1Wed, Jan 18 Physics 107, Spr 2006 1Physics 107Ideas of Modern Physics• Main emphasis is Modern Physics: essentially post-1900• Why 1900?– Two radical developments:Relativity & Quantum Mechanics• Both changed the way we think as much asdid Galileo and Newton.(uw.physics.wisc.edu/~rzchowski/phy107)Wed, Jan 18 Physics 107, Spr 2006 2Goals of the course• Learn a process for critical thinking, and apply it to evaluate physical theories• Use these techniques to understand therevolutionary ideas that embody modern physics.• Implement the ideas in some basic problems.• Understand where physics is today,and where it is going.Wed, Jan 18 Physics 107, Spr 2006 3What will we cover?• Scientific observation and reasoning.• Motion and energy.• Relativity.• Quantum Mechanics.• Gravity.• Particle theory and cosmology.Wed, Jan 18 Physics 107, Spr 2006 4Single atoms and quantum wavesEntire galaxiesWed, Jan 18 Physics 107, Spr 2006 5How do we do this?• Lectures• Demonstrations• In-class interactive questions• Homework• Discussion sectionsWed, Jan 18 Physics 107, Spr 2006 6What do you need to do?• Read the textbooks Physics for poets Physics of everyday phenomena• Come to the lectures 9:55 MWF in 2241 Chamberlin Hall• Participate in discussion section One per week, starting Jan 23• Do the homework Assigned most Wednesdays, due the following Wednesday• Write the essay On an (approved) physics topic of your choice, due Apr 26• Take the exams Three in-class hour exams, one cumulative final exam2Wed, Jan 18 Physics 107, Spr 2006 7What do you get?• An understanding of the physical universe.• A grade– 15% HW– 15% essay– 20% each for 2 of 3 hour exams (lowest dropped)– 30% from cumulative final examWed, Jan 18 Physics 107, Spr 2006 8Where’s the math?• Math is a toolthat can often help to clarify physics.• In this course we use algebra and basic geometry.• We will do calculations, but also focus onwritten explanation and reasoning.Wed, Jan 18 Physics 107, Spr 2006 9Observation and Science• Look around - what yousee is the universe.• What can you say abouthow it works?Wed, Jan 18 Physics 107, Spr 2006 10What Aristotle sawEarthAirWaterFireCelestialbodiesWed, Jan 18 Physics 107, Spr 2006 11Earth, air, water, fire…• For terrestrial objects…and aether, from which celestial bodies are formedWed, Jan 18 Physics 107, Spr 2006 12Aristotle’s ideas about motion• Earth moves downward,Water downward,Air rises up, Fire rises above air.Objects move in straight lines.• Celestial bodies are perfect.They move only in exact circles.3Wed, Jan 18 Physics 107, Spr 2006 13Motion of the celestial bodiesApparent motion of stars:Rotation about a pointevery 24 hours.Moon, sun, and planetswere known to move withrespect to the stars.Wed, Jan 18 Physics 107, Spr 2006 14Motion of the stars over 6 hrsWed, Jan 18 Physics 107, Spr 2006 15Daily motion of sun & planets over 1 yearMovie by R. Pogge,Ohio StateWed, Jan 18 Physics 107, Spr 2006 16Aristotle’s crystal spheresEarth/WaterAirMoon (28 days)FireMercury (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)Wed, Jan 18 Physics 107, Spr 2006 17Detailed Observations ofplanetary motion (Ptolemy)Observational notes from Ptolemy’s Almagest85-165An instrument similarto Ptolemy’sWed, Jan 18 Physics 107, Spr 2006 18Retrograde planetary motionRetrograde motion of MarsApparent motion not always ina straight line.Mars appears brighter duringthe retrograde motion.4Wed, Jan 18 Physics 107, Spr 2006 19Epicycles, deferents, and equants:the legacy of PtolemyEpicycle reproduced planetary retrograde motion Wed, Jan 18 Physics 107, Spr 2006 20Ptolemy’s universe• In ‘final’ form– 40 epicycles anddeferents– Equants andeccentrics for sun,moon, and planets.– Provided detailedplanetary positionsfor 1500 yearsWed, Jan 18 Physics 107, Spr 2006 21More detailed observations, +some philosophy (Copernicus)• Ptolemy’s system worked, but seemed alittle unwieldy, contrived.• Required precise coordination of planetarypaths to reproduce observations.• Imperfect circular motionagainst Aristotle.• Copernicus revivedheliocentric (sun-centered) universe– But retained epicycles for accuracy comparableto Ptolemy1473-1 543Wed, Jan 18 Physics 107, Spr 2006 22The heliocentric universe• Sun-centered• Planets orbitingaround sun.• Planets still onepicycles (not shown).• But the (imperfect)theory is attractive inseveral ways.Wed, Jan 18 Physics 107, Spr 2006 23Advantage: “Natural”explanation of Retrograde motionRetrograde motion observed asplanets pass each other.Wed, Jan 18 Physics 107, Spr 2006 24Comparing Ptolemy and CopernicusPtolemy’s Earth-centeredCopernicus sun-centeredWhich is the better theory?5Wed, Jan 18 Physics 107, Spr 2006 25How 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 observational evidence of orbital motion: Relative positions of stars did not shift with Earth’s motion (parallax) Stars weren't brighter when Earth is closer (opposition).No observational evidence of rotation: Daily motions are as easily explained by a fixed earth. The motions do not require a rotating earth.Both explained contemporaneous observations.Wed, Jan 18 Physics 107, Spr 2006 26Advantage:A ‘good’ theory makes predictionsEarthhalf-illuminatedVenus9.549.17Saturn5.205.22Jupiter1.521.52Mars1.001.00Earth0.7230.719Venus0.3870.376MercuryActualCopernicusPlanetBut, at the time, these predictions could not be tested!Wed, Jan 18 Physics 107, Spr 2006 2720 years of detailed observations(Tycho Brahe & Johannes Kepler)• Brahe’s exacting observationsdemanded some dramaticrevisions in planetary motions.Both Ptolemy’s andCopernicus’ theorieswere hard-pressed atthis detailed level.1546-1601Wed, Jan 18 Physics 107, Spr 2006 28Kepler’s elliptical orbits• Contribution of Kepler:– first consideration of non-circular orbits in over1000 yrs of thinking.– No more epicycles required!1571-1630CircularorbitElliptical orbitDetailed observations required a radicalnew concept for an explanation.Wed, Jan 18 Physics 107, Spr 2006 29Some common threads• ‘Philosophical’ considerations,such as complexity and symmetry,can lead to revolutionary
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