Abstract: Newton’s Principa has always been an occasion for numerous discussions and the three laws of motion, described in it, is not an exception. In this paper it would be shown

Abstract: Newton’s "Principa" has always been an occasion for numerous discussions and the three laws of motion, described in it, is not an exception. In this paper it would be shown different views and concepts related to Newton's philosophy, it will also put forward and be discussed various interpretations and different definitions of this three laws. Will also be described the physical sense of what Newton said, and their application to science.

Introduction: As Weisstein (2007) mentioned: «Isaac Newton - english physicist and mathematician who was born into a poor farming family. Luckily for humanity, Newton was not a good farmer!» And saying this, he was absolutely wright, because he wrote this about a person who is regarded as a key figure in a scientific revolution, which could be proven by a theory of Westfall et al. (1995), he wrote: “ Scientists, philosophers and historians agree that Newton’s achievements represent the peak of scientific revolution that began in the late sixtieth century.” Also sir Isaac Newton often named the most influential person in science ever, because his scientific discoveries covered not only Mathematics and Mechanics, but also lots and lots of aspects of different sciences! However sir Isaac Newton is often regarded as a certain genius, he never considered him self as a genius, once he told: “If I have ever made any valuable discoveries, it has been owing more to patient attention, than to any other talent.” From all of newton’s innovations in mechanics there are three, which really stand out of others, modern scientists usually combine them in a group called “3 Newton’s Laws Of Motion”. This three laws appeared first in Newton’s work Philosophiæ Naturalis Principia Mathematica 1686, which is latin for "Mathematical Principles of Natural Philosophy". These three laws describe the motion of bodies, bind the physical quantities describing it, and give it their mathematical foundations.

Body: In the first law, which is also often called” “Law of Inertia” Newton (1687) writes: “Actioni contrariam semper et æqualem esse reactionem: sive corporum duorum actiones in se mutuo semper esse æquales et in partes contrarias dirigi." Nowadays there are a lot of various translations of this original latin words, the most famous of them is concidered to be Motte's (1792) in histranslation of "Principa": "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." Despite the ability to interpret it as a mere paraphrasing or changing the order of words, in works of Maclaurin (1968) or Buchwald and Cohen (2001) we can also meet a very comman modern interpretation, which sounds like: "A body always perseveres in its state of rest, or of uniform motion in a right line, till by some external influance it be made to change its state." A well-known Newton's first law, is also a cause for many researchers to convict of Sir Isaac Newton of plagiarism, point is that lots of individuals consider that there were some natural philosophers before newton, who came up with the same ideas. The most often-arguments are: Thomas Hobbes’s discourse on the state of the bodies in his famous Leviathan (1651) and also some works of René Descartes. No matter how simple could that uncomplicated Newton's law seem to the modern man, this definition has given humanity the concept about the physics of the resting body, also it implies the fact that any non-linear motion means the presence of some acceleration, which is reflected in Newton's works on circular motion in his principa.

Every self-respecting schoolboy when he saw the inscription: , can proudly say that he recognized that this is the mathematical formulation of newton’s second law. And, in general, he would not be 100% right, because this form of record is just the popular derivation from it, Newton (1687) himself wrote: “Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur. " Again, as in the case with the law of Inertia and even worse, there are present lots and lots of different translations and different definitions of this law, but the one which is considered the closest to Newton is again the original Motte’s (1792) translation: “The alteration of motion is ever proportional to the motive force impressed; and is made in the direction of the right line in which that force is impressed." (Something around this words could be also found in numerous works of different researchers such as Helmholz (1973), Sommerfeld (1952) and so on…)Therefore, the most common way to describe this law mathematically is: , so it is very easy to derive the above writen equation from it: . But even at this point, there is still some controversy, the problem is that nowadays physicists claim that Newton’s second law does not apply to non-inertial frames of reference, which, at it’s turn, is not consistent with the Newton’s definition, first this was widely discussed in Mach’s (1902) work “The science of mechanics”. Use Newton's second law in non-inertial frames of reference adopted in the alternative form, in the form of French mathematician Jean le Rond d’Alembert, which, according to Cornelius Lanzcos (1970), could be written as: . For example one of the supporters of this theory was Barford (1973), who defined the Newton's second law: “In any internal frame of referencing the rate of change of momentum of a point particle is equal to the force acting on it.” This sort of definition could be called the most laconic, because it is very short, but it gives us complete information about the law, without any unnecessary facts, which are easy to find in plenty of sources.

This law is not only describing bodies motion in a fairly simple way as it might seem, it also defines such physical quantity in our live as mass, 2d newton’s law defines mass as quantitative measure of inertia (property of bodies to maintain its speed in direction and magnitude) or according to interpretation of French (1971): “Inertial mass is the technical phrase, for that property which determines how difficult it is for a given applied force to change the state of motion of an object.”

Newton (1687): “Actioni contrariam semper et æqualem esse reactionem: sive corporum duorum actiones in se mutuo semper esse æquales et in partes contrarias dirigi.” Motte’s (1792) translation: “ To every action there is always opposed an equal reaction: or the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. ” And this is Newton’s formulation, again extended by Motte’s translation, of Newton’s third Law. Mathematically it could be described in this way: , and according to Saletan and Cromer (1971): “This equation: is more familiar as a starting point of classical mechanics.” However this is a very beautiful phrase, the third law is not very refined, by the theory of Barford (1973): Newton’s third law, in compartment with two other, is a “very incomplete statement”, the deal is, says the researcher, that this law could be only applied, when the forces depend “neither upon any intrinsic directional properties of the objects nor upon their velocities.” This law is also was used by Newton, to derive the law of conservation momentum, which is a very important law in mechanics.

Looking through all of the above written, and generalizing numerous literary sources, it could be safely said, that natural philosophy is never in a static development stage. And more than once would be to make sure that quantity of researchers in every field of physics directly proportional to the number of views, each scientist looks at the physics behind the process in his own way, which implied the fact, that even truism can get many different interpretations, and each will be in its true. Further research can focus on means and aims that Newton had, also on describing his laboratory methods and motivations.

1) 2007 Eric W. Weisstein

2) http://scienceworld.wolfram.com/biography/Newton.html

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