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September 18, 2009
Surface Waves
In the comments to my previous post, Thomas Schaefer suggested that I look at the same issue (of the energy density having a linear term, rather than being quadratic in the amplitude of the wave) for the case of surface waves. I don’t think that’s actually the case.
But surface waves are the simplest example I know where one obtains a (highly) nontrivial dispersion relation from relatively simple physics. So it’s fun to review them, anyway.
September 16, 2009
The Sound of One Physicist Wailing
One of the delights of teaching elementary physics is discovering some basic thing that you thought you understood, but actually didn’t. Usually, this occurs late at night, while preparing your lecture for the next morning. And you wonder whether you’ll be able to keep a straight face, the next morning, as you say words you’re no longer quite so sure are true.
I’ve been teaching about waves in a non-technical course. One of the points I like to emphasize is that the energy density, or the intensity, of the wave is quadratic in the amplitude. There are lots of examples of that, with which you are doubtless familiar: electromagnetic waves, transverse waves on a stretched string, …
But we’re studying sound, now. So I thought I would reassure myself that the same is true of sound waves …