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Buoyancy of Hot Air Balloons
publish date: 2026/05/20 22:35:58.651406 UTC
A hot-air balloon floats upward because heating the air inside the balloon envelope causes it to become less (1) than the surrounding outside air.
Correct Answer
(1) dense
Explanation
Heating the air causes its molecules to move faster and spread out, making the air inside the balloon less dense than the cool outside air. As a result, the weight of the balloon system is less than the buoyant force exerted by the displaced air.
Reference
Basic Physics: A Self-Teaching Guide