atoms and stars ist 2420 class 10, march 30 winter 2009 instructor: david bowen course web site:
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Atoms and StarsIST 2420
Class 10, March 30Winter 2009
Instructor: David BowenCourse web site: www.is.wayne.edu/drbowen/aasw09
3/30/09 Atoms and Stars, Class 10 2
Agenda
• Work Due: Report for Lab 10 on lenses • Upcoming assignments• Review of readings• Lab 9 Part 1: Circle
o Turn Part 1 (Circle) and Part 2 (Ellipse) in together
o So that you can make the connection between the two parts
3/30/09 Atoms and Stars, Class 10 3
Getting Work In
• From the Syllabus: “all work to be counted in the regular course grade must be in” by the last regular class on December 8
• Over half the class has not yet turned in Essay 1. This is 10% of the course grade all by itself, or one full letter grade.
• Many people have fewer than three lab reports turned in. Lab reports count 20%, two full letter grades.
3/30/09 Atoms and Stars, Class 10 4
Essay 2
TOPIC: What has this course been about? You should answer this question with a core concept or idea, perhaps with dependent parts, and illustrated by referring to course experiences, such as labs and discussions, and materials, such as readings, notes, lab materials, and so on. A starting point is the “Course Description” section in the Syllabus. You can agree with, make changes to, or disagree with this description, but if you disagree, include an equivalent description – that is, one that covers the course as a whole.
3/30/09 Atoms and Stars, Class 10 5
Essay 2 (cont’d)
• This topic does NOT ask for a simple listing of all of the topics and activities (“laundry list”), and does not ask for an evaluation of me or the course (that’s for SET).
• The topic asks for “a” core concept and suggests a starting point for your analysis
• Due 12/1. Note that we have not covered all of the core topics yet.
• Review Syllabus for other requirementso All quotes must have references
3/30/09 Atoms and Stars, Class 10 6
Final Topics / Info Sheet
• Final will be cumulativeo Could even be repeatso Use the review session! Especially if you left
questions blank on the Midterm• Information sheet
o You will get a clean copy with the Finalo Some answers directly on this sheeto But you must be able to use other words than
the ones on the sheet
3/30/09 Atoms and Stars, Class 10 7Atoms and Stars, Class 10 7
Upcoming …• Next week (April 6):
o Reader: The Atomic Nature of Mattero Manual: Lab 9 – the Ellipseo Hold Lab 9 – the Circle to hand in 9 as a whole
• April 20: SET• Essay 2 due
• April 27 (last regular class)o Review for Final Examo Due: all work to count in regular grade
• May 4: nothing that night but the Final Exam
3/30/09 Atoms and Stars, Class 10 8Atoms and Stars, Class 10 8
Final Topics & Earlier Classes
C = Class, S = Slide• Q4a: C9S20-21, 24-25• Q4b: C9S25-27• Q5a&b: C9S24, 25• Q6a: C9S18• Q6b: C7S12-22 & C7S27• Q7a: C6S18• Q7b: C7S14-25, 30 and Kepler’s general
life
3/30/09 Atoms and Stars, Class 10 9Atoms and Stars, Class 10 9
Final Topics & Earlier Classes (cont’d)
• Q10 Galileo: made observations with telescope, but suggestion that he did experiments after theories
• Q10 Newton: used Kepler’s Laws to verify his, but C10S17, 18, 28 - 30
• Q14: C10S13 (summary), US to come• Q15: each of Copernicus, Brahe, Kepler,
Galileo & Newton is a case. C10S11 - 12• Q16a-c: #2(C9S33-38)
3/30/09 Atoms and Stars, Class 10 10Atoms and Stars, Class 10 10
Final Topics & Earlier Classes (cont’d)
• Q16a-c: #1(C10S22-27)• Q16a-c#3 to come• Q17a: C8S10-11• Q17b: C8S14• Q17c: C8S17• Q18: C8S16-17
3/30/09 Atoms and Stars, Class 10 11Atoms and Stars, Class 10 11
Final Topics & Earlier Classes (cont’d)
• Q15: Summary of religious conflict for individualso Copernicus declared heretical but near the end of
his lifeo Brahe – little conflict (because he was part of the
government?)o Kepler: Hounded and exiled by both Catholics
and Lutherans, problems with his mothero Galileo: “weaseled” out of religious restrictions,
prosecution and conviction by Inquisition
3/30/09 Atoms and Stars, Class 10 12Atoms and Stars, Class 10 12
Final Topics & Earlier Classes (cont’d)
• Q15: Summary of religious conflict for individuals (cont’d)o Newton (in these notes):
• To protect his professorship, kept his religious views private
• Rewarded by new government for standing up to King James on the question of requiring faculty to be strong Catholics
o General: each felt we could learn about God by studying the natural world.
• Trying to improve the theories of their time• Thought they were making marginal improvements
3/30/09 Atoms and Stars, Class 10 13
Contributions of Major Cultures (to the rise of science) (Q14)
• Prehistoric: attention and observation, e.g. recording phases of Moon
• Early urban: primarily procedures (recipes)• Greek: theories, that is idea of theories as
natural explanationso Frank M. Snowden: role of Blacks as equals
then• Islamic: preserved Greek science, improved
observations• Renaissance: united theory and experiment
3/30/09 Atoms and Stars, Class 10 14Atoms and Stars, Class 10 14
Picking on Aristotle…
• Counterexamples (at various times)o Projectile trajectory bent (Aristotle himself)o Arrow should fly faster sideways than forwards
• More area for air to push againsto Top should stop turning
• No surface for air to turn top by pushingo Heavier objects do not fall fastero Growing concept of inertia – tendency to keep
moving once motion is startedo Heliocentric models more accurate
3/30/09 Atoms and Stars, Class 10 15
Galileo’s Telescope
• Galileo had about ten telescopes• Only a few survive• It looked like the kind of toy telescope a child might have made
with scissors and tape — a lumpy, mottled tube about as long as a golf club and barely wider in girth, the color of 400-year-old cardboard, burning with age. The spyglass, one of two surviving, has left Florence for the first time to be the highlight of a Galileo exhibition at the Franklin.
But near one knobby end was a bit of writing that sent Derrick Pitts, chief astronomer of the Franklin Institute here, into rapture. The tube’s focal length is “piedi 3,” the inscription said, three feet. It was in the hand of Galileo Galilei. “Absolutely amazing,” Dr. Pitts said.
Dennis Overbye, The New York Times, March 27
3/30/09 Atoms and Stars, Class 10 16Atoms and Stars, Class 10 16
Readings – Isaac Newton
• Newton 1642 – 1717 b to English rural farming family, father died before his birth
• Seems to have been an unhappy childhood, mother left him with grandparents
• Did not want to go into farming, sent to (Aristotelian) Cambridge University 1661 (19 yrs)
• Studied on his own, cutting edge of math, Physics
3/30/09 Atoms and Stars, Class 10 17Atoms and Stars, Class 10 17
Isaac Newton• 1672 paper on optics – refraction of light,
bending rays through prism, breaking it up into colors, white light is combination of all colorso Careful experimental worko Invented reflecting telescope (curved mirror
acts as lens), elected Fellow of Royal Societyo Much continuing criticism from Aristotelians
and Cartesians, shunned publication (Q10)
3/30/09 Atoms and Stars, Class 10 18Atoms and Stars, Class 10 18
Isaac Newton
• Became professor at Cambridge, required to become a priest, fervent student of theology, kept unorthodox and heretical views private (Q10)o 1675 requirement for priesthood dropped,
Newton saved from having to resign• Lifelong interest in alchemy, arcane
knowledge, secret codes (Q10)
3/30/09 Atoms and Stars, Class 10 19Atoms and Stars, Class 10 19
Isaac Newton
• Royal Society (and Paris Academy of Sciences) new, active (publishing, paid positions, prizes – very modern)o More permanent than earlier – e.g. state
charterso Also state astronomical observatories, botanical
gardenso Much service to government, but Charles II
ridiculed Royal Society for “weighing of air.” However, this was actually critical
3/30/09 Atoms and Stars, Class 10 20Atoms and Stars, Class 10 20
Isaac Newton
• 1684 and earlier, thoughts of Kepler’s Laws and a central force discussed in London – Edward Haley, Robert Hooke, Christopher Wren
• Haley went to Cambridge to ask Newton about the orbit of a planet in a 1/d2 force, Newton checked notes from 1666 and said it would be an ellipse, Haley awestruck
3/30/09 Atoms and Stars, Class 10 21Atoms and Stars, Class 10 21
Isaac Newton
• Later, nine-page note to Haley who then encouraged publication, but Newton improved his work
• 1687 Royal Society published Newton’s Principia Mathematica Philosphia Naturalis (Mathematical Principles of Natural Philosophy) or just plain Principia
3/30/09 Atoms and Stars, Class 10 22Atoms and Stars, Class 10 22
Isaac Newton - Principia• Newton’s three laws of motion: (Q9a)
1. Inertia – bodies at rest stay at rest, bodies in motion stay in straight-line motion unless acted on by an outside force
2. F = ma (not explicit) Force (size and direction), mass, acceleration (size and direction)
3. For every action, equal and opposite reactiono If A has force F on B, then B has force –F on A
o Minus sign means equal in size but opposite in directiono Example of earth and sun: forces are equal in size, but F
= ma says that the sun’s much larger mass means it hardly moves, while the earth goes whipping around
3/30/09 Atoms and Stars, Class 10 23Atoms and Stars, Class 10 23
Newton’s Law of Universal Gravitation (Q9a)
• “Universal” means that it applies to all pairs of masses m1 and m2. For three masses, it applies to all pairs (m1 and m2, m1 and m3, and m2 and m3).o “1,” “2” and “3” above only identify the masses. The
subscript “2”, for example, does NOT mean “squared” – that would be a superscript (above the “m”)
o Does not mean “before” or “after” here• G is called the “Universal Gravitational Constant”
since the same value applies in all cases. Measure it once and you know it.
• “d” is the distance between the two masses.
3/30/09 Atoms and Stars, Class 10 24Atoms and Stars, Class 10 24
Newton’s Law of Universal Gravitation
• F is the gravitational force between the masses
• In algebra, symbols “butted up” against each other (such as G, m1 and m2 below) are multiplied
• The Law:• The force is attractive: it attracts each mass
towards the other.
221
d
mmGF
3/30/09 Atoms and Stars, Class 10 25Atoms and Stars, Class 10 25
Isaac Newton – Principia(Q9b)
• Showed Galileo’s s t2 in footnote, for constant Force and acceleration
• Uses both calculus and geometry, since no one besides Newton yet knew calculus
• Body (planet) orbiting attractive central force sweeps out equal areas in equal times (Kepler’s second law) plus reverse (K2 implies central force)
3/30/09 Atoms and Stars, Class 10 26Atoms and Stars, Class 10 26
Isaac Newton – Principia (Q9b)
• Also, inverse square law of gravity implies t2 r3, and reverse
• Shows that motion in a medium does not follow these laws, against Descarte’s theory of forces transmitted by vortices
• Treats motion of moon around earth, planets around sun, moons of Jupiter and Saturn all similar, geocentrism doesn’t worko Connected moon’s motion with gravity on earth
3/30/09 Atoms and Stars, Class 10 27
Isaac Newton – Principia
• Acceleration of moon in orbit consistent with acceleration of terrestrial gravitation
• One set of laws for celestial and terrestrialo United them
• Neither Earth nor Sun is fixed at centero Center of Mass (balance point) at resto But even that is moving around center of
galaxy, and galaxy is pulled by other galaxieso Science often changes what is important
3/30/09 Atoms and Stars, Class 10 28Atoms and Stars, Class 10 28
Isaac Newton - Principia
• Then new areas for research:o More precise orbitso Effects of planets on each other (perturbations)o Shape of eartho Tideso Comet orbits (found orbit of 1680 comet)
• In first edition, concludes with alchemy (Q10)• Second, ends with praise to God (Q10)
3/30/09 Atoms and Stars, Class 10 29Atoms and Stars, Class 10 29
Isaac Newton - Principia• Second, ends with praise to God (Q10)
o God can be known by His effects on nature• God as Great Clockmaker (Q10)
o Newton acknowledges that he does not enquire into causes of gravity (“hypotheses non fingo”)• Not trying to explain everything
• Principia made Newton famous at 44• Still a recluse• Breakdown in 1693, perhaps from depression
over failure of work on alchemy
3/30/09 Atoms and Stars, Class 10 30Atoms and Stars, Class 10 30
Isaac Newton
• Stood up to King James on Catholic faculty, rewarded with post when William and Mary of Orange overthrew Jameso Warden of English Mint
• Also president of Royal Society• Abused his power in Royal Society; when
Leibniz sued over priority in invention of calculus, Newton wrote the report
3/30/09 Atoms and Stars, Class 10 31Atoms and Stars, Class 10 31
Isaac Newton - Opticks
• Today we use Leibniz’s notation in calculus• 1704 published Opticks, “proof by
experiment”o Light as particles or corpuscles, today we think of
light more as waveso Reflections from thin layers like oil film on watero Queries to spark further researcho Ending: studying nature reveals our duty to God
(Q10)
3/30/09 Atoms and Stars, Class 10 32Atoms and Stars, Class 10 32
Isaac Newton
• Theology (still hid heretical views) fit with ideas of time, his laws were used by others to argue for:o Existence of Godo Sacredness of propertyo Legitimacy of social hierarchy, duty, enlightened
self-interest• Refused rites of Anglican church at death but
buried at its Westminster Abbey
3/30/09 Atoms and Stars, Class 10 33Atoms and Stars, Class 10 33
Isaac Newton
• Science and technology still largely separate during his time
• More influence of technology on science than the reverse
• Some interplay in area of scientific instruments – improved by science
• Role of alchemy, printing of handbooks of recipes and methods for artisans
• Francis Bacon: theorist of scientific method
3/30/09 Atoms and Stars, Class 10 34Atoms and Stars, Class 10 34
Expanding Circles
• Implication #1: eventually, expanding circles must meet and overlap
• Three examples in this course:o Isaac Newton (this class)o James Clerk Maxwell (last week)o Ludwig Boltzmann (later)
3/30/09 Atoms and Stars, Class 10 35Atoms and Stars, Class 10 35
Expanding Circles
• Implication #1: eventually, expanding circles must meet and overlap
• Possible interactions:o Withdrawalo One wins out over the othero Compromiseo Synthesiso ???
3/30/09 Atoms and Stars, Class 10 36Atoms and Stars, Class 10 36
Expanding Circles
First example: celestial and terrestrial mechanics• Case of Newton (and Kepler) uniting terrestrial
and celestial mechanicso Newton – new theory united themo Each is understood more accurately and causallyo A bonus – applies to all motion, calculus, applied
in technology, model for new scienceo Led to understanding interactions of planets and
discovery of Neptune (a future class)
3/30/09 Atoms and Stars, Class 10 37Atoms and Stars, Class 10 37
Reading: What is Gravity?
• Newton: we do not know what gravity is• DB: After 20th century, two explanations
o These don’t agree, so that is a problem, but a possible unification
• Explanation #1: 1915: Einstein’s General Theory of Relativityo Gravity is due to the bending of space by
masseso Analogy of a ball rolling on a sheet of rubber
around a heavy object
3/30/09 Atoms and Stars, Class 10 38Atoms and Stars, Class 10 38
What is Gravity? (cont’d)
• Explanation #2: Quantum Mechanics (applies to very small objects) about 1925:o All forces, including gravity, are due to the
exchange of (very small) particles between objects
o Particles observed for weak, strong (nuclear) and electromagnetic forces (photon for e-m)
o Not yet observed for gravitational forceo Difficult to find, but would be serious if not found
3/30/09 Atoms and Stars, Class 10 39Atoms and Stars, Class 10 39
What is Gravity? (cont’d)• Both General Relativity and Quantum Mechanics
are well-established science• Explanations for gravity from General Relativity
and Quantum Mechanics have not yet been reconciled (two theories explaining same thing)o Would be called Quantum Theory of Gravityo Does not yet existo Are reconciled in latest theories, e.g. String Theory, but
this does not yet have experimental verification – we do not yet even know what experiments to do or how to do them
• String Theory may turn out to explain itself
3/30/09 Atoms and Stars, Class 10 40Atoms and Stars, Class 10 40
Status of Newton’s Laws• Are scientific theories reliable? Many hedges
in this course, for example:o Scientific knowledge is provisionalo Experiments do not prove theorieso One experiment can overturn a theoryo Science has a limited scope – a boundaryo Science is not an adequate basis for livingo Scientists often do not follow scientific method
• Maybe only foolish people use science? Not!
3/30/09 Atoms and Stars, Class 10 41Atoms and Stars, Class 10 41
Status of Newton’s Laws• Range of authority for Newton’s Laws:
o Objects moving slower than about three million miles per hour
o Objects weighing more than about 0.000,000,000,000,000,000,01 pounds (19 zeroes)
o Objects weighing less than about (31 zeroes) 40,000,000,000,000,000,000,000,000,000,000 lb
• Within this range of authority, Newton’s Laws are extremely reliable and precise
3/30/09 Atoms and Stars, Class 10 42Atoms and Stars, Class 10 42
Status of Newton’s Laws• Newton’s Laws have passed stringent tests
o Control of spacecrafto Use in design and control of countless machineso 1846 predicted mass and orbit of Neptune from
its effect on the orbit of Uranus (productive)• For very small masses (molecular), Quantum
Mechanics is needed instead• For very fast objects, Special Relativity• For very massive objects, General Relativity
3/30/09 Atoms and Stars, Class 10 43Atoms and Stars, Class 10 43
Why Europe?
• Why did modern science arise in Europe?• One idea – two influences came together
o Theoretical movement from the Church drive for clear doctrines (often said to be characteristic of Western Christianity)
o Reliable commercial procedures, documented, for faster commercial production and training, driven by trade – apprenticeship too slow
• The two pillars of science – theory and experiment
3/30/09 Atoms and Stars, Class 10 44Atoms and Stars, Class 10 44
Two parts
• Newton ends the “Stars” part of this course• Next week starts the “Atoms” part• So what? Why is the “Stars” part important?
o 1543 Copernicus’s De Revolutionibus to 1687 Newton’s Principia
o Step by little step, but looking back: overthrowo Geocentric to heliocentric
• But not really – Newton has mutual interaction between sun and earth – both move around common “Center of Gravity”
3/30/09 Atoms and Stars, Class 10 45Atoms and Stars, Class 10 45
Two parts• “Center of Gravity” – the balance point.
– Where the see-saw would balance if the sun was on one end and the earth on the other
• But sun so much more weighty (one-third of a million times) than earth that Center of Gravity is inside sun
o Held in place by spheres to mutually influencing
o Abstract idea of perfection to reality-based leading to technology
o Union of terrestrial and celestialo Overthrow of authority (Aristotle, church), rise
of individual, development of science
3/30/09 Atoms and Stars, Class 10 46Atoms and Stars, Class 10 46
So?
• This course looks backwards to how science came about
• The point is, how will you use science?o Are statements by scientists reliable?
• Depends on whether that science is still developingo Logical reasoning (Aristotle) and/or strong
belief (church and Copernicus through Newton) are not enough for validity
• “Show me the evidence”o Value of theory (still to come)
3/30/09 Atoms and Stars, Class 10 47
Converting Sixteenths to Decimal (Q1)
• Converting inches and sixteenths to decimal inches, and pounds and ounces to decimal pounds:o How many sixteenths of an inch are there in
one inch?o How many eighths of an inch are there in one
inch?o On exams, will be given ounces in a pound (16)
if needed, but not sixteenths of an inch in an inch
3/30/09 Atoms and Stars, Class 10 48
Converting Sixteenths to Decimal (Q1)
• Converting inches and sixteenths to decimal inches, and pounds and ounces to decimal pounds:1. Divide # sixteenths by 16 (result between 0 and
1), call this “X” (make it a whole number)2. Check: multiply X by 16, get about the original
number of sixteenths – SHOW THIS CHECK ON DATA SHEET !!!
3. Add X to # whole inches to get decimal inches
3/30/09 Atoms and Stars, Class 10 49
• Example 1: Convert 5 3/16 to decimal inches
Converting Sixteenths to Decimal
a) Take 3, divide by 16b) 3 ÷ 16 = .1875, round to .2
i. Check: .2 × 16 = 3.2, about = 3 so OKc) 5 3/16 = 5.2
a) Take 7, divide by 16b) 7 ÷ 16 = . 4375, ~.4
i. Check: .4 × 16 = 6.4, about = 7 so OKc) 8 7/16 = 8.4
• Example 2: Convert 8 7/16 to decimal inches
(Don’t touch the 5!!!)
3/30/09 Atoms and Stars, Class 10 50
Converting Sixteenths to Decimal
• Groups example 3: convert 9 13/16 to decimal inches (13/16 = .8125) 9.8
• Alone example 4: convert 12 5/16 to decimal inches (5/16 = .3125)12.3
• Only convert to decimals once for each situation!
3/30/09 Atoms and Stars, Class 10 51
Converting Sixteenths to Decimal
• Converting 16ths to decimal & the check:
• The Goal is the tenths!!!
Start: 16thsGoal: decimal
Check: 16ths
Step 1: divide by 16
Step 2: multiply by 16
Step 3: Equal?
Lab 9
3/30/09 Atoms and Stars, Class 10 53
Experiment 9
• Measure length of curved lines by winding string around line, measuring string
• Possible sources of error: (a) stretching, (b) thickness (middle of string along the curve)o Protect against these!!!
• To multiply by , calculate length differences etc.: convert lengths from inches and sixteenths to decimal inches INCLUDING CHECK !!!
3/30/09 Atoms and Stars, Class 10 54
Experiment 9
• Circle part and ellipse part are connected. DO NOT treat them as separate.
• When you turn them both in, additional questions (not in manual):o Are measurement errors for circle and ellipse
the same, or different?o If they are different, how can this be the case?
Experiment 9 (new)• Put in both Part 1 and Part 2: care with
techniqueo String goes under plastic part of pinso Center of string is centered on the circle / ellipseo Care not to stretch string
• There will be a contradition and you must recognize ito If you are going to blame contradiction on string
method, what about that method is bad?
3/30/09 Atoms and Stars, Class 10 55