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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
2/9/05 Atoms and Stars, Class 5 2
Handouts• PowerPoint notes
• Passbacks
Names• Initial by your name on signin list
• Go through class names again
2/9/05 Atoms and Stars, Class 5 3
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
2/9/05 Atoms and Stars, Class 5 4
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
2/9/05 Atoms and Stars, Class 5 5
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?
2/9/05 Atoms and Stars, Class 5 6
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
2/9/05 Atoms and Stars, Class 5 7
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
2/9/05 Atoms and Stars, Class 5 8
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
2/9/05 Atoms and Stars, Class 5 9
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
2/9/05 Atoms and Stars, Class 5 10
Readings (Speed of Light cont’d)
• After Einstein (1905), speed of light is maximum velocity for any object
• Also = c in E = mc2
2/9/05 Atoms and Stars, Class 5 11
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.
2/9/05 Atoms and Stars, Class 5 12
Reading (Euclid’s Elements)
• Proposition 13:A straight lineconsists of tworight angles(180º): CBE + EBD = 180º
• Next, Proposition 15.
2/9/05 Atoms and Stars, Class 5 13
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.
2/9/05 Atoms and Stars, Class 5 14
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)
2/9/05 Atoms and Stars, Class 5 15
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
2/9/05 Atoms and Stars, Class 5 16
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
2/9/05 Atoms and Stars, Class 5 17
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”
2/9/05 Atoms and Stars, Class 5 18
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)
2/9/05 Atoms and Stars, Class 5 19
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
2/9/05 Atoms and Stars, Class 5 20
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?
2/9/05 Atoms and Stars, Class 5 21
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)
2/9/05 Atoms and Stars, Class 5 22
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
2/9/05 Atoms and Stars, Class 5 23
Lab 7 – Density (cont’d)
Additional point:• Displaced water
has same volumeas object thatdisplaced it(Archimedes in bath – “Eureka”)
2/9/05 Atoms and Stars, Class 5 24
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!
2/9/05 Atoms and Stars, Class 5 25
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
2/9/05 Atoms and Stars, Class 5 26
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)
2/9/05 Atoms and Stars, Class 5 27
Density as Demo (cont’d)
• Null hypothesis: if two quantities are equal within their accuracies, they are effectively equal
2/9/05 Atoms and Stars, Class 5 28
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: __________
2/9/05 Atoms and Stars, Class 5 29
Density as Demo (cont’d)
Analysis (use Excel spreadsheet)Dumbbell
• Specific gravity: __________
• Weight change, air to water:__________
• Weight of displaced water: __________
Wood
• Specific gravity: __________
2/9/05 Atoms and Stars, Class 5 30
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:
2/9/05 Atoms and Stars, Class 5 31
Density as Demo (cont’d)
TheoryWeight difference(air to water) isweight W of displacedwater, and is due towater pressure.(This theory has explanatory power.)
2/9/05 Atoms and Stars, Class 5 32
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
2/9/05 Atoms and Stars, Class 5 33
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?
2/9/05 Atoms and Stars, Class 5 34
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
2/9/05 Atoms and Stars, Class 5 35
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
2/9/05 Atoms and Stars, Class 5 36
ISP 3360 – break time
ISP 3340 starts
2/9/05 Atoms and Stars, Class 5 37
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
2/9/05 Atoms and Stars, Class 5 38
End for ISP 3340
Lab