Synthesized answer
According to the passages, Newton’s First Law states: “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” [1]. The phrase “perseveres in its state” means that a body will remain at rest forever if no force acts on it, and if it is already moving uniformly in a straight line, it will continue that motion unchanged unless a force intervenes. For example, “projectiles persevere in their motions, so far as they are not retarded by the resistance of the air, or impelled downwards by the force of gravity” [1]. This shows that a projectile’s natural tendency is to keep moving in a straight line, but external forces like air resistance or gravity alter that state.
For rest, the law implies that a body at rest will stay at rest unless a force compels it to move. The passages do not give a direct example of a body at rest, but the principle is stated clearly in Law I [1]. For uniform motion, the example of a top is given: “A top, whose parts by their cohesion are perpetually drawn aside from rectilinear motions, does not cease its rotation, otherwise than as it is retarded by the air”…
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
← 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…
f all never suffers any change in the state of its motion or rest from the actions of any two bodies between themselves. But in such a system all the actions of the bodies among themselves either happen between two bodies, or are composed of actions interchanged between some two bodies; and therefore they do never produce any alteration in the common centre of all as to its state of motion or rest. Wherefore since that centre, when the bodies do not act mutually one upon another, either is at rest or moves uniformly forward in some right line, it will, notwithstanding the mutual actions of…
cting upon each other (excluding outward actions and impediments) is either at rest, or moves uniformly in a right line. For if two points proceed with an uniform motion in right lines, and their distance be divided in a given ratio, the dividing point will be either at rest, or proceed uniformly in a right line. This is demonstrated hereafter in Lem. XXIII and its Corol., when the points are moved in the same plane; and by a like way of arguing, it may be demonstrated when the points are not moved in the same plane. Therefore if any number of bodies move uniformly in right lines, the common…
ppen after the same manner, whether the ship is at rest, or is carried uniformly forwards in a right line. COROLLARY VI. If bodies, any how moved among themselves, are urged in the direction of parallel lines by equal accelerative forces, they will all continue to move among themselves, after the same, manner as if they had been urged by no such forces. For these forces acting equally (with respect to the quantities of the bodies to be moved), and in the direction of parallel lines, will (by Law II) move all the bodies equally (as to velocity), and therefore will never produce any change in…
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…
More questions about this book
- 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?
- Beyond a simple definition, what characteristics of "forces" can be inferred solely from their described effects in Laws I and II, and what implications does this have for observing physical phenomena?
- 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?