The force that opposes lift is drag. Drag is the resistance of a fluid to the motion of an object through it. In the case of an aircraft, drag is created by the friction of the air against the aircraft's surface and by the pressure difference between the front and back of the aircraft. Drag increases as the aircraft's speed increases.

Lift is the force that opposes weight. Lift is created by the difference in air pressure between the upper and lower surfaces of the aircraft's wings. The higher the airspeed, the greater the lift.

In order to fly, an aircraft must have enough lift to overcome its weight. However, too much drag can slow the aircraft down and cause it to lose lift. Therefore, it is important to find a balance between lift and drag in order to achieve efficient flight.