1. Lift: This is the upward force that opposes gravity. It is generated by the wings, which are designed to create a difference in air pressure above and below the wing. The air moving over the curved top of the wing travels a longer distance and faster than the air under the wing, resulting in lower pressure above and higher pressure below. This pressure difference creates lift, pushing the plane upward.

2. Thrust: This is the forward force that propels the airplane through the air. It is generated by the engines, which convert fuel into energy to push the plane forward. Thrust overcomes the force of drag.

While these are the main forces, it's important to note that there are two other forces that play a role:

* Gravity: This pulls the airplane downward. It is the force that the plane needs to overcome to stay in the air.

* Drag: This is the force that resists the airplane's motion through the air. It is caused by friction between the air and the airplane's surfaces.

The balance of these four forces – lift, thrust, gravity, and drag – determines the flight path and performance of an airplane.