2/9/05 Atoms and Stars, Class 5 1

Atoms and StarsIST 2420

and IST 1990http://www.is.wayne.edu/drbowen/aasW05

Class 5: February 9

Fall 2005

David Bowen

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Handouts• PowerPoint notes

• Passbacks

Names• Initial by your name on signin list

• Go through class names again

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Due this week• Assignments go in the “IN” folder

o Report for Lab 3 (Density)o Essay 1

For next week…• Reader Pp 74 – 79 & 90 - 104• Manual Pp 35 – 41, Experiment 8• Turn in Report for today’s Lab 3 Part 2• Midterm: March 9, Questions for Midterm

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Late Assignments• OK, there is a penalty for late assignments –

they may not be turned back quickly

Making up a Missed Class• Class: a one page summary of the class.

Strict page limit. This makes it hard.

• Lab. Photocopy of data sheet, together with your write-up for experiment

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Science in the News• Kansas State School Board considering

adding Intelligent Design to Biology curriculum (NPR/WDET 2/8/05)o Three years ago, added Creation Scienceo Two years ago, new school board removed ito This is another new school board

• Comments: Life Sciences expected to be important basis for “new economy”o Starting in 20th century, science drives

technologyo Support for science: growing or declining?

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ReadingsSpeed of Light

• Sound slow enough that we can hear lag

• Light is faster, we cannot ordinarily see lag

• Most Greeks believed light has infinite speedo Hero of Alexandra: light travels from eye, when

we open eyes we see stars instantly, so speed is infinite

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Readings (Speed of Light cont’d)• Arabs Avicena and Alhazen 11th cent: light is

something, cannot be in two places at once• Roger Bacon ~1250 and Francis Bacon

~1600 believed light has finite speed• Johannes Kepler ~1600 light has infinite

speed• Rene Descarte ~1625 said if light speed

infinite, lunar eclipse position would lag, not observed, so must be infinite

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Readings (Speed of Light cont’d)• Galileo experiment: time round trip on

hilltops at different distances. Done by others, no difference seen.

• 1165 Robert Hooke said light might just be “exceeding quick”

• 1676 Danish astronomer Ole Roemer used eclipses of Io, moon of Jupiter, to measure speed of light

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Readings (Speed of Light cont’d)

• Motion in orbit regular, like a clock (here, Io)• “Late” eclipse in Earth position 2 due to light

traveling across diameter of earth’s orbit• Estimated speed at 140,000 mi/sec• Modern value 186,000 mi/sec

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Readings (Speed of Light cont’d)

• After Einstein (1905), speed of light is maximum velocity for any object

• Also = c in E = mc2

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Reading

Euclid (Pp 74 – 79), book Elements

Proof in mathematics and geometry

• Postulate #4: all right angles (90º) are equal

• Common notion #1: things equal to the same thing are equal. If a = c and b = c then a = b

• Common notion #3: if equals are subtracted from equals then the remainders are equal. If a = b then a – c = b – c.

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Reading (Euclid’s Elements)

• Proposition 13:A straight lineconsists of tworight angles(180º): CBE + EBD = 180º

• Next, Proposition 15.

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Reading (Euclid’s Elements)

• Proposition 15: Iftwo straight linescut each other,the vertical anglesare equal (i.e. AEC = DEB)

• Proof on next slide, relies upon earlier Postulate #4, Common Notions #1 & #3, and Proposition #13.

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Reading (Euclid’s Elements)

AEC + CEB = 180º(AEB is a straight line)

DEB + CEB = 180º(DEC is a straight line)

AEC + CEB = DEB + CEB(Things equal to the same thing are equal)

AEC = DEB (subtract CEB from each,equals subtracted from equals are equal)

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Reading (Euclid’s Elements)

• Proposition 47:PythagoreanTheorem

• For a right triangle (has one right angle),a2 + b2 = c2

o Example: 3, 4, 5 triangle, 32 + 42 = 9 + 16 = 2552 = 25, so 32 + 42 = 52

• Formula known to Egyptians, maybe earlier, but proven by Pythagoras

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Reading (Euclid’s Elements)

• Mathematicso start with assumptionso draw unarguable conclusionso assumptions can be wrong – spherical geometry

• on a sphere, angles of a triangle add up to less than 360º

• Physical science can be put on this basis (axiomatic)o Assumptions and results can be overturned with new

experiments

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Lab Reports

1. Cover Sheeto Your nameo Experiment, number and titleo Lab date and date that report turned ino Full names of groupo In a scientific paper, this would be the

“setting”

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Lab Reports (cont’d)2. Data sheet

o Procedure – what you dido Observations and/or measurements – what

you saw and/or measured as a result of the Procedure

o Be specific, include detail, sketches helpo If you copy it over or type it, include the original also

• (I may go to initialing them during lab)

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Lab Reports (cont’d)

3. Answers to questions, explanations, hypotheses, theories, tables, calculations

Main ideas:

• Keep data separate from the resto What you dido What you saw and/or measured

• Good detail in procedure and observations

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Lab 2 - Sea of Air• Many people said they could hear air

rushing out of the spheres when valve opened. Positive pressure inside would push spheres apart. Must have heard air rushing in. (gauge pressure = difference from atmospheric pressure)

• When thick bottles did not implode in ice water, someone said to listen when top opened. Good! What was the hypothesis?

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Lab 7 – Density

Question asked – what is the density of air?

• 0.00129 gm / cm3

(grams per cubic centimeter)o Compare to water, 1 gm / cm3

(by definition of the gram)

• Or 0.0805 lb / ft3 or ~1¼ oz / ft3

o Compared to water at 62.4 lb / ft3

• (objects weight less in air than in vacuum)

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Lab 7 – Density (cont’d)How to avoid drowning:• Density less than 1, float. Greater than 1, sink• Less density, float higher• Density = Weight (in air) / Volume• Breath in, Volume is larger, Density is less,

you float or float higher• Flailing arms, push water out, add to volume

o Plus attract attention, keep warm

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Lab 7 – Density (cont’d)

Additional point:• Displaced water

has same volumeas object thatdisplaced it(Archimedes in bath – “Eureka”)

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Lab 7 – Density (cont’d)• This lab involved many quantities

o Weight of object in air (A) and in water (B)• Weight of floating objects in water = zero

o Weight of water with and without object in it• Difference = weight of displaced water (C)

• For floating object, push it under water

o Density = A / Co Also A – B

• Common to get confused: use better labels!

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Density as Demo• Bigger objects – one sinking, one floating• Volume of displaced water = volume of

object (Archimedes)• Different method for measuring weight of

displaced water – remove it to bottle• Accuracy of measurement – estimate by

repeating measurements• Null hypothesis – if difference is within

accuracy, cannot say it is different than zero

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Density as Demo (cont’d)

• Specific gravity =weight of object ÷ weight of displaced water.o no units, since it is weight divided by weighto also = object’s density ÷ water’s densityo water’s density = 1 gm / cm3, so specific gravity

of an object = its density in gm / cm3

o (cm3 is common abbreviation for cubic centimeter)

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Density as Demo (cont’d)

• Null hypothesis: if two quantities are equal within their accuracies, they are effectively equal

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Density as Demo (cont’d)Observations (lb and oz)Dumbbell• Object weight in air: __________• Object weight in water:

__________• Weight of displaced water: __________Wood• Object weight in air: __________• Weight of displaced water: __________

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Density as Demo (cont’d)

Analysis (use Excel spreadsheet)Dumbbell

• Specific gravity: __________

• Weight change, air to water:__________

• Weight of displaced water: __________

Wood

• Specific gravity: __________

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Density as Demo (cont’d)

• Pressure at a depth = weight of the column of water aboveo Pressure increases with depth because there is

more water aboveo An object weighs less in water because greater

water pressure on pushing up on bottom compared to lesser on top pushing down

Theory:

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Density as Demo (cont’d)

TheoryWeight difference(air to water) isweight W of displacedwater, and is due towater pressure.(This theory has explanatory power.)

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Measurements

• Physical Science (Physics, Chemistry, Astronomy) now has mathematical theories that make numerical predictions that are checked against measurementso Exception is Geologyo Earlier, mostly qualitative theories checked

against observations (some mathematical)

• Life sciences currently mostly qualitative

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Measurements (cont’d)• Measurements have accuracy, must check

how accurately your measurements areo Repetition is a good methodo Results agree with theory if they are within

measurement accuracy

• Why are Life Sciences not mathematical?o Started later?o More difficult, takes longer?o A different type of science?

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Lab• Measurements (here with stopwatches)

o Checking: have two people run five 10-sec trials on classroom clock

o If you see a cluster of times close together and others far off, the others may be mistakes or “outliers” (not both)

o Average the clustero Is the spread on the cluster reasonable? Time it

off on the classroom clock or the stopwatch

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Lab (cont’d)• Add data & questions from previous slide to

your lab report, use as standard below• Do track experiment, A to E only, with

heavy and light metal spheres• Projectiles (Part II)

o Follow directions hereo Accept level start only - reject trials in which

projectile starts out angling upwardso Consider null hypothesis – no difference

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ISP 3360 – break time

ISP 3340 starts

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ISP 3340

• Pictures for Moodle?

• Postings in Moodle – need to get going

• Other articles on course web site – password needed

• Essay 1 on Rocks of Ages and other articleso Due February 23o Title page must list topic and descriptive title

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End for ISP 3340

Lab