G-forces represent a measure of acceleration relative to Earth’s gravity. An acceleration of 1G is equivalent to the acceleration due to free fall, approximately 9.8 meters per second squared. These forces are experienced whenever there is a change in speed or direction, making objects feel heavier or lighter. While often associated with gravity, G-forces are primarily generated by mechanical forces acting upon an object or body.
The Nature of Lateral G-Forces
Lateral G-forces, often denoted as Gy, describe acceleration acting perpendicular to the body’s spine, from side to side. This differs from vertical G-forces (head-to-foot) and longitudinal G-forces (front-to-back). Lateral G-forces are felt as a sideways push, common in sharp turns or impacts.
These forces are frequently encountered during cornering in high-performance vehicles, such as race cars or aircraft. For instance, Formula One drivers routinely experience 4-6 Gs while cornering. While other G-force directions are more prevalent in aviation, lateral G-forces can still occur, particularly in thrust-vectored aircraft during flat turns. The unique direction of lateral G-forces presents distinct challenges for the human body compared to vertical or longitudinal forces.
How Lateral G-Forces Affect the Body
Lateral G-forces impose unique stresses on the human body. These forces can cause internal organs to shift within the torso, potentially affecting their normal function. The body’s soft tissues are particularly deformable under such loads.
Significant strain is also placed upon the skeletal structure, especially the spine and ribs, as the body attempts to resist the sideways displacement. Muscles work intensely to counteract these forces, leading to fatigue and discomfort. While lateral G-forces generally have less direct impact on blood flow to the brain compared to head-to-foot G-forces, severe or prolonged exposure can still disrupt normal physiological processes and potentially lead to injury.
Factors Influencing Lateral G Tolerance
An individual’s ability to tolerate lateral G-forces is influenced by several factors. The duration of exposure is significant; brief, momentary peaks of G-force are generally tolerated better than sustained exposure. The rate at which the G-force builds, known as the rate of onset, also plays a role, with rapid onset forces being more challenging to withstand.
Individual characteristics such as overall health, physical fitness, and body positioning contribute to G-tolerance. Factors like age, abnormal blood pressure, and even height can influence how well a person withstands these forces. External factors, including the use of restraint systems like seatbelts and specialized harnesses, and protective gear, effectively mitigate the effects of lateral G-forces by providing support and limiting body displacement.
Limits of Human Lateral G Tolerance
The precise limits of human tolerance to lateral G-forces vary widely depending on the specific conditions. For very brief durations, such as those experienced in high-impact events like car crashes, humans can survive extremely high G-levels. For example, British race car driver David Purley survived a deceleration estimated at 180 Gs for an instant during a crash.
For sustained exposure, human tolerance to lateral G-forces is considerably lower. While humans can generally tolerate high levels of lateral G-forces if properly restrained, the threshold for severe injury from lateral forces is around 12 Gs for short durations. In typical road driving, advisory speed limits for turns are often set to limit lateral G-forces to approximately 0.22 G to ensure safety and prevent vehicle rollover. In car crashes, G-forces exceeding 50 Gs are associated with traumatic brain injuries, and values above 70 Gs commonly lead to serious injuries or fatalities, emphasizing the importance of vehicle safety features and restraint systems.