# Coriolis force

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## Coriolis force

(kor-ee-**oh**-liss, ko-ree-) A concept introduced to simplify calculations on the motion of bodies observed from a rotating frame of reference, such as the Earth. The effect of the Coriolis force is to deflect the object in a direction perpendicular to its course.

## Coriolis Force

(named after the French scientist G. Coriolis), one of the inertia forces introduced to account for the effect of a rotating frame of reference on the relative motion of a material point. The Coriolis force is equal to the product of the mass of the point by its Coriolis acceleration and is directed opposite to this acceleration.

The effect accounted for by the Coriolis force is such that in a rotating frame of reference a point moving not parallel to the axis of this rotation either is deflected in the direction perpendicular to its relative velocity or exerts pressure on the body obstructing such motion. On the earth, this effect is governed by the planet’s rotation and consists in the fact that a free-falling body is deflected from the vertical to the east (to the first approximation), while bodies moving along the earth’s surface in the direction of the meridian are deflected from their direction of motion to the right in the northern hemisphere and to the left in the southern hemisphere. These deflections are extremely small owing to the slow rotation of the earth and are noticeable only at great velocities of motion (as in the case of rockets or long-range artillery shells) or when the motion is of great duration (for example, the erosion of the corresponding river banks [*see*BAER’S LAW] or the formation of certain air and sea currents).

In engineering, Coriolis forces are taken into account in the theory of gyroscopes and turbines.

S. M. TARG