Aristotle tried to base his physics on actual observations of the world, but due to inadequate observations and hidden assumptions, nearly all of it is wrong. He separated the cosmos into the terrestrial and celestial regions. In the terrestrial region, all matter is made of a mixture of the four elements. Each element has its natural resting place, and all matter moves to its natural place, unless acted upon by a force. In the celestial region, everything moves in circles. Furthermore, the earth itself is a sphere sitting at rest at the center of the universe.
The second of two episodes on Aristotle.
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