Two new mechanical analogues for teaching a.c. power flow over a lossless line are suggested. The first analogue is simple. It illustrates the phase angle between the sending end voltage and the receiving end voltage. The second analogue is somewhat more complicated and mathematically exactly analogous to the a.c. power flow model. It uses a concept which is familiar to every human: the inertia of mass. With this analogue we illustrate not only the voltage phase shift but also the maximum power over a line.
