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Why does heating gas in an air balloon makes the balloon rise?

Melissa Norris

in Studying

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1 answer

Bethany Evans on December 8, 2019

The temperature of a gas can be seen as the force with which the molecules that make up the gas repel each other. The molecules in hot air repel each other more of the molecules in the cold air, so the hot air is less dense than cool air (AFAIR air at sea level and room temperature weighs around 1 kilogram per cubic meter). This is also the reason hot air balloons are open: If air could not escape the balloon then (assuming the balloon was not elastic) heating the air would increase the air pressure inside the balloon, but not affect the density and thus not produce any lift.

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