Why do balloons filled with hydrogen gas move up in the air?

see full answer

Your Exam Success, Personally Taken Care Of

1:1 expert mentors customize learning to your strength and weaknesses – so you score higher in school , IIT JEE and NEET entrance exams.

An Intiative by Sri Chaitanya

(Unlock A.I Detailed Solution for FREE)

Best Courses for You

JEE

NEET

Foundation JEE

Foundation NEET

CBSE

Detailed Solution

Balloons filled with hydrogen gas move up in the air because hydrogen is lighter (less dense) than air, so the balloon experiences a buoyant force that pushes it upward.

The principle: A body immersed in a fluid (air qualifies) experiences an upward buoyant force equal to the weight of the fluid displaced (Archimedes’ principle). If the weight of the balloon + gas is less than the weight of the displaced air, the net force is upward, causing rising.
Hydrogen has much lower molecular mass than the average molecular mass of air (~2 vs ~29 g/mol). Because of this the hydrogen-filled balloon displaces a volume of air heavier than the hydrogen inside it, so net upward force.
Thus hydrogen balloons ascend until density of surrounding air equals balloon system or until balloon bursts / leaks.

Watch 3-min video & get full concept clarity