**Gravitational Field Strength on the earth’s surface is defined as the force per unit mass experienced by a small test mass placed on the earth’s surface (in the gravitational field of the earth).**

So the Gravitational Field Strength at this point is expressed by the formula, g = G *M*/r^2

where M = mass of the earth =**5.97 x** ** 10^{24}** kg,

r = radius of the Earth =

**6367 km**,

G = Universal Gravitational constant=

**N m**

*6.67 x 10*^{-11 }^{2}kg

^{-2}

[ visit this link to see the *derivation* of the Gravitational Field Strength formula]

Now putting all the numerical values in the equation we get the Gravitational Field Strength on the earth’s surface = **g = G M/r^2 = 9.8 N/Kg**

Observation: This is the same as the acceleration due to gravity, which is what is expected since Newton’s 2nd law says a = F/m = force per unit mass