Page 75 - Innovator's Science-8

With an increase in altitude, both density and pressure decrease rapidly.

Air pressure is important for the following reasons :
1. It creates wind: When air moves, it becomes wind. The difference in

atmospheric pressure gives rise to the wind system of the Earth.
2. It influences weather: Changes in weather are related to changes in

the atmospheric pressure.
Air movement (upward and down wards), caused due to differences
in pressure, creates cloudy and clear skies, brings rain or fine

weather.
3. Weather Forecasting: Changes in air pressure give important clues for

forecasting weather.

High speed winds accompany Reduced Air Pressure

Moving air is called wind. It has been found that fast blowing wind
creates a region of low pressure. Let us perform the following activity to
explain that fast blowing wind creates a region of low or reduced air
pressure.

Activity-2 Aim: To observe that high speed winds are
accompanied by reduced air pressure.
Experiential Learning
Materials Required: Two balloons of equal size, blowing
stick, thread, water. air
Procedure: Two inflated balloons
• Take two balloons of equal size. Fill a li le water (containing a little
water each) hanging
into both the balloons to make them slightly from a stick.
heavier and more stable.
• Inflate both the balloons by filling air into them
and e their mouths properly with strong
threads. Hang the two inflated balloons about 10
cm apart on a s ck with the help of threads ed
to their mouths.
• If you blow air (or wind) hard in the gap between When air (or wind) is blown
in the space between the
the two balloons, from your mouth, you see that two balloons, they
the two balloons come closer. come closer.
Observation: When the high speed air moves through the gap in between the
balloons, the pressure of air fills in the gap. The air pressure on the outside of the
balloons being higher, pushes the two balloons towards each other and makes them
come closer.
Conclusion: High speed winds are accompanied by reduced air pressure.

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Science-8