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NCERT Solutions Exploring Society: India and Beyond Chapter 2 c) Atmospheric pressure — THINK ABOUT IT

Book page 35 Updated on2026-09-05

Q1.
Why do you think it would be important to measure atmospheric pressure? Who are the people most likely to use such measurements?
Answer

Because atmospheric pressure is the earliest warning we have. Rain, wind and cloud tell you what the weather is; a falling barometer tells you what it is about to become.

Normal pressure at the sea coast ≈ 1013 mb
Pressure falling below 1000 mb → a ‘depression’ or low-pressure system
A deepening depression → storm → cyclone

Who uses these measurements:

WhoWhy they need it
MeteorologistsTo spot a depression forming and issue a storm or cyclone warning
Fishermen and sailorsTo decide whether it is safe to go out to sea
Disaster management authoritiesTo evacuate a coastal belt in time
Pilots and air traffic controlAircraft altimeters work on air pressure; wrong pressure means wrong height
Mountaineers, trekkers, army units at high altitudeLow pressure means less oxygen — they must plan pauses to acclimatise
FarmersA falling barometer means rain is likely — do not leave a harvested crop out
Why pressure predicts weather: Wind is simply air moving from high pressure to low pressure. Where pressure drops sharply, air rushes in from all sides, is forced upward, cools, condenses and forms thick cloud. So a low reading on a barometer is really the first sign of that whole chain beginning.
Q2.
People who journey to places at a high altitude are advised to make pauses on the way to allow the body to acclimatise. Our army personnel serve in high-altitude places like Khardung la in Ladakh, which is over 5600 metres above sea level. It is hard to imagine how they live and work in places where the oxygen level is so low — the atmospheric pressure there is generally about 650 millibars!
Answer

Compare the two numbers the chapter gives you:

At the sea coast: about 1013 mb
At Khardung La (over 5600 m): about 650 mb
Difference = 1013 − 650 = 363 mb — roughly a third of the air pressure is missing

Every breath a soldier takes at Khardung La therefore brings in only about two-thirds as much oxygen as the same breath at the coast. The body responds by breathing faster and making the heart work harder, which is why visitors feel breathless, dizzy or tired at high altitude.

What acclimatising means: stopping for a day or two at an intermediate height, moving slowly, drinking plenty of water and not exerting on the first days. Given that time, the body makes more red blood cells and breathes more efficiently, so the same thin air carries enough oxygen. Soldiers posted in Ladakh, Siachen and similar posts go through a staged acclimatisation programme before they take up duty.

Why pressure falls with height: Atmospheric pressure is the weight of the air above you. Climb a mountain and you leave part of the atmosphere below you, so there is less air pressing down — the air becomes ‘thinner’, and the same lungful holds fewer oxygen molecules.
Think about it further: The soldiers are not the only ones affected. Water boils at a lower temperature up there, so cooking takes far longer; helicopters get less lift from the thin air; and even a small wound heals more slowly. Respect for what our army personnel manage at those heights is very much the point of this box.
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