Two balloons are balanced on a yardstick, and when one balloon is filled with air, it tips the balance, proving that air molecules have mass and are pulled down by gravity. A balloon can also be weighed empty and full on a precise scale.

1. Cut a piece of string about 1–2 feet long and tie it into a loop.
2. Find the midpoint of a yardstick and loop the string around it, tying the other end to the roof or a stand.
3. Clip two inflated balloons of equal size to the ends of the yardstick with binder clips. Adjust until the stick balances horizontally.
4. Let the air out of one balloon by pricking the very top of it. Do not burst it as pieces of balloon may be lost, affecting the weight.
5. Observe that the side with the inflated balloon tilts downward, showing that air has weight.
6. Alternatively, a balloon can be weighed on a precise scale both empty and full of air.

Balancing Balloons - Air Has Weight - funsciencedemos:

Mass & Change: Balloon with and without air - chemtaiji: https://www.youtube.com/watch?v=kriCueCtuf8

📄 Weighty Matters: The Air Around Us - Small Step For STEM: https://www.smallstepforstem.com/air-weight-experiment/

• Try using different amounts of air in the balloon to see if the scale tips more strongly.
• Try with different sizes or types of balloons to test consistency.

• Supervise children when using scissors or tying balloons.
• Do not overinflate balloons - they may pop suddenly.
• Keep popped balloon pieces away from small children (choking hazard).

• Why does the inflated balloon weigh more than the empty balloon?
• How does this experiment show that air molecules have mass?
• Why does gravity affect air the same way it affects solid objects?
• If air has weight, why don’t we usually notice it pressing on us?
• How does the weight of air relate to atmospheric pressure?