Suspended beneath is a gondola or wicker basket, which carries passengers and a source of heat, in most cases an open flame caused by burning liquid propane. By heating the air inside the balloon with the burner, it becomes lighter than the cooler air on the outside. Hot Air Ballooning Hot Air Balloon Air Balloon Hot Air 1) a hot air balloon stays on the ground (or descends) when the air inside it is too cool. How do hot air balloons work science . Essentially, hot air is lighter than cool air because it has less mass per unit of volume. Inside the hot air balloon, there is going to be lots of hot air. The balloon is also referred to as an “envelope.” they then use a small gas fan to fill up this envelope. Hot air balloons are based on a very basic scientific principle: This ingenious application of science describes how balloons rise up and how the design allows pilots to control altitude and vertical speed. How do hot air balloons work? 11) forget a hot air ball...