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UW-Madison PHYSICS 107 - Ideas of Modern Physics

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Physics 107 Ideas of Modern PhysicsGoals of the courseWhat will we cover?PowerPoint PresentationHow do we do this?What do you need to do?What do you get?Where’s the math?Observation and ScienceAristotle’s ideas about motionMotion of the celestial bodiesMotion of the stars over 6 hrsDaily motion of sun & planets over 1 yearAristotle’s crystal spheresYou figure it out!Detailed Observations of planetary motion (Ptolemy)Retrograde planetary motionEpicycles, deferents, and equants: the legacy of PtolemyPtolemy’s universeMore detailed observations, + some philosophy (Copernicus)The heliocentric universeAdvantage: “Natural” explanation of Retrograde motionComparing Ptolemy and CopernicusHow can we tell if it is ‘correct’?Advantage: A ‘good’ theory makes predictions20 years of detailed observations (Tycho Brahe & Johannes Kepler)Kepler’s elliptical orbitsSome common threadsAn important differencePhysics 107, Fall 2006 1Physics 107Ideas of Modern Physics•Main emphasis is Modern Physics: Post-1900 Physics•Why 1900?–Two radical developments:Relativity & Quantum Mechanics•Both changed the way we think as much as did Galileo and Newton.(www.hep.wisc.edu/~herndon/107-0609)Physics 107, Fall 2006 2Goals of the course•Learn a process for critical thinking, and apply it to evaluate physical theories •Use these techniques to understand the revolutionary ideas that embody modern physics.•Implement the ideas in some basic problems.•Understand where physics is today, and where it is going.Physics 107, Fall 2006 3What will we cover?•Scientific observation and reasoning.•Motion and energy.•Relativity.•Quantum Mechanics.•Gravity.•Particle theory and cosmology.Physics 107, Fall 2006 4From the microscopically smallSingle atoms and quantum wavesTo the incredibly largeEntire galaxies and the universeModern Physics:Physics 107, Fall 2006 5How do we do this?•Lectures•Demonstrations•In-class interactive questions•Homework•Discussion sectionsHW 1: Chap 3 Conceptual 6, 28, 32Chap 3 Problems 6, 10, 16Physics 107, Fall 2006 6What do you need to do?•Read the textbookPhysics Concepts and Connections•Come to the lectures9:55 MWF in 2241 Chamberlin Hall•Participate in discussion sectionOne per week, starting Sept 11th•Do the homeworkAssigned most Wednesdays, due the following Wednesday•Write the essayOn an (approved) physics topic of your choice, due Dec 8•Take the examsThree in-class hour exams, one cumulative final examPhysics 107, Fall 2006 7What do you get?•An understanding of the physical universe.•A grade–15% HW and Discussion Quizzes–15% essay–20% each for 2 of 3 hour exams (lowest dropped)–30% from cumulative final examPhysics 107, Fall 2006 8Where’s the math?•Math is a tool that can often help to clarify physics.•In this coursewe use algebra and basic geometry.•We will do calculations, but also focus on written explanation and reasoning.Physics 107, Fall 2006 9Observation and Science•Look around - what you see is the universe.•What can you say about how it works?Physics 107, Fall 2006 10Aristotle’s ideas about motion•Terrestrial objects move in straight lines.Earth moves downward, Water downward, Air rises up, Fire rises above air. •Celestial bodies are perfect. They move only in exact circles.•Where did Aristotle concentrate his work?–Celestial bodies, most interesting problem of the dayPhysics 107, Fall 2006 11Motion of the celestial bodiesApparent motion of stars:Rotation about a point every 24 hours.Moon, sun, and planets were known to move with respect to the stars.Physics 107, Fall 2006 12Motion of the stars over 6 hrsQuickTime™ and aVideo decompressorare needed to see this picture.Physics 107, Fall 2006 13Daily motion of sun & planets over 1 yearQuickTime™ and aVideo decompressorare needed to see this picture.Movie by R. Pogge, Ohio StatePhysics 107, Fall 2006 14Aristotle’s crystal spheresEarth/Water/Air/FireMoon (28 days)Mercury (1 yr)Venus (1 yr)Sun (1 yr)Mars (2 years)Jupiter (12 years)Saturn (30 years)Firmament (1000 yrs)Prime mover (24 hrs)Cristal sphere (49000 yrs)Already Complex!Physics 107, Fall 2006 15You figure it out!Assuming that the planets and stars are moving around the earth you would expect:A. The planets to move faster than the stars since they are closer.B. The stars to move faster than the planets.C. We wouldn’t know what to expect.I would say it would be helpful to have more information!Physics 107, Fall 2006 16Detailed Observations of planetary motion (Ptolemy)Observational notes from Ptolemy’s Almagest85-165An instrument similar to Ptolemy’sPhysics 107, Fall 2006 17Retrograde planetary motionContinued observation revealed that the problem was even more complex than first believed!Retrograde motion of Mars.Apparent motion not always in a perfect circle.Mars appears brighter during the retrograde motion.Physics 107, Fall 2006 18Epicycles, deferents, and equants:the legacy of PtolemyEpicycle reproduced planetary retrograde motionPhysics 107, Fall 2006 19Ptolemy’s universe•In ‘final’ form–40 epicycles and deferents–Equants and eccentrics for sun, moon, and planets.–Provided detailed planetary positions for 1500 years–Very complex!–However good for what was needed, navigation.Physics 107, Fall 2006 20More detailed observations, + some philosophy (Copernicus)•Ptolemy’s system worked, but seemed a little unwieldy, contrived.•Required precise coordination of planetary paths to reproduce observations. •Imperfect circular motion against Aristotle.•Copernicus revived heliocentric (sun-centered) universe1473-1543Physics 107, Fall 2006 21The heliocentric universe•Sun-centered•Planets orbiting around sun.•Theory didn’t perfectly predict planetary motion. Only discovered later.•But the (imperfect) theory is attractive in several ways.Physics 107, Fall 2006 22Advantage: “Natural” explanation of Retrograde motionRetrograde motion observed as planets pass each other.Physics 107, Fall 2006 23Comparing Ptolemy and CopernicusPtolemy’s Earth-centeredCopernicus sun-centeredWhich is the better theory?Physics 107, Fall 2006 24How can we tell if it is ‘correct’?But a rotating and revolving Earth seemed absurd!Both motions require incredibly large speeds: Speed of rotation ~ 1280 km/hour Orbital Speed: 107,000 km/hr = 30 km/sec! No


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UW-Madison PHYSICS 107 - Ideas of Modern Physics

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Exam 2

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Lect 01

Lect 01

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Exam 1

Exam 1

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Exam 3

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