Lecture02_10 - Physics19 GreatIdeasofPhysics Lecture2:

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Physics 19 Great Ideas of Physics Lecture 2: From Aristotle to Copernicus
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Aristotle: The Realist An orphan who became a student at  Plato’s Academy He tutored Alexander the Great and  founded his own school, the Lyceum Aristotle held that each type of  substance had a natural place, and had  a natural tendency to move toward it Heavy things naturally fall to the earth Celestial objects naturally move in circles The way things behave is due to their nature  and composition Aristotle’s ideas dominated Western  thinking for almost 2000 years! Aristotle (384-322 BC)
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Aristotle and the  Geocentric Universe
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Aristotle and the Geocentric Model According to Aristotle’s  idea of “natural motion”: The Earth  had  to be at the  center of the universe If not it would fall there! The Earth is too big to move! The stars and planets  had   to move in perfect, circular  orbits The heavens must be perfect,  and therefore eternal Circular motion is eternal and  therefore “perfect”
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Aristarchus (~310 – 230 BC) Proposed a heliocentric  model (complete with  rotating Earth) in ancient  times Measured (poorly) the  Earth-Sun distance Sound method, bad data Deduced that Sun is  much larger than Earth If the Earth is too big to  move, how can the Sun?!
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The Problem of Parallax Aristotle devised a clever  argument against a  heliocentric model: If the earth moves relative to  the stars, the angle between  two stars should change as  the Earth gets closer and  farther away He was right! Why wasn’t this noticed?
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“Saving the Appearances” Until the last few centuries, our knowledge of the  heavens was limited to: The Sun The Moon The stars – seemingly never changing The five planets Mercury, Venus, Mars, Jupiter and Saturn
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Lecture02_10 - Physics19 GreatIdeasofPhysics Lecture2:

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