1 Atoms and Stars IST 2420 Class 12, November 24 Fall 2008 Instructor: David Bowen Course web site:...

11/24/08 Atoms and Stars, Class 12 11

Atoms and StarsIST 2420

Class 12, November 24Fall 2008

Instructor: David BowenCourse web site: www.is.wayne.edu/drbowen/aasf08

11/24/08 Atoms and Stars, Class 12 2Atoms and Stars, Class 12 2

Agenda

• Assignments, passbacks, initial signin sheet• The semester is ending• Upcoming assignments• Essay 2• Reading: Chemistry• Waves and the Uncertainty Principle• Lab 7: Specific gravity


Upcoming …

• Don’t put off Essay 1!!! See me instead.• This week (November 24):

o Reader: Chemistryo Manual: Lab 7: Specific Gravityo Turn in Lab 9 as a whole

• Next week (December 1:)o Essay 2 due via Blackboardo Lab 11 – The Orbiting Bottleo SET


Upcoming …

• December 8 (last regular class)o Review for Final Examo 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


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)


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!


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.


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 requirementso All quotes must have references


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


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

clockmakero Role of God in celestial motion is possible but

not required – maybe “hand of God” as causeo We cannot escape this change (explanation)


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 authorityo Practical changes are too small to detect


Fact? (cont’d)

• So science offers practical certainty, but not philosophic certaintyo Also, scientific knowledge changes

• Does religion offer certainty?o Each claims to be certain, but they disagreeo 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

The Development of Chemistry


Readings – Galileo and Later

1450 1500 1550 1600 1650 1700 1750

Copernicus

BraheKepler

GalileoDescartes

NewtonBacon

The Rise of Science(the core of this course)

The Greeks


Readings – Chemistry (Q10c#2, d)

• Chemistry developed after Newton (who started physics) from:o Alchemy – transmutation of elementso Medicineo Industry – much demand for chemicals 1700so Mechanical approach from Descartes & Newton

• 1700 still the four Aristotelian elementso Earth – fixed volume & shapeo Water – fixed volume only


Chemistry• 1700 still Aristotelian elements

o Air – volume & shape expanded to containero 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 watero But liquids supposed to evaporate into airo Fire combined with liquid = air? Many types?

• Water could be solid, liquid, vapor –differ by fire?


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 cloudyo 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)


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


Chemistry

• Antoine Lavoisier (1743 – 1794)o Graduated in law but continued science studieso Accurate weighing, also many practical resultso (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


Chemistry

• Calx of mercury (oxide of mercury) when heated gave off air (gas) that supported combustion and lifeo Priestley found this air better (5×) for combustion

and life than “common air” (air) – “eminently respirable air”

• Lavoisier had assumed it was common airo Lavoisier confirmed this, but common air was

then a mixture


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 watero Lavoisier – water was not an element,

combination with oxygen for all combustion


Chemistry

• Lavoisier named flammable air “hydrogen” for “water former”

• Lavoisier and others formed new chemical terminology – speaking well was like reasoning wello Oxide – combination with oxygeno Names indicated amount of oxygen (ous < ic)

• Sulfurous acid H2SO3

• Sulfuric acid H2SO4


Chemistry

• Lavoisier terminologyo Gas – any vaporo 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?


Chemistry

• John Dalton (1766 – 1844), meteorologisto 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 ratioso Dalton proposed formulae based on these –

chemical atomism


Chemistry

• John Dalton (1766 – 1844), meteorologisto Dalton proposed formulae based on theseo Many of his formulae were wrong

• Example: he said water is HO• More were right, enough to straighten out the errors

over timeo (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


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


Experiment IV (not done) (Q11)

• Chemical composition of water

• Electrical current decomposes water: H2O 2H + O

Lab ManualPg 13


Atomic Nature of Matter (Review)

• 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


Brownian Motion (Review)

Jagged tracks of pollen particles.

Gas molecules mode visible. Jagged tracks explained as due to collisions with gas molecules.

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)


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)


Expanding Circles (Q15)Example 3: Statistical Mechanics• Ludwig Boltzmann, end of 19th century

o Physicists had never accepted idea of atomso Boltzmann (Austrian physicist) one of firsto 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 ideaso May have contributed to Boltzmann's 1906 suicide


Expanding Circles• Now Boltzmann honored as pioneer

o Statistical Mechanics very important• Significantly modified by Quantum Mechanics.

• Second Law of Thermodynamicso 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


Expanding CirclesStatistical Mechanics• Theory: molecules in a gas move and

collide randomly, governed by laws of statistics and by Newton’s Lawso 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


A Taste of Statistical Mechanics• See next slide, but here is the explanation

o “Gas” with spaces for 4 atomso Gas divided into left & right halveso Two green atoms, two blueo In each half, the 4 atoms arrange randomlyo Atoms too small to see, we see the average color in

each halfo One chance for left being green, right blueo Another chance for the oppositeo 4 chances for mixed – turquoise

• Chances get more lopsided with more atoms


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

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, staro One location (or center)o Newton’s three laws govern motion

• Waveo Examples: waves in water, sound waves, radio

waveso Spread out, exists in many placeso “Wave Equations” governed motion (not

Newton)


Two different types of things

Particle WavePosition: Definite – one

position (center)Spread out, no one place

Try to catch it – result is:

Get all or none Only get part, if that

Collision with another:

Ricochet, bounce, shatter

Pass through each other

Existence: All by itself In something – the “medium” (before Maxwell)


Demonstrations• PhET (Physics Education Technology)

http://phet.colorado.edu/simulations/sims.php?sim=Gas_Properties

o Particles: Gas Properties – they bounceo Waves: Sound >> Interference by Reflection

• Interference: light peak, dark trougho 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.htmlo Confine a wave – it spreads out


Particles collide…

Particles of gas mix together, collide


but waves pass through each other

Sound wave and its reflection(type – sound - is unimportant here)


Waves “interfering”

Confine a wave and it spreads out


Waves• Wavelength –

distance between peaks (or troughs)

• Fixed speed• Until 20th century,

Wave / Particle – we thought everything was one or the other

Wavelength


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 slideo Led to “Uncertainty Principle”

• Irreducible uncertainty in our knowledge


Uncertainty Principle

• 1795 Carl Friedrich Gauss (college student)

• Uncertainty called (“sigma”, LC Greek s)• Also Uncertainty Principal 1927 Werner

Heisenberg – cannot locate particle exactly



• No practicaleffect atmacroscopic levelo 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 levelo Uncertainties are large on atomic scaleo What underlies our reality is strange



• Example: A = 20 / C

• Uncertainty small for large masses, large for small masses, atoms have very small masses

C A

2 10 Divide by small number, get big number. Divide by larger number, get smaller number.5 4

Experiment 9


Experiment 9: overall

• Important conclusions from Part 1 (Circle):o The formula is almost certainly correcto Value of almost certainly correcto 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?

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 scaleo Use string slings for block and dumbbell


Experiment 7

• Using the fish scales:o Turn ono 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


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



• 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 watero H = change in height with/without block


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



• 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



• Measuring length starting from 1” can be more accurate, but be carefulo Subtract the 1 from the end readingo What is the distance between two marks below?

• 1½” or 2½”?

1 Atoms and Stars IST 2420 Class 12, November 24 Fall 2008 Instructor: David Bowen Course web site:...

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