In cartoons, a baby grabs the string of a single helium balloon and floats right out of its baby carriage. Why can’t people really float into the air using helium balloons? Helium And Nitrogen Helium balloons float in air because helium is lighter than air: it has fewer electrons, protons and neutrons than air atoms –air is mostly nitrogen. Helium’s molecular weight is only 4 while nitrogen’s is 28. Because of this, the interior of the helium-filled balloon is lighter than the air around it, so it floats.
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