Synthesized answer
Based solely on the passages, the characteristics of "forces" that can be inferred from their described effects in Laws I and II are that they are the cause of any change in a body's state of motion, and that their effect is quantitative and directional. Law I states that a body remains at rest or in uniform motion unless "compelled to change that state by forces impressed thereon" [5], so a force is the necessary agent for any deviation from rest or uniform straight-line motion. Law II specifies that the "alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed" [1][5], meaning the effect (change in motion) is directly proportional to the force's magnitude and occurs along the force's line of action.
These characteristics imply that to observe physical phenomena, one must look for changes in motion—specifically, deviations from rest or uniform straight-line motion—as the primary evidence of an impressed force. The passages also note that the "quantities and mathematical proportions" of forces are investigated, and these are later compared with "the phænomena of Nature" [3]. Therefore,…
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
ortional to the motive force impressed; and is made in the direction of the right line in which that force is impressed. If any force generates a motion, a double force will generate double the motion, a triple force triple the motion, whether that force be impressed altogether and at once, or gradually and successively. And this motion (being always directed the same way with the generating force), if the body moved before, is added to or subducted from the former motion, according as they directly conspire with or are directly contrary to each other; or obliquely joined, when they are…
ected to bodies should depend upon the nature and quantity of those bodies, as we see they do in magnetical experiments. And when such cases occur, we are to compute the attractions of the bodies by assigning to each of their particles its proper force, and then collecting the sum of them all. I here use the word attraction in general for any endeavour, of what kind soever, made by bodies to approach to each other; whether that endeavour arise from the action of the bodies themselves, as tending mutually to or agitating each other by spirits emitted; or whether it arises from the action of…
orces, but investigating the quantities and mathematical proportions of them; as I observed before in the Definitions. In mathematics we are to investigate the quantities of forces with their proportions consequent upon any conditions supposed; then, when we enter upon physics, we compare those proportions with the phænomena of Nature, that we may know what conditions of those forces answer to the several kinds of attractive bodies. And this preparation being made, we argue more safely concerning the physical species, causes, and proportions of the forces. Let us see, then, with what forces…
as much drawn or pressed by that other. If you press a stone with your finger, the finger is also pressed by the stone. If a horse draws a stone tied to a rope, the horse (if I may so say) will be equally drawn back towards the stone: for the distended rope, by the same endeavour to relax or unbend itself, will draw the horse as much towards the stone, as it does the stone towards the horse, and will obstruct the progress of the one as much as it advances that of the other. If a body impinge upon another, and by its force change the motion of the other, that body also (because of the…
← Definitions The Mathematical Principles of Natural Philosophy (1846) by Isaac Newton , translated by Andrew Motte Axioms, or Laws of Motion Section I → 596269 The Mathematical Principles of Natural Philosophy (1846) — Axioms, or Laws of Motion Andrew Motte Isaac Newton AXIOMS, OR LAWS OF MOTION. LAW I. Every body perseveres in its state of rest, or of uniform motion in a right line, unless it is compelled to change that state by forces impressed thereon. Projectiles persevere in their motions, so far as they are not retarded by the resistance of the air, or impelled downwards by the force…
More questions about this book
- Explain Newton's First Law of Motion, using only the provided examples, in a way that clarifies what "perseveres in its state" truly means for both rest and uniform motion.
- How does the second law's emphasis on "alteration of motion" and the direction of the "motive force" distinguish it from merely describing existing motion, and what does this imply about the nature of force itself?
- If a student only understood Law I, how might their understanding of the *cause* of changing motion be incomplete, and how does Law II specifically address this gap?
- Given the initial context of Euclid and the title "Axioms," what significance might Newton have intended by presenting these fundamental principles as "Axioms, or Laws of Motion" rather than hypotheses or observations?