- Physical Chemistry I
Spring 2015, Unique 51170
Extra Credit Assignment 1
Fermi problems are a fantastic way to develop basic problem
solving skills, as well as dazzle your friends at cocktail
parties. To solve a Fermi problem, you don't look up your
facts or the answer on the Google, you guestimate. You solve
the problem using logic, general knowledge of the world,
reasonable approximation of unknowns, back-of-the envelope
calculations, and dimensional analysis. They are named after
the physicist Enrico Fermi, who used to start his freshman physics
class at the University of Chicago every year with the problem
"how many piano tuners are in Chicago?" This is something
that no one really knows (except perhaps the head of the piano
tuners local 101), but the point is that you can come to a
reasonable estimate by guestimating how many pianos are in
Chicago, and then assuming the law of supply-and-demand holds, how
many tuners are necessary to service all of those pianos.
(The Wikipedia page on Fermi problems covers this and other cute
examples if you are interested.) The point is not to get
exactly the correct answer, but to get a reasonable estimate (say
within a factor of 2, 5, or 10), with essentially no work.
Most importantly, the skills necessary to navigate Fermi problems
successfully are absolutely essential to critical problem solving
in the physical sciences.
We have reached a point in this course where Fermi problems about energy can touch on almost every aspect of life, and become extremely important when making personal decisions about where and how to access, store, and expend energy.
Problem: How much farmland in the United States would have to be devoted to the cultivation of corn for this country to completely replace gasoline with ethanol as a fuel source for cars?
Assignment: Write out your answer to this question, clearly identifying all of your assumptions and how you are choosing to solve this problem. Give as much information as you need for us to evaluate the reasonableness of your answer.
Your answer will be due at the beginning of class on Tuesday, 17 February, to receive credit.