Analyzing electric machines from the perspective of rotating magnetic fields typically involves moving coordinate frames, where the basic mathematical form of Faraday’s law of electromagnetic induction no longer applies directly. The common approach is to introduce vector or coordinate transformations. Drawing an analogy with D’Alembert’s principle of introducing inertial forces in non-inertial frames, this book introduces the innovative physical concept of “Entrainment Electromotive Force (EEMF)” to resolve this challenge when writing voltage equations in any coordinate system moving relative to the physical windings. This chapter furthermore establishes the four-coil primitive machine physical model, with orthogonal two-phase windings on both stator and rotor, derives its flux linkage, voltage, and torque equations, and analyzes the fundamental electromechanical energy conversion principles revealed by these equations. Finally, the primitive machine model is applied to quantitatively explain the operation of DC machines and two-phase transformers.