Why it would require greater applied mechanical force to rotate an electric dynamo when electric power is being supplied to an external resistance load than rotating the dynamo without the load - the change of kinetic energy per unit time is diminished in the presence of electric power supplied to the external load so that the internal generating conductors inside the dynamo cannot move faster than without the load. to barely rotate the dynamo without rotational acceleration what is needed at least is applied mechanical power equals the electric power needed in the load.