CoachThe atmosphere is the deep layer of air wrapped around the whole Earth. Its weight squeezes the air at the bottom — where we live — and squeezed air pushes hard on every surface it touches. That push is called air pressure.
Examples
Example 36.5 (The straw)
You think you pull juice up a straw. In truth, you cannot pull a liquid at all — try pulling water with your fingers! What you really do is suck the air out of the straw. With the air gone from inside, the atmosphere pressing down on the juice in the glass pushes juice up the empty straw to your mouth. Every sip is the atmosphere doing the lifting; you only clear the road.
Example 36.6 (Suction cups and crushed bottles)
The bathroom hook’s rubber cup is pressed flat to the tiles, squeezing the air out from underneath: now the atmosphere pushes the cup against the wall with nothing behind it pushing back — pinned by the sky itself. And screw the cap onto an empty plastic bottle high on a mountain, then drive down into the valley: the bottle crumples as if squeezed by a ghost hand. More air presses outside than the thin mountain air sealed inside — the atmosphere wins, and the bottle folds.
Example 36.7 (Thinner with height)
Climb, and you leave part of the ocean below you: less air above means a weaker push. Your ears pop in a fast cable car as the pressure outside changes; mountaineers gasp in air grown thin. And here the mountain-tea mystery of last year surrenders: with the atmosphere pressing less on the water, boiling comes easier — water on great peaks boils well below , too cool for a proper brew.