It says that #Pprop1/V#...and thus it has NO FORMAL application to hot air ballooning...because pressure is formally constant. (Of course, as the balloon ascends, the atmospheric pressure DOES decrease...but to a first approx. we ignore this...)
On the other hand, #"Charles' Law"# holds that #VpropT#...and so if we enclose a volume of gas in a canopy, and give it a good blast with a gas burner the canopy inflates with hot gas...and will occupy a volume of air that MAY HAVE a greater mass than the mass of the balloon, the canopy, and the balloonists..and so the balloon floats...
Alternatively we could use helium gas, or dihydrogen gas...(of course, the fate of the Hindenburg has discouraged the use of combustible gases in lighter than air technology).
