Talk:Newton's laws of motion/Archive 2

message: Starting Archive2 for Newton's laws of motion, initially to include threads where the last comment was made before 2008 or not dated.  R. Baley (talk) 19:39, 25 January 2008 (UTC)

message: The theoretical acceleration of a body as per applied force can be only calculated using an altered energy formula E = 1/2mv^2, which is this F = 1/2ma^2. (it would be F = ma^2/200 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 = 1/2ma^2 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)
thread_title:  BE AWARE: The calculation of second law of Newton by Newton is wrong 

message: -Ste|vertigo 20:02, 16 May 2006 (UTC)
thread_title:  What happend to the Second Law section, and why is the Second Law Historical development section so apparently out of place? 

message: 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)
thread_title:  The applicability 

message: 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)
thread_title:  Mergefrom [[Newtonian mechanics]] 

message: 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)
thread_title:  Problem with Newton's Law #1 

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

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

message: 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)
thread_title:  Multiple layers of vandalism 

message: 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)
replies: text: 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  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)
thread_title:  Simple Introduction 

message: 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 mdv/dt\!. If m\! is dependent on velocity (and thus indirectly upon time) as we would now hold, then m\! has to be included in the derivative, giving d(mv)/dt\! or dp/dt\!.
: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)
replies: text: 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)
replies: text:  Newton did infact include mass within the derivative, writing dp/dt rather than m dv/dt but at the same time we must also remember that mass is always constant in classical mechanics. Treating rockets as variable mass systems and writing dp/dt = m dv/dt + v dm/dt is a misleading fallacy, albeit unfortunately prevalent among elementary text book writers. The fallacious and misleading nature of this treatment is exposed in detail in Kleppner and Kolenkow's Introduction to Mechanics. Loom91 08:43, 14 December 2006 (UTC)
replies: text: Thanks, I see the confusion now. I think the typical textbook approach is used because it happens to give the same result for the force (and looks simpler) when the calculation is done from the frame of reference of the rocket (v=0). Itub 16:30, 14 December 2006 (UTC)
replies: text: K&K demnstrated with a simple example that writing F = m dv/dt + v dm/dt is not only logically wrong, it can also give the incorrect answer. It's always preferable to use a constant mass system and apply conservation of momentum. Loom91 08:02, 15 December 2006 (UTC)
replies: text: See note "motu" below. For those who don't believe that Newton's formulation is equivalent to "Force = rate of change of momentum", please consult (i) on-line versions of the Principia, paying special attention to Definitions I and II (i.e. the first lines of text in the book) and (ii) if you distrust your ability to understand early-18th century mathematical English (I wouldn't blame you), consult the recent translation by I. Bernard Cohen which is (a) into modern English and (b) scrupuously annotated. PaddyLeahy 19:16, 5 August 2007 (UTC)
thread_title:  Isn't momentum version of second law also important in classical mechanics? 

message: I don't know about other high-schoolers, but I find physics (at the very least) a respectable subject, and often I find it even a little fun, even if it is frustrating.
But I think the vandal problem is starting to show up on this page.  I have never heard of the "conservation of butter" before, and I don't think it should even be mentioned in this article.
This article should be closed to general editing (I'm VERY NEW editing wise, so I don't know all of the protocol involved with shutting an article to non-"member" editing).  I'll go ahead and remove the little snippet about butter myself... but can this article be locked away from vandals?
Thanks, Nick 04:38, 9 January 2007 (UTC)
replies: text: What you want is called semi-protected which prevents unregistered users and users registered for less than four days from editing the article. This can only be imposed by an administrator. Unfortunately, their policy is only to impose it in extreme cases and then only for short periods. I think it should be used here, but I am not an administrator. JRSpriggs 09:58, 9 January 2007 (UTC)
replies: text: I am repeating myself, but see Help:Reverting. JRSpriggs 10:16, 9 January 2007 (UTC)
replies: text: Well, Nick, it appears that they decided to give us semi-protected status after all, contrary to my expectations. I hope it helps. JRSpriggs 12:06, 12 January 2007 (UTC)
thread_title:  Vandals 

message: In the detailed section on the third law of motion, the third paragraph has this sentence:
Usually the planet is less massive than the star and thus displays greater changes in it's state of motion.
"It's" should read "its"; as "it's" means "it is" or "it has" and is clearly incorrect in this context. —The preceding unsigned comment was added by 68.55.57.57 (talk) 21:35, 25 January 2007 (UTC)
thread_title:  Bad punctuation 

message: In my opinion the first line of the article is only partly correct. The second law of motion was first formulated, in a quadratic form, by Christiaan Huygens. At least he should receive some credit. I would suggest to change the first line into:
Newton's laws of motion are three physical laws which provide relationships between the forces acting on a body and the motion of the body. The laws were first compiled by Sir Isaac Newton, but the second law is a reformulation and generalization of a law formulated earlier by Christiaan Huygens.Robvhoorn 15:06, 10 April 2007 (UTC)
replies: text: Actually none of the laws were formulated by Newton. As far as I know, both the first and the second law were first formulated by Galileo, the father of modern physics. Huygens formulated the third law. The achievement of Newton was recognising that these three laws could provide an axiomatic framework for the entire science of classical mechanics. Loom91 09:35, 11 April 2007 (UTC)
thread_title:  Newton's Second Law originated from Christiaan Huygens 

message: Newton was a great man who was very clever and created the three laws of motion.Right now in my 6th grade science class we are discussing him.He was very helpful to us although some might not realize it. Thanks Newton!!!
p.s we had to create a game called newtonology in this class —The preceding unsigned comment was added by 76.189.1.232 (talk) 00:12, 26 April 2007 (UTC)
thread_title:  newtonology! 

message: Can anyone please tell me the impacts of Newton's laws on society and give examples if possible?
: Newton's laws form the basis of mechanical engineering, so basically everything around you was made with its help. That's one hell of an impact. Loom91 07:41, 28 June 2007 (UTC)
thread_title:  Impacts 

message: First Law is PROBLEMATIC as stated:
The main problem is one word in the first sentence for both definitions.  The word "external" should be replaced by either the word "net" or "total".  An "external force" is a force that acts on an object inside the system from some object which is outside of the system (see the physics classic text Keith R. Symon, "Mechanics - 3rd edition", Addison Wesley Longman, 1971, p. 160).  If we neglect the Earth's spin and motion about the sun, we normally might think a book resting on a table is subject to Newton's 1st Law.  The book is the system.  The system is not changing its acceleration and will continue to do so until a NET (or TOTAL) force acts upon the book.  However, there are two external forces acting on the book:  gravity (from the Earth) and a normal force (from the table).  Remember that our system is the book and the Earth and table are outside the system; thus, both of these forces are external forces. Hence, there are external forces acting on the book and by the definition presented by Wikipedia (and the usual definition of an external force) one could not apply Newton's 1st Law to this book.  However, most physics texts would apply Newton's 1st Law to this book.  
The hockey puck used in the later example has external forces applied to it (gravity from the Earth and a normal force from the ice).  Your choice of "external force" would remove any possible example on the Earth because gravity is always applied to any object on the Earth (and in fact the Earth itself from the sun). 
The simplest solution that would correct this issue is to simply replace "external force" by "net (or total) force". —Preceding unsigned comment added by Paul Bonneau (talk • contribs) 
: All physics texts I've seen explicitly make the point that Earth is not an inertial frame and that Newton's first law can NOT be applied to objects in it. Nevertheless, it is used to solve problems, but that's only an approximation. It can be experimentally shown that Earth is not an inertial reference frame. See, for example, Physics by Halliday and Resnick. The correct wording is net external force. Also, please sign your comments using ~~~~ and create new sections when starting ew discussions. Loom91 11:36, 6 July 2007 (UTC)
thread_title:  Modest change 

message: Down toward the bottom, we find this statement: "However, since the speed of rotation and revolution change relatively slowly, the inertial force is tiny." This makes it sound like the CHANGE of "speed" (probably should be frequency) of rotation and revolution is what makes an earth-based frame not inertial, rather than the fact it is rotating and revolving at all. I believe this is wrong, but am a bit reluctant to modify this article due to lack of qualification. Paul Bonneau 18:56, 5 July 2007 (UTC)
replies: text: I changed it.--Patrick 13:06, 6 July 2007 (UTC)
thread_title:  Modest change 

message: I removed the following statement, which is dead wrong:
:Newton believed that mass was constant and independent of velocity. To interpret "motion" (motu) as momentum gives a false impression of what Newton believed.
On the contrary, prior to introducing the laws of motion, Newton defines "quantity of matter" (= our mass) and "quantity of motion" as quantity of matter times velocity. So "motu" here means exactly the modern (classical) notion of momentum. I have taken the liberty of reordering the discussion of the second law a bit as well. PaddyLeahy 18:51, 5 August 2007 (UTC)
thread_title:  Motu 

message: Hi! I've spotted some problems with some important statements:
From the "Newton's laws of motion":
"First Law
If no net force acts on a particle, then it is possible to select a set of reference frames, called inertial reference frames, observed from which the particle moves without any change in velocity."
From the "Inertial frame of reference" :
"An inertial frame of reference, or inertial reference frame, is one in which Newton's first and second laws of motion are valid. In other words, a reference frame that is neither rotating nor accelerated."
This is a circular definition of an inertial frame of reference. There is a problem with this definition of the 1. Newton's law.
Also, an inertial reference frame is usually defined as one in which the first law is valid, the second law is not mentioned in the definition.
From the "Frame of reference" : 
"An inertial frame of reference is defined as one in which Newton's first law holds true. That is, one in which a free particle travels in a straight line (or more generally a geodesic) at constant speed "
Here the first Newton's law is defined differently, in the spirit of general relativity. This inconsistencies are confusing to a student trying to understand the Newton's laws.
Yamps 18:16, 21 August 2007 (UTC)
replies: text: There are various self-consistent ways of describing Newton's laws and defining "force", "inertial reference frame" etc.  The one currently in the article is that favored by User:Loom91.  It doesn't necessarily jive with the philosophy of editors of other articles, such as inertial frame of reference. Rracecarr 19:27, 21 August 2007 (UTC)
replies: text:  To clarify Rracecarr, it is possible to give the traditional statement of N1L, in which case it is only valid for a certain class of reference frames and invalid for others (this validity being taken as the definition of an inertial reference frame). It is also possible to give the modern statement of N1L, in which case it is itself a definition of inertial reference frames and ttherefore universally valid (as all definitions must be). This should not be a matter of personal choice. Both viewpoints are equally tenable and both should be mentioned in all articles on the topic. Loom91 19:20, 22 August 2007 (UTC)
replies: text: Thanks for the response. Valid arguments indeed, but one can easily get confused because of the direct reference from one approach to another. It seems to me now that in the "Inertial frame of reference" article it should be stated to which formulation it refers, or maybe the link to that article should be from the original Newton's formulation. Yamps 21:12, 22 August 2007 (UTC)
thread_title:  Definiton of an inertal frame of refrence and the First Law 

message: Sorry, but i have learned in class that Newtons first law states that:
An object will remain stationary or at a constant velocity unless acted upon by a force...
just thought you guys might want to revise that section if what im saying is correct  —Preceding unsigned comment added by 124.180.194.158 (talk) 08:14, 17 September 2007 (UTC)
replies: text: That's pretty much what it says.  Where it says "in motion" that means "stationary or at constant velocity" (stationary is just the special case of the constant velocity being zero).  The language probably could be made clearer, but at the moment it's very concise; I'm torn. --Bth 12:01, 19 September 2007 (UTC)
thread_title:  Something is wrong...I think 

message: I think the laws are ok as stated in the intro.  Bth changed NL2 in the intro from f=ma to f=dp/dt.  I reverted.  I agree that this is a more general definition, but it is probably harder to grasp, and it is not the way most people first hear the law.  Someone coming to the article having last heard of Newton in 6th grade is more likely to be confused by the more general form, whereas f=ma might jog the memory.  The current statement of NL3 is not very specific either: to every action there is an equal and opposite reaction.  I can think of lots more precise ways to word that.  But that is the traditional wording, and so I think that's what belongs in the intro. Rracecarr 14:56, 19 September 2007 (UTC)
thread_title:  Brief statements of the laws in the intro 

message: I'm no expert on Newton's Laws, but I am pretty sure "turdmonkeys" is not a term he would have used. (as seen in the header, "statements of the turdmonkeys") As I'm pretty much a newbie here (and in the middle of doing my Physics homework), I'll leave the actual editing to more experienced persons.
Jedikaiti 22:37, 23 October 2007 (UTC)
thread_title:  Vandals at it again... 

message: This article should only need one statement of the laws, however it makes sense to have a brief summary at the top - because that is often what people are looking for. To have the laws stated three times in different ways is a little confusing - and very messy. I tried to rewrite the introductory section a while back - though it was reverted - would anyone object if I tried again to combine the two redundant statements into just one redundant statement?
The main problem seems to be that everyone prefers a different way of saying the laws - which isn't too much of a problem, however it leads to constant re-reversion. As I don't think we will ever get a consensus over the "right" way to state the laws (because the Latin is the only correct version) I think we should at least tidy the article up so that the people changing the introductory statements don't drastically effect the flow of the text.
Anyone have any ideas about the best way to proceed? This topic is of immense importance so we should be aiming for at least a Good article. Conrad.Irwin 21:34, 11 November 2007 (UTC)
replies: text: In the interest of accuracy and NPOV, we must give all the different statements. Loom91 (talk) 20:13, 18 November 2007 (UTC)
thread_title:  Three statements of the laws? 

message: I think that many parts of this page are overly complicated for someone who just needs to scan through this for help on a science paper. I’m not saying get rid of all the technical stuff but just add a section with the simpler version of the laws and placed so that they stand out and you don’t have to hunt for them. Crazydjman 02:51, 16 November 2007 (UTC)
thread_title:  Layman's terms 

message: What about the fourth law about superposition of forces? Sevcsik (talk) 16:18, 20 November 2007 (UTC)
thread_title:  4th law 

message: An Observer would like to pose a question relating to an example on the main page, the ball on the floor of the stationary aircraft.
The Observer questions the bracketed statement (i.e. the ball does not remain stationary) because he observes events from a different frame of reference. The Observer explains it this way.
The Observer presumes that the ball rests on the floor of the aisle, only due to Gravity. Without Gravity the ball could be placed stationary, off the floor, where it can have no frictional force act on it.
This clear plexiglass aircraft is open at the rear like a Hercules.
The Observer is not inside this plexiglass aircraft,  with the stationary zero gravity ball suspended in it. The Observer is observing events from beside the runway, looking directly at the suspended ball.
The aircraft has an accelerating force applied to it and it begins to move. "The ball remains stationary" as it has no accelerating force or frictional force applied to it. If the aircraft had no end on the fuselage, the aircraft would disappear while the ball remained in its' original position, because no accelerating force, no frictional force, was applied to it.
Alternatively, if the Observer accepted that the ball was at rest on the floor he could conclude this from his observation. The ball is attempting to remain staionary, however frictional force from the accelerating aircraft are applied to the circumference of the ball causing it to roll. Any accelerating force on the ball is from friction and is fractional to the accelerating force on the aircraft.
There is a contradiction evident between the bracketed statement (the ball is not stationary) and the Observation as described. To the Observer it appears that events relating to the ball confirm Newton's Law. How does the author of the Main Page reconcile the difference for the Observer?--Layman1 03:25, 1 December 2007 (UTC)
thread_title:  A Question relating to the Main Page example - ball in aircraft? 

message: 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.
-- You are incorrect. The types of units one uses in no way changes the validity of the law in question. The confusion stems from the English units of force and mass. A pound-force and a pound-mass are not identical though they are often used interchangeably in layman's terms and even in many (sloppy) textbooks. Wikipedia has a discussion on this somewhere that I've referred to when teaching this.
Thus, it is completely correct to write: 1 [pound-force] = 1 [pound-mass] * 32.174 [ft/sec^2]. This is correct because 1 pound-force equals just that: the force necessary to accelerate 1 pound-mass at a rate 32.174 ft/sec^2. Or, 1 pound-force is the force (weight) of 1 pound-mass under the influence of Earth's gravitational force field, which, since it is proportional to mass, is taken as an acceleration of 32.174 ft/sec^2 at the surface. 
The metric system avoids this confusion with F=ma because it distinguishes between mass [kilograms] and force [N], but you pay for it in other formulae (those involving frequency, for example). In the metric system a mass of 1 kilogram weighs 9.8 Newtons because: 9.8 [Newtons] = 1 [kg] * 9.8 [m/s^2]. Thus, 1 Newton is defined as 1 (kg-m)/s^2. 
Your first assertion that mass must be constant is true - sort of. Really, F = d(mv)/dt. That is, Force equals the derivative (rate of change) of momentum (mass*velocity). So either mass, or velocity, or both can change as a result of (or cause) force. 
::I disagree, F=ma is true at all times and all three can change with time. It is a bit like saying that Distance=Speed x Time is only true if the speed is constant, nonsense. Rolo Tamasi (talk) 00:04, 25 January 2008 (UTC)
replies: text: See the discussion below, titled "Isn't momentum version of second law also important in classical mechanics?" for some issues with rockets and other systems with variable mass. Itub 18:26, 16 January 2007 (UTC)
thread_title:  Newton's Second Law 

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

message: In the latin sentence as well as in 
there is no question of momentum or rate of change or neither of a resultant force. So, why say there is? </br> --Aïki 04:26, 19 January 2006 (UTC)
thread_title:  No momentum in Law II 

message: 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 ?
:: The discussion page is for discussing improvements to the article only.TStein (talk) 20:44, 11 July 2008 (UTC)
replies: text:  This has the cause and effect backward though.  The damage absorbs the energy of impact and keeps it from bouncing.  TStein (talk) 20:44, 11 July 2008 (UTC)
thread_title:  a question ?