When an object falls through the air, it accelerates due to gravity. This acceleration does not continue indefinitely, as a natural limit exists to how fast any object, including a human, can fall through Earth’s atmosphere. This concept defines the maximum speed a person can reach during a descent.
What is Terminal Velocity?
Terminal velocity represents the fastest speed an object can achieve while falling through a fluid, such as air. As an object falls, two main forces are at play: the downward pull of gravity and the upward force of air resistance, also known as drag. Initially, gravity causes the object to accelerate, increasing its speed. As the object’s speed grows, the force of air resistance also increases because it collides with more air particles at a faster rate.
Eventually, the air resistance precisely balances the force of gravity. At this point, the net force acting on the object becomes zero, meaning there is no longer any acceleration. The object then continues to fall at a constant speed, which is its terminal velocity. This equilibrium between gravity and air resistance defines the object’s maximum falling speed in that environment.
How a Human’s Body Affects Terminal Velocity
Terminal velocity is not a single fixed number for a human, as several factors influence it. A person’s body position is a primary determinant, affecting the surface area exposed to the air. For instance, a spread-eagle position, with outstretched arms and legs, maximizes surface area and increases air resistance. Conversely, a streamlined, headfirst dive minimizes this area, reducing drag.
The individual’s mass also plays a role; a more massive person experiences a higher terminal velocity because a greater drag force is needed to balance their increased gravitational pull. Clothing and equipment can also alter a person’s aerodynamic properties and weight, further affecting air resistance. Additionally, air density impacts terminal velocity; denser air at lower altitudes provides more resistance, resulting in a lower terminal velocity, while thinner air at higher altitudes allows for higher speeds.
The Real-World Numbers for Humans
For a human falling through the atmosphere, terminal velocities vary based on the factors mentioned. In a common “belly-to-earth” or spread-eagle position, a human’s terminal velocity is approximately 120 miles per hour (190-200 km/h). This position maximizes air resistance, leading to a lower terminal speed.
However, by adopting a more streamlined, headfirst or feet-first position, individuals can significantly reduce their surface area. This reduction in drag allows for higher speeds, with terminal velocities reaching over 200 miles per hour (320 km/h). A human typically takes about 12 seconds and 450 meters (1,500 feet) of fall distance to reach terminal velocity in a belly-down position. The danger in such a fall stems not from the speed itself, but from the sudden impact upon reaching the ground.