Monterey Bay Aquarium Research Institute
Marine Botany

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Lift Forces

Every time you fly in an airplane, you rely on the force of lift to hold your vehicle aloft. Lift is due to a difference in pressure between the top and bottom of an object in flow. In the picture of an airfoil below, observe how the streamlines are compressed above the wing but further apart below the wing. velocity and pressure

This means that average velocity is higher above the wing but lower below it. Since pressure must decrease as velocity increases, the pressure above the wing is lower than the pressure below it. This difference in pressure produces a net upward force.

Lift Force = 1/2 * r * CL *Aplanform * u2

flow over planform

Aplanform = Planform Area (surface area looking up at the object)

r = Fluid Density


CL = Coefficient of Lift (proportionality coefficient--empirically determined)

u = Fluid Velocity

Among other things, this equation indicates that higher velocities produce greater lift forces.

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copyright Elizabeth Nelson, Judith Connor 1999, 2000   Non-profit educational uses permitted.    

Last updated: Feb. 05, 2009