Your mention of radial coordinates jogged my memory. The angle in radians is the arc length / radius. The radius in this case is L. Since the arc length approaches dL as the length of dL decreases, dL/L approaches dA. I think that's the reasoning that's being used. Thanks for your help.
I took a lot of physics in college, but we rushed through everything so fast that I never felt like I had a chance to master the material. Now, many years later, I'm trying to work through the material again, taking my time to, hopefully, really understand it.
If a rapidly rotating gyroscope attached to a perch is released in a horizontal position -- that is, so that the axis of the gyroscope is horizontal -- the gyroscope will precess around it's perch. Let L represent its angular momentum. Let dL represent a small change in that momentum. Let dA...