In
fluid dynamics, the
drag equation is a formula used to calculate the force of
drag experienced by an object due to movement through a fully enclosing
fluid. The formula is accurate only under certain conditions: the objects must have a blunt form factor and the fluid must have a large enough
Reynolds number to produce
turbulence behind the object. The equation is
- is the drag force, which is by definition the force component in the direction of the flow velocity,
- is the mass density of the fluid,
- is the flow velocity relative to the object,
- is the reference area, and
- is the drag coefficient – a dimensionless coefficient related to the object's geometry and taking into account both skin friction and form drag.