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), [email protected] 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 308 301 303 305 309 310 302 314 313 304 307 311 312 306 [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] [email protected] 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 (AAB,ABB...) 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) 1 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) 6 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 2 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*Lcm3 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 3 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, 0.0032nSigFig. = 2, 3.20nSigFig = 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 4 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 ( [email protected] ) Andrew Sanville ([email protected] ) q More information at: http://www.engr.wisc.edu/current/coe-ulc-tutoring-undergraduatelearning-center.html (Just google “Undergraduate Learning Center uw madison”) 5
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