These simple DC motors are good for students of all levels to play with and to explain. You all understand how a DC motor works, but the one in the upper right has the insulation, on the copper wire in contact with the paper clips taped to the 9 volt battery, completely removed. It is not insulated on one side and conducting on the other. If you look carefully, small sparks are visible at the contact points, when the motor is running. Does the copper loose contact with the paper clip? If so, how far separated do they have to be for a spark? Why would contact be lost?