Air Around Us - NCERT Solutions for Class 6 Science
Air is a mixture of gases that surrounds the Earth and forms its atmosphere. It is essential for life on Earth, as it provides oxygen for respiration, carbon dioxide for photosynthesis, nitrogen for plant growth, and other gases for various biological and chemical processes. Air also influences the weather, the climate, and the environment by carrying heat, moisture, pollutants, and particles across different regions.
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In this article, you will learn more about the air around us. You will discover its composition, properties, pollution, and activities and experiments you can do to explore it. By the end of this article, you will be able to:
Identify the main gases and other components of air
Describe some physical properties of air and how they affect its behavior
Explain how air pollution is caused and how it impacts human health, the environment, and the climate
Perform some fun and educational activities and experiments to demonstrate the concepts of air
Ask and answer questions about air using your own observations and reasoning
Composition of Air
Air is a mixture of gases that makes up about 99% of the Earth's atmosphere. The primary element of air is nitrogen gas, which accounts for 78% of the air composition. Oxygen is the second most abundant gas, with 21% of the air composition. The remaining 1% consists of other gases and water vapor, such as argon, carbon dioxide, neon, helium, krypton, hydrogen, xenon, methane, and ozone. Air chemistry is the study of the composition and properties of air. Sometimes, the word "atmosphere" is used instead of the word "air". Standard Dry Air is a scientific unit of measurement that represents the composition of gases at sea level at 15C and 101325 Pa. Here is a table that shows the composition of Standard Dry Air by volume percentage:
ElementVolume by %Symbol
Helium< Properties of Air
Air is not just a mixture of gases, but also a substance that has physical properties, such as density, pressure, temperature, and humidity. These properties affect how air behaves and interacts with other objects and substances. For example, air can expand, contract, flow, exert force, transfer heat, and dissolve water. Let's look at some of these properties in more detail.
Density of Air
Density is the mass of a substance per unit volume. It is measured in kilograms per cubic meter (kg/m). The density of air depends on its composition, temperature, and pressure. The more molecules there are in a given volume of air, the higher its density. The higher the temperature of air, the lower its density. The higher the pressure of air, the higher its density. The average density of air at sea level and 15C is about 1.225 kg/m. This means that 1 cubic meter of air weighs about 1.225 kilograms.
Density affects how air moves and mixes with other gases. For example, when air is heated, it becomes less dense and rises. When air is cooled, it becomes more dense and sinks. This creates convection currents that drive the circulation of air in the atmosphere. Also, when two gases with different densities come into contact, they tend to diffuse and mix until they reach a uniform density. This is why we can smell perfume or smoke even if they are released far away from us.
Pressure of Air
Pressure is the force exerted by a substance per unit area. It is measured in pascals (Pa) or newtons per square meter (N/m). The pressure of air depends on its density and height. The more molecules there are in a given area of air, the higher its pressure. The higher the height of air above a surface, the lower its pressure. This is because the weight of the air above decreases as we go up in the atmosphere. The average pressure of air at sea level and 15C is about 101325 Pa or 101.325 kPa. This means that 1 square meter of air exerts a force of about 101325 newtons on the surface below it.
Pressure affects how air flows and changes its state. For example, when air moves from a high-pressure area to a low-pressure area, it creates wind. When air is compressed or expanded by changing its pressure, it also changes its temperature and volume. This is why we use pumps and compressors to inflate tires or balloons, or refrigerators and air conditioners to cool or heat air.
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Temperature of Air
Temperature is the measure of how hot or cold a substance is. It is measured in degrees Celsius (C) or kelvin (K). The temperature of air depends on its energy and heat transfer. The more kinetic energy the molecules of air have, the higher its temperature. The more heat energy that is transferred to or from air by radiation, conduction, or convection, the higher or lower its temperature. The average temperature of air at sea level and 15C is about 288 K. This means that the molecules of air have an average kinetic energy of about 0.038 electronvolts (eV).
Temperature affects how air expands and contracts and how much water vapor it can hold. For example, when air is heated, it expands and becomes less dense. When air is cooled, it contracts and becomes more dense. This affects the buoyancy and stability of air masses in the atmosphere. Also, when air is heated, it can hold more water vapor before it becomes saturated. When air is cooled, it can hold less water vapor and may condense into clouds or precipitation.
Humidity of Air
Humidity is the amount of water vapor in the air. It is measured in grams per cubic meter (g/m) or as a percentage of saturation (%). The humidity of air depends on its temperature and pressure. The higher the temperature of air, the more water vapor it can hold before it becomes saturated. The higher the pressure of air, the less water vapor it can hold before it becomes saturated. The average humidity of air at sea level and 15C is about 10 g/m or 66%. This means that 1 cubic meter of air contains about 10 grams of water vapor.
Humidity affects how comfortable we feel and how clouds and precipitation form. For example, when the humidity of air is high, eroding vegetation, killing wildlife, and disrupting ecosystems.
Climate change: Air pollution can affect the climate by altering the radiation balance, changing the cloud formation, and enhancing the greenhouse effect.
Prevention and Reduction of Air Pollution
Air pollution can be prevented and reduced by using cleaner and renewable sources of energy, improving the efficiency and emission standards of vehicles and industries, implementing regulations and policies to limit the emission of pollutants, monitoring and reporting the air quality and pollution levels, raising awareness and educating the public about the causes and effects of air pollution, and adopting personal habits and practices that reduce the consumption and waste of resources. Some of these habits and practices are:
Using public transportation, biking, walking, or carpooling instead of driving.
Turning off or unplugging appliances and devices when not in use.
Using energy-efficient appliances and devices.
Using natural or organic products instead of synthetic or chemical ones.
Recycling, reusing, or composting materials instead of throwing them away.
Planting trees and plants that purify the air and provide oxygen.
Air Activities and Experiments for Class 6
Air is a fascinating topic that you can explore through various activities and experiments. These activities and experiments can h