Final answer:
Terminal velocity is achieved when the net force on a falling object is zero, due to the balance between the object's weight and the upward drag force. As a result, the object falls at a constant speed and does not accelerate further.
Step-by-step explanation:
Terminal velocity is the constant velocity achieved by a falling object, which occurs when the weight of the object is balanced by the upward drag force. When an object reaches terminal velocity, the net force on the object is zero. This situation arises when the force of gravity (downward force) is exactly counteracted by the drag force (upward force), which typically increases as the velocity of the object increases. This balance of forces means there is no more acceleration and the object continues to fall at a constant speed.
For example, a skydiver will reach terminal velocity when the air drag equals their weight. The drag force is proportional to the square of the velocity, especially at high speeds and when turbulence is a factor. The terminal speed for a person can be calculated when this drag force is set equal to the person's weight.