Empirical Earth · Rotation & How We Measure It
Foucault's pendulum & the Coriolis effect
The claim
“If Earth spun we’d feel it or be flung off; nothing actually detects rotation.”
What is true
A pendulum can be turned by things other than the Earth: how it is released, asymmetry in the suspension. Museum pendulums are usually driven.
What is measured
A Foucault pendulum’s swing turns 15.04° × sin(latitude) per hour, zero at the equator, a full circle at the poles, measuring Earth’s spin indoors.
What would show this is wrong
a pendulum whose precession rate did not follow 15.04°/hr × sin(latitude).
Sources
- IERS Conventions. Sidereal rotation period and Earth-orientation parameters. International Earth Rotation and Reference Systems Service. Earth rotation / IERS link
- Foucault's pendulum (1851). L. Foucault, Panthéon demonstration; precession rate = Ω·sin(latitude). Standard classical mechanics (Goldstein; APS Physics History). Foucault pendulum link
- The Coriolis effect. G.-G. de Coriolis (1835); f = 2Ω sin φ; hemispheric reversal of cyclone rotation. Standard geophysical fluid dynamics (Holton, Dynamic Meteorology ); NOAA. Coriolis effe link
- Foucault pendulum — precession ∝ sin(latitude), one sidereal day. The swing plane veers 360°×sin(latitude) per sidereal day (~11.25°/h at Paris, ~32 h per turn); Foucault released the bob fr link
- Samuel Rowbotham (“Parallax”), Zetetic Astronomy: Earth Not a Globe , 1865. The founding text of the modern flat-Earth movement, and the source of most of the arguments answered in this refe link
The full entry, with the working →