When an object moves through air, the air closest to the object’s surface is dragged along with it, pulling or rubbing at the air that it passes. This rubbing exerts a force on the object opposite to the direction of motion—friction drag.
The thin layer of air closest to the surface of a moving object is called the boundary layer. This is where friction drag occurs.
What is the difference between this drag and the drag that appears when an object is in a free fall? if it is the same, how a molecule of a fluid that is sticked to the object can produce friction and thus heat?