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We know that hydrogen and helium are lighter that air. Therefore it is certain that they would create a lifting force when enclosed in a balloon. How do we describe the relationship of balloon size and related lift?

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The force is given by Archimedes' principle. For a balloon of mass $m$ containing a volume $V$ of some gas of density $rho_g$, immersed in air of density $\rho_a$, the net upward force is $$F=-mg+V(\rho_a-\rho_g)g.$$

Some show of an attempt to research the question before posting it here would be quite welcome, though.

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