CBSE Notes Class 6 Chapter 15 Air Around Us

The air around us is a vital part of our daily lives. It forms an invisible yet essential blanket called the atmosphere, surrounding the Earth and extending for miles above its surface. This layer of air supports life by providing oxygen and plays a crucial role in regulating temperature and weather patterns and protecting us from harmful solar radiation.

1.0Introduction

Our Earth is enveloped by a thin layer of air that extends several kilometres above its surface, known as the atmosphere. As we ascend higher into the atmosphere, the air becomes thinner and less dense.

Until the eighteenth century, air was commonly believed to be a single substance. However, scientific experiments have since demonstrated that air is, in fact, a mixture of various gases. 

While the air may seem simple and uniform, it is a complex mixture of various gases, each with unique properties and importance in maintaining balance in our environment. 

Class 6 Science Notes Chapter 15, "Air Around Us," helps us understand the composition and function of air, which is crucial to appreciating its significance in sustaining life on Earth.

2.0Atmosphere

Air is the invisible gaseous medium surrounding us, primarily composed of oxygen and nitrogen. It enables essential processes like respiration. Air is transparent and colourless, occupies space, and surrounds us.

The thin blanket of air surrounding the Earth’s surface is called the atmosphere.

The atmosphere is divided into five distinct layers based on temperature variations, which change with increasing altitude. As we ascend, the air becomes thinner. The five layers are as follows:

• Troposphere: The lowest layer, closest to Earth’s surface, contains over 75% of the atmosphere's mass and most of its water vapour, responsible for weather phenomena like clouds and storms.
• Stratosphere: Located above the troposphere, this layer houses the ozone layer that protects against UV radiation. Airplanes fly here, and thin clouds can occasionally form.
• Mesosphere: The third and coldest layer, reaching about 80 km above Earth, where most meteoroids burn up, creating shooting stars.
• Thermosphere: A hot layer where temperatures can exceed 1500°C. Space shuttles and satellites orbit here, with very thin air.
• Exosphere: The outermost layer, starting around 480 km above Earth, where air thins out and molecules escape into space.

3.0Constituents of Air

Air is primarily composed of two major gases: nitrogen and oxygen. Together, they make up almost all of the air around us. The remaining portion comprises various other gases, water vapour, and tiny particles. This mixture of gases, water vapour, and particles makes up the air we breathe, and its composition can differ slightly depending on geographical regions and environmental factors.

1. Nitrogen: Approximately 78% of the air is nitrogen. It plays an essential role in plant growth, as plants absorb nitrogen through a series of microbial processes that convert it into usable forms.
2. Oxygen: About 21% of the air is oxygen, which is crucial for the survival of all living organisms. Oxygen is necessary for respiration and also aids in combustion processes.
3. Carbon Dioxide: Although it makes up less than 1% of the air, carbon dioxide is vital for life on Earth. It is released when organisms respire and during combustion. Green plants use carbon dioxide during photosynthesis to produce oxygen.
4. Water Vapour: Water vapour is created when water evaporates and enters the atmosphere. The water vapour, or humidity, varies by location and time of day. It plays a vital role in weather and climate.
5. Dust and Smoke: Air also contains tiny dust particles and smoke, which can harm health. These particles vary in concentration depending on location and environmental conditions, such as pollution and wind. Smoke contains a mix of gases and solid particles, contributing to air pollution.

4.0Availability of Oxygen in Water and Soil

Animals in water and soil can breathe because air is dissolved in both. Air allows aquatic animals to respire in water, which we observe as bubbles when heating water. In soil, air is trapped between particles, and adding water to soil shows bubbles as air is displaced. Burrowing animals use this air to breathe, and after heavy rain, earthworms come to the surface when their air pathways are blocked by water.

5.0Balance of Oxygen in the Atmosphere

It is well known that humans and animals cannot survive without plants, as plants produce oxygen through photosynthesis. The complementary respiration processes in animals and photosynthesis in plants maintain the oxygen balance in the atmosphere.

6.0Importance of Air

Air serves numerous essential purposes:

1. Wind: Moving air, called wind, is crucial in various activities. Wind powers windmills, which are used for:
2. • Drawing water from tube wells.
   • Running flour mills.
   • Producing electricity through modern wind turbines.
   • Distributing pollen and seeds from flowers, helping plants reproduce.
2. Flight: The presence of air makes flight possible for birds, insects, and even human-made inventions like aeroplanes and parachutes.
3. Sailing: Boats and yachts rely on air (wind) to sail.
4. Water Cycle: Air plays a crucial role in the water cycle, helping with processes like evaporation, condensation, and precipitation, which are essential for life on Earth.