Drag is the mechanical force that is generated by the contact of a solid body with a fluid. In the air crafts case the contact of the aircraft against the airflow. For drag to be generated, the aircraft must be in contact with the airflow or flying against it because if there is no airflow, there is no drag. Fluid Dynamics it how the fluid is created. It is the sub discipline of fluid mechanics that deals with fluid flow. Drag is generated by the difference in velocity between the aircraft and the airflow and for this to work there must be motion between the object and the fluid. If there is no motion, there is no drag. It makes no difference whether the aircraft moves through static air or whether the air moves past a static aircraft. To minimize drag, it is necessary that a streamline design must created, so that the air flows around the plane smoothly, creating less drag.
"If you stick your hand out of a car window while moving, you'll experience a very simple demonstration of drag at work. The amount of drag that your hand creates depends on a few factors, such as the size of your hand, the speed of the car and the density of the air. If you were to slow down, you would notice that the drag on your hand would decrease"(Marshall Brain).