Aristotelian physics

Aristotelian physics

Overview
Aristotelian Physics the natural sciences, are described in the works of the Greek philosopher Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

 (384 BC – 322 BC). In the Physics
Physics (Aristotle)
The Physics of Aristotle is one of the foundational books of Western science and philosophy...

, Aristotle established general principles of change that govern all natural bodies; both living and inanimate, celestial and terrestrial—including all motion, change in respect to place, change in respect to size or number, qualitative change of any kind, and coming to be and passing away.
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Aristotelian Physics the natural sciences, are described in the works of the Greek philosopher Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

 (384 BC – 322 BC). In the Physics
Physics (Aristotle)
The Physics of Aristotle is one of the foundational books of Western science and philosophy...

, Aristotle established general principles of change that govern all natural bodies; both living and inanimate, celestial and terrestrial—including all motion, change in respect to place, change in respect to size or number, qualitative change of any kind, and coming to be and passing away. As Martin Heidegger, one of the foremost philosophers of the twentieth century, once wrote,
To Aristotle, physics is a broad term that includes all nature sciences, such as philosophy of mind, body, sensory experience, memory and biology, and constitutes the foundational thinking underlying many of his works.

Ancient concepts


Some concepts involved in Aristotle's physics are:
  1. Teleology
    Teleology
    A teleology is any philosophical account which holds that final causes exist in nature, meaning that design and purpose analogous to that found in human actions are inherent also in the rest of nature. The word comes from the Greek τέλος, telos; root: τελε-, "end, purpose...

    : Aristotle observes that natural things tend toward definite goals or ends insofar as they are natural. Regularities manifest a rudimentary kind of teleology.
  2. Natural motion: Terrestrial objects tend toward a different part of the universe according to their composition of the four elements. For example, earth, the heaviest element, tends toward the center of the universe—hence the reason for the Earth being at the center. At the opposite extreme the lightest element, fire, tends upward, away from the center. The relative proportion of the four elements composing an object determines its motion. The elements are not proper substances
    Substance theory
    Substance theory, or substance attribute theory, is an ontological theory about objecthood, positing that a substance is distinct from its properties. A thing-in-itself is a property-bearer that must be distinguished from the properties it bears....

    in Aristotelian theory or the modern sense of the word. Refining an arbitrarily pure sample of an element isn't possible; They were abstraction
    Abstraction
    Abstraction is a process by which higher concepts are derived from the usage and classification of literal concepts, first principles, or other methods....

    s; one might consider an arbitrarily pure sample of a terrestrial substance having a large ratio
    Ratio
    In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...

     of one element relative to the others.
  3. Terrestrial motion: Terrestrial objects move downward or upward
    Buoyancy
    In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

     toward their natural place. Motion from side to side results from the turbulent collision and sliding of the objects as well as transformations between the elements, (generation and corruption).
  4. Rectilinear motion: Ideal terrestrial motion would proceed straight up or straight down at constant speed. Celestial motion is always ideal, it is circular and its speed is constant.
  5. Speed, weight and resistance: The ideal speed of a terrestrial object is directly proportional to its weight. In nature, however, the matter obstructing an object's path is a limiting factor that's inversely proportional to the viscosity
    Viscosity
    Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

     of the medium.
  6. Vacuum isn't possible: Vacuum
    Vacuum
    In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...

     doesn't occur, but hypothetically, terrestrial motion in a vacuum would be indefinitely fast.

  1. Continuum: Aristotle argues against the indivisibles of Democritus
    Democritus
    Democritus was an Ancient Greek philosopher born in Abdera, Thrace, Greece. He was an influential pre-Socratic philosopher and pupil of Leucippus, who formulated an atomic theory for the cosmos....

     (which differ considerably from the historical
    Corpuscularianism
    Corpuscularianism is a physical theory that supposed all matter to be composed of minute particles, which became important in the Seventeenth century. Among the leading corpuscularians were Rene Descartes, Robert Boyle, and John Locke....

     and the modern
    Atomic theory
    In chemistry and physics, atomic theory is a theory of the nature of matter, which states that matter is composed of discrete units called atoms, as opposed to the obsolete notion that matter could be divided into any arbitrarily small quantity...

     use of the term atom
    Atom
    The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons...

    ).
  2. Aether: The "greater and lesser lights of heaven", (the sun, moon, planets and stars), are embedded in perfectly concentric crystal spheres
    Celestial spheres
    The celestial spheres, or celestial orbs, were the fundamental entities of the cosmological models developed by Plato, Eudoxus, Aristotle, Ptolemy, Copernicus and others...

     that rotate eternally at fixed rates. Because the spheres never change and (meteorite
    Meteorite
    A meteorite is a natural object originating in outer space that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects called meteoroids, but they are also sometimes produced by impacts of asteroids...

    s notwithstanding) don't fall down or rise up from the ground, they cannot be composed of the four terrestrial elements. Much as Homer
    Homer
    In the Western classical tradition Homer , is the author of the Iliad and the Odyssey, and is revered as the greatest ancient Greek epic poet. These epics lie at the beginning of the Western canon of literature, and have had an enormous influence on the history of literature.When he lived is...

    's æthere (αἰθήρ)
    Aether (mythology)
    Aether , in Greek mythology, is one of the Protogenoi, the first-born elementals. He is the personification of the upper sky, space, and heaven, and is the elemental god of the "Bright, Glowing, Upper Air." He is the pure upper air that the gods breathe, as opposed to the normal air that mortals...

    , the "pure air" of Mount Olympus
    Mount Olympus
    Mount Olympus is the highest mountain in Greece, located on the border between Thessaly and Macedonia, about 100 kilometres away from Thessaloniki, Greece's second largest city. Mount Olympus has 52 peaks. The highest peak Mytikas, meaning "nose", rises to 2,917 metres...

     was the divine counterpart of the air (άήρ, aer) breathed by mortal
    Immortality
    Immortality is the ability to live forever. It is unknown whether human physical immortality is an achievable condition. Biological forms have inherent limitations which may or may not be able to be overcome through medical interventions or engineering...

    s, the celestial spheres are composed of a special element, eternal and unchanging, with circular natural motion.
  3. Terrestrial change:
    Unlike the eternal and unchanging celestial aether
    Aether (classical element)
    According to ancient and medieval science aether , also spelled æther or ether, is the material that fills the region of the universe above the terrestrial sphere.-Mythological origins:...

    , each of the four terrestrial elements are capable of changing into either of the two elements they share a property with: e.g. the cold and wet (water
    Water (classical element)
    Water is one of the elements in ancient Greek philosophy, in the Asian Indian system Panchamahabhuta, and in the Chinese cosmological and physiological system Wu Xing...

    ) can transform into the hot and wet (air
    Air (classical element)
    Air is often seen as a universal power or pure substance. Its supposed fundamental importance to life can be seen in words such as aspire, inspire, perspire and spirit, all derived from the Latin spirare.-Greek and Roman tradition:...

    ) or the cold and dry (earth
    Earth (classical element)
    Earth, home and origin of humanity, has often been worshipped in its own right with its own unique spiritual tradition.-European tradition:Earth is one of the four classical elements in ancient Greek philosophy and science. It was commonly associated with qualities of heaviness, matter and the...

    ) and any apparent change into the hot and dry (fire
    Fire (classical element)
    Fire has been an important part of all cultures and religions from pre-history to modern day and was vital to the development of civilization. It has been regarded in many different contexts throughout history, but especially as a metaphysical constant of the world.-Greek and Roman tradition:Fire...

    ) is actually a two step
    Gray code
    The reflected binary code, also known as Gray code after Frank Gray, is a binary numeral system where two successive values differ in only one bit. It is a non-weighted code....

     process. These properties are predicated of an actual substance relative to the work it's able to do; that of heating or chilling and of desiccating or moistening. The four elements exist only with regard to this capacity and relative to some potential work. The celestial element is eternal and unchanging, so only the four terrestrial elements account for coming to be and passing away; also called "generation and corruption" after the Latin title of Aristotle's De Generatione et Corruptione (Περὶ γενέσεως καὶ φθορᾶ)
    On Generation and Corruption
    On Generation and Corruption , , also known as On Coming to Be and Passing Away) is a treatise by Aristotle. Like many of his texts, it is both scientific and philosophic...

    .
  4. Celestial motion: The crystal spheres carrying the sun, moon and stars move eternally with unchanging circular motion. They're composed of solid aether
    Aether (classical element)
    According to ancient and medieval science aether , also spelled æther or ether, is the material that fills the region of the universe above the terrestrial sphere.-Mythological origins:...

    and no gaps exist between the spheres. Spheres are embedded within spheres to account for the wandering stars, (i.e. the modern planet
    Planet
    A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...

    s, which appear to move erratically in comparison to the sun, moon and stars). Later, the belief that all spheres are concentric was forsaken in favor of Ptolemy
    Ptolemy
    Claudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...

    's deferent and epicycle
    Deferent and epicycle
    In the Ptolemaic system of astronomy, the epicycle was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets...

    . Aristotle submits to the calculations of astronomer
    Astronomer
    An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...

    s regarding the total number of spheres and various accounts give a number in the neighborhood of 50 spheres. An unmoved mover
    Unmoved mover
    The unmoved mover is a philosophical concept described by Aristotle as a primary cause or "mover" of all the motion in the universe. As is implicit in the name, the "unmoved mover" is not moved by any prior action...

    is assumed for each sphere, including a prime mover
    Primum movens
    Primum movens , usually referred to as the Prime mover or first cause in English, is a term used in the philosophy of Aristotle, in the theological cosmological argument for the existence of God, and in cosmogony, the source of the cosmos or "all-being".-Aristotle's ontology:In book 12 of his...

    for the sphere of fixed stars. The unmoved movers do not push the spheres (nor could they, they're insubstantial and dimensionless); rather, they're the final cause
    Four causes
    Four Causes refers to a principle in Aristotelian science that is used to understand change. Aristotle described four different types of causes, or ways in which an object could be explained: "we do not have knowledge of a thing until we have grasped its why, that is to say, its cause", He argued...

     of the motion, meaning they explain it in a way that's similar to the explanation "the soul is moved by beauty". They simply "think about thinking", eternally without change, which is the idea of "being qua being"
    Metaphysics (Aristotle)
    Metaphysics is one of the principal works of Aristotle and the first major work of the branch of philosophy with the same name. The principal subject is "being qua being", or being understood as being. It examines what can be asserted about anything that exists just because of its existence and...

     in Aristotle reformulation of Plato's theory
    Theory of Forms
    Plato's theory of Forms or theory of Ideas asserts that non-material abstract forms , and not the material world of change known to us through sensation, possess the highest and most fundamental kind of reality. When used in this sense, the word form is often capitalized...

    .


While consistent with common human experience, Aristotle's principles were not based on controlled, quantitative experiments, so, while they account for many broad features of nature, they do not describe our universe in the precise, quantitative way we have more recently come to expect from science. Contemporaries of Aristotle like Aristarchus
Aristarchus of Samos
Aristarchus, or more correctly Aristarchos , was a Greek astronomer and mathematician, born on the island of Samos, in Greece. He presented the first known heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe...

 rejected these principles in favor of heliocentrism
Heliocentrism
Heliocentrism, or heliocentricism, is the astronomical model in which the Earth and planets revolve around a stationary Sun at the center of the universe. The word comes from the Greek . Historically, heliocentrism was opposed to geocentrism, which placed the Earth at the center...

, but their ideas were not widely accepted. Aristotle's principles were difficult to disprove merely through casual everyday observation, but later development of the scientific method
Scientific method
Scientific method refers to a body of techniques for investigating phenomena, acquiring new knowledge, or correcting and integrating previous knowledge. To be termed scientific, a method of inquiry must be based on gathering empirical and measurable evidence subject to specific principles of...

 challenged his views with experiment
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...

s, careful measurement, and more advanced technology such as the telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

 and vacuum pump
Vacuum pump
A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. The first vacuum pump was invented in 1650 by Otto von Guericke.- Types :Pumps can be broadly categorized according to three techniques:...

.

Elements


Aristotle taught that the elements
Classical element
Many philosophies and worldviews have a set of classical elements believed to reflect the simplest essential parts and principles of which anything consists or upon which the constitution and fundamental powers of anything are based. Most frequently, classical elements refer to ancient beliefs...

 which compose the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

 are different from the one that composes the heavens. He believed that four elements
Classical element
Many philosophies and worldviews have a set of classical elements believed to reflect the simplest essential parts and principles of which anything consists or upon which the constitution and fundamental powers of anything are based. Most frequently, classical elements refer to ancient beliefs...

 make up everything under the moon (the terrestrial): earth
Earth (classical element)
Earth, home and origin of humanity, has often been worshipped in its own right with its own unique spiritual tradition.-European tradition:Earth is one of the four classical elements in ancient Greek philosophy and science. It was commonly associated with qualities of heaviness, matter and the...

, air
Air (classical element)
Air is often seen as a universal power or pure substance. Its supposed fundamental importance to life can be seen in words such as aspire, inspire, perspire and spirit, all derived from the Latin spirare.-Greek and Roman tradition:...

, fire
Fire (classical element)
Fire has been an important part of all cultures and religions from pre-history to modern day and was vital to the development of civilization. It has been regarded in many different contexts throughout history, but especially as a metaphysical constant of the world.-Greek and Roman tradition:Fire...

 and water
Water (classical element)
Water is one of the elements in ancient Greek philosophy, in the Asian Indian system Panchamahabhuta, and in the Chinese cosmological and physiological system Wu Xing...

.
He also held that the heavens are made of a special, fifth element called "aether
Aether (classical element)
According to ancient and medieval science aether , also spelled æther or ether, is the material that fills the region of the universe above the terrestrial sphere.-Mythological origins:...

", which is weightless and "incorruptible" (which is to say, it doesn't change). Aether is also known by the name "quintessence"—literally, "fifth substance".
He considered heavy substances such as iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 and other metals to consist primarily of the element earth, with a smaller amount of the other three terrestrial elements. Other, lighter objects, he believed, have less earth, relative to the other three elements in their composition.

Motion


Aristotle held that each of the four terrestrial (or worldly) elements move toward their natural place, and that this natural motion would proceed unless hindered. For instance, because smoke
Smoke
Smoke is a collection of airborne solid and liquid particulates and gases emitted when a material undergoes combustion or pyrolysis, together with the quantity of air that is entrained or otherwise mixed into the mass. It is commonly an unwanted by-product of fires , but may also be used for pest...

 is mainly air, it rises toward the sky but not as high as fire. He also taught that objects move against their natural motion only when forced (i.e. pushed) in a different direction and only while that force is being applied. This idea had flaws that were apparent to Aristotle and his contemporaries. It was questionable, for example, how an arrow
Arrow
An arrow is a shafted projectile that is shot with a bow. It predates recorded history and is common to most cultures.An arrow usually consists of a shaft with an arrowhead attached to the front end, with fletchings and a nock at the other.- History:...

 would continue to fly forward after leaving the bowstring; which could no longer be forcing it forward. In response, Aristotle suggested the air behind an arrow in flight is thinned and the surrounding air, rushing in to fill that potential vacuum
Vacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...

, is what pushes it forward. This was consistent with his explanation of a medium, such as air or water, causing resistance
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...

 to the motion of an object passing through it. The turbulent motion
Fluid dynamics
In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...

 of air around an arrow in flight is very complicated, and still not fully understood.

A vacuum, or void, is a place free of everything, and Aristotle argued against the possibility. Aristotle believed that the speed of an object's motion is proportional to the force being applied (or the object's weight in the case of natural motion) and inversely proportional to the viscosity of the medium; the more tenuous a medium is, the faster the motion. He reasoned that objects moving in a void, could move indefinitely fast and thus, the objects surrounding a void would immediately fill it before it could actually form.

Natural place


The Aristotelian explanation of gravity is that all bodies move toward their natural place. For the element earth, that place is the center of the (geocentric) universe, next comes the natural place of water (in a concentric shell around that of earth). The natural place of air is likewise a concentric shell surrounding the place of water. Sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

 is between those two. Finally, the natural place of fire is higher than that of air but below the innermost celestial sphere, (the one carrying the Moon). Even at locations well above sea level, such as a mountain top, an object made mostly of the former two elements tends to fall and objects made mostly of the latter two tend to rise.

Medieval commentary


The Aristotelian theory of motion came under criticism and/or modification during the Middle Ages
Middle Ages
The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

. The first such modification came from John Philoponus
John Philoponus
John Philoponus , also known as John the Grammarian or John of Alexandria, was a Christian and Aristotelian commentator and the author of a considerable number of philosophical treatises and theological works...

 in the 6th century. He partly accepted Aristotle's theory that "continuation of motion depends on continued action of a force," but modified it to include his idea that the hurled body acquires a motive power or inclination for forced movement from the agent producing the initial motion and that this power secures the continuation of such motion. However, he argued that this impressed virtue was temporary; that it was a self-expending inclination, and thus the violent motion produced comes to an end, changing back into natural motion. In the 11th century, the Persian polymath Avicenna
Avicenna
Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā , commonly known as Ibn Sīnā or by his Latinized name Avicenna, was a Persian polymath, who wrote almost 450 treatises on a wide range of subjects, of which around 240 have survived...

, in The Book of Healing
The Book of Healing
The Book of Healing is a scientific and philosophical encyclopedia written by Abū Alī ibn Sīnā from Asfahana, near Bukhara in Greater Persia. Despite its English title, it is not in fact concerned with medicine...

(1027) was influenced by Philoponus' theory in its rough outline, but took it much further to present the first alternative to the Aristotelian theory. In the Avicennan theory of motion, the violent inclination he conceived was non-self-consuming, a permanent force whose effect was dissipated only as a result of external agents such as air resistance, making him "the first to conceive such a permanent type of impressed virtue for non-natural motion." Such a self-motion (mayl) is "almost the opposite of the Aristotelian conception of violent motion of the projectile type, and it is rather reminiscent of the principle of inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...

, i.e., Newton's first law of motion."

The eldest Banū Mūsā
Banu Musa
The Banū Mūsā brothers , namely Abū Jaʿfar Muḥammad ibn Mūsā ibn Shākir , Abū al‐Qāsim Aḥmad ibn Mūsā ibn Shākir and Al-Ḥasan ibn Mūsā ibn Shākir , were three 9th-century Persian scholars of Baghdad who are known for their Book of Ingenious Devices on automata and mechanical devices...

 brother, Ja'far Muhammad ibn Mūsā ibn Shākir (800-873), wrote the Astral Motion and The Force of Attraction. The Persian physicist, Ibn al-Haytham (965-1039), discussed the theory of attraction between bodies. It seems that he was aware of the magnitude
Magnitude (mathematics)
The magnitude of an object in mathematics is its size: a property by which it can be compared as larger or smaller than other objects of the same kind; in technical terms, an ordering of the class of objects to which it belongs....

 of acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

 due to gravity and he discovered that the heavenly bodies "were accountable to the laws of physics
Physical law
A physical law or scientific law is "a theoretical principle deduced from particular facts, applicable to a defined group or class of phenomena, and expressible by the statement that a particular phenomenon always occurs if certain conditions be present." Physical laws are typically conclusions...

". The Persian polymath Abū Rayhān al-Bīrūnī (973-1048) was the first to realize that acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

 is connected with non-uniform motion, part of Newton's second law of motion. During his debate with Avicenna
Avicenna
Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā , commonly known as Ibn Sīnā or by his Latinized name Avicenna, was a Persian polymath, who wrote almost 450 treatises on a wide range of subjects, of which around 240 have survived...

, al-Biruni also criticized the Aristotelian theory of gravity for denying the existence of levity or gravity in the celestial sphere
Celestial sphere
In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with the Earth and rotating upon the same axis. All objects in the sky can be thought of as projected upon the celestial sphere. Projected upward from Earth's equator and poles are the...

s and for its notion of circular motion
Circular motion
In physics, circular motion is rotation along a circular path or a circular orbit. It can be uniform, that is, with constant angular rate of rotation , or non-uniform, that is, with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves circular motion of...

 being an innate property
Intrinsic and extrinsic properties
An intrinsic property is an essential or inherent property of a system or of a material itself or within. It is independent of how much of the material is present and is independent of the form the material, e.g., one large piece or a collection of smaller pieces...

 of the heavenly bodies
Astronomical object
Astronomical objects or celestial objects are naturally occurring physical entities, associations or structures that current science has demonstrated to exist in the observable universe. The term astronomical object is sometimes used interchangeably with astronomical body...

.

In 1121, al-Khazini
Al-Khazini
Abu al-Fath Abd al-Rahman Mansour al-Khāzini or simply Abu al-Fath Khāzini was a Muslim astronomer of Greek ethnicity from Merv, then in the Khorasan province of Persia .-References:...

, in The Book of the Balance of Wisdom, proposed that the gravity and gravitational potential energy of a body varies depending on its distance from the centre of the Earth. Hibat Allah Abu'l-Barakat al-Baghdaadi
Hibat Allah Abu'l-Barakat al-Baghdaadi
Abu'l-Barakāt Hibat Allah ibn Malkā al-Baghdādī was an Islamic philosopher and physician of Jewish-Arab descent from Baghdad, Iraq. Abu'l-Barakāt, an older contemporary and father-in-law of Maimonides, was originally known by his Hebrew birth name Nathanel before his conversion from Judaism to...

 (1080–1165) wrote a critique of Aristotelian physics entitled al-Mu'tabar, where he negated Aristotle's idea that a constant force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...

 produces uniform motion, as he realized that a force applied continuously produces acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...

, a fundamental law of classical mechanics
Classical mechanics
In physics, classical mechanics is one of the two major sub-fields of mechanics, which is concerned with the set of physical laws describing the motion of bodies under the action of a system of forces...

 and an early foreshadowing of Newton's second law of motion. Like Newton, he described acceleration as the rate of change of speed
Speed
In kinematics, the speed of an object is the magnitude of its velocity ; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as...

.

In the 14th century, Jean Buridan
Jean Buridan
Jean Buridan was a French priest who sowed the seeds of the Copernican revolution in Europe. Although he was one of the most famous and influential philosophers of the late Middle Ages, he is today among the least well known...

 developed the theory of impetus
Theory of impetus
The theory of impetus was an auxiliary or secondary theory of Aristotelian dynamics, put forth initially to explain projectile motion against gravity...

 as an alternative to the Aristotelian theory of motion. The theory of impetus was a precursor to the concepts of inertia
Inertia
Inertia is the resistance of any physical object to a change in its state of motion or rest, or the tendency of an object to resist any change in its motion. It is proportional to an object's mass. The principle of inertia is one of the fundamental principles of classical physics which are used to...

 and momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...

 in classical mechanics. Buridan and Albert of Saxony
Albert of Saxony (philosopher)
Albert of Saxony was a German philosopher known for his contributions to logic and physics...

 also refer to Abu'l-Barakat in explaining that the acceleration of a falling body is a result of its increasing impetus. In the 16th century, Al-Birjandi
Al-Birjandi
Abd Ali ibn Muhammad ibn Husayn Birjandi was a prominent 16th century Persian astronomer, mathematician and physicist who lived in Birjand, Iran.- His works :...

 discussed the possibility of the Earth's rotation. In his analysis of what might occur if the Earth were rotating, he developed a hypothesis similar to Galileo Galilei
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...

's notion of "circular inertia", which he described in the following observational test
Experiment
An experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...

:

Life and death of Aristotelian physics



The reign of Aristotelian physics lasted for almost two millennia, and provide the earliest known speculative theories of physics. After the work of Galileo, Descartes, and many others, it became generally accepted that Aristotelian physics were not correct or viable.
Despite this, scholastic science survived into the late seventeenth century, (perhaps later), when universities amended their curricula.

In Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

, Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

's theory was first convincingly discredited by the work of Galileo Galilei
Galileo Galilei
Galileo Galilei , was an Italian physicist, mathematician, astronomer, and philosopher who played a major role in the Scientific Revolution. His achievements include improvements to the telescope and consequent astronomical observations and support for Copernicanism...

. Using a telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...

, Galileo observed that the moon was not entirely smooth, but had craters and mountains, contradicting the Aristotelian idea of an incorruptible perfectly smooth moon. Galileo also criticized this notion theoretically – a perfectly smooth moon would reflect light unevenly like a shiny billiard ball, so that the edges of the moon's disk would have a different brightness than the point where a tangent plane reflects sunlight directly to the eye. A rough moon reflects in all directions equally, leading to a disk of approximately equal brightness which is what is observed. Galileo also observed that Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...

 has moons
Galilean moons
The Galilean moons are the four moons of Jupiter discovered by Galileo Galilei in January 1610. They are the largest of the many moons of Jupiter and derive their names from the lovers of Zeus: Io, Europa, Ganymede and Callisto. Ganymede, Europa and Io participate in a 1:2:4 orbital resonance...

, objects which revolve around a body other than the Earth. He noted the phases
Planetary phase
Planetary phase is the term used to describe the appearance of the illuminated section of a planet. Like lunar phases, the planetary phase depends on the relative position of the sun, the planet and the observer....

 of Venus, convincingly demonstrating that Venus, and by implication Mercury, travels around the sun, not the Earth.

According to legend, Galileo dropped balls of various densities
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 from the Tower of Pisa
Leaning Tower of Pisa
The Leaning Tower of Pisa or simply the Tower of Pisa is the campanile, or freestanding bell tower, of the cathedral of the Italian city of Pisa...

 and found that lighter and heavier ones fell at almost the same speed. In fact, he did quantitative experiments with balls rolling down an inclined plane, a form of falling that is slow enough to be measured without advanced instruments.

A heavier body falls faster than a lighter one of the same shape in a dense medium like water, and this led Aristotle to speculate that the rate of falling is proportional to the weight and inversely proportional to the density of the medium. From his experience with objects falling in water, he concluded that water is approximately ten times denser than air. By weighing a volume of compressed air, Galileo showed that this overestimates the density of air by a factor of forty. From his experiments with inclined planes, he concluded that all bodies fall at the same rate neglecting friction.

Galileo also advanced a theoretical argument to support his conclusion. He asked if two bodies of different weights and different rates of fall are tied by a string, does the combined system fall faster because it is now more massive, or does the lighter body in its slower fall hold back the heavier body? The only convincing answer is neither: all the systems fall at the same rate.

Followers of Aristotle were aware that the motion of falling bodies was not uniform, but picked up speed with time. Since time is an abstract quantity, the peripatetics postulated that the speed was proportional to the distance. Galileo established experimentally that the speed is proportional to the time, but he also gave a theoretical argument that the speed could not possibly be proportional to the distance. In modern terms, if the rate of fall is proportional to the distance, the differential equation for the distance y travelled after time t is
with the condition that . Galileo demonstrated that this system would stay at for all time. If a perturbation set the system into motion somehow, the object would pick up speed exponentially in time, not quadratically.

Standing on the surface of the moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 in 1971, David Scott
David Scott
David Randolph Scott is an American engineer, test pilot, retired U.S. Air Force officer, and former NASA astronaut and engineer, who was one of the third group of astronauts selected by NASA in October 1963...

 famously repeated Galileo's experiment by dropping a feather and a hammer from each hand at the same time. In the absence of a substantial atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...

, the two objects fell and hit the moon's surface at the same time.

With his law of universal gravitation
Newton's law of universal gravitation
Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them...

 Isaac Newton
Isaac Newton
Sir Isaac Newton PRS was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived."...

 was the first to mathematically codify a correct theory of gravity. In this theory, any mass is attracted to any other mass by a force which decreases as the inverse square of their distance. In 1915, Newton's theory was replaced by Albert Einstein
Albert Einstein
Albert Einstein was a German-born theoretical physicist who developed the theory of general relativity, effecting a revolution in physics. For this achievement, Einstein is often regarded as the father of modern physics and one of the most prolific intellects in human history...

's general theory of relativity
General relativity
General relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

. See gravity for a much more detailed complete discussion.

See also


Disputed works are marked by *, and ** marks a work generally agreed to be spurious.
  • (184a) Physics
    Physics (Aristotle)
    The Physics of Aristotle is one of the foundational books of Western science and philosophy...

     (or Physica)
  • (268a) On the Heavens
    On the Heavens
    On the Heavens is Aristotle's chief cosmological treatise: it contains his astronomical theory and his ideas on the concrete workings of the terrestrial world...

     (or De Caelo)
  • (314a) On Generation and Corruption
    On Generation and Corruption
    On Generation and Corruption , , also known as On Coming to Be and Passing Away) is a treatise by Aristotle. Like many of his texts, it is both scientific and philosophic...

     (or De Generatione et Corruptione)
  • (338a) Meteorology
    Meteorology (Aristotle)
    Meteorology is a treatise by Aristotle which contains his theories about the earth sciences. These include early accounts of water evaporation, weather phenomena, and earthquakes....

     (or Meteorologica)
  • (391a) On the Universe** (or De Mundo)
  • (402a) On the Soul
    On the Soul
    On the Soul is a major treatise by Aristotle on the nature of living things. His discussion centres on the kinds of souls possessed by different kinds of living things, distinguished by their different operations...

     (or De Anima)
  • The Parva Naturalia
    Parva Naturalia
    The Parva Naturalia are a collection of seven works by Aristotle, which discuss natural phenomena involving the body and the soul:* Sense and Sensibilia * On Memory...

     ("Little Physical Treatises"):
  • (481a) On Breath
    On Breath
    On Breath is a philosophical treatise included in the Corpus Aristotelicum but usually regarded as spurious...

    ** (or De Spiritu)
  • (486a) History of Animals
    History of Animals
    History of Animals is a zoological natural history text by Aristotle.-Arabic translation:The Arabic translation of Historia Animalium comprises treatises 1-10 of the Kitāb al-Hayawān .-See also:...

     (or Historia Animalium)
  • (639a) Parts of Animals (or De Partibus Animalium)
  • (698a) Movement of Animals (or De Motu Animalium)
  • (704a) Progression of Animals (or De Incessu Animalium)
  • (715a) Generation of Animals
    Generation of Animals
    The Generation of Animals is a text by Aristotle.-Arabic translation:...

     (or De Generatione Animalium)
  • (791a) On Colors
    On Colors
    On Colors is a treatise attributed to Aristotle but sometimes ascribed to Theophrastus or Strato. The work outlines the theory that all colors are derived from mixtures of black and white...

    ** (or De Coloribus)
  • (800a) On Things Heard
    On Things Heard
    On Things Heard is a work which was formerly attributed to Aristotle, but is now generally believed to be the work of Strato of Lampsacus. Our extant version of On Things Heard is made up of long extracts included in Porphyry's Commentary on Ptolemy's Harmonics, and is thus partial. The extracts...

    ** (or De audibilibus)
  • (805a) Physiognomonics** (or Physiognomonica)
  • (815a) On Plants
    On Plants
    On Plants is a work, sometimes attributed to Aristotle, but generally believed to have been written by Nicolaus of Damascus, which deals with a number of plant related topics.The work is divided in two parts...

    ** (or De Plantis)
  • (830a) On Marvellous Things Heard
    On Marvellous Things Heard
    On Marvellous Things Heard is a collection of thematically arranged anecdotes traditionally attributed to Aristotle. The material included in the collection mainly deals with the natural world...

    ** (or De mirabilibus auscultationibus)
  • (847a) Mechanics** (or Mechanica)
  • (859a) Problems
    Problems (Aristotle)
    The Problems is an Aristotelian or possibly pseudo-Aristotelian collection of problems written in a question and answer format as its authenticity has been under questioning. The collection, gradually assembled by the peripatetic school, reached its final form anywhere between the third century BC...

    * (or Problemata)
  • (968a) On Indivisible Lines
    On Indivisible Lines
    On Indivisible Lines is a short treatise attributed to Aristotle, but likely written by a member of the Peripatetic school some time before the 2nd century BC....

    ** (or De Lineis Insecabilibus)
  • (973a) The Situations and Names of Winds
    The Situations and Names of Winds
    The Situations and Names of Winds is a spurious work sometimes attributed to Aristotle. The text lists winds blowing from twelve different directions and their alternative names used in different places...

    ** (or Ventorum Situs)
  • (974a) On Melissus, Xenophanes, and Gorgias
    On Melissus, Xenophanes, and Gorgias
    On Melissus, Xenophanes, and Gorgias is a short work falsely attributed to Aristotle. The work was likely written during the 1st century AD. or later by a member of the peripatetic school.-References:...

    **

Further Reading

  • Katalin Martinás, “Aristotelian Thermodynamics,” Thermodynamics: history and philosophy: facts, trends, debates (Veszprém, Hungary 23-28 July 1990), 285-303.