Atmospheric pressure — AQA GCSE Physics
Test yourself on Atmospheric pressure with AQA GCSE practice questions.
7 days Premium · Then free forever · No card, no charge
Atmospheric pressure explained
Held on by gravity, the atmosphere is a shell of gas roughly a hundred kilometres deep around an Earth whose radius is over six thousand kilometres.
Read the full explanation
Proportionally, it is thinner than the skin of an apple, so diagrams drawing it as a thick band are misleading. It has no sharp top; it simply thins out with increasing altitude. Air is a gas and can be compressed, so the weight of all the air above squeezes the air at the bottom into a smaller volume. That makes the air near the ground the densest, with its particles closest together, and the density falls steadily as you rise. Half of the whole atmosphere by mass lies below about 5.5 km. This thinning is why aircraft cabins are pressurised and why climbers at altitude breathe harder.
Your focus
- Describe the Earth's atmosphere as a thin layer relative to the size of the Earth.
- Explain why air density is greatest near the ground in terms of the weight of air above.
- Compare the spacing of air particles at ground level and at high altitude.
Atmospheric pressure exam tips
Marking Points
- Describe the atmosphere as a thin layer relative to the size of the Earth.
- State that the density of the atmosphere decreases as altitude increases.
- Explain that air particles are spaced further apart at higher altitudes.
- Link the greater density of air near the ground to the weight of the air above compressing it.
Examiner Tips
- 💡Use the phrase 'thin compared with the size of the Earth' when describing the atmosphere's extent.
- 💡Remember that density relates to particle spacing; explicitly state that particles are closer together near the surface due to the weight of air above.
Common Mistakes
- Drawing or describing the atmosphere as a thick shell comparable with the radius of the Earth; correction: it is a very thin layer.
- Saying the atmosphere has a definite upper surface; correction: it gradually thins out into space.
- Confusing lower density with lower temperature as the reason the air is thin at altitude; correction: density decreases due to less weight of air above.
- Claiming the air is less dense high up because gravity does not act there; correction: gravity acts at all altitudes but the compressive weight of air above is less.