We filled bottles with very cold water, then emptied it out. This meant that the air in the bottles was very cold. We wet the caps and placed them upside down on top of the bottles. We placed our hands gently around the bottles but did not squeeze.
What happened? The caps jumped up and down on the top of the bottles…Pop Top!!
Why? When we placed our hands around the bottles, we warmed the air inside them.
Although a drinks bottle with no liquid in it looks empty, it is full of air.
If the air in the bottle is warmed, it expands and will take up more space, and try to escape, making the caps jump.
Next we placed balloons on the top of the bottles and placed our hands around them again. When the air inside the bottles was warmed by our hands the balloons inflated a little. We put the bottles into warm water and some inflated even more.
