1. The field of dynamics that deals with air and other gases in motion, the forces that set them in motion, and the results of such motions: Aerodynamics is the study of the effects of air in motion on an object, either on objects moving through air, such as aircrafts or automobiles, or stationary objects affected by moving air, for example bridges or tall buildings.

The two primary forces in aerodynamics are lift and drag.

"Lift" refers to, usually upward, forces perpendicular to the direction of motion of an object traveling through the air. For example, airplane wings are designed so that their movement through the air creates an area of low pressure above the wing and an area of high pressure beneath it. The pressure difference produces the lift needed for flight which is typical of "airfoil" design.

"Drag" forces are parallel and opposite to the object's direction of motion and are caused largely by friction.

Large wings can create a significant amount of lift, but they do so at the expense of generating a great deal of drag. Extended "spoilers" on aircraft wings make the the wings capable of high lift even at low speeds, so low landing speeds can still provide enough lift for a gentle "touchdown".