Experiencing extreme forces is a part of high-speed travel and advanced machinery. G-force, a measure of acceleration, helps us understand the intensity of these experiences. While we encounter small G-forces daily, the sensation of higher levels, such as 7Gs, is far more profound. This level of force pushes the limits of human endurance and dramatically impacts the body.
Understanding G-Force
G-force, or gravitational force equivalent, quantifies the acceleration an object or person experiences relative to Earth’s gravity. One G represents the standard force of gravity we feel when standing still on Earth’s surface. This is approximately 9.8 meters per second squared (m/s²). When a vehicle speeds up, slows down, or changes direction, it generates G-forces that can make us feel heavier or lighter.
Accelerating rapidly in a car, for instance, pushes you back into your seat. A sudden stop makes you feel thrown forward. On a roller coaster, a steep drop might create a feeling of weightlessness (less than 1G), while a tight loop can press you firmly into your seat (more than 1G).
The Immediate Sensation of 7Gs
Experiencing 7Gs means your body is subjected to seven times the force of Earth’s gravity. This level creates a sensation of immense weight and pressure. It feels as though an invisible, colossal hand is pressing you firmly into your seat, making every limb feel incredibly heavy. For example, a 135-pound person would momentarily feel like they weigh over 1,000 pounds.
Movement becomes extremely difficult as your muscles struggle against this amplified weight. Your head, which normally weighs around 10-12 pounds, can feel like it weighs 70-84 pounds, making it challenging to even turn. Breathing can become labored, and your entire body might feel frozen in place, as if encased in concrete. This intense pressure is due to the body’s inertia resisting rapid acceleration, causing fluids and tissues to be pushed downwards with significant force.
Physiological Impact and Risks
Sustaining 7Gs significantly impacts the body’s physiological functions, primarily by disrupting blood flow. Under strong positive G-forces, blood is forcefully pulled away from the head and towards the lower extremities. The heart struggles to pump blood against this immense pressure, leading to a significant reduction in cerebral blood circulation. This lack of oxygenated blood to the brain triggers a series of visual disturbances.
The first symptom is tunnel vision, where peripheral vision narrows, leaving only a central field of view. This can progress to “greyout,” a loss of color vision, making everything appear in shades of gray. If the G-force continues unabated, it can lead to “blackout,” a complete loss of vision, although consciousness may still be retained. The most severe outcome is G-induced Loss of Consciousness (G-LOC), which occurs when the brain is deprived of sufficient blood flow, resulting in temporary loss of awareness. Recovery from G-LOC is prompt once the G-forces subside, though a period of disorientation can follow.
Where 7Gs Are Experienced
High G-forces are primarily experienced in environments designed for extreme acceleration. Fighter jets are a prime example, where pilots routinely encounter significant G-forces during maneuvers like tight turns or steep climbs. Modern fighter aircraft like the F-18 Super Hornet are capable of pulling 7Gs, and some can even reach 9Gs. Pilots flying these high-performance aircraft wear specialized G-suits that inflate around the legs and abdomen to help maintain blood pressure in the upper body and brain.
Human centrifuges are another controlled environment where individuals, particularly pilots and astronauts, experience high G-forces for training and research. These large rotating machines simulate the physiological stresses of high-G flight, allowing individuals to practice techniques to resist its effects and improve their G-tolerance. While some roller coasters can generate significant G-forces, often reaching 4-5.5 Gs, they rarely sustain 7G levels, as such forces would be unsafe for the general public without specialized equipment and training.