Aritstotle: 384-322 BC

1. Aritstotle: 384-322 BC Aristotle was the student of Plato who was the student of Socartes. Aristotle was an accomplished individual whose work would influence the course of history: Teacher – Most Famous Student : Alexander the Great First Biologist Cosmologist Physicists - Developed Aristotelian Mechanics Philosopher

2. Aristotle Aristotle was a keen observer of nature. By looking at nature, he attempted to deduce the workings of nature. The weakness of Aristotle and his followers was the complexity of the world. Unlike Galileo and modern scientists who build controlled experiments which are designed to restrict the number of things which might change (temperature, pressure, volume, etc.), Aristotle’s followers worked with systems where hundreds of things changed.

3. Aristotelian Mechanics According to Aristotle, all objects on Earth have a natural motion (rest) and a preferred location in the universe. 2) A force (push or pull) is required to cause an object on Earth to move or leave its natural location. 3) Applying a force to an object gives the object “impetus.” As the object moves, it uses up impetus. once the object is out of impetus, the object returns to rest at its natural location.

4. Aristotelian Mechanics 4) According to Aristotle, the universe is composed of five elements (different types of mater): Earth Water Air Fire Eather 5) Outer space was filled with Eather, a fluid through which the stars and planets traveled with no resistance. 6) All object on Earth were composed of various amounts of the remainingfour elements.

5. Aristotelian Mechanics 7) The Earth is a stationary sphere at the center of the universe. 8) The natural place of each element in the universe was determined by observation: Eather Fire Air Water Earth

6. Aristotelian Mechanics Example: According to Aristotle, when we burn a log, we release fire and air that was contained in the log. The smoke and fire rise because the natural location of fire and air is above that of earth.

7. Falling Body Predictions 1) Heavier objects fall toward the Earth at a greater rate since they have more Earth element.

8. Falling Body Predictions 0 2 4 2) Each object falls to the Earth at a constant speed. 6 8

9. Copernicus Platonic ideas including the Ptolemaic solar system dominated for over 1500 years. Nicolaus Copernicus (1473-1543) was a polish monk who didn’t find the Ptolemaic solar system to be satisfactory from a philosophical view due to the large number of epicycles. Copernicus proposes a heliocentric system of the universe with Earth being just another planet orbiting the sun in uniform circular motion (circle at constant speed).

10. Copernicus Copernicus reserved publication of his book, On the Revolutions of the Heavenly Spheres, till he was near death to avoid confrontation with the church which was dominated by Aristotelian thinkers. His work and its consequences gave a new political meaning for the word revolution. Note: Most people were illiterate. The exception was the wealthy and the clergy since they ran the government and studied scriptures. They were well educated in all subjects including Aristotelian Mechanics.

11. Copernicus In his book, Copernicus also included a discussion of epicycles and other platonic ideas. Thus, his radical ideas were almost lost. However, the heliocentric solar system did have a powerful effect on Galileo and Kepler. There is also some arguments supporting that other famous people of this time became Copernicans including Dante and Shakespeare.

12. Testing Models What evidence supported the Copernican model of the solar system? Answer: None at this time Galileo was a devoted Copernican and would begin collecting data that led to the downfall of the Ptolemaic solar system. However, when the church offered to rule in his favor if he could prove that the Earth moved, he had no proof.

13. Astrology People of the 1500’s were strong believers in witch craft and in astrology. The ruling class believed that their actions were ruled by the stars. Most academicians including Kepler made a living by casting Royal horoscopes. Conjunction is an astronomical event in which planets are aligned. During the 1500’s, the minor planets were predicted to align (looks like a very bright star). However, the Ptolemaic tables were off a few days and the Copernican tables were worse.

14. Tycho Brahe A Danish noble who realized that the reason the astronomical tables incorrectly predicted the date of the conjunction was that no one had made the necessary precise measurements of the stars. Brahe built the best astronomical observatory and instruments of the time. His measurements of the locations of the stars were 5 times more precise than previous measurements.

15. Tycho Brahe Brahe was not a nice man. He especially didn’t like the serious Johannes Kepler who he toyed with. Brahe had a silver nose because his nose had been cut-off during a sword fight. On his death bed, Brahe begged Kepler to analyze his data and to publish Brahe’s model of the solar system. However, Brahe’s family kept the data since they thought it might be worth money so Kepler broke in and stole the data.

16. Tychonic Universe In the Tychonic Universe, the Sun orbits the Earth, but all other planets orbit the Sun. This model is important because it eliminated the concept of the crystal spheres and freed astronomers from the concept that all motion had to be circular. Tycho’s most important contribution was his precise measurements since the new measurements showed that Mar’s orbit could not be explained using a circle.

17. Johannes Kepler (1571-1630) Kepler was one of the great geniuses of all time. He developed the laws of planetary motion and almost developed the Calculus. Kepler had a rough life: Father deserted family Raised in Orphanage Rough Marriages Religious Persecution Mother tried as a witch Children were unsuccessful

18. Johannes Kepler Kepler began wandering Europe on January 1, 1600. He eventually went to see Brahe where he spent eighteen months working for Brahe and trying to get Brahe to show him his measurements. Once he has Brahe’s data, he spends sixteen years analyzing data before he finds that three statements can describe all of the motions in the heavens (Kepler’s Laws of Planetary Motion).

19. Kepler’s 1st Law All planets travel in ellipses with the Sun at one foci. This discovery is forced upon Kepler by the eccentricity of the orbit of Mars which are shown in Brahe’s data!! x This drawing is exaggerated for the 5 major planets with Mars being the most eccentric at only 8% away from a circle.

20. Kepler’s 2nd Law All planets trace out equal area in equal time. This will later be found to be a consequence of conservation of angular momentum. x When a planet is far from the sun it moves slower such that the area traced out is the same for the same amount of time.

21. Kepler’s 3nd Law The period (time required to complete a revolution – i.e. the year) for a planet squared is proportional to the cube of the radius of its semi-major axis. x a

22. Kepler’s Laws Kepler’s laws were incredibly powerful in that they explained all know observations with just three ideas. They also gave support to the Copernican model of the solar system. Kepler couldn’t explain why his laws were true!! He simply knew that they fit the data. It will take Isaac Newton to provide the synthesis that Aristotle had done previously.