What in the world ...? (answer) Sunday, December 14, 2008

People are starting to ask me for the answer to last week's "What in the world ...?" puzzle, so here you go:

A giant Foucault pendulum swings from the north tower of the Oregon Convention Center in Portland. The 900-pound (408-kg) bob may be the largest in the world. It is suspended by a 27-m (90-foot) wire, among the world's longest.

Here are some additional pictures of the Foucault pendulum hanging at the Oregon Convention Center.

First demonstrated in 1851, Leon Foucault devised the apparatus to show the rotation of the Earth.

Because the pendulum is free to swing on any plane, its apparent path changes as the Earth rotates underneath it. At the north and south poles, the plane of the pendulum will rotate once per day. On the equator, it won't change at all. At points in between, its rate varies with the sine of the latitude. (In Portland, which is close to 45 degrees north, each cycle is about 1.4 (the square root of 2) days.)

You can read more about the history and physics of Foucault pendula here and here. Wikipedia has a list of pendula here.

As usual, Jef was on track when he recognized the tower of the OCC. But I have to admit that I was surprised when my brother, Stuart, emailed me with the correct answer barely two hours after I posted it. (Well, he didn't identify the OCC, but he did figure out that it was a Foucault pendulum ... pretty impressive.)

[below] The Oregon Convention Center sports twin glass towers that make a distinctive mark on the Portland skyline. (The north tower is on the right.)