynthesis. Animals 'breathe in oxygen' and 'breathe out carbon dioxide'. This shows the interdependence of plants and animals. The algae in the oceans and other water bodies replace about 90% of all oxygen used on our planet.

 

Other uses of air

1. Wind helps in kite flying
2. Air is used to blow balloons
3. Air is used in cars and cycle tyers
4. Parachutes can fly due to air.
5. Air helps in the movements of sailing yachts, gliders and airplanes
6. Birds and insects can fly only in the presence of air.
7. Air helps in the dispersal of seeds and pollen of flowers.
8. Wind drives the windmill. The windmill is used to draw water from tube wells to run flour mills and generate electricity.