The picture below (Figure 2.1 in Understanding flight), shows "the airflow around a wing. Periodically smoke has been introduced to show the changes in the speed of the airflow. The first thing to notice is that the air going over the top of the wing reaches the trailing edge before the air that goes under the wing. In fact, the air that passed under the wing has a somewhat retarded velocity compared to the velocity of air some distance from the wing". Source: David F. Anderson and Scott Eberhardt (2000), Understanding flight, McGraw-Hill, Washington, D.C. ...