A stationary object resting upon the ground experiences two forces, the weight force as well as the normal reaction force of the ground. These forces sum to zero. The ground however experiences the weight force acting downwards upon it. What other force acts upon the ground to prevent it from experience a net force downwards? Is it the normal force of the ground immediate below? If we continue this until we get to the centre of the earth, what is the normal reaction force of an infinitesimally thin piece of ground immediately about the centre of the Earth?