Work (physics)

“ Having aided the student in choosing his apparatus or constructing it, and given him some insight into the secrets of physical manipulation, the author, in the second part of the book, gives directions for making experiments illustrative of the principal laws of physics, as the equilibrium of forces, motion, acoustics, light, magnetism, heat, etc. The work appears to be very well adapted to meet the wants of the reader for whom it is intended. ”

“ The work done by a machine equals the work done upon it, or the energy given out by a machine equals the energy received by it. These two quantities of work must each be composed of a force factor and a space factor. Therefore two forces and two spaces are to be considered in the operation of a machine. The force factor of the work done on the machine is called the force or effort. It is the force applied to the machine. The force factor of the work done by a machine is called the weight or resistance. ”

“ Solution.—Since the force employed is 500 lbs., and the distance is 2 × 5280 ft., the work done is 500 × 2 × 5280 or 5,280,000 ft.-lbs.
106. Energy.—In the various cases suggested in the paragraphs upon work, an agent, a man, an animal or a machine, was mentioned as putting forth an effort in order to do the work. It is also true that in order to perform work an agent must employ energy, or the energy of a body is its capacity for doing work. ”

“ 'The Philosophy of Nature takes up the material, prepared for it by physics out of experience, at the point to which physics has brought it, and again transforms it, without basing it ultimately on the authority of experience. Physics therefore must work into the hands of philosophy, so that the latter may translate into a true comprehension (Begriff) the abstract universal transmitted to it, showing how it issues from that comprehension as an intrinsically necessary whole. ”

“ After mass and energy there is one physical quantity which plays a very fundamental part in modern physics, known as Action. Action here is a very technical term, and is not to be confused [Pg 153] with Newton’s ‘Action and Reaction.’ In the relativity theory in particular this seems in many respects to be the most fundamental thing of all. ”

“ This ideal has often played an effective part in popular lectures, but in the workshop of the serious inquirer it has discharged scarcely the least function. What has really been achieved in mechanical physics is either the elucidation of physical processes by more [Pg 160] familiar mechanical analogies, (for example, the theories of light and of electricity,) or the exact quantitative ascertainment of the connexion of mechanical processes with other physical processes, for example, the results of thermodynamics. ”

“ This difference we can clearly recognize through the application of the concept of energy to mechanics. We then learn that statics is the science of work, or the energy of position, and that dynamics is the science of living force, or of the energy of motion.
By work in the mechanical sense we mean the expenditure of force required for the locomotion of physical bodies. While a cube of lead is geometrically equal to a cube of glass, we experience a great difference between them when we lift them from the floor to a table. ”

“ There is obviously one domain and order of processes in nature which exactly fulfils those requirements, and is really in the fullest sense “natural,” that is, quite easily understood, quite rational, quite amenable to computation and measurement, quite rigidly subordinate to laws which can be formulated. These are the processes of physics and chemistry, and in a still higher degree those of movement in general, the processes of mechanics in short. ”

“ We have defined energy to be the power of doing work, and although every one has a general notion of what is meant by work, that notion may not be sufficiently precise for the purpose of this volume. How, then, are we to measure work? Fortunately, we have not far to go for a practical means of doing this. Indeed, there is a force at hand which enables us to accomplish this measurement with the greatest precision, and this force is gravity. ”

“ It doesn’t matter very much what invention you are working on you ought to read a first book on physics and one on chemistry and what’s more you should study them if you expect to ever invent anything of magnitude.
A book on physics tells all you need to know in the beginning about matter, force, motion, the principles of machines, the mechanics of liquids and gases, electricity and magnetism, sound, heat and light. ”

“ I knew also that, just as the exact squaring of the circle and the transmutation of metals brought out some great mathematical discoveries and much of modern chemistry, so perpetual motion had brought out the greatest of all generalizations of physics—the conservation of energy. ”

“ Elementary statics and mechanics will serve as an early introduction to physics, which combines with the easiest portions of chemistry. Long before physics is formally presented, it must be foreshadowed by many things stimulating the attention. Notice is directed to clocks, mills, the most familiar phenomena of atmospheric pressure, to electrical and magnetic toys, etc. In burgher schools, at least, so much must be said about buildings and machines as is necessary to incite to further study in the future. ”

“ Physiological or chemical explanations must finally be recast in terms of physics, to satisfy the modern scientist’s sense of finality, and physics must be made to run in terms of impact, pressure, displacement in space, regrouping of material particles, coördinated movements and a shifting of equilibrium. ”

“ For the analysis of mechanical phenomena, a metrical notion, derived from experience, and bearing the designation work, has proved itself useful. A machine can be set in motion only when the forces acting on it can perform work. ”

“ Mechanics went on inventing "perpetual motions," but, however plausible they looked, somehow or other they wouldn't work. Do away with friction to the greatest possible extent; overcome one obstacle here and another there; increase the time the machine would run indefinitely—still, to a state of equilibrium would it come at last. From these empirical observations mechanics learned, what philosophers might have learned years ago, that experience affords the only sure test of the validity of our notions. ”

“ If they have any desire to construct a similar mechanism, they will follow the aforesaid motions of the heavens, etc., not only by one means alone but by many, more swiftly through thoughtful study than by any amount of instruction.
For whoever is well versed in the theory of calculus and sets to work at any given project, will discover any desired motion by a thousand and more ways, by one or another gearing of wheels; which an industrious mechanic will carry out in actuality and without too much difficulty. ”

“ Büchner. Physics, as I stated to you on another occasion, “makes us acquainted with eight different forces—gravitation, mechanical force, heat, light, electricity, magnetism, affinity, cohesion, which, inseparably united to matter, form and give shape to the world. These [pg 643] forces are, with few exceptions, mutually convertible, so that nothing is lost in the process of conversion” (p. 18) . ”

“ Mechanics deals with the laws of energy and motion, physics with molecular changes of matter, but neither physics nor mechanics would have gone far, had they stopped to answer the questions as to what motion, energy, matter are in themselves. ”

“ This point of view is that from which Geometry separates itself from Mathematics in general, Descriptive Geometry from Geometry in general, still more from which Kosmical Physics, Hydraulics, Aerostatics, branch away from Natural Philosophy,—in other words, the point of view from which special sciences are seen to separate themselves from the more general sciences to which they are subordinate. ”

“ The triumph of exact science in the foregoing problem consisted in establishing a numerical connection between the pointer reading of the weighing-machine in one experiment on the elephant and the pointer reading of the watch in another experiment. And when we examine critically other problems of physics we find that this is typical. The whole subject-matter of exact science consists of pointer readings and similar indications. ”

“ In physics, chemistry, mechanics, and other sciences there are many problems in which the behavior of distance, of time, of speed, heat, volume, electrical current, weight, acceleration, pressure, and many other physical quantities are related to each other. ”

“ The development of physics on the speculative side has led, then, to the idea, gradually become more definite and fixed, of a universal medium, the existence of which is a matter of inference. To this medium properties have been assigned which are such as to enable us to form an intelligible, consistent conception of the mechanism by means of which phenomena, the mechanics of which is not capable of direct observation, may be logically considered to be produced. ”

“ We are asked to consider gravitative energy, heat energy, mechanical energy, chemical energy, and electrical energy. When we inquire what is meant by energy, we are informed that it means ability to do work, and that work is measurable as a pressure into a distance, and is specified as foot-pounds. ”

“ The instrument is on the table, but, as it is far too small to be seen at a distance, I have arranged a large model to illustrate its action. The object of this machine is to measure how much work an engine has done during any time, and show the result on a dial, so that a workman may read it off at once without having to make any calculations.Fig. 4.Before I can explain how work is measured, perhaps I had better say a few words about the meaning of the word "work." Work is done when pressure overcomes resistance, producing motion. Neither motion nor pressure alone is work. ”

“ Statics and Dynamics.—We must first turn our attention to a technical distinction of Mechanics into two portions, according as the forces about which we reason produce rest, or motion; the former portion is termed Statics, the latter Dynamics. If a stone fall, or a weight put a machine in motion, the problem belongs to Dynamics; but if the stone rest upon the ground, or a weight be merely supported by a machine, without being raised higher, the question is one of Statics.
3. Equilibrium.—In Statics, forces balance each other, or keep each other in equilibrium. ”

“ In all mechanical processes, and as all physical processes present a mechanical side, in all physical processes, work plays a determinative part. Electrical forces, also, produce only changes in which work is performed. To the extent that forces come into play in electrical phenomena, electrical phenomena, be they what they may, extend into the domain of mechanics and are subject to the laws which hold in this domain. ”

“ For, just as either geometry or analysis may be employed to solve correctly a particular problem, though one has far more power and capability, generally speaking, than the other; or, just as either the idea of the reflexion of images or that of the reverberation of sounds may be used to represent certain physical forces and conditions, so may the idea of the attractions and repulsions of centres, or that of the disposition of magnetic fluids, or that of lines of force, be applied in the consideration of magnetic phenomena. ”

“ It consists, broadly speaking, in showing that, although the particles, points, and instants with which physics operates are not themselves given in experience, and are very likely not actually existing things, yet, out of the materials provided in sensation, it is possible to make logical constructions having the mathematical properties which physics assigns to particles, points, and instants. ”

“ The field of pure or classical mechanics is limited to the above two kinds of energy, work and kinetic energy, though these do not exhaust the manifoldness of the mechanical energies. Accordingly, other branches of mechanics dealing with the corresponding phenomena are added to the classical mechanics described above. ”

“ Accordingly, the greatest achievements in physical science have consisted in resolving one observed law of the production of motion into the laws of other known modes of production, or the laws of several such modes into one more general mode; as when the fall of bodies to the earth, and the motions of the planets, were brought under the one law of the mutual attraction of all particles of matter; when the motions said to be produced by magnetism were shown to be produced by electricity ”

“ The principles of the science of mechanics, the only example yet existing of a complete physical theory, are altogether formed from the data of experience by the abstractive method. The class of objects to which the science of mechanics relates,—viz.,—material bodies,—are defined by means of those sensible properties which they all possess, viz., the property of occupying space, and that of resisting change of motion. The two classes of phenomena to which the science of mechanics relates are distinguished by two words, motion and force ”

“ Research in quantum mechanics, to take one example on which my background allows me to speak at least semi-intelligently, might incorporate work from particle physicists doing empirical work with cloud chambers, high-energy particle physicists doing other empirical work with particle accelerators, and still other particle physicists investigating the mathematics behind spontaneous symmetry breaking. ”

“ 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. ”