In 1917, Albert Einstein had already explained the relationship between space and time, yet his attempt to design an airplane wing that year was based on an incomplete theory of flight. Despite this, inaccurate explanations of how planes fly still circulate today. So, how do planes stay aloft? Air is a fluid medium and things that are heavier than air require an upward force, called lift, to stay aloft. The most pervasive false explanation of this lift is the “Longer Path” or “Equal Transit Time” explanation, which states that air molecules traveling over the top of a curved wing cover a longer distance than those traveling underneath. This has been debunked as air molecules floating above and below the wing don’t need to meet back up. In reality, the air traveling above reaches the wing’s trailing edge much faster than the air beneath. To generate lift, the wing affects the movement of the air around it, splitting the air into pathways above and below the wing, following the wing’s contour. The air that’s routed above experiences centripetal acceleration, gathering more speed than the air traveling below, resulting in a decrease in pressure above the wing and an increase in pressure below the wing, creating the upwards force of lift. The faster the plane travels, the greater the pressure difference, and the greater that force. To precisely model air’s flow around a wing and detail how lift is generated, engineers use a set of formulas called the Navier-Stokes equations. More than a century after Einstein’s attempt to design an airplane wing, lift remains a confounding concept. When it feels like everything is going to fall apart, keep in mind that it is simply the laws of fluid dynamics at work. This video was made possible with help from Marriott Hotels. With over 590 hotels and resorts around the world, Marriott Hotels celebrates the curiosity that drives us to explore. See what TED-Ed and Marriott are doing together and plan your next journey at Marriott Hotels.