x4 - Department of Physics

Welcome to Physics 201
Today s Topics
§ The Physics 201 Team
§ Course Formality and Course Overview
§ Q&A
§  Ch 1: Physics and Measurement
Physics 201 Homepage
The Physics 201 Team
Ø Faculty (lectures):
☻ Instructor: Prof. Yibin Pan (me), pan@hep.wisc.edu 4283 CH.
262-9569
Ø Teaching Assistants (labs, discussions):
J Yu Huang
J Nicole Vassh
J Jonathan Brown
J Steven Casper
J Benjamin Lemberger
J Patrick Vanmeter
J Brandon Wilson
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huang76@wisc.edu
vassh@wisc.edu
jhbrown2@wisc.edu
scasper3@wisc.edu
blemberger@wisc.edu
pvanmeter@wisc.edu
bdwilson3@wisc.edu
http://www.physics.wisc.edu/undergrads/courses/fall2014/201/index.html
Physics Department Homepage
http://www.physics.wisc.edu
Physics 201 Course Composition
q  Text: Physics for Scientists and Engineers, 9th ed . Serway/Jewett
q  Lectures: TR 9:55 am
q  Discussion Sessions: 2/week. (Grading: quizzes, participation, etc.)
q  Labs: Mandatory. Each missing lab = - 1 letter grade level (AAB,ABB...)
q  Homework: ~10 problems/week online by Webassign.net
q  Exams: (3 middle-terms + final)
q  Office Hours. (Faculty: by appointments, TAs: as scheduled)
q  Your home time: > 5 hours/week + homework.
q  Honor credit: see email announcement (to be sent soon)
q  Grading:
§ Homework:
100 pts
§ Laboratory:
50 pts (plus missing lab penalty)
§ Discussion:
50 pts = quizzes(35) + discussions(15).
§ Midterm 1:
100 pts
§ Midterm 2:
100 pts
§ Midterm 3:
100 pts
§ Final Exam:
200 pts
Lectures
q  Style:
•  PPT + white board + demos
q  Subjects:
•  Key concepts.
•  Tricky issues
•  Interactive problem solving
v  Lectures are NOT meant to be complete.
•  It is a supplement to your own learning
•  Do read materials BEFORE the lecture.
à Our lectures are designed with the assumption
that you ve read the corresponding sections !
•  Review materials after the lectures.
 Lecture notes will be posted after each lecture
Effectiveness = Preview + Lecture + Review
(Final grades are based on curved and weighted component scores)
Previous semester curve: 21% A, 34% (AB,B), 40% (BC,C), 5% D , (+4 F)
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Exams and Exam Policy
Some Practical Issues
q  Exam Dates:
§  Midterms (5:30-7:00 pm, rooms TBA)
•  Exam 1: Monday, Sep 29
•  Exam 2: Monday, Oct 27
•  Exam 3: Monday, Nov 24
§  Final: Tuesday Dec 16 (2:45-4:45 pm, rooms TBA), cumulative.
q  If you have a conflict with above exam dates, inform your professor
(me) asap, normally at least 2 weeks before the scheduled date.
Alternative exam arrangements are granted only for valid reasons.
Given the size of the class, our flexibility is very imited.
§  Popular excuses:
•  Academic/athletic conflicts: can be considered
•  Medical emergency: can be considered
•  Attending weddings/ visiting friends/Family reunion plan:
NOT to be considered.
202
Physics 201 and 202
201
205/249
Cosmology
Light and Optics
Electro-Magnetism
Sub-Sub-Atomic:
Elementary Particles
Thermodynamics
Sub-Atomic:
Nuclear Physics
Heat, Temperature,
Pressure, Entropy,..
Oscillation and Waves
Classical Mechanics
Laws of motion
Force, Energy,
Momentum,…
Classical
Many-Atoms:
Molecules, solids
Atomic Structure
Quantum Theory
Relativity
Modern
q  Course Web:
http://www.physics.wisc.edu/undergrads/courses/fall2014/201/index.html
q  When sending me emails:
§  Include phrase Phy201 somewhere in the subject line.
§  Mentioning your section # is helpful.
q  Homework assignments are posted each Wednesday evening
and due by 11 pm of the following Wednesday.
q  Lecture notes will be posted after each lecture on the same
day. A draft will be available the night before (can be late).
Follow the links on course web.
q  One discussion session this (first) week
q  First lab starts in week of Sep 14th (3rd week)
q  Please all sign up for WebAssign. (www.webassign.net)
§  Ask your TA for section key. (You still need to purchase
access code)
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Math Background Requirements
q  High school math
§  Basic formulas, linear and quadratic equations,…
§  Sine, cosine, tangent,….
q  Vectors
q  Some calculus
Calculus evaluation: Are you comfortable with these?
*Notations:
*Definitions:
*Formulas:
df(x) d 2 f(x)
,
, ∫ f(x)dx, ∫ab f(x)dx
dx
dx 2
df
Δf
≡ lim
, ∫ f(x)dx ≡ lim ∑ f ( x )Δx
i
i
dx Δx → 0 Δx
Δx → 0 i
2
i
df(x)
d
f(x)
b f(x)dx
1 ,2
, ∫ f(x)dx, ∫a
d(
ax
)
2
dx2
1
d( sin (x))
dx
= ax , ∫ axdx = ax 2 ,
= cos (x)
dx
2
dx
*Equations and solutions:
df 2(x)
= −ω2 x ⇒ f(x) = A cos (ωx + φ)
dx 2
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Physics and Physical Quantities
q  Physics is a branch of fundamental Science that covers everything
Physics:
Theory  Observation
§  Theory: Mathematical Relationship of Physical Quantities
§  Observation: Measurements of Physical Quantities
Units of Time, Length, and Mass
q  Time(T), length (L), and mass(M) are three fundamental
physical quantities in mechanics.
§  From which other physical quantities can be defined (next page)
q  International standard (SI) units for them.
SI Main
q  A Physical Quantity ( e.g. time, mass, length...) is expressed by
Time
Length
Mass
Numerical Value(s) + Unit
s
m
kg
SI alternative
Non-SI
ms, µs,…
day, hour,…
km, cm, mm,.. ft, yd, in,..
g, t,…
lb, ounce,..
q  How are they defined?
A Physical Quantity without value or unit are meaningless.
Time
Length
Mass
Derived Units
q  Basic units can be used to construct derived units
for other quantities:
e.g.
§ 
§ 
§ 
§ 
§ 
§ 
§ 
Area= La*Lb m2, Volume = La*Lb*Lcm3
Speed = distance/time  m/s
Density = mass/volume  kg/m3
Force  kg m/s2 (≡Newton)
Energy  kg m2/s2 (≡Joule)
Power  kg m2/s3 (≡Watt)
…
q  Units reflect dimensions of corresponding quantities:
§  e.g. m2  L2, m3  L3, kg/m3  M/L3, …
§  Further reading dimensional analysis
Original
Solar day
Meter Bar in France
Modern
Atomic oscillation
Distance light travels
Kilogram Block in France
Conversion of Units: A Recipe by Example
q 
q 
1. 
2. 
3. 
4. 
5. 
Example: In an old American physics textbook, the density of
iron is listed as 4.91 x102lb/ft3. What is the iron density in SI?
Recipe:
Write down the quantity in its full form (value + unit)
§  4.91 lb/ft3
Find conversion formulas:
§  1 lb = 0.4536 kg, 1 ft = 0.3048 m
For each conversion formula, construct an identity with the
desired unit in numerator position:
§  1 = (0.4536 kg)/(1 lb), 1 = (0.3048 m)/ (1 ft)
Put identities besides units of the quantity in Step 1.
Cancel undesired units, and do algebra.
§  4.91 x102lb (0.4536 kg)/(lb) /( ft (0.3048 m) /(ft) )3
= 7.86 x 103 kg/m3
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Significant Figures (Sig. Figures)
q  Every measurement has errors, one needs to be accurate, but not
excessively-accurate.
§  Question: A ruler has smallest scale of 1 cm, when used to
measure a string of ~59 cm long, which of the following readings
are improper?
•  59.2 cm
•  58.8 cm
•  59.0 cm
•  59 cm
•  59.02 cm
§  Answer: .
•  59 is too inaccurate  one more digit can be estimated
•  59.02 is over accurate  the last digit can not be read
•  59.2, 58.9, 59.0 are all possibly OK (depending on reading).
•  Note 59 ≠ 59.0 !
q  In measurements and in calculations only keep significant figures.
Order Of Magnitude Estimation
q  Often, a rough guesstimation on the physics quantities
before detailed measurement is useful (and possible.)
Quick quiz:
How many sand grains in a palm?
§  100
§  1000
§  millions
§  billions
Quick estimation:
N= total volume / sand size
~ 10 cm3 / (0.01 cm)3
~ 10 million
Rules On Sig. Figures
q  Rule 1:
§  In direct measurement, keep all sure digits plus only one
estimated digit. e.g. 41.2 cm, 23.5s, ...
Ø  These (“sure” + “estimated” ) digits are called significant figures
(sig. figure), with the estimated one being called least sig. figure
q  Rule 2:
(Definition). Number of sig. figures = number of significant digits not
counting leading zeros
e.g.41.2 nSigFig = 3, 0.0032nSigFig. = 2, 3.20nSigFig = 3.
q  Rule 3:
In additions or subtractions, the least significant figure of the final
result can not be more accurate than that of any operands. e.g. 13.8m
+2.05m-0.062m (=15.788m) =15.8m
q  Rule 4:
In multiplication or division, the N of sig. figures of the final result
equals the lowest num. of sig. figures among all operands.
e.g. 13.8 m x 2.05 m x 0.062 m (=1.75398) = 1.8 m3
Always keep all digits until final result and then perform rounding.
One more Exercise
q  A solid block of iron has a volume measured as 0.22 cm3, how
many iron atoms in this block? (known: ρ= 7.86 g/cm3, Atomic
mass of iron = 55.93 u, 1u = 1.6606 x 10-27 kg, 1g = 10-3 kg)
A: 20
B: 20,000
C: 2x1022
D: 2x1033
q  Solution:
§  Method 1:use order of magnitude estimation.
(hint: ever heard of Avogadro s number? 6.022x1023?)
§  Method 2: detailed calculation
•  The block has mass m = ρV = 7.86 g/cm3 * 0.22 cm3 = 1.7 g
•  Mass of iron atom = 55.93 u = 55.93 * 1.6606x 10-27 kg/u = 92.88 x 10-27 kg
•  Number of iron atoms in the block
= 1.7 g /(92.88 x 10-27 kg) = 1.7 g x (10-3 kg /g) /( 92.88 x 10-27 kg)
= 1.8 x 1022
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A Challenging Quiz
q  Measured data:
q  Challenge
Mass of Atoms (in unit u)
Ø Anything special?
Hydrogen
1.01
§  All masses are (near) full numbers !
Helium
3.02
Oxygen
15.99
Sodium
22.99
Aluminum
26.98
Iron
55.93
U 238
238.05
Ø  This strongly suggests?
à Atoms are made of particles with
mass = u.
Resources
q  Your Instructor (me ) and your TAs
q  Supplemental Instruction (SI) Program (next page).
q  The Physics Club: http://ups.physics.wisc.edu/drupal/
q  Private Tutoring by Physics Graduate Students (fee):
http://www.physics.wisc.edu/sites/default/files/Private%20Tutor
%20List%20-%20Fall%202014_1.pdf
Facts
§  Atom is made of:
protons + neutrons + electrons
§  Mproton ~ Mneutron ~ 1 u
§  1u = 1.6605 x 10-27 kg
§  Melectron << 1u
Supplemental Instruction for
Physics 201
q  Extra instruction lead by fellow students to help with the
coursework
q  You can sign up using the student center
q  Sessions held at 4:30 Monday and Wednesday
q  If you sign up, attendance is mandatory
q  Our Physics 201 SI facilitators this semester are
Tyler Maule ( tmaule@wisc.edu )
Andrew Sanville (amsanville@gmail.com )
q  More information at:
http://www.engr.wisc.edu/current/coe-ulc-tutoring-undergraduatelearning-center.html (Just google “Undergraduate Learning Center
uw madison”)
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