Inertness

“ Its activity is proved by its power of spontaneously setting other matter in motion, and of itself obeying their mutual impulse, and moving under the influence of its own and other force; inertness, in refusing to move unless obliged to do so by a force impressed externally, or mutually exerted between itself and other matter, and by persisting in its state of motion or rest unless disturbed by some external cause. ”

“ We can push a light boat rapidly through the water; but we may go on increasing its freight, till we are barely able to stir it. This property of matter, then, by which it resists the reception of motion, or rather by which it reacts and requires an adequate force in order that any motion may result, is called its inertness, or inertia. That matter has such a property, is a conviction flowing from that idea of a reaction equal and opposite to the action, which the conception of all force involves. ”

“ The other properties of matter, such as mobility, impenetrability, and divisibility, relate to extension, or to a particular impression caused on our senses. The difficulties that may be raised on these points are solved by the preceding paragraphs.
Inertness, or indifference to rest or motion, is a purely negative property. It is the incapacity of all action, the absence of an internal principle productive of change, the purely passive disposition to receive all that is communicated to it. ”

“ The truth is that such complete physical inertness has the effect of clogging the action of the blood, of retaining the impurities of the system, and of eventually bringing about a host of small nervous disorders that induce in turn mental anxiety—the worst possible drain upon the nervous organisation. ”

“ Hence what physicists call “force of inertia” is not a passive resistance proceeding from the inertia of matter, but an active exertion of the molecular powers, and has been so called only because, all other things being equal, its intensity is proportional to the mass of the inert body.160 Evidently, inertia itself cannot resist or check the advance of an impinging body. Nothing but a positive action can do it; for nothing but a positive action can communicate to the advancing body that impetus in the opposite direction which alone is competent to neutralize the impetus of the advance. ”

“ One class of philosophers, recognizing the self-existent character of motion, has exhausted ingenuity in the effort to deduce attraction from it, of course wittingly or unwittingly bringing into co-operation the occult force inertia, to obtain vis viva. Another class would deduce all motion from attraction: while in the attempt to contrive a mechanism to explain resiliency—the most incomprehensible of all in a body without parts—immensely greater complications and difficulties have been introduced. Inertia, so far as I am aware, has always been accepted as an inscrutable fact, or ignored. ”

“ Inertia, a passive power, is as death, being passive animation; and inertia enabling a body to act against force, is nothing short of active inertia, or vis inertiæ, which means the force of inability. This monstrous perversion of a natural fundamental principle, and by such high authority, pervades the whole of the established philosophy. It makes the planets, which are but clumps of deadly inert matter, gravitate themselves through space; and makes inert atoms competent to perform attraction on each other wherever they exist. ”

“ The heavenly bodies are actually in this condition: they continue to move, not because any new forces are applied to them; but, having been once set in motion, they continue in motion because there is nothing to stop them. This property in bodies to persevere in the state they are actually in,—if at rest, to remain at rest, or, if in motion, to continue in motion,—is called inertia. The inertia of a body (which is measured by the force required to overcome it) is proportioned to the quantity of matter it contains. ”

“ LECTURE XVI.
INERTIA.
Inertia.—The Hammer.—The Storing of Energy.—The Fly-wheel.—The Punching Machine.
INERTIA.
523. A body unacted upon by force will continue for ever at rest, or for ever moving uniformly in a straight line. This is asserted by the first law of motion (Art. 485) . It is usual to say that Inertia is a property of all matter, by which it is meant that matter cannot of itself change its state of rest or of motion. Force is accordingly required for this purpose. ”

“ Everybody knows that the characteristic feature of matter is what we call inertia. If matter is at rest, a force is needed to set it in motion. If it is in motion, it needs a force to stop it. It needs one to accelerate the movement and one to alter the direction. This resistance which matter offers to the forces which tend to modify its condition of rest or movement is what we call inertia. But different bodies may offer a different degree of resistance to these forces. If a force is applied to an object, it will give it a certain acceleration. ”

“ The resistance that a mass of matter opposes to a change in its position or rate and direction of movement, is called inertia. That it should actively oppose anything has been already pointed out as reason for denying that matter is inert, but inertia is the measure of the reaction of a body when it is acted upon by pressure from any source tending to disturb its condition of either rest or motion. ”

“ The inert causes of motion, or new configuration, consist of the parts of matter, which are introduced within the spheres of activity of the principles above described. Thus, when an apple falls on the ground, the principle of gravitation is the efficient cause, and the matter of the apple the inert cause. If a bar of iron be approximated to a magnet, it may be termed the inert cause of the motion, which brings these two bodies into contact ”

“ To this objection I reply that there is in social science, as in Nature, a vis inertia; that is to say, there is a tendency in matter to remain at rest if unmoved by any external agency, and also of persisting to move, after it has once been set in motion. The vis inertia of some bodies is greater than that of others, and depends upon their weight and density. ”

“ To make it clear that this is really the natural generalization of the law of inertia, I shall beg you to permit me a bit of fiction. The law of inertia, as I have said above, is not imposed upon us a priori; other laws would be quite as compatible with the principle of sufficient reason. If a body is subjected to no force, in lieu of supposing its velocity not to change, it might be supposed that it is its position or else its acceleration which is not to change. ”

“ We get numerous examples of this property of the inertia of bodies in our daily experience. Many of the accidents that befall people in various ways are due to this property of the inertia of matter. A cyclist is riding a machine down-hill, and loses control over his machine, with the result that he runs into a wall, and is killed. Now what has happened? The cyclist has participated in the motion of the machine, with the result that when the machine has been suddenly stopped, the body has been thrown forward owing to the momentum it had acquired. ”

“ If it be said that the velocity of a body cannot change, if there is no reason for it to change, may we not just as legitimately maintain that the position of a body cannot change, or that the curvature of its path cannot change, without the agency of an external cause? Is, then, the principle of inertia, which is not an à priori truth, an experimental fact? Have there ever been experiments on bodies acted on by no forces? ”

“ If we consider that rest or motion when once established is the normal state of matter, then the force which causes a change causes a breach of the law of inertia. But if we consider that the liability to be moved, or to have motion stopped by force, is itself a property of matter, then the application of force with such result is merely calling into operation the law of inertia. ”

“ I abstract here from the fact that a certain intensity of the consciousness is required for its impulsiveness to be effective in a complete degree. There is an inertia in the motor processes as in all other natural things. In certain individuals, and at certain times (disease, fatigue) , the inertia is unusually great, and we may then have ideas of action which produce no visible act, but discharge themselves into merely nascent dispositions to activity or into emotional expression. The inertia of the motor parts here plays the same rôle as is elsewhere played by antagonistic ideas. ”

“ Inertia, as it regards matter, is a term sufficiently well understood both in a state of rest and of motion. As it is not my intention to attempt a description of functions of the mind according to strict mathematical terms, I shall resign the exclusive use of the word at present, and adopt two others, which, according to the sense they have acquired from usage, will, I believe, supply its place with accuracy. Apathy will represent the inertia of a passive mind; industry that of an active mind. ”

“ No man of sound common sense could ever have doubted that a pressure or force is requisite to set a body in motion in a given direction and that a contrary pressure is required to stop suddenly a body in motion. Though the law of inertia was first formulated with anything like exactness by Galileo, the facts at the basis of it were known long previously to men of the stamp of Leonardo da Vinci, Rabelais, and others, and were illustrated by them with appropriate experiments. ”

“ A. If a body is at rest, inertia is that quality by which it will forever remain so, unless acted upon by some force from without; and if a body is in motion, it will continue on at the same speed, in a straight line, forever, unless it is quickened, retarded, or turned from its path by some other force. ”

“ The common theory of an inert body is one that is wholly passive, having no power of itself to move or do anything, except as some agency outside itself compels it to move in one way or another, and thus endows it with energy. Thus a stone or an iron nail are thought to be inert bodies in that sense, and it is true that either of them will remain still in one place for an indefinite time and move from it only when some external agency gives them impulse and direction. ”

“ On the other hand, under the influence of the mechanics of his day, which had hardly distinguished between inertia, or the inability of a body to change itself, and resistance or the ability of bodies to oppose one another, he concluded that, as inertia is passive, so is resistance, and refused to recognize that in collision the mutual resistance of moving bodies is a force, or active power, of changing their movements in opposite directions. ”

“ The act from which such a centre receives its first existence is called the substantial form; and it has a spherical character, inasmuch as it constitutes a virtual indefinite sphere.
XIII. The essence of a primitive element of matter is by no means a mystery. The essential definition of such an element is “a substance fit to cause and to receive mere local motion.”
XIV. Inertia is an essential property of material substance, no less than activity and passivity. Inertia admits of no degrees. ”

“ It is the equivalent of mass, or the amount of matter as measured by gravity, and is a fixed quantity; for inertia is as inherent as any other quality, and belongs to the ultimate atoms and every combination of them. It implies the ability to absorb energy, for it requires as much energy to bring a moving body to a standstill as was required to give it its forward motion. ”

“ Since these philosophers think it necessary to prove the law of inertia, they of course do not suppose it to be self-evident; they must, therefore, be of opinion that previously to all proof, the supposition of a body's moving by internal impulse is an admissible hypothesis; but if so, why is not the hypothesis also admissible, that the internal impulse acts naturally in some one particular direction, not in another? If spontaneous motion might have been the law of matter, why not spontaneous motion toward the sun, toward the earth, or toward the zenith? ”

“ When we conceive that inertia is resistance to deflection, it becomes a proposition, easily comprehended, that rigidity is resistance to the differential deflection of the molecular parts of a body. Every one of its minute parts must be moved if the body is moved, and the regional parts as distinguished from the molecular parts cannot be moved without fracturing the body. Thus we see that rigidity can be explained simply as a mode of motion without resort to occult force. ”

“ To us it appears inconceivable that once it required the profoundest meditation to discover the first law of motion, the inertia, as it is called, of matter, in virtue of which the motion of a body does not change without an external cause ”

“ Self-induction—or “self” as the electrical workers call it—is a real inertia. The surrounding medium offers resistance to the force which tends to establish an electric current, and to that which tends to stop a current already set up; just as matter resists the force which tends to cause it to pass from rest to movement, or from movement to rest. There is, therefore, a real electrical inertia as well as mechanical inertia. ”

“ The inert, passive atoms, incapable of guiding themselves, are ruled by vital force, which calls them, makes them come, takes hold of them, places and disposes of them according to certain laws, and forms this marvellously-organised body, which the anatomist and the physiologist contemplate with wonder. ”

“ Nothing could move—the inertia of matter itself held it in place until it was too late—everything close to those centers of action simply flared into turgid incandescence and added its contribution to the already hellish whole. ”

“ What is that mysterious force which causes two bodies to attract each other in the direct ratio of their masses and an inverse ratio of their distance ? Two bodies attract each other ! Then matter is not inert ! ”