Balancing Balloons

Challenge

What happen when two balloons inflated to different pressures are allowed to equalize?

Supplies

• • 2 Balloons

  • 2 Drink bottle caps

What to do

• 1. Glue the two caps together at the threaded ends

  2. Inflate one balloon 80% full

  3. Attach end of balloon to a bottle cap

  4. Inflate other balloon 20% full

  5. Attach end of balloon to other bottle cap

  6. Ask the audience what will happen when the balloons are allowed to interact

Inquiry Questions

• • Did your prediction happen?

  • Why did the big balloon get bigger?

  • Can you get two balloons to remain the same size?

What’s happening?

Most of the time we think of systems equalizing, it means the components each get the same amount of the resource. Here, the big balloon got bigger and the small balloon got smaller. How is that equalizing?

When you try to inflate a balloon, what is the hardest part? Usually getting started is most difficult and as the balloon gets larger, it becomes easier to inflate. It take roughly an equal amount of force to stretch the latex, no matter how big it is, but when the balloon is larger, there is more surface area able to generate the stretching force so it's easier to inflate. When the two balloons are connected and allow to equalize, the small one gets smaller. Because even a small difference in pressure between the large balloon and the small balloon will accelerate as more air moves from one to the other, it can be challenging to get two balloons to stay the same size for long.