For the basic principle of motors and electromagnetic induction, when a wire loop with a current running through it is put in a magnetic field, wouldnt it only spin until it reached a certain point (i.e. flat, 180 degrees) before it stopped? What accounts for this? Is it that the loop must use AC and that the current reverses for every half turn? Or would dc work too for induction? Or is it a a property of the way the field of the current changes as it moves through space?