# Sunday Function

If you go to the bank and open a savings account, the banker might tell you about the virtues of compound interest. He may say something like “Even if you never deposit anything, the rate of change of the money in your account is proportional to the amount of money in your account. The more…

# Nonlinear Optics, Back-of-Envelope Numbers

If you take a flashlight and shine it at a wall or through a prism or do pretty much anything with the light, you’ll find that the effects of the light change in direct proportion to the amount of light the flashlight’s putting out. Twice the light, twice the reflection from the wall. Twice the…

# Sunday Function

Here’s an odd little bit of math for you this Sunday. It’s defined in terms of recurrence. Recurrence happens when a function is defined in terms of itself. This happens more than you might think – one famous example is the Fibonacci sequence, which is informally defined by saying “To get the next term in…

# A Conspiracy of Digits

A few days ago there was an interesting math problem posed on the right-leaning lawprof blog The Volokh Conspiracy. It’s a cute problem in itself, and it makes a nice discussion example about the role of computers in modern physics. The problem is this: Find a ten-digit number with the following two properties (in base…

# How to Teach Physics to Your Dog

Because I’m a bad busy person, this review of Chad Orzel’s How to Teach Physics to Your Dog is only, oh, about 8 months late. You have probably all bought it already. But in case you haven’t, I’ll tell you what you’re getting into. If you wander over to your local bookstore’s science section, you’ll…

# A train leaves Cleveland…

The new academic year is starting, and if there’s one thing students love it’s a good word problem. If Sue is four times as old as John will be when Sue is one year than John… So in that spirit I was amused to find basically this kind of problem in a college physics textbook…

# Sunday Function

So I spent two weeks in Wyoming, participated in a wedding in Louisiana, moved two apartments worth of stuff, visited Louisiana again to get a marriage license for myself (20 days left!), collected data for an experiment demonstrating a new result we’re trying to get published quickly (hot topic, lots of competition), and so forth.…