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Air, Water, and Weather - Properties and Composition of Air

Grade 4CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Air is a mixture of various gases. The major components are Nitrogen (78%78\%), Oxygen (21%21\%), and other gases like Carbon Dioxide (CO2CO_2), Argon, and water vapor (1%1\%).

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Air occupies space: Even an 'empty' container is filled with air. This can be seen when a balloon expands as we blow air into it.

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Air has weight: An inflated balloon or ball is heavier than a deflated one because of the mass of the air particles inside.

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Air exerts pressure: Air pushes against everything it touches in all directions. This is called atmospheric pressure, which helps us use tools like a drinking straw or a dropper.

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Air supports burning: Oxygen (O2O_2) is essential for combustion. Without air, a fire cannot keep burning.

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Air is needed for life: Living things need Oxygen (O2O_2) for respiration, and plants need Carbon Dioxide (CO2CO_2) for photosynthesis.

📐Formulae

Composition of Air≈78%N2+21%O2+1% Other gases\text{Composition of Air} \approx 78\% N_2 + 21\% O_2 + 1\% \text{ Other gases}

Pressure=ForceArea\text{Pressure} = \frac{\text{Force}}{\text{Area}}

Photosynthesis: 6CO2+6H2O→SunlightC6H12O6+6O2\text{Photosynthesis: } 6CO_2 + 6H_2O \xrightarrow{\text{Sunlight}} C_6H_{12}O_6 + 6O_2

💡Examples

Problem 1:

A candle is lit and then covered with a glass jar. After a few seconds, the flame goes out. Why does this happen?

Solution:

The flame goes out because the supply of Oxygen (O2O_2) is cut off.

Explanation:

Air contains O2O_2 which is necessary for burning. Once the jar is placed over the candle, the limited O2O_2 inside is used up, and the flame can no longer be sustained.

Problem 2:

Explain how we are able to drink juice through a straw using the concept of air pressure.

Solution:

By sucking through the straw, we reduce the air pressure inside it.

Explanation:

When we suck on a straw, we remove the air inside, creating a low-pressure area. The higher atmospheric pressure acting on the surface of the juice pushes the liquid up into the straw and into our mouth.

Problem 3:

If you weigh an empty football and then weigh the same football after pumping air into it, which weight will be higher?

Solution:

The football filled with air will be heavier.

Explanation:

This demonstrates the property that air has weight. Even though air is invisible and light, it is made of matter and adds to the total mass of the object.