Here's how it works:

* Heating the air: The burner heats the air inside the balloon, causing the gas molecules to move faster and spread further apart.

* Expansion and buoyancy: This expansion makes the air inside the balloon less dense than the surrounding air. Because it is less dense, the hot air rises, lifting the balloon.

* Controlling altitude: By adjusting the burner's heat output, pilots can control the temperature of the air inside the balloon, thus controlling its altitude.