Aristotelian physics
To Aristotle, 'physics' was a broad field including subjects which would now be called the philosophy of mind, sensory experience, memory, anatomy and biology.
Objects made of these elements have natural motions: those of earth and water tend to fall; those of air and fire, to rise.
He did not conduct experiments in the modern sense, but relied on amassing data, observational procedures such as dissection, and making hypotheses about relationships between measurable quantities such as body size and lifespan.
Aristotle's principles were difficult to disprove merely through casual everyday observation, but later development of the scientific method challenged his views with experiments and careful measurement, using increasingly advanced technology such as the telescope and vacuum pump.
In claiming novelty for their doctrines, those natural philosophers who developed the "new science" of the seventeenth century frequently contrasted "Aristotelian" physics with their own.
According to Aristotle, the Sun, Moon, planets and stars – are embedded in perfectly concentric "crystal spheres" that rotate eternally at fixed rates.
The concentric, aetherial, cheek-by-jowl "crystal spheres" that carry the Sun, Moon and stars move eternally with unchanging circular motion.
[12] The most significant early critique was made in terms of geometry by the 11th-century Arab polymath al-Hasan Ibn al-Haytham (Alhazen) in his Discourse on Place.
Now however it is understood that at any time prior to achieving terminal velocity in a relatively resistance-free medium like air, two such objects are expected to have nearly identical speeds because both are experiencing a force of gravity proportional to their masses and have thus been accelerating at nearly the same rate.
This became especially apparent from the eighteenth century when partial vacuum experiments began to be made, but some two hundred years earlier Galileo had already demonstrated that objects of different weights reach the ground in similar times.
The cause, according to Aristotle, must be a power (i.e., force) that drives the body as long as the external agent remains in direct contact.
A little later on, he broadens the range of the material cause to include letters (of syllables), fire and the other elements (of physical bodies), parts (of wholes), and even premises (of conclusions: Aristotle re-iterates this claim, in slightly different terms, in An.
And it is a feature of musical harmonics (first noted and wondered at by the Pythagoreans) that intervals of this type do indeed exhibit this ratio in some form in the instruments used to create them (the length of pipes, of strings, etc.).
But they conceal (or at any rate fail to make patent) a crucial feature of Aristotle’s concept of efficient causation, and one which serves to distinguish it from most modern homonyms.
There must be a mover, distinct (at least in some sense) from the thing moved, which is exercising its motive capacity at every moment of the projectile’s flight (see Phys VIII.
[24]The final cause is that for the sake of which something takes place, its aim or teleological purpose: for a germinating seed, it is the adult plant,[25] for a ball at the top of a ramp, it is coming to rest at the bottom, for an eye, it is seeing, for a knife, it is cutting.
Mechanism, at least as practiced by Aristotle’s contemporaries and predecessors, may have been explanatorily inadequate – but at least it was an attempt at a general account given in reductive terms of the lawlike connections between things.
Simply introducing what later reductionists were to scoff at as "occult qualities" does not explain – it merely, in the manner of Molière’s famous satirical joke, serves to re-describe the effect.
But more than that, there is a point to describing the world in such teleologically loaded terms: it makes sense of things in a way that atomist speculations do not.
PA I.4): but we then go on to show how their parts relate to one another: why it is, for instance, that only blooded creatures have lungs, and how certain structures in one species are analogous or homologous to those in another (such as scales in fish, feathers in birds, hair in mammals).
And the answers, for Aristotle, are to be found in the economy of functions, and how they all contribute to the overall well-being (the final cause in this sense) of the animal.
[32] Hibat Allah Abu'l-Barakat al-Baghdaadi (1080–1165) wrote al-Mu'tabar, a critique of Aristotelian physics where he negated Aristotle's idea that a constant force produces uniform motion, as he realized that a force applied continuously produces acceleration, a fundamental law of classical mechanics and an early foreshadowing of Newton's second law of motion.
[35] Buridan and Albert of Saxony also refer to Abu'l-Barakat in explaining that the acceleration of a falling body is a result of its increasing impetus.
[37] He described it in terms of the following observational test: "The small or large rock will fall to the Earth along the path of a line that is perpendicular to the plane (sath) of the horizon; this is witnessed by experience (tajriba).
After the work of many pioneers such as Copernicus, Tycho Brahe, Galileo, Kepler, Descartes and Newton, it became generally accepted that Aristotelian physics was neither correct nor viable.
According to legend, Galileo dropped balls of various densities from the Tower of Pisa and found that lighter and heavier ones fell at almost the same speed.
His experiments actually took place using balls rolling down inclined planes, a form of falling sufficiently slow to be measured without advanced instruments.
[40] Standing on the surface of the Moon in 1971, David Scott famously repeated Galileo's experiment by dropping a feather and a hammer from each hand at the same time.
[41] The first convincing mathematical theory of gravity – in which two masses are attracted toward each other by a force whose effect decreases according to the inverse square of the distance between them – was Newton's law of universal gravitation.
Modern scholars differ in their opinions of whether Aristotle's physics were sufficiently based on empirical observations to qualify as science, or else whether they were derived primarily from philosophical speculation and thus fail to satisfy the scientific method.
What this diagram does not show is how Aristotle explained the complicated curves that the planets make in the sky. To preserve the principle of perfect circular motion, he proposed that each planet was moved by several nested spheres, with the poles of each connected to the next outermost, but with axes of rotation offset from each other. Though Aristotle left the number of spheres open to empirical determination, he proposed adding to the many-sphere models of previous astronomers, resulting in a total of 44 or 55 celestial spheres .
