# Coriolis force The Coriolis force is the apparent sideways deflection of anything moving in a rotating frame. It is not a real [[Force]] — nothing pushes — but in the rotating frame of a spinning planet the bookkeeping requires it, and its consequences are entirely real. It deflects moving air and [[Water]] to the right in the northern hemisphere and to the left in the southern — a consequence of [[Newton's_laws_of_motion|Newtonian]] mechanics viewed from a spinning platform — and it is the reason large-scale flows on [[Earth]] rotate at all. ## Scale is the whole story The deflection is weak, so it only matters when a motion lasts long enough for it to accumulate — hours and hundreds of kilometres. That is why it organises cyclones, ocean gyres, and the jet streams that concern [[Aviation]], and why it does nothing whatever to a draining bathtub, where the [[Vorticity]] already present in the water from filling overwhelms it by orders of magnitude. The bathtub claim is the most durable piece of folklore in [[Fluid_dynamics]] and it is worth killing on sight. What actually spins up a drain is [[Vortex_stretching]]. ## What it builds Because pressure gradients end up balanced against Coriolis deflection rather than driving flow straight down them, wind runs along isobars instead of across — geostrophic balance, the organising principle of [[Geophysical_fluid_dynamics]] and every [[Atmospheric_model]]. It sets the direction of hurricane rotation and prevents them forming at the equator, where the effect vanishes. It bends long-range artillery, biases [[WT!Northern_Agricultural_Center_of_Excellence|regional]] wind patterns, and appears in the laboratory as a rotating tank whose [[Simulation|reproduction]] of planetary flow fits on a tabletop. **Microsim brief (next pass):** Rotating disc the viewer fires a puck across; the puck flies straight in the fixed frame and curves in the rotating one. Toggle between frames to show it is bookkeeping, not a push. **On the spine:** [[Geophysical_fluid_dynamics]] · [[Vorticity]] · [[Vortex_stretching]] · [[Atmosphere_of_Earth]] · [[Weather_forecasting]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Coriolis_force) : [Wikitube](https://en.wikitube.io/wiki/Coriolis_force) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_WT!Thury_Hydrodynamics_Compendium]], [[PORTAL_Physics]], [[PORTAL_Complex_system]]. --- *Fluid seed wave · 2026-09-10 · seed register · microsim layer pending.*