Terminal Velocity

Terminal velocity is the speed at which a falling object stops accelerating because air resistance has grown to match its weight. Drag scales with the square of speed, so as an object falls faster, drag rises faster than gravity can compensate, and the two forces converge on a balance point — net force zero, acceleration zero, velocity constant from then on. It is an equilibrium, not a ceiling imposed from outside.

The value depends on mass, cross-sectional area, drag coefficient, and the density of the medium, not on how far the object has fallen. A skydiver in a stable belly-to-earth position has a large presented area and reaches roughly 55 m/s (about 195 km/h); the same skydiver diving head-down minimizes area and can exceed 150 m/s. A raindrop's terminal velocity — a few meters per second for a typical drop — is why rain falls at a survivable speed instead of accelerating the whole way down from cloud height, and why a mouse can survive a fall that would kill a horse: at small scale, area-to-mass ratio is higher, so terminal velocity is lower.

Terminal velocity is reached asymptotically, not instantly — an object approaches it exponentially, spending most of its acceleration in the first few seconds and then flattening out. A skydiver's parachute works by abruptly increasing drag area, which forces a new, much lower terminal velocity and produces the deceleration felt at deployment, not by "stopping" the fall in any more exotic sense.