Basic Theoretical Physics: A Concise Overview P3. This concise treatment embraces, in four parts, all the main aspects of theoretical physics (I . Mechanics and Basic Relativity, II. Electrodynamics and Aspects of Optics, III. Non-relativistic Quantum Mechanics, IV. Thermodynamics and Statistical Physics). It summarizes the material that every graduate student, physicist working in industry, or physics teacher should master during his or her degree course. It thus serves both as an excellent revision and preparation tool, and as a convenient reference source, covering the whole of theoretical physics. It may also be successfully employed to deepen its readers’ insight and. | 8 2 Force and Mass mentioned a different viewpoint is also possible and it is better to keep an open mind on these matters than to fix our ideas unnecessarily. Finally the problem of planetary motion dating back to the time of Newton where one must in principle distinguish between the inertial mass mt entering and a gravitational mass ms which is numerically identical to mt apart from a universal constant which is usually replaced by unity is far from being trivial ms is defined by the gravitational law Ms ms r R F r y s-----s--------- Y r R 2 r R where r and ms refer to the planet and R and Ms to the central star sun while y is the gravitational constant. Here the gravitational masses play the role of gravitational charges similar to the case of Coulomb s law in electromagnetism. In particular as in Coulomb s law the proportionality of the gravitational force to Ms and ms can be considered as representing an active and a passive aspect of The fact that inertial and gravitational mass are indeed equal was first proved experimentally by Eotvos Budapest 1911 6 thus we may write ms mt m. Newton s Third Axiom Action and Reaction . Newton s third axiom states that action and reaction are equal in magnitude and opposite in This implies inter alia that the active and passive gravitational masses are equal see the end of the preceding section . on the one hand a body with an active gravitational charge Ms generates a gravitational field Ms r R r Y r R 2 r R in which on the other hand a different body with a passive gravitational charge ms is acted upon by a force . F ms G r . The relations are analogous to the electrical case Coulomb s law . The equality of active and passive gravitational charge is again not self-evident but in the considered context it is implied that no torque arises see also Sect. . Newton also recognized the general importance of his third axiom . with regard to the application of tensile stresses or .
