For 10 points, name this weakest of the four fundamental forces, a theory of which was supposedly devised by Isaac Newton after an apple fell on his head.
The Pound-Rebka experiment confirmed the existence of a red shift associated with this force. The potential energy associated with this force is equal to the kinetic energy at an object's escape velocity. It is proportional to the product of the (*) masses of two objects over the square of the distance between them by Newton's Law of Universal [this]. For 10 points, name this weakest of the four fundamental forces, a theory of which was supposedly devised by Isaac Newton after an apple fell on his head.
The Pound-Rebka experiment confirmed the existence of a red shift associated with this force.
{gravity} [or {gravitational} force; or {gravitational} red shift until "{red}"]