All four forces—lift, thrust, drag, and weight—interact continuously in flight and are in turn affected by such things as the torque effect of the propeller, centrifugal force in turns, and other elements, but all are made subject to the pilot by means of the controls.

The four primary physical characteristics that define a fixed-wing airplane are the Fuselage, Wings, Empennage (Tail), and Landing Gear. The Fuselage is the main body of the aircraft that holds the passengers, cargo, and cockpit. The Wings are the airfoils attached to the fuselage that provide the necessary "lift" to keep the plane in the air. The Empennage refers to the entire tail assembly, including the vertical stabilizer (fin) and horizontal stabilizers, which provide stability and control over the aircraft's "pitch" and "yaw." Finally, the Landing Gear (undercarriage) consists of the wheels or skids that support the plane while it is on the ground and allow it to take off and land safely. From a physics perspective, these characteristics are often discussed in relation to the four forces of flight: Lift (generated by the wings), Weight (the force of gravity on the fuselage and contents), Thrust (generated by the engines), and Drag (the air resistance acting against the plane's motion). Together, these structural components and aerodynamic forces allow an airplane to achieve controlled, sustained flight.