Top Stories #9 - Rockwell’s Foucault pendulum is swinging again

Grove City College is running down our Top Ten stories of 2021. This story was originally published April 23.

Grove City College’s Foucault pendulum is swinging again thanks to a pair of students who were initially puzzled by the device.

Roommates Mackenzie Gongaware, a sophomore Mechanical Engineering major, and Grace Barnes, a sophomore Computer Science major, noticed the pendulum last spring as they passed through Rockwell Hall of Science. Meant to be a dynamic and visible demonstration of the Earth’s rotation, instead it hung motionless, in the dark behind a glass door on the first floor.

“We got weirdly intrigued by it,” Barnes said. “We didn’t know what its purpose was, but the sign behind it told us to check its position throughout the day, so we would visit it periodically and look for any changes.” And, despite the women convincing themselves more than once that the pendulum moved, it hadn’t. Not for a while.

The Foucault pendulum is supposed to demonstrate the rotation of the Earth as a steel bob, suspended from a fixed point in the ceiling, swings back and forth, its arc methodically moving 360 degrees with each turn of the Earth. But that had not happened in years. While it was part of Rockwell’s original design, the pendulum has a spotty history. For most of the building’s 90 years, it hasn’t been in regular use. The sign was likely a left over from the 1990s, the last time it was repaired.

Gongaware and Barnes thought “it was sad to see a noteworthy part of Rockwell’s history being forgotten,” and out of curiosity and a desire to see the pendulum actually work as advertised, they reached out to the Physics faculty about repairing it.

“When Grace and Mackenzie approached me last fall about their interest in getting it swinging again, I thought it was a terrific idea,” Dr. James Clem, assistant professor of Physics said. “Since I started here in 2013, I’ve had some interest in getting it going again, but never had the time to devote to it.”

Clem agreed to advise them, but both students passed on the opportunity to get academic credit for the project, which they saw as a distraction from schoolwork.

“They saw it and they wanted to do something about it,” Clem said. “Not for credit, but just to satisfy their curiosity. It’s what all good scientists do.”

Gongaware and Barnes found there was nothing significantly wrong with the pendulum’s steel bob or the wire that it swings on. The problem with the pendulum was one of power. While one can start a pendulum easily enough with a little push, air resistance and friction will eventually stop it.

“It’s like a kid on a swing, if you do not have someone to push them and they are not pumping their legs, they will eventually come to a stop,” Barnes said. “To keep the pendulum in motion, there is a driving mechanism underneath the floor that exerts magnetic forces on the steel bob.”

That mechanism, which is activated when the bob swings over a sensor, was added to the pendulum when it was completely overhauled in the 1990s and had stopped working.

“That circuit is what needed the most attention,” Gongaware said. With some help from the Electrical Engineering Department, they were able to rewire the device. “We reinstalled the circuit and from there it was a lot of trial and error and changing variables to get it to both swing without dying down and complete its cycle,” she said. Thanks to a camera that Clem installed, they were able to monitor the pendulum remotely and calibrate it accurately.

“Now, the pendulum is both swinging constantly and at the correct rate,” Gongaware said. Each Foucault pendulum completes the cycle at a different rate depending on its location’s latitude. At the North Pole, it takes the same 24 hours that the Earth does to turn on its axis. In Grove City, the cycle is completed in roughly a day and a half – 36 hours and 22 minutes.

To make sure the pendulum stays on track, freshman Physics major Brynn Graybill is working on a program to monitor its movement more accurately.

Leon Foucault designed his namesake pendulum around 1850 and put it on display in 1851 at the Paris Observatory. It is a simple experiment that very visibly demonstrates an established scientific fact and, in the last century, Foucault pendulums became a mainstay of museums, public buildings and college science centers. There is one at the United Nations headquarters in New York and another in the Children’s Museum in Pittsburgh, which used to be the Buhl Planetarium.

The original Rockwell Hall version was simple – a metal bob hanging from a wire inside a well about the size of a closet that went from the basement to the third floor. It was apparently started manually and stopped naturally. By the mid-1960s, the pendulum had fallen into a state of disrepair and it stayed that way until Dr. James Downey ’81, an alumnus and former Physics professor, oversaw a complete overhaul and upgrade. Then, as now, the work was largely completed by students who really wanted to see the pendulum become operational.

When he joined the faculty in 1992, Downey said the pendulum was in bad shape. The bob was missing, the steel wire it had hung on needed to be replaced and the experiment meant to make an unseen scientific fact visible was hidden away, behind closed doors that looked more like they opened to a broom closet than a device to spark scientific wonder.

“I was a Physics major at Grove City, and I did not even know the pendulum shaft was there,” Downey said.

Working with students and College maintenance staff, Downey had the base of the pendulum moved from the basement to the first floor to accommodate the force driver and increase the device’s visibility. The solid wooden door to the well on that floor was replaced with a glass window. Lights and the signage that so intrigued Gongaware and Barnes was added.

The missing bob was replaced with one designed with the help of Downey’s father-in-law, who worked for McInnes Steel in Corry, Pa. “He and I designed the bob to make one that looked pretty classic and the folks at the steel company manufactured it,” he said. Downey recalls the project as fun and said he is glad to hear the pendulum is swinging again.

“Grace’s and Mackenzie’s work on the project is commendable given their dedication and diligence to get it working and working correctly,” Clem said. “The Foucault is an important part of the culture and tradition of Grove City College. I strongly feel that their work will make it a great historical centerpiece to an already historical building,” he added.

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