In this way numerous lines of argument converge on the third law. (with quote from the Scholium to the laws of motion (1729:p37)). ‘ in infinitum with a motion perpetually accelerated’ -Ī situation contradicting the first law." Of two bodies, and the system would move in the line AB Were the case, there would be an unbalanced force in the system Imagined B to attract A more strongly than A attracts B. "in demonstrating the validity of the third law in the case of twoīodies attracting each other, Newton Justification lay in his application of an elastic model ofĪnd then Westfall (1971:472) had already pointed out that Or theoretical investigation of elasticity and that, for Newton, its "the evidence suggests that the third law originated in the empirical On the other hand, Fraser (2005:53) thought that Relativity of motion in terms of which the idea of an absolute force That is, his treatment of impact depended on his accepting a Of the common centre of gravity, in which the two bodies do have equalįorces. Recognising that for every impact, there is a frame of reference, that The Wasteīook suggests that Newton came to deny the intuitively obvious by Had seemed obviously false to the great majority of those who beforeġ665 had attempted to analyze the force of percussion. Have equal motions, the conclusion that they press each other equally "Except for the special case in which p and r For example, R S Westfall (1971), 'Force in Newton's Physics' (at p.348) considering the Waste book, wrote that As also argued by Fraser (2005), some of the relevant arguments relate to the equal actions on bodies at both ends of a compressed spring.Īll of these sources may give insight into Newton's thinking, but there remain always dangers of anachronism and misinterpretation in reading such documents and on some points, the language of the sources can permit different authors to draw different conclusions about their content and implications. Much of the ingredient thinking on dynamics that went into the 'Waste Book' appears to have related to the problem of formulating laws that would account acceptably for the phenomena of bodies in collision. when two bodies press against each other, it was not so obvious at first that the action and reaction were also equal in size. The 'Waste Book' casts some light on the origins and justification of the third law, as discussed in the Fraser paper cited above (p.50): this mentions that while Newton's words suggest he thought it was obvious that action and reaction were opposite in direction, e.g. The 'Waste Book' seems to be the only Newton manuscript source offering advance hints of the third law before the 1684 manuscript 'De motu' (an initial precursor of 'Principia', written on the stimulus of questions put to Newton by Edmund Halley, and sent to Halley and to the Royal Society). There is also some related material in another notebook of the period ( 'Questiones quaedam philosophicae', 'Certain philosophical questions'). It is a notebook started in 1665, and it is discussed by a number of authors, including D Fraser (2005), "The third law in Newton's Waste book" ( Studies in History and Philosophy of Science Part A 36(1):43-60). Much early thinking about what became the laws of motion in the Principia, including the third law, can be found in Newton's "Waste Book".
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