Drag equation
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 equation is: F d = 1 2 ρ u 2 c d A {\displaystyle F_{\rm {d}}\,=\,{\tfrac {1}{2}}\,\rho \,u^{2}\,c_{\rm {d}}\,A} where F d {\displaystyle F_{\rm {d}}} is the drag force, which is by definition the force component in the direction of the flow velocity, ρ {\displaystyle \rho } is the mass density of the fluid, u {\displaystyle u} is the flow velocity relative to the object, A {\displaystyle A} is the reference area, and c d {\displaystyle c_{\rm {d}}} is the drag coefficient – a dimensionless coefficient related to the object's geometry.