OBJECTS INTERACT OVER LONG DISTANCES THROUGH FIELDS. THE STRONGEST FIELD FORCE OVER LONG DISTANCES IS THE GRAVITATIONAL FORCE. UNLIKE THE OTHER MAJOR FIELD FORCE, ELECTROMAGNETISM, GRAVITATION IS ONLY ATTRACTIVE, PULLING BOTH ANY TWO OBJECTS IN THE UNIVERSE TOWARD THE CENTER OF MASS OF THE SYSTEM WITH A FORCE THAT IS DIRECTLY PROPORTIONAL TO THE PRODUCT OF THE MASSES INVOLVED AND INVERSELY PROPORTIONAL TO THE SQUARE OF THE DISTANCE BETWEEN THEM.

Gravity is, by far, the force with which we are most familiar. It is applied to us every moment of every day. As such, we sometimes take for granted that it is there, and don't often think about the how or why of it. One of Newton's best and biggest leaps of intuition was that this gravitational force is UNIVERSAL, meaning it is applied between any two objects, anywhere in the universe. Despite this, the phenomenon of gravity still poses a bit of a puzzle to physicists.