How does a hot air balloon fly?

Answer 1

The flame of the burner heats the air inside the balloon making the air less dense because it expands giving it a larger volume it is less dense than the air outside the balloon therefore it rises

Answer 2

A hot air balloon is powered by hot air, hot air is lighter (less dense) then the air outside of the balloon (More dense) Heat rises, so the heated air, pushes up into the balloon allowing the balloon to lift. The more heat, the faster it will go, the less heat, the slower it will go, until it starts to descend. Decent is relatively slow, because the air is slowly cooling, however the cooler the air the faster the decent is. To avoid rapid falling, heat it applied to reheat the air so the decent goes slowly.

Answer 3

A controled fire heats the air inside the balloon. Since hot air rises, and the air around the balloon is cooler than the air in the balloon, it generates lift.