Eötvös Effect

a phenomenon in which two objects, one at rest and the other moving relative to the earth, have different values of the acceleration of gravity at the same point.

The Eötvös effect is caused by a change in the centrifugal component of the force of gravity; this component is dependent on the velocity of an object. When an object is moving in the direction of the earth’s rotation, that is, from west to east, its velocity is added to the velocity of the rotation, and the centrifugal force increases; there is, consequently, a reduction in net gravitational force. Conversely, when the motion is against the rotation of the earth, the gravitational force increases.

The magnitude, in gals, of the Eötvös effect (the Eötvös correction) is

Δg = 0.00405V cos ɸ sin A + 0.00000121V²

where ɸ is the latitude, A is the azimuth of the motion reckoned clockwise from the north, and V is the speed of the object relative to the earth (in km/hr). The Eötvös effect is taken into consideration when the force of gravity is being measured with the pendulum apparatus and gravimeters carried on moving ships and aircraft. The term with V² is negligible when V < 15 km/hr.

The Eötvös effect is named for L. von Eötvös, who was the first to point out its existence and to develop an instrument for its laboratory demonstration.