Measure Earth’s Rotation With a Victorian Pendulum

A DIY build turns a Foucault pendulum into a hands-on way to observe Earth’s rotation, using simple hardware, a camera, and a precise release.

A simple science project can let you see Earth’s rotation with your own eyes: build a Victorian-style Foucault pendulum and compare its motion to a pendulum that stays in a fixed plane.

The demonstration. named after physicist Léon Foucault. is a classic way to visualize how the ground beneath you turns while the pendulum’s plane of swing remains effectively steady.. The result is a gradual change in the pendulum’s swing direction over time. which you can capture and measure using basic DIY tools.

The build described for this version keeps the parts approachable.. You’ll need a heavy weight. such as a small mushroom anchor. along with fishing line and a swivel—items that can be picked up at a sporting goods store.. The pendulum also needs a proper suspension point. such as an eye hook installed in the ceiling. so the system hangs freely enough to respond to small changes in motion.

While the mechanical setup is the centerpiece, the method also relies on recording.. A camera is used to capture the pendulum’s results. and the release is staged using a lighter or another source of flame.. The key is to let the pendulum start swinging cleanly by burning a thread that was holding it still. ensuring the release isn’t accompanied by sideways force.

That detail matters because even a small push can distort the experiment from the start. By using flame to remove the restraining thread, the build aims for a controlled release so the motion you measure is driven by physics rather than by how the pendulum was released.

How much rotation you observe depends on your latitude, because Earth’s rotation affects the apparent rate at which the swing plane turns. In the example given, at 33 degrees north you can estimate 360*sin(33)/24, which works out to about 8.17 degrees of rotation per hour.

The builder reported a somewhat larger number than that estimate, and the difference was attributed to likely error sources.. In this setup. the measurement depends on reading an angle from captured camera frames in Photoshop. which introduces opportunities for inaccuracy.. Small pendulums are also noted as being incredibly sensitive, meaning minor measurement or setup issues can shift the results.

Finding and correcting the source of discrepancy is part of the experiment’s appeal. and the report suggests that if errors are identified. the original creator would be interested in hearing about them.. In other words. the project is presented not just as a demonstration. but as a practical measurement exercise where improving technique can make the results closer to the expected rotation.

It also helps to understand what makes museum versions different.. Traditional museum pieces tend to be much larger. use ultra-low-friction pivots. and keep the pendulum moving with electromagnets. since a pendulum can’t continue indefinitely without losing energy.. Those enhancements reduce drift and energy loss, which is why they can sustain motion long enough for clearer, longer-duration observation.

For anyone considering the build. the biggest lesson is that the experiment’s success hinges on both careful release and careful measurement.. The steps may look straightforward. but the combination of sensitive small-scale motion and camera-based angle estimation means setup choices can have an outsized effect on what you record over time.

Foucault pendulum DIY Earth rotation experiment camera measurement Victorian science physics at home pendulum motion