Lever

“ Anthropologists have often asked, what was that lever-power lying enfolded in the dark womb of some remote semi-human brain, which, by first stirring, lifting, and vitalizing other potential and latent faculties, gave birth to man? Would it be rash to assume that this lever-power was a vigorous movement of the faculty of wonder? ”

“ Just so, when an iron lever is applied to a weight which a great many hands cannot move, with the fulcrum, which the Greeks call ὑπομὁχλιον, lying as a centre in a right line under the lever, and with the tongue of the lever placed under the weight, one man's strength, bearing down upon the head of it, heaves up the weight. ”

“ AS we are on the subject of leverage, we will take some examples of levers in Art and Nature, without, however, even attempting to exhaust the topic.
On the right hand of the illustration is shown a very familiar example of a lever, namely, nut-crackers, with a nut between them. This useful implement is simply an adaptation of levers of the second kind, the power being represented by the human hand, the weight by the nut, and the fulcrum being the joint of the instrument. ”

“ This practical knowledge no doubt sufficed for a vast number of generations of men who used the lever habitually, without making specific study of the relations between the force expended, the lengths of the two ends of the lever, and the weight raised. ”

“ No matter what part of the human body we examine, we shall find that its mechanical work is performed by means of bony levers. Having seen how the head is moved as a lever of the first order, we are now to choose a part which will show us the plan on which levers of the second order work, and there are many reasons why we should select the foot. It is a part which we are all familiar with; every day we can see it at rest and in action. The foot, as we have already noted, serves as a lever in walking. ”

“ To increase the length of a lever is to increase its power at one end, and the distance through which it moves at the other; hence the faculty of bounding or leaping possessed in such perfection by many quadrupeds.34 If the wing be considered as a lever, a small degree of motion at its root produces an extensive sweep at its tip. ”

“ The lever must be looked upon as a straight line, which has three principal points, namely, the one on which the load is placed, and which is to be raised, the appui or rest which is the centre round which it turns, and which the French mechanics call orgueil, and lastly the human arm, which is the power that puts the lever into motion. ”

“ II. Lever of second class. III. Lever of third class. F. Fulcrum. P. Power. W. Weight. a. Power-arm. b. Weight-arm. Application to the Body.—In the body the bones serve as levers; the turning points, or fulcrums, are found at the joints; the muscles supply the power; and parts of the [pg 252] body, or things to be lifted, serve as weights. For these levers to increase the motion of the muscles, it is necessary that the muscles be attached to the bones near the joints, and that the parts to be moved be located at some distance from the joints. ”

“ Among the moving elements the first to be considered is the lever, which really forms a broad classification comprising many elements that will hardly be recognized as levers at first blush. Levers in some form are to be found in practically every machine. A wheel, a gear, and a pulley are really levers in disguise, as will be explained presently.
Of course everyone knows that a simple lever consists of a rigid bar that swings on a fulcrum. ”

“ Fig. 205.—"Lever" watch escapement.
In the illustration a tooth has just passed under the "impulse face" b of P1. The lever has been moved upwards at the right end; and its forked end has given an impulse to R, and through it to the balance-wheel. The spring winds up. The pin C prevents the lever dropping, because it no longer has the notch opposite to it, but presses on the circumference of R. As the spring unwinds it strikes the lever at the moment when the notch and C are opposite. ”

“ It contains the lever, pulley and wheel and axle. The second or inclined plane group includes those having a sloping surface. It contains the inclined plane, the wedge, and the screw.
121. The Lever.—The lever is one of the simple machines most frequently used, being seen in scissors, broom, coal shovel, whip, wheelbarrow, tongs, etc. The lever consists of a rigid bar capable of turning about a fixed axis called the fulcrum. In studying a lever, one wishes to know what weight or resistance it can overcome when a certain force is applied to it. ”

“ As the distances of the power and weight from the fulcrum of a lever may be varied at pleasure, and any assigned proportion given to them, a lever may always be conceived having a power equal to that of any given machine. ”

“ Hence we have here a lever or pair of levers of the third order. The effort arm of a pair of tongs is always shorter than the weight arm and the pressure on the sugar lump is always less than that exerted on the tongs by the hand. ”

“ Our draft is to be the most difficult subject in lever escapements; it is to be represented just as if it were working in a watch; it is to represent a good and reliable action in every respect, one which can be applied without special difficulty to a good watch, and is to be “up to date” in every particular and to contain the majority of the best points and conclusions reached in our analysis.
Specifications for Lever Escapement:
The pallets are to be equidistant; the wheel teeth of the “club” form; there are to be two rollers; wheel, pallet, and balance centers are to be in straight line. ”

“ On the principle of the lever are made, scales for weighing different quantities of various kinds of things; the steelyard, which answers the same purpose by a single weight, removed to different distances from the fulcrum on a graduated arm, according as the body to be weighed is more or less in quantity; and the bent lever balance, which, by the revolution of a fixed weight, increasing in power as it ascends in the arc of a circle, indicates the weight of the counterpoise. ”

“ But along with the extension a broad lever is to be used to force the bone from without inward, the lever being placed at the nates or a little farther up, and some person is to steady the patient's body, so that it may not yield, either by grasping him at the buttocks with his hands, or this may be effected by means of another similar lever, adjusted to one of the grooves, while the patient has something laid below him, and he is secured, and the dislocated thigh is to be turned gently from within outward at the knee. ”

“ If, therefore, the tongue of a lever lying on a fulcrum goes too far under the weight, and its head exerts its pressure too near the centre, it will not be able to elevate the weight, nor can it do so unless, as described above, the length of the lever is brought to equilibrium by the depression of its head. ”

“ The lever is an extremely simple mechanical power; it has only one moving part. Friction produces but little effect upon it, so that the laws which we have given may be actually applied in practice, without making any allowance for friction. In this we notice a marked difference between the lever and the pulley-blocks already described. ”

“ If you were to fasten a piece of string to the middle of one of the ribs and to pull it, you would find you were working on a lever, with the fulcrum at the backbone, with the weight acting at the sternum, and the power at the point where your string was tied. ”

“ All forms of the lever and all the principal kinds of hinges are to be met with in our own frames. The valvular arrangements of the blood-vessels are unapproached by any artificial apparatus, and the arrangements for preventing friction are so perfect that two surfaces will play on each other for fourscore years or more and never once trouble their owner by catching or rubbing so as to be felt or heard. ”

“ To reach a formula expressing the powers of the lever, it supposes a lever which does not, like the stick, admit of being bent, but is absolutely rigid, and it supposes a fulcrum not having a broad surface, like that of one ordinarily used, but a fulcrum without breadth, and it supposes that the weight to be raised bears on a definite point, instead of bearing over a considerable portion of the lever. ”

“ I claim, 1st, A tool for opening sheet metal cans, composed of a hand lever, B, carrying a tooth, c, and connected to tongs, A, or other equivalent means, capable of clamping said tooth-carrying lever to the can, as set forth.
2d, Placing the tooth, c, in an oblique direction, when the same is used in combination with the hand lever, B, and clamping device A, substantially as and for the purpose described. ”

“ Although the third order of lever is particularly inefficient when the fulcrum is rigid and immobile, it possesses singular advantages when these conditions are reversed, i.e. when the fulcrum, as happens with the air, is elastic and yielding. ”

“ If, for example, a weight, hung by a cord at the extremity of a lever arm, oscillates in the manner of a pendulum, it will not weigh at each instant on the lever but by the vertical component of its weight ”

“ Let the man be stretched upon a large board, or bench, like that upon which we stretch those who have dislocation of the spine, and along nearly its whole length let certain gutters be scooped out, in breadth and depth not more than three fingers, and not more than four fingers distant from one another, so that the extremity of the lever being inserted into them may impel the limb wherever it is required. ”

“ Weight.
Fig. 118—Diagram of the foot lever. F. Fulcrum at ankle joint. W. Body weight expressed as pressure against the earth. While the muscle power acts through the distance ab, the fulcrum support (body) is forced through the distance FE. Loss of Muscular Force.—Using a small spring balance for measuring the power, a light stick for a lever, and a small piece of metal for a weight, and arranging these to represent some lever of the body (as the [pg 254] forearm) , it is easily shown that the gain in motion causes a corresponding loss in muscular power. ”

“ When an upward pressure is applied to the foot of the lever a, it causes the upper arm c d of the elbow piece b c d to describe an arc of about a quarter of an inch from left to right, thereby communicating a corresponding movement to the pair of levers e e, working on the pivots f f ”

“ Just as it takes four men to raise a load with a lever five feet long, and only two men to lift the same load with a ten-foot lever, so the longer the arms, the easier they are to draw, and the shorter, the harder. ”

“ The third kind of lever is employed but seldom, [Pg 77] but its properties may be observed with advantage whilst a long ladder is raised, as the man who raises it, is obliged to exert an increasing force until the ladder is nearly perpendicular. ”

“ One of the muscles of a frog's leg is fixed at one extremity in a nip, and attached at the other extremity to a little lever forming part of a galvanic circuit. A weight, hung on this lever, serves to give the muscle the required tension. ”

“ You understand the simple lever power, the most simple of all mechanical principles; you know that I can take a lever, and by getting a first-rate good purchase, I can hold as much as twenty men can roll ”

“ It is true that the bones of the arch are loosely bound together by passive ties or ligaments, but as these cannot be lengthened or shortened at will, Nature had to fall back on the use of muscular engines for the maintenance of the foot as an arched lever. Some of these are shown in Fig. 8. The foot, then, is a lever of a very remarkable kind; all the time we stand or walk, its rigidity, its power to serve as a lever, has to be maintained by an elaborate battery of muscular engines all kept constantly at work. No wonder our feet and legs become tired when we have to stand a great deal. ”