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Grade 8 Intermediate About 15 min Version 1 Awaiting review Premium

Air pressure from the Terai to Everest

We live at the bottom of an ocean of air. The weight of the air above us presses on everything in all directions; at sea level this atmospheric pressure is about 101 kPa, which is like 10 tonnes on every square metre. We do not feel it because the air inside our bodies pushes back. Air pressure is strong enough to hold up a card under an upside-down glass of water. The higher you go, the less air there is above you, so the pressure falls: a sealed bag of snacks puffs up in the mountains, and water boils at a lower temperature.

What you will learn

  • Explain that air exerts pressure in all directions.
  • Describe how air pressure changes with altitude.
  • Explain everyday effects of low air pressure in the mountains.

Before you start

  • Know that pressure = force ÷ area.

Materials

  • A glass of water and a stiff card
  • A sealed packet of snacks

Equipment

  • Barometer

Procedure

  1. Start in Biratnagar. Record the air pressure, the force on the card and the boiling point of water.
  2. Travel to Kathmandu and record again.
  3. Climb to the top of Everest and record again. Watch the snack bag.

How this simulation is simplified

  • Air pressure is modelled as 101.3 kPa × e^(−altitude ÷ 8400 m); real values vary with weather.
  • The card is 8 cm × 8 cm, and water's boiling point falls by about 1 °C for every 300 m of height.