Physics on the Back of an Envelope


Physics 309 Spring 2004
Room 202 OCNPS, W 10-11
L. Weinstein
683 5803
Room 217 Oceanography and Physics Building
Room 104 Nuclear and Particle Research Facility, 1021 W 47th St, Norfolk, VA 23529
Office Hours: Fri 10-11 Learning Center and Monday 10-11, OCNPS 217
weinstei(deletethisjunk)@physics.odu.edu

Physicists should be able to estimate the order-of-magnitude of anything. How many atoms of Julius Caesar do you
eat every day? How much waste does a nuclear power plant generate? This 1 credit course will develop concepts,
relations and numbers useful for estimation. We will discuss the concepts as a group and attack the problems as a
group. I intend to lecture as little as possible. The course will not cover new material but will make use of already
acquired (or at least already taught) knowledge. It will try to help students apply physics to real-life questions and
understand which physical effects are appropriate on which scales. The corequisite is Physics 232.

Here is the master list of questions

New questions added 2004:

  1. One way to achieve artificial gravity in space is to spin a space station.  How fast would a space station need to spin to have earth gravity at the periphery?
  2. Humans need to be shielded from cosmic rays in order to live in space.  How much shielding would a space station need?  You may calculate either mass shielding or magentic shielding. 
  3. Addition to #5 (of 1/13/2004 list): How long would it take a prisoner to collect enough dental floss to escape over a wall?

FINAL EXAM: WEDNESDAY MAY 5, 8:30-11:30, OCNPS 202

Cool links:

Logarithmic map of the universe

NEWS and Homework:

Here are some sample tests:
2002 midterm
sample midterm

Date
 Problems
Solved
in Class
 Homework
Problems
(Due next class)
1/14/04
 1, 5, 14, 29
 24, 25, 31
1/21/04
 12, 88 (started)
 19, 20, 21
1/28
 88 (86, 97)
 7, 13, 30
2/4
 18, 56
 8, 9, 27
2/11
 50
 35, 44, 49
2/18
 51, 61
 36, 53, 62
2/25
 54
 101, 103, 120
(see hint below)





















For questions assigned 2/25 (which are due after Spring Break), you need the following information: 1) MWe are MegaWatts-eelctric. The thermodynamic efficiency of a power plant is about 30%. 2) The efficiency of photovoltaic cells is 5-10%. 3) The oxidation of one Carbon atom yields about 1.5 eV (electron-Volts). 4) The fission of one Uranium-235 nucleus yields about 100 MeV.

Please express your answer to problem 101 in a) tons, and b) 100-ton railroad cars.
Midterm Wednesday March 3.

March 3: Midterm Exam.  No homework due.  Please let me know which homework problems you want for March 17.  If you don't choose some, I will.

Important numbers to be memorized for the exam: 

Population of the Earth: 6*10^9
R_earth = 6*10^6 m
d_earth-sun = 1.5*10^11 m
d_earth-moon = 4*10^8 m 
solar flux (at Earth orbit) = 1400 W/m^2
G = 7*10^(-11) N-m^2/kg^2
density of water = 1000 kg/m^3 = 1 kg/l = 1 g/cm^3
density of air (@stp) = 1 kg/m^3
density of iron = 10 tons/m^3
1 year = pi * 10^7 s
avogadro's number = N_A = 6*10^23
1 e = 1.6*10^(-19) Coulombs
molecular binding energy = 1.5 V
cell size = 5 * 10 ^(-6) m
atom size = 10^(-10) m

Chemistry stuff:
1 mole of gas at STP has V = 22.4 l
1 mole of gas has m (in grams) = molecular weight
specific heat of water = 1 cal/g-K

Units:
1 m^2 = 10^3 l = 10^6 cm^3
1 ton = 10^3 kg = 10^6 g
1 atmosphere = 1 bar = 10^5 Pascal = 10^5 N/m^2 = 760 mm Hg = 10 m H2O = 15 psi

Note that the atom size can be derived from Avogadro's number and the density of water.

Your grade in the class will depend partially on homework and class participation.   Please do both!



Last modified: Wed Jan 7 13:23:49 EST 2004