Two balloons of different sizes are connected by a tube. When the connection is opened, air moves from one balloon to the other, often causing the smaller balloon to deflate while the larger balloon grows even bigger. This shows how air pressure and elasticity interact in surprising ways.

1. Inflate two balloons to different sizes.
2. Tie each balloon securely onto the ends of a piece of plastic tubing.
3. If using a valve, close it before attaching the balloons.
4. Allow air to pass between the balloons.
5. Observe which way the air flows and how the sizes of the balloons change.

Predict what will happen when these two balloons are connected - Steve Mould:

📄 Two-balloon experiment - Wikipedia: https://en.wikipedia.org/wiki/Two-balloon_experiment

• Inflate both balloons to the same size and see if there is any movement of air.
• Try balloons made from different materials or thicknesses.
• Attach more than two balloons with connectors to create a chain and test how air moves.

• Do not overinflate balloons, as they may burst.
• Keep balloons away from small children who may choke on broken pieces.
• Use eye protection if inflating balloons to large sizes.

• Why does the smaller balloon often deflate into the larger one instead of the other way around? (Because the pressure inside a smaller balloon is actually greater due to the elasticity of the rubber, so air flows into the larger balloon where pressure is lower.)
• How does this demonstrate that pressure depends on both volume and material stretch? (The stretched rubber wall contributes to internal pressure, not just the amount of air.)
• What does this experiment suggest about stability in physical systems? (Systems often move toward lower energy states—in this case, air redistributes until the forces balance.)