Talk:Newton's laws of motion

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Contents 1 Newton's Second Law 2 Something's Missing 3 No momentum in Law II 4 Disputed section: Paragraphs deleted from Third Law section 4.1 Newton's third law limitations 5 a question ? 6 Mohist's scientific theory 7 BE AWARE: The calculation of second law of Newton by Newton is wrong 8 What happend to the Second Law section, and why is the Second Law Historical development section so apparently out of place? 9 The applicability 10 Mergefrom Newtonian mechanics 11 Problem with Newton's Law #1 12 Derivative Notation 13 Something Missing 14 Multiple layers of vandalism 15 Simple Introduction 16 Isn't momentum version of second law also important in classical mechanics?

[edit] Newton's Second Law

I have made some additions to this section. Its is not correct to assume NSL implies F=ma. This formula is only correct on 2 conditions, the mass is constant and SI units are use. If SI usings are not use (eg feet, yards..etc) the constant of proportionality is not unity. In many cases F=ma cannot be used, eg a rocket is burning fuel and it is hence getting less massive. This will cause m to change and F=ma is no longer valid.

[edit] Something's Missing

Is it just me or is Newton's second law gone Xykon 09:16, 31 May 2006 (UTC)

[edit] No momentum in Law II

In the latin sentence as well as in [1] there is no question of momentum or rate of change or neither of a resultant force. So, why say there is?
--Aïki 04:26, 19 January 2006 (UTC)

[edit] Disputed section: Paragraphs deleted from Third Law section

I deleted these paragraphs: The forces acting between particles A and B lie along parallel lines, but need not lie along the line connecting the particles. One example of this is a force on an electric dipole due to a point charge, when the dipole points in a direction perpendicular to the line connecting the point charge and the dipole. The force on the dipole due to the point charge is perpendicular to the line connecting them, so there is a reaction force on the point charge in the opposite direction, but these two force vectors are parallel and, even when extended to a line, they never cross each other in space. (Delete this whole Paragrph. This is not true)

For long-range forces such as electricity and gravitation, the third law may cease to apply.(Delete this Sentence, even for long distance forces this law applies equally well)

because discussions should be on the discussion page, not in the article. I'm not expressing a view on which contributor is right. --Heron 12:37, 30 January 2006 (UTC)

[edit] Newton's third law limitations

The third law is not always true. It fails to hold for electromagnetic forces, for example, when the interacting bodies are far apart or rapidly accelerated and, in fact, it fails for any force which propagate from one body to another with finite velocities.
Source: Mechanics, by Keith R. Symon, University of Wisconsin, Addison-Wesley Publishing Company, Inc., chap. 1-4

But in situations in which bodies influence each other at a distance, as for example through the long-range forces of electricity or gravitation, Newton's third law may cease to apply.
Source: Physics - A new introductory course, Particles and Newtonian Mechanics, by A. P. French and A. M. Hudson, by the Science Teaching Center at the Massachusetts Institute of Technology, p. 13-8.

with cases of extreme acceleration, problems do not fall under newtonian physics; they are analyzied with reletivistic physics. The claim about gravity is outright false. Indeed, earth is gravitationally drawn towards stars hundreds of light-years away, but since gravity drops off as the inverse square of distance, the force is incredibly minute. I have seen at least 4 physics books and none of them ever mention newton's third law not applying. I'm not sure about the electromagnetic forces, but I know gravity is still equal and opposite even at great distances.

College Physics seventh edition, by Raymond A. Serway, Jerry S. Faughn, Chris Vuille, and Charles A. Bennett (published by Thomson Brooks/Cole) says "an isolated force can never occur in nature" (page 90). --Crucible Guardian 08:47, 17 February 2006 (UTC)

If no valuable counter-references is brought in, the Wikipedia:Neutral point of view official policy will have to be applied.
--Aïki 00:29, 31 January 2006 (UTC)

Newton's third law as formulated by Newton is valid only when for electrostatic force and gravitational force instantaneous action at a distance is assumed.

However, it would be very silly to state that newton's third law is wrong because it fails to be a relativistic law of physics.

The demand on a theory of physics is that it forms a self-consistent system, and that it agrees with observation to within the accuracy of available observational data.

On a more abstract level we can see that Newton's third law asserts conservation of momentum. The principle of conservation of momentum is just as important in relativistic dynamics as in newtonian dynamics, so in a more abstract sense Newton's third law is still just as valid. --Cleonis | Talk 14:34, 21 February 2006 (UTC)

[edit] a question ?

say theres two cars 1 in motion and 1 stationary , the car in motion strikes the stationary car , which car will have the most damage ? would the stationary car absorb the momentum from the car in motion therefore causing more damage to the stationary car? please help me on this one ?

Assuming that the cars have the same mass they will sustain similar damage. This regardless of whether they remain welded together or bounce apart. This is most easily seen from the 3rd law 'action and reaction are equal and opposite'. The driver of the moving car sees the other 'approaching' at speed. This is the same in his frame of reference as the driver of the stationary car sees in his. Alacrid 19:32, 15 November 2006 (UTC)

[edit] Mohist's scientific theory

From this referenc article:

2400 years ago, the Chinese Mohist philosophers collected their writings in a book called the Mo Ching. Mohism disappeared, but we can still read this in the Mo Ching:

The cessation of motion is due to the opposing force ... If there is no opposing force ... the motion will never stop. This is true as surely as an ox is not a horse.

Here's a perfectly clear a statement of Newton's first law of motion, 2100 years before Newton's Principia. The Principia was part of a scientific revolution, while the statement in the Mo Ching is largely forgotten.

[edit] BE AWARE: The calculation of second law of Newton by Newton is wrong

The theoretical acceleration of a body as per applied force can be only calculated using an altered energy formula E = 1 / 2mv², which is this F = 1 / 2ma². (it would be F = ma² / 200 when calculated in the units I used.)

In other words: Energy, Time and Force are mathematically more or less on equal footing regards the relationship between mass, acceleration and velocity.

see http://www3.sympatico.ca/slavek.krepelka/ttf2/force1.htm

Hm, when I tried F = 1 / 2ma² on the highway today, the other car got completely wrecked, unfortunately. I never had that problem with F = ma. — Shastra 19:22, 12 June 2006 (UTC)

Force can said as dE/dx(E is the energy) not dE/dt. And as far as i know differentiation,d(mv²/2)/dx is mvdv/dx i.e. ma.You cannot directly differentiate you have got to apply the chain rule.Subhash 05:31, 15 August 2006 (UTC)

also i read richard feynman lectures ( the introduction 1963). he says that it is right that the first is easy to understand (newton) but near correct and the second is correct 100% (relativity theory) and it requires more previus knowlage to understand it. and teachers have many dificult moments like this: do to choose the easy but uncoreect that gets the concept or the hard to teach and to understand but correct and up to date.

[edit] What happend to the Second Law section, and why is the Second Law Historical development section so apparently out of place?

-Ste|vertigo 20:02, 16 May 2006 (UTC)

[edit] The applicability

What I think as far as I have read is that The First Law is the law of inertial reference frames(It defines an inertial frame of reference). It says that an inertial reference frame ithat whose acceleration is zero. The second law defines the force. It says that the force applied on a body is dL/dt.Where L is the linear momentum The third law tells us about the interaction between two bodies. It says that when a body applies a force on another body,the other applies an equal and opposite force on the first body.

All the three laws are applicable only together.One cannot say that Newton's second law is not applicable for an accelerated frame since it is defined only for an inertial frame of reference. I have written this in the discussion because i'm afraid no one will believe me.It is my personal experience.Otherwise why would a law represent a special case of the other law formulated by the same person?If one turns the pages of Newton's principia mathematica the truth can be seen.Subhash 05:26, 15 August 2006 (UTC)

[edit] Mergefrom Newtonian mechanics

There was talk of merging Newtonian mechanics into Classical mechanics, but the naysayers seemed more numerous than the proponents (esp. on the Talk:Classical mechanics page). The Newtonian mechanics page offers a very shallow treatment of the subject. I suggest merging that page into this one, and turning Newtonian mechanics into a redirect. --Ling.Nut 13:12, 21 September 2006 (UTC)

[edit] Problem with Newton's Law #1

Just thought I'd let whoever it may concern know that Newton's First Law has been changed, so that "Objects Suck Dick to Stay in Motion". Someone may want to change it back to the textbook version.

It is not necessary to point that out. We see the changes in the article just as quickly as we see your message. Please sign your contributions to talk with four tildas ~~~~. Better still you could revert the change yourself. JRSpriggs 04:55, 25 September 2006 (UTC)

[edit] Derivative Notation

Newton's second law: historical development

The derivatives should be written in Newton's own method, f'(x), rather than in Liebniz notation. 199.126.237.235 00:49, 27 October 2006 (UTC)

It should also be written in Latin, Newton's own language. Loom91 17:08, 28 October 2006 (UTC)

[edit] Something Missing

The first bullet-point that occurs in the section entitled "Newton's first law: law of inertia" ends abruptly. The sentance below is also missing text from the start. 84.65.92.40 19:42, 31 October 2006 (UTC)

I think that you were looking at the article during one of the periods between an act of vandalism and when someone reverts it. It would be more efficient to simply revert the vandalism yourself, rather than telling us about it. We see the vandalism itself as soon as we see your message. JRSpriggs 10:55, 1 November 2006 (UTC)

If you want to try reverting vandalism yourself, please read Help:Reverting. JRSpriggs 08:07, 2 November 2006 (UTC)

[edit] Multiple layers of vandalism

Since this article is vandalized with great frequency, it often happens that two or three or more acts of vandalism occurr between reversions. So when you notice vandalism and want to revert it (see Help:Reverting), please check that you are reverting to a version which contains no vandalism. Thank you. JRSpriggs 10:48, 2 December 2006 (UTC)

[edit] Simple Introduction

Some other science articles are starting to produce introductory versions of themselves to make them more accessible to the average encyclopedia reader. You can see what has been done so far at special relativity, general relativity and evolution, all of which now have special introduction articles. These are intermediate between the very simple articles on Simple Wikipedia and the regular encyclopedia articles. They serve a valuable function in producing something that is useful for getting someone up to speed so that they can then tackle the real article. Those who want even simpler explanations can drop down to Simple Wikipedia. I propose that this article as well consider an introductory version. What do you think?--Filll 22:43, 12 December 2006 (UTC)

To me, this article seems about as simple as they get. But if you think that you can write something even simplier, then go for it. Put {{seeintro}} at the top of this article and then click on the red-link and start writing. Do not forget to put it in a category. You can copy text from this article and then simplify it, if you wish. JRSpriggs 08:09, 13 December 2006 (UTC)

[edit] Isn't momentum version of second law also important in classical mechanics?

The article says:

However, it must be remembered that for Newton, mass was constant and independent of velocity. To take "motion" (motu) as meaning momentum gives a false impression of what Newton believed. Since he took mass as constant (part of the constant of proportionality) it can, in modern notation, be taken to the left of the derivative as . If is dependent on velocity (and thus indirectly upon time) as we would now hold, then has to be included in the derivative, giving or .

Using momentum in the terminology (which would never have occurred to Newton) is a latter-day revision of the law to bring it into correspondence with special relativity.

However, I seem to remember from college that using F = dp/dt was necessary for solving problems with classical rockets, because mass changes with time. (The change of mass with respect to time is due to fuel consumption, not to relativistic effects. ;-) Itub 13:17, 13 December 2006 (UTC)

To Itub: You are right of course. The mass must be included within the derivative even non-relativistically. And I remember reading a statement by Petr Beckmann (no friend to relativity) that Newton did in fact include the mass inside the derivative. However, I have not seen Newton's orginal text translated from Latin to English in a reliable source to verify that for myself. Some people seem to be convinced that he excluded it. So I do not know which way to go here. If you have a source confirming Newton's position, please correct the text and add the reference. JRSpriggs 04:35, 14 December 2006 (UTC)