The air drag is proportional to air pressure and the square of velocity. If we assume that the air pressure grows linearly with depth, we'll get the following e

The air drag is proportional to air pressure and the square of velocity. If we assume that the air pressure grows linearly with depth, we'll get the following equation for acceleration: F/m = a = x'' = g - px - qx•x'•x' Here g-px accounts for linear decrease of gravity, qx is the air pressure, and x'^2 is the square of velocity. That's a tricky equation and even wolframlpha cant solve it.