Properties of Air

Air is all around us, even though we cannot see it. It is invisible, but we can feel its presence, such as when the wind blows or when we breathe. For example, when we inhale, air enters our body through the nose, and if we blow on our hand, we can feel the air. Air occupies space, as shown when we blow air into a balloon and it expands. Even though air is invisible, it has weight, and this is why we feel air pressure around us. Air is essential for all living things because we need it to breathe.

• Temperature regulation: The earth receives energy from the sun. This energy is reflected by the earth in the form of heat. The constituents of air surrounding the earth, such as water vapour and carbon dioxide, absorb a part of this heat and give it to the other constituents of air. As a result, the earth’s surface remains warm and thereby becomes suitable for the living world on the earth. If there were no air on the earth, the average temperature of the earth’s surface would have been very low.
• Transmission of sound: All the sounds that we hear reach us through the surrounding air. The density of air also changes due to changes in its temperature. In winter, the density of the air increases. We can hear the whistle of a distant train clearly early in the morning in winter. Air is useful as a medium for the transmission of sound.

1. Aim: To demonstrate that air has weight.

2. Requirements: A stick (from a broom or a paper/plastic straw), thread, two rubber balloons and air (for inflating the balloon)

3. Procedure

• Tie a thread at the centre of the stick and hang it so that it stays horizontal.
• Tie two uninflated rubber balloons of the same size at both ends of the stick.
• Ensure the stick remains balanced and horizontal.
• Remove one balloon, inflate it with air, and tie it back to its original position.
• Observe the balance of the stick.

4. Conclusion: The side with the inflated balloon goes down, showing that the air inside the balloon has weight. This proves that air, like all matter, has mass and weight.

Balloons

1. Aim: To demonstrate the effect of atmospheric pressure and that it acts equally in all directions.

2. Requirements: An injection syringe (without the needle)

3. Procedure

• Take the syringe and pull the piston back without covering the inlet hole. Observe that the piston moves easily and stays in place when you release it.
• Now, tightly cover the inlet hole of the syringe with your thumb.
• Try pulling the piston again and observe the force required. It's harder to pull the piston this time.
• Once you pull the piston out and release it, observe that it gets pushed back in immediately.
• Repeat the experiment by holding the syringe in different positions (vertical, horizontal, and inclined) and observing the behaviour of the piston.

4. Conclusion: When the inlet hole is closed, pulling the piston creates lower pressure inside the syringe compared to the outside air pressure. The higher atmospheric pressure pushes the piston back in. Repeating the experiment in different positions shows that the atmospheric pressure acts equally in all directions, confirming that air pressure is uniform regardless of orientation.

Air pressure

1. Aim: To observe condensation and understand the relationship between temperature, humidity, and moisture in the air.

2. Requirements: glass and ice cubes.

3. Procedure

• Fill a glass with ice cubes until it is about three-fourths full.
• Let the glass sit for a few minutes, and observe the outside of the glass.
• Notice how water droplets form on the outer surface of the glass.

4. Conclusion: The ice cubes in the glass cool the air around it. As the warm air comes into contact with the cold surface of the glass, the water vapour in the air cools, condenses, and turns into liquid water droplets on the outside of the glass. This process is called condensation.

This experiment also explains humidity, the amount of water vapour in the air. When the air is cooler at night or early morning, it cannot hold as much water vapour, leading to dew formation. In contrast, warmer air in the afternoon can hold more water vapour, making the air feel dry.

Water droplets collected outside the glass