Talk:Theory of impetus
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From my research, it is not likely that Jean Buridan DID reject the Aristotelian concept of the first diagram. In fact, the translation that we have linked to states:
But because of the resistance of the air (and also because of the gravity of the stone) which strives to move it in the opposite direction to the motion caused by the impetus, the latter will weaken all the time. Therefore the motion of the stone will be gradually slower, and finally the impetus is so diminished or destoyed that the gravity of the stone prevails and moves the stone towards its natural place.
This does not indicate that there is an intermediate period, as the article suggests. It is more likely that Buridan stuck with the Aristotelian concepts, especially since he did not appear to devote any serious time to clarifying this supposed break between himself and Aristotle. —Preceding unsigned comment added by Arathon (talk • contribs) 17:12, 12 December 2007 (UTC)
[edit] Contradiction between this article and the 'Avicenna' article and 'Inertia' article
This article currently mistakenly claims
"In the 14th century, Jean Buridan rejected the notion of Avicenna that a motion-generating property, which he named impetus, dissipated spontaneously (a two stage theory)."
whereas the article on Avicenna contradicts this and correctly claims
"In mechanics, Ibn Sīnā developed an elaborate theory of motion, in which he made a distinction between the inclination and force of a projectile, and concluded that motion was a result of an inclination (mayl) transferred to the projectile by the thrower, and that projectile motion in a vacuum would not cease.[46] He viewed inclination as a permanent force whose effect is dissipated by external forces such as air resistance.[47] His theory of motion was thus consistent with the concept of inertia in Newton's first law of motion.[46] Ibn Sīnā also referred to mayl to as being proportional to weight times velocity, a precursor to the concept of momentum in Newton's second law of motion.[48] Ibn Sīnā's theory of mayl was further developed by Jean Buridan in his theory of impetus."
It was the Hipparchus and Philoponus evanescent or self-dissipating impetus theory that Buridan rejected, not Avicenna's theory which he adopted. To be corrected...--Logicus (talk) 15:49, 20 January 2008 (UTC)
Logicus made the following corrective edit on 21 January:
"The Theory of impetus was an auxiliary or secondary theory of Aristotelian dynamics introduced to explain projectile motion against gravity, first by Hipparchus in antiquity and subsequently by Philoponus, and was the ancestor of the concept of momentum in classical mechanics.
Trajectory according to Avicenna, rejected by Buridan[citation needed]
In the 14th century, Jean Buridan rejected the Hipparchan-Philoponan notion that the motive force, which he named impetus, dissipated spontaneously, and adopted the Avicennan impetus theory in which (i) it is only corrupted by the resistances of the medium and of gravity in the case of anti-gravitational motion, but would otherwise be permanently conserved in the absence of any resistances to motion, and in which (ii) gravity is also a downward projector and creator of downward impetus, unlike in the radically different Hipparchan-Philoponan theory in which gravity only destroys impetus but never creates it."
--Logicus (talk) 16:13, 22 January 2008 (UTC)
Impetus dynamics is not well explained here, and so I propose to add the following text after the first paragraph immediately above as a provisional improvement that can be expanded on:
'The problem for Aristotelian dynamics posed by the continuation of projectile motion against the resistance of gravity post-projection, such as a stone thrown upwards, was the question of what is the mover that keeps it moving upwards against gravity after the original projector stops pushing it, given the core principle of Aristotelian dynamics that all motion against resistance requires a conjoined mover, but there is no visibly apparent mover in such 'detached' motions. Whereas Aristotle had tentatively suggested the auxilary theory that the propellant is the medium which is endowed with an incorporeal motive force impressed within its parts by the original projector as they also excite the medium in the original action of throwing the projectile, impetus theoreticians found this theory empirically inadequate and refuted. So they replaced it with the alternative theory that the impressed motive force is impressed directly within the projectile itself by the original projector rather than in the medium, thereby dispensing with the intermediary propelling agent of the medium in Aristotle's theory as redundant. Thus impetus dynamics was a secondary theory of Aristotelian dynamics that saved its core principle from refutation by projectile motion and observed it by identifying an internal impetus as its conjoined mover rather than the external medium. What all variants of impetus dynamics had in common was the theory that an incorporeal motive force - be it called an impressed force, mayl or impetus - is impressed within the projectile by some projector.'
--Logicus (talk) 19:02, 22 January 2008 (UTC)
[edit] Projectile trajectory diagram's unsourced
Projectile trajectory diagrams of Philoponus and Albert Saxony have been flagged as unsourced, and most likely mistaken. Probably only Galileo ever represented projectile motion as zero elevation horizontal projection, as part of his celestial dynamics and cosmogony in which the planets are put into orbit by a 90 degree deflection into the horizontal by God after a period of free-fall from their point of creation beyond Saturn.
The error here may well be that what were intended as vertically upward projectile trajectories in their textual discussions implicitly referred to here may have been misinterpreted as horizontal trajectories by reading history backwards through Galilean spectacles. For whilst it is certainly the case that it can be mathematically demonstrated that the resultant of a downward uniform acceleration due to the vertical gravitational inclinatio ad contraria and a horizontal uniform deceleration to a state of rest due to the horizontal gravitational inclinatio ad quietem in some scholastic dynamics can produce the two and three stage projectile scholastic projectile trajectories for oblique projections depicted in Rupert Hall's PhD thesis - published as Ballistics in the 17th century - which are more realistic than Galileo's mistaken parabolic trajectories, nevertheless these would not produce any more than two-stage trajectories at most for horizontal projections, namely a curvilinear stage and also a second vertical stage for those special cases when the horizontal impetus is wholly destroyed by gravity before the projectile reaches the ground.
The current diagrams of Philoponus and Albert of Saxony projectile trajectories should be deleted as false and unsourced in order to avoid the misleading impression that scholastic dynamicists were silly fools and that Galileo was not grossly mistaken about projectile trajectories.--Logicus (talk) 19:59, 2 February 2008 (UTC)
