terminal velocity

The constant speed a falling object approaches when air drag has grown to exactly balance gravity. Not the _maximum_ speed in any imposed sense — the speed at which the net force is zero, so acceleration is zero, so velocity stops changing. For linear drag `F_drag = k v` with mass `m`, terminal velocity is `v_t = mg / k` (or `g/k` in the per-unit-mass form `dv/dt = g − kv`). It's an _asymptote_, not a _cap_: from below, the object asymptotically approaches `v_t`; from above (e.g. a thrown-down rock), it asymptotically _decelerates_ toward the same value. Raindrops, parachutists, and dust motes all live their entire fall in this asymptotic regime.