Mechanical power

“ It is not always practicable to employ numerous hands for the purpose, nor is a steam-engine or other great source of power at all times available. But what are called the mechanical powers enable the forces at our disposal to be greatly increased. One man, by their aid, can exert as much force [Pg 100] as several could without such assistance; and when they are employed to augment the power of several men or of a steam-engine, gigantic weights, amounting sometimes to hundreds of tons, can be managed with facility. ”

“ In the mechanical world do we not always find that the greater the exhibition of power the steadier and quieter the movement becomes? It is the rickety engine of but few horse-powers that goes with a fizz and a clatter, while the massive engine that supplies the motive power for acres of machinery goes almost noiselessly; and the sublimest exhibition of power in the universe—the movement of the heavenly bodies—proceeds in absolute quiet. ”

“ Mechanical powers are simple arrangements by which we gain power at the expense of time; thus, if a certain weight can be raised to a certain height by unassisted strength, and the same thing is afterwards done with one tenth part of the exertion, through the use of a mechanic power, it will be found to occupy ten times as much time. ”

“ The man who aspires to construct any great mechanical engineering work, like the Brooklyn Bridge, for example, must know the exact mechanical power of every piece of machinery he employs, as also the exact mechanical value of every piece of iron that enters into the structure; and these things he cannot know unless he is familiar with the entire series of iron manipulations, from those of the foundery to those of the machine-tool shop. ”

“ Yet this remarkable contrivance, with all its massive steel beams and chains and cog wheels, employs no other principles than the simple ones of lever and pulley and inclined plane that we have just examined. The power that must be applied to produce a given effect may be calculated to a nicety. The capacities of the machine are fully predetermined in advance of its actual construction. But of course this is equally true of every other form of power-transmitter with which the modern mechanical engineer has to deal. ”

“ Action and reaction being equal, the power exerted in raising or moving one heavy body must be exerted reversely against the earth, or other fixed body serving as a fulcrum to the lever, or for the attachment of one extremity of a tackle or series of pullies, or for the securing of the capstan spindle. Let the attachments of the machine and its object, however, be both afloat, and then any of the mechanical powers, like that of the wedge, will have an efficiency of double that of its ordinary operation where one part is a fixture. ”

“ How to Experiment with Machines.—Any one who possesses the slightest bent for mechanics can work out improvements on devices like egg-beaters and monkey-wrenches and feel their way as they go along.
But when it comes to designing and building real machines where numerous levers, gears, and springs are combined to make a working unit you should by all means read up on the subjects of work, energy and power, learn about the six mechanical powers—and the action of machines in general. ”

“ In this instrument, therefore, the power acts upon the weight to a mechanical disadvantage, inasmuch as a greater power is necessary to support or move the weight than would be required if the power were immediately applied to the weight, without the intervention of a machine. We shall, however, hereafter show that the advantage which is lost in force is gained in despatch, and that in proportion as the weight is less than the power which moves it, so will the speed of its motion be greater than that of the power. ”

“ As the mechanical power of the screw depends upon the relative magnitude of the circumference through which the power revolves, and the distance between the threads, it is evident, that, to increase the220 efficacy of the machine, we must either increase the length of the lever by which the power acts, or diminish the magnitude of the thread. ”

“ As soon as a boy begins to take an interest in moving parts of machinery, vehicles, locomotives, and what not, he perceives that the application of power results in the motion of bodies, and again that bodies in motion are productive of power. A wheel moved by muscular, or other mechanical power, is made by machinery to elevate water, and elevated water can be made in descending to run machinery. The windlass, or other12 wheel, turned by applied force, lifts buckets from wells—raises stone, and elevates heavy bodies, if desired. ”

“ The force exercised by the human hand in lifting a weight either with or without rope and pulley is, in every definitional sense of the word, mechanical force. For the arm and hand are only the implements, or mechanical contrivances of nature, by which the will-power transmutes itself into work, or, more properly speaking, transmits itself from the point of force-generation to that of force-expenditure. And this is precisely the office performed by all mechanical contrivances for the transmission--not transmutation--of force. ”

“ God is in the bush like a clenched dark fist, or a thrust phallus.{235}”
So it is with every natural thing. It has a vital relation with all other natural things. Only the machine is absolved from vital relation. It is based on the mystery of neuters. The neutralising of one great natural force against another, makes mechanical power. Makes the engine’s wheels go round. ”

“ It is easy to conceive, that when forces applied to mechanical instruments are in equilibrium, if the least addition be made to one of them, it will preponderate and overcome the effort. But the want of a perfect polish or smoothness in the parts of all instruments, and the rigidity of all ropes, which increases with the tension, are great impediments to motion, and in compounded engines are found to diminish about one fourth of the effect of the power. ”

“ A.--The mechanical powers are certain contrivances, such as the wedge, the screw, the inclined plane, and other elementary machines, which convert a small force acting through a great space into a great force acting through a small space. ”

“ For from hence are easily deduced the forces of machines, which are compounded of wheels, pullies, levers, cords, and weights, ascending directly or obliquely, and other mechanical powers; as also the force of the tendons to move the bones of animals. ”

“ The study of motors and motive power is one which calls for the highest engineering qualities. In this, as in every other of the mechanical arts, theory, while it has an important function, occupies second place. ”

“ Of that class of mechanical agents by which motion is transmitted,—the lever, the pulley, the wedge, and many others,—it has been demonstrated, that no power is gained by their use, however combined. Whatever force is applied at one point can only be exerted at some other, diminished by friction and other incidental causes ”

“ When energy has been stored in a fly-wheel, it can be withdrawn either as a small force acting over a great distance, or as a large force over a small distance. In the latter case the fly-wheel acts as a mechanical power, and in this form it is used in the very important machine to be next described. A model of the punching machine is shown in Fig. ”

“ In any machine, constructed in whatever manner to increase the force which I can exert, it is certain that what I gain in force I must lose in the velocity which I communicate. This is not a contingent truth, borrowed from and limited by observation; for a man of sound mechanical views applies it with like confidence, however novel be the construction of the machine. ”

“ The mechanic in moving large bodies secures the aid of lever, screw, or inclined plane, and is obliged to apply as much energy as the body offers resistance. In mechanics the principle of the correlation and conservation of forces is always acknowledged and obeyed; hence the unerring certainty of performance and the stability of the vast and intricate structures of the age. When large bodies are to be moved, physical energy is applied in the form of great power at low speed ”

“ This shows within what distinct limits machine-problems lie, and that they allow themselves to be readily separated from the general problems of Mechanics, as we have already maintained.
While the science of Mechanics examines motion caused in the most general cases by the action of mechanical forces, Machine-mechanics occupies itself with certain special cases only, with motions produced by a limited circle of means. It draws its first laws from the same fountain as Mechanics, to which, as the more comprehensive science, it is subordinate. ”

“ As to the mechanic powers, the single lever makes no resistance by friction; but if, by the motion of the lever in lifting the fulcrum, or place of support, be changed further from the weight, the power will be decreased thereby.
6. In any wheel of any machine, running upon an axis, the friction on the axis is as the weight upon it, the diameter of the axis, and the angular velocity. ”

“ In following the course of invention and rediscovery during the middle ages, and in subsequent times, we see two main causes of the superiority of our own useful arts to those of the ancients—the extended application of mechanical and chemical science. The discovery of the various problems in mechanics, which paved the way for the multiplication of human force, and the introduction of new motor powers, occupied chiefly the latter half of the sixteenth and the seventeenth century. ”

“ By an appropriate combination of valves and pistons, of wheels and levers, and numerous other contrivances put together in strict conformity with the principles of mechanics, in which the most delicate allowances are made for unavoidable friction, and the attraction of gravitation is either annihilated by counterbalancing weights or turned to account as a source of power, a machine is constructed which strikingly illustrates the importance, not only of the particular character of the different parts of which it is composed, but of the relations of these parts to each other. ”

“ All fully developed machinery consists of three essentially different parts, the motor mechanism, the transmitting mechanism, and finally the tool or working machine. The motor mechanism is that which puts the whole in motion. It either generates its own motive power, like the steam engine, the caloric engine, the electro-magnetic machine, &c., or it receives its impulse from some already existing natural force, like the water-wheel from a head of water, the wind-mill from wind, &c. ”

“ Energy distributed between two Bodies: Projection and Propulsion.—Hitherto the effort by which a machine is moved has been treated as a force exerted between a movable body and a fixed body, so that the whole energy exerted by it is employed upon the movable body, and none upon the fixed body. This conception is sensibly realized in practice when one of the two bodies between which the effort acts is either so heavy as compared with the other, or has so great a resistance opposed to its motion, that it may, without sensible error, be treated as fixed. ”

“ In those phases of the machine, which are most favourable to the transmission of force, the fly-wheel shares the effect of the power with the load, and retaining the force thus received directs it upon the load at the moments when the transmission of power by the machine is either feeble or altogether suspended. ”

“ As, however, the actual machinery itself, deriving its existence from various sources, and having its own characteristic features and methods of classification and treatment, forms a quite distinct and special subject, a separation of its scientific mechanical problems from those of Mechanics in general is possible, and indeed has already been made. ”

“ Mechanics are still living who firmly believe in the possibility of realizing a mechanical perpetual motion,—to spin, pump, or drive carriages or machinery, by means of a constantly descending weight. ”

“ The mechanism of both is composed of wheel-work, with contrivances to put it in motion, and to regulate its movements. The moving or maintaining power in large clocks is a weight suspended by a cord to a cylinder. ”

“ It must be admitted, too, that the sense of the reality of this separation has been felt not only by Engineers or others actually engaged in machine design, but also by those theoretical writers who have had any practical knowledge of machinery, in spite of the increasing tendency in the treatment of mechanical science to thin away machine-problems into those of pure mechanics. ”

“ Whilst in the first system, which we may call kosmical, the external measurable mechanical forces are opposed by similar external forces, in the second, the machine system, there are opposed to all external forces others concealed in the interior of the bodies forming the system, and appearing there,—and acting in exactly the required manner,—in consequence of the action of the external forces. ”

“ This has been overcome by the invention of the dynamo-machine, which has been brought to such a state of perfection that by it we are enabled to convert mechanical into electrical force, and back again into mechanical force, with a marginal loss of not more than 20 per cent. ”

“ When the nature and properties of the mechanic powers and other machines have been explained, the force of these observations will be more distinctly perceived. The effects of props and fixed points in sustaining a part of the weight, and sometimes the whole, both of the weight and power, will then be manifest, and every machine will furnish a verification of the remarkable proportion between the velocities of the weight and power, which has enabled us to explain what might otherwise be paradoxical and difficult of comprehension. ”