What you need

• A plastic drinks bottle
• Water

Instructions

1. Fill the bottle with water so it is very nearly full
2. Put the lid on tightly and throw the bottle in the air. Watch it carefully on the way up and down
3. The air inside the bottle will form a spherical bubble as it’s falling!

Results and Explanation

When the bottle is in free-fall, surface tension forces the air into a bubble with the least possible surface area – a sphere. In space, the same effect can be seen with liquid drops in air.