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 5
FINAL EXAM: Thursday, May 8, 8:30-11:30, OCNPS 303
Here is the master list of questions
Logarithmic
map of the universe
| Date |
Problems Solved in Class |
Homework Problems (Due next class) |
| 1/16/08 |
1,4 |
7,10 |
| 1/23/08 |
11, 12, 24, 26, 31 |
19, 40 |
| 1/30/08 |
29, 30, 34, 37(start) |
36, 37 |
| 2/6/08 |
36, 37 |
45, 49, 50 |
| 2/13/08 |
raindrop terminal speed Earth's KE 51, 53, 56, 57 |
64, 67 |
| 2/20/08 |
54, 65, 66 crater size and asteroid KE mass of air in lecture hall |
71, 72 |
| 2/27/08 |
71, 72, 78 |
|
| 3/5/08 |
midterm |
|
| 3/19/08 |
scaling area, volume, gravity, collisions, jump height |
1) Make a 1/10 scale of bridge. Let it
collapse. What speed should you film it at so it appears real? 2) How does I scale with length? 3) If you double the radius of an 8-dimensional sphere, what happens to its surface area? |
| 3/26/2008 |
Dimensional analysis circle, ellipse, pulley bohr radius |
see below |
| 4/2/2008 |
Dimensional analysis pendulum, gravitational light bending |
see below Contact me Monday if you need help. |
due 2 April:
1) For circular orbits, use dimensional analysis to derive Kepler's
third law for periods and radii.
2) Use dimensional analysis to estimate the radius of a black
hole.
due 9 April:
1) Derive the height of the atmosphere as a function of the
appropriate variables.
Calculate your result numerically. Hint: the temperature,
$kT$, should be one of your
variables.
2) What is the drag force on an object moving at speed $v$ through
a fluid? Calculate your
result numerically for a car
at highway speed.
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.
Order of Magnitude Physics A high level, 3 credit, course on estimation from CalTech.
My forthcoming book on estimation for the general public.