Physics and Natural Sciences
Colder at the top
A mountain top is closer to the Sun than the valley below. Why is it colder?
- Hint 1How much closer to the Sun is the summit, compared with the distance from the Earth to the Sun?
- Hint 2What mostly heats the air: sunlight passing through it, or the ground?
- A few kilometres is nothing next to 150 million km, so the extra sunlight is negligible.
- Air is mostly heated from below, by the ground, which absorbs sunlight.
- Air that rises meets lower pressure, expands and does work on its surroundings, so it cools.
- Higher up there is also less air above to trap the heat radiated by the ground.
- So temperature falls with height, by several degrees per kilometre.
Where it lands: The air is heated from the ground, and rising air expands and cools; the tiny change in distance to the Sun does not matter.
The trap: Saying 'there is less air so it holds less heat' without the mechanism: expansion cooling and heating from below.
What a tutor might ask next: Why can the summit still give you serious sunburn?
Now do one out loud. In the interview you think aloud with a tutor. Try a Physics problem with hints, follow-ups and Mia's feedback on how you think.