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๐ฌ Think about it
Let go of an open balloon and the air rushes out; puncture a cycle tube and it hisses flat. In both, air moves — but which way, and why? That same simple rule, scaled up to the whole sky, is what makes the wind blow. Let's uncover it.
Which way does air move, and why do winds form?
- Air moves from a region of high pressure to a region of low pressure.
- This moving air is what we call wind.
- So differences in air pressure cause winds to blow.
- A larger pressure difference gives a faster wind.
How do land breeze and sea breeze form?
- By day, land heats faster than water, so air above land warms, rises and leaves low pressure.
- Higher-pressure air from the sea blows to the land — a sea breeze.
- At night, the water is warmer, so low pressure forms over the sea.
- Air then blows from land to sea — a land breeze.
Sea Breeze
Land Breeze
Blows during the
daytime
.
Blows during the
night-time
.
Land
gets heated faster than water during the day.
Water
stays warmer than land at night.
Low pressure forms
over the land
(warm air rises).
Low pressure forms
over the sea
.
Wind blows
from sea to land
.
Wind blows
from land to sea
.
In this Activity, we will join an inflated and an uninflated balloon to watch which way the air flows.
Materials needed
Two similar thin rubber balloons, a drinking straw, and rubber bands or thread.
Procedure
1. Fix one end of the straw into an uninflated balloon and tie it tight.
2. Inflate the second balloon and hold its mouth so no air escapes.
3. Insert the free end of the straw into the inflated balloon and tie it (no leaks).
4. Predict, then observe, what happens to the two balloons.
2. Inflate the second balloon and hold its mouth so no air escapes.
3. Insert the free end of the straw into the inflated balloon and tie it (no leaks).
4. Predict, then observe, what happens to the two balloons.
Observation
Air moves from the inflated balloon into the uninflated one. After a while both reach almost the same size and the flow stops.
Explanation
Air flows from the higher-pressure (inflated) balloon to the lower-pressure (uninflated) one. It stops when the pressures become equal — just as winds flow from high to low pressure.
โ Summary
- Air flows to the empty balloon
- Stops when pressures equalise
- High pressure to low pressure
โก A step further
- The SI unit of pressure is N/m², also called the pascal (Pa).
- The practical unit of air pressure is the millibar (mb), equal to 100 Pa.
- Air pressure is also given in hectopascal (hPa), also equal to 100 Pa.
Important Definitions
- Wind — Air moving from a region of high pressure to a region of low pressure.
- Sea breeze — The daytime wind that blows from the sea to the land.
- Land breeze — The night-time wind that blows from the land to the sea.
๐ NCERT Question 9 — Fig. 6.25 shows trees along
Fig. 6.25 shows trees along the sea coast on a summer afternoon. Identify which side is land — A or B — and explain.
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๐ NCERT Question 10 — Describe an activity to show
Describe an activity to show that air flows from a region of high pressure to a region of low pressure.
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