Natural Motion
Objects move toward their proper place. earth and water downward, fire and air upward
Nebula ...
natural motion: In Aristotelian physics, the motion of objects toward their natural places - fire and air upward and earth and water downward.
wind (meteorology) (NASA Thesaurus) A natural motion of the air, especially a noticeable current of air moving in the atmosphere parallel to the Earth's surface.
Aristotle considered this an example of unnatural motion, and it required further explanation. In Aristotle's physics, objects at rest are expected and don't need an explanation.
When they are out of their natural place they have natural motion, requiring no external cause, which is towards that place; so bodies sink in water, air bubbles up, rain falls, flame rises in air. The heavenly element has perpetual circular motion.
Because we make observations from Earth, knowledge of Earth's natural motions is essential. As described above, our planet rotates on its axis daily and revolves around the sun annually. Its axis precesses and nutates.
 See also: Degree, Solar System, Earth, Second, Time
  
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