Standard Gravity

Standard gravity, or standard acceleration due to free fall, usually denoted by g₀ or g_n, is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. It is defined as precisely 9.80665 m/s2, or about 35.30394 (km/h)/s (≈32.174 ft/s2 or ≈21.937 mph/s). This value was established by the 3rd CGPM (1901, CR 70) and used to define the standard weight of an object as the product of its mass and this nominal acceleration. The acceleration of a body near the surface of the Earth is due to the combined effects of gravity and centrifugal acceleration from rotation of the earth (but which is small enough to be neglected for most purposes); the total (the apparent gravity) is about 0.5 percent greater at the poles than at the equator.

Although the symbol g is sometimes used for standard gravity, g (without a suffix) can also mean the local acceleration due to local gravity and centrifugal acceleration, which varies depending on one's position on Earth (see Earth's gravity). The symbol g should not be confused with G, the gravitational constant, or g, the symbol for gram. The g is also used as a unit for any form of acceleration, with the value defined as above; see g-force.

The value of g₀ defined above is a nominal midrange value on Earth, originally based on the acceleration of a body in free fall at sea level at a geodetic latitude of 45°. Although the actual acceleration of free fall on Earth varies according to location, the above standard figure is always used for metrological purposes. (The actual average sea-level acceleration on Earth is slightly less.)