Undergraduate physics on the web

Last month, give or take, I ran across a page of links to applets designed to demonstrate various principles of physics. The demo has long (probably always) been a staple of physics classes. I vividly remember a couple. In one, interfering laser beams were progressively filtered down to the point the detector could register individual photons landing left or right.

But the one I really remember involved the lecturer, an iron ball and a chain. The ball hung from the chain, which was anchored far up at the ceiling, centered left-to-right. At rest, the ball hung at maybe waist height. The lecturer carefully brought the ball toward the left, until it was at head height, and placed it directly against his nose. He then let go, noting that it was very important to hold completely still and not to give the ball an extra push. The ball swung slowly to the right, then back to the left. Conservation of energy being what it is, and some small amount having been dissipated by friction, the ball returned just short of its original position, to the relief of all concerned.

I doubt there's anything quite so memorable on the page I mentioned, though to be fair I've only chased a small portion of the links. As is typical with such collections, some of the links are broken, some of the apps don't work and many are a bit on the clunky side. Nonetheless, it's really great to be able to google around a bit and see a virtual demonstration with moving parts that illustrates a given principle much more effectively than mere text. This is the kind of thing that simply wasn't available to the general public a generation ago, or available at all two generations ago, and so one of the many small ways in which the web makes life just that bit better.

On the other hand, the actual physical world has always been available to all, and careful observation has always been repaid in understanding. It worked for Newton and Gallileo, so there must be something to it ...