From time to time, I stumble across cool experiments that are fun to try – sometimes by accident! Here’s one I discovered the other day: a simple way to show how air expands when it gets hot, and shrinks when it cools down.
- 1 2-litre plastic drinks bottle
- Access to hot water (tap or kettle) – be careful!
- A flat surface you can place the bottle on, upside-down
Fill the bottle with hot water, put the lid on and swish it round a little (make sure the outside of the bottle is hot). Take the lid off, pour the water down the sink, and place the bottle upside-down on the surface. Watch as the bottle collapses in on itself, without any warning and completely at random!
The air inside the bottle when you place it upside-down has been heated by the hot surfaces of the bottle. As it cools, it shrinks – and with less air pressure to hold the bottle in its normal shape, the bottle collapses. This experiment also has a couple of bonuses: firstly, it’ll make trying to squish the bottles down for recycling easier, as it does it for you – and secondly, it’s really good at making people jump!