Welcome to Physics 5 Foundations of Mechanics

1
Welcome to Physics 5Foundations of Mechanics
2
What is Physics?

• RPs view
• Goal Quantitatively understand principles that
  underlie the Ultimate Question of Life, the
  Universe, and Everything
• Mathematics is the language for expressing our
  theories
• Any good theory must make predictions, be
  disprovable
• Experimental results are crucial both in testing
  theoretical predictions and in uncovering new
  phenomena for which there are no theoretical
  predictions
• Physics has had great success in describing what
  is known about nature using a rather small set of
  principles
• Occasionally, the answer will be

3
Example Buoyancy

• Given a tub of water, it is observed that certain
  objects float on the surface, while other
  objects sink
• Caveman approach classify each object you find
  as either being a floater or sinker
• No predictive power, not testable, not
  disprovable
• Empirical approach examine many cases, look for
  patterns
• Example find wooden objects are floaters,
  metal objects are sinkers
• No real understanding of buoyancy yet
• Perhaps a pattern emerges
• Objects heavier than an equal volume of water
  sink, those lighter float
• But this only explains buoyancy
• A real theory gravitational force between objects

4
Which Physics Course Should I Take?

• Physics 3
• Less rigorous than Physics 5 minimal use of
  calculus
• Covers material most useful for premedical
  students (e.g., fluid mechanics)
• Not suitable for physics concentrators
• Physics 5
• More rigorous than Physics 3, moderate use of
  calculus
• Intended for science concentrators
• Meets requirements for physics concentration
• Physics 7
• Most rigorous introduction to mechanics,
  extensive use of calculus
• Intended for physics/science concentrators who
  have previously studied physics
• Possible to switch between Physics 5 and 7
• Physics 5/7 students take same labs
• Similar material, same course hours, etc.

5
Course Goals

• Learn how the mechanical motion of physical
  objects can be described and predicted from a few
  basic principles
• One of the first great successes of Natural
  Science
• See how the behavior of much that we see around
  us
• Develop an understanding of how to analyze and
  solve problems
• Identify the essential elements of a problem
• Use reasoning to find a solution
• Understanding the connection between theory and
  experiment in the sciences
• Analysis of laboratory data and errors
• Comparison with predictions
• Make connections between mechanics and other
  areas of physics / science

6
Course Elements

• Lectures that teach the key concepts in Mechanics
• Description of underlying physics principles
• Application of principles by working out simple
  examples
• Demonstrations to illustrate the concepts
• Conference sections that provide a less formal
  setting for answering questions and working out
  detailed examples
• TA and schedule to be announced
• Weekly homework assignments
• Solving homework problems is absolutely essential
  to learning physics
• Weekly laboratory meetings
• Hands-on exploration of the concepts and
  applications of class material
• Will perform 4 project labs during the semester

7
Help!!!!!!!!!!!!!!!!!!!!

• Each member of the Physics 5 team will hold
  office hours to provide additional help as needed
• RPs office hours
• Monday 130 230
• Tuesday 130 230
• Friday 230 330
• Office hours will be held in BH 524
• Office hours for conference section leader, lab
  supervisor will be posted in the near future
• Contact info will be posted on Course Info page
  as it becomes known
• RP partridge_at_hep.brown.edu, [phone]
• Note RP will usually be at Fermilab Wed
  afternoon, Thursday

8
Course Schedule
9
Course Materials

• Text
• Fundamentals of Physics 7th Edition, Vol. 1, by
  Halliday, Resnick, and Walker
• Course web site
• Currently giving WebCT a try
• Will post lectures, course materials, handouts,
  announcements, etc. here
• Lab info
• Prof. Ford will make lab information available on
  the web stay posted

10
Course Grading

• Grading based on your homework, labs, and exam
  scores
• Homework Lowest HW score will be dropped from
  grade
• Homework due at end of class on Wednesday (first
  assignment due 9/14)
• Late homework will not be accepted
• Exams 2 midterm exams and a final
• Midterms October 14 and November 4, 830 950
  in BH 166
• Final Wednesday, December 14, 900 1200 (to
  be confirmed)
• Breakdown for course grade
• 20 Homework assignments
• 20 Laboratory exercises
• 30 Midterm exams
• 30 Final exam
• Numerical borderlines will be set after final
  exams are graded
• Borderlines will not be set higher than 85
  (A/B), 75 (B/C), and 60 (C/NC or S/NC)

11
Measurement

• Physics relies on quantitative measurements of
  stuff
• Length, speed, mass, etc.
• What exactly is a measurement?
• Example Harvard Bridge has a length of 364.4
  Smoots
• Determined by laying Oliver Reed Smoot Jr. on
  bridge roadway and marking off successive lengths
• Not sure how they measured the 0.4 Smoot part
• Measurement consists of determining a physical
  quantity (length) of something (Harvard Bridge)
  in comparison to a standard (Smoot)
• Isnt a Smoot an arbitrary choice for a standard
  unit of length?
• Indeed, but so is the foot, meter, second, etc.
• Clearly, a Smoot is not the best choice to
  measure lengths in
• What if Smoot grows taller? Or isnt around when
  you need to measure something?
• We will use Système International d'Unités (SI)
  units
• Length meter (m)
• Mass kilogram (kg)
• Time second (s)

12
Length

• Meter was originally defined to be 10-7 the
  length between the north pole and equator
• For many years, the definition of a meter was set
  by the distance between markings on a particular
  platinum-iridium bar
• Standard length could be propagated by making
  bars whose length matched the standard
• Example length standard used by Prof. Eli
  Whitney Blake
• Found with 1883 note from person checking
  calibration stating Return this bar to Queen and
  Co. and demand what you paid for it
• As measurements became more precise, improved
  standards have become necessary
• Current standard 1 m is the distance traveled by
  light in 1/299 792 458 s
• Arbitrary length standard replaced by arbitrary
  choice for speed of light

13
Mass

• Mass plays two roles in mechanics
• Determines an objects resistance changes in
  its velocity
• Determines the gravitational force on the object
• As near as we can tell, an objects inertial
  and gravitational masses are identical
• This equivalence led Einstein to develop the
  general theory of relativity, from which comes
  curved space-time, black holes, an expanding
  universe
• SI unit of mass is the kilogram (kg)
• Standard kilogram set by block of
  platinum-iridium kept in France
• Balance can be used to compare an unknown mass
  against a standard
• Example block of material will float if its mass
  is less than the mass of an equal volume of water

14
Time

• Measurement of time based on a quantity that
  varies in a consistent manner
• Example electronic clock counts oscillations of
  an alternating voltage
• Standard unit of time 1 s 9 192 631 770
  oscillations of the light emitted by a Cesium 133
  atom
• Time is the most peculiar unit
• How do we know that time always proceeds at a
  constant rate?
• Favorite sci-fi scenario hero/villain learns how
  to slow/stop time, with everyone frozen while
  good/evil is done
• Special relativity is worth learning just to know
  how peculiar time is!!

15
Natural Units

• Speed of light relates units of length and time
• Incorporated into modern definition of length
• Example Light-year distance traveled by light
  during 1 year of time
• Quantum mechanics relates time and energy
• Energy of a photon is proportional to its
  frequency E hf
• Constant of proportionality h is called Plancks
  Constant
• Could measure time in units of inverse Joules
• Relativity relates mass and energy
• An object with mass has energy
• E mc2!
• Mass, length, and time are thus fundamentally
  inter-related
• Natural units h 2p, c 1
• Still need one arbitrary unit that sets the
  scale of all that we measure
• This bugs me!!!

16
Measurement Summary

• Physical quantities are measured in terms of
  units
• We will use SI units of m, kg, s
• Other quantities can be broken down into these
  units (e.g., 1 Joule 1 kg m2/s2)
• A measurement is meaningless without its units
  dont leave them out!!
• See text for extensive discussion on how to
  convert between units (e.g., 1 kg 1000 g) and
  use the proper number of significant digits