Definition
An apparent deflection of moving objects (including air masses) caused by the Earth's rotation. In the Northern Hemisphere, freely moving objects appear to deflect to the right of their path; in the Southern Hemisphere, to the left. In aviation, it is most commonly referenced in two ways: as a major influence on global wind patterns and weather systems, and as a vestibular illusion in which a pilot tilting the head while the aircraft is in a prolonged turn experiences a powerful false sensation of movement on a different axis.
Plain English
Because the Earth is spinning, things moving across its surface, like air or water, look like they are curving instead of going straight. Pilots also use the same name for a separate problem: if you tilt your head during a steady turn, your inner ear gets fooled and you suddenly feel like the aircraft is rolling, pitching, or yawing when it isn't.
Context Anchor
Seen in aviation weather discussions, especially when learning why winds curve around areas of high and low air pressure instead of moving straight across them.
Derivation
Named after Gaspard-Gustave de Coriolis, a 19th-century French mathematician who described the deflection mathematically in 1835. Knowing it is named after a person, not a physical force in the ordinary sense, helps explain why it is called an apparent or fictitious effect, not a real push.
Why Pilots Care
Shapes large-scale wind patterns that determine headwinds, tailwinds, and weather systems pilots must plan around.
Analogy
If you roll a ball straight across a spinning playground merry-go-round, someone standing on the merry-go-round sees the ball appear to curve. The ball is not steering itself; the surface under the observer is rotating.
Grounding Statement
Picture a large mass of air moving north or south while Earth turns underneath it; from the ground, that moving air appears to bend rather than go straight.
Intuition Check
Do not think of the Coriolis effect as a strong sideways push on your airplane during normal flying. It mainly matters for large-scale motion, such as winds and weather systems moving over long distances.
Example Sentence 1
The Coriolis effect causes air flowing toward a low-pressure system in the Northern Hemisphere to spiral inward counterclockwise rather than moving in a straight line.
Example Sentence 2
Pilots account for the Coriolis effect when estimating cross-country wind drift over long distances.