So here is the circuit I came up with to represent back emf in a DC motor with rotational inertia. When current is applied to the motor it spins. When it rotates, the motor acts as a generator and creates a voltage (back emf) as shown (sorry for the incorrect notation, I don't know the correct notation for a generator, so I just put the two bars of the battery on each end of the resistor that represents the motor). Therefore, as soon as the engine starts rotating, the reading on the voltmeter increases while the reading on the current decreases. My question is, does the power dissipated by the motor increase or decrease or stay constant (since P=VI and V increases while I decreases)? ---------------- An additional question. Is there any way to measure this back EMF? If something is unclear please tell me so I can edit. edit: I carried out a series of experiments (using the circuit arrangement shown in the diagram, where the M/G block represents a DC motor that is also acting as a generator as it rotates) that demonstrate that the power calculated from the reading of the ammeter and voltmeter is greater when the motor is rotating than when it is still when applying the same voltage to the circuit. This is how I am explaining it to myself. The rotational inertia (which is considerable in the motor I am using) inputs electrical power into the system, therefore increasing the total electrical power measured. Is my argument sound? I am still confused because I thought back EMF would reduce the power output instead of increasing it. Am I making a mistake somewhere?