Question

if gravitation is the power by which all bodies tend towards each other, then why do all bodies tend towards the centre of the earth?

Answer 1

Gravitational force is force which is always attractive in nature and thus all bodies tend toward each other but the acceleration due to gravity on the mass of the body i.e. mg always applied downwards towards the centre of the earth thus, all the bodies tend towards the centre of the earth.

Answer 2

Because its nature who always believe in Symmetry's call. And we physicist also do that. Gravitational always tend to act or it do acts at every point on the earth surface even at the depths if the observer sees from the space .. But the whole contributions comes from the center this is like center of mass .. Center of mass between 2 bodies gives the gravitational effect not the body all the time .. You can imagine the path way of sun and earth .. calculate the center of mass what you get is earth is going around at the same time sun also moves and goes around slightly in the less radius around their center of mass