Planetary Motion: Historical Description and Newton's Universal Gravitation, Slides of Physics

Download Planetary Motion: Historical Description and Newton's Universal Gravitation and more Slides Physics in PDF only on Docsity! Planetary Motion I. Historical Description of Planetary Motion A. Greek Philosophers’ model (300 B.C) 1) Earth is at the center of the Universe 2) Sun, Moon, Stars are fixed in concentric spheres revolving around Earth B. Planets have retrograde motion 1) Planets appear to move backwards sometimes 2) Ptolemy (200 A.D.) explains with Epicycles a) Circles not spheres for sun, moon, planets b) Smaller circular motions on the larger orbit c) Explained retrograde motion docsity.com C. Copernicus and Galileo: Heliocentric Solar System 1. Sun is center of Solar System, planets including Earth, revolve around sun 2. Explains retrograde motion, plus other of Galileo’s observations 3. Used circles for the orbits: didn’t work for everything D. Kepler’s Planetary Motion (1571-1630) 1. Assistant to Tycho Brahe, who had the best observations yet of the sky 2. Devised 3 laws from the data: Testable Rules or Empirical Laws a) Planetary orbits are ellipses, not circles b) Orbital radius sweeps out equal areas in equal times c) 23 Tr  s 2 2 3 Gm 4constant  T r docsity.com III. Moon and Satellite motion A. Moon orbits Earth according to Kepler’s Laws = Satellite 1) Phases of the moon a) Full b) Half c) New 2) Eclipses a) Lunar: Earth’s shadow covers the moon b) Solar: Moon blocks the sun from the Earth B. Tides: Moon’s Gravitation affects oceans, creating bulges 1) High Tides: closest and farthest from the moon 2) Low Tides: midway from the moon docsity.com C. Other Satellites 1) Anything in orbit of the Earth is a satellite: many man-made objects 2) They obey Kepler’s Laws: 3) We can manipulate r and T to get any distance or period we want a) Sychronous orbit: T = 24 h, satellite stays over same place all day b) Calculate r for a synchronous = 42,000 km (7 times re) c) Make r shorter, T becomes shorter d) Make T shorter, r becomes shorter e 2 2 3 Gm 4constant  T r docsity.com