Gforce

G-force, or g-force, is a unitless measure of the acceleration experienced by a body, expressed as a multiple of standard gravity. It is defined as the instantaneous acceleration a divided by g, where g equals 9.80665 m/s^2 at Earth's surface. G-force describes how strongly a person or object feels pushed or pulled due to acceleration, and is distinct from the gravitational force acting on mass.

In practice, g-forces are measured with accelerometers and used to describe loads on aircraft, spacecraft, and riders on amusement rides. A reading of 1 g corresponds to standard Earth gravity; 2 g means twice that acceleration, and so on. The direction of the acceleration matters, but the magnitude is the primary value when discussing the load on the body (load factor).

Common contexts include aviation and spaceflight, where pilots experience high positive g during turns or pulls, and astronauts experience g during launch and reentry. Roller coasters and simulators also generate high g-forces. Negative g (less than 1 g, including values approaching zero) can produce a sensation of weightlessness or a redistribution of blood flow.

Biological effects depend on magnitude and duration. Short bursts up to 3-4 g are common and tolerated by healthy individuals; sustained or very high g can cause fainting, grey-out or red-out, and in extreme cases injury. Mitigation methods include g-suits, anti-G straining maneuvers, and training in centrifuges.

The term g-force is sometimes used loosely to refer to gravitational acceleration in a location or to describe the total experienced acceleration in a dynamic context. It is not a separate type of force; rather, it expresses how much inertial force a body experiences compared to its weight in Earth gravity.