The equations of motion are the equations that govern the motion of a vehicle. Newton’s laws of motion are the important bases for aircraft performance analysis. The aircraft must be designed to produce the aerodynamic forces in such a way that they support the aircraft’s motion as much as possible in the most efficient way. A coordinate system should be defined prior to the derivation of equations of motion. Aircraft motion can be either un-accelerated flight or accelerated flight. A perturbed-state motion is a flight for which all motion variables are defined relative to a known steady-state flight condition. The applications of a “perturbed-state motion” are usually covered in the area of “flight stability and control”. The general equations of motion are applied, and new forms of equations of motion are derived. Each section is accompanied with a figure that depicts the aircraft with the forces involved.