What makes a balloon “fly”?
The balloon’s burner heats up the cold air that has been blown into the envelope by the cold inflation fan. As the air in the envelope is heated, it expands and become less dense. This causes the air inside the envelope to weigh less than the surrounding (or ambient) air. Once the weight of the entire balloon system, including the fuel and passengers, is lighter than the surrounding air that is displaces, the balloon will lift off of the ground and begin to fly.
Cold air is blown into the envelope, then the burner heats up the cold air in the envelope. As the air in the envelope is heated it expands and becomes less dense. This causes the air inside the envelope to weigh less than the surrounding air. When the weight of the balloon system including passengers is lighter than the surrounding air the balloon will lift off and begin to fly.
