Upon jumping from the plane, the diver experiences three forces; a downward force from his weight; opposed by a lift force (equal to the weight of the air he displaces); and an upward drag force = ½ . (C_{D.}(RHO).V^{2}.A).

Initially the largest force is the wight of the jumper, leading an increase in downward velocity due to newtons second law, however as can be seen from the drag equation, this increase in velocity will lead to a larger increase in drag force, slowing the divers acceleration, until the downward forces = the up. At this point the diver is at his terminal velocity. When he releases his parachute, there is again a massive increase in the drag force due to the larger frontal area (A), thereby decelerating the diver until he again reaches a new, reduced, terminal velocity.