Experiment #1: Hot air bottle with a bang!

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.

You’ll need:

  • 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!

What’s happening? 
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!


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