molecular motion
The three basic modes of molecular motion, as originally described by Rudolf Clausius. [4]
In science, motion is the movement of a body through a distance of space, at a constant velocity, or at an accelerated speed, in an inertial reference frame.

In circa 350BC, Greek philosopher Aristotle, who considered the earth to be spherical, albeit stationary and at the center of the universe, explained motion as the realization of the specific nature of a specific body, with natural motion defined as the tendency of a body to seek its natural place, and with the all bodies conceptualized as being comprised of four elements: earth, water, air, fire, each of decreasing density, respectively. [1] In regards to the element fire and motion, according to Aristotle:

“For any two portions of fire, small or great, will exhibit the same ratio of solid to void; but the upward movement of the greater is quicker than that of the less.”

Aristotelian universe
A pre-Aristotle flat earth model (c.350BC), wherein earth (unmovable), the center of the universe, was the heaviest of elements, followed by water, air, and fire, in decreasing density, and "motion" was tendency of bodies to seek or achieve their natural place in the order of the universe; a model that was part physics (four elements and two forces), i.e. Empedocles standard model (450BC), and part theology, in particular Nun cosmology (3100BC), which included the notion of good and evil.
Hence, denser elements tend to rise; lighter elements fall; earth is the heaviest element; fire the lightest.

In Aristotle's time, according to his own account, all pre-Socratic philosophers, including the school of the atomic theorists, Leucippus (c. 440 BC) and Democritus (c. 460–370 BC), believed in a flat earth universe. [2]

In 1687, English physicist Isaac Newton introduced the laws of motion, in the form of three equations (first law of motion, second law of motion, and third law of motion), according to which motion was the result of causative "forces". [3]

The following are related quotes:

“As to the question of the origin and nature of motion in things, they, Leucippus and Democritus, too, ignored, just as blithely as the others.”
— Aristotle (c.350BC), Metaphysics (985b4-22)

Motion an effect by which a body either changes, or has a tendency to change its position: that is to say, by which it successively corresponds with different parts of space, or changes its relative distance to other bodies.”
Baron d’Holbach (1770), The System of Nature (pgs. 16)

1. (a) Koyre, Alexandre. (1978). Galileo Studies (ch. 1). Humanities Press.
(b) Mirowski, Philip. (1989). More Heat than Light: Economics as Social Physics, Physics as Nature’s Economics (pg. 110). Cambridge University Press.
2. (a) Aristotle. (c.350BC). De Caelo, 294b, 13-21.
(b) Fontaine, Didier. (2002). “Flat Worlds: Today in Antiquity”, Memorie della Societa Astronomica Italiana, 3(1): 257-62.
3. Newton, Isaac. (1687). Principia. Publisher.
4. Williams, R.J.P. and da Silva, J.R.R. Frausto. (2008). The Chemistry of Evolution: the Development of our Ecosystem (pg. 80). Elsevier.

See also
Perpetual motion
Perpetual motion of the first kind
Perpetual motion of the second kind
Perpetual motion of the living kind
Induced movement

External links
Motion (physics) – Wikipedia.

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