This book covers primarily gravitational physics, with emphasis on Newtonian and General Relativity approximations in terms of the gravitational radiation flux force potential (the source of gravity). It discuss in length both the theoretical and experimental aspects of modern gravitational physics, e.i. old theories, in relation to a new mechanical theory of gravity, presented in the book. Presented are four parts of a unified theory of gravity, different fields themselves in terms of that unified theory. This also includes a quantum theory of gravity as well.