<P> The gravity of Earth, which is denoted by g, refers to the acceleration that is imparted to objects due to the distribution of mass within Earth . In SI units this acceleration is measured in metres per second squared (in symbols, m / s or m s) or equivalently in newtons per kilogram (N / kg or N kg). Near Earth's surface, gravitational acceleration is approximately 9.8 m / s, which means that, ignoring the effects of air resistance, the speed of an object falling freely will increase by about 9.8 metres 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). </P> <P> The precise strength of Earth's gravity varies depending on location . The nominal "average" value at Earth's surface, known as standard gravity is, by definition, 9.80665 m / s . This quantity is denoted variously as g, g (though this sometimes means the normal equatorial value on Earth, 9.78033 m / s), g, gee, or simply g (which is also used for the variable local value). The weight of an object on Earth's surface is the downwards force on that object, given by Newton's second law of motion, or F = ma (force = mass × acceleration). Gravitational acceleration contributes to the total acceleration, but other factors, such as the rotation of Earth, also contribute, and, therefore, affect the weight of the object . </P> <P> A perfect sphere of uniform mass density, or whose density varies solely with distance from the centre (spherical symmetry), would produce a gravitational field of uniform magnitude at all points on its surface, always pointing directly towards the sphere's centre . The Earth is not spherically symmetric, but is slightly flatter at the poles while bulging at the Equator: an oblate spheroid . There are consequently slight deviations in both the magnitude and direction of gravity across its surface . The net force (or corresponding net acceleration) as measured by a scale and plumb bob is called "effective gravity" or "apparent gravity". Effective gravity includes other factors that affect the net force . These factors vary and include things such as centrifugal force at the surface from the Earth's rotation and the gravitational pull of the Moon and Sun . </P>

What is the value of gravity on earth
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