How do Hot-Air Balloons Fly?

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A hot air balloon consists of a basket to carry the passengers, a gas burner and a large airtight nylon envelope with a big opening at the base. The balloons fly when the air inside is lighter than the air outside to obtain a lift. The gas burner heats the air inside the balloon. Hot air is lighter, making the balloon ascend in the air and stay air borne. To descend to the earth, the burner is turned off and slowly the balloon comes down.

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