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Atoms and Stars
IST 2420
Class 14, April 21
Winter 2008
Instructor: David Bowen
Course web site:
www.is.wayne.edu/drbowen/aasw08
4/21/07
Atoms and Stars, Class 14
1
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
4/21/07
Atoms and Stars, Class 14
2
Upcoming …
• Tonight, April 21 (last regular class)
o Lab 11 – the Orbiting Bottle
• Checking up on Newton
o Review for Final Exam
o Due: all work to count in regular grade
• Final Exam: next Monday, April 28
o Nothing that night but the Final Exam
4/21/07
Atoms and Stars, Class 14
3
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.
4/21/07
Atoms and Stars, Class 14
4
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
4/21/07
Atoms and Stars, Class 14
5
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
4/21/07
Atoms and Stars, Class 14
6
ths
16
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.
4/21/07
Atoms and Stars, Class 14
7
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.
4/21/07
Atoms and Stars, Class 14
8
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
4/21/07
Atoms and Stars, Class 14
9
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?
4/21/07
Atoms and Stars, Class 14
10
Experiment 9
• Some past reports have said that the formula for
the ellipse was trusted more than the experimental
measurement
o
o
o
o
Both are actually based on measurements
The power of authority
Also, not trusting your techniques
But in this case, the authority was not trustworthy
• Many said no use in repeating measurements
o 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
4/21/07
Atoms and Stars, Class 14
11
Re-emphasizing Main Points
• Two pillars of science
o Experiment: makes science reliable
• Scientists led astray by logic (Aristotle) and belief
(church and geocentrism, Inquisition)
• Experiments base science on direct experience
o 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
4/21/07
Atoms and Stars, Class 14
12
Re-emphasizing Main Points
• I have the experiments in this course to:
o Give you direct experience
o Illustrate experiments described in class
o Illustrate social nature of science within the lab
groups
4/21/07
Atoms and Stars, Class 14
13
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
4/21/07
Atoms and Stars, Class 14
14
Knowledge or Certainty
• 1795
• Science is discussion and argument
preceding knowledge
• Also Uncertainty Principal 1927 Werner
Heisenberg – cannot locate particle exactly
o Irreducible uncertainty or fuzzy focus
4/21/07
Atoms and Stars, Class 14
15
Knowledge or Certainty
• No practical
effect at
macroscopic 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
4/21/07
Atoms and Stars, Class 14
16
What is Science?
Moti Nissani, What Is Science?
• Difficult or impossible to give a dictionarytype definition for science
• (DB) Working scientists rarely think about
the history or philosophy of science
• Start with philosophy of Thales – free
inquiry
4/21/07
Atoms and Stars, Class 14
17
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
4/21/07
Atoms and Stars, Class 14
18
What Is Science? (cont’d)
o Scientists “on the trail” have personal concerns
• Argument and community lead to progress
o Semmelweiss and deaths in maternity ward
•
•
•
•
•
•
4/21/07
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
Atoms and Stars, Class 14
19
What Is Science? (cont’d)
• Theories unify many hypotheses and
experiments
o 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
4/21/07
Atoms and Stars, Class 14
20
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
us
o Colors shifted redder (“red shift”)
o First evidence for Big Bang
4/21/07
Atoms and Stars, Class 14
21
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
4/21/07
Atoms and Stars, Class 14
22
Relativity
• Reminder about what this is about
o Computer simulation
• Often very difficult to tell whether or not
our measurements are in a moving
coordinate system
o 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
4/21/07
Atoms and Stars, Class 14
23
Special Relativity
• For fast-moving objects
o
o
o
o
Max speed = c (speed of light)
Objects foreshortened
Time slows down
But the traveling person says the same about
you!
o Space and time  space-time
o E = mc2
 light has mass, is bent by gravity
4/21/07
Atoms and Stars, Class 14
24
General Relativity
• For very heavy objects
o Space and time warp, cause gravity
o 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
4/21/07
Atoms and Stars, Class 14
25
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)
4/21/07
Atoms and Stars, Class 14
26
Quantum Mechanics
4/21/07
Atoms and Stars, Class 14
27
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)
4/21/07
Atoms and Stars, Class 14
28
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)
4/21/07
Ricochet,
bounce, shatter
All by itself
Atoms and Stars, Class 14
29
Demonstrations
• PhET (Physics Education Technology)
http://www.colorado.edu/physics/phet/web-pages/simulations-base.html
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
4/21/07
Atoms and Stars, Class 14
30
Particles collide…
Particles of gas mix together, collide
4/21/07
Atoms and Stars, Class 14
31
but waves pass through each other
Sound wave and its reflection
(type – sound - is unimportant here)
4/21/07
Atoms and Stars, Class 14
32
Waves “interfering”
Confine a wave and it spreads out
4/21/07
Atoms and Stars, Class 14
33
Waves
• Wavelength –
distance between
peaks (or troughs)
• Fixed speed
• Until 20th century,
Wave / Particle –
we thought
everything was one
or the other
4/21/07
Wavelength
Atoms and Stars, Class 14
34
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
4/21/07
Atoms and Stars, Class 14
35
Uncertainty Principle
• 1795 Carl Friedrich Gauss (college student)
• Also Uncertainty Principal 1927 Werner
Heisenberg – cannot locate particle exactly
4/21/07
Atoms and Stars, Class 14
36
Quantum Mechanics
• At molecular level and smaller, waves and
particles merge – everything is both
o Wave – spread out, cannot contain it
o Particle – have it or don’t
o 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
4/21/07
Atoms and Stars, Class 14
37
Quantum Mechanics (cont’d)
• Accounts for properties of ordinary
materials
o
o
o
o
o
Theoretical: keeps matter from collapsing
Color
Solid (strength), elastic, gaseous
Solid state electronics – semiconductors
Forces – due to exchanges of particles
• No Newtonian “action at a distance”
• E.g. electrical force carried by photons – particles of
light
4/21/07
Atoms and Stars, Class 14
38
Conflict!
• Heavy (G.R.) and small (Q.M.) –
mathematical conflict. Example: Black Hole
o 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
4/21/07
• “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 Atoms and Stars, Class 14
39
Issues:
• “Anthropic Principle” – physical rules seem
to favor life
o Room for God inside science?
o But “Inflationary Universe” may explain this
• Dark Matter
o 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
4/21/07
Atoms and Stars, Class 14
40
Issues (cont’d):
• Dark Energy
o Big Bang should be
slowing down
o But outer half of universe
is accelerating!
o Current hypothesis is that
dark energy at outside
fringe is attracting the inner parts.
Source: NASA
• Between these two, we see only 5%. The
universe is still surprising us!
4/21/07
Atoms and Stars, Class 14
41
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 Dalton
o Developing hypotheses and theories is creative
o Has a boundary but expands aggressively
 not a complete basis for living
o
o
o
o
4/21/07
Now drives technology
We all use it
Conflicts with some, but not all, religious beliefs
People of all ethnicities have been able to contribute
Atoms and Stars, Class 14
42
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 horizontal
o Use formulae
• Large hand motion to get bottle moving,
then small hand motions to sustain motion
during measurements
4/21/07
Atoms and Stars, Class 14
43
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
4/21/07
Atoms and Stars, Class 14
44
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
4/21/07
Atoms and Stars, Class 14
45
Review for Final
4/21/07
Atoms and Stars, Class 14
46