Observe a Foucault pendulum
Compare the swing plane’s slow turn with the prediction for the instrument’s latitude. A large, well-controlled installation is more useful than a short improvised pendulum.
What you need
- Museum or other suitable Foucault installation
- Known latitude and marked swing-plane reference
- Clock and observation log
Collect the readings
- Record latitude and the installation’s intended swing reference. Note how the pendulum is launched and driven; support forces and an elliptical swing can introduce other precession.
- Trace the swing direction at repeated intervals against a fixed floor reference. Avoid confusing the changing position of the bob within one swing with a change of the swing plane.
- Enter latitude in the precession tool. Compare the predicted degrees per hour with the accumulated observed turn, retaining the sign convention.
- At the equator the ideal rate is zero. A large nonzero turn there suggests instrument dynamics rather than the ideal Foucault signal. For home construction, suspension safety and a controlled release are essential.
Compare the predictions
Ideal precession is Ω sin(latitude).
A northern and southern instrument turn in opposite senses under the same viewing convention.
Release torque, damping and support asymmetry can mask a slow precession.
Open the related calculation →