Here’s a bit more about fluid drag:

[*]Fluid resistance is proportional to the speed **v* only at very low speeds where the dominant source of resistance is viscosity (the internal friction of fluids)[]At the speeds of ordinary objects in air (including bicyclists, tossed baseballs, airplanes in flight, and Cirri descending under parachutes), the force of fluid resistance is *approximately* proportional to *v*^{2}, the square of the speed.[/list]When a Cirrus of weight *W* is descending under its parachute at a steady speed *v*, the downward force of gravity is exactly balanced by the upward force of fluid resistance. Using the *v*^{2} formula, this says that

*W* = *kv*^{2},

where *k* is a coefficient that depends on the shape and size of the parachute and the density of the air. Solving this expression for the descent speed *v*, we find

*v* = (*W/k*)^{1/2}.

In other words, the descent speed is proportional to the square root (also known as the 1/2 power) of the weight *W*. As a rule of thumb, this means that every 2% decrease in the weight gives a 1% reduction in the descent speed.

This analysis also applies to those situations in which a person descends under a parachute *without* an airplane attached (amazingly, it does happen!).

Cheers,

Roger