The Physics of Motion, Impetus, and Projectile Dynamics: How Abu'l-Barakat al-Baghdadi and Ibn al-Haytham Anticipated Newton's Laws

In modern physics education, the formulation of the fundamental Three Laws of Classical Mechanics is universally attributed to Sir Isaac Newton’s 1687 masterwork Philosophiae Naturalis Principia Mathematica.

Yet, centuries before Newton, Galileo Galilei, or René Descartes, the foundational physical concepts of inertia, momentum (impetus), accelerated motion under continuous force, and equal-and-opposite reaction were systematically formulated, mathematically debated, and empirically defended by Islamic polymaths in Baghdad, Cairo, and Isfahan.

By challenging and dismantling the flawed physics of Aristotle—which dominated ancient European thought for over a millennium—scholars such as Ibn Sina (Avicenna), Al-Hasan Ibn al-Haytham (Alhazen), Abu'l-Barakat al-Baghdadi, and Ibn Bajjah (Avempace) laid the direct conceptual foundations of modern kinematics and classical dynamics.

---

1. Dismantling Aristotelian Physics: The Flaw of Anti-Peristasis

Aristotelian physics asserted a fundamental falsehood regarding projectile motion: Aristotle claimed that an object requires a continuous, external physical pusher at every instant to remain in motion. To explain why an arrow continues flying after leaving the bowstring, Aristotelians invented the theory of anti-peristasis—claiming that the displaced air rushes behind the arrow to push it forward.

In the 11th century, Ibn Sina dismantled this dogma in Kitab al-Shifa (The Book of Healing):

"If the motion of a projectile were caused by the pushed air, then an arrow would fly faster if shot into a gale-force headwind! The truth is that the mover imparts to the moved object an internal inclination or power of motion (Mayl), which continues to sustain its velocity until overcome by external air resistance." — Ibn Sina (Avicenna), 11th Century

+-----------------------------------------------------------------------------+
|                 EVOLUTION OF CLASSICAL MECHANICS: ARISTOTLE TO NEWTON       |
+-----------------------------------------------------------------------------+
| Aristotelian Physics     | External air pushes moving objects continuously. |
| Ibn Sina's *Mayl*        | Mover imparts internal inclination (*Mayl/Impetus*)|
| Al-Baghdadi's Mechanics  | Continuous force causes acceleration ($F \propto a$)|
| Ibn Bajjah's Rule        | Velocity equals motive force minus resistance.   |
| Newton's Laws (1687)     | Formal mathematical synthesis in the Principia.  |
+-----------------------------------------------------------------------------+

---

2. Anticipating Newton's First Law (The Law of Inertia)

Newton's First Law of Motion states: An object at rest stays at rest, and an object in motion stays in motion with the same velocity and in the same direction unless acted upon by an unbalanced external force.

Centuries earlier, Ibn Sina articulated this exact principle of perpetual inertial motion in a vacuum:

"If a body were to move in a pure vacuum where it encounters no external resistance (such as friction or air), it would continue to move indefinitely with uniform velocity in a straight line, never coming to rest on its own." — Ibn Sina, Kitab al-Shifa

Simultaneously, in his optical and physical experiments, Al-Hasan Ibn al-Haytham (965–1040 CE) stated in Kitab al-Manazir:

"A moving body encounters resistance, and if the force of motion ceases to be opposed by resistance, it preserves its movement perpetually."

---

3. Abu'l-Barakat al-Baghdadi: Anticipating Newton's Second Law ($F = ma$)

The greatest mechanical breakthrough of the Islamic Golden Age was achieved by the 12th-century Baghdad philosopher-physicist Hibat Allah Abu'l-Barakat al-Baghdadi (c. 1080–1165 CE) in his masterpiece Kitab al-Mu'tabar.

Aristotle had claimed that a constant force produces a constant velocity ($F \propto v$). Al-Baghdadi proved this false, demonstrating that a constant continuous force produces accelerated motion:

"When a force operates continuously upon a body, it does not produce a uniform speed; rather, it produces an acceleration—imparting successive increments of speed at each successive interval of time." — Abu'l-Barakat al-Baghdadi, 12th Century

+-----------------------------------------------------------------------------+
|                 AL-BAGHDADI'S FORCE-ACCELERATION PRINCIPLE                  |
+-----------------------------------------------------------------------------+
| Aristotelian Error       | Force ($F$) = Mass ($m$) × Constant Velocity ($v$)|
| Al-Baghdadi's Discovery  | Continuous Force ($F$) generates Acceleration ($a$)|
| Newtonian Formulation    | $\mathbf{F = m \cdot a}$ (Second Law of Motion)  |
| Free-Fall Gravitation    | Speed of a falling body increases continuously   |
|                          | because gravitational attraction acts constantly!|
+-----------------------------------------------------------------------------+

Al-Baghdadi applied this principle to gravitational free-fall, correctly explaining why falling rocks strike the ground with greater destructive force the higher they fall from: because gravity acts as an uninterrupted force that constantly increases the object's speed (Acceleration).

---

4. Ibn Bajjah (Avempace) and Newton's Third Law (Action and Reaction)

In 12th-century Zaragoza (Islamic Spain), the Andalusian polymath Ibn Bajjah (Avempace) formulated the relationship between motive power and mechanical resistance:

• Ibn Bajjah's Law: The velocity of an object is proportional to the difference between the motive force ($P$) and the medium's resistance ($M$): $\text \propto (P - M)$.
• Action and Reaction: Ibn Bajjah analyzed collisions, showing that every exerted force encounters a corresponding resistance from the opposing body—a conceptual formulation directly cited by Galileo Galilei in his early treatises (Pisan Dialogues) and later refined into Newton’s Third Law (To every action there is an equal and opposite reaction).

---

5. The Transmission Pathway to the Scientific Revolution

In the 14th century, French scholastic philosophers Jean Buridan and Nicole Oresme at the University of Paris adopted the Arabic concept of Mayl, translating it into Latin as Impetus.

Buridan’s Impetus Theory—which directly bridged medieval mechanics to Galileo, Descartes, and Newton—was an exact translation of the mechanical principles formulated by Ibn Sina and Abu'l-Barakat al-Baghdadi three centuries prior.

---

6. Conclusion: Honoring the Pioneers of Modern Physics

Science is a grand, continuous relay race across civilizations. The universal laws of mechanics that allow modern aerospace engineers to launch rockets into orbit and calculate planetary trajectories were not conceived in a sudden historical vacuum.

They were forged through centuries of fearless empirical inquiry by Muslim physicists who dared to question classical Greek dogma, proving that the physical cosmos is governed by rational, discoverable mathematical laws established by the Supreme Architect of the universe.