What is Flight
There are different approaches to flight. If an object has a lower density than air, then it is buoyant and is able to rise and float in the air without using energy; a lighter than air craft is known as an aerostat. A heavier than air craft, known as an aerodyne, includes flighted animals and insects, fixed-wing aircraft and rotorcraft. Because the craft is heavier than air, it must use the force of lift to overcome its weight. The wind resistance caused by the craft moving through the air is called drag and is overcome by propulsive thrust except in the case of gliding.
Some vehicles also use thrust for flight, for example rockets and Harrier Jump Jets.
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