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Physics in the medieval Islamic world
Physics in the medieval Islamic world
Physics in the medieval Islamic world
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The natural sciences saw various advancements during the Golden Age of Islam (from roughly the mid 8th to the mid 13th centuries), adding a number of innovations to the Transmission of the Classics (such as Aristotle, Ptolemy, Euclid, Neoplatonism).[1] During this period, Islamic theology was encouraging of thinkers to find knowledge.[2] Thinkers from this period included Al-Farabi, Abu Bishr Matta, Ibn Sina, al-Hassan Ibn al-Haytham and Ibn Bajjah.[3] These works and the important commentaries on them were the wellspring of science during the medieval period. They were translated into Arabic, the lingua franca of this period.

Islamic scholarship in the sciences had inherited Aristotelian physics from the Greeks and during the Islamic Golden Age developed it further. However the Islamic world had a greater respect for knowledge gained from empirical observation, and believed that the universe is governed by a single set of laws. Their use of empirical observation led to the formation of crude forms of the scientific method.[4] The study of physics in the Islamic world started in Iraq and Egypt.[5] Fields of physics studied in this period include optics, mechanics (including statics, dynamics, kinematics and motion), and astronomy.

Physics

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Islamic scholarship had inherited Aristotelian physics from the Greeks and during the Islamic Golden Age developed it further, especially placing emphasis on observation and a priori reasoning, developing early forms of the scientific method. With Aristotelian physics, physics was seen as lower than demonstrative mathematical sciences, but in terms of a larger theory of knowledge, physics was higher than astronomy; many of whose principles derive from physics and metaphysics.[6] The primary subject of physics, according to Aristotle, was motion or change; there were three factors involved with this change, underlying thing, privation, and form. In his Metaphysics, Aristotle believed that the Unmoved Mover was responsible for the movement of the cosmos, which Neoplatonists later generalized as the cosmos were eternal.[1] Al-Kindi argued against the idea of the cosmos being eternal by claiming that the eternality of the world lands one in a different sort of absurdity involving the infinite; Al-Kindi asserted that the cosmos must have a temporal origin because traversing an infinite was impossible.

One of the first commentaries of Aristotle's Metaphysics is by Al-Farabi. In "'The Aims of Aristotle's Metaphysics", Al-Farabi argues that metaphysics is not specific to natural beings, but at the same time, metaphysics is higher in universality than natural beings.[1]

Optics

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Cover of Ibn al-Haytham's Book of Optics

One field in physics, optics, developed rapidly in this period. By the ninth century, there were works on physiological optics as well as mirror reflections, and geometrical and physical optics.[7] In the eleventh century, Ibn al-Haytham not only rejected the Greek idea about vision, he came up with a new theory.[8]

Ibn Sahl (c. 940–1000), a mathematician and physicist connected with the court of Baghdad, wrote a treatise On Burning Mirrors and Lenses in 984 in which he set out his understanding of how curved mirrors and lenses bend and focus light. Ibn Sahl is credited with discovering the law of refraction, now usually called Snell's law.[9][10] He used this law to work out the shapes of lenses that focus light with no geometric aberrations, known as anaclastic lenses.

Ibn al-Haytham (known in Western Europe as Alhacen or Alhazen) (965-1040), often regarded as the "father of optics"[11] and a pioneer of the scientific method, formulated "the first comprehensive and systematic alternative to Greek optical theories."[12] He postulated in his "Book of Optics" that light was reflected upon different surfaces in different directions, thus causing different light signatures for a certain object that we see.[13] It was a different approach than that which was previously thought by Greek scientists, such as Euclid or Ptolemy, who believed rays were emitted from the eye to an object and back again. Al-Haytham, with this new theory of optics, was able to study the geometric aspects of the visual cone theories without explaining the physiology of perception.[7] Also in his Book of Optics, Ibn al-Haytham used mechanics to try and understand optics. Using projectiles, he observed that objects that hit a target perpendicularly exert much more force than projectiles that hit at an angle. Al-Haytham applied this discovery to optics and tried to explain why direct light hurts the eye, because direct light approaches perpendicularly and not at an oblique angle.[13] He developed a camera obscura to demonstrate that light and color from different candles can be passed through a single aperture in straight lines, without intermingling at the aperture.[14] His theories were transmitted to the West.[12] His work influenced Roger Bacon, John Peckham and Vitello, who built upon his work and ultimately transmitted it to Kepler.[12]

Taqī al-Dīn tried to disprove the widely held belief that light is emitted by the eye and not the object that is being observed. He explained that, if light came from our eyes at a constant velocity it would take much too long to illuminate the stars for us to see them while we are still looking at them, because they are so far away. Therefore, the illumination must be coming from the stars so we can see them as soon as we open our eyes.[15]

Astronomy

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Main article: Astronomy in the medieval Islamic world
14th century manuscript of al-Mulakhkhas fi al-Hay’ah, Jaghmini's treatise on astronomy

The Islamic understanding of the astronomical model was based on the Greek Ptolemaic system. However, many early astronomers had started to question the model. It was not always accurate in its predictions and was over complicated because astronomers were trying to mathematically describe the movement of the heavenly bodies. Ibn al-Haytham published Al-Shukuk ala Batiamyus ("Doubts on Ptolemy"), which outlined his many criticisms of the Ptolemaic paradigm. This book encouraged other astronomers to develop new models to explain celestial movement better than Ptolemy.[16] In al-Haytham's Book of Optics he argues that the celestial spheres were not made of solid matter, and that the heavens are less dense than air.[17] Some astronomers theorized about gravity too, al-Khazini suggests that the gravity an object contains varies depending on its distance from the center of the universe. The center of the universe in this case refers to the center of the Earth.[18]

Mechanics

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Impetus

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John Philoponus had rejected the Aristotelian view of motion, and argued that an object acquires an inclination to move when it has a motive power impressed on it. In the eleventh century Ibn Sina had roughly adopted this idea, believing that a moving object has force which is dissipated by external agents like air resistance.[19] Ibn Sina made distinction between 'force' and 'inclination' (called "mayl"), he claimed that an object gained mayl when the object is in opposition to its natural motion. So he concluded that continuation of motion is attributed to the inclination that is transferred to the object, and that object will be in motion until the mayl is spent. He also claimed that projectile in a vacuum would not stop unless it is acted upon. This conception of motion is consistent with Newton's first law of motion, inertia, which states that an object in motion will stay in motion unless it is acted on by an external force.[20] This idea which dissented from the Aristotelian view was basically abandoned until it was described as "impetus" by John Buridan, who may have been influenced by Ibn Sina.[19][21]

Acceleration

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In Abū Rayḥān al-Bīrūnī text Shadows, he recognizes that non-uniform motion is the result of acceleration.[22] Ibn-Sina's theory of mayl tried to relate the velocity and weight of a moving object, this idea closely resembled the concept of momentum[23] Aristotle's theory of motion stated that a constant force produces a uniform motion, Abu'l-Barakāt al-Baghdādī contradicted this and developed his own theory of motion. In his theory he showed that velocity and acceleration are two different things and force is proportional to acceleration and not velocity.[24]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Physics in the medieval Islamic world

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Physics in the medieval Islamic world refers to the systematic study and theoretical advancements in the physical sciences, encompassing , (including , dynamics, , and theories of motion), and astronomy-related physics, pursued by scholars across the Islamic world from the 8th to the 14th centuries during the . This era, spanning regions from in Spain to the in and extending to Persia and , was marked by the translation and expansion of Greek, Indian, and Persian texts into , fostering an environment of empirical experimentation and mathematical innovation that laid foundational principles for later European science. A cornerstone of these developments was the field of optics, where Ibn al-Haytham (965–1040 CE), also known as Alhazen, revolutionized the discipline through his seminal work Kitāb al-Manāẓir (, completed around 1021 CE). In this seven-volume treatise, Ibn al-Haytham rejected ancient emission theories of vision, instead proposing that light rays emanate from objects to the eye, and he conducted controlled experiments to demonstrate refraction, reflection, and the formation of images via the , establishing an early form of the based on , , and verification. His quantitative approach to light propagation and atmospheric phenomena, such as rainbows and halos, influenced subsequent scholars and was translated into Latin in the 13th century, impacting figures like and . In , Islamic scholars advanced theories of motion and equilibrium, critiquing and extending . The (9th century CE) explored and in their Book on the Measurement of Plane and Spherical Figures and , describing self-operating machines and pumps that demonstrated principles of and . Al-Bīrūnī (973–1048 CE) contributed to by measuring the specific gravities of metals and gems with unprecedented precision, using balances to determine densities and challenge Aristotelian notions of natural places. Later, al-Khazīnī (1115–1150 CE) formalized the of weights in The Book of the Balance of Wisdom, applying to levers, inclined planes, and , while (1080–1164/5 CE) proposed a as an inherent force in moving bodies, prefiguring concepts of . Practical engineering flourished with Ismāʿīl al-Jazarī (1136–1206 CE), whose Book of Knowledge of Ingenious Mechanical Devices detailed over 100 automata, including crankshafts, camshafts, and programmable machines powered by water and gears, bridging theoretical with applied . Astronomy intersected with physics through kinematic models and observational instruments, enhancing understandings of motion and gravity. Nasīr al-Dīn al-Ṭūsī (1201–1274 CE) developed the "Ṭūsī couple," a geometric device resolving from circular ones, which resolved Ptolemaic inconsistencies and influenced . These efforts, supported by institutions like the in , emphasized empirical data from observatories, such as those in , and trigonometric tools refined by al-Battānī (858–929 CE), whose precise solar and lunar tables advanced . Overall, medieval Islamic physics not only preserved ancient knowledge but innovated through experimentation, profoundly shaping the trajectory of global scientific thought.

Historical Context

Influences from Ancient Traditions

The medieval Islamic scholars built upon traditions by systematically translating and commenting on key texts, particularly those of , which formed the bedrock of early Islamic physics. (d. 873) and his school in 9th-century played a pivotal role in this process, translating over 100 Greek works into Syriac and then Arabic, including Aristotle's Physics rendered by Hunayn's son Ishaq ibn Hunayn (d. 911). These translations preserved and critiqued Aristotelian concepts such as natural motion—whereby the four elements (earth, water, air, and fire) seek their natural places, with heavy elements like earth moving downward and light ones like fire upward—and the theory of the elements as the fundamental constituents of matter. Commentaries by scholars in the Baghdad school, influenced by Greek commentators like , adapted these ideas to Islamic intellectual frameworks, emphasizing empirical scrutiny while maintaining the hierarchical cosmology of sublunary elemental changes and celestial eternal motion. Ptolemaic astronomy was similarly incorporated through translations of Ptolemy's and Handy Tables in the late , which Islamic astronomers refined by creating over 200 zījes (astronomical tables) based on new observations to update parameters like planetary eccentricities. These works integrated Ptolemaic geocentric models—featuring deferents, epicycles, and equants—with , employing theorems such as the and early (sines and cosines) to compute planetary longitudes and spherical positions, thus laying geometrical foundations for physical models of . , translated and commented upon in the same translational efforts, provided the rigorous deductive framework essential for analyzing physical phenomena like motion and within Islamic science. Indian influences complemented these Greek imports, particularly through the adaptation of Brahmagupta's (d. 668) astronomical tables and numerical systems by scholars like (d. c. 850). Brahmagupta's Brahmasphutasiddhanta (c. 628), translated into Arabic as Zij al-Sindhind around 773 under Caliph , introduced decimal place-value notation, the zero concept, and sine tables for astronomical calculations, which al-Khwarizmi incorporated into his Zij and Kitab al-Jabr wa-l-Muqabala, standardizing Indian methods for Islamic use in computing planetary positions and solving equations relevant to physical measurements. Early adaptations often reconciled ancient ideas with Islamic theology, as seen in the work of (d. c. 870), who rejected Aristotle's notion of an eternal in his treatise On First Philosophy. Drawing on Aristotelian arguments against actual infinities but aligning them with Quranic creation ex nihilo (e.g., Koran 36:79–82), al-Kindi posited a temporally finite cosmos brought into being by God as the simple, unitary First Cause, thus critiquing and theologically harmonizing Greek physics with monotheistic principles.

Development of Scientific Method

In the medieval Islamic world, the development of the in physics represented a pivotal shift toward empirical rigor, integrating , formulation, and controlled experimentation to challenge and refine inherited philosophical traditions. Building briefly on Greek influences such as Aristotle's logic, scholars emphasized verifiable over speculative reasoning, laying groundwork for modern . This evolution was marked by a commitment to systematic testing, where physical phenomena were probed through repeatable procedures rather than deductive assertion alone. Philosophical underpinnings for this methodological advancement were provided by (c. 872–950), who synthesized reason with empirical observation in his critiques of Aristotelian metaphysics. In works like the Book of Letters and On the One and Unity, reconstructed metaphysics as a , distinguishing "being" as both a mental and an external while rejecting existence as a mere . He applied Aristotelian methods from the to resolve theological disputes, such as God's , by prioritizing rational demonstration supported by observable principles over unexamined assumptions. This framework encouraged later physicists to blend logical analysis with direct scrutiny of natural processes. The integration of with physics further strengthened this empirical approach, exemplified by (c. 780–850), whose enabled precise physical modeling. In Kitāb al-jabr wa al-muqābala, developed systematic methods for solving equations, treating unknowns as both numerical and geometrical magnitudes, which bridged abstract math to tangible phenomena. This algebraic ontology influenced medieval Islamic philosophers like and , facilitating models of physical systems such as celestial motions and hydrostatic balances. Ibn al-Haytham (965–1040) epitomized the application of controlled experimentation in physics through his (Kitāb fī al-Manāẓir), where he outlined a cycle of , , and verification. He conducted anatomical dissections of the eye to link its structure to vision mechanisms and designed repeatable experiments to test theories of propagation, such as using a to demonstrate rectilinear rays. These methods refuted earlier emission theories of vision, establishing experimentation as essential for optical physics. Al-Biruni (973–1048) advanced precise measurement techniques, applying to determine with remarkable accuracy. From a mountain vantage, he measured horizon dip angles and heights, yielding a radius estimate of approximately 6340 km—within 1% of the modern value—using formulas like a≈2hδ2a \approx \frac{2h}{\delta^2}, where hh is height and δ\delta is the dip angle. For specific gravity, he invented a conical flask device to compare weights of substances displaced in water, enabling density calculations for minerals and metals that informed hydrostatic principles. Observatories like , established in 1259 under , institutionalized systematic data collection in physics-related astronomy. Equipped with large instruments such as a 40-meter mural quadrant and , the facility gathered quantitative observations from a team of scholars, compiling the Ilkhani Zij tables by 1272. This collaborative effort produced datasets on planetary positions, fostering non-Ptolemaic models and emphasizing empirical verification over theoretical conformity.

Optics

Theories of Vision and Light Propagation

In medieval Islamic scholarship, theories of vision and marked a significant departure from models, particularly the extramission theories espoused by and , which posited that visual rays emanated from the eye to "touch" objects for perception. These ideas were critiqued for failing to explain phenomena like eye damage from bright sunlight, as rays from the eye would imply vulnerability to external sources rather than the reverse. (c. 965–1040), in his seminal Kitab al-Manazir (), decisively rejected extramission in favor of an intromission model, arguing that vision occurs when rays from objects enter the eye, forming an image on the through geometric projection. This framework emphasized that travels in straight lines from luminous sources or illuminated objects, enabling the eye to receive structured visual forms without emitting anything outward. Al-Kindi (c. 801–873), an early pioneer, contributed foundational ideas in his treatise De Radiis (On Rays), describing light as propagating in straight lines from sources like the sun or stars, influencing both physical and metaphysical interactions. He viewed rays as carriers of force, extending beyond mere vision to affect matter at a distance, though his work retained elements of emission compatible with earlier traditions. Building on this, Ibn Sina (Avicenna, 980–1037) refined the conception in his Kitab al-Shifa (Book of Healing), portraying light not as a corporeal entity but as a sensible quality inherent to transparent media, transmitted instantaneously across space without measurable delay. This instantaneous propagation aligned light with other perceptual qualities like color, distinguishing it from slower-moving bodies and underscoring its role in immediate sensory experience. Ibn al-Haytham grounded his intromission theory in empirical demonstrations, notably using the —a darkened chamber with a small —to show how light rays project inverted images of external objects onto a surface, confirming straight-line and refuting emission models. By observing solar eclipses through this device, he illustrated that light enters the eye passively, forming a coherent based on the geometry of rays from the object. Theological dimensions enriched these physical theories, as seen in Al-Ghazali's (1058–1111) Mishkat al-Anwar (Niche of Lights), where light symbolizes divine emanation, illuminating creation and human perception as a manifestation of God's transcendent reality. Al-Ghazali integrated optical insights with Sufi , positing that physical light rays reflect a higher spiritual light that enables true knowledge, bridging empirical observation and divine ontology without contradicting intromission principles.

Refraction and Optical Devices

In the late , the Persian mathematician Ibn Sahl (c. 940–1000) made a groundbreaking contribution to the understanding of through his geometric derivation of what is now recognized as a precursor to . Working at the court of , he formulated the relationship between the angles of incidence and refraction for light passing through planar and spherical interfaces, stating that the ratio of the sines of these angles remains constant for a given medium. This was detailed in his 984 treatise On Burning Instruments (Kitāb al-ḥarrāqāt), where he applied the principle to optimize the focusing properties of lenses and curved mirrors. The law can be expressed as: sin⁡isin⁡r=n\frac{\sin i}{\sin r} = n where ii is the angle of incidence, rr is the angle of refraction, and nn is a constant depending on the refractive indices of the media involved. Ibn Sahl's work marked the first quantitative treatment of refraction independent of earlier approximations, enabling precise calculations for optical paths. Building on Ibn Sahl's foundation, Ibn al-Haytham (965–1040), also known as Alhazen, advanced the quantitative study of refraction in his monumental Book of Optics (Kitāb al-Manāẓir, c. 1011–1021). He compiled extensive tables of refraction angles for light transitioning between air, water, and glass, correcting inaccuracies in Ptolemy's earlier measurements by conducting controlled experiments with refraction instruments. Ibn al-Haytham also analyzed atmospheric refraction, explaining phenomena such as the apparent elevation of celestial bodies near the horizon and the formation of rainbows as resulting from dispersion, refraction, and internal reflection within spherical water droplets in the atmosphere. His calculations demonstrated that rainbows arise from sunlight undergoing two refractions and one reflection in raindrops. Later, Kamāl al-Dīn al-Fārisī (1267–1319) built on this by experimenting with a water-filled glass sphere to confirm the mechanism and calculate that the primary bow corresponds to a deviation angle of approximately 42 degrees. These insights provided a mechanistic understanding of optical bending in layered media, emphasizing empirical verification over qualitative descriptions. Practical applications of and reflection emerged in the development of optical devices, including lenses and burning mirrors. Ibn Sahl's explicitly described concave mirrors and lenses designed to concentrate sunlight for igniting fires, using his refraction law to determine optimal curvatures for maximum focal intensity. These advancements in and optical devices profoundly influenced European science after Latin translations of key Arabic texts circulated in the 13th century. Ibn al-Haytham's directly shaped Witelo's Perspectiva (1270), which adopted and expanded his tables and atmospheric analyses, while Ibn Sahl's law informed later works on lens design. By the 17th century, drew on these foundations in Ad Vitellionem Paralipomena (1604), integrating principles into his model of retinal , thus bridging medieval Islamic to modern astronomy and .

Astronomy

Critiques of Geocentric Models

In the early 11th century, (Alhazen, c. 965–1040) mounted a significant challenge to in his treatise al-Shukūk ʿalā Baṭlamyūs (Doubts Concerning , c. 1020), arguing that key elements of the model violated fundamental physical principles. He specifically critiqued the equant point, a device in 's system where the center of a planet's epicycle moves uniformly around the equant but not the deferent's geometric center, rendering the motion non-uniform and thus physically implausible under Aristotelian assumptions of uniform for celestial bodies. demonstrated mathematically that this configuration led to inconsistencies, as the epicycle's center could not maintain uniform speed relative to both points simultaneously, undermining the model's claim to represent real . He extended this to epicycles, rejecting them as imaginary constructs rather than descriptions of actual physical bodies, insisting that astronomical theories must align with observable rather than mere mathematical expedients. These arguments initiated a "tradition of doubt" in Islamic astronomy, prioritizing physical realism over 's authority. Al-Biruni (973–1048), another pioneering critic, incorporated precise observational measurements into his challenges against geocentric assumptions, particularly in works like al-Qānūn al-Masʿūdī (The Masudic Canon, c. 1030). He calculated the inclinations of planetary orbits to the with high accuracy, using trigonometric methods to determine angles such as Mercury's 7° inclination and Venus's 3°25', revealing discrepancies in Ptolemy's parameters that suggested the model inadequately captured orbital tilts without additional adjustments. These measurements, derived from sightings in Ghazna and , highlighted inconsistencies in predicting planetary latitudes, prompting Al-Biruni to hypothesize Earth's daily rotation on its axis as a viable alternative to fixed geocentrism, arguing it could explain apparent stellar motion without invoking complex deferents. He supported this with geometric proofs, noting that rotation would simplify explanations for phenomena like the varying lengths of day and night, though he remained neutral on full , emphasizing empirical verification over dogmatic adherence. By the 13th century, Nasir al-Din al-Tusi (1201–1274) advanced these critiques through innovative geometric models at the Maragheh observatory, culminating in his Tadhkira fī ʿilm al-hayʾa (Memoir on the Science of Astronomy, c. 1260). The Tusi couple, a device comprising a smaller circle rotating inside a larger one (twice its diameter) in the opposite direction at double speed, generated linear oscillation from uniform circular motions, resolving Ptolemaic inconsistencies in planetary latitudes without resorting to the equant or non-uniform speeds. This mechanism allowed al-Tusi to reformulate the lunar and planetary models using only eight spheres in uniform rotation, eliminating the crank mechanism in Ptolemy's lunar theory that violated physical uniformity and achieving predictions accurate to within 10 arcminutes. Al-Tusi's approach integrated physics by ensuring all motions adhered to Aristotelian principles, critiquing Ptolemy's observational proofs of Earth's fixity as inconclusive and paving the way for non-geocentric refinements. Observational programs at major Islamic observatories further underscored these physical challenges to uniform in Ptolemaic astronomy. In , under Caliph (r. 813–833), systematic measurements of solar and lunar positions in the revealed discrepancies in Ptolemy's tables, such as errors in timings that implied non-uniform orbital speeds for the . Similarly, the 13th-century produced refined data on planetary retrogrades, exposing inconsistencies in Ptolemy's assumptions about fixed equators and uniform deferent motions through adjusted epicycle radii and inclinations, highlighting the geocentric model's physical limitations in matching without ad hoc modifications. These observations, combining astrolabes and quadrants, compelled astronomers to prioritize physical principles. Islamic physicists also integrated into critiques of geocentric cosmology, particularly challenging the Aristotelian notion of solid crystalline spheres carrying celestial bodies. Ibn al-Haytham argued in his al-Shukūk ʿalā Baṭlamyūs (c. 1020) that multiple solid spheres would impede from distant , as through successive crystalline layers would distort rays in ways unobserved in the uniform transmission of across the heavens. This physical objection, grounded in studies of bundles through glass spheres, supported views of fluid or imaginary orbs, aligning astronomy more closely with observable principles rather than rigid mechanical carriers.

Celestial Mechanics and Gravity

In the medieval Islamic world, scholars began to explore the physical principles underlying , challenging and extending Aristotelian notions of motion and . While distinguished between terrestrial bodies, governed by linear motions toward or away from the Earth's center, and celestial bodies, which moved in perfect circles with uniform speed due to their quintessence, Islamic physicists sought to apply unified physical laws to both realms. This effort linked astronomical observations to concepts of attraction and , laying groundwork for later developments in . Al-Khazini (c. 1115–1130), in his Book of the Balance of Wisdom (Mizan al-Hikma), advanced early ideas on by differentiating between , , and , and proposing that the weight of a body varies with its distance from the Earth's center. He argued that the heaviness (al-thiqal) of an object is directly proportional to its distance from this center, stating that "the relation of to is as the relation of distance to distance from the center." This formulation represented a significant departure from strict Aristotelian constancy of , recognizing variation based on position, though the direct proportionality contrasted with later inverse laws. Al-Khazini's work integrated hydrostatic balances with these gravitational insights, using them to explain why bodies seek the Earth's center. Ibn Bajjah (Avempace, 1085–1138) contributed to theories of natural motion applicable to celestial bodies, extending while critiquing its rigid separations. In his commentaries on Aristotle's Physics and De Caelo, he analyzed ordered celestial movements as natural, akin to elemental motions on , and proposed that uniform in the heavens could arise from inherent tendencies without constant external movers. This approach implied a continuity between terrestrial and celestial dynamics, where forces like inclination (mayl) could govern both, foreshadowing unified theories of motion. Ibn Bajjah's ideas preserved and modified Greek principles, influencing later astronomers by emphasizing physical causes over purely metaphysical ones. Al-Biruni (973–1048) further developed concepts of universal attraction, positing that gravitational pull toward the Earth's center was not unique to our planet but a property shared by all heavenly bodies. In works like The Mas'udic Canon, he described objects falling due to an attractive force directed at the Earth's center, extending this to suggest that celestial bodies exert similar attractions, pulling toward their own centers. This universal perspective challenged Aristotelian exclusivity of terrestrial gravity, integrating it into a broader cosmic framework supported by his precise measurements of Earth's radius and planetary positions. Critiques of the Aristotelian between terrestrial and celestial physics gained traction among Islamic scholars, who argued for a unified applicable across the cosmos. Ibn Sina (, 980–1037) attempted such unification in his Physics and De Caelo commentaries, explaining celestial through emanated intelligences and souls that impart physical inclination (mayl) to spheres, bridging sublunary linear forces with supralunary uniformity. He critiqued pure quintessence by subordinating it to physical causes, allowing gravity-like attractions to influence heavenly dynamics without violating observed uniformity. These efforts highlighted tensions in Aristotelian models, where celestial perfection clashed with empirical irregularities. Observational data from planetary motions provided empirical support for these non-uniform force ideas, as scholars noted deviations from perfect circles that implied varying attractions. Al-Biruni's detailed records of planetary positions and velocities, for instance, revealed inconsistencies in geocentric models, suggesting dynamic s akin to acting unevenly on celestial bodies. Such data, combined with critiques of Ptolemaic equants from earlier astronomical work, underscored the need for physical explanations beyond static separations, influencing the integration of into astronomy.

Mechanics

Statics and Hydrostatics

In the medieval Islamic world, and formed key branches of , emphasizing principles of equilibrium, balance, and fluid pressures in stationary systems. Scholars built upon ancient Greek foundations, such as those of and , while developing original theoretical frameworks and practical instruments that integrated mathematics, experimentation, and engineering. This work not only refined concepts of weight and but also supported applications in , astronomy, and , fostering precise measurement techniques that influenced later European . Thābit ibn Qurra (836–901), a prominent and physician from , made significant contributions to the theory of centers of gravity and the balancing of levers. In his treatise Kitāb fī Ṣifat al-wazn (Book on the Nature of Weight), he analyzed equilibrium conditions for equal-armed balances, deriving mathematical proofs for how weights achieve stability based on their positions relative to the fulcrum. Thābit's Kitāb fī ‘l-qarasṭūn (Book on the ) further elaborated a deductive theory of the unequal-armed balance, treating it as a mathematical discipline that explained through geometric proportions rather than mere empirical observation. These works, preserved in multiple Arabic manuscripts and later translated into Latin, marked a shift toward a more systematic of weights (‘ilm al-athqāl), distinguishing from practical mechanics. Ibn al-Haytham (965–1040), known in the Latin West as Alhazen, advanced by adapting and expanding Archimedean principles on and . In his recension of Archimedes' , he provided a detailed mathematical treatment of how submerged or partially immersed objects experience upward buoyant forces equal to the weight of the displaced fluid, incorporating geometric proofs to explain stability in fluids. Ibn al-Haytham's explorations of varying heaviness based on distance from the Earth's center, as preserved in later compilations, integrated these ideas with broader theories of and equilibrium, emphasizing experimental verification through balanced setups. His contributions, though partially surviving through quotations, underscored the role of in understanding stationary fluid systems. Experimental methods in relied heavily on refined weighing instruments like (qarasṭūn) and equal-armed balances (mīzān), which enabled precise comparisons of weights and densities. These devices, regulated under the ḥisba system for market accuracy, allowed scholars to test equilibrium under various conditions, such as immersion in fluids, by adjusting arms and counterweights to achieve balance. Al-Isfizārī (fl. early ), in his corpus on weights, systematized the , describing its mechanical principles and applications for verifying specific gravities through static setups that minimized errors from or misalignment. Such methods, detailed in treatises like al-Khāzinī's Kitāb mīzān al-ḥikma, promoted a blend of and practice, ensuring reproducible results in hydrostatic experiments. Al-Khāzinī (fl. 1115–1130), an and under Seljuk patronage, innovated with his hydrostatic balance, a pivotal instrument for measuring specific gravities of substances. Described in Kitāb mīzān al-ḥikma (The Book of the Balance of Wisdom), the device featured a beam balance with a suspended pan for the sample and a fluid reservoir, allowing effects to be quantified by observing shifts in equilibrium when substances were immersed. This design improved upon earlier models by incorporating adjustable arms and precise calibrations, enabling determinations of densities for solids, liquids, and alloys with high accuracy, as verified through extensive trials. Al-Khāzinī's work integrated hydrostatic theory with practical utility, advancing the experimental foundation of in Islamic science. Engineering applications of and appeared in the hydraulic devices of Badi‘ al-Zamān al-Jazarī (1136–1206), whose inventions demonstrated equilibrium principles in stationary systems. In Kitāb fī ma‘rifat al-ḥiyal al-handasiyya (Book of Knowledge of Ingenious Mechanical Devices), al-Jazarī detailed water-raising machines, such as the third device—a counterweighted scoop-wheel driven by flow—that maintained static balance through geared mechanisms and pivots to lift without external power. These systems relied on precise weight distribution and fluid equilibrium to ensure stable operation, optimizing in arid regions while showcasing the integration of into functional . Al-Jazarī's designs, blending and , exemplified how hydrostatic balance supported broader mechanical innovations.

Dynamics and Impetus Theory

In the medieval Islamic world, dynamics emerged as a key area of inquiry within natural philosophy, building on Aristotelian foundations while introducing novel concepts to explain the initiation and sustenance of motion, particularly in projectiles. Scholars critiqued and refined Aristotle's model, which posited that projectile motion required continuous propulsion by the surrounding medium, such as air, to overcome resistance. A pivotal contribution came from Ibn Sina (Avicenna, d. 1037), who introduced the concept of mayl (inclination) as an internal, impressed force that sustains after the initial throw. According to Ibn Sina, this mayl qasri (violent inclination) is a permanent potency acquired by the projectile from the thrower, enabling it to continue moving by displacing resisting media like air, rather than relying on the medium itself as the mover. He critiqued Aristotle's notion of void resistance, arguing that in a hypothetical void, motion would persist indefinitely due to the unchanging mayl, thereby reinforcing the impossibility of a true void while providing a more coherent explanation for observed projectile trajectories. This theory marked a shift toward viewing motion as driven by an internal principle, influencing later European impetus theories. Al-Farabi (d. 950), in his commentaries on Aristotle's Physics, categorized motions dynamically according to their causes, distinguishing between those governed by natural tendencies—such as elemental heaviness or lightness—and those influenced by will or external compulsion. He expanded Aristotle's categories to include positional motion for celestial bodies, emphasizing that voluntary motions, driven by rational souls or intellects, differ from purely natural ones by incorporating purposeful agency. This framework highlighted the interplay between inherent natures and willful intervention, laying groundwork for understanding complex dynamic systems in both terrestrial and cosmic contexts. Building on these ideas, Abu'l-Barakat al-Baghdadi (d. 1164/5) advanced a more radical view, positing that inherently causes changes in motion, including , rather than merely sustaining . He argued that an impressed in projectiles expends itself over time, interacting with natural inclinations to produce successive increments of motion, which explains why falling bodies speed up. This conceptualization prefigured modern notions of as the agent of motion's variation, rejecting Aristotle's uniform motion under constant and integrating violent and natural inclinations dynamically. These theoretical developments found practical application in texts, where principles of impetus and force were employed to optimize catapults and . For instance, in the 12th-century treatise by Mardi ibn Ali al-Tarsusi, descriptions of traction trebuchets and mangonels incorporated dynamic considerations, such as the imparted inclination from tensioned ropes to maximize range and impact against fortifications. Such works demonstrated how mayl-like forces could be engineered for sustained motion in warfare, blending philosophical dynamics with empirical adjustments for and . Philosophically, Islamic thinkers adapted Aristotle's definition of motion as the actualization of potentiality, infusing it with Neoplatonic and theological elements to reconcile divine agency with natural processes. and Ibn Sina viewed motion as a hierarchical emanation from the Necessary Existent, where potentialities are realized through intermediary causes like natures or souls, avoiding pure while preserving . This adaptation emphasized motion's teleological aspect, with dynamic forces serving as instruments of divine wisdom in the .

Kinematics and Acceleration

In the medieval Islamic world, kinematics advanced beyond Aristotelian uniform motion to encompass descriptions of non-uniform speeds and changes in , laying groundwork for understanding through theoretical and geometric analyses. Scholars critiqued and refined Greek models, emphasizing the role of inclination (mayl) in sustaining and altering motion. This period saw a shift toward recognizing that falling bodies do not maintain constant but due to inherent forces, with contributions that anticipated later European developments in . Al-Biruni (973–1048 CE), a Persian polymath, realized that acceleration is connected with non-uniform motion in falling bodies, proposing that the speed increases due to the Earth's attractive force. This insight, derived from observational analysis, highlighted non-uniform motion as a fundamental aspect of kinematics. Ibn Sina (Avicenna, 980–1037 CE), in his Kitab al-Shifa (The Book of Healing), analyzed projectile paths as resulting from compound motions: an initial violent inclination (mayl qasri) imparted by the thrower causes straight-line progression, compounded with the body's natural elemental tendency toward circular motion within its sphere. This geometric conceptualization explained the curved trajectory without relying on air propulsion, positing that the impressed force persists until dissipated by resistance. Such models used Euclidean geometry to decompose and visualize paths, providing a qualitative framework for non-uniform trajectories. Building on these ideas, Abu'l-Barakat al-Baghdadi (c. 1080–1164 CE), in his Kitab al-Mu'tabar, advanced the link between and , asserting that a constant applied produces increasing over time, with proportional to the change in speed rather than sustaining uniform motion. He explained falling bodies' speedup as the continuous addition of mayl against resistance, serving as an early precursor to the modern relation between , mass, and . This theoretical innovation distinguished from its rate of change, emphasizing 's role in kinematic variation. Scholars approximated kinematic behaviors through geometric constructions and observational timing of motions along inclines or from heights, such as towers, to discern patterns in speed changes without advanced . These methods complemented mathematical modeling, where described curved trajectories—approaching parabolic forms in analyses—by resolving them into component lines and circles for predictive visualization. Impetus theory briefly referenced here as a temporary sustainer of motion further informed these kinematic descriptions.

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