Force

Collier's New Encyclopedia (1921)

in physics, an influence or exertion which, if made to act on a body, has a tendency to move it when at rest, or to affect or stop its progress if it be already in motion. The strength of man's arms is a force, so is the power of a horse or ox to pull a vehicle, or turn a wheel, or set in action an agricultural machine. Gravity, friction, elasticity of springs or gases, electrical or magnetical attraction or repulsion are forces. Accelerated force is the increased force which a body exerts in consequence of the acceleration of its motion. Active force is force which tends to move another body from a state of rest. Animal force is the muscular strength of man, horses, asses, cattle, or other animals viewed as a moving power. Composition of forces is produced by two other forces acting on a body. If they operate in the same direction the resultant or the resulting force will be the sum of both. If the two forces act in opposite directions and are equal, they will make the body remain at rest; and if they are unequal, they will move in the direction of the greater force; and with a force equivalent to their difference. If the lines of direction make an angle with each other, the resultant will be a mean force in an intermediate direction. If many forces act, the resultant is the line of motion or state of rest produced by their conjoint action. Resolution of forces is the decomposition of a force into the forces which have combined to produce it. The theory of the conservation of force, or of energy, is the doctrine or principle that in all cases force is conserved-i. e., kept in existence even when it appears to perish. Just as a certain definite amount of matter exists in the universe, to which man cannot add, and from which he cannot subtract an atom, so a definite amount of force, incapable of being increased or diminished, exists like the former, in the universe. It can, however, be transformed so as to look quite unlike its former self; but in every case the force or energy communicated to a body or system of bodies is withdrawn from some fund of energy previously existing. The theory of the correlation of force, or energy, is the doctrine or principle that the different kinds of force in the universe are so correlated together that any one can be transformed into an exactly equivalent amount of another. There is equality when one can do precisely the same amount of work as any other. It has long been known that in a machine, the screw for example, what is gained in power is lost in velocity, and vice versa. At first sight motion and heat seem to have no relation to each other; but if a moving body be suddenly arrested in its career, as, for instance, a bullet by a target, heat will be generated, and the same number of units of the work which the motion was capable of effecting can be achieved also by the heat. Conversely sery, , a certain amount of heat can produce an equivalent one of motion; thus the working energy communicated to the piston of a steam engine is withdrawn from the heat of the steam, and exactly balances the latter. By equilibrium of forces is meant the action of forces which, balancing each other, produce an equilibrium or state of balance, or rest in the body or bodies on which they operate. An impulsive force is a force which acts on a body for an unappreciably short time, as when one body strikes another. Kinetic force is the actual force excited by a moving body as distinguished from the potential forces which it is capable of creating. Potential force is the whole force which a body in motion can exert, as distinguished from the kinetic force which it is exerting at the specific moment of time. The measure of force is the measurement of the magnitude of a force, which is done by noting the momentum which it communicates to a body in a unit of time. The unit of force is the force which acting on a pound mass would, in one second, produce a velocity of a foot per second. Mechanical force is force of a mechanical nature acting on material bodies. It may be either that of the active force of a body in motion, or the tension or resistance opposed by a body at rest. Molecular forces are those which by means of certain attractions and repulsions retain the atoms of matter side by side without their touching each other. When a force tends to produce rotation about a fixed point the tendency is called MOMENT.