Atmospheric Pressure
Build confidence in Atmospheric Pressure for GCSE Physics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. A separate (triple) physics topic: atmospheric pressure is caused by the weight of the air above a surface and decreases as height increases.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
The atmosphere is a thin layer of air round the Earth, and it gets less dense with increasing altitude. This is a Triple-only topic.
Atmospheric pressure is caused by air molecules colliding with a surface. The molecules in the atmosphere create a pressure by striking any surface they meet, and the pressure is the total effect of all those collisions.
Atmospheric pressure decreases as altitude increases. The reason is that as altitude rises, the number of air molecules above a surface decreases, so the weight of air above it is less and the pressure it exerts is lower. The air is also less dense higher up.
Revision notes
What causes atmospheric pressure
Air molecules colliding with a surface create atmospheric pressure.
The atmosphere is a thin layer of air round the Earth, and it becomes less dense with increasing altitude.
Why pressure falls with altitude
As altitude increases, the number of air molecules above a given surface decreases.
The weight of air above that surface is therefore smaller, so the pressure it exerts is lower. The reduced density higher up also means fewer collisions per second.
The atmosphere's structure
The atmosphere is thin compared with the size of the Earth.
Density falls continuously with height rather than stopping at a fixed boundary, which is why atmospheric pressure declines gradually rather than abruptly.
Key points
- The atmosphere is a thin layer of air round the Earth.
- Atmospheric pressure is caused by molecular collisions.
- The atmosphere gets less dense with altitude.
- Pressure decreases as altitude increases.
- Fewer molecules are above a surface higher up.
- The weight of air above is therefore less.
Worked examples
Example 1
Explain what causes atmospheric pressure. [2 marks]
Model answer
Air molecules in the atmosphere collide with surfaces (1 mark), and the total effect of all these collisions produces the atmospheric pressure (1 mark).
Example 2
Explain why atmospheric pressure decreases as altitude increases. [3 marks]
Model answer
As altitude increases, the number of air molecules above a given surface decreases (1 mark). The weight of air above that surface is therefore smaller (1 mark), so the pressure it exerts is lower (1 mark).
Example 3
State how the density of the atmosphere changes with altitude. [1 mark]
Model answer
The atmosphere becomes less dense as altitude increases (1 mark).
Common mistakes
Saying pressure increases with altitude.
It decreases, because there is less air above.
Not mentioning the weight of air above.
That is the key part of the explanation and usually carries a mark.
Saying the atmosphere has a sharp upper boundary.
Density falls continuously with height.
Confusing atmospheric pressure with pressure in a liquid.
The principle is similar, but the atmosphere's density varies with height.
Exam tips
- Explain pressure through molecular collisions.
- Link falling pressure to fewer molecules and less weight above.
- State that density decreases with altitude.
- Remember this is a Triple-only topic.
Key terms
- Atmosphere
- The layer of air surrounding the Earth.
- Atmospheric pressure
- Pressure caused by air molecules colliding with surfaces.
- Altitude
- Height above sea level.
- Density
- Mass per unit volume, decreasing with altitude here.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.