Forbes, JOHN

1710-1759. Scottish officer, prominent at Louis burg and Fort Duquesne, which he named Fort Pitt. Forbes, SIR JOHN, M.D., D.C.L., F.R.S., 1787-1861. Scottish physician, knighted 1853; ed. Medical Review, 1836-48. IMG:content-0130.png:[merged small][subsumed][ocr errors][subsumed][merged small][merged small][merged small][merged small][merged small][merged small] velocity-change in one second, we may write from (1) ---(2), which translated into words shows us that force is the time rate of change of momentum, or it is numerically equal to the momentum generated in one second. If we multiply both members of (2) by t, we get ft=mv (3). The left hand member of (3) or the product of the force by the time during which it acts is called an Impulse. Thus for any given change in the momentum of a body the force is inversely proportional to the time during which it acts. If we multiply the numerator and denominator of the right-hand member of (2) by v and remem mv2 ber that vt-s, we may write f= (4): since the energy of a moving body is proportional to mv, we may define force further to be the space rate of change of energy, or the rate of transference of energy. An attractive force or an Attraction is the mutual action between two bodies in virtue of which if they were free to move they would approach each other. A repelling force or a Repul sion is the mutual action between two bodies in virtue of which if they were free to move they would recede from each other. In order that an agent may exert force, it must meet with