Flight relies on two principles of aerodynamics, or the study of how air moves around objects: thrust and lift. Thrust is when an object is pushed forward with force. Planes use their jet engines to achieve thrust: the engines suck in air, compress it, mix it with gas, and ignite the mixture it in a burst of energy that shoots out the back of the engine, which pushes the plane forward. Jet engines produce so much thrust that planes can fly at extremely fast speeds of up to 600 miles per hour (mph)! That’s a lot faster than cars, which drive anywhere from 55 to 75 mph on highways. Lift is the force that drives a plane upward and keeps it in the air. In order to produce lift, planes rely on their wings, which have a special shape called an airfoil. The top of the wing bulges out to create a smooth bump. When the wing moves through air, incoming air particles either go above or below it. Thanks to the bump, the air on top of the wing moves faster than the air on the bottom of the wing. These particle speeds create lower air pressure above the wing and higher air pressure underneath it—this concept is called Bernoulli’s Principle. The high air pressure pushes the wing up, creating lift. Thrust and lift are always fighting two other principles of aerodynamics: drag and gravity. Drag is when a moving object blocks the flow of air, slowing the object down. You can feel drag if you put your hand out the window of a moving car—your arms get pushed backwards as the air rushes by. Planes needs to have enough thrust to overcome the amount of drag it produces, so they’re designed to have air flow as smoothly as possible around the body (this is called being aerodynamic). Gravity is the force that pulls all objects down toward the earth. Lift can overcome gravity if it is strong enough—the engineers who build planes do a series of equations to find the perfect wing size and flying speed to create the right amount of lift, based on the weight of the plane. These combating forces mean planes have to fly at high speeds in order to stay in the air, which is just as well. When was the last time you wished a flight would last a little longer?
