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 voltage, and what property is chosen to represent current.[5] In the mobility analogy the analogue of voltage is velocity and the analogue of current is force.[6] Mechanical impedance is defined as the ratio of force to velocity, thus it is not analogous to electrical impedance.