The Herzstein Foucault Pendulum at the Houston Museum of Natural Science, suspended from a 61-foot cable, unexpectedly stopped swinging this month after decades of operation. HMNS explained on TikTok that the electromagnetic drive that provides corrective nudges to overcome friction failed. Technician Johnny Hemberger said the mechanism needs maintenance after long-term use, and repairs are already underway. The pendulum — first demonstrated by Léon Foucault in 1851 — visually demonstrates Earth's rotation.
Houston Museum's Historic Foucault Pendulum Stops After Decades — Here's Why
The Foucault Pendulum at the Museum of Natural Science Feb 27, 2008. Wednesday, Feb. 27, 2008, in Houston. (Eric Kayne/Houston Chronicle)
Visitors to the Houston Museum of Natural Science noticed something unusual this month: the museum's Herzstein Foucault Pendulum, which had swung for decades, came to a sudden stop.
What Happened
The suspended bob hangs from a 61-foot-long cable and typically traces a slowly rotating path as the Earth turns, often knocking down pegs placed around its base. The museum posted a video on its TikTok channel explaining that the pendulum stopped because the electromagnetic drive that provides periodic corrective nudges failed.
How the Mechanism Works
All large Foucault pendulums require occasional impulses to overcome mechanical friction and air resistance. At HMNS, a metal collar near the top of the cable delivers a subtle electromagnetic tug that keeps the swing going in the same plane as the cable moves. When that drive mechanism ceased functioning this month, the pendulum lost the small energy boosts it needs and came to rest.
"In our case, this mechanism has stopped," said HMNS technician Johnny Hemberger, noting that mechanical systems need maintenance from time to time after decades of near-continuous operation.
Repair Status and Visitor Reaction
The museum says repair work is underway and staff expect the exhibit to be restored soon. In a follow-up TikTok clip, HMNS asked visitors to "enjoy the rare phenomenon while it lasts," referring to the unusual sight of a stationary pendulum that normally demonstrates Earth's rotation.
Why It Matters
The Foucault Pendulum was first demonstrated by French physicist Jean Bernard Léon Foucault in Paris in 1851. It provides a simple, powerful visual proof of Earth's rotation: the pendulum's swing plane remains essentially fixed in space while the planet turns beneath it, producing the appearance of a rotating path.
Bottom Line: A mechanical drive failure—not a problem with the physics—temporarily halted the Herzstein Foucault Pendulum. The museum is repairing the device and expects the exhibit to resume normal operation.
