Why do the sides of a plastic bottle buckle?

Answer 1

Air pressure can buckle the sides of a plastic bottle. If a bottle is capped, it isolates the air inside. At the time the cap went on, inside and outside air pressure were equal. Cool the bottle and the sides will buckle in because the inside air cools, becomes less dense and then its pressure goes down. Cap an empty soda bottle and stick it in the fridge for fifteen or twenty minutes. Look at what happens. Want more drama? Same empty soda bottle. Run a couple of cups of hot water out of the tap in it. Cap it and shake it for ten seconds or so. Uncap it and dump out the water and replace the cap right away. What is in hand is a bottle of pretty warm air that is isolated inside the bottle. Put that in the fridge for ten minutes. Major buckling.