COLUMBUS, Ohio (AP) — Shiny metal balls swing hypnotically from museum ceilings worldwide, knocking over tiny objects arranged in a circle on the floor.
These Foucault pendulums elegantly demonstrate that Earth is spinning.
They are named for French physicist Jean Foucault, who in 1851 was the first to prove the point using laboratory equipment instead of astronomical observations.
Columbus' first Foucault (pronounced Foo-koh) pendulum was installed 50 years ago at COSI's original home at 280 E. Broad St.
When the science center moved to its current location on the Scioto River, it installed a new pendulum in 1999. It greets visitors at the entrance.
COSI's Leonard Sparks, known as "Mr. Science," explains how the pendulum works to thousands of visitors and considers it an icon of the museum.
"These are classic scientific models that demonstrate phenomena of our universe," Sparks said. "It's the first thing you see. It kind of sets the tone, it poses the first inquiry."
The pendulum's cable is 38.5 feet long and swings with the help of a motorized electromagnet.
Columbus' position on the globe — 40 degrees north of the equatorial line — means that the ball, or plumb bob, at the end of COSI's pendulum travels along a fixed plane that appears to rotate roughly 10 degrees per hour.
A pin at the end of the bob topples two steel balls at opposite sides of a circular stand about every 7 minutes, 42 seconds. It takes about 18.5 hours for all 144 balls to go down.
Foucault showed off his cannon-ball pendulum in Paris, further validating astronomer Nicolaus Copernicus' discovery that Earth rotates and revolves around the sun — not the other way around.
That revelation was profound, said Jim Fowler, an Ohio State University math lecturer.
"Once you can get your head around the idea that the Earth is rotating, it doesn't seem so crazy to think that the Earth might also be revolving around the sun," he said.
The idea was considered heresy when Copernicus shared it with Pope Paul III in 1543.
It's easy to see why man thought for so long that Earth was the center of the universe.
"It sure doesn't feel like the Earth is moving — terra firma and all that," Fowler said. "And if you look up at the sky, you can watch the stars spinning around every night."
There are hundreds of Foucault pendulums swinging worldwide and at least seven in Ohio.
COSI's first pendulum was designed by Clintonville resident Paul Herman, who is now 93.
Herman, a retired television repairman, machinist, U.S. Navy veteran and amateur radio hobbyist, earned an engineering degree in 1982.
He recently visited COSI to admire the remake of his pendulum. The original will be on display during COSI's birthday celebration this year.
"When I look at this, it's trigonometry," said Herman, with a youthful fascination. "If you know how energy is transferred, that's really the basis of the universe, the secret of life."
Cleveland State University had one of the nation's longest Foucault pendulums. It featured a cylindrical 40-pound lead bob that hung 211 feet in an air shaft in a university building, said Bill Becker, the school's archivist.
The building was converted to apartments in 2004, and the pendulum was removed.
In Cincinnati, Xavier University's pendulum is in the lobby of its physics department.
"We build it into our lectures," said Heidrun Schmitzer, a physics professor. "We let (students) measure the period and length of the pendulum. We also have them calculate what the apparent rotation should be at the latitude of Cincinnati. Mathematically, it's actually not so easy."
Marco Fatuzzo, the chairman of Xavier's physics department, said he remembers an enormous European pendulum that traced a pattern in sand.
Today, because of computerization, "You almost lose that simple beauty of doing that elegant experiment," he said.
For Herman, whose creation started it all in Columbus, the future is bright.
"The basis of knowledge has expanded enormously in my lifetime," he said. "Young people can start where I am now and go on. And they will."