FORCE, in mechanics, denotes that combination of' matter and motion which produces a change in the state or position of a body. According to this definition, the muscular power of animals, as like wise pressure, impact, gravity, &c., are considered as effects of motion in other bodies ; it being evident, from daily ex perience, that bodies exposed to any free action have force imparted to them, or are themselves thereby imbued with power. All forces, however various, are measured by the elects -which they pro duce in like circumstances, whether the effect be creating, accelerating, retarding, or deflecting motions.
When we any that a force is represent ed by a right line, A B, it is to be under stood that it would cause a material body, situated at A, to run over the line A B, which is called the direction of the force, so as to arrive at B at the end of a given time, while another force would cause the same body to have moved a greater or less distance from A in the same time.
The force of a body in motion is a power residing in that body, so long as it continues its motion • by means of which, it is able to move other bodies lying in its way, or to lessen, destroy, or overcome the force of any other moving body, which meets it in an opposite direction; or, to surmount the largest dead pressure or resistance.
Force is quantity by velocity, before or after impact ; and if quantity is increased, velocity, is diminished. Nature and art is a display of the transfer and reception of force, ad infinitum, and what is lost by one body, is gained by other bodies, by these transferred again, and sometimes collected or concentrated, and at other times scattered and diffused. To trace the sources and distribution, is to analyze nature ; but it is the most general of all laws, that wherever there is force, there is some matter, in some fit motion ; and wherever there is matter in motion, there is resulting force.
Of course, there are no innate, or mir aculous forces—no attraction—no repul sion—no elastic force—no vital force—all are derived from previous motions in other bodies, and the phenomena depend on the quantities of the agents and pa tients, on the direction of their velocity, and on various reactions.
Composition of forces takes place when two or more forces, differently directed, act upon the same body at the same time. As the body then cannot obey them all, it will move in a direction somewhere between their line. This is called the composition and resolution of forces or of motion. But, if the body be impelled by equal force, acting at right angles to each other, it will move in the diagonal of a square, and instances in nature, of mo tion produced by several powers acting at the same time, are innumerable.
All machines are impelled either by the exertion of animal force, or by the appli cation of other powers of nature. The latter comprise the elements of water, air, and fire. The former is more com mon, yet so variable as hardly to admit of eilculation. It is derived from the 'muscular lever of the animal acting against the ground, and thepower of the muscles to act is derived from the gas fixed by respiration. It depends not only on the vigor of the individual, but on the different strength of the particular muscles employed. Every animal exer tion is attended by fatigue of the muscles; it soon relaxes, and would speedily pro dace exhaustion. The most profitable mode of applying the labor of animals is to vary their muscular action, and revive its tone by short and frequent intervals of repose. The ordinary method of com puting the effects of human labor is from the weight which it is capable of elevat ing to a certain height, in a given time, the product of these three numbers ex pressing the absolute quantity of perfor mance. This was reckoned by Bernoulli and Desaguliers, at 2,000,000 lbs. avoir dupois, which a man could one foot in a day. But, our civil engineers have gone much further, and are accustomed, in their calculations, to assume that a laborer will lift 10 lbs. to a height of 10 feet every second, and is able to continue such exertion for 10 hours each day, thus accumulating the performance of 3,600, 000 one foot.