Understanding How Airplanes Fly 

The Four Fundamental Forces
 
When an aircraft is flying straight and level, it is subject to four primary forces: lift, gravity, thrust, and drag.

These forces interact to maintain equilibrium: Lift counters gravity, while thrust counters drag.

• Thrust: This force propels the airplane forward through the air and is generated by a propeller or jet engine. 
• Drag: The resistance of air that acts to slow the airplane's forward motion. 
• Gravity: The natural force that pulls all objects toward the Earth. 
• Lift: An upward force generated by the airflow above and below the wings. Air moves faster over the wing's upper surface and slower beneath it, creating a pressure difference that enables the airplane to remain airborne.