volume_mute
Buoyant Force vs. Altitude
publish date: 2026/05/20 22:17:25.103660 UTC
volume_mute
An unanchored toy balloon filled with helium rises high into the sky. As it reaches higher altitudes where the outside air density decreases, what happens to the buoyant force acting on the balloon?
Correct Answer
The buoyant force decreases because a given volume of thinner air weighs less.
Explanation
As altitude increases, the atmosphere becomes thinner and its density drops. Because a fixed volume of this high-altitude air weighs less than the same volume of dense sea-level air, the weight of the displaced air—and thus the upward buoyant force—gradually decreases as the balloon climbs.
Reference
Basic Physics: A Self-Teaching Guide