Atoms and Stars
IST 2420
Class 12, November 24
Fall 2008
Instructor: David Bowen
Course web site: www.is.wayne.edu/drbowen/aasf08
1
Agenda
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Assignments, passbacks, initial signin sheet
The semester is ending
Upcoming assignments
Essay 2
Reading: Chemistry
Waves and the Uncertainty Principle
Lab 7: Specific gravity
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2
Upcoming …
• Don’t put off Essay 1!!! See me instead.
• This week (November 24):
o Reader: Chemistry
o Manual: Lab 7: Specific Gravity
o Turn in Lab 9 as a whole
• Next week (December 1:)
o Essay 2 due via Blackboard
o Lab 11 – The Orbiting Bottle
o SET
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Upcoming …
• December 8 (last regular class)
o Review for Final Exam
o Due: all work to count in regular grade
• Work can be turned in later (up to one year after the
end of this semester – this course only) but will
count for a Change of Grade after the regular grades
are turned in. See the Syllabus for this.
• 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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Essay 2 (Review)
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.
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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. At the end of tonight’s class, we
will have covered all of the core topics.
• Review Syllabus for other requirements
o All quotes must have references
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Effects of Newton’s Laws
• Changed view completely from planets
locked on spheres with earth fixed at center
(Aristotle) to bodies mutually acting on
each other through known laws, with
nothing fixed
• Each (Copernicus to Newton) saw
themselves as making marginal changes to
improve model supported by religion
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Newton’s Laws (cont’d)
• However, looking back from where we are,
Newton made it possible to see a universe
without a God (except for setting up
universe and starting it off)
o Newton: “clockwork universe,” God as
clockmaker
o Role of God in celestial motion is possible but
not required – maybe “hand of God” as cause
o We cannot escape this change (explanation)
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What Can We Trust as a Fact?
• As practical matters, Newton Laws, Special
Relativity, General Relativity and Quantum
Mechanics (all 20th Century) are extremely
accurate, within their range of authority.
• Philosophically, each of the more recent
ones undermines the earlier ones, even
within their range of authority
o Practical changes are too small to detect
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Fact? (cont’d)
• So science offers practical certainty, but not
philosophic certainty
o Also, scientific knowledge changes
• Does religion offer certainty?
o Each claims to be certain, but they disagree
o Each claims to be eternal and unchanging, but
they have changed
• My conclusion: humans cannot have
universal, eternal truth, but we can do well
enough for any practical purpose
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The Development of Chemistry
Readings – Galileo and Later
The Rise of Science
(the core of this course)
Copernicus
Brahe
Kepler
Galileo
Descartes
The Greeks
Bacon
Newton
1450
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1500
1550
1600
1650
Atoms and Stars, Class 12
1700
1750
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Readings – Chemistry (Q10c#2, d)
• Chemistry developed after Newton (who
started physics) from:
o
o
o
o
Alchemy – transmutation of elements
Medicine
Industry – much demand for chemicals 1700s
Mechanical approach from Descartes & Newton
• 1700 still the four Aristotelian elements
o Earth – fixed volume & shape
o Water – fixed volume only
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Chemistry
• 1700 still Aristotelian elements
o Air – volume & shape expanded to container
o Fire - passed through container walls
• 1727 – Stephen Hale: released “fixed” air
(put out flames) from solids, much interest
• 1749 Jean-Jacques DeMairan evaporated
liquids (e.g. ether) in a vacuum, froze water
o But liquids supposed to evaporate into air
o Fire combined with liquid = air? Many types?
• Water could be solid, liquid, vapor –differ by fire?
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Chemistry
• How could “big four” be elements?
• 1750s Joseph Black experiments with
“magnesia alba,” gave off “fixed air” that
extinguished flame (CO2), denser than
“common air,” turned limewater cloudy
o Use limewater test to show fixed air came from
fermentation & charcoal combustion, would not
support life
• “Fixed air” became specific name for this gas (CO2)
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Chemistry
• 1766 Henry Cavendish: “inflammable air” H
• 1772 Joseph Priestley obtained “fixed air” in
other ways, demonstrated solubility in water
(& taste – birth of carbonated beverage
industry)
o Many other types of air – “dephlogisticated air” O
• Phlogiston theory of combustion – burning releases
phlogiston – from Germany, industrially useful
– Phlogiston theory before Caloric and Kinetic theories of heat
• When air is saturated with phlogiston, combustion and
life cease
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Chemistry
• Antoine Lavoisier (1743 – 1794)
o Graduated in law but continued science studies
o Accurate weighing, also many practical results
o (Calcination – turn a metal to powder (“calx”) by
heating in air below melting point – phlogiston
theory explained this as driving off phlogiston)
o But Lavoisier’s weighing showed that weight of
calx increased, for all metals – a problem for
phlogiston theory of combustion
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Chemistry
• Calx of mercury (oxide of mercury) when
heated gave off air (gas) that supported
combustion and life
o Priestley found this air better (5×) for combustion
and life than “common air” (air) – “eminently
respirable air”
• Lavoisier had assumed it was common air
o Lavoisier confirmed this, but common air was
then a mixture
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Chemistry
• 1778 Lavoisier showed this air also formed
acids, named it oxygen (“acid former”) (but
we now know that hydrogen makes acid)
• 1783 Cavendish’s assistant told Lavoisier
about Cavendish’s experiment of applying
spark to inflammable air (H), finding dew
which was identified as water
o Lavoisier – water was not an element,
combination with oxygen for all combustion
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Chemistry
• Lavoisier named flammable air “hydrogen”
for “water former”
• Lavoisier and others formed new chemical
terminology – speaking well was like
reasoning well
o Oxide – combination with oxygen
o Names indicated amount of oxygen (ous < ic)
• Sulfurous acid H2SO3
• Sulfuric acid H2SO4
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Chemistry
• Lavoisier terminology
o Gas – any vapor
o Air – the atmosphere, a mixture (80% N, 20% O)
o Fire was caloric (no correct theory until 19th
century – started by Count Rumford)
• John Dalton (1766 – 1844), meteorologist
o Converted to chemistry when he understood air
was a mixture – why didn’t different gases
separate by gravity?
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Chemistry
• John Dalton (1766 – 1844), meteorologist
o Also gases dissolved in water proportional to
pressure – why?
o Hypothesized gases composed of atoms, each gas
interacted with itself (see later slide)
o “Law of definite proportions” – chemicals
combined by weight in simple ratios
o Dalton proposed formulae based on these –
chemical atomism
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Chemistry
• John Dalton (1766 – 1844), meteorologist
o Dalton proposed formulae based on these
o Many of his formulae were wrong
• Example: he said water is HO
• More were right, enough to straighten out the errors
over time
o (DB) Physicists did not accept chemical atomism
until they accepted Maxwell and Boltzmann at the
end of 19th century
o (DB) Direct observations of atoms in 20th century
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Chemistry (DB)
• John Dalton (1766 – 1844), meteorologist
o What led Dalton to hypothesize atoms?
• Characteristics of matter
– Solids cannot occupy the same space
– Some liquids can
– All gases can
• Why didn’t lighter gas rise, heavier sink?
– Composition of atmosphere the same to 15,000 feet
– Fog
• Gases could interpenetrate if it was atoms with lots of
empty space in between
• Water could be gas, liquid, solid, these forms must
have atoms
• Extended to all liquids and solids
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Experiment IV (not done) (Q11)
• Chemical
composition
of water
• Electrical
current
decomposes
water: H2O
 2H + O
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Lab Manual
Pg 13
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Atomic Nature of Matter
(Review)
• 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
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Brownian Motion (Review)
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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Expanding Circles
Implication #1, Example 3
Expanding Circles (Q16)
• Review: science started out as isolated areas
• Then areas expand – science always
pushing its boundaries
• Implication #1: What happens when two
expanding circles meet?
• Implication #2: What happens when circles
fill the space?
o My answer: science drives technology (see
C8S15-19 for details)
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Expanding Circles
• Implication #1: What happens when two
expanding circles meet? I promised three
examples (Q15)
1. Newton uniting celestial (stars) and terrestrial
(on land) – already done (C12S12)
2. James Clerk Maxwell uniting Electricity and
Magnetism (Class 9, November 3)
3. Ludwig Boltzmann uniting atoms and
Newton’s Laws (this class)
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Expanding Circles (Q15)
Example 3: Statistical Mechanics
• Ludwig Boltzmann, end of 19th century
o Physicists had never accepted idea of atoms
o Boltzmann (Austrian physicist) one of first
o Worked out Newtonian mechanics for a gas of
colliding atoms and molecules - Statistical Mechanics
•
With J. Willard Gibbs – now has his own stamp
o DB: “Atomic Theory meets Isaac Newton”
o Same results as Thermodynamics (accepted, see later)
•
Also explained how those results came about (explanatory)
• Other physicists still sharply rejected these ideas
o May have contributed to Boltzmann's 1906 suicide
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Expanding Circles
• Now Boltzmann honored as pioneer
o Statistical Mechanics very important
• Significantly modified by Quantum Mechanics.
• Second Law of Thermodynamics
o If a hot object and a cold one are in contact,
energy always goes from hot to cold
• Atoms in hot object more energetic (Rumford),
travel more
• Slowed down by collisions with slower atoms from
cold object, but these are sped up
• Statistical Mechanics explains why this happens
• Demonstration – diffusion – atoms of dye
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Expanding Circles
Statistical Mechanics
• Theory: molecules in a gas move and
collide randomly, governed by laws of
statistics and by Newton’s Laws
o Too many particles to follow each, so calculate
the averages
• Once particles mix, essentially no chance of
their separating again
• Computer simulation of this mixing
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A Taste of Statistical Mechanics
• See next slide, but here is the explanation
“Gas” with spaces for 4 atoms
Gas divided into left & right halves
Two green atoms, two blue
In each half, the 4 atoms arrange randomly
Atoms too small to see, we see the average color in
each half
o One chance for left being green, right blue
o Another chance for the opposite
o 4 chances for mixed – turquoise
o
o
o
o
o
• Chances get more lopsided with more atoms
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A Taste of Statistical Mechanics
• Start with gas (4
slots) and atoms
• We see average
of color in each
half
• Most common is
mixed
• Odds more
lopsided with
more atoms
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Two Different Types of Things
Background for reading for 12/8,
“Knowledge or Certainty “
Two different types of things
• Particle (“thing,” “object”)
o Examples: baseball, soup can, projectile, star
o One location (or center)
o Newton’s three laws govern motion
• Wave
o Examples: waves in water, sound waves, radio
waves
o Spread out, exists in many places
o “Wave Equations” governed motion (not
Newton)
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Two different types of things
Particle
Wave
Position:
Definite – one
position (center)
Spread out, no one
place
Try to catch it –
result is:
Collision with
another:
Existence:
Get all or none
Only get part, if
that
Pass through each
other
In something – the
“medium” (before
Maxwell)
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Ricochet,
bounce, shatter
All by itself
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Demonstrations
• PhET (Physics Education Technology)
http://phet.colorado.edu/simulations/sims.php?sim=Gas_Properties
o Particles: Gas Properties – they bounce
o Waves: Sound >> Interference by Reflection
• Interference: light  peak, dark  trough
o http://www.colorado.edu/physics/2000/schroedinger/big_interference.html
–
some areas gray (unlit)
• Light: early 1800s, Thomas Young proved light
is a wave – “double slit experiment”
o http://www.colorado.edu/physics/2000/schroedinger/two-slit2.html
o Confine a wave – it spreads out
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Particles collide…
Particles of gas mix together, collide
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but waves pass through each other
Sound wave and its reflection
(type – sound - is unimportant here)
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Waves “interfering”
Confine a wave and it spreads out
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Waves
• Wavelength –
distance between
peaks (or troughs)
• Fixed speed
• Until 20th century,
Wave / Particle –
we thought
everything was one
or the other
11/24/08
Wavelength
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Wave-Particle Duality
• In 20th century, with rise of Quantum
Mechanics, we understood that everything
was both.
o For a wave, x (position) and v (velocity)
connected – see later slide
o Led to “Uncertainty Principle”
• Irreducible uncertainty in our knowledge
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Uncertainty Principle
• 1795 Carl Friedrich Gauss (college student)
• Uncertainty called  (“sigma”, LC Greek s)
• Also Uncertainty Principal 1927 Werner
Heisenberg – cannot locate particle exactly
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Uncertainty Principle
• No practical
effect at
macroscopic level
o A philosophical problem with The Mechanical
Universe and with “The God’s eye view” or
The Clockwork Universe over age of universe
• Important at atomic and molecular level
o Uncertainties are large on atomic scale
o What underlies our reality is strange
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Uncertainty Principle
• Example: A = 20 / C
C
A
2
10 Divide by small number, get big
number. Divide by larger number, get
4
smaller number.
5
• Uncertainty small for large masses, large for small
masses, atoms have very small masses
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Experiment 9
Experiment 9: overall
• Important conclusions from Part 1 (Circle):
o The formula is almost certainly correct
o Value of  almost certainly correct
o The method for measuring C is valid within .1” or .2”
• Method: putting pins along path, looping string along pins,
removing string and measuring its length
• Circle part and ellipse part are connected. DO
NOT treat them as separate.
• Should measurement errors be the same, or
different?
• If they are different, how can this happen?
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Experiment 7
Specific Gravity
Experiment 7
• Checking on Archimedes: saw water rise when he got
into bathtub, ran through city shouting “Eureka”
• Displaced water – submerse object in water, water
level rises, this is displaced water = volume of object
• Specific Gravity – property of material:
SG: (object’s weight)/(displaced water’s weight)
• S.G. is a help in identifying the material
• Weighing objects (wood block, dumbbell, displaced
water):
o Weight in pounds and ounces using fish scale
o Use string slings for block and dumbbell
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Experiment 7
• Using the fish scales:
o Turn on
o Wait for numbers to stop flashing
• While numbers are flashing, scale is adjusting the
zero
• Will show 0 0 when flashing stops
o After numbers have stopped flashing, THEN
attach weight and read it
• Reading is pounds and ounces
• Convert ounces to decimal pounds by dividing by 16
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Experiment 7 (cont’d)
• Converting pounds and ounces to decimal
pounds:
1. Divide # ounces by 16 (result between 0 and 1),
call this “X” (round to nearest tenth)
2. Check: multiply X by 16, should get about the
original # ounces – SHOW THIS CHECK ON
DATA SHEET !!!
3. Add X to # pounds to get decimal pounds
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Experiment 7 (cont’d)
• Converting inches and sixteenths to decimal
inches:
o Same as for pounds and ounces to decimal
ounces, INCLUDING CHECK !!! (previous
Slide)
• For step # 5, ignore rounded edges and
grooves in block: V = L × W × H
• Same for #6, volume of water
o H = change in height with/without block
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Experiment 7 (cont’d)
• For both wood block and dumbbell:
o Find object’s weight and weight of displaced
water, divide to find Specific Gravity
• For wood block only:
o Find object’s volume and compare to volume of
displaced water. Archimedes: volumes the same
• For dumbbell only:
o Find object’s weight “in water,” compare with
weight “in air” (normal) and weight of
displaced water
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Experiment 7 (cont’d)
• For #7, you will probably have to use
different amounts of water in the tub for
each object.
o Hold object down if necessary (i.e. wood),
cover with water, remove object, then start that
part of the lab
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Experiment 7 (cont’d)
• Measuring length starting from 1” can be
more accurate, but be careful
o Subtract the 1 from the end reading
o What is the distance between two marks below?
• 1½” or 2½”?
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