Physics 231 Wade Fisher August 29 2012 Topic 1a: Introduction, Units, Significant Figures

Physics 231
Topic 1a: Introduction, Units, Significant Figures
Wade Fisher
August 29 2012
MSU Physics 231 Fall 2012
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Physics 231:
Non-calculus Introductory Physics
Instructor: Wade Fisher
[email protected]
Office: 3234 BPS
Phone: 517-884-5556
Walk-in Hours: 10:15-11:30 Monday
1248 BPS or by appointment
MSU Physics 231 Fall 2012
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Physics 231:
Non-calculus Introductory Physics
PHY 231 webpages:
(Section 2) http://www.pa.msu.edu/~fisherw/Phy231_Fall2012/
(All Sections) http://www.nscl.msu.edu/~brown/231-fall-2012/
Lectures & Notes:
Section 2: 9:10-10:00 AM (Mon. Wed. Fri.)
 Lecture notes are available before the lecture without solutions to
problems, and after lecture with solutions
 Notes are in PDF format
 Not everything we will do in class can be in the lecture notes!
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Homework
Homework is to be done online using LON-CAPA
 http://msu.lon-capa.org
 Assignments are usually due Wednesdays at 11PM
The deadline is very strict.
Being away from a network connection is no excuse.
Do not wait until the last minute!
Check the syllabus and LON-CAPA for each week’s deadline.
 Assignments are somewhat unique to each student
You are strongly advised to NOT copy solutions from the LON-CAPA chat box
Homework is your chance to learn, so do not waste your time/money by
copying the work of others
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Exams
Exams are closed-book ( 2 midterm exams + 1 final )
 You can bring your own equation sheets: one double-sided 8.5/11” sheet
 Exams may contain material from the textbook, homework and quizzes
 Exams will consist of both conceptual and numerical problems
 Make up exams by appointment only and as a rule are scheduled BEFORE the
regular exam date
 We will hold review sessions in class prior to exams
 Students with disabilities that require special arrangements should inform me
ASAP (1st two weeks of class) and well ahead of the exams
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Extra Credit Quizzes
We will be doing in-class quizzes using i>Clickers
 Quizzes will be given randomly throughout the semester
You must have in i>Clicker to participate
Be on time, quizzes are often at the beginning of class.
There are NO make-ups for quizzes
You must take quizzes in this section. No credit for quizzes in other sections.
Quiz points: 3 for correct answers, 1 for incorrect answers
Scores will be posted occasionally – check to ensure you're registered
You must register your i<Clicker: http://www.iclicker.com/registration
 Even if you have registered before, you need to re-register!
 You MUST enter the preceding “A” before your student ID
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Extra Credit Quizzes
You must use your own and ONLY your own
i>Clicker in class
 If you are found to be using another
person's i>Clicker, all clickers will be
confiscated
 This will be considered a violation of
the rules governing academic
dishonesty
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Physics Learning Center
The Strosacker Physics Learning Center is located in BPS 1248
 Details and schedule found on the PHY 231 website
 The PLC is a cooperative learning center, not a help room. TAs will
encourage group work and will help groups who get stuck.
 Group work
 A very effective learning tool for both strong and weak students
 You must do your own assignments and must learn how to do problems on
your own
 Do as much as you can of the assignments before group work – PREPARE!
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Grading
Grade
Awarded
Minimum
Average Grade
4.0
92%
Midterm Exams (2)
3.5
84%
Final
35%
3.0
76%
Homework
25%
2.5
68%
Clicker Quizzes
5%
2.0
60%
1.5
52%
1.0
44%
Grade Source
Max %
20% each
Total:
105%
Quiz points are based on 75% of the maximum quiz score
 IE, you can miss 25% of quiz points and get full credit
Homework points are based on 90% of the maximum homework score
 IE, you can miss 10% of homework points and get full credit
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Textbook & Reading
Essential College Physics, Volume 1
• The syllabus lists the relevant chapters for
each lecture and homework
• Reading assignments will be given at the end
of each class
• All material in the assigned reading can be on
homework/exams and not everything can be
covered in class
• Lecture notes are NOT a replacement for the
textbook
Amazon: $63.92
eBook: $33.99
(CourseSmart.com)
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Class Schedule
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Syllabus – PHY 231
Everything we've just covered is detailed within the PHY 231 syllabus
 The syllabus can be found on the course website
http://www.pa.msu.edu/~fisherw/Phy231_Fall2012/
 You must read the syllabus!
 It is your responsibility to know and understand the
course policies.
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How to Suceed in PHY231

Read the book before coming to class. Some quizzes will be on the reading material,
even material that has not been covered in class.
 Go to the Physics Learning Center frequently! The TAs are there to help you learn.
 Always attend the lectures.
 Recognize that learning physics is different than many other subjects
 Physics is about understanding concepts and connecting your knowledge with
these concepts. Physics is not about memorizing facts.
 Many physics concepts will be contrary to your instincts, but not contrary to
your intellect. Be willing to think things through!
 Keep working continuously – do the reading assignments, think about what you
learned in lecture, keep thinking AS WE GO. Memorizing facts is not sufficient,
so cramming before an exam is rarely effective.
 Physics requires advanced problem solving strategies that likely differ from
what you are used to. Understanding the concepts helps you set up solutions to
problems. Equation hunting is not a good strategy.
 Little is learned by copying or memorizing the solution of another student.
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DOs and DON'Ts
DON'T...
 ...use LON-CAPA postings from others before you have given a problem a genuine
attempt yourself. If you have to frequently look at how others solved the problem, it
means you aren't understanding the material well.
 ...try to memorize LON-CAPA problems; it is unlikely that you will get many
problems in exams that are exactly like the homework
 ...base your entire study routine on LON-CAPA. Bring variation in your studies and
practice questions that are not phrased like LON-CAPA (eg, questions in the book)
 ...wait until the last weeks of the semester to ask for help if you need it (ie, if you're
working hard but still are not doing well)
 ...cheat on exams, quizzes, homework
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DOs and DON'Ts
DON'T...
 …use your cell phone in class.
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DOs and DON'Ts
DO...






...read the syllabus
...come to class
...come to class prepared
...go to the Physics Learning Center if you get stuck
...work with others, but remember that for exams you are on your own
...ask me for help if you work hard and still do not perform well on the exams (the
earlier, the better)
 ...ask any question that you like; the only stupid question is one you don't ask
 ...call me 'Wade', instead of Dr./Prof. Fisher
Contact me via email or talk to me after class, only use phone in emergencies.
To avoid having your email end up in my spam folder:
Use your msu email (not yahoo, gmail, etc)
Use an identifying subject for email (eg, 'Question on PHY 231')
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Clicker Quiz 1:
How important is it to learn physics?
A) Very important
B) Somewhat important
C) It may never matter
D) Not important
E) Complete waste of time
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Why Learn Physics?
Example:
Tacoma Narrows Bridge (c. 1940)
World renowned for its exemplary feat
of engineering
Golden
Gate
BronxWhiteStone
Tacoma
Narrows
Year
1937
1939
1940
Cost
$35M
$20M
$6.4M
Length
4200 ft
2300 ft
2800 ft
Width
90 ft
74 ft
39 ft
Ratio:
Width to
Length
1 : 47
1 : 31
1 : 72
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Why Learn Physics?
Example: Physics of aneurysms
Key concept for:
• Human medicine
• Veterinary medicine
In other classes, you learn the names of bones, how
to treat broken bones, where to drill to replace
things.
Physics teaches you HOW and WHY it works (and
how to understand the system as a whole)
Key to innovation!
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Why Learn Physics?
Example: Dark Matter & Dark Energy
Bullet Cluster
• Cosmological measurements have told
us that our universe is not made the
way we thought.
• IE, what we see in telescopes
corresponds to what we are all made
out of: atoms (stars, gases, planets)
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Why Learn Physics?
Example: Dark Matter & Dark Energy
• Cosmological measurements have told
us that our universe is not made the
way we thought.
Bullet Cluster
• IE, what we see in telescopes
corresponds to what we are all made
out of: atoms (stars, gases, planets)
• But this is only 4% of what’s out there!
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Today's Lecture:
Key Concepts

Syllabus

SI Units

Mass: kilograms (kg)

Length: meters (m)

Time: seconds (s)

Units and conversions

Dimensional Analysis

Scientific Notation (e.g., 4.3x1012 and 2.3E4)

Significant Figures
Covers chapter 1 in Rex & Wolfson
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Système Internationale (SI) Units
Unit
Meter
kil ogram
Second
Ampere
Kelvin
Mole
candela
Abbreviation
m
kg
s
A
K
mol
cd
Base unit for
length
mass
tim e
curre nt
temperature
amount of a substance
lumi nous intensity
 MKS (or MKSA) unit system
 Based on powers of 10 relative to base units
 All other units derive from these (Area: m2, Speed: m/s, etc)
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Clicker Quiz
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Unit Conversions
It is frequently useful (or necessary) to convert between different unit
conventions
 miles/hour to m/s
 mcg/liter to molarity
 PSI to Newtons/m2
As a concrete example, consider a common medical conversion:
 Patient needs 1 mg / 20 mL, nurse has a 1L bag of saline and a syringe of 0.2
molar medicine. What to do?
 An estimated 50-100k deaths occur each year due to medication errors, ~10% of
these are traced to conversion errors.
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Unit Conversion Example
Treat conversions as algebraic equivalencies:
Convert by multiplying your existing units by a numerical equivalent of 1.0
Jon has walked 3 miles in 1 hour, what is his average speed in m/s?
Given: 1 mile = 1609.3 m
ie, 1.0 = ( 1609.3 m/ 1 mile )
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Dimensional Analysis
Dimensions should be treated as algebraic quantities
 If you know the dimensions you want in the end of a calculation, it helps you plan
your work and check your math
Example:
 Calculate the distance traveled in 10 seconds by an object starting at rest and
traveling at constant acceleration
 You need to know what units to use for acceleration!
Relevant equation: x = xo + vo t + ½ a t2
Given: xo = 0 vo = 0
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A Wide Range of Units
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Scientific Notation
 For very large or very small numbers the scientific notation is
advantageous.
 Write number as mantissa x 10Exponent
 Example:
0.000000001 = 1 × 10-9
34000000 = 3.4 × 107
 Alternative notation: 3.4E7 (CAPA, computers)
1 m = 1E3 mm
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Significant Figures
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Significant Figures
Two statements:
 The population of the USA is 294,109,799
 The population of the USA is 294,000,000 = 2.94×108
 First statement implies precision that is simply not warranted
 Second statement claims that the population is somewhere between 293M
and 295M. This is justified!
General Rules:
 The number of digits we write down in a number specifies the precision with
which we can claim to know the number
 All non-zero figures are signficant (except exponent in scientific notation)
 Zeros only count when
They are between non-zero figures
They are to the right of a non-zero figure and there is a decimal point
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Significant Figures Example
An athlete must bicycle around a circular track for a
time trial. His coach tells him that the radius of the
circular track is 40.2 m. How far must he ride?
Formulae: C = π × D = 2 π × R
D = diameter of the circle
R = radius of the circle
π = 3.14159265.....
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How to Solve Problems
There are no general rules but here are some pointers:
1) READ the problem carefully!
2) Summarize (throw away unnecessary info)
3) Visualize (drawing can often help)
4) Convert units (consistency)
5) Set up equations:
Plug in numbers if not comfortable with solving sets of equations
If confident, plug in numbers at last moment
6) Check whether answers make sense
7) In exams: once you have solved a problem, check calculations one
more time at the end of exam. Especially important if you tend to
make small mistakes
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Problem: The diameter of the orbit of the earth around the sun is 4x1011 m.
(1) What is the distance traveled by the earth in 1 year?
(2) In the polar coordinate System with the sun in the center, over what angle
does the earth travel in 0.30 year?
Question 1:
Question 2:
a) 1x1012 m
a) 108 degrees
b) 2x1012 m
b) 120 degrees
c) 2.5x1012 m
c) 1.88 radians
d) 1.3x1023 m
d) 1.1x102 degrees
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Friday's Lecture
Rex & Wolfson Chapter 2: Motion in 1 Dimension
Homework: Optional Set 0
Due Monday 9/3
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Defining Standard Units
Platinum-Iridium
Kilogram Prototype
Original definition of the meter: 1/10,000,000 of earth's arc length
 Today: 1m = distance light travels in 1/299,272,458 s
The kilogram was originally defined at 1 dm3 of water
 The kilogram defined by a fixed “prototype” of matter
Standards are important: when you buy 1kg of gold, you want to get it right!
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Defining Standard Units
Cesium Atomic Clock
National Institute of
Standards and Technology
(NIST)
Original definition of the second: 1/86,400 of a solar day
 1960: based on a tropical year
 Since 1967: 9,192,631,770 periods of radiation corresponding to the transition between
two hyperfine states of the ground state of 133Cesium
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Accuracy vs Precision
Calibration of experimental
apparatus can limit both
accuracy and precision
Intrinsic calibration of measuring
instrument can limit precision
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Very Large and Very Small Numbers
0.000000000000001=10-15=1E-15 femto (f)
0.000000000001=10-12=1E-12 pico (p)
0.000000001=10-9=1E-9 nano (n)
0.000001=10-6=1E-6 micro ()
0.001=10-3=1E-3 milli (m)
0.01=10-2=1E-2 centi (c)
0.1=10-1=1E-1 deci (d)
1=100=1E+0
10=101=1E+1 deca (da)
100=102=1E+2 hecto (h)
1000=103=1E+3 kilo (k)
1000000=106=1E+6 mega (M)
1000000000=109=1E+9 giga (G)
10000000000=1012=1E+12 tera (T)
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Greek Alphabet
We will use some of those…
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2D Geometrical Objects
object
surface
circumference
square
Length2
4xlength
triangle
½x base x height Side1+side2+side3
circle
x radius2
2 x  x radius
Radius=diameter/2
rectangle
Length x height
2xlength +
2xheight
oval
xr1xr2
-
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Area of triangle: ½ base x width = ½x4ux5u = 10u2
(u: unit of length in drawing above)
10u2 = 68.4cm2 1 u2 = 6.84cm2
Full square: 9x9u2 = 81u2 corresponds with 81x6.84 = 554 cm2
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3D Geometrical Objects
object
surface
volume
6xlength2
length3
2hw+2lh+2wh
hlw
sphere
4r2
4/3 x r3
cylinder
2rh
r2h
cube
rectangle
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Solving Quadratic Equations
ax 2  bx  c  0
a0
 b  b 2  4ac
x
2a
In general there are 2 solutions. In physics problems,
One of them is often not realistic and is thrown out.
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Calculate the length of the shorter of two sides of a
rectangle, which has an area of 24 m2 and a perimeter
(circumference) of 22 m.
A = lh
C = 2l+2h
h
24 = lh so l = 24/h
22 = 2l+2h = 2x24/h+2h = 48/h+2h
-2h2+22h-48 = 0
 22  22  4(2)(48)  22  10
h

2(2)
4
h  8 h  3
l  3 l  8
2
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ax 2  bx  c  0
a0
 b  b 2  4ac
x
2a
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