Physics on the Back of an Envelope

Physics 309 Spring 2009

Room 303 OCNPS, W 11-12
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: Mon 11-12 Learning Center and by apppointment
weinstein -at- odu -dot- edu

Textbook: "Guesstimation, Solving the world's problems on the back of a cocktail napkin", Weinstein and Adam, Princeton Press, 2008.

Physicists should be able to estimate the order-of-magnitude of anything. How many atoms of Julius Caesar do you inhale with each breath? 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.

Your grade in the class will depend on tests, homework and class participation.

Midterm: March 4
FINAL EXAM: TBD

Here is the master list of questions

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)
1/14/08	5, 11, 12	13, 14, read chap 1
1/21/08	7, 15, 18, 26	19, 27, 28, read chap 3
1/28/08	23, 29, 30, density	31, 33, 40
2/4/08	gas used last year gas wasted in traffic 34, 36	44, 78, 79
2/11/08	80, 89	43, 71
2/18/08	90	74, 94, 95
2/25/08	T_Earth w/o atmo, 96	read 105, 107 do 106, 108
3/4/08	midterm
3/18/08	81, 134	63, 69
3/25/2008	63, 69	67, 68
4/1/2008

Homework questions:

Important numbers (memorize these):

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 = 4 J/g-K

Units:
1 m^3 = 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
1 m/s = 2 mph (approx)

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

Useful links

Lies and Damn Lies: The Art of Approximation in Science This is a great course on estimation methods, given at MIT. I plan to steal from it liberally.

Order of Magnitude Physics A high level, 3 credit, course on estimation from CalTech.

Last modified: Tue Jan 13 13:23:49 EST 2009