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Weather maps show storms spinning one way north of the equator and the other way south of it. The sideways push behind that is named after a man who never set out to study weather. Gustave Coriolis was working on machines. This post covers his life, what the Coriolis effect is, how big it really is on Earth with worked numbers, and what students can learn from him.
Who was Gustave Coriolis?
The MacTutor biography records that Gaspard-Gustave de Coriolis was born in Paris in 1792 and died there on 19 September 1843. He grew up in Nancy and was placed second of all the students entering the École Polytechnique in 1808. After working as an engineer in the Vosges, he had to support his family when his father died, and in 1816 he took a teaching post at the École Polytechnique, recommended by Cauchy.
His health was poor for most of his life. Even so, he became professor of mechanics at the École Centrale in 1829, succeeded Navier at the École des Ponts et Chaussées and in the Académie des Sciences in 1836, and became director of studies at the École Polytechnique in 1838.
Why do we say "work" in physics?
Coriolis studied friction, hydraulics and how well machines performed. MacTutor credits him with introducing the term "work" in its present scientific meaning, in his 1829 book Du calcul de l'effet des machines (On calculating the effect of machines). Poncelet, who published in the same year, acknowledged that the word came from Coriolis. Coriolis even proposed a unit of work, the dynamode, equal to 1000 kilogram-metres, as a sensible measure for a person, a horse or a steam engine. The word stuck; the unit did not.
Where did the Coriolis force come from?
In an 1835 paper, Sur les équations du mouvement relatif des systèmes de corps (On the equations of relative motion of systems of bodies), he showed that the laws of motion can be used in a rotating frame of reference if an extra term is added to the equations of motion.
The meteorologist Anders Persson, in How do we understand the Coriolis force? (1998), points out that the discovery was linked to early nineteenth-century mechanics and industrial machines, not to the earth sciences. Coriolis approached it through the energy of rotating machinery. Persson also stresses a point students often miss: the Coriolis force changes an object's direction but does no work on it.
How big is the Coriolis effect on Earth?
First, Earth's rotation rate. NASA's Earth fact sheet gives the sidereal rotation period as 23.9345 hours, which is 86,164 s.
ω = 2π / 86,164 s ≈ 7.29 × 10⁻⁵ rad/s.
For horizontal motion at latitude φ, the sideways acceleration is a = 2ωv sinφ. In the northern hemisphere it deflects moving objects to the right.
Worked example 1: a thrown ball. A ball travels horizontally at 30 m/s at latitude 30° (sin 30° = 0.5) for 2 s.
a = 2 × 7.29 × 10⁻⁵ × 30 × 0.5 ≈ 2.19 × 10⁻³ m/s².
Sideways drift = ½at² = 0.5 × 2.19 × 10⁻³ × 2² ≈ 4.4 × 10⁻³ m.
About 4 mm over a 60 m throw. Wind, spin and your aim matter far more.
Worked example 2: a wind. Air moves at 10 m/s at the same latitude.
a = 2 × 7.29 × 10⁻⁵ × 10 × 0.5 ≈ 7.3 × 10⁻⁴ m/s².
If that acted in a fixed direction for one hour, it would add 7.3 × 10⁻⁴ × 3600 ≈ 2.6 m/s of sideways velocity.
In practice the push turns with the wind, which is why large air masses curve into spirals. The lesson is the time scale: tiny per second, large over hours and hundreds of kilometres.
Mistakes to avoid:
Using cos instead of sin. For horizontal motion, the vertical part of Earth's rotation, ω sinφ, does the deflecting. It is zero at the equator and largest at the poles.
Applying it to things at rest. The Coriolis term needs motion relative to the rotating frame. A parked car feels none.
Forgetting the factor of 2. It is 2ωv, not ωv.
The Coriolis force is not named in the official JEE (Main) 2026 syllabus, so treat this as enrichment. The related idea of pseudo forces in accelerating frames is covered in our guide to pseudo forces and non-inertial frames. Rotating frames are much easier to watch than to imagine, and the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read.
What can a student take from how he worked?
Practical problems lead to deep ideas. Measuring the output of machines gave physics the word "work" and a new force.
Name things clearly. A good term, like "work", can outlast every other part of a theory.
Check the size before the story. A force that sounds dramatic can be a few millimetres in practice.
Look at energy and force together. Seeing that the Coriolis force does no work clarifies what it can and cannot do.
Try it: at latitude 45°, how much sideways acceleration does a car moving at 25 m/s feel?
