The Visualization of Frequency-Modulation Transients by Means of Mechanical Models

It has long been known that electrical circuits have equivalent mechanical circuits, and that the correspondence between the two can be established in two ways, namely, either voltage
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force, current
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velocity, capacitance
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compliance, etc., or voltage
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velocity, current
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force, capacitance
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mass, etc. If, however, one searches for a mechanical model which preserves the elegance and strength of Argand's vectorial diagram, in which voltages at or near the center frequency of a band-pass circuit can be represented by stationary or slowly rotating phasors, the classical equivalent mechanical circuits are inadequate, and a new form of equivalence must be adopted. This article describes this new equivalence which is obtained, for a large class of important circuits, by dropping Kirchhoff's laws and utilizing Thevenin's theorem, so that the mechanical models so established give a correct and easily visualized representation of input and output voltages; albeit intermediate points in the electrical circuits do not correspond generally to intermediate points in the mechanical model.