Drag force is determined by the density of the fluid through which the object is moving (in this case air), the velocity the object is moving,
the reference area (if the case of a sphere, the cross sectional area), a co-efficient and a constant.
Other things being equal (i.e. for a given kick of a given football etc.), the drag experienced is proportional to the density of the air.
Using the ideal gas law, air density is determined by air pressure and temperature.
Air pressure reduces with increasing altitude and you can see by how much with our
air pressure calculator
Temperature also decreases with increasing altitude (by about 0.0065 K/m at altitudes below 11km).
This is the same as saying the temperature falls by about 0.0065 Celsus per meter ascent below 11km.
Another important factor in calculating air density is humidity.
However, when it comes to football matches, all these thing are also very weather dependent...
Last updated June 2010