The gravity of Earth, denoted g, refers to the acceleration that the Earth imparts to objects on or near its surface. In SI units this acceleration is measured in metres per second per second (in symbols, m/s2 or m·s-2) or equivalently in newtons per kilogram (N/kg or N·kg-1). It has an approximate value of 9.81 m/s2, which means that, ignoring the effects of air resistance, the speed of an object falling freely near the Earth's surface will increase by about 9.81 metres (about 32.2 ft) per second every second. This quantity is sometimes referred to informally as little g (in contrast, the gravitational constant G is referred to as big G).
There is a direct relationship between gravitational acceleration and the downwards weight force experienced by objects on Earth, given by the equation F = ma (force = mass × acceleration). However, other factors such as the rotation of the Earth also contribute to the net acceleration.
Although the precise strength of Earth's gravity varies depending on location, the nominal "average" value at the Earth's surface, known as standard gravity is, by definition, 9.80665 m/s2 (32.1737 ft/s2). This quantity is denoted variously as gn, ge (though this sometimes means the normal equatorial value on Earth, 9.78033 m/s2), g0, gee, or simply g (which is also used for the variable local value). The symbol g should not be confused with g, the abbreviation for gram (which is not italicized).
Read more about Gravity Of Earth: Variation in Gravity and Apparent Gravity, Estimating g From The Law of Universal Gravitation, Comparative Gravities of The Earth, Sun, Moon, and Planets
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