Why the weight of a body varies
The force of gravity on a body varies slightly from place to place on the earth for two reasons. First, the shape of the earth, and secondly, its rotation. The earth is not a perfect sphere, but bulges at the equator, so that if a body is taken from a pole to the equator its distance from the center of the earth will increase. Consequently, in accordance with Newton’s law of gravitation, the gravitational pull on it will get less.