Talk:Inertia/Archive 1

message: moved from talk:gyroscope
What is inertia and in what units is it measured?--Light current 02:16, 24 October 2005 (UTC)
thread_title:  What is inertia 

message: I suggest that inertia is an imaginary concept with no definition in physics. It has no units. Mass and momentum have units. But inertia is just lack of momentum. I think the article should be altered to reflect this fact. AS it stands the article is misleading.--Light current 22:28, 24 October 2005 (UTC)
thread_title:  Imaginary concept 

message: :Interesting subject! There is enough stuff above to create an article just for this subject. I suggest you do one, if it's not already done: is it? Title? 'Before, during and after Newton', or else. It would be easier to discuss all those interesting points that you have introduce.
:Regarding 1), I did not know that it was a slogan.</br> 
:As for 2), it does not say that's what Aristotle said, just that his concepts could be interpreted nowadays with this formula. 1) & 2) have to be read together, not separatly. </br>
:Finally, in the theories of physics used nowadays, there is no such thing as a medium who resist to the motion of an object, and if it where so, that would be considered as a force, force in the sense that it is use nowadays.  --Aïki 17:49, 7 January 2006 (UTC)
thread_title: Interesting subject!

message: Thanks for the appreciative suggestion, to be considered ! I reply in bracketed inserts to your comments in quotes:
AIKI: "Regarding 1), I did not know that it was a slogan." 
[The typical phraseology of the 20th century literature on the alleged inertial-dynamics and scientific revolution tends to be the 'forced versus force-free motion' mantra of the ilk 'in Aristotle's dynamics motion requires a force but not in Newton's', which seems to me fair game for being termed a 'slogan' or 'mantra'. But as such it is not merely simplifying, but of course seriously falsifying, because in neither dynamics is there any force-free motion in the real world, and moreover in an externally force-free pure void for which Aristotle predicted interminable motion, then continuing motion would be caused by the internal force of inertia in Newton's dynamics. 
The two main errors of this mantra are first that it invalidly compares the behaviour of a body that is wholly unperturbed by gravity in Newton's dynamics with that of a body with gravity that brings it to rest or prevents its motion in Aristotle's dynamics, that is, it compares the behaviour of a body under two crucially different sets of dynamical initial conditions; and secondly it wholly overlooks the role of Newton's FORCE of inertia. These errors are illustrated in such as the following example of this mantra from pp17-18 of Stephen Hawking's 1988 A Brief History of Time, but into which I have inserted the crucially different initial conditions it omits and that hopefully make its invalid malcomparison, and thus its anti-Aristotelian prejudice, somewhat clearer:
'Before Galileo and Newton people believed Aristotle who said that the natural state of a body [WITH GRAVITY] was to be at rest and that it moved only if driven by a force or impulse [TO OVERCOME ITS GRAVITY]...but after them we believe whenever a body is not acted on by any force [AND SO NOT BY GRAVITY] it will keep on moving.' [NB Slightly paraphrased]
Newton's criticism of this exposition based on his comments quoted above would presumably be that in both ancient atomist and Aristotle's dynamics a body without gravity not acted upon by any force would also keep moving.
At least since the publication of Westfall's 1970 Force in Newton's Physics, which argued the dynamics of the Principia was based on two forces rather than one, namely 'impressed force' which causes uniform acceleration and the 'force of inertia' which causes uniform motion and also rest to persevere, it has increasingly come to be accepted that the 19th century positivist view that the only force in Newton's dynamics was impressed force, such as portrayed by Mach, is seriously mistaken. Perhaps one of the most forceful ways to illustrate this error is simply to ask what is the force by which the body is said to be "carried in uniform motion" along the sides of the parallelogram in Newton's exposition of the famous 'parallelogram of forces' in the Principia's Corollary 1 of its prefatory axiomatics ? Newton's parallelogram of forces is surely a parallelogram of inherent forces. It seems it was Cohen's acceptance of Westfall's analysis that eventually by 1999 forced him to concede Newton did not abandon the fundamental principle of Aristotelian dynamics that all (actual) motion requires a mover, and from which it would seem to follow that by the same token he had previously claimed Newton's dynamics wholly overthrew Aristotelian dynamics to found a new physics because it breached this principle, then rather it was a continuation and development of it, thus arguably dispelling the leading myth of post-medieval scientific modernity in a fundamental dichotomy between 'yesterday' and 'today' that the 'forced versus force-free motion' mantra asserts.
AIKI: "As for 2), it does not say that's what Aristotle said, just that his concepts could be interpreted nowadays with this formula."
[And nor does my text say the formula F = mv is what Aristotle said, but just that his concepts CANNOT POSSIBLY be interpreted by that formula, neither nowadays nor at any time, if m here denotes inertially resistant mass. This is crucially because they provably did not include any concept of bodies having any inertial resistant mass m, a much later innovation. Hence the Keplerian formula F = mv contradicted Aristotle's two different predictions of infinite speed when there is no gravitational resistance to motion (Physics 4.8.215a29f and Heavens 3.2.301b), which both presumed there is no inertial resistance to motion either, whereby R = 0 in Aristotle's law v @ F/R.] 
AIKI "1) & 2) have to be read together, not separatly." [Why ?] 
=====On medium=====
AIKI: "Finally, in the theories of physics used nowadays, there is no such thing as a medium who resist to the motion of an object [Then how come some bodies float in water ?], and if it where so, that would be considered as a force, force in the sense that it is use nowadays." 
[Are you really trying to claim there is no such subject in modern physics as fluid mechanics that studies the resistance to motion by fluid media ? Or that according to modern physics there is no such thing as a terrestrial atmosphere whose resistance to motion could incinerate insufficiently insulated space shuttle's ? And nor does my text say the resistance of a medium was ever considered not to be a force in any sense. What are you trying to claim here ? However, I should perhaps clarify that both the variables 'F' and 'R' in my formula v @ F/R refer to forces, F being the motive force and R the resisting force.] 
The comment does perhaps raise the issue of the changing recognition or not of various different resistances to motion in the history of physics and their analysis as forces. In fact I suggest the main development in dynamics from Aristotle to Newton was that of identifyimg what the various resistances to motion are and whether they should be subtracted from the motive force, as in Philoponus's v @ F - R, or whether it should be divided by them, as in Aristotle's 
v @ F/R. Note that in Euler's Newtonian law a = F/m, 'F' really refers to net force, that is, motive forces minus resisting forces, but if instead 'F' refers to gross force it can be expressed more fully as a = (F - R)/m to reveal its possible historical roots in both Philoponus's v @ F - R and Aristotle's v @ F/R. In Newtonian dynamics some resistances to motion, such as the buoyancy upthrust of a fluid medium, are to be subtracted from the motive force, but it is to be divided by others such as inertial resistance m. Stoke's Law for the terminal speed of gravitational fall in a fluid medium provides an interesting study in this problem, and some such as Stephen Toulmin have even claimed it is the modern vindication of Aristotle's law v @ F/R.
On this analysis it seems that both Aristotle and Philoponus may have discovered a part of the eventual 'Newtonian truth' in respect of the mathematical analysis of the role of resistance in determining the speed of motion and answering the key question of whether it divides or subtracts from the motive force.]
--80.6.94.131 19:16, 10 January 2006 (UTC)
thread_title: 10 JANUARY: A.BELLAMY REPLIES TO AIKI 7 JANUARY AS ABOVE

message: AIKI: "Finally, in the theories of physics used nowadays, there is no such thing as a medium who resist to the motion of an object [Then how come some bodies float in water ?], and if it where so, that would be considered as a force, force in the sense that it is use nowadays." 
[Are you really trying to claim there is no such subject in modern physics as fluid mechanics that studies the resistance to motion by fluid media ? Or that according to modern physics there is no such thing as a terrestrial atmosphere whose resistance to motion could incinerate insufficiently insulated space shuttle's ? And nor does my text say the resistance of a medium was ever considered not to be a force in any sense. What are you trying to claim here ? However, I should perhaps clarify that both the variables 'F' and 'R' in my formula v @ F/R refer to forces, F being the motive force and R the resisting force.] 
The comment does perhaps raise the issue of the changing recognition or not of various different resistances to motion in the history of physics and their analysis as forces. In fact I suggest the main development in dynamics from Aristotle to Newton was that of identifyimg what the various resistances to motion are and whether they should be subtracted from the motive force, as in Philoponus's v @ F - R, or whether it should be divided by them, as in Aristotle's 
v @ F/R. Note that in Euler's Newtonian law a = F/m, 'F' really refers to net force, that is, motive forces minus resisting forces, but if instead 'F' refers to gross force it can be expressed more fully as a = (F - R)/m to reveal its possible historical roots in both Philoponus's v @ F - R and Aristotle's v @ F/R. In Newtonian dynamics some resistances to motion, such as the buoyancy upthrust of a fluid medium, are to be subtracted from the motive force, but it is to be divided by others such as inertial resistance m. Stoke's Law for the terminal speed of gravitational fall in a fluid medium provides an interesting study in this problem, and some such as Stephen Toulmin have even claimed it is the modern vindication of Aristotle's law v @ F/R.
On this analysis it seems that both Aristotle and Philoponus may have discovered a part of the eventual 'Newtonian truth' in respect of the mathematical analysis of the role of resistance in determining the speed of motion and answering the key question of whether it divides or subtracts from the motive force.]
--80.6.94.131 19:16, 10 January 2006 (UTC)
thread_title: On medium

message: 1- For the existance of media, you are right. But I cannot remember why I added this part on medium, even after reviewing (rapidly,I admit) your texts! If I remember, I will come back to tell you.
2- What is the @ for? Doe's it means = ? (Please, if it is possible, give me a brief answer.) Thank you.</br> --Aïki 01:07, 11 January 2006 (UTC)
thread_title: On medium: answer from Aïki

message: AIKI, with respect to your acceptance of the standard view that F = mv represents the Aristotelian theory of the effect of a force, the following exposition may be helpful for yourself and others in explaining why its apparent implication that a constant force produces a constant speed in Aristotelian dynamics is mistaken.
DOES A CONSTANT FORCE PRODUCE A UNIFORM OR ACCELERATED MOTION ?
One of the traditional key claims of the mistaken thesis that Newton's dynamics overthrew Aristotelian dynamics is that in the latter a constant force produces a constant speed, whereas in Newton's it causes a uniform acceleration. But as usual this standard history misrepresents both of these dynamics by air-brushing them to produce the illusion of a revolution, when in fact Newton's dynamics was a revisionary development of the scholastic Aristotelian dynamics developed by Avicenna and the Paris school, and also of the new theory of inertia of Kepler's development of Aristotelian dynamics. For on the one hand this claim overlooks Newton's force of inertia, which causes uniform motion to persevere. And on the other hand, in scholastic Aristotelian impetus dynamics such as eventually adopted and developed by Galileo, primary forces such as gravity produce uniformly accelerated motion (in a void) by means of continually creating and impressing fresh successive and equal amounts of the secondary force of impetus within bodies. And because the internal force of impetus causes uniform motion to continue in the absence of all resistance, its uniform accumulation caused by gravity therefore produces uniformly accelerated motion. 
Consequently the historical truth of the matter is that both Aristotelian and Newton's dynamics similarly posited two different kinds of force, namely a kind of primary or external force that produces uniform acceleration, such as gravity or Newton's concept of impressed force in general, and secondary internal forces that cause uniform motion to continue in the absence of all resistance, such as the force of impetus in Aristotelian dynamics or the force of inertia in Newton's development of Aristotelian dynamics. This development both revised and fused together the latter's two different auxiliary theories of impetus and Kepler's theory of inertia - the latter was an inherent resistance to all motion proportional to mass invoked to prevent infinite speed in the absence of any other resistance to a motive force - to form Newton's highly idiosyncratic hybrid concept of 'the force of inertia' that both causes (uniform) motion and resists (accelerated) motion.
Finally, it should be noted that in Aristotle's law of motion v @ F/R, v refers to the average speed of the whole motion from rest (i.e. d/t) rather than instantaneous speed and therefore does not distinguish whether the motion is constant or accelerated. And hence Newton's a @ F/m entails Kepler's v @ F/m. Aristotle's own separate supposition that a constant force produces a constant speed must be inferred (or not) from other analyses or as a logically implicit presupposition (Drabkin argued it was logically implicit in the rules of violent motion elaborated in Physics 7.5), but he certainly accepted gravitational fall was accelerated as a matter of fact, whatever the dynamical explanation. But whatever, it would seem that at least since the 10th century and Avicenna's impetus theory of projectile motion and of gravitational fall in which gravity is its continual primary projector, there was a specific variant of Aristotelian dynamics in which a primary propelling force produces a uniformly accelerated motion. The Avicennan impetus theory, subsequently adopted and developed by the Paris schools of Burdian et al in the 14th century and Galileo in his post-Pisan later mechanics in the 17th century, was apparently the third major auxiliary theory of Aristotelian dynamics devised to save its core theory that all real motion requires a conjoined motive force from refutation by identifying the force of projectile motion which has no apparent conjoined force. It replaced both Aristotle's original auxiliary theory of the air as the conjoined mover and then the Hipparchan-Philoponan impetus theory of an essentially self-decaying impermanent impressed internal force. 
At the beginning of the 20th century, in his strenuous efforts to prove his alma mater Paris University (i.e. Buridan et al), rather than Galileo and Newton, had been the originators of allegedly anti-Aristotelian inertial-dynamics in the 15th century, the highly influential French philosopher and historian of science Pierre Duhem mistakenly miscast impetus theory as the revolutionary overthrow of Aristotelian dynamics because he claimed it contradicted its basic principle that all motion requires a 'contiguous' mover, by which he meant an external conjoined mover rather than a conjoined mover that may be either external or internal. But this restriction was patently mistaken, because it placed no such restriction on the mover, as patent in its various theories of the internal mover of gravity, of the internally impressed force of the air in projectile motion, and of the internal moving souls of the planets. In short, the idea of internal motive forces, both inherent (gravity) and contingent (impressed force) stems from Aristotle himself. Thus far from being the wholesale overthrow of Aristotelian dynamics that breached its most fundamental principle, rather its supplementary impetus theory was its saviour and further development that fully observed its core principle that all actual motion requires a conjoined mover. But unfortunately Duhem's crucial error was by copied by such as Kuhn and Cohen and others in portrayals of Newtonian physics as revolutionary.
--80.6.94.131 17:14, 13 January 2006 (UTC)
thread_title: Is F = mv in Aristotelian dynamics?