So I've noticed my little sister's helium balloons floating at the ceiling. Made me wonder if someone could create a device that could harvest energy from this buoyancy. What if I tied a very long rope to a huge balloon filled with helium, and rolled the other end of the rope to a gear attached to a generator of sort. As the balloon goes up, the rope would rotate the gear, generating electricity. Would that work? more importantly, would it be efficient to make such a device? English isn't my first language, so I apologize in advance!