The formula for calculating average drag on an object is FD = 0.5 * ρ * v^2 * CD * A, where FD is the drag force, ρ is the density of the fluid, v is the velocity of the object, CD is the drag coefficient, and A is the frontal area of the object.
The average drag on an object is affected by the density of the fluid, the velocity of the object, the drag coefficient, and the frontal area of the object. Other factors that can also impact drag include the shape of the object, surface roughness, and the fluid's viscosity.
The expression for average drag on an object can be derived using the basic principles of fluid mechanics, such as Bernoulli's equation and the conservation of momentum. The derivation involves integrating the pressure and shear stress over the surface of the object and taking into account the different forces acting on the object.
The units for average drag are typically Newtons (N) or pounds (lbs) in the English system of units, and dynes (dyn) or grams (g) in the metric system of units.
In most cases, the drag force on an object cannot be zero, as there will always be some resistance from the fluid. However, in certain conditions, such as when an object is streamlined and moving at a constant velocity in a uniform fluid, the drag force can be reduced to a very small value.