Do two balloons tied together fly farther than a balloon?

Answer

Dear An,

How far a balloon flies depends on the wind speed and the time the balloon stays in the air.
The latter depends on how fast the gas in the balloon diffuses through the wall and on how high it has to land. This is the same for every balloon, and whether you tie them together or not makes no difference.

However, if you hang a load on it (a card, for example) then two linked balloons will of course go
climb higher than if a single balloon had to lift its weight. And because they come down from higher, they will take longer. How much longer? This is a possible topic for a project, because you know the gas laws, Archimedes’ law and you can determine the time for the diffusion experimentally.