Hello, If free fall is defined as falling with the absence of friction, then what interactions does an object participate in if it falls with friction? The first obvious answer is that the object participates in a contact friction interaction with the air (or air friction). The second answer is a long-range gravitational interaction, which pulls the falling object toward the center of the earth. But what other interactions are at play? For example, if air is matter, and if the falling object contacts air, therefore compressing it, could we call this a contact compression interaction, where the air is pushing the object in whatever opposite direction the object is pushing the air? What really is air friction? A contact friction or contact compression interaction? If there is indeed a contact compression interaction with the air, how does this interaction affect the motion of the falling object, and how does it differ from the contact friction's effect on the falling object? Thanks for the help.