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Hot Air Balloons
Because of the hot air! Modern hot air balloons consist of a bag called the "envelope" capable of containing air heated to 250 degrees Farenheit (or more!) and commonly made of nylon with a mouth of nomex or other heat resistant material nearest the burner; the "gondola" which carries the passengers and a source of heat, usually a burner using propane fuel. The heated air inside the envelope makes it buoyant because it has a lower density than the cooler air around it. The rising hot air exerts pressure on the top hemisphere of the envelope and provides lift. The amount of lift provided by a hot air balloon depends on the difference between the temperature of the ambient air outside the envelope, and the heated air inside the envelope. Lift is also affected by the humidity in the air, and the altitude about sea level. Posted: Tuesday 4th March 2008, 8:23 PM |