Lecture 1: Physics 103

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Lecture 1 Physics 103

• Welcome!
• Introduction to the course
• Physics in the World
• Chapter 1

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Physics 103 The Cast of Characters

• Lectures (Faculty)
• Matthew Herndon, herndon_at_hep.wisc.edu
• Office hours Wed 330-430, 4219 Cham.
• Tao Han, than_at_hep.wisc.edu
• Laboratory and Discussion (Teaching Assistants)
• 11 TAs 29 sections! (May get bigger!!)
• All sections are full.
• Note Faculty and TAs do not have access to the
  registration system. You should go to the
  physics department office for registration help.

http//tycho.physics.wisc.edu/courses/phys103/fall
09
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Introduction

• Hours per week
• 2 hours
• 2 hours
• 2 hours
• 2 hours
• 4 hours
• 1 hour
• 2 hours

• Basic Course Philosophy
• read about it (text by Serway, Vuille)
• think about it (pre-flight, lectures)
• collaborative learning (discussion)
• experiment with it (labs)
• challenge yourself (homework)
• test your knowledge (disc quizzes)
• close the loop (office hours, tutoring)

We present several opportunities and formats in
which you can learn physics. Please make the best
use of our contact hours, capitalizing on the
format that works best for you. You will do the
learning. Were here to both teach and help you
learn.
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Lectures

• Come prepared
• Read material assigned from text
• See Planner
• Do Preflight on the web 5 of your grade
• Preflight 1 for Next Wednesday (Can be done 5
  days in advance.)
• Lecture itself includes
• Mostly Concepts
• Demos
• Interactive problem solving (questions during
  lecture)
• Collaborate with your colleagues everywhere
  except in exams and quizzes
• DO NOT expect to learn by passively sitting and
  listening in the lecture - please participate
• Lectures are NOT complete - homework,
  discussions, quizzes, and labs are needed to
  complete learning in this course
• Lecture slides are placed on the web after
  lecture
• Ask questions if you dont understand

Participation you learn by doing!
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Discussion and Lab

• Discussion - 15 of your grade
• Work Problems -- collaboratively in groups with
  TA
• Tuesday, Thursday
• Homework due Friday after discussion
• Quizzes due on Sunday after homework (do it
  early!)
• Discussion sections are mandatory
• There is no way to makeup a discussion session
• With a valid excuse attendance credit can be
  given (documented emergency or academic conflict)
  inform us in advance
• Lab - 15 of your grade
• Also led by your TA
• Work in groups of 3
• Prelab questions and quizzes or lab notebook
  review in lab
• Labs are mandatory
• Must do at least 8 of 10 labs to pass this course
• Labs can be made up with a valid excuse
• Make up missed labs during week of lab or midterm
  exam weeks
• Consult with TA to arrange time

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Exams Homework

• Exams
• 3 Midterms 30 of your grade, 1 final 20 of
  your grade
• Multiple Choice, Bring a formula sheet(1 side
  hand written)
• Check that you have no conflicts with exam times,
  listed in timetable , Oct. 8, Nov. 5, or Dec 3
  at 545-700 PM or a final at 1225 AM on
  Thursday, Dec 17.
• Exams are mandatory, unexcused absence will
  result in failure of the course.
• Given an excused absence exam grade will be
  assigned based on other exam scores
• Take the practice exams under time constraint
  with your formula sheet
• Homework 15 of your grade
• Important for learning, maybe most important!
• Web-based
• Some hints are given
• Try to not use the help button right away
• Try again till you get it right!

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A Story

• People have been intrigued by unusual natural
  phenomena
• E.g., Solar eclipses
• Mythology developed around it
• Great for literature and arts!
• Scientific pursuit centered around the following
  method
• Design experiments and make observations of
  physical phenomena
• Propose theories that explain the observations
• Best theories make predictions that can be tested
• Discard theories that dont work.
• Eventually scientists discovered physical laws
  that enable prediction of planetary and lunar
  motion and thus eclipses
• Aristotle, Ptolemy, Copernicus, Tycho Brahe,
  Kepler, Galileo, Newton
• Laid foundations of modern mechanics
• Reliable navigation was not possible without this
  knowledge
• Industrial revolution followed
• Positive feed-back gt new physics discoveries,
  new discoveries in other fields of interest to
  you - microscopes for biology

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Motion of the celestial bodies
Apparent motion of stars Rotation about a point
every 24 hours. Moon, sun, and planets were known
to move with respect to the stars.
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Motion of the stars over 6 hrs
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Daily motion of sun planets over 1 year
Movie by R. Pogge, Ohio State
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Retrograde planetary motion
Ptolemys observations of retrograde motion of
Mars Previous theories couldnt explain
this! Continued observation revealed that the
problem was even more complex than first
believed! - Retrograde motion of Mars. - Apparent
motion not always in a perfect circle. - Mars
appears brighter during the retrograde motion.
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Epicycles, deferents, and equantsPtolemys
Theory
Earth Centered Epicycle reproduced planetary
retrograde motion, very complex. Needed
epicycles for every planet
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The heliocentric universe
Copernicus Competing Theory

• Sun-centered
• Planets orbiting around sun.
• Theory didnt perfectly predict planetary motion.
  Only needed elliptical orbits
• But the (imperfect) theory was already attractive
  in several ways.

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Advantage Natural explanation of Retrograde
motion

• Retrograde motion observed as planets pass each
  other.

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Comparing Ptolemy and Copernicus

• Ptolemys Earth-centered

Copernicus sun-centered
Which is the better theory?
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How can we tell if it is correct?
Both explained contemporaneous observations.

• But a rotating and revolving Earth seemed absurd!

Both motions require incredibly large speeds
Speed of rotation 1280 km/hour Orbital Speed
107,000 km/hr 30 km/sec! No observational
evidence of orbital motion Relative positions
of stars did not shift with Earths motion
(parallax) Stars weren't brighter when Earth is
closer (opposition). No observational evidence
of rotation Daily motions are as easily
explained by a fixed earth. The motions do not
require a rotating earth.
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Advantage A good theory makes predictions
half-illuminated Venus
Earth
We keep the theories that work And teach them to
you here! What did we get out of this Accurate
navigations charts!
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Importance of Physics Awareness

• Large number of Inventions. X-rays, ultrasound,
  IPod (last years Nobel prize)
• Knowledge of physics is useful in all professions
  and in everyday situations.
• Do you want to buy stock in a company that
  advertises to make perpetual motion machines to
  generate free energy?
• Is Hydrogen an energy source?
• Will simply going to fuel cell cars eliminate all
  harmful gas emissions?
• Knowing physics lets you make correct choices
  whether in investment or in voting!
• But, you must read and learn,
• Challenge yourself, enjoy physics 103 and 104
• If you are a pre-med, you will be able to do the
  physics portion of your MCAT exam!

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Course Outline

• Mechanics
• kinematics
• energy
• momentum
• rotational motion
• gravity
• Solids Fluids
• Heat
• Waves

Rockets and Satellites Satellite TV, GPS,
Maps Effective water distribution better
understanding of the heart and blood flow Energy
efficient air-conditioning, heat Understanding
of light waves Radio, TV, Cell phones, microwave
ovens
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Units

• To communicate the result of a measurement for a
  quantity, a unit must be defined
• Defining units allows everyone to relate to the
  same fundamental amount
• Length L meters
• Mass M kilograms
• Time T seconds
• Dimensional Analysis
• Both sides of an equation must have the same
  dimensions
• Can be used to verify equations, answers

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A Concept

• All of these quantities have units
• Distance measured in meters, miles, feet
• Time measured in seconds, hours, years
• Speed meters per second, miles per hour
• Fundamental units
• Derived units
• Speed meters per second (m/s), miles per hour
  (mph)

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Significant Figures

• There is uncertainty in every measurement, this
  uncertainty carries over through the calculations
• Use rules for significant figures to approximate
  the uncertainty in results of calculations
• A significant figure is one that is reliably
  known
• All non-zero digits are significant
• Zeros are significant when
• between other non-zero digits
• after the decimal point and after another
  significant figure
• can be clarified by using scientific notation
• Significant figures in a final result equals
  significant figures in the least accurate of the
  factors being combined
• Hint Keep at least one more significant figure
  in your calculation than needed until the very
  end, then round your final answer

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Significant Figure Example

• You are asked to calculate a trajectory for a
  space ship to the moon to 1 accuracy.
• If your off by more than 1 you might miss the
  moon and not have enough fuel to correct course
  and land!
• 1 is the accuracy we ask for in the homework
  questions
• Formula distance 1/2 accelerationtime2 x
  1/2at2
• Steps. Choose acceleration and calculated time.
  Confirm the ship covers the distance and arrives
  at the right place!
• x 506,000,000m, t 100400sec, a 0.1004 m/s2
• Known to 1 precision 1 part in 100 or 3
  decimal places
• Case 1 After figuring out t and a we round off
  to 1 precision x 1/2at2 1/210000020.100
  500,000,000m
• Case 2 We keep 4 significant figure to be safe
  x 1/2at2 1/210040020.1004
  506,024,032m
• In case 1 we are 1.2 off. You just killed the
  astronauts!
• Lesson to get 1 accuracy keep 4 digits and
  round at end

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Question A

• A very good fastball pitcher can throw the ball
  100 mph. What is the ball speed in m/s?
• (5 miles is approximately 8 km)
• 4444 m/s
• 44.44 m/s
• .4444 m/s

Order of magnitude estimate A mile is of order
103 meters An hour is of order 103
seconds Therefore, the answer should be of order
102 m/s
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Units, Significant Figures, Estimates

• Fundamental Units
• Length L meters
• Mass M kilograms
• Time T seconds
• Dimensional Analysis
• Both sides of an equation must have the same
  dimensions
• Can be used to verify equations, answers vd/t,
  m/s m/s
• Significant Figures
• Final significant figures determined by number
  with the least significant figures used in the
  calculation
• Keep as many extra digits as you like along the
  way(at least 4 if 1 precision needed) and round
  at the end
• Order of magnitude estimates also useful to
  double check answers