Kepler's Laws Explained: Why Earth Moves Fastest in January | Physics Explained 7.1

Earth is closest to the Sun in January, and moving fastest. Why? This lesson tells the story from Ptolemy's circles-on-circles to Copernicus (with an animation of Mars's backward "retrograde" loop), then Tycho Brahe's data and Kepler's three laws: elliptical orbits (drawn with two pins and a loop of string), equal areas in equal times, and T²/r³ being the same for every planet. Worked examples: a moon's distance from its planet, the area Earth sweeps each day, and the period of a satellite 1,500 km up. Chapters: 0:00 Intro 1:05 Earth-centered or Sun-centered? 2:54 Kepler's first law: ellipses 4:16 Worked example: a moon's distance 5:20 Kepler's second law: equal areas 6:04 Worked example: Earth's daily sweep 7:00 Kepler's third law: periods and distances 7:52 Worked example: a satellite's period 9:00 How, but not why 9:21 Common mistakes 9:52 Recap 10:29 Check yourself 11:46 Up next Physics Explained, Chapter 7: Newton's Law of Gravitation (lesson 1 of 3) Adapted from Physics by OpenStax (https://openstax.org/details/books/ph..., licensed under CC BY 4.0 (https://creativecommons.org/licenses/.... The animations and narration are original to Prime Mover. OpenStax is not affiliated with this channel and does not endorse it. Prime Mover: learn it, build it, share it.