Air Expands on Heating

Did you know that not just metals but air expands on heating as well? But how? What makes air expand on heating? What is a land breeze? And what is a sea breeze? Let us know more!

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Introduction

Air expands on heating. Why does this happen? It is because the particles of air on becoming warm, move away from each other and take up more space. So we can say that air on becoming hot occupies more space. Since the particles move away from each other, the air becomes less dense and lighter in weight.

As a result, warm air rises up. On the contrary, on cooling the particles of air come closer to each other. Due to this, the volume of air becomes less, the air becomes more dense and heavier. This can be demonstrated by a simple activity.

Browse more Topics under Winds Storms And Cyclones

• Air Exerts Pressure
• Thunderstorms and Cyclones

Activity I

• Materials Required: balloons, trough, ice cold water, hot water, bottle
• Method: Take a bottle. Tie the balloon tightly on the neck of the bottle. Place the bottle in a container having hot water. Record your observation. Now place the bottle in cold water. Again observe.

• Observation: When the bottle is placed in hot water, the balloon expands. When the bottle is placed in cold water, it contracts.
• Inference: This happens because when the bottle is placed in hot water, the air in it becomes warm and expands due to which balloon also expands. When the bottle is placed in cold water, the air in the bottle contracts due to which balloon also contracts.

Daily life examples where you can see the air expands on heating

• Hot air balloon rises up: This is because the air in the balloon expands on heating. It also becomes lighter hence rises up.

• Monsoon Winds: Monsoon winds are caused due to more heating of land at the equator during summer months. Due to this, the air above the land at equator rises up. The moisture-laden winds from oceans towards southern hemisphere blow towards the equator. These are the monsoon winds which cause rainfall.
• Land Breeze and Sea Breeze: They are caused due to uneven heating of the air. The land always gets heated and gets cooled faster as compared to water. In coastal areas, during the daytime, the air above the land gets heated very quickly as compared to water in the sea. The air above the land is hotter and lighter rises up. The cool air above the sea rushes towards land to take its place. This causes sea breeze. During night land gets cooled faster whereas sea is still hot. The air above the sea being comparatively hotter rises up. The air above the land rushes towards the sea. This causes the land breeze.

Let us learn Thunderstorms and cyclones in detail.

What Causes Winds?

Wind is caused due to uneven heating of the earth. Different parts of the earth receive the different amount of heat. The Equator receives direct sun rays due to which it gets more heated up as compared to poles where the sun rays are slanting. The air from the equator rises up and cold air from poles rushes towards the equator to take its place. This causes the convection current in air called winds.

Questions For You

Q1. A fire alarm usually detects smoke in case of fire. Where should such an alarm be placed in a room?

1. Near the door
2. On the floor
3. On any wall
4. On the ceiling

Ans: (d) on the ceiling. This is because the hot air of fire will rise up towards the ceiling and will be easily detected.

Q2. A flag mounted on a flag post near the sea coast flutters in the direction of the sea. At what time of the day does this happen – at midnight or in the afternoon?

Ans: This happens during midnight. This is because land breeze blows during midnight which flutters the flag in the direction of the sea.