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Mechanics

science concerned with physical bodies subjected to forces or displacements

Mechanics (Greek μηχανική) is the branch of science concerned with the behavior of physical bodies when subjected to forces or displacements, and the subsequent effects of the bodies on their environment. The scientific discipline has its origins in Ancient Greece with the writings of Aristotle and Archimedes. During the early modern period, scientists such as Galileo, Kepler, and especially Newton, laid the foundation for what is now known as classical mechanics. It is a branch of classical physics that deals with particles that are either at rest or are moving with velocities significantly less than the speed of light. It can also be defined as a branch of science which deals with the motion of and forces on objects.

Arabic Machine Manuscript. Unknown date (at a guess: 16th to 19th centuries).
CONTENT : A - F, G - L, M - R, S - Z, See also, External links

Quotes

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Quotes are arranged alphabetically by author

A - F

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  • People get a lot of confusion, because they keep trying to think of quantum mechanics as classical mechanics.
  • Within a certain kind of environment, an activity may be checked so that the only meaning which accrues is of its direct and tangible isolated outcome. One may cook, or hammer, or walk, and the resulting consequences may not take the mind any farther than the consequences of cooking, hammering, and walking in the literal — or physical — sense. But nevertheless the consequences of the act remain far-reaching. To walk involves a displacement and reaction of the resisting earth, whose thrill is felt wherever there is matter. It involves the structure of the limbs and the nervous system; the principles of mechanics. To cook is to utilize heat and moisture to change the chemical relations of food materials; it has a bearing upon the assimilation of food and the growth of the body. The utmost that the most learned men of science know in physics, chemistry, physiology is not enough to make all these consequences and connections perceptible. The task of education, once more, is to see to it that such activities are performed in such ways and under such conditions as render these conditions as perceptible as possible.
  • To the art of mechanics is owing all sorts of instruments to work with, all engines of war, ships, bridges, mills, curious roofs and arches, stately theatres, columns, pendent galleries, and all other grand works in building. Also clocks, watches, jacks, chariots, carts and carriages, and even the wheel-barrow. Architecture, navigation, husbandry, and military affairs, owe their invention and use to this art.
    • William Emerson (1754/73) The Principles of Mechanics. Preface; Cited in: R.S. Woolhouse (1988) Metaphysics and Philosophy of Science in the Seventeenth and Eighteenth Centuries: Essays in Honour of Gerd Buchdahl. p. 29.

G - L

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  • The work before us is a proof that the doctrine of mechanics is of the utmost importance to mankind in general, and to civil society in particular, which could hardly subsist without it.
    The author of this work is Mr. W. Emerson who is well known in the literary world, from several ingenious writings with which he has obliged the public; some of which have passed under our consideration since the commencement of the Review. In this treatise Mr. Emerson has laid down the fundamental principles both of theory and practice, and demonstrated most of them from the common elementary geometry, and the rest from the common rules of algebra; which is certainly the best method of rendering a treatise of this kind useful to the generality of readers, the fluxionary calculus being too difficult for them to understand.
    The work is divided into thirteen sections: the 1st. contains the general laws of motion. 2. The laws of gravity, the descent of heavy bodies, and the motion of projectiles. 3. The properties of the mechanical powers; the balance, the leaver, the wheel, the pulley, the screw, and the wedge. 4. The descent of bodies upon inclined planes, and in curve surfaces; and the motion of pendulums. 5. The center of gravity, and its properties. 6. The centers of percussion, oscillation, and gyration. 7. The quantity and direction of the pressure of beams of timber, by their weight; and the forces necessary to sustain them. 8. The strength of beams of timber in all positions; and their stress by any weight acting upon them, or by any forces applied to them. 9. The properties of fluids, the principles of hydrostatics, hydraulics, and pneumatics, 10. The resistance of fluids, their forces and actions upon bodies; the motions of ships, and the positions of their fails. 11. Methods of communicating, directing, and regulating any motion in the practice of mechanics. 12. The powers and properties of compound engines; of forces acting within the machines; and concerning friction. 13. The description of compound machines or engines, and the methods of computing their powers or forces; with some account as the advantages or disadvantages of their construction.
  • The laws of motion of visible and tangible, or molar, matter had been worked out to a great degree of refinement and embodied in the branches of science known as Mechanics, Hydrostatics, and Pneumatics. These laws had been shown to hold good... throughout the universe on the assumption that all such masses of matter possessed inertia and were susceptible of acquiring motion, in two ways, firstly by impact, or impulse from without; and, secondly, by the operation of certain hypothetical causes of motion termed 'forces,' which were usually supposed to be resident in the particles of the masses themselves, and to operate at a distance, in such a way as to tend to draw any two such masses together, or to separate them more widely.
  • [J]eder Fortschritt in der Theorie der partiellen Differentialgleichungen auch einen Fortschritt in der Mechanik herbeiführen muss.
  • Experimental physics was particularly interested in the processes taking place inside the atom, and in this field the classical mechanics was failing conspicuously and completely. Perhaps its most spectacular failure was with the fundamental problem with the structure of the atom.
  • Another conspicuous failure of classical mechanics was with one aspect of the problem of radiation. ...Imagine a crowd of steel balls rolling about on a steel floor. ...There must... be a steady leakage of energy from... causes, such as air resistance and the friction of the floor, so the balls will eventually lose energy, and, after no great length of time, will be found standing at rest on the floor. The energy of their motion seems to have been lost... most of it has been transformed into heat. The classical mechanics predicts that this must happen; it shows that all energy of motion, except possibly a minute fraction of the whole, must be transformed into heat whenever such a transformation is physically possible. It is because of this that perpetual-motion machines are a practical impossibility.
  • The need for a fundamentally different approach to the study of physical processes at the molecular level motivated the development of relevant statistical methods, which turned out to be applicable not only to the study of molecular processes (statistical mechanics), but to a host of other areas such as the actuarial profession, design of large telephone exchanges, and the like. In statistical methods, specific manifestations of microscopic entities (molecules, individual telephone sites, etc.) are replaced with their statistical averages, which are connected with appropriate macroscopic variables. The role played in Newtonian mechanics by the calculus, which involves no uncertainty, is replaced in statistical mechanics by probability theory, a theory whose very purpose is to capture uncertainty of a certain type.
  • Herschel has noticed how the Stagirite obstructed the progress of astronomy by not identifying celestial with terrestrial mechanics, but laying down the principle that celestial motions were regulated by peculiar laws, thus placing them entirely without the pale of experimental research, while at the same time the progress of mechanics was impeded by the [his] assumption of natural and unnatural motions.

M - R

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  • All this, the positive and physical essence of mechanics, which makes its chief and highest interest for a student of nature, is in existing treatises completely buried and concealed beneath a mass of technical considerations.
    • Ernst Mach The Science of Mechanics (1893) Preface to the first edition, , p. vii.
  • The history of the development of mechanics is quite indispensable to a full comprehension of the science in its present condition. It also affords a simple and instructive example or the processes by which natural science generally is developed.
    • Ernst Mach The Science of Mechanics (1893) Introduction.
  • Another evil, and one of the worst which arises from the separation of theoretical and practical knowledge, is the fact that a large number of persons, possessed of an inventive turn of mind and of considerable skill in the manual operations of practical mechanics, are destitute of that knowledge of scientific principles which is requisite to prevent their being misled by their own ingenuity. Such men too often spend their money, waste their lives, and it may be lose their reason in the vain pursuits of visionary inventions, of which a moderate amount of theoretical knowledge would be sufficient to demonstrate the fallacy ; and for want of such knowledge, many a man who might have been a useful and happy member of society, becomes a being than whom it would be hard to find anything more miserable. The number of those unhappy persons — to judge from the patent-lists, and from some of the mechanical journals — must be much greater than is generally believed.
  • [T]he mere fact that a quantitative majority of causations are of vitalistic type, does not in the least mean that science can neglect the huge, co-existing volume of mechanistic-type causations. Both aspects of causal description are required in all sciences. In physics, for example, which seeks to describe the most ultimate, or elementary reaction tendencies of matter, the attempt is now being made to resolve all complex masses into ultra-simple proton and electron systems. The influence of each proton-electron microcosm, then must be traced in its most far-reaching effects upon the physical behavior of the macrocosmic mass of which it forms a single unit. The causal influences of the total mass, on the other hand, upon its constituent proton-electron systems, and upon other free-lance proton-electron systems, must be described.
  • The ancients considered mechanics in a twofold respect; as rational, which proceeds accurately by demonstration, and practical. To practical mechanics all the manual arts belong, from which mechanics took its name. But as artificers do not work with perfect accuracy, it comes to pass that mechanics is so distinguished from geometry, that what is perfectly accurate is called geometrical; what is less so is called mechanical. But the errors are not in the art, but in the artificers. He that works with less accuracy is an imperfect mechanic: and if any could work with perfect accuracy, he would be the most perfect mechanic of all; for the description of right lines and circles, upon which geometry is founded, belongs to mechanics. Geometry does not teach us to draw these lines, but requires them to be drawn; for it requires that the learner should first be taught to describe these accurately, before he enters upon geometry; then it shows how by these operations problems may be solved.
  • Rational mechanics must be the science of the motions which result from any forces, and of the forces which are required for any motions, accurately propounded and demonstrated. For many things induce me to suspect, that all natural phenomena may depend upon some forces by which the particles of bodies are either drawn towards each other, and cohere, or repel and recede from each other: and these forces being hitherto unknown, philosophers have pursued their researches in vain. And I hope that the principles expounded in this work will afford some light, either to this mode of philosophizing, or to some mode which is more true.
  • I'm proud to publish this book under my own name, though I don't fully understand the mechanics of its production or the nature of the personality I assume in delivering it. I had no conscious work to do on the book at all. I simply went into trance twice a week, spoke in a "mediumistic" capacity for Seth, or as Seth, and dictated the words to my husband, Robert Butts, who wrote them down.

S - Z

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  • Not one word is said here of acausality, wave mechanics, indeterminacy relations, complementarity, … etc. Why doesn’t he talk about what he knows instead of trespassing on the professional philosopher’s preserves? Ne sutor supra crepidam. On this I can cheerfully justify myself: because I do not think that these things have as much connection as is currently supposed with a philosophical view of the world.
  • My greatest concern was what to call it. I thought of calling it 'information,' but the word was overly used, so I decided to call it 'uncertainty.' When I discussed it with John von Neumann, he had a better idea. Von Neumann told me, 'You should call it entropy, for two reasons. In the first place your uncertainty function has been used in statistical mechanics under that name, so it already has a name. In the second place, and more important, no one really knows what entropy really is, so in a debate you will always have the advantage.'
    • Claude Elwood Shannon Scientific American (1971), volume 225, page 180 : Explaining why he named his uncertainty function "entropy".
  • When he meets a simple geometrical construction, for instance in the honeycomb, he would fain refer it to physical instinct, or to skill and ingenuity, rather than to the operation of physical forces or mathematical laws; when he sees in a snail, or nautilus, or tiny foraminiferal or radiolarian shell a close approach to sphere or spiral, he is prone of old habit to believe that after all it is something more than a spiral or a sphere, and that in this "something more" there lies what neither mathematics nor physics can explain. In short, he is deeply reluctant to compare the living with the dead, or to explain by geometry or by mechanics the things which have their part in the mystery of life.
  • Ничего не признаю, кроме материи. В физике, химии и биологии я вижу одну механику. Весь космос только бесконечный и сложный механизм. Сложность его так велика, что граничит с произволом, неожиданностью и случайностью, она дает иллюзию свободной воли сознательных существ. [1]
    • Konstantin Eduardovich Tsiolkovsky from Монизм Вселенной ("Monism of the Universe"), 1931(?) (= "The Cosmic Philosophy", 1932 ?)
    • Translation: I recognize nothing that is not material. In physics, chemistry and biology I see only mechanics. The Universe is nothing but an infinite and complex mechanism. Its complexity is so great that it borders on randomness, giving the illusion of free will.
  • The reader will recollect that we are here speaking of the Principia as a mechanical treatise only... As a work on dynamics, its merit is, that it contains a wonderful store of refined and beautiful mathematical artifices, applied to solve all the most general problems which the subject offered. It can hardly be said to contain any new inductive discovery respecting the principles of mechanics; for though Newton's "Axioms or Laws of Motion," which stand at the beginning of the book, are a much clearer and more general statement of the grounds of mechanics than had yet appeared, it can hardly be said that they contain any doctrines which had not been previously stated or taken for granted by other mathematicians.
  • No force however great can stretch a cord however fine into an horizontal line which is accurately straight.
    • William Whewell Elementary Treatise on Mechanics, The Equilibrium of Forces on a Point (1819).
  • It is so characteristic, that just when the mechanics of reproduction are so vastly improved, there are fewer and fewer people who know how the music should be played.

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