A sealed packet of chips puffs up tight during a flight. No air got in — so what happened?
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High up, the cabin air is at lower pressure, so it presses on the packet less. The gas particles trapped inside still push out just as hard, but now meet less squeeze from outside — so they win, and the packet balloons. Same particles, less outside pressure.
Wet washing dries on the line on a sunny, breezy day — without ever boiling. How?
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The fastest liquid particles at the surface escape into the air as vapour — that's evaporation, and it happens well below boiling. Sun adds energy so more particles can escape, and a breeze sweeps the escapees away so more can follow. Liquid quietly becomes gas.
A balloon shrinks in the freezer but doesn't pop or lose any air. Where did the size go?
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The cold removes energy, so the gas particles slow down and hit the balloon's walls less hard and less often. With weaker pushing from inside, the balloon caves in a little. Warm it again and the particles speed up and fill it back out — no air ever left.