Skydiving is fundamentally a demonstration of physics in action, particularly the concept of terminal velocity. A person exiting an aircraft will generally reach terminal velocity in a very short amount of time, typically under fifteen seconds from the moment of exit. This maximum, constant speed is a dynamic state achieved when the two primary forces acting on the falling body become perfectly balanced. The specific duration and final speed depend heavily on the body’s orientation and the resulting interaction with the surrounding air.
Understanding Terminal Velocity
Terminal velocity represents the fastest speed a falling object can attain while moving through a fluid, such as the atmosphere. This maximum velocity is achieved when the downward force of gravity is precisely counteracted by the upward force of air resistance, also known as drag. When these two forces become equal, the net force acting on the skydiver drops to zero.
Because the net force is zero, the skydiver stops accelerating and maintains a constant speed for the rest of the freefall. As a person begins to fall, gravity is the dominant force, causing acceleration. However, as speed increases, the opposing force of air resistance also grows proportionally, creating a constantly changing dynamic.
The Timeframe for Reaching Maximum Speed
For a skydiver in the most common orientation, the stable, belly-to-earth position, the time required to reach terminal velocity is remarkably brief. On average, a skydiver in this spread-out posture will achieve maximum speed within ten to twelve seconds after leaving the plane. The speed reached is typically around 120 miles per hour, although this varies based on the skydiver’s mass and gear.
During this initial phase, the skydiver is accelerating, but the rate of acceleration continuously decreases. This reduction occurs because as the skydiver’s speed increases, the air resistance pushing back against them grows exponentially. The increasing drag force progressively reduces the net downward force, eventually stopping acceleration when the forces are balanced.
The distance covered during this acceleration phase is relatively short, typically around 1,500 feet before the skydiver settles into steady terminal velocity. Once this speed is reached, the sensation of falling changes to a sensation of being supported by the rush of air. The speed remains constant until the skydiver changes their body position or deploys the parachute, altering the balance of forces.
How Skydiver Position Affects Freefall Dynamics
The specific value of a skydiver’s terminal velocity is highly dependent on the body’s posture, which alters the drag coefficient. The drag coefficient measures how much resistance a body encounters moving through the air. It is largely determined by the cross-sectional area presented to the airflow. A larger cross-sectional area, like the wide surface of the belly-to-earth position, creates more drag.
The high drag of the belly-to-earth position results in a lower terminal velocity. Skydivers can intentionally reduce their cross-sectional area by tucking their limbs in or adopting a vertical orientation, such as a head-down dive. This more streamlined shape significantly reduces drag, allowing the gravitational force to dominate for longer and resulting in a much higher terminal velocity.
A skydiver in a head-down position can easily reach speeds between 150 and 180 miles per hour. Some advanced speed dives can exceed 200 miles per hour. The ability to manipulate the body’s shape and surface area allows skydivers to instantly change their freefall dynamics and control their fall rate. By shifting posture, a skydiver can immediately increase their terminal velocity to match or adjust to other jumpers in the sky.