Basically any LTI differential equation can be modeled as a network of Rs, Ls, and Cs. You can get fancier if you want by adding nonlinear elements. In other w

Basically any LTI differential equation can be modeled as a network of Rs, Ls, and Cs. You can get fancier if you want by adding nonlinear elements. In other words, anything you can describe as a differential equation has an analogous circuit. In fact, I've read the claim (though I cannot, for the moment, find the reference) that the term analog was first applied to circuits which were being built to solve LTI differential equations: the circuit was the analogue of the equation, thus it was an analogue (eventually, just analog) circuit.