Why does a sealed bag of chips puff up in the sun or on a mountain flight?
Two gas laws are at work.
Two gas laws are at work. Heat it and the gas volume rises with absolute temperature (Charles's law, V ∝ T). Take it up a mountain or in a plane and the outside pressure drops, so the trapped gas expands to a bigger volume (Boyle's law, PV = constant). Either way the packet puffs out — and can burst if it expands too far.
Key point
V ∝ T (Charles) and PV = constant (Boyle) — heat or low outside pressure expands the trapped gas.
Common mistake
thinking extra air somehow leaks into the sealed bag.
Memory tip
same gas, more volume: heat it (Charles) or drop the outside pressure (Boyle).
Tap to watch or see it right here — the app stays open (it only opens a quick search if nothing embeddable is found).