Fermi Problems

After the introductory days of the course I felt like I had been blabbing at them too much and I had a block day to plan for. At out school we have a pretty normal 7 period day, but on Tuesdays and Wednesdays we run a block schedule with 90 minute periods. I thought that may be another day of trying to discuss would kill the students so instead I thought I would take the liberty of introducing them to a very basic topics of physics, a Fermi Problem.

From my assignment for the day (in a Forum post)

A Fermi Problem is a great exercise in making estimates of answers to burning questions on people's minds today. Really. They are a powerful tool that physicists use to make sure their answers and experiments make sense before they commit to them or make decisions based on them. Enrico Fermi would use them to warm up the crowd at physics conventions in the 1920's.There are several forums below and each is a Fermi problem. Randomly choose five and solve the problems with a partner. Problems usually solve this way:

  1. Decide what pieces of information you need to know.
  2. Make powers of ten estimates of those values (which might require some research).
  3. Combine the information into a final power of ten answer.

As you write your responses please include your thoughts on each of the points above, and if you did research include links to where you found the information that you needed to complete the problems.

After they play around with these for a while I asked them in another forum to make their own Fermi problems and try each others out. It is a fun day and it gets at the basics of breaking problems down into their parts, qualitative guesses, and a little of the history of physics.

What I did not know is how well it would dovetail into my next necessity. I needed them to ask questions about power needs in Nicaragua. Well, after we were done with regular Fermi problems we did just that, and some great questions came out of that. Most especially, how much energy will a rural Nicaraguan school need? I asked them:
  1. How many Joules will we need per school?
  2. How many people know what a Joule is?
  3. Have we arrived at our first thing we need to know?

What is energy and what is a joule? We had discovered our first unit of study.