Lecture 9 Review before Exam 1 Development of Science - PDF document

Lecture 9 – Review before Exam 1 Development of Science Announcements Falling bodies Observation • Today - Review before Exam I e Homework 4 due l t i c e o j r P n o i P 2 = ka 3 t o m d o h t e • Wednesday, October 1: Exam I m l a t n e Covers Chapters 1 - 5 of March; 1 – 2 of Lightman m Teleology r i e p x Development of science through classical physics E (except electricity and magnetism and waves not e s p i l E l covered) = t b i r O • Monday, October 6: Solutions to exam; Continue Classical physics – Electromagnetism F = GMm/R 2 and electromagnetic waves R s / w v 2 a a L m = n o Entropy, 2 nd Law a i t = a v r F e s n of Thermodynamics Heat o C Nature of Exam Nature of Exam • Questions: True/false; multiple choice • Questions: Multiple choice; short written answers • Problems: Work out numerical answer • Problems: Work out numerical answer • Essay questions: Give answer in short paragraph • Essay questions: Give answer in short paragraphs • Equations are provided on cover sheet: • Equations are provided on cover sheet: Overview of course (from Lecture 1) Role of Mathematics (various ) • To discover what science (physics) is about • The natural language of science is mathematics • Is it objective discovery of facts about nature? • The workings of nature appear to be described by simple laws • Is it human invention of ways to describe what we see around us? • Mathematics allows laws to be written in succinct form • What are the great ideas of science (physics)? • Mathematics allows the equations to be • How does science (physics) affect our world transformed to make bold conclusions and to view? make unambiguous tests of the laws • The approach we will take is to describe the conceptual structure of physics in a historical • Allows important applications to ordinary experience perspective (following the texts with additions) • Quantitative problems are an essential part of physics • How has physics evolved? • In this course we consider simple but • Revolutions in science – in human thought important example problems • How has it affected world views?

Lecture 9 – Review before Exam 1 Review -- 1 Role of Physics in the “Big Picture”? • What is Scientific Knowledge? A brief taste (from Lect. 2) • What questions are “scientific” • “ ‘It struck me that the more we learn about the • What statements are scientific? --- Examples changes in human life after the 16 th century’ – • Feynman’s answer: “The test of all [scientific] knowledge is when most scholars mark the onset of the experiment.” modern world – ‘the clearer it becomes that [the • What are other types of knowledge? --- Examples change] was unprecedented and radical’ ” • “People began to value institutions such as • How did our present definition come about? private property, to question religion’s public • What steps in history were particularly important? role, and to adapt a Newtonian, scientific world • Powers answer: “… no single idea has had a more profound or view” ubiquitous impact on what the human race has become, or what • Viewed as regression by some - a spiritual loss it has worked upon the face of the planet, than the vesting of (Nietsche) – unleashing of unstainable authority in experiment.” capitalism (Marx) … • When did this happen? What were other movements in human history that occurred in the same period(s)? • Unquestionably an enormous effect on our lives • How did this happen? How did (does) science advance? Robert Pipin, The University of Chicago Magazine, August, 2003 What do we observe in the sky? Review -- 2 • What have people observed in the sky since • Sun, Moon, Stars in eternal, regular motion long before recorded history? • From a point in the Northern Hemisphere, the • Sun, Moon, Stars, Planets stars appear to move as shown: • Ancient Observations - which are still useful! • Ancient Cosmologies - facts or invention? • Problem of the Planets (Wanderers) • The strange motion of the planets exemplifies two competing world views • Each view appears to be the product of a deep human desire to “know” • Astrology treats the motion as somehow related to life on earth - leads to fortune telling, horoscopes, …. • Astronomy searches for explanations in simple laws - leads to new science Problem of the Planets Motion of Sun, Moon, Planets • The motion of each planet - Mercury, Venus, Mars, Jupiter & along the “Zodiac” Saturn - follows a different path at a different speed along the “Zodiac” • Their speed varies and sometimes they move backward! • Sun moves through the constellations • Observe directly by the position of the stars at sunrise and sunset

Lecture 9 – Review before Exam 1 In the Beginning . . . Review -- 3 Ancient Cosmology: Babylon, Egypt, ... • The development of Science • Golden Age of Classical Greece Culture HEAVEN 500BC - 200AD • Dark Ages of Europe up Golden Age of Islam 200AD - 1300AD OCEAN • Renaissance EARTH 1300’s -- 1600’s • “Classical Physics” culminated in “experimental method”, Newton’s laws, conservation laws, 2 nd law TARTARUS (and later Maxwell and others) (Abyss below Hades) 1600’s - 1800’s. Timeline Review -- 4 Middle “Modern” Asia, Egypt Greece, Rome Renaissance Ages Physics • Great Advances in Science Mesopotamia 500 BC -- 200 AD Al-Khawarizmi Copernicus • Accurate description of the motions of the sun, moon, 0 stars. Essential for calendar. -1000 1000 2000 Ptolomy • Philosophy dominated by Plato and Aristotle Aristotle Plato Newton Galileo • Plato believed in higher order, ideals Erastosthenes Kepler Aristarchus • Aristotle was observational scientist – defined Physics Ibn al-Hytham (Natural Philosophy) • Ideas of Motion: Perfect perpetual motion in heavens; Natural state of rest for objects to earth • Evidence for spherical earth, moon, sun and measurements of their sizes and distances centuries • See Timeline description of lives of various B.C. ! (Erastosthenes, Aristarchus) scientists on WWW pages. • The only problems: The "planets” • Complex earth-centered models assuming motion described by circles (Ptolemy, around 150 AD) What observations indicate that Measuring the earth the earth is spherical? Eratosthenes, 4th Cent. BC • In a lunar eclipse, the shadow of the earth on the Librarian of the great library at Alexandria moon is like that of a sphere Long shadow Sun Moon SUN Earth Shadow Earth Short shadow DEMONSTRATION • Shadows depend upon • North-South Location Appearance of Moon during eclipse By other measurements and geometry, Greek scientists found the distance to the moon and sun!

Lecture 9 – Review before Exam 1 How large is the Moon? How Far? Amazing Discoveries and Measurements • (also due to Aristarchus) Ancient Greece • In a lunar eclipse, the time the moon is in the • 1. Observe that the Moon appears spherical and shadow of the earth depends on the moon’s size & reflects light from sun distance. • Observation: At the moon the earth’s shadow is earth observer very nearly twice the diameter of the moon Θ m Moon S M s sun SUN Right triangle Θ Earth Shadow Earth diameter = 2 m half-moon Dark side of moon blocks view of X stars - showing it is a solid sphere. S M Measured distanced to Moon and Sun! Review -- 5 Earth Centered Model of • Pre-Renaissance Science Sun, Moon, Stars 200AD - 1400AD • Physics dominated by Aristotle's thinking: sun • Perfect perpetual motion in heavens; tendency to come to rest for objects on earth • “Dark Ages” in Europe North pole moon • “Golden Age” of Islam Rotation • Preserved heritage of Classic Greek Science Al-Khawarizmi, mathematician and astronomer whose major works introduced Hindu-Arabic numerals and the concepts of algebra into European mathematics. • Great scientists such as Ibn al-Haytham who discovered laws of optics (credited by Powers for the stars EARTH scientific method), and Ibn Sina who wrote great works on medicine and other fields Very Logical Picture! But no way to know distance to stars before time of Galileo. Alternative Pictures of the Universe: Alternative Pictures: How to determine How to determine which is “correct”? which is “correct”? • Aristarchus (c 250 BC) • Ptolemy (150AD): • Earth centered model (Ptolemy ca. 150AD)? Copernicus (1473-1543) Planets move on circles Sun is the center of the (epicycles) centered on universe. All planets another circle (deferent) • Sun Centered Model (Aristarchus ca. 250 BC (including Earth) move about which moves uniformly the Sun (in circles). and Copernicus (1473-1543)) around the Earth. • Problem of the Planets - These tiny points of light moving in strange patterns in the sky lead to new understanding of physics - the “Copernican Revolution”