Foucault pendulum · Coriolis precession simulation

Can a swinging pendulum reveal that the Earth turns — without ever looking at the sky?

▶ Run the simulationSee the measured result

Units: hours (full swing-plane rotation at the Paris Panthéon, φ = 48°50'47" N; Foucault 1851 reported ~11.3°/h ≈ 31.8 h)

How the lab tests it

Integrate the rotating-frame 2-D oscillator with energy-conserving RK4 at latitude φ; at each turning point record the swing-line azimuth, least-squares fit azimuth against time, and compare the fitted precession rate to Ω·sin φ. The 'day' is sped up so the rosette precesses in ~1 minute. ?lat=<deg> sets the latitude.

What it checks

the swing plane PRECESSES at the rate Ω·sin φ — a full turn per sidereal day at the pole, none at the equator — so the slow rotation of the swing line is the ground (the Earth) turning beneath the pendulum, exactly as Foucault demonstrated in 1851. The measured rate matches Ω·sin φ to 0.00% at 90°, 45°, 30° and 0°.