First law of motion

“ That all bodies, if at rest, will continue so, as is declared by the first law of motion, until some force moves them; or, if in motion, will continue so, until some force stops them, appears so much a matter of course, that we can at first hardly see any good reason why it should be dignified with the title of the first great law of motion ”

“ We might restate the first law of motion in the form "Every body tends to move in the track in which it actually does move, except in so far as it is compelled by material impacts to follow some other track than that in which it would otherwise move." ”

“ For in all cases, as in the simple ones just given, we can identify the greatest force only by the resulting motion. It is impossible for us ever to get evidence of the occurrence of motion in any other direction than that of the greatest force; since our measure of relative greatness among forces is their relative power of generating motion. And clearly, while the comparative greatness of forces is thus determined, no multiplication of instances can add certainty to a law of direction of movement which follows immediately from the persistence of force. ”

“ Putting aside for the present any discussion of force, a conception first made really definite by Newton, and only imperfectly grasped by Galilei, we may interpret this law as meaning that a body has no more inherent tendency to diminish its motion or to stop than it has to increase its motion or to start, and that any alteration in either the speed or the direction of a body's motion is to be explained by the action on it of some other body, or at any rate by some other assignable cause. ”

“ It has been demonstrated by science that motion is persistent—cannot be created or annihilated—and the demonstration has been accepted by a great body of scientific men. Antecedently to this demonstration Newton had propounded three laws of motion, one of which is that action and reaction are equal and in opposite directions. In this law the persistence of motion or the indestructibility of energy was implied, but at first its full significance was not understood, perhaps not even by Newton himself. ”

“ THE Second Law of Motion being proved for constant Forces which act in parallel lines, and the Third Law for the Direct Action of bodies, it still required great mathematical talent, and some inductive power, to see clearly the laws which govern the motion of any number of bodies, acted upon by each other, and by any forces, anyhow varying in magnitude and direction. ”

“ Sect. 2.—Generalization of the Third Law of Motion.—Centre of Oscillation.—Huyghens.
The Third Law of Motion, whether expressed according to Newton’s formula (by the equality of Action and Reaction) , or in any other of the ways employed about the same time, easily gave the solution of mechanical problems in all cases of direct action; that is, when each body acted directly on others. But there still remained the problems in which the action is indirect;—when bodies, in motion, act on each other by the intervention of levers, or in any other way. ”

“ A further principle of great importance, of which only very indistinct traces are to be found before Newton's time, was given by him as the Third Law of Motion in the form: "To every action there is always an equal and contrary reaction ”

“ His next law is that when a body A exerts a force on a body B, then B also exerts a force on A which is equal in amount but opposite in direction. This means that forces that operate between different parts of a planet produce no net force upon the whole planet, so that the mass of a planet can be treated as if it is concentrated at a point. These are his three laws of motion. ”

“ In revising our successive judgments concerning a body’s course or velocity, we take for granted that there is an actual course and an actual velocity—we take for granted that there are fixed points in space with respect to which all motions are absolute; and we find it impossible to rid ourselves of this idea. Nevertheless, absolute motion cannot even be imagined, much less known. Motion as taking place apart from those limitations of space which we habitually associate with it, is totally unthinkable. For motion is change of place ”

“ Motion is the product of a force generated by the Word and by Resistance, which is Matter. But for Resistance, Motion would have had no results; its action would have been infinite. Newton's gravitation is not a law, but an effect of the general law of universal motion. ”

“ When we say that the force which retains the planets in their orbits is resolved into gravity, or that the force which makes substances combine chemically is resolved into electricity, we assert in the one case what is, and in the other case what might, and probably will ultimately, be a legitimate result of induction. In both these cases motion is resolved into motion. The assertion is, that a case of motion, which was supposed to be special, and to follow a distinct law of its own, conforms to and is included in the general law which regulates another class of motions. ”

“ Here, then, we have at once a physical basis for Newton's Second Law of Motion, the results of which are entirely in harmony with observation and experiment, and whose conception fully satisfies all the Rules of Philosophy; as it is simple in conception, fully agrees with observation and experiment, and satisfactorily explains the Second Law of Motion sought to be explained. ”

“ In mechanics, Descartes can hardly be said to have advanced beyond Galileo. The latter had overthrown the ideas of Aristotle on this subject, and Descartes simply "threw himself upon the enemy" that had already been "put to the rout." His statement of the first and second laws of motion was an improvement in form, but his third law is false in substance. The motions of bodies in their direct impact was imperfectly understood by Galileo, erroneously given by Descartes, and first correctly stated by Wren, Wallis, and Huygens. ”