Experiment 2 (Expansion and contraction of gases)

What happens to the air inside a balloon when we make it hot and then cold?

• Water
• A pot
• A balloon
• A plastic bottle
• A stove
• Thread
• Matches (if needed)

(Implied by the aim) Hot air will make the balloon bigger, and cold air will make it smaller.

1. Attach the balloon to the top of the plastic bottle using the thread. (See diagram below.)
2. Pour water into the pot, turn on the stove, and heat the water.
3. Place the bottle with the balloon into the pot of hot water. Observe what happens. (See diagram below.)

Experiment on the expansion and contraction of air

4. Remove the bottle from the hot water and place it into cold water. Observe the changes.

• When the bottle with the balloon was placed in hot water, the air in the balloon took up more space, making the balloon expand.
• When the bottle was placed in cold water, the air in the balloon took up less space, making the balloon shrink.

• This experiment proves that hot air expands (takes up more space), and cold air contracts (takes up less space).