Analogies can also be developed for distributed elements such as transmission lines but the greatest benefits are with lumped element circuits. Mechanical analogies are required for the three passive electrical elements, namely, resistance, inductance and capacitance. What these analogies are is determined by what mechanical property is chosen to represent ''effort'', the analogy of voltage, and the property chosen to represent ''flow'', the analogy of current.[5] In the impedance analogy the effort variable is force and the flow variable is velocity.[6]