The answer to your question is a bit more complex than you were probably expecting, but here goes... Part 1
force of air resistance on a parachute (figuring the parachute is
basically spread out flat against the air) is directly proportional to
the parachute's surface area, so long as the parachute is moving fairly
quickly through the air. That means that if you double the surface area
you double the force of air resistance:
= SurfaceArea x OtherStuff Part 2
where we've gotta do a little math... The net downward force on the
parachuter is the force of gravity minus the force of air resistance.
= (9.81 m/s^2 x Mass) - (SurfaceArea x OtherStuff)
The net force on the parachuter determines their acceleration (the rate at which they speed up or slow down): F=ma, so...
(Mass x Acceleration) = (9.81m/s^2 x Mass) - (SurfaceArea x OtherStuff)
Do a little rearranging and you get this:
Acceleration = 9.81 m/s^2 - (SurfaceArea)(OtherStuff)/(Mass) Part 3
from knowing the Acceleration to knowing the actual Speed is tricky,
because that "OtherStuff" actually includes the parachuter's velocity.
I'm not going to go into the details of solving that for you here, but
i think the basic gist should be clear: The Moral of This Story
More Surface Area = Falling More Slowly
(republished on 07/30/06)