# [Nasa: What is Lift?](https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/what-is-lift/) ![[NASA lift graphical view.png]] Lift occurs when a moving flow of gas is turned by a solid object. The flow is turned in one direction, and the lift is generated in the opposite direction, according to Newton’s Third Law of action and reaction. Because air is a gas and the molecules are free to move about, any solid surface can deflect a flow. For an aircraft wing, both the upper and lower surfaces contribute to the flow turning. Neglecting the upper surface’s part in turning the flow leads to an incorrect theory of lift. # [NASA: Lift From Flow Turning](https://www.grc.nasa.gov/www/k-12/airplane/right2.html) ![[NASA lift from flow turning.png]] ## **Force = Mass x Acceleration** - Lift is a force. From [[Newton's Laws]] (second law) of motion, a force **F** is produced when a mass **m** is accelerated - $F=m\times a$ - An **acceleration** is a change in velocity $V$ with a change in time $t$ - $F=m\times \frac{V_1-V_0}{t_1-t_0}$ - We have written this relationship as a difference equation, but it is recognized that the relation is actually a differential from calculus. - $F=m\times \frac{dV}{dt}$ - $dV =$ change in velocity of the fluid - $dt =$ difference in time - $\frac{dV}{dt} =$ acceleration The important fact is that a force causes a change in velocity; and, likewise, a change in velocity generates a force. The equation works both ways. A velocity has both a **magnitude** called the speed and a direction associated with it. Scientists and mathematicians call this a [vector quantity](https://www.grc.nasa.gov/www/k-12/airplane/vectors.html). So, to change either the speed or the direction of a flow, you must impose a force. And if either the speed or the direction of a flow is changed, a force is generated. # Understanding Aerodynamic Lift - The Efficient Engineer <div class='iframe-container'><iframe width="560" height="315" src="https://www.youtube.com/embed/E3i_XHlVCeU?si=PAfFQQN5OADoTgkt" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share" referrerpolicy="strict-origin-when-cross-origin" allowfullscreen></iframe></div>