1Two things about air and heat
The ground warms the air — and air gets thin up high
You only need two ideas. Watch each one:
The ground heats the air
Sunlight mostly zips straight through clear air. It's the ground that catches the light, warms up, and then heats the air sitting right on top of it. So the warmest air hugs the ground.
Air gets thin up high
Air is squishy. Down low a tall stack of air presses down and packs it tight. Up high there's less air on top, so it's thin and spread out — fewer bits of air bouncing around.
2Two ways to think about "going up"
Closer to the Sun, or up into thin air?
When you climb, two things change at once. People reach for one of them. We'll test which one actually matters:
A step closer to the Sun
The peak pokes up toward the Sun — so maybe it catches more warmth?
Up into thinner air
You also climb into thin, low-pressure air, far above the warm ground.
3Your turn — be the Sun
Shine the Sun and watch what actually heats up
Slide the Sun brighter and dimmer. Watch where the warmth goes: the sunlight passes through the air, the ground soaks it up and glows hot, and then the warm ground heats the air just above it. Keep an eye on the two thermometers.
4Now lift a puff of air up the mountain
Catch a puff of warm valley air and carry it up 🎈
Forget the Sun for a second. We've sealed a puff of warm valley air into a stretchy bag. Up high there's less air pressing in, so the bag can puff out. The big question is what that does to its temperature. Guess first — then lift it.
Guess before you lift it
Up high there's less air pressing in, so this sealed puff will swell out as it rises. Forget the Sun — just think about the swelling. When a puff of air spreads out like that, what happens to its temperature?