Helium Versus Air and Buoyancy
Country: United Kingdom
Date: Winter 2013-14
If you had a balloon full of helium and it was underwater can it lift more weight than a similar air filled balloon?
In theory yes, but practically speaking the difference would be so small to be negligible. This is because the buoyancy force is equal to the weight of fluid displaced (water). The opposing force is the weight of the balloon, which is very small compared to the weight of water displaced. By filling the balloon with helium you can reduce the weight of the balloon at a given volume as compared to an air filled balloon, but since the balloon weight in either case is negligible compared to the buoyancy force anyway, it really has no practical effect.
John C Strong
Thanks for the question. Let us assume the balloons are of equal volume and have the gasses at the same temperature and pressure. Since the mass of the helium gas would be less than the mass of air, a helium balloon would lift more weight than an air filled balloon.
I hope this helps. Please let me know if you have more questions.
Since the difference in density between the gas filled bag and sea water determines the lifting capacity (buoyancy), you are correct. Helium would be better, although much more expensive.
Click here to return to the Physics Archives
Update: November 2011