There are four main forces that act upon an aircraft in straight and level flight: lift, drag, thrust, and gravity. Lift opposes gravity, and thrust opposes drag. Drag is a byproduct of lift that acts in opposition of motion, as the aircraft moves through the air, the air molecules flowing over the body create small amounts of friction on the skin of the aircraft. Drag is increased as the speed of the aircraft increases due to a greater volume of air flowing over the wing in a given period of time. In order to overcome drag an aircraft requires thrust provided from the engines. Larger aircraft that produce more drag require more thrust in order to travel at the same speeds a smaller lighter aircraft would travel at. In order counteract the effects o gravity, an aircraft must produce lift.

In order counteract the effects of gravity, an aircraft must produce lift. When a fluid flows over a surface it generates a force,  the perpendicular component of this force is known as lift. Lift is one of the force that allows aircraft to sustain flight. According to Bernoulli's Theorem, when a fluid speeds up across a surface, its pressure decreases. Therefore, when air flows over the cambered top of a wing, it travels faster than it does on the flat bottom portion of the wing. This creates a decrease in air pressure over the top of the wing and relatively less  air pressure under the wing which creates a perpendicular vertical force. Another contributing factor to the lifting force created by a wing is associated with Newton's Third Law of motion which states that "for every action force, there is an equal and opposite reaction force". The wing of an aircraft is slightly tilted upward into the oncoming wind, as the wind strikes the bottom of the wing it is deflected downward causing an equal and opposite force pushing upward on the wing. The wing can produce more or less lift depending on its angle of attack into the oncoming wind.