Dear student, the value of 'g' is not same everywhere on the earth. The acceleration due to gravity is directed towards the centre of the earth, and follows the inverse square law, i.e the force of gravity is inversely proportional to the square of distance between the centre of the earth and the object. Since our earth is not a perfect sphere, gravity isn’t the same all over it. The earth’s radius is lesser at the poles and more at the equator. This creates a difference of 0.017m/sec^2 in the acceleration due to gravity. With Regards!