An object moving through the atmosphere drags the air molecules with it. During this process, collisions with the air molecules provide some resistance to the objects motion. Generically, the force generated by the air resistance is called drag force. This force increases when the air gets denser and when the object is moving faster through the air. Additionally, the drag force also depends on the cross section area of the object moving through the air. Based on this information, use dimensional analysis to express the drag force FD in terms of the object speed v, cross section area A and the air density .