4/21/07Atoms and Stars, Class 141 Atoms and Stars IST 2420 Class 14, April 21 Winter 2008...

4/21/07 Atoms and Stars, Class 14 1

Atoms and StarsIST 2420

Class 14, April 21Winter 2008

Instructor: David BowenCourse web site:

www.is.wayne.edu/drbowen/aasw08


Agenda

• Assignments, passbacks, initial signin sheet• Class information

o Email if much work will be late• Review of readings• Updating the course• Emphasizing main points one more time• Review for Final


Upcoming …

• Tonight, April 21 (last regular class)o Lab 11 – the Orbiting Bottle

• Checking up on Newtono Review for Final Examo Due: all work to count in regular grade

• Final Exam: next Monday, April 28o Nothing that night but the Final Exam


Course Grades

• If you are turning a bunch of work in at the end, I may not get it graded in time for the regular grades (see the Syllabus).

• If this is you (turning it in late), what grade do you want for the regular grade? D, E, W, I

• Email me to let me know – otherwise it’s my decision.


Your Current Status

• Grades I have for you:o Online Grade Report, link off the course web

site (see first slide)o Enter first name, last name, password the get

report• Grade you are headed for:

o Grade What-If on course web site• Ask for help with these if you are having

problems


Opportunities for Q & A

• Tonight during the Review Session• Day of the Final, Monday April 21, 5 – 6

PM (normal office hours) in the regular classroom (100 Shapero)

• Call, email, set up an appointment• IM to WSU web guy


16ths on the Final

• Doing the math for converting 16ths (inches, ounces) to decimal (inches, pounds)o If this type of problem is on the Final, there will

also be a table of all divisions by 16, with a few non-16ths extras thrown in

• 1/16 = .0625, 2/16 = .1250, 3/16 = .1875, 3/7 = .4286, 4/16 = .2500, etc.

o So the result of the division will be there, but you will have to know what you are looking for.


Makeup for Final Exam

• Let me know by email that you want a makeup, within 24 hours after the Final (University regulation)

• Date / Time, building and room to be settled by email.


Experiment 9• The technique for measuring the

circumference is valid.o The definition of the circumference is the

distance around the outside.o For the Circle, most groups get between 0

discrepancy and 0.2”• The formula for the circumference of the

circle (d) is correct• Formula for circumference of ellipse is

incorrect – actually, there is no simple formula


Experiment 9

• So there are two problems this presents:1. Recognize that there is a discrepancy for the

ellipse• 2 inches and more discrepancy cannot be

attributed to the technique• Cut string to shorter (theoretical) length – does

not possibly go around• Can be hard to admit

2. If there is a real discrepancy, what do you do?


Experiment 9• Some past reports have said that the formula for

the ellipse was trusted more than the experimental measuremento Both are actually based on measurementso The power of authorityo Also, not trusting your techniqueso But in this case, the authority was not trustworthy

• Many said no use in repeating measurementso Results would be the same

• No! Every technique has a limit, will have variations when you push that limit. Where is the limit of the string technique?

• It is never easy, but scientists will eventually come down on the side of experiment


Re-emphasizing Main Points

• Two pillars of scienceo Experiment: makes science reliable

• Scientists led astray by logic (Aristotle) and belief (church and geocentrism, Inquisition)

• Experiments base science on direct experienceo Theory: makes science valuable

• Once you have a reliable theory, it tells you the answer in advance, can use it as technology

• Two quotes from Copi, Reader Pg 8


Re-emphasizing Main Points

• I have the experiments in this course to:o Give you direct experienceo Illustrate experiments described in classo Illustrate social nature of science within the lab

groups


Readings: Knowledge or Certainty

Jacob Bronowksi• Absolute certainty is impossible in science

o Looking at an object with infrared, then visible, then x-rays should yield greater detail. Infrared is very blurry, visible is pretty good, but x-rays are too high energy to be focused. Perfect detail of “God’s-eye” view is impossible

o Statistical uncertainty in measurements - Gauss


Knowledge or Certainty

• 1795

• Science is discussion and argument preceding knowledge

• Also Uncertainty Principal 1927 Werner Heisenberg – cannot locate particle exactlyo Irreducible uncertainty or fuzzy focus


Knowledge or Certainty

• No practicaleffect atmacroscopic level, but a philosophical problem with The Mechanical Universe and with “The God’s eye view”

• But certainty leads to tragedy – Nazis• (DB) Certainty and power combined


What is Science?

Moti Nissani, What Is Science?• Difficult or impossible to give a dictionary-

type definition for science• (DB) Working scientists rarely think about

the history or philosophy of science• Start with philosophy of Thales – free

inquiry


What Is Science? (cont’d)

• Then hypothesis and experiment (Torricelli)• Falsifiability – reason and logic have not

been not sufficient to discover the truth in science (DB: belief, either)o But contradiction by experiment does not

always mean rejection of hypothesis – can lead to reexamination of experiment or modification of hypothesis

o Scientists “on the trail” have personal concerns



o Scientists “on the trail” have personal concerns• Argument and community lead to progress

o Semmelweiss and deaths in maternity ward• Neighboring ward far safer• Did priest’s visit scare patients?• Washing hands – doctors did dissections beforehand• This fixed the problem• Profession slow to accept this change• Even scientists can be closed-minded, resist change



• Theories unify many hypotheses and experimentso Price is often inaccessibility to non-scientists

• Scientists usually not concerned with these issues or with philosophical uncertainty

• Science many not be perfect, but it can still be very good

• Many use technology but not the scientific foundation


Doppler Effect (Review)

• Video• Frequency of wave higher if source is

moving towards us, lower if moving away• Evidence that stars are moving away from

uso Colors shifted redder (“red shift”)o First evidence for Big Bang


Physical Science: Current Status

• Newton’s Laws, Maxwell’s Equations and similar classical theories (before ~ 1900) describe world we know and see

• For things the size of molecules and smaller, need Quantum Mechanics

• Very fast, need Special Relativity• Very heavy, need General Relativity• All three have weird things going on


Relativity

• Reminder about what this is abouto Computer simulation

• Often very difficult to tell whether or not our measurements are in a moving coordinate systemo Earth spins on axis, moves around Sun, Sun

moves around Galaxy, is Galaxy moving?• Theory of Relativity says we can only tell

relative motion, not absolute

http://www.is.wayne.edu/drbowen/Class-Room_Models/Welcome.htm


Special Relativity

• For fast-moving objectso Max speed = c (speed of light)o Objects foreshortenedo Time slows downo But the traveling person says the same about

you!o Space and time space-timeo E = mc2

light has mass, is bent by gravity


General Relativity

• For very heavy objectso Space and time warp, cause gravityo Perihelion (closest approach to sun) of

Mercury’s ellipse not fixed as in Newton’s Laws, but advances 43 seconds of arc per century (observed), other effects in addition

o Says light bends twice as much as Special Relativity says, observed 1918


General Relativity (cont’d)

• “Einstein Halo” – light from far galaxy bent by near galaxy

• Variation on gravitational lens

• 12 found so far• Picture: New York Times, 12/6/05,

Pg D4 (Science)


Quantum Mechanics


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://www.colorado.edu/physics/phet/web-pages/simulations-base.html

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

http://www.colorado.edu/physics/phet/web-pages/simulations-base.html

http://www.colorado.edu/physics/2000/schroedinger/big_interference.html

http://www.colorado.edu/physics/2000/schroedinger/two-slit2.html


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• Momentum p = m × v (m = mass, amount of matter)

o Led to “Uncertainty Principle”• Irreducible uncertainty in our knowledge


Uncertainty Principle

• 1795 Carl Friedrich Gauss (college student)

• Also Uncertainty Principal 1927 Werner Heisenberg – cannot locate particle exactly


Quantum Mechanics

• At molecular level and smaller, waves and particles merge – everything is botho Wave – spread out, cannot contain ito Particle – have it or don’to Q.M.: wave gives chance of “catching” particle

• Cannot be made certain• Uncertainty Principle

o Carries over to regular world, makes clockwork universe impossible over age of universe


Quantum Mechanics (cont’d)

• Accounts for properties of ordinary materialso Theoretical: keeps matter from collapsingo Coloro Solid (strength), elastic, gaseouso Solid state electronics – semiconductorso Forces – due to exchanges of particles

• No Newtonian “action at a distance”• E.g. electrical force carried by photons – particles of

light


Conflict!• Heavy (G.R.) and small (Q.M.) –

mathematical conflict. Example: Black Holeo Competing theories of gravity – “embarrassing”

• G.R.: gravity caused by masses warping space-time• Q.M. – gravity due to exchange of “gravitons” (not

found yet)o “String Theory” might unite these two

• “Theory of Everything” – accelerating expansion(!)• Matter and energy composed of elemental vibrating

strings and membranes• Eleven dimensions, seven curled up too small to

experience directly – may have indirect experience• Theory still developing, no unique experimental

evidence yet


Issues:

• “Anthropic Principle” – physical rules seem to favor lifeo Room for God inside science?o But “Inflationary Universe” may explain this

• Dark Mattero Galaxies spinning fast, not enough mass to hold

them together so they should be flying apart but this is not observed

o Must be Dark Matter at center of galaxies


Issues (cont’d):

• Dark Energyo Big Bang should be

slowing downo But outer half of universe

is accelerating!o Current hypothesis is that

dark energy at outsidefringe is attracting the inner parts.

• Between these two, we see only 5%. The universe is still surprising us!

Source: NASA


The end of the ride• 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 technologyo We all use ito Conflicts with some, but not all, religious beliefso People of all ethnicities have been able to contribute


Lab 11: Orbiting Bottle• Swing bottle on string

o Measure distance from finger to middle of water, convert to decimal feet (÷ inches by 12)

o Measure weight of bottle, convert to decimal pounds

o Time ten “orbits” or circles (count from zero!)o Measure angle down from horizontalo Use formulae

• Large hand motion to get bottle moving, then small hand motions to sustain motion during measurements


Orbiting Bottle

• String pulls in two directions, H and V

• Two formulae for FH

1. FV (up) balances W (down), then angle determines FH

2. Inward force to move bottle in circular orbit

• Two should agree, roughly


Lab 11: Orbiting Bottle

• If your two results (A & B) for the horizontal (inward) force, FH, agree, then your data are consistent with Newton’s Laws (including Universal Law of Gravitation).

• See Theory section for the proof of this


Review for Final

4/21/07Atoms and Stars, Class 141 Atoms and Stars IST 2420 Class 14, April 21 Winter 2008...

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