13 january 2010modern physics ii lecture 11 university of san francisco modern physics for frommies...
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13 January 2010 Modern Physics II Lecture 1 1
University of San Francisco
Modern Physics for Frommies II
The Universe of Schrödinger’s Cat
Lecture 1
13 January 2010 Modern Physics II Lecture 1 2
Agenda• Administrative matters• Physics and the Scientific Method• Notation and Units• Mass vs. Weight• Some History
13 January 2010 Modern Physics II Lecture 1 3
Administrative Matters
• Lecture Location and Time: Fromm Hall Wednesdays 1 PM – 2:40 PM Prompt start.
• Lecturer: Terrence A. Mulera – HR 102• Office Hours: TBA and by appointment• Contact Information:
– e-mail: mulera@mail.usfca.edu– Phone: (415) 422-5701
13 January 2010 Modern Physics II Lecture 1 4
Monday Tuesday Wednesday Thursday Friday Saturday Sunday 0800
0900 0940 121 Lab 11
1000 1030 120 Lab 13
1030 121 Lab 13
1100 1135 120 Lab 11
1125
1200
1215
1215
1300 1320 1330 120 Lab
1330 210 Lab
1300 Mod. Phys. II Fromm Inst.1
1330 121 Lab 14
1400
1440
1500 1515
1515
1600 1615
1600 Colloquium
1700
1800
1900
2000
1 13 January to 6 March only
13 January 2010 Modern Physics II Lecture 1 5
Administrative Matters 2
• Class Wikis– http://modphysfromm2.wiki.usfca.edu/ or link from Fromm
web site.• .pdf notes, 4/page posted hopefully night before class. These may
change by time of lecture.– Hard copies. How many do we need?
• Power Point® slides posted immediately following lecture. Will include any changes to .pdf notes
– Material from preceding class (Albert Einstein’s Universe) still available at http://modernphysicsfrommies.wiki.usfca.edu/
13 January 2010 Modern Physics II Lecture 1 6
Administrative Matters 3
• USF Physics and Astronomy Colloquia– Open to the public– Wednesday afternoons 4 -5 PM in HR 127
• Light refreshments at 3:30 PM
– First colloquium will be sometime after start of regular USF spring semester.
• Schedule of colloquia will be provided as soon as it is available. Will also be posted in Fromm Hall.
13 January 2010 Modern Physics II Lecture 1 7
Thanks for the cartoon to Moose’s, 1652 Stockton St., San Francisco, CA
Please turn off or silence cell phones and pagers.
13 January 2010 Modern Physics II Lecture 1 8
Physics and the Scientific MethodPhysics and the Scientific Method•Physics is a science
-Limited to that which is testable
•Concerned with how rather than why
•Best defined in terms of the “Scientific Method”
•Formulated in the 17th century
•Other concerns reserved to Philosophy, Metaphysics and Theology.
13 January 2010 Modern Physics II Lecture 1 10
Example: Newtonian GravitationExample: Newtonian Gravitation
Observations: Things fall, planets orbit in ellipses etc.
Empirical Law: There is an attractive force between objects which have mass.
Theory: Newton’s Law of Gravitation
1 22
ˆm m
F G rr
13 January 2010 Modern Physics II Lecture 1 11
Testing: Good agreement with experiment and observation.
Measurement of falling objectsCelestial mechanics pre-1900
Refinement of Theory and Further Testing: 1905 – 1920
Einstein’s theory of general relativityEddington’s observation of bending lightPrecession of Mercury’s orbit
13 January 2010 Modern Physics II Lecture 1 12
Future Refinement and Testing: Quantum gravity?
CAVEAT: A scientific theory can never be proved, it can only be shown to be not incorrect to the limit of our ability to test it.
Alternatively, if you cannot devise an experiment which will disprove your conjecture, your conjecture is not science.
- Karl Popper (1902-1994)
13 January 2010 Modern Physics II Lecture 1 14
Helen Quinn, What is Science, Physics Today (July 2009)
Posted on Wiki
http://modphysfromm2.wiki.usfca.edu
13 January 2010 Modern Physics II Lecture 1 15
Scientific NotationScientific NotationVery large and very small numbers with many zeros before or after the decimal point are inconvenient in calculations.
For convenience we write them as
.
10ba0
1
1
2
2
e.g. 1.0 1.0 10
0.1 1.0 10
10.0 1.0 10
0.01 1.0 10
100.0 1.0 10
.
0( ) 1
110
10n
n
Anything
13 January 2010 Modern Physics II Lecture 1 16
Results usually presented as 1 digit to left of decimal with exponent adjusted accordingly, i.e.
Multiplication:
Division:
Exponents add and/or subtract
2 320 10 2.0 10 .
1 2 1 21 2 1 210 10 10b b b ba a a a
1
1 2
2
1 1
22
1010
10
b
b b
b
a a
aa
2 2 2
2
10 10
10 10
b b
b b
a a
a a
010 101 10
10 10
n n
n n
13 January 2010 Modern Physics II Lecture 1 17
UnitsUnitsMostly rationalized mks units, i.e. distance in meters, mass in kilograms, time in seconds.
Occasional use of cgs units, i.e. centimeters, grams, seconds and of “English” units, i.e. ft., slugs, seconds
Special units. e.g. light years, parsecs, fermis, barns introduced as needed
Mass vs. Weight
13 January 2010 Modern Physics II Lecture 1 18
Mass vs. WeightMass vs. WeightMass (if non zero) is a measure of the quantity of matter present.
e.g. 1 kg of say air corresponds to n molecules of air
2 kg corresponds to 2n molecules
Mass is independent of the gravitational environment of the matter.
1 kg on Earth = 1 kg on Mars = 1 kg in interstellar space etc.
Alternatively, mass is a measure of an object’s resistance to acceleration.
F ma
13 January 2010 Modern Physics II Lecture 1 19
Weight is a force on an object due to gravity.
2
On Earth's surface
9.8 m/secW F mg g
Units: kg m/sec2 Newton (N)
Weight is dependent on the gravitational environment of the object.Weight on Earth 3 x weight on Mars 6 x weight on moon.
Common usage: Weights quoted in kg with environment understood to be surface of Earth.
Further confusion: lbs. are units of weight, mass units are slugs.
1 slug x (32 ft/sec2) = 1 lb
13 January 2010 Modern Physics II Lecture 1 20
A Brief History of Views of the Universe
Arbitrary definition of “Modern Physics”
Post 1900 CE
Two major foundations
Relativity
Quantum Mechanics
Where were we? Where are we?
Maybe we can ask: Where are we going?
“It’s difficult to make predictions, especially about the future.” - Yogi Berra
13 January 2010 Modern Physics II Lecture 1 21
The Ancients (mostly Greeks):
Physics from the Greek physika meaning “natural things” or the study of nature.
All of the ancient civilizations tried to understand their worlds in terms of myths.
Anthromorphizication of natural forces
e.g. Egyptian sun god, Ra
Greek mythology: Zeus, Athena, Aphrodite, Aeres etc.
Ca. 600 BC the Pre-Socratics began to apply reason to the comprehension of nature
What is the underlying order that is hidden in nature?
13 January 2010 Modern Physics II Lecture 1 22
What is the most basic substance in the universe?
Is the structure of nature based on mathematics, processes or substances?
Some of the Players
Thales (600 BC): H2O is the primary and simplest element
Anaximander: World composed of interacting, aggressive opposites
Anaximenes: Like Thales only air rather than H2O
Empedocles: Earth, air, fire and water
Paramendes: Processes. Matter is conserved.
Pythagoras: Defined the world in terms of mathematics. Coined the term philosopher.
Leucippus and Democritus: Elementary particles. Coined the term atom.
13 January 2010 Modern Physics II Lecture 1 23
Socrates → Plato → Aristotle
Earth and its place in the universe: geocentricComplex system of interlocking spheres with names like prime mover, cycles and epicycles.
.
.
Aside: A heliocentric theory was proposed as early as the 6th century BC by non other than Pythagoras.
Physical phenomena: 4 elements. Properties and motions of objects could be described in terms of the chemical reaction properties of these elements.
Motion: 4 basic typesAlteration: Chemical reactionNatural local motion: Weight falling, smoke risingHorizontal or violent motion: Pushing, pulling, throwing
Celestial motion: Involves the interlocking spheres mentioned above.
Ptolemaic model.
13 January 2010 Modern Physics II Lecture 1 24
Archimedes of Syracuse (287 – 212 BC)
Archimedes Thoughtful by Fetti (1620)
Killed by a Roman soldier at the siege of Syracuse (2nd Punic war)
13 January 2010 Modern Physics II Lecture 1 25
Discoveries and Inventions Credited to Archimedes
Hydrostatics: Archimedes principle
Principle of levers: “Give me a place to stand on, and I will move the Earth.”
Block and tackle systems
Archimedes screw
Military weapons:
Archimedes claw
Death ray (mirrors focusing the Sun on enemy ships) Possibly apocryphal but principle verified by MIT
13 January 2010 Modern Physics II Lecture 1 26
Mathematics:
Infinitesimals. Calculus?
Value of
Area under the arc of a parabola
Attempted to calculate the number of sand grains which the universe could contain. Lead to his devising a system of dealing with extremely large numbers using powers of myriads (10,000 in Greek).
13 January 2010 Modern Physics II Lecture 1 27
Interregnum: Aristotle - Renaissance
Not much happening in physics but lots going on in history
Rome dominates the classical world
Rome falls ca. 450 AD
Dark ages in Europe ca. 450 – 750 AD
Light of classical civilization preserved in Islamic countries. Returned to the West in the Middle ages, 750 – 1350 AD.
Concept of the zeroAlgebraAnatomyStar chartsPre-Copernican heliocentric theories
Black Death strikes Europe, 1347 AD, third of population dies
13 January 2010 Modern Physics II Lecture 1 28
Renaissance: Ca. 1400- 1600 AD The Copernican Revolution
Observation → Tables of planetary motion
Geocentric (Ptolemaic) model noticeably inaccurate and difficult to calculate.
“ If I had been present at the creation, I would have recommended a simpler design for the universe”
- Alphonso X (1221 – 1284)
King of Spain
13 January 2010 Modern Physics II Lecture 1 29
Nicholas Copernicus (1473-1543)
Tried a heliocentric model much like that proposed by Aristarchus 1700 years earlier.
Model was successful but not overly so.
Assumed orbits were perfect circles, required reintroduction of complexity
Few converts over 50 years
13 January 2010 Modern Physics II Lecture 1 30
Tycho Brahe (1546 – 1601)
Greatest of the early observational astronomers.
Naked eye, telescope was invented shortly after his death.1
1 arcminute degree60
13 January 2010 Modern Physics II Lecture 1 31
Observed a “new star” or nova.
Observed the 1563 alignment of Jupiter and Saturn.
Noted that it occurred two days later than predicted by the Copernicus model
Spent the next 30 years compiling stellar and planetary measurements.
13 January 2010 Modern Physics II Lecture 1 32
Convinced planets orbit Sun
No stellar parallax Earth stationary. Sun orbits Earth
Few took this model seriously
13 January 2010 Modern Physics II Lecture 1 33
Johanes Kepler (1571 – 1630)
Tycho’s assistant. Inherited data base upon Tycho’s death.
Elliptical orbits
13 January 2010 Modern Physics II Lecture 1 34
Speculated that some force (like magnetism) originating from the Sun was responsible for planetary motion.
3
2
aM
T
T =
13 January 2010 Modern Physics II Lecture 1 35
Galileo Galilei (1564 -1642)
1608: 1st working refracting telescopes
Hans Lippershey, Zacharias Janssen, Jacob Metius in the Netherlands
Galileo greatly improved design in 1609
13 January 2010 Modern Physics II Lecture 1 36
Three objections to Kepler’s heliocentric theories:
(1) The Earth cannot move because birds, falling stones etc, would be left behind.
Inertia later Newton’s 1st law. Galilean relativity
(2) Non circular orbits are contradictory to the non changing perfection of the heavens.
Novae, supernovae, comets already observed
Telescopes allowed observation of sunspots, mountains on Moon
(3) No stellar parallax observed.
Telescope stars are much farther away than Tycho thought
13 January 2010 Modern Physics II Lecture 1 37
Final nails in the coffin:
The moons of Jupiter, a miniature Solar System
Observation of the phases of Venus can only be explained in terms of a heliocentric model.
Observation of the transit of Mercury across the face of the Sun
CLEA exercise
See wiki
13 January 2010 Modern Physics II Lecture 1 39
Newtonian Mechanics (translational)
Three laws of motion:
1) A body at rest or in constant rectilinear motion remains at rest or in motion unless acted upon by an outside force.
2)F ma
3) Momentum is conserved
i i f fm v m v
Action - Reaction
There are rotational extensions to these laws:
e.g. N I
13 January 2010 Modern Physics II Lecture 1 40
Newton’s Law of Gravitation
1 22
ˆm m
F G rr
2
1Applying the 3 laws of motion with a force
allowed Newton to derive Kepler's Laws.r
Angular momentum, L mvr
This must also be conserved. Careful, it’s a vector so direction as well as magnitude is conserved
i fL L
L r mv
13 January 2010 Modern Physics II Lecture 1 41
Leonhard Euler (1736-1783)
Jean Le Rond d’Alembert (1717-1783)
Joseph Louis Lagrange a.k.a. Giusseppe Lodovico Lagrangia
(1736-1813)
William Rowan Hamilton (1805-1865)
13 January 2010 Modern Physics II Lecture 1 42
Triumphs:
Celestial mechanics, planetary orbits
Navigation
Mechanical Engineering and the Industrial Revolution
The above Classical Mechanics was accompanied by the 2nd great triumph of pre-20th century physics, Classical Electromagnetic Theory, a.k.a. Classical Electricity and Magnetism, a.k.a. Classical Electrodynamics.
13 January 2010 Modern Physics II Lecture 1 43
Electrical charge
Ancient Greece, ca. 600 B. C.
Rub a rod of amber or hard rubber with a cloth.
After rubbing, rod is able to attract small bits of paper or other light material.
No real advance in understanding until ca. 1600 A. D.William Gilbert (court physician to Elizabeth I) studied materials that act like amber.
“electric” (elektron is Greek for amber)
Electric: modern term is “insulator”Non-electric: “conductor”
13 January 2010 Modern Physics II Lecture 1 44
About 100 years later Charles Du Fay showed that there are 2 forms ofelectrification.
attractionIf you rub various insulators → repulsion
Postulate: There are 2 types of electrical charges like charges repel unlike charges attract
Benjamin Franklin: Assign (+) charge to one type and (-) charge to the other.
Which is ± is arbtrary. Consistent use of a sign convention allows a very concise mathematical formulation of experimental facts.
13 January 2010 Modern Physics II Lecture 1 45
Franklin’s arbitrary choice: rubbing glass rod w/silk → (+) rubbing amber or hard rubber → (-)
Hindsight: Picking signs opposite to Franklin’s choice → more “sensible” conceptual picture.
“Hindsight is always 20-20” - .Anonymous
J. J. Thomson ca. 1900Discovered the electron. Its charge under the Franklin convention is (-)
13 January 2010 Modern Physics II Lecture 1 46
Coulomb’s Law
1 2
1 22
0
Force between 2 charges, and , separated by a distance
1
4
q q r
q qF
r
William Gilbert (1544-1603)
Charles du Fay (1698-1739)
Benjamin Franklin (1706-1790)
Charles de Coulomb (1736-1806)
13 January 2010 Modern Physics II Lecture 1 47
Magnetism:
“The nation that controls magnetism controls the universe. ”
-Diet Smith in Chester Gould’s Dick Tracy, New York Daily News Syndicate (1962)
13 January 2010 Modern Physics II Lecture 1 48
Magnetism
Historical:
Interactions between ferromagnetic materials (Fe, Ni, Co)Forces of attraction and repulsionResemble but are quite distinct from electrostatic
Use of permanent magnet in Earth’s magnetic field as compass for navigation.
In 1819 Ørsted showed connection between electric current and magnetism.
Faraday and others, culminating in Maxwell’s equations.
13 January 2010 Modern Physics II Lecture 1 50
Maxwell’s Equations (differential form)
t
t
0
000
0
EB
BE
B
E
j
E. M. wave equation2
20 0 2
0t
E
E
where
m/sec10x31 8
00
c
2
2
2
2
2
22
zyx
2
In traveling wave equation
1this is
v
13 January 2010 Modern Physics II Lecture 1 51
Triumphs:
Electrical Engineering, Electric power and communication
Wireless communication
Radar
Modern optics
First electronic computers
13 January 2010 Modern Physics II Lecture 1 52
The Deterministic UniverseDeterminism The future is completely determined by the past. The future can be predicted if enough is known
of the past.
What is enough?
Consider a universe whose component objects are labeled with the index i. Each object has mass mi.
If we know the initial position, xiI, and velocity, viI of each particle plus the resultant or sum of all the forces acting on it as a function of time, Fi(t), then we can, in principle, calculate the final position, xiF, and velocity, viF. ,
xiI
viI
Fi(t)
xiF
viF
13 January 2010 Modern Physics II Lecture 1 53
“There is nothing new to be discovered in physics now. All that remains is more and more precise measurement.”
-1900
“Heavier than air flying machines are impossible.”
-1895
“X-rays will prove to be a hoax.”
-1896
Kelvin, Lord William Thomson (1824-1907)
13 January 2010 Modern Physics II Lecture 1 55
Wilhelm Röntgen
1845 - 1923
Mrs. Röntgen né Anna Ludwig
1872 - 1919
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