Phil 201 1st EditionExam # 2 Study Guide Lectures: 1 - 8Lecture 9 (February 24)The Ptolemaic (geocentric) model of the cosmosQ: In what century did Ptolemy produce his work?90 ADQ: One of the motivations for epicycles was to give an explanation for retrograde motion. What is retrograde motion, and how is it explained in the Ptolemaic model?Retrograde motion is motion that is opposite to another object. Retrograde motion is shown by the epicycles rotating apposite directions.Q: Ptolemy actually used multiple epicycles (epicycles on top of epicycles) in his models. His final model of the solar system contained approximately 80 circles (!). Why did he do this? What did he gain by adding more epicycles?Having all of these circles allowed Ptolemy to tweak his system by varying size and rotation of the circleThe "two realms" doctrineQ: How does the "terrestrial" realm differ from the "celestial" or "heavenly" realm?The laws of “terrestrial” are different than the laws of “heaven”.The terrestrial realm is always changing and imperfect while the heavenly realm is unchanging ad perfect.Copernicus - heliocentric modelQ: How did Copernicus' model differ from Ptolemy's, and how was it similar?Copernicus’s model is very similar to Ptolemy but Copernicus switches the Sun and the Earth. Ptolemy had earth-centered. They both use perfect circle and epicycles; Copernicus uses epicycles to fine tune system. They both use many (70-80) epicycles.Q: How is retrograde motion explained in Copernicus' model?Q: Did Copernicus eliminate the use of epicycles altogether?No, he used epicycles to fine-tune his system to fit data already observed.Kepler - three laws of planetary motionQ: What was Kepler trying to explain when he developed his early model of the cosmos based on relationships between the five Platonic solids?The five Platonic solids could explain the distance relationships between the six planets that were known at that time. All solids were put in a sphere thatrepresented Saturn’s orbit.Q: Why did Kepler abandon the theory that all planetary orbits must be perfectly circular?He got observed data from Tycho Brahe and calculated the true orbit of Mars. Then he looked at alternative shapes of orbits that God could have created. Q: What is Kepler's first law of planetary motion (the "Ellipse law")?Planets move in ellipses, not circles.Q: What is Kepler's second law of planetary motion (the "equal areas" law)?Planets will speed up when closer to the sun and slow down further from the sun but they “sweep out equal areas in equal times”.Q: What is Kepler's third law of planetary motion (the law that relates orbital distances to orbital periods)?There is a precise relationship of how long it takes a planet to orbit the Sun and the average distance of it from the sun. The closer to the sun, the shorter the year.Galileo - telescopic observations of Moon and JupiterQ: How did Galileo use his observations of mountains on the moon, and satellites orbiting Jupiter, to support the Copernican model of the cosmos?Since the moon showed marks and mountains, it shows that it is not entirely different from Earth. This supports the statement that heavenly bodies are not different than earthly bodies. This is evidence against the two realms.Newton - laws of motion, law of universal gravitationQ: What is Newton's law of universal gravitation?Every thing is attracted to other every other thing, with forces in proportion to each thing’s mass and inversely to the distance between them. What did Newton find troubling about his law of gravity?Newton didn’t like the “action at a distance” part of his law; he considered it an occult power. He wanted a mechanistic explanation.How is the physics of fallings bodies (example: the trajectory of a cannonball) related to the physics of orbiting bodies (example: the moon orbiting the earth), in Newtonian physics?Thinking of a cannonball, it traces a parabolic path. If shot with enough velocity, the cannonball will curve around the earth with the shape of the earth. Falling and orbiting are the same thing, orbiting just has too much horizatonal velocity that it keeps missing the Earth.How does this relationship undermine the "two realms" doctrine?Blackboard Notes, Philosophy 201. Author: Kevin