... ofq1q2, whereas the gravitational force is always attractive, since “gravitationalcharges” always have the same sign, while the gravitational constant leads toattraction (see (17.4)).Certainly, ... (17.3)Similar considerations apply to gravitational forces; in fact, “gravitationalmass” could also be termed “gravitational charge”, although an essentialdifference from electric charges is that inter ... 2d-surface in space. As an example, thesurface z = xy2is triangulated (i.e., paved)by a grid of small squares. If all the squaresare oriented in the same way as the out-ermost boundary line,...