In the first part complex mechanical impedance and admittance (mo¬bility) are introduced and it is shown that analogy between mathematical expressions for electrical and mechanical systems leads to two different types of mechanical diagrams for which the designations impedance and admittance diagrams are used. The admittance diagram proves to be the more natural as it represents a simplified picture of the mechanical sy¬stem, and it is in fact possible to draw this diagram by inspection without recourse to any electric analogy of mathematical expressions. Kirchhoff's laws are applied to mechanical systems, and examples of the composition of mechanical diagrams are given including levers, mechanical filters and gramophone pick-ups. Mechanical impedances are derived for systems with lumped and with distributed constants, e. g. vibrating rods and springs. The reciprocity between admittance and impedance diagrams is investigated, and it is shown how one type of diagram may be derived by inversion of the other. Possibilities and limitations of the analogies are discussed.
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