3/5/07Atoms and Stars, Class 81 Schedule: Review (Q & A) up to 6 PM Midterm (about one hour) Pass...

3/5/07 Atoms and Stars, Class 8 1

Schedule:• Review (Q & A) up to 6 PM• Midterm (about one hour)• Pass out the Notes and return

graded work, turning work in• Class• Lab 13 (parallax)


Atoms and StarsIST 2420

Class 8, March 5Winter 2007

Instructor: David BowenCourse web site: www.is.wayne.edu/drbowen/aasw07


Agenda• Assignments and passbacks• Handouts: these notes• Contributions of major cultures• Lab 8.2• “Expanding circles” – a model of scientific

progress• Physical Science and natural disasters• Upcoming assignments• Lab 13: Parallax


Contributions of Major Cultures (to the rise of science) (Q21)

• Prehistoric: attention and observation, e.g. recording phases of Moon

• Early urban: primarily procedures (recipes)• Greek: theories, that is idea of theories as

natural explanationso Frank M. Snowden: role of Blacks as equals

then• Islamic: preserved Greek science, improved

observations• Renaissance: united theory and experiment


Lab 8 Part 2

Dropping objects• Can from different heights

o Impact increases with greater height (speed), not weight

• Can and blocko Aristotle said heavier object would fall fastero Three groups saw same time to fall (expected result)o One group said block hit first

• Reasons were confused• One report said they repeated this – hit at same time.

– Good idea, but the different results should have resulted in more questions


Expanding CirclesWhat Happens When Science Progresses?

• “Science is Progressive” (two meanings)• Science always has a boundary• Science makes progress beyond boundary

o Past discoveries become new tools (barometer)o Extend theories beyond current experiments

• Important in science, but can be misleading• Some scientists say that any religion is incompatible

with science, but actually, that is an extension (more)

• Old questions still important; new answers


Expanding Circles

• After rise of science, most revolutionary scientific advances (late 19th and 20th centuries) extend scope, leave core valid (at least numerically – watch for Quantum Mechanics later)1. Newton (our common idea)2. Special relativity (max speed, energy = mass)3. General relativity (gravity, creation of space)4. Quantum Mechanics (uncertainty at atomic

level and smaller)


Expanding Circles• “Expanding circles of

knowledge” (DB)o Exact shape (circle)

unimportant – “blob”o Science moves boundary

outo Progresses (expands) by

extending known into new territory• Theory and experiment


Expanding Circles

Review:• Greek and later science developed isolated

areas of knowledgeo Air and water pressureo Speed of lighto Falling and sliding objectso Motions of the planets and stars


Expanding Circles

• Implication #1: eventually, expanding circles must meet and overlapo Different approaches, different theories – will

not agree


Expanding Circles

• Implication #2: circles could meet and fill the spaceo What happens then?


Natural Disasters #1

• Hurricanes, tornadoes, earthquakes, tsunamis, mudslides

• Hurricanes best understoodo Rising air over warm ocean – spirals

counterclockwise as seen from above in Northern Hemisphere due to earth’s rotation

o Picks up water vapor, condenses out higher up


Natural Disasters #2• Hurricanes best understood

o When water condenses, air heats again – “fuel”o Strength: indicated by low pressure in the eye

• No storm, 30” Mercury – if eye gets to 27”, get out of there! (Katrina)

o Very large size, winds to about 200 mpho Called typhoons in Asia

• Tornadoes also circular, form over land, smaller but higher winds (about 300 mph)o Less well understood than hurricanes

(“supercell”)



• Earthquakeso “Plate Tectonics” gives general explanationo Earth molten when formed ~ 4.5 BYAo Cooled, surface condensed into continents (thin

“plates”) floating on molten core (“magma”)o Currents in core, like currents in boiling water,

carry plates, like the skin on cooking puddingo Plates crash into each other earthquakes


Example: North & South America were joined to Europe and Africa, magma is boiling up at Mid-Atlantic Ridge, pushing them apart.

Geography and species from before split match across Atlantic ocean



• Earthquakeso As plates crash, tension in “crust” builds up longer time between quakes larger quakeo Cannot presently tell when quake will happen

• Tsunami – wave formed from underwater earthquakeo Sensors, warning system, disaster network can

move population out – Hawaii and Alaska monitoring centers

o No such system in Asian 2004 tsunami, in place now



• Mudslideso Deforestation and development mean

vegetation on hillsides being cut backo People living in these areas due to growth in

populationo Heavy rains weaken hillsideo Depth of mud can be hundreds of feet or moreo Can be foreseen, but weak societies cannot act



• Natural Disasterso At present, we cannot predict or control theseo We are learning a lot about them

• Earthquake and hurricane construction codes• Modern buildings in California much better against

quakes, in Florida against hurricaneso Prediction will come first, control is a maybe


For next class

• Next class – in two weeks, on March 19o WSU Spring Break March 12 - 17o Reader: “The Planet Mars and Kepler’s Three

Laws of Planetary Motion,” “The Crime and Punishment of Galileo Galilei”

o Read the manual, Experiment 10 (Lenses)o Turn in report on Experiment 13


Experiment 13

• Parallax – line of sight changes angle when object viewed from different positionso Geocentric – no parallax for stars, earth does not

change position (fixed at center)o Heliocentric – earth does change position, we should

see parallax for stars.o Lack of observed parallax an early argument against

heliocentric systemo But really, stars too far away for crude angle

measurements then – we see it now• Also, the most direct distance measurement for

objects we cannot travel to


Experiment 13

• Follow lab manual, answer all questions• Two measurements of distance to an object:

parallax measurement and direct measuremento Are the two equal? Angle measurement is

“weak link.” Can probably measure to ½ºo Repeat distance calculation with larger angle -

½º• Check and show all calculations• Check with Instructor if results disagree


Experiment 13 - Parallax• A-B = “Baseline”• Measure distance from Baseline

to Po Two methods, direct and parallax

• Parallax measurements:o Distance A to B (ruler)o Angle A (protractor)o Angle B (protractor)o (Check: one angle > 90º, other < 90º)o Then calculate distance to P using formula in

manual


Experiment 13

3/5/07Atoms and Stars, Class 81 Schedule: Review (Q & A) up to 6 PM Midterm (about one hour) Pass...

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