The Mysterious Balloon Experiment

Fully inflated rocket balloons to show shape

Sometimes, the simplest and most basic experiments can offer great surprises. Over the past year, I’ve explored such an experiment, a balloon experiment. It turns out that not only children but also adults and even MENSA members have a hard time predicting what will happen. Will you be able to?


  • A pole or a rock that measures about 1.5 meters
  • A chair
  • 2 balloons
  • 2 clothespins
  • String
  • Tape
  • A pump
  • A pen


  1. Tape a piece of string to either side of the pole or stick. Attach the two clothespins to each string. Then attach the balloons to the clothespins without inflating them.
  2. Use a chair or something similar to balance the pole over the edge. Mark the balance point on the pole with a pen.
  3. Imagine that you remove one balloon, pump in full of air and hang it back. You then place the stick with the balance point in the same place. What will happen? Will the pole balance on the same point? Will it swing up or down on the side that now holds an inflated balloon?
  4. Do the experiment and find out.

I first did this experiment during a course for elementary school teachers. The idea was to give them a classroom activity to illustrate that air consists of something and weighs something. I was confident that the teachers would predict what would happen. But I was wrong. About one-third thought the inflated balloon would swing upwards, another third would balance on the same point as before, and the last third would swing downwards. I found a similar level of confusion when I did the balloon experiment with our teachers at Scientist Factory, all of whom have a bachelor’s degree or higher. Only those who specialized in chemistry and physics knew the answer.

Members of MENSA Norway were also not sure when I tried the activity on them during a lecture. Nobody thought the inflated balloon would tilt upwards, but about half thought the pole would balance the same way as before. I have given a lot of thought to why people are so confused by this balloon experiment, so when a school asked me if I had a science project they could use for their science camp, there was no doubt on what to choose.

A high school class took the assignment and performed the balloon activity with 20 elementary school-aged children and 16 adults aged 20-80. The results confirm my findings. There was great confusion about what would happen across all age groups. As many as 47% thought that the balloon would swing upwards, 36% thought it would swing downwards, and 17% thought it would balance in the same place as before. When the young scientists removed the eight-year-old participants from the study, the results were more even, with 25% saying it would swing upwards, 38% saying it would swing downwards, and 37% saying it would stay in the same place.

Shows several balloons against a blue sky background to illustrate the topic of this article which is the mysterious balloon experiment

The following is an excerpt from the rapport:

“Many participants responded that the weight remains the same, which is wrong. They probably assume that air weighs nothing, and they cannot imagine that it makes a difference. That means they cannot picture that the air inside the balloon has a higher density than the air below it, and thus not that it will swing downwards. We found it surprising that a high percentage of those aged between 20 and 80 thought that the balloon would swing upwards. The general population appears to lack knowledge about the weight of air.”

We can ask if there’s any point in knowing about the properties of air. Do we need to be able to imagine the particles in a gas? My answer is a clear yes. Understanding gas is a central element for understanding important cycles on Earth such as the water cycle and nitrogen cycle. These processes are essential for all life. Knowledge about gases also enables us to understand how we can protect ourselves from harmful substances. Not to mention our carbondioxide emissions! I personally find it hard to grasp that every time I emit several tens of kilograms carbondioxide every time I use up the gasoline in my car since I cannot see it. If you agree with me, try spreading this experiment to children and adults everywhere.

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