Standard gravity, usually denoted by g₀ or g_n, is the nominal acceleration due to gravity at the Earth's surface at sea level, defined to be precisely 9.80665 m/s² (approx. 32.174 ft/s²). This value was established by the 3rd CGPM (1901, CR 70).^{[1] [2]}

The symbol g is sometimes also used for standard gravity, but g strictly means the local acceleration due to gravity, 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 abbreviation for gram. The g (sometimes written "gee") is also used as a unit of acceleration, with the value defined as above; see g-force.

The value of g₀ defined above is a nominal midrange value on Earth, representing the acceleration of a body in free fall at sea level at a geodetic latitude of about 45.5°. It is larger in magnitude than the average sea level acceleration on Earth, which is about 9.797645 m/s². Although the actual strength of gravity on Earth varies according to location, for weights and measures and many calculation purposes the standard gravity figure is used.

The SI unit of acceleration due to gravity (or, indeed, any acceleration), namely meters per square second, can also be written as newton per kilogram. The numeric value stays the same: g_n = 9.80665 N/kg. This alternative representation can be understood by noting that the gravitational force acting on an object at the Earth's surface is proportional to the mass of the object: for each kilogram of mass, the Earth exerts a nominal force of 9.80665 newtons (though, as stated, the precise value varies depending on location).

Because the acceleration due to gravity is the force acting on unit mass (in SI units, 1 kg) it is often referred to as the gravitational field in analogy with the electric field which is the electrostatic force on a unit charge.

[edit] Calculating g₀

Using the mass and radius of Earth:

[edit] References

1. ^ The international system of units (SI) - United States Department of Commerce, NIST Special Publication 330, 2001, p. 29
2. ^ The International System of Units (SI) - Bureau international des poids et mesures, 8th edition, 2006, p. 142-143

[edit] See also

• Earth's gravity
• g-force, a measure of acceleration
• G, the gravitational constant in Newton's law of gravity
• Gravitational acceleration