What You Need:
- Plastic bottle
- Water and balloon
- With the help of an adult, fill a plastic bottle with hot water (not boiling hot) and fill a bowl with cold water. Let them sit for 1 minute, then empty the bottle quickly.
- Stretch a balloon over the open end of the bottle and push the bottle down into the cold water.
- The balloon will inflate into the bottle.
The warm water heats the bottle, which in turn heats the air inside the bottle after the water is poured out. When the bottle is placed in the cold water, the air inside cools and contracts. This causes air from the outside to be drawn in, pulling the balloon in and inflating it inside the bottle.