Physics XI Content
1. A rigid, lighter than air balloon filled with Helium cannot continue to rise indefinitely. Why?
The density of the atmospheric air is different at different level. The density of the air at upper level is less in comparison to the lower level. When the balloon rises up in air, the weight of the displaced air decreases as the density of the air decreases with height. Hence the upthrust decreases and becomes equal to zero then the balloon stops to rise.