In fluid dynamics, the drag equation is a practical formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid.

The equation is attributed to Lord Rayleigh, who originally used L² in place of A (with L being some linear dimension). But see Section 7 of Book 2 of Newton's Principia Mathematica; in particular Proposition 37. The force on a moving object due to a fluid is:

where

The reference area A is typically defined as the area of the orthographic projection of the object on a plane perpendicular to the direction of motion. For non-hollow objects with simple shape, such as a sphere, this is exactly the same as a cross sectional area. For other objects (for instance, a rolling tube or the body of a cyclist), A may be significantly larger than the area of any cross section along any plane perpendicular to the direction of motion. Airfoils use the square of the chord length as the reference area; since airfoil chords are usually defined with a length of 1, the reference area is also 1. Aircraft use the wing area (or rotor-blade area) as the reference area, which makes for an easy comparison to lift. Airships and bodies of revolution use the volumetric coefficient of drag, in which the reference area is the square of the cube root of the airship's volume. Sometimes different reference areas are given for the same object in which case a drag coefficient corresponding to each of these different areas must be given.

Mel Jason Smalls (born January 4, 1979), better known as Drag-On, is an American rapper from The Bronx, New York City.

Drag-On was originally signed to Interscope Records under the Ruff Ryders Entertainment imprint, where he released his successful debut album, Opposite of H2O, which debuted at #5 on the Billboard 200 and eventually sold over 500,000 copies and earned a gold certification from the RIAA. After leaving Interscope, Drag-On joined Virgin Records and released his second album, Hell and Back in 2004. The album failed to gain the success of his debut, only reaching 47 on the Billboard 200, and was quickly dropped from Virgin. He also appears in the 2003 film Cradle 2 the Grave as Miles and in the 2001 film Exit Wounds (both starring Ruff Ryders labelmate DMX).