I have never read his original works, but I would say that he must have used length, volume, time, velocity, acceleration, momentum or force, and maybe (kinetic) energy. Which quantities appeared in his work and which did he introduce to physics?

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    $\begingroup$ The concepts of length, volume, and time dates back to the beginning of science, for example. Pythagorean era. I am (almost) sure that the concepts (not accurate mathematical formulation) of velocity and laws of motion dates back at least to the Islamic golden age (8th century to the 14th century). References: ibn sina, Al-Biruni, ... $\endgroup$
    – C.F.G
    Dec 25, 2022 at 6:30
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    $\begingroup$ The main quantity introduced by Newton was force. $\endgroup$ Dec 25, 2022 at 14:25

1 Answer 1


Yes to @Alexandre Eremenko 's comment -- provided 'force' is understood in a sense consistent with accelerative force (i.e. something that can produce change of motion in accordance with Newton's second law of motion: in contrast, for example, to a force according to Kepler, which would maintain velocity and without which a body would come to rest, see Bruce Stephenson's 'Kepler's Physical Astronomy' linked below)). With that condition, force indeed looks like a Newtonian introduction.

The need for such a proviso about the meaning in which 'force' is understood shows, however, that there is a problem with the question. The question names various modern-day labels for physical quantities, without pausing to consider whether these terms have had more than one meaning over time. In this way it suggests a mistake of anachronism: of assuming that the modern meaning of the term extends backwards over time.

In the case of 'force', the term has had a complex history. Back when physics was written in Latin, corresponding words 'vis' and 'virtus' could stand, indefinitely, for almost any sort of physical power, force or virtue. So it would be easy to find references to 'vis' or 'virtus' prior to Newton, but it will also be found that these earlier references do not mean the kind of (accelerative) force that Newton was discussing. Studies of the early history, showing the variety of early concepts of force, and how slowly they became clarified, can be found for example in Westfall (1971) "Force in Newton's Physics". Also Kepler's 'force', quite different than Newton's (because it maintains motion against a tendency for a body to come to rest) is discussed in Bruce Stephenson's (1987) "Kepler's Physical Astronomy".

Newton's contributions are not well measured by identifying which modern concepts he introduced. In some cases, where the modern concept did not yet exist in Newton's time, Newton also did not introduce it, but he did provide an important foundation on which the modern concept could later be built.

This is also practically how Einstein described Newton's lasting contributions. When asked in 1919 to comment on an article suggesting "Newton overthrown" (by relativity theory), Einstein answered by disagreeing with that simplistic idea:-

"No one must think that Newton's great creation can be overthrown in any real sense by this or by any other theory. His clear and wide ideas will for ever retain their significance as the foundation on which our modern conceptions of physics have been built."

(See 'Science' (New Series, vol.LI, no.1305, Jan 2, 1920, at pp.8-10).)

(Original German: "Niemand aber soll denken, daß durch diese oder irgendeine andere Theorie Newtons große Schöpfung im eigentlichen Sinne verdrängt werden könne. Seine klaren und großen Ideen werden als Fundament unserer ganzen modernen Begriffsbildung auf dem Gebiet der Naturphilosophie ihre eminente Bedeutung in aller Zukunft behalten.")

Einstein was saying that Newton introduced foundations on which (the whole of? -- 'ganzen') our modern physics conceptions were built -- but without making a statement that Newton introduced particular modern physical quantities.

An arguable example of the difference is found in Newton's 'Principia' book 1 proposition 1, where Newton demonstrates that the motion of a body subject to a centripetal force takes place by equal areas relative to the center of force (i.e. in a sense that we would interpret as that of Kepler's second law, concerning equal-area motion). Commentators have occasionally expressed the thought that prop. 1 is obvious in view of the constancy of angular momentum when there is no couple or turning force. A significant point, though, is that when Newton wrote his work there was no concept of angular momentum, and proposition 1 does not introduce it (since the demonstration makes no reference to mass). But without proposition 1, there would also not have been the foundation or stepping-stone that it provides towards the concept of angular momentum.

Similar observations can be made in the cases of some other modern physical quantities.

  • $\begingroup$ What is "accelerative force"? $\endgroup$
    – Leos Ondra
    Dec 26, 2022 at 12:15
  • $\begingroup$ "when Newton wrote his work there was no concept of angular momentum" Ok, so this is one quantity he didn't use. $\endgroup$
    – Leos Ondra
    Dec 26, 2022 at 12:16
  • $\begingroup$ @Leos Ondra : "accelerative force" explained by amendment, also see the Stephenson and Westfall references. $\endgroup$
    – terry-s
    Dec 26, 2022 at 18:14

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