The standard acceleration due to gravity near the Earth's surface, often denoted as "Earth standard gravity", is a constant approximately equal to 9.807 m/s². The lowercase letter g is commonly used to represent it. It is normally simplified to
9.8 but is officially
The acceleration due to gravity varies slightly from g at different places on Earth, due to the Earth's rotation, variances in the distribution of the Earth's mass, and the location's elevation. Consequently, a standard value of g (as given above) is often adopted when high precision is not necessary.
The familiarity of the acceleration due to gravity, leads to its usage as a common unit in various settings. A prominent example is its use as a unit for acceleration, be it a measure of thrust a ship is undergoing or the amount of acceleration due to spin-gravity experienced at various levels on a station. A similar usage is as a shorthand for a force, referred to as "g-forces" or "gs". This is due to the direct relationship of forces with mass and acceleration. With this shorthand, a force is thus described in a mass-independent way as a multiple of the acceleration due to gravity, and thus the force can be thought of as a multiple of an object's weight (on Earth).
- Uppercase G represents a different physical constant and therefore the interchanging of the two symbols is a common mistake that should be avoided.
- A common misconception is that g-force is an expression of force, but is actually an expression of an object's acceleration. To recover the experienced force, the number of g-forces must be multiplied by the object's mass.
Since humanity evolved on Earth, many of the body's biological systems evolved to function optimally when experiencing the downward force of gravity, with a magnitude of 1g. Survival in “
low-g”, or “
null g” can lead to tissue atrophy especially of bone and muscle. In such low gravity situations, the sense of equilibrium can be impaired (or non-existent), leading to a loss of orientation and vertigo. Low-g also complicates injuries as bodily fluids may not properly drain and thus exacerbate damage or retard recovery.
Sustained exposure to “
high-g” will lead to excessive and deleterious stresses on soft tissue. Over short periods, bruising of organs, dislocation of joints, and loss of consciousness are common. Over long periods, the probability of aneurysms and strokes increases rapidly. Individuals of more advanced age are at particular risk of experiencing these complications.
High Thrust Space TravelEdit
A number of safety mechanisms have been invented and widely utilized. Physically, gimbaled "crash couches" help to properly orientate the body and provide padding to soften the experienced acceleration, particularly in short duration, high-g maneuvers. Crash couches in military ships, and those for the crew in civilian ships, can administer a drug cocktail to mitigate the biological stresses of high acceleration. This cocktail is known as ''juice" in English and as “
dzhush” in Belter Creole.
- The moon's acceleration due to gravity is at the inner ear's detection threshold. Consequently, momentarily loss of orientation and balance can be experienced. This phenomenon was documented by the Apollo astronauts but has not been depicted in the books.