An object moving through air experiences a resistive force known as drag. For a macroscopic object whose speed is
sufficiently fast, the drag force FD is:
proportional to v2;
proportional to the cross-sectional area A;
proportional to the density of air ρ
in the opposite direction to v.
Putting it all together: FD = C ρ A
v2,
where the constant C is of the order of one and depends on the object's
shape.