Atoms and StarsIST 2420

and IST 1990

Class #11: November 16 and 21

Fall 2005 sections 001, 005, 010 and 981

Instructor: David BowenCourse web site: www.is.wayne.edu/drbowen/aasf05

Moodle: techtools.culma.wayne.edu/moodle

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• Handoutso Class 11 Noteso Table of specific gravities for Lab o POL – get handout on revisions to schedule

This item is also a reminder about lab schedule changes for face-to-face people, who got this handout last week

• Initial the sign-in sheet• Labs following short class: Order is 7, 10, 9

Tonight

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• New Topic for Essay 2 (due Mon 12/5 / Wed 12/7)What has this course been about? This question can be answered by describing one or a few principal themes, and using course materials, such as readings, notes, lab materials, and so on. Start with the “Course Description” section in the Syllabus. You can agree with, make changes to, or disagree with this description, but if you disagree, include an equivalent description – that is, one that covers the course as a whole.

Tonight (repeat)

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Newton’s Law of Universal Gravitation (from last week)

• “Universal” means that it applies to all pairs of masses m1 and m2. For three masses, it applies to all pairs (m1 and m2, m1 and m3, and m2 and m3).

o “1,” “2” and “3” above only identify the masses. The subscript “2”, for example, does NOT mean “squared” – that would be a superscript (above the “m”)

• G is called the “Universal Gravitational Constant” since the same value applies in all cases. Measure it once and you know it.

• “d” is the distance between the two masses.

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Newton’s Law of Universal Gravitation (cont’d)

• F is the gravitational force between the masses

• In algebra, symbols “butted up” against each other (such as G, m1 and m2 below) are multiplied

• The Law:

• The force is attractive: it attracts each mass towards the other.

221

d

mmGF

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Science / WMD in Iraq

• Predictions of WMD notbased on evidence, butprojections from pasto Intelligence agencies said

they could not be positive

• A habit of scientists: “tolerance for ambiguity” – this means:o Deciding on A Vs B? Wait for evidence

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Telling your story…

• I have learned of a number of interesting stories in this class, stories about taking classes this semester.o Examples: pregnant, called away to Louisiana

after Katrina, evacuated in Texas after Rita, dancer for Pistons

• Offer from DIS Newsletter editor: tell your story in 250 words, email it to me (d.r.bowen@wayne.edu), get your story in the Newsletter.

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Experiment 7

• Specific Gravity – property of material:SG: (object weight)/(displaced water weight)

• S.G. help in identifying the material• Displaced water – immerse object in water,

water level rises, this is displaced water• Weighing objects (wood block, dumbbell,

displaced water):o Weight in pounds and ounces using fish scaleo Use string slings for block and dumbbell

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Experiment 7

• Converting pounds and ounces to decimal pounds:1. Divide # ounces 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 # ounces – SHOW THIS CHECK ON DATA SHEET !!!

3. Add X to # pounds to get decimal pounds

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Experiment 7 (cont’d)

• For #7, you will probably have to use different amounts of water in the tub for each object.o Hold object down if necessary (i.e. wood),

cover with water, remove object, then start that part of the lab

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Experiment 7 (cont’d)

• Converting inches and sixteenths to decimal inches:o Same as for pounds and ounces to decimal

ounces, INCLUDING CHECK !!! (Slide 10)

• For step # 5, ignore rounded edges and grooves in block: V = L × W × H

• Same for #6, volume of watero H = change in height with/without block

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• General – light is easier to see than bunny• Lenses are in tissue paper inside envelopes• Labels on envelopes do not mean anything• Each envelope has five lenses – keep track by

type – write a description of each lenso Three convex with

increasing thicknesso One concaveo Other types: plane, plano-convex, plano-concaveo Need to match measurements with lens later

Lab 10: Lenses

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• Exercise I. o For this part, start with the lens touching the

paper. As you move the lens towards you, if you see a dramatic change in the image, keep the lens closer to the paper.

• Afterwards – what happens as you move lens past the point of dramatic change?

o What type of lens is magnifying? Reducing?o For magnifying lens, how does focal length

vary with curvature?

Lab 10 (cont’d)

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Lab 10 (cont’d)• Exercise II: image properties

o Real (can be projected on a screen) Vs virtual (behind lens, can be seen but not projected)

o Inverted (upside down) Vs non-invertedo Magnified (larger than object) Vs reduced

• Measure focal length in mmo Measuring focal length

for reducing lens• Skip this

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Lab 10 (cont’d)• Exercise III (telescope):

o Two lenses are objective (closer to object) and eyepiece (closer to your eye)

o Good telescope – focal length for objective is longer than for eyepiece –choose lenses

o Good idea to make screen for objective: cut hole in card, slightly smaller than lens, tape lens to card, bend card to stand lens up

• Do not do the WRITING ASSIGNMENT

eye

obj

f

fM

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Experiment 9

• Measure curved shapes by winding string around shape, measuring string

• Possible sources of error: stretching, thickness (middle of string along the curve)

• To calculate length differences: convert both lengths from inches and sixteenths to decimal inches INCLUDING CHECK !!! (Slide 10)

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For next class (#12):• Lamphere: no class on 11/23 (#12 on 11/30)

o Tuesday 11/22 is a Thursdayo Wednesday 11/23 is a Friday

• Reader: Chemistry, New York Times on Kansas & Big Bang (emails)

• IST 1990 4 credits: Essay 2 due – turn it in via Moodle

• Moodlers: postings

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For next class (#12):• Experiments 7 & 9 due

Upcoming…• Class 13 (12/5 & 12/7) Lab session (watch

for changes to procedures), 2420 Essay 2 due, Student Evaluation of Teaching

• Class 14 (12/12 & 12/14) Review for Final, 1990 Essay 3 due

• Where the info is: Class 12 or 13• Final Exam: 12/19 & 12/21

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Upcoming…

• Watch for:o A printout of my records of your grades (probably

Week 13 lab session)• If there is a difference, I will want to see graded assignment

o “Grade what-if” – calculate your grade, explore what your grade options are

• Excel spreadsheet, download from course web site (Slide 1)

• Finishing all work

• Redoing work