Transcript Atoms and Stars IST 3360 and IST 1990

Atoms and Stars, IST 2420
Midterm Makeup in 122 Cohn
Monday, November 17
4:50 – 5:50 PM
Atoms and Stars
IST 2420
Class 11, November 17
Fall 2008
Instructor: David Bowen
Course web site: www.is.wayne.edu/drbowen/aasf08
Agenda
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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
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Upcoming …
• Don’t put of Essay 1!!! See me instead.
• This week (November 17):
o Remember to initial the sign-in sheet
o Reader: The Atomic Nature of Matter
o Manual: Lab 9 – the Ellipse
• Next week (November 24):
o Reader: Chemistry
o Manual: Lab 7 – Specific Gravity
o Hand in Lab 9 as a whole
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Upcoming …
• Two weeks, December 1: Essay 2 due via
Digital Dropbox in Blackboard
o Lab 11 – the Orbiting Bottle
o SET
• Three weeks: December 8. (last regular
class)
o Lab 4 – The Chemical Composition of Water
o Review for Final Exam
o Due: all work to count in regular grade
• Four weeks: December 15. Nothing that
night but the Final
Exam
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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” key
o To see what happens if you miss assignments,
put in zeroes for those (this is what I will do)
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Semester is Ending!
• If you have been relying on being able to
turn work in late, it is time to get going
o Alternatives: D, F, I, drop – see counselor!
• Getting ready for Final:
o Read Information Sheet carefully – a lot of
information there
o Look at Final Topics carefully
o Use Review Session!
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Expanding Circles (Review)
• Implication #1: eventually, expanding
circles must meet and overlap
o Different approaches, different theories – will
not agree
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Expanding Circles (Review)
• Implication #2: circles could meet and fill
the space
o What happens then?
o DB: what happens is what makes science
valuable
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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)
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Expanding Circles
• Implication #1: eventually, expanding
circles must meet and overlap
• Possible interactions:
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o
o
Withdrawal
One wins out over the other
Compromise
Synthesis
???
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Expanding Circles
First example: celestial and terrestrial mechanics
• Case of Newton uniting terrestrial and celestial
mechanics
o Newton – new theory united them
o Each is understood more accurately and causally
o A bonus – applies to all motion, calculus, applied in
technology, model for new science
o Led to understanding interactions of planets and
discovery of Neptune (a future class)
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Expanding Circles
• Expanding Circles – my conclusion
o When two domains meet, become fused into one with a
bonus
o Not a compromise – both areas transformed
• Implications:
o This is additional evidence for science
•
If theories were imaginary, different imaginations would rule
o Hard to attack just one area of science, since they are
becoming more tightly tied together
•
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Creationists and Intelligent Design advocates finding they have
to attack 4.5 billion year age of earth, Big Bang, etc. (readings),
radioactive dating
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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 away
o Galaxy ~100,000 light years across
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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 distancemeasuring devices got shorter in direction
of motion.
• Didn’t work.
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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
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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
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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.
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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 Relativity
o Gravity is due to the bending of space by
masses
o Analogy of a ball rolling on a sheet of rubber
around a heavy object
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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 force
o Difficult to find, but would be serious if not found
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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 Gravity
o Does not yet exist
o 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
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Status of Newton’s Laws
• Are scientific theories reliable? Many hedges
in this course, for example:
o
o
o
o
o
o
Scientific knowledge is provisional
Experiments do not prove theories
One experiment can overturn a theory
Science has a limited scope – a boundary
Science is not an adequate basis for living
Scientists often do not follow scientific method
• Maybe only foolish people use science? Not!
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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
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Status of Newton’s Laws
• Newton’s Laws have passed stringent tests
o Control of spacecraft
o Use in design and control of countless machines
o 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
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“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
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“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)
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Update: What is a planet?
• 1846 Neptune discovered from changes to orbit of
Uranus, using Newton’s Laws
o Predicted position and mass
o Productivity
• Pluto discovered 1930, orbit radius ~30 AU
• 2002 – 2006 other solar system objects found by
looking for motion between exposures
o 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
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New “planets”
(cont’d)
• Neptune outermost
“real” planet
• New ones near
Kuiper belt
(asteroids)
• “Reals” formed
from dust cloud,
forced orbits to
circular
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New “planets” (cont’d)
• “Classification” - what is a planet?
o Follows “description” in development of
science
o What are the real differences?
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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
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What are these things??
Category
Star
Greek
“Fixed” – travel
together
Modern
Shines with own
light
Planet
“Wanderer” –
does not travel
with stars, Earth
not a planet
Only one, like
planet
Circles a star,
shines by reflected
light (New: clears
out orbit)
Circles a planet,
reflected light
Moon
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Exoplanets
• Exoplanet – outside our solar system
o Circle other stars, shine by reflected light
o Can they support life?
• Methods:
o Star wobbles (Newton’s Third Law)
o Dip in brightness of star as planet passes over
o Just this week: direct observation
• Count: 327 around 278 stars
o None earthlike yet
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Exoplanets
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Three waves of science?
1. Physical science – the subject of this course –
mature, quantitative (95%)
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Very controversial when it was new
• 1400 – 1800 AD, although very long roots & still developing
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Now pretty much settled for everyday objects
2. Biological or life science – qualitative (30%?)
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Much newer, evolution is the basis, still controversial
publicly, but for scientists it is settled
• 1800 – 1935 AD
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Coming into general use in society & economy
Will qualitative change to quantitative?
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Three waves of science?
3.Cognitive science – how emotions and the
mind work – just starting (5%)
o Will be as controversial, if not more
o 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
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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 Dalton
o Developing hypotheses and theories is creative
o Has a boundary but expands aggressively
 not a complete basis for living
o Now drives technology (coming up)
o We all use the technology
o 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
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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 down
o Aristotle: air, earth, fire & water are elements
o First discoverers of atoms disproved Aristotle, thought
atoms were the Greek elements
o Today we still call atoms “elements,” but not in the
same sense – they are made of other things
o Still have question of what (if anything) is elemental
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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?
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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,
reactions
o Hydrogen most common atom in universe
• Rare by itself on earth
o Life primarily C, H, O, N
• Atoms small enough to be invisible - waves
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Atomic Nature of Matter
• First direct evidence 1827 Robert Brown (10c#2)
o Noticed spores jiggling under microscope
o “Brownian motion” – bombarded by molecules
• Robert Brown, 1827
o 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 - compounds
o Molecules have separate properties from atoms
o Burning is combination with O
• New - modern automobiles very little CO
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Brownian Motion
Jagged tracks of pollen
particles.
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Gas molecules mode visible.
Jagged tracks explained as
due to collisions with gas
molecules.
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Brownian Motion
Imagine the red molecules were so small that we couldn’t see
them – blue ones would “jostle” for no apparent reason.
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Atomic Nature of Matter
• 1811 (Amedeo) Avogadro’s hypothesis
(now Law)
o At same T & P, equal Vs of gas have equal #s
o 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 mass
o Nucleus – mass but very little volume
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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 attract
o Nucleii positive, repel each other
o Atoms neutral; number of e = number of p
• (not = under special circumstances)
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Atomic Nature of Matter (end)
• Electrons in shells (2, 8, 18, …)
o If shells filled, element is inert
o Unfilled shells determine activity
o #p = atomic number, chemical characteristics
• Same element even if atom loses or gains electrons
• Antimatter – anti-electron (1932), antineutron, anti-proton
o Annihilate  100% energy (light)
• Nuclear reactions normally 1%
• End of article…
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Element, Compound, Mixture
(Q10 a-b)
• Element: matter with all atoms the same
o Examples: C, S, H, O
• Compound: made up of the same molecules
o Examples: H2O, CO2
o Matter with all molecules the same
o Atoms bond together into chemical
combination
o Always the same composition
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Element, Compound, Mixture
(end)
• Mixture (Q10a-b)
o Atoms and molecules not close enough to bond
o Composition varies
o 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
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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 – unchanging
o Universal – the same everywhere
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Epistemology (end)
• Science doesn’t do “eternal”
o Scientific truth is provisional – subject to change
o 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
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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
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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
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Experiment 9
• Good technique (both parts):
o When you stick pins in, leave some of metal
shaft exposed – string goes around this part
o 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
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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 !!!
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Experiment 9
• Part 1: Circle
o Data Sheet: Assignments 1 – 15
o Analysis: Assignments 16 – 24
o If Assignment 16 discrepancy > .2 inches, show me
how you did it
• Part 2: Ellipse
o Data Sheet: Assignments 25 – 32 & 36
o 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?
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