Talk:Newton's laws of motion

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This article was the subject of a Wiki Education Foundation-supported course assignment, between 12 February 2024 and 14 June 2024. Further details are available on the course page. Student editor(s): Wkuehl9947 (article contribs). Peer reviewers: Lupe.b007.

— Assignment last updated by Ahlluhn (talk) 00:57, 31 May 2024 (UTC)

Semi-protected edit request on 21 July 2024

In the paragraph:

"Acceleration can likewise be defined as a limit:$$a={\frac {dv}{dt}}=\lim _{\Delta t\to 0}{\frac {v(t+\Delta t)-v(t)}{\Delta t}}.$$Consequently, the acceleration is the second derivative of position, often written ${\frac {d^{2}s}{dt^{2}}}$."

Change the equation:

${\frac {d^{2}s}{dt^{2}}}$

to:

${\frac {d^{2}p}{dt^{2}}}$

So that p matches the position variable name Traviskaufman (talk) 22:44, 21 July 2024 (UTC)

References

No, the variable for position is s. Johnjbarton (talk) 14:39, 22 July 2024 (UTC)

Inaccurate paraphrasing of newton's second law

Newton's second law is paraphrased as "At any instant of time, the net force on a body is equal to the body's acceleration multiplied by its mass or, equivalently, the rate at which the body's momentum is changing with time.". Change in momentum is only equal to mass times change in acceleration if the mass of the body is constant. It might be best to simply remove the part about acceleration times mass and rephrase it as "At any instant of time, the net force on a body is equal to the rate at which the body's momentum is changing with time." Michaelmay123 (talk) 18:28, 19 September 2024 (UTC)

It is my understanding that both statements of Newton's 2nd law are only true if the mass of the body remains constant. It is common to see Newton's 2nd law refer specifically to a particle or rigid body, rather than simply a body. The implication is that the mass of a particle or rigid body does not change with time. See Euler's laws of motion; I have added this to "See also".

When dealing with a body whose mass is changing with time, such as a rocket accelerating as the result of thrust associated with ejection of a high-speed mass of gas from a nozzle, a slightly different equation is required. Dolphin (t) 03:05, 20 September 2024 (UTC)

The "changing mass" Newton's formula is often misused, some/many would argue. Yes, it works, but the notion of a body as an entity that loses its mass by becoming more than one body is, philosophically, quite, ahm,... silly? Take for example a rubberband gun: the gun of mass M-m and a bullet of mass m are taken as two bodies (total mass M). And so should be a rocket of mass M-dm and the expelled gas of mass dm, at any instant of time. Ponor (talk) 14:39, 20 September 2024 (UTC)

" zeroeth law"

zero is not an ordinal. Fail Fail Fail Athanasius V (talk) 13:13, 22 September 2024 (UTC)

Sometimes used in physics. For example, see Zeroth law of thermodynamics. Dolphin (t) 13:19, 22 September 2024 (UTC)

Is the so-called "modern form" of Newton's second law compatible with Newton's authentic law?

The article introduces the second law in the modern form F = ma. Newton's authentic law, however, reads that the force F is not "equal" but proportional to its effect on the motion of the body on which it is impressed. Provided that this effect should be correctly measured ma, the authentic law of Newton would read F ~ ma, or, algebraically, F = ma times constant of proportionality. As this constant is missing in the "modern form", it must be inferred that this form is not compatible with Newton's authentic law, in other words: it is not Newton's law, and "classical" mechanics, which is undoubtedly based on F = ma, is not Newtonian mechanics. This should be mentioned, to say the least. 2003:D2:9724:5375:5978:EDD7:4D63:85CD (talk) 16:32, 17 October 2024 (UTC)

If you have a source to support this claim, post it. Otherwise I will go on assuming that mass is defined as the proportionality constant implied by Newton. Johnjbarton (talk) 16:44, 17 October 2024 (UTC)

We agree that there is "a proportionality constant implied by Newton", as you put it. Now, there are two terms, F and (ma), which are said to be "proportional" to each other. "Mass" m is a part of the term (ma) that is said to be proportional to F. Therefore, by basic mathematical reasoning, m is not available as "proportionality constant" between F and (ma). Note, please, that the proportion reads F ~ (ma), not F ~ a, and, algebraically written, not F/a = m, but F/ma = c = constant. This can also clearly be seen if one writes (dp/dt) instead of (ma). If F ~ (dp/dt), and F/(dp/dt) = c = constant, it is evident that the constant cannot be m. Right? 2003:D2:9724:5357:95E5:D83:52F7:AC49 (talk) 07:52, 26 October 2024 (UTC)

The term "Newtonian mechanics" is ubiquitously used as a catch-all that includes many ideas not introduced by Newton himself, e.g., the principle of inertia, and the concepts of work and energy. There's nothing that Wikipedia can or should do to change this terminology. Moreover, the article as it stands already explains this. XOR'easter (talk) 20:20, 17 October 2024 (UTC)

Of course Wikipedia can and should do something. It is not required to "change the terminology", if only here and there Wikipedia would point to the fact (here admitted) that "Newtonian mechanics" is NOT Newton's mechanics, and that the famous "second law of motion", F = ma, is NOT Newton's law but Leonhard Euler's: See L. Euler, Découverte d'un nouveau principe de Mécanique, Mem. Acad. Roy. Sci. Berlin, vol. 6, 1750 (1752), pp. 185-217. I take this reference from Giulio Maltese, La Storia di 'F = ma', Firenze (Olschki), 1992, p. 218. 2003:D2:9724:5357:95E5:D83:52F7:AC49 (talk) 08:02, 26 October 2024 (UTC)

The Maltese reference seems to be in Italian. Here is another more recent book chapter by Maltese on the same subject:

• Maltese, G. (2003). The Ancients’ Inferno: The Slow and Tortuous Development of ‘Newtonian’ Principles of Motion in the Eighteenth Century. In: Becchi, A., Corradi, M., Foce, F., Pedemonte, O. (eds) Essays on the History of Mechanics. Birkhäuser, Basel. https://doi.org/10.1007/978-3-0348-8091-6_9

Contrary to your claim, the essential message of the Maltese work is that the modern form of the physical model attributed to Newton was developed over many years by many people. (This is a very common story line in the history of science). This is inline with the History section of the article. As always, these sections can be improved but no radical change is needed. For that purpose this reference is probably better:

• Coelho, R.L. On the Concept of Force: How Understanding its History can Improve Physics Teaching. Sci & Educ 19, 91–113 (2010). https://doi.org/10.1007/s11191-008-9183-1

Johnjbarton (talk) 14:41, 26 October 2024 (UTC)