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๐ฌ Think about it
High-speed winds can rip the roof clean off a house — and oddly, leaving your windows open during a storm can save it. How can fast-moving air lower the pressure, and why would open windows help? Two balloons and a puff of breath will show us.
What happens to air pressure where wind moves fast?
- Blowing air into the gap between two hanging balloons makes them move together.
- The fast-moving air creates a low-pressure area between them.
- The higher surrounding pressure pushes the balloons inward.
- So high-speed winds are accompanied by reduced air pressure.
Example:
Blowing harder lowers the pressure even more, so the balloons rush together faster.
Why do high-speed winds blow roofs off houses?
- Fast wind over a roof lowers the air pressure above it.
- The pressure below the roof is then higher than above it.
- If this difference is large and the roof is weak, the roof is pushed up and off.
- Keeping doors and windows open lets air through, reducing the pressure difference and protecting the roof.
In this Activity, we will blow between two hanging balloons to see how fast air changes the pressure.
Materials needed
Two balloons of the same size, strings, and a stick.
Procedure
1. Inflate both balloons and tie strings to them.
2. Hang them from a stick with a gap of 6–10 cm.
3. Blow air into the narrow space between them and note what happens.
4. Now blow harder and observe again.
2. Hang them from a stick with a gap of 6–10 cm.
3. Blow air into the narrow space between them and note what happens.
4. Now blow harder and observe again.
Observation
The balloons move towards each other, and they move faster when you blow harder.
Explanation
Blowing creates fast-moving air, which lowers the pressure between the balloons. The higher surrounding pressure pushes them together. So high-speed winds bring reduced air pressure.
โ Summary
- Blow between the balloons
- They move together
- Fast wind = low pressure
โ
Test Yourself
-
Which way does air move to form wind?
View Answer
From a region of high pressure to a region of low pressure. -
What causes a sea breeze?
View Answer
By day, land warms faster, air rises and low pressure forms over land, so air blows in from the sea. -
What happens to air pressure where wind moves fast?
View Answer
It is reduced — high-speed winds lower the air pressure. -
Why should doors and windows be kept open during a storm?
View Answer
To reduce the pressure difference across the roof, helping prevent it from being blown off. -
A bigger pressure difference gives what kind of wind?
View Answer
A faster (higher-speed) wind.
Important Definitions
- High-speed winds and pressure — Fast-moving air is accompanied by reduced (lower) air pressure.
๐ NCERT Question 13 — Explain why holes are made
Explain why holes are made in banners and hoardings.
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