Abstract: In response to the current state of fluid mechanics and aerodynamics textbooks, which provide incomplete or even conflicting summaries of the mechanisms behind lift and drag generation in aircraft, this paper attempts to analyze the various mechanisms of lift and drag forces based on basic conservation laws. By applying the law of momentum conservation, it discusses the causes of low-speed steady lift, supersonic steady lift, and unsteady lift. Utilizing the principle of energy conservation, it examines the generation mechanisms of added-mass drag, form drag, induced drag (vortex drag), and wave drag. This paper provides a unified understanding on the lift and drag generation in aircraft.