Hinglish

Pressure, Wind and Humidity

Class 7 Social Science · Chapter 2: Understanding the Weather · NCERT Exploring Society: India and Beyond section 2.3

Learn

Before a thunderstorm the air can feel "heavy". Atmospheric pressure is the push of the air's weight. It is higher at sea level and lower up in the mountains, where the air is thinner and carries less oxygen, so climbers feel breathless and must pause to acclimatise. A barometer measures it in millibars (mb): about 1013 mb at the coast, but only about 650 mb at Khardung La in Ladakh, where soldiers serve above 5600 m. A reading below 1000 mb signals a depression, which may grow into a storm or cyclone.

Wind is air moving from high pressure to low pressure. Pilots, sailors and farmers watch its speed and direction; strong wind also dries soil faster. A wind vane points in the direction the wind comes from (a wind sock does this at airports), and an anemometer's spinning cups measure its speed in km/h: the faster they spin, the stronger the wind.

Humidity is the amount of water vapour in the air, measured as relative humidity with a hygrometer: 100% means the air is saturated. Dry weather is about 20–40%, humid weather 60–80%. When Zoya's coastal city is at 84% and Kabir's inland city at 52% on equally hot days, Kabir's laundry dries faster and Zoya sweats more, because water evaporates slowly into damp air. Museums and food factories control humidity carefully.

Explore: match the instrument.

  1. Sort each clue.

Remember

  • Pressure falls with height; a barometer reads it in mb, and below 1000 mb is a depression.
  • Wind moves from high to low pressure (wind vane, anemometer); humidity is measured with a hygrometer.

Quick check

Wind always blows from …

  1. high pressure to low pressure
  2. low pressure to high pressure
  3. cold places to the Sun
  4. the sea to the mountains only
Answer

high pressure to low pressure. Pressure differences drive the wind.

Think about it

Why do mountaineers climb in stages instead of going straight to the top?

One answer

Air pressure and oxygen drop with height; pausing lets the body acclimatise and avoid altitude sickness.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.