AQA · GCSE · Physics
Course version: 8463 · Version from Sept 2016
So as height increases there is always less air above a surface than there…
Full specification wording
Atmospheric pressure: So as height increases there is always less air above a surface than there is at a lower height.
The key word here is 'always'.
Checked against the AQA 8463 specification (opens in a new tab) on .
- Point 4 of 6
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The key word here is 'always'. Take any two heights: everything above the upper one is also above the lower one, and the lower surface carries the extra slab of air between them. For example, a hiker at sea level has the entire atmosphere pressing down, whereas a climber on Mount Everest has far less air above them. Thus, the air above a lower surface is always greater than the air above a higher one, regardless of weather. The average density of the air above also falls as the surface rises, because the densest air near the ground is left below. This explains why the link between height and atmospheric pressure has no exceptions. Remember that this entire topic on atmospheric pressure is assessed exclusively at Higher Tier.
What earns the marks
- State that the amount of air above a surface always decreases as height increases.
- Explain that a lower surface carries an extra layer of air compared to a higher one.
- Identify that the average density of the air decreases as altitude increases.
- Conclude that atmospheric pressure always decreases with height due to the reduced weight of air above.
Common mistakes and how to put them right
Arguing that weather or temperature could reverse the relationship.
Put it right: The decrease in the amount of air with height is absolute and always holds true.
Treating the air between the two heights as though it sits above both surfaces.
Put it right: The extra slab of air only sits above the lower surface.
Confusing the density of the air at a specific height with the average density of all the air above it.
Put it right: Average density of the column must be considered.
Exam tips
- Answer comparison questions by explicitly naming the extra layer of air that the lower surface carries.
- Keep in mind that questions on atmospheric pressure and height are exclusively for Higher Tier candidates.
Try the lesson
The start of the Atmospheric pressure: So as height increases there is always less air above a surface than there is at a lower height. lesson, made from checked teaching notes for this specification point.
Have a go first
A hiker walks from the bottom of a valley up to the top of a hill. How does the amount of air above the hiker change during the climb?
Listen
The key word here is 'always'. Take any two heights: everything above the upper one is also above the lower one, and the lower surface carries the extra slab of air between them. For example, a hiker at sea level has the entire atmosphere pressing down, whereas a climber on Mount Everest has far less air above them. Thus, the air above a lower surface is always greater than the air above a higher one, regardless of weather. The average density of the air above also falls as the surface rises, because the densest air near the ground is left below. This explains why the link between height and atmospheric pressure has no exceptions. Remember that this entire topic on atmospheric pressure is assessed exclusively at Higher Tier. A strong answer earns marks for these points. State that the amount of air above a surface always decreases as height increases. Explain that a lower surface carries an extra layer of air compared to a higher one. Identify that the average density of the air decreases as altitude increases. Conclude that atmospheric pressure always decreases with height due to the reduced weight of air above. A common slip: Arguing that weather or temperature could reverse the relationship. Instead, the decrease in the amount of air with height is absolute and always holds true. Exam tip: Answer comparison questions by explicitly naming the extra layer of air that the lower surface carries.
Key words
Say what each word means before you turn the card.
extra layer of air
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average density
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comparing heights
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See every definition
- extra layer of air
- The slab of air between two heights that sits above the lower surface only, so a lower surface carries it compared to a higher one.
- average density
- The density of all the air above a surface, which falls as the surface rises because the densest air near the ground is left below.
- comparing heights
- Taking any two heights, where everything above the upper one is also above the lower one, and the lower surface carries the extra slab of air between them.
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