Terminal velocity is the maximum constant speed an object reaches as it falls through a fluid—usually air—when the downward force of gravity is exactly balanced by the upward force of air resistance (drag).
When an object first starts to fall, gravity causes it to accelerate. As its speed increases, so does the air resistance acting against it. Eventually, the drag force grows large enough to equal the gravitational pull, and at that point:
- The net force becomes zero
- The object stops accelerating
- It continues to fall at a steady speed—this is the terminal velocity
Factors that affect terminal velocity include:
- The object’s mass and shape
- Cross-sectional area
- Density of the fluid it’s falling through
- Drag coefficient (related to how streamlined the object is)
For example, a skydiver in free fall reaches terminal velocity after a few seconds, typically around 53 m/s (190 km/h) in a belly-down position. Deploying a parachute greatly increases air resistance, reducing terminal velocity and allowing a safe landing.
Terminal velocity illustrates the balance between forces and shows how motion in real environments is shaped by more than just gravity.