Air pressure from the Terai to Everest
Travel from Biratnagar to the top of Everest with a barometer, a sealed snack bag and a glass of water held up by a card, and see how air pressure changes with height.
Core concept
The air around us presses on everything; its pressure falls as you go higher
Topic: Pressure
We live at the bottom of an ocean of air. The weight: The pull of gravity on something, measured in newtons. It is less on the Moon. All key words of the air above us presses on everything in all directions; at sea level this atmospheric pressure: How much force presses on an area. A sharp knife has high pressure at its edge. All key words 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: How hot or cold something is, measured in degrees Celsius (°C). All key words.
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
- Start in Biratnagar. Record the air pressure, the force on the card and the boiling point of water.
- Travel to Kathmandu and record again.
- 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.