Terminal velocity is the maximum velocity an object reaches when it is falling under the force of gravity or another constant driving force. The object is subject to a resistance that increases as the velocity increases, and when the resistance equals the driving force, terminal velocity occurs.
Terminal velocity follows Newton's first law of physics, which states that every object does not move or continues moving in a straight line unless it is forced to change by an outside force. An object starts at rest, then when released, the object begins free fall and accelerates with the force of gravity acting upon it. The air resistance, or drag, increases until it equals the weight of the object. Terminal velocity magnitude depends on the weight, drag coefficient, air density and size of the object.