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Atoms and Stars, IST 2420Midterm Makeup in 122 Cohn
Monday, November 174:50 – 5:50 PM
Atoms and StarsIST 2420
Class 11, November 17Fall 2008
Instructor: David BowenCourse web site: www.is.wayne.edu/drbowen/aasf08
11/17/08 Atoms and Stars, Class 11 3
Agenda
• Assignments and passbacks• Upcoming assignments• Relativity• Expanding Circles – Implication #1• Update: planets and exoplanets• Readings: Atomic Nature of Matter • Converting Sixteenths to Decimal• Lab 9 Part 2 (Ellipse): Archimedes’ Exploits
11/17/08 Atoms and Stars, Class 11 4
Upcoming …• Don’t put of Essay 1!!! See me instead.• This week (November 17):
o Remember to initial the sign-in sheeto Reader: The Atomic Nature of Mattero Manual: Lab 9 – the Ellipse
• Next week (November 24):o Reader: Chemistryo Manual: Lab 7 – Specific Gravityo Hand in Lab 9 as a whole
11/17/08 Atoms and Stars, Class 11 5
Upcoming …• Two weeks, December 1: Essay 2 due via
Digital Dropbox in Blackboardo Lab 11 – the Orbiting Bottleo SET
• Three weeks: December 8. (last regular class)o Lab 4 – The Chemical Composition of Watero Review for Final Examo Due: all work to count in regular grade
• Four weeks: December 15. Nothing that night but the Final Exam
11/17/08 Atoms and Stars, Class 11 6
Grade What-If
• Grade What-If (on course web site – see first slide for this URL)o Reminder: to get current course average, do
NOT put anything in for assignments you haven’t been graded for yet
• If you put anything in, remove it using “delete” keyo To see what happens if you miss assignments,
put in zeroes for those (this is what I will do)
11/17/08 Atoms and Stars, Class 11 7
Semester is Ending!
• If you have been relying on being able to turn work in late, it is time to get goingo Alternatives: D, F, I, drop – see counselor!
• Getting ready for Final:o Read Information Sheet carefully – a lot of
information thereo Look at Final Topics carefullyo Use Review Session!
11/17/08 Atoms and Stars, Class 11 8
Expanding Circles (Review)
• Implication #1: eventually, expanding circles must meet and overlapo Different approaches, different theories – will
not agree
11/17/08 Atoms and Stars, Class 11 9
Expanding Circles (Review)
• Implication #2: circles could meet and fill the spaceo What happens then?o DB: what happens is what makes science
valuable
11/17/08 Atoms and Stars, Class 11 10
Expanding Circles
• Implication #1: eventually, expanding circles must meet and overlap
• Three examples in this course:o Isaac Newton (review, this class)o James Clerk Maxwell (Class 9, November 3)o Ludwig Boltzmann (later class)
11/17/08 Atoms and Stars, Class 11 11
Expanding Circles
• Implication #1: eventually, expanding circles must meet and overlap
• Possible interactions:o Withdrawalo One wins out over the othero Compromiseo Synthesiso ???
11/17/08 Atoms and Stars, Class 11 12
Expanding Circles
First example: celestial and terrestrial mechanics• Case of Newton 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)
11/17/08 Atoms and Stars, Class 11 13
Expanding Circles
• Expanding Circles – my conclusiono When two domains meet, become fused into one with a
bonuso Not a compromise – both areas transformed
• Implications:o This is additional evidence for science
• If theories were imaginary, different imaginations would ruleo Hard to attack just one area of science, since they are
becoming more tightly tied together• Creationists and Intelligent Design advocates finding they have
to attack 4.5 billion year age of earth, Big Bang, etc. (readings), radioactive dating
11/17/08 Atoms and Stars, Class 11 14
Limits on Space Travel
• The idea of space travel has always been attractive.
• Einstein’s Special Theory of Relativity (1905) set limitations on space travel.o Maximum possible speed is speed of light –
one year to travel one light year (but today we cannot reach even a small fraction of this)
o Nearest star is 4 light years awayo Galaxy ~100,000 light years across
11/17/08 Atoms and Stars, Class 11 15
Background
• Before 1905, we could not see expected changes in the speed of light when the direction of the earth changed as it orbited the sun.
• Tried to explain this by saying that distance-measuring devices got shorter in direction of motion.
• Didn’t work.
11/17/08 Atoms and Stars, Class 11 16
Relative Motion
• Newton said that speeds in the same direction should add, nothing special about light.
• Simulation – car traveling on top of a railroad car:http://www.is.wayne.edu/drbowen/Class-Room_Models/Welcome.htm
• Speed of car with respect to station = speed of railroad car + speed of car on railroad car
• Speed of light could be exceeded – no issue for Newtonian view
11/17/08 Atoms and Stars, Class 11 17
Relative Motion
Relative motion of rr-car and car on top. car speed wrt station = rr-car speed + car speed on top of rr-car
11/17/08 Atoms and Stars, Class 11 18
Special Relativity• Newtonian Relativity simple, correct at normal
speeds, but wrong for very high speeds (light).• Einstein’s Theory of Special Relativity (1905)
said constant measured speed of light is a property of space and time themselves. No explanation – that’s the way things are, a fundamental condition.
• Space and time went from the passive stage for the universe to active players in the drama.
• Revolutionary, but it works.
11/17/08 Atoms and Stars, Class 11 19Atoms and Stars, Class 10 19
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
11/17/08 Atoms and Stars, Class 11 20Atoms and Stars, Class 10 20
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
11/17/08 Atoms and Stars, Class 11 21Atoms and Stars, Class 10 21
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
11/17/08 Atoms and Stars, Class 11 22Atoms and Stars, Class 10 22
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!
11/17/08 Atoms and Stars, Class 11 23Atoms and Stars, Class 10 23
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
11/17/08 Atoms and Stars, Class 11 24Atoms and Stars, Class 10 24
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
11/17/08 Atoms and Stars, Class 11 25
“Stars” Summary
• Long human interest in astronomy• Greeks (Aristotle and Ptolemy) geocentric• Catholic Church gave this additional
importance• Copernicus – first modern heliocentric
theory – simpler, more accurate• Brahe – accurate continuing measurements
11/17/08 Atoms and Stars, Class 11 26
“Stars”Summary
• Kepler – Three Laws, orbits are ellipses – a descriptive theory – what the patterns are
• Galileo – observations calling aspects of Aristotle’s and Church’s astronomy into doubt
• Newton – explanatory theory – why the orbits are ellipses, etc. (because of the force)
11/17/08 Atoms and Stars, Class 11 2727
Update: What is a planet?
• 1846 Neptune discovered from changes to orbit of Uranus, using Newton’s Lawso Predicted position and masso Productivity
• Pluto discovered 1930, orbit radius ~30 AU• 2002 – 2006 other solar system objects found by
looking for motion between exposureso Quaoar, 2003 VB12 (“Sedna”), 2004 DW, Xena
• Xena larger than Pluto – is it a planet?• 39 to 97 AU (very flattened ellipse)• Plane ~ 43° to ecliptic
11/17/08 Atoms and Stars, Class 11 2828
New “planets” (cont’d)
• Neptune outermost “real” planet
• New ones near Kuiper belt (asteroids)
• “Reals” formed from dust cloud, forced orbits to circular
11/17/08 Atoms and Stars, Class 11 2929
New “planets” (cont’d)
• “Classification” - what is a planet?o Follows “description” in development of
scienceo What are the real differences?
11/17/08 Atoms and Stars, Class 11 30
2007 Change
• New planets are not planets, neither is Pluto (“planetoid”)o Now, eight planets
• New characteristic of planet: has cleared its orbit of other bodies
30
11/17/08 Atoms and Stars, Class 11 31
What are these things??
Category Greek Modern
Star “Fixed” – travel together
Shines with own light
Planet “Wanderer” – does not travel with stars, Earth not a planet
Circles a star, shines by reflected light (New: clears out orbit)
Moon Only one, like planet
Circles a planet, reflected light
31
11/17/08 Atoms and Stars, Class 11 32
Exoplanets
• Exoplanet – outside our solar systemo Circle other stars, shine by reflected lighto Can they support life?
• Methods:o Star wobbles (Newton’s Third Law)o Dip in brightness of star as planet passes overo Just this week: direct observation
• Count: 327 around 278 starso None earthlike yet
11/17/08 Atoms and Stars, Class 11 33
Exoplanets
11/17/08 Atoms and Stars, Class 11 34
Three waves of science?
1. Physical science – the subject of this course – mature, quantitative (95%)
• Very controversial when it was new• 1400 – 1800 AD, although very long roots & still
developing• Now pretty much settled for everyday objects
2. Biological or life science – qualitative (30%?)• Much newer, evolution is the basis, still controversial
publicly, but for scientists it is settled• 1800 – 1935 AD
• Coming into general use in society & economy• Will qualitative change to quantitative?
11/17/08 Atoms and Stars, Class 11 35
Three waves of science?
3.Cognitive science – how emotions and the mind work – just starting (5%)o Will be as controversial, if not moreo Potential for controversy: Science of Desire :
The Gay Gene and the Biology of Behavior & The God Gene (spirituality) / Dean Hamer• Spirituality predestined for some, denied to others?• A single gene is unlikely to be the sole cause
o Will call into question how we view ourselves
11/17/08 Atoms and Stars, Class 11 36
Summary, Once More…• Strong dose of the value of science here• One more time, about science:
o Two pillars – repeatable experiment (what makes it reliable) and explanatory theory (what makes it valuable)
• Developed 1400 – 1800 AD: Copernicus to Daltono Developing hypotheses and theories is creativeo Has a boundary but expands aggressively
not a complete basis for livingo Now drives technology (coming up)o We all use the technologyo Conflicts with some, but not all, religious beliefs
• People do not agree on what “Christian” is, let alone other religions
o People of all ethnicities have been able to contribute
11/17/08 Atoms and Stars, Class 11 37
Two parts• Newton ended the “Stars” part of this course• This week starts the “Atoms” part• “Element” – Greeks understood this to be
something fundamental, without parts, not made from other things, could not be broken downo Aristotle: air, earth, fire & water are elementso First discoverers of atoms disproved Aristotle, thought
atoms were the Greek elementso Today we still call atoms “elements,” but not in the
same sense – they are made of other thingso Still have question of what (if anything) is elemental
11/17/08 Atoms and Stars, Class 11 38
And now…
• “Atoms”• Before Einstein & E = mc2, matter and
energy separate• Atomic Theory – all matter is made up of
atoms• Start by looking at our knowledge of atoms• Then, how did this knowledge come about?
11/17/08 Atoms and Stars, Class 11 39
Readings“Atomic Nature of Matter”, Hewitt• All matter is atoms (“Atomic Theory”)
o Atoms are elements – “indivisible” – mostly empty (10c#1)
o 109 types total, 90 are natural, rest radioactive• Each type has its own properties, e.g. weight,
reactionso Hydrogen most common atom in universe
• Rare by itself on eartho Life primarily C, H, O, N
• Atoms small enough to be invisible - waves
11/17/08 Atoms and Stars, Class 11 40
Atomic Nature of Matter• First direct evidence 1827 Robert Brown (10c#2)
o Noticed spores jiggling under microscopeo “Brownian motion” – bombarded by molecules
• Robert Brown, 1827o See next slides, or
http://www.is.wayne.edu/drbowen/Class-Room_Models/Welcome.htm http://www.colorado.edu/physics/phet/web-pages/simulations-base.html
o Now we have more direct evidence• Atoms bond into molecules – many types (10c#1)
o Molecules - compoundso Molecules have separate properties from atomso Burning is combination with O
• New - modern automobiles very little CO
11/17/08 Atoms and Stars, Class 11 41
Brownian Motion
Jagged tracks of pollen particles.
Gas molecules mode visible. Jagged tracks explained as due to collisions with gas molecules.
11/17/08 Atoms and Stars, Class 11 42
Brownian Motion
Imagine the red molecules were so small that we couldn’t see them – blue ones would “jostle” for no apparent reason.
11/17/08 Atoms and Stars, Class 11 43
Atomic Nature of Matter
• 1811 (Amedeo) Avogadro’s hypothesis (now Law)o At same T & P, equal Vs of gas have equal #so Each atom, molecule heavier gas heavier
• Amu = atomic mass unit• C 12 amu, H 1 amu, O 16 amu, U 238
amu, H2O 18 amu – also combine in gm, lb etc.• Atom has electrons orbiting nucleus
o Electrons – volume but very little masso Nucleus – mass but very little volume
11/17/08 Atoms and Stars, Class 11 44
Atomic Nature of Matter
• Electron, e – negative charge, flow of electrons is electrical current
• Nucleus has neutrons, n (no charge) and protons, p (positive charge)o Cube 3/8” would weigh 133,000,000 tons
• Like charges repel, unlike charges attracto Nucleii positive, repel each othero Atoms neutral; number of e = number of p
• (not = under special circumstances)
11/17/08 Atoms and Stars, Class 11 45
Atomic Nature of Matter (end)
• Electrons in shells (2, 8, 18, …)o If shells filled, element is inerto Unfilled shells determine activityo #p = atomic number, chemical characteristics
• Same element even if atom loses or gains electrons
• Antimatter – anti-electron (1932), anti-neutron, anti-protono Annihilate 100% energy (light)
• Nuclear reactions normally 1%
• End of article…
11/17/08 Atoms and Stars, Class 11 46
Element, Compound, Mixture(Q10 a-b)
• Element: matter with all atoms the sameo Examples: C, S, H, O
• Compound: made up of the same moleculeso Examples: H2O, CO2
o Matter with all molecules the sameo Atoms bond together into chemical
combinationo Always the same composition
11/17/08 Atoms and Stars, Class 11 47
Element, Compound, Mixture (end)
• Mixture (Q10a-b)o Atoms and molecules not close enough to bondo Composition varieso Examples:
• Air (mostly N and O) but variable– Amount of greenhouse gases an issue – CO2
• Earth – composition extremely variable– Add various fertilizers
• Dough – vary composition for different breads• Cinnamon and sugar
o Constituents could in principle be separated
11/17/08 Atoms and Stars, Class 11 48
Epistemology
• Several times you have asked me “Is this absolutely true?” I tend to hesitate with questions like this – here is why.
• Epistemology – the study of knowledge – why do we accept things as true?
• Two properties we would like for truth:o Eternal – unchangingo Universal – the same everywhere
11/17/08 Atoms and Stars, Class 11 49
Epistemology (end)• Science doesn’t do “eternal”
o Scientific truth is provisional – subject to changeo We keep learning new things and improving
theories• Religions have problems with “universal”
o Each religion claims universality but how can different religions differ, if there is one truth?
o For science and religion, Galileo agreed with modern Catholic doctrine – there is one truth• Reinterpret Bible if it disagrees with accepted science
11/17/08 Atoms and Stars, Class 11 50
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
11/17/08 Atoms and Stars, Class 11 51
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
11/17/08 Atoms and Stars, Class 11 52
Experiment 9
• Good technique (both parts):o When you stick pins in, leave some of metal
shaft exposed – string goes around this parto Do not stretch string (thread doesn’t stretch
much at all, thicker twine can stretch)o Use a pen to make marks on the string, measure
between the marks
11/17/08 Atoms and Stars, Class 11 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 !!!
11/17/08 Atoms and Stars, Class 11 54
Experiment 9
• Part 1: Circleo Data Sheet: Assignments 1 – 15o Analysis: Assignments 16 – 24o If Assignment 16 discrepancy > .2 inches, show me
how you did it• Part 2: Ellipse
o Data Sheet: Assignments 25 – 32 & 36o Analysis: Assignment 33
• In Addition (overall, 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?