What is called "Drag Force"? When there is a relative velocity between a fluid  (liquid or gas) and a moving object, the object will experience a force that we call "Drag Force", which opposes the relative motion and points in the direction in which the fluid flows relative to the body. One thing to clarify: It doesn't matter whether the object moves through the fluid or the  fluid moves past the object, either case will be considered as relative velocity between the two.