a thermal drop - on - demand ink jet print head in which a heat delay means is provided covering a predetermined part of the resistive element . upon connection of an electrical signal to energize the resistive element , nucleation occurs at an uncovered location on the resistive element and formation of the bubble proceeds in a direction toward the covered part of the resistive element to thereby utilize the inertial effect of the controlled bubble motion to eject a drop of ink in a more energy - efficient manner .