Atoms and Stars IST 2420 Class 11, April 6 Winter 2009 Instructor: David Bowen Course web site:

Atoms and StarsIST 2420

Class 11, April 6Winter 2009

Instructor: David BowenCourse web site: www.is.wayne.edu/drbowen/aasw09

4/6/09 Atoms and Stars, Class 11 2

Agenda

• Assignments and passbacks• Upcoming assignments• Relativity• Review and update: planets and exoplanets• Readings: Atomic Nature of Matter • Converting Sixteenths to Decimal• Lab 9 Part 2 (Ellipse): Archimedes’ Exploits


Upcoming …• This week:

o Remember to initial the sign-in sheeto Due in Reader: The Atomic Nature of Mattero Hold Lab 9 Part 1 (Circle), hand in both parts

togethero Manual: Lab 9 – the Ellipse

• Next week (April 13):o Due in Reader: Chemistryo Manual: Lab 7 – Specific Gravityo Hand in Lab 9 as a whole


Upcoming …

• Two weeks, 4/20o Essay 2 due via Digital Dropbox in Blackboardo Lab 11 – the Orbiting Bottleo SET

• Three weeks: 4/27 (last regular class)o Review for Final Examo Due: all work to count in regular grade

• Four weeks: May 4o 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!o All work for grade at regular time due by 4/27

• Getting ready for Final:o Read Information Sheet carefully – a lot of

information thereo Look at Final Topics carefullyo Use Review Session!


Note on Lab 10 (Lenses)

• Singular: lens• Plural: lenses


Limits on Space Travel

• The idea of space travel has always been attractive.

• Einstein’s Special Theory of Relativity (1905) set limitations on space travel.o Maximum possible speed is speed of light –

one year to travel one light year (but today we cannot reach even a small fraction of this)

o Nearest star is 4 light years awayo Galaxy ~100,000 light years across


Background

• Before 1905, we could not see expected changes in the speed of light when the direction of the earth changed as it orbited the sun.

• Tried to explain this by saying that distance-measuring devices got shorter in direction of motion.

• Didn’t work.


Relative Motion

• Newton said that speeds in the same direction should add, nothing special about light.

• Simulation – car traveling on top of a railroad car:http://www.is.wayne.edu/drbowen/Class-Room_Models/Welcome.htm

• Speed of car with respect to station = speed of railroad car + speed of car on railroad car

• Speed of light could be exceeded – no issue for Newtonian view

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


Relative Motion

Relative motion of rr-car and car on top. car speed wrt station = rr-car speed + car speed on top of rr-car


Special Relativity• Newtonian Relativity simple, correct at normal

speeds, but wrong for very high speeds (light).• Einstein’s Theory of Special Relativity (1905)

said constant measured speed of light is a property of space and time themselves. No explanation – that’s the way things are, a fundamental condition.

• Space and time went from the passive stage for the universe to active players in the drama.

• Revolutionary, but it works.

4/6/09 Atoms and Stars, Class 11 13Atoms and Stars, Class 10 13

Reading: What is Gravity?(REVIEW)

• Newton: we do not know what gravity is• DB: After 20th century, two explanations

o These don’t agree, so that is a problem, but a possible unification

• Explanation #1: 1915: Einstein’s General Theory of Relativityo Gravity is due to the bending of space by

masseso Analogy of a ball rolling on a sheet of rubber

around a heavy object


What is Gravity? (cont’d)

• Explanation #2: Quantum Mechanics (applies to very small objects) about 1925:o All forces, including gravity, are due to the

exchange of (very small) particles between objects

o Particles observed for weak, strong (nuclear) and electromagnetic forces (photon for e-m)

o Not yet observed for gravitational forceo Difficult to find, but would be serious if not found


What is Gravity? (cont’d)• Both General Relativity and Quantum Mechanics

are well-established science• Explanations for gravity from General Relativity

and Quantum Mechanics have not yet been reconciled (two theories explaining same thing)o Would be called Quantum Theory of Gravityo Does not yet existo Are reconciled in latest theories, e.g. String Theory, but

this does not yet have experimental verification – we do not yet even know what experiments to do or how to do them

• String Theory may turn out to explain itself


Status of Newton’s Laws• Are scientific theories reliable? Many hedges

in this course, for example:o Scientific knowledge is provisionalo Experiments do not prove theorieso One experiment can overturn a theoryo Science has a limited scope – a boundaryo Science is not an adequate basis for livingo Scientists often do not follow scientific method

• Maybe only foolish people use science? Not!


Status of Newton’s Laws• Range of authority for Newton’s Laws:

o Objects moving slower than about three million miles per hour

o Objects weighing more than about 0.000,000,000,000,000,000,01 pounds (19 zeroes)

o Objects weighing less than about (31 zeroes) 40,000,000,000,000,000,000,000,000,000,000 lb

• Within this range of authority, Newton’s Laws are extremely reliable and precise


Status of Newton’s Laws• Newton’s Laws have passed stringent tests

o Control of spacecrafto Use in design and control of countless machineso 1846 predicted mass and orbit of Neptune from

its effect on the orbit of Uranus (productive)• For very small masses (molecular), Quantum

Mechanics is needed instead• For very fast objects, Special Relativity• For very massive objects, General Relativity


“Stars” Summary

• Long human interest in astronomy• Greeks (Aristotle and Ptolemy) geocentric• Catholic Church gave this additional

importance• Copernicus – first modern heliocentric

theory – simpler, more accurate• Brahe – accurate continuing measurements


“Stars”Summary

• Kepler – Three Laws, orbits are ellipses – a descriptive theory – what the patterns are

• Galileo – observations calling aspects of Aristotle’s and Church’s astronomy into doubt

• Newton – explanatory theory – why the orbits are ellipses, etc. (because of the force)


What Are These Things? retrograde / no retrograde: applies to entire rows

Type Ancient idea Copernican Idea Modern idea

Star All rotate together around stationary earth

Fixed in sky, appear to rotate due to earth’s rotation

Shines with its own light (a nuclear reactor)

Sun Like a star (no retrograde motion)

Fixed at center of universe / solar system (Newton: no fixed center)

A star

Planet Wanders among stars, has retrograde motion

Large object orbiting sun

Orbits a star, shines by reflection from star

Earth Fixed at center of universe / solar system

One of the planets circling our sun, rotates as it orbits

One of the planets circling our sun (a star)


What Are These Things?Type Ancient idea Copernican Idea Modern idea

Moon Only one known, circles Earth

Galileo found moons of Jupiter

Anything that orbits a planet – many known, 66 in solar system

Galaxy Not known (could see stars and planets in a band (“Milky Way”) but did not understand why

Not known (could see stars and planets in a band (“Milky Way”) but did not understand why

A large group of stars, 10 million to 1 trillion, Milky Way is our Galaxy seen from within

Comet Surprise Surprise Orbits sun, has coma (tail)

Asteroid Surprise Surprise Orbits sun, has no visible coma (tail)


Update: What is a planet?

• 1846 Neptune discovered from changes to orbit of Uranus, using Newton’s Lawso Predicted position and masso Productivity

• Pluto discovered 1930, orbit radius ~30 AU• 2002 – 2006 other solar system objects found by

looking for motion between exposureso Quaoar, 2003 VB12 (“Sedna”), 2004 DW, Xena

• Xena larger than Pluto – is it a planet?• 39 to 97 AU (very flattened ellipse)• Plane ~ 43° to ecliptic


New “planets” (cont’d)

• Neptune outermost “real” planet

• New ones near Kuiper belt (asteroids)

• “Reals” formed from dust cloud, forced orbits to circular


New “planets” (cont’d)

• “Classification” - what is a planet?o Follows “description” in development of

scienceo What are the real differences?


2007 Change

• New planets are not planets, neither is Pluto (“dwarf planet”)o Now, eight planets

• New characteristic of planet: has cleared its orbit of other bodieso Why Pluto and others in our solar system

rejected

26


Exoplanets

• Exoplanet – outside our solar systemo Circle other stars, shine by reflected lighto Can they support life?

• Methods:o Star wobbles (Newton’s Third Law)o Dip in brightness of star as planet passes overo Very recent: direct observation

• Count: 327 around 278 starso None earthlike yet


Exoplanets


Three waves of science?

1. Physical science – the subject of this course – mature, quantitative (95%)

• Very controversial when it was new• 1400 – 1800 AD, although very long roots & still

developing• Now pretty much settled for everyday objects

2. Biological or life science – qualitative (30%?)• Much newer, evolution is the basis, still controversial

publicly, but for scientists it is settled• 1800 – 1935 AD

• Coming into general use in society & economy• Will qualitative change to quantitative?


Three waves of science?

3.Cognitive science – how emotions and the mind work – just starting (5%)o Will be as controversial, if not moreo Potential for controversy: Science of Desire :

The Gay Gene and the Biology of Behavior & The God Gene (spirituality) / Dean Hamer• Spirituality predestined for some, denied to others?• A single gene is unlikely to be the sole cause

o Yesterday: can edit (delete) memories (animals)o Will call into question how we view ourselves


Summary, Once More…• 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 technology (coming up)o We all use the technologyo Conflicts with some, but not all, religious beliefs

• People do not agree on what “Christian” is, let alone other religions

o People of all ethnicities have been able to contribute


Two parts• Newton ended the “Stars” part of this course• This week starts the “Atoms” part• “Element” – Greeks understood this to be

something fundamental, without parts, not made from other things, could not be broken downo Aristotle: air, earth, fire & water are elementso First discoverers of atoms disproved Aristotle, thought

atoms were the Greek elementso Today we still call atoms “elements,” but not in the

same sense – they are made of other thingso Still have question of what (if anything) is elemental


And now…

• “Atoms”• Before Einstein & E = mc2, matter and

energy separate• Atomic Theory – all matter is made up of

atoms• Start (this week) by looking at our

knowledge of atoms• Then (next week), how did this knowledge

come about?


Readings“Atomic Nature of Matter”, Hewitt• All matter is atoms (“Atomic Theory”)

o Atoms are elements – “indivisible” – mostly empty (11c#1) but now not indivisible

o 109 types total, 90 are natural, rest radioactive• Each type has its own properties, e.g. weight,

reactionso Hydrogen most common atom in universe

• Rare by itself on eartho Life primarily C, H, O, N

• Atoms small enough to be invisible - waves


Atomic Nature of Matter• First direct evidence 1827 Robert Brown (11c#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• Atoms bond into molecules – many types (11c#1)

o Molecules - compoundso Molecules have separate properties from atomso Burning is combination with O

• New - modern automobiles very little CO

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

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


Brownian Motion

Jagged tracks of pollen particles.

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


Brownian Motion

Imagine the red molecules were so small that we couldn’t see them – blue ones would “jostle” for no apparent reason.


Atomic Nature of Matter

• 1811 (Amedeo) Avogadro’s hypothesis (now Law)o At same T & P, equal Vs of gas have equal #so Each atom, molecule heavier gas heavier

• Amu = atomic mass unit• C 12 amu, H 1 amu, O 16 amu, U 238

amu, H2O 18 amu – also combine in gm, lb etc.• Atom has electrons orbiting nucleus

o Electrons – volume but very little masso Nucleus – mass but very little volume


Atomic Nature of Matter

• Electron, e – negative charge, flow ofelectrons is electrical current

• Nucleus has neutrons, n (no charge) and protons, p (positive charge)o Cube 3/8” would weigh 133,000,000 tons

• Like charges repel, unlike charges attracto Nuclei positive, repel each other (electrical force)

• “Strong Force” overcomes electrical, retains themo Atoms neutral; number of e = number of p

• (not = under special circumstances)


Atomic Nature of Matter (end)

• Electrons in shells (2, 8, 18, …)o If shells filled, element is inerto Unfilled shells determine activityo #p = atomic number, chemical characteristics

• Same element even if atom loses or gains electrons

• Antimatter – anti-electron (1932), anti-neutron, anti-protono Annihilate 100% energy (light)

• Nuclear reactions normally release 1% of E = mc2

• End of article…


Element, Compound, Mixture(Q11 a-b)

• Element: matter with all atoms the sameo Examples: C, S, H, O

• Compound: made up of the same moleculeso Examples: H2O, CO2

o Matter with all molecules the sameo Atoms bond together into chemical

combinationo Always the same composition


Element, Compound, Mixture (end)

• Mixture (Q11a-b)o Atoms and molecules not close enough to bondo Composition varieso Examples:

• Air (mostly N and O) but variable– Amount of greenhouse gases an issue – CO2

• Earth – composition extremely variable– Add various fertilizers

• Dough – vary composition for different breads• Cinnamon and sugar

o Constituents could in principle be separated


Epistemology

• Several times you have asked me “Is this absolutely true?” I tend to hesitate with questions like this – here is why.

• Epistemology – the study of knowledge – why do we accept things as true?

• Two properties we would like for truth:o Eternal – unchangingo Universal – the same everywhere


Epistemology (end)• Science doesn’t do “eternal”

o Scientific truth is provisional – subject to changeo We keep learning new things and improving

theories• Religions have problems with “universal”

o Each religion claims universality but how can different religions differ, if there is one truth?

o For science and religion, Galileo agreed with modern Catholic doctrine – there is one truth• Reinterpret Bible if it disagrees with accepted science


Converting Sixteenths to Decimal (Q1)

• Converting inches and sixteenths to decimal inches, and pounds and ounces to decimal pounds:o How many sixteenths of an inch are there in

one inch?o How many eighths of an inch are there in one

inch?o On exams, will be given ounces in a pound (16)

if needed, but not sixteenths of an inch in an inch


Converting Sixteenths to Decimal (Q1)

• Converting inches and sixteenths to decimal inches, and pounds and ounces to decimal pounds:1. Divide # sixteenths by 16 (result between 0 and

1), call this “X” (make it a whole number)2. Check: multiply X by 16, get about the original

number of sixteenths – SHOW THIS CHECK ON DATA SHEET !!!

3. Add X to # whole inches to get decimal inches


Experiment 9

• Good technique (both parts):o When you stick pins in, leave some of metal

shaft exposed – string goes around this parto Do not stretch string (thread doesn’t stretch

much at all, thicker twine can stretch)o Use a pen to make marks on the string, measure

between the marks


Experiment 9

• Measure length of curved lines by winding string around line, measuring string

• Possible sources of error: (a) stretching, (b) thickness (middle of string along the curve)o Protect against these!!!

• To multiply by , calculate length differences etc.: convert lengths from inches and sixteenths to decimal inches INCLUDING CHECK !!!


Experiment 9

• Part 1: Circleo Data Sheet: Assignments 1 – 15o Analysis: Assignments 16 – 24o If Assignment 16 discrepancy > .2 inches, show me

how you did it• Part 2: Ellipse

o Data Sheet: Assignments 25 – 32 & 36o Analysis: Assignment 33

• In Addition (overall, not in manual):o Are measurement errors for circle and ellipse the same,

or different?o If they are different, how can this be the case?

Documents

Atoms and Stars IST 2420 Class 11, April 6 Winter 2009 Instructor: David Bowen Course web site: