The gravity is the force of mutual attraction experienced by two objects with mass .
It is one of the four fundamental forces yet seen in nature: the electromagnetic force , the weak nuclear force , the strong nuclear force and gravity .
Gravity is the most important regarding the functioning of the universe : nuclear forces are so short that they only manifest in the atomic and subatomic world ;
the electromagnetic force can act at any distance, but it is based on the existence of two types of charge so that different loads are attracted and equal charges are repulsed , that is, the large-scale result is neutral. On the other hand, the force of gravity is always attractive and acts at any distance, which is why it is always present everywhere. It is causing the Earth to turn around the Sun. and that the Sun moves around the center of the Milky Way .
Apart from that, the gravitational force is, among the four fundamental forces, the least understood by modern physicists. These aspire to formulate the Great Unified Theory , in which the four forces are united in a physical model that describes the behavior of the universe as a whole. At this moment, the force of gravity is the most problematic, the one that resists the union.