1. Lift: This is the upward force that opposes gravity and keeps the plane in the air. It is generated by the wings, which are designed to create a difference in air pressure above and below them.

2. Thrust: This is the forward force that propels the plane through the air. It is generated by the engines, which use propellers or jets to push air backwards.

3. Drag: This is the force that opposes the plane's motion through the air. It is caused by friction between the plane's surfaces and the air.

4. Weight: This is the force of gravity acting on the plane's mass. It pulls the plane downwards.

For a plane to fly, the lift force must be greater than the weight force, and the thrust force must be greater than the drag force. This is known as equilibrium.

Let me know if you'd like more details on any of these forces!