page_title: History of gravitational theory
section_title: European Renaissance
hierarchical_section_title: History of gravitational theory / European Renaissance
caption_attribution_description: English: Pisa experiment by Galileo Galilei. Drawn by Theresa Knott
context_page_description: In physics, theories of gravitation postulate mechanisms of interaction governing the movements of bodies with mass. There have been numerous theories of gravitation since ancient times. The first extant sources discussing such theories are found in ancient Greek philosophy. This work was furthered by ancient Indian and medieval Islamic physicists, before gaining great strides during the Renaissance and Scientific Revolution, culminating in the formulation of Newton's law of gravity. This was superseded by Albert Einstein's theory of relativity in the early 20th century.
  Greek philosopher Aristotle believed that objects tend toward a point due to their inner gravitas. Vitruvius understood that objects fall based on their specific gravity. In the 7th century CE, Brahmagupta spoke of gravity as an attractive force. The Aristotelian concept of gravity began to be rejected, initially by Islamic physicists, starting in the 11th century with Ibn Sina's theory of impetus. The following century, Abu'l-Barakāt al-Baghdādī described gravitational acceleration. The works of Ibn Sina and al-Baghdādī were translated into Latin by the 14th century, influencing Jean Buridan and Albert of Saxony.
context_section_description: In the 14th century, both the French philosopher Jean Buridan and the Merton College of Oxford rejected the Aristotelian concept of gravity. They attributed the motion of objects to an impetus (akin to momentum), which varies according to velocity and mass; Buridan was influenced in this by Ibn Sina's Book of Healing. Buridan and Albert of Saxony (c. 1320–1390) adopted Abu'l-Barakat's theory that the acceleration of a falling body is a result of its increasing impetus. Influenced by Buridan, Albert developed a square law regarding the relationship between the speed of an object in free fall and either the time or space elapsed. He also theorized that mountains and valleys are caused by erosion—displacing the Earth's centre of gravity. Also in this century, the Merton College developed the mean speed theorem, which was proved by Nicole Oresme (c. 1323–1382) and would be influential in later gravitational equations.
  Leonardo da Vinci (1452–1519) wrote that the "mother and origin of gravity" is energy. He describes two pairs of physical powers which stem from a metaphysical origin and have an effect on everything: abundance of force and motion, and gravity and resistance. He associates gravity with the 'cold' classical elements, water and earth, and calls its energy infinite. Leonardo did not publish his manuscripts and they had no direct influence on subsequent science. By 1514, Nicolaus Copernicus had written an outline of his heliocentric model, in which he recognized Earth's centre as the centre of both its revolution and the Moon's orbit. In 1533, German humanist Petrus Apianus described the exertion of gravity:
  Since it is apparent that in the descent [along the arc] there is more impediment acquired, it is clear that gravity is diminished on this account. But because this comes about by reason of the position of heavy bodies, let it be called a positional gravity [i.e. gravitas secundum situm]
  Galileo Galilei derived his kinematics from the 14th-century Merton College and Jean Buridan. In the early 17th century, Galileo found that, counter to Aristotle's teachings, all objects in free fall tend to accelerate equally in relation to the duration of their fall. In a 1604 letter to Paolo Sarpi, Galileo correctly hypothesized that the distance of a falling object is proportional to the square of the time elapsed.
  In 1609, Johannes Kepler published Astronomia nova, in which he established his first two laws of planetary motion; the first of these determines that planetary orbits are ellipses. Galileo received a copy of this book from Kepler, as well as a letter from Federico Cesi which treats elliptical orbits as common knowledge, but never implemented them himself. Galileo had been trying to determine the path of an object falling from rest towards the center of the Earth, but used a semicircular orbit in his calculation. In his Dialogue Concerning the Two Chief World Systems (1632), he put forth the basic principle of relativity, which establishes that the laws of physics are the same in any system moving at a constant speed in a continuous direction.
  A disciple of Galileo, Evangelista Torricelli reiterated Aristotle's model involving a gravitational centre, adding his view that a system can only be in equilibrium when the common centre itself is unable to fall.
caption: Illustration of Galileo's Leaning Tower of Pisa experiment[g]
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