The jet force can be divided into components. The "forward" component of this force is generally referred to as thrust. The upward component of jet force is referred to as lift. There are also two other forces that impact motion of aircraft. Drag, which is also referred to as air resistance, is the force that opposes motion. As such, it acts against both components of the jet force (both the thrust and the lift). The fourth and final force is the weight itself, which acts directly downward.