PHY 102 1nd Edition Lecture 4Outline of Last Lecture I. Blue Book 1.1 #2, 4II. The Age of Measurement (continued)III. MallardIV. Blue Book 1.2 #2, 4Outline of Current Lecture I. Copernican RevolutionII. Two competing theoriesIII. BraheIV. KeplerV. Blue Book 2.2 #1Current LectureI. Copernican Revolutiona. 1800 years after Aristarchus, his idea of heliocentrism was revived by Nicolaus Copernicusi. Afraid to publish his theory (because earth wasn’t at the center of the universe)b. Copernicus, finding the geocentric model too complicated, placed the sun at the center with planets and earth moving around it on circles with uniform motionc. Complicated or not, the geocentric model is the only alternative if the heliocentric model cannot explain all the phenomena that the geocentric model canThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. Indeed heliocentric model explains all the phenomena that the geocentricmodel doesII. With the (re)invention of the heliocentric model, there were two competing theoriesof the cosmos: geocentric and heliocentrica. Which one is correct?i. Which one agreed with observation?1. BOTH until…III. New and very precise observations were made by Tycho Brahea. Proved geocentric and heliocentric theories wrongi. Choose the better theory and improve on itIV. Johannes Keplera. Through a very careful and painstaking mathematical analysis of Mars, Kepler found the key to a successful correction to the heliocentric modelb. Kepler’s laws of planetary motion = three laws that govern the motion of planets around the suni. First Law1. Each planet moves on an ellipse, with the sun at on of its fociii. Second Law1. The planet sweeps equal areas in equal time intervals2. Planet moves faster when closer to the suniii. Third Law1. T2 = ka3 or (T1/T2)2 = (a1/a2)3a. Where “T” is period and “a” is the semi-major axisb. “T” measured in secondsc. “a” measured in metersV. Blue Book 2.2
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