Drag Force
The drag force is a force which acts on a moving object, resisting the forward motion of the object. How large a drag force on an object depends on the fluid (the medium of travel), the speed of the object and the size and shape of the object. In the case of a baseball curving this is really important because the drag plays a factor of how much a baseball curves and which direction. There are three types of drag: friction, form and induced. (for a baseball travelling through the air. See Diagram.
