# Gravity Definitions for Land Surveyors

**gravimeter-**^{1} Instrument for measuring variations in the magnitude of the gravitational field of the Earth. ^{2} In geodesy, a weighing device or instrument of sufficient sensitivity to register variations in the weight of a constant mass when the mass is moved from place to place on the Earth, thereby subjecting it to the influence of gravity at those places.

**gravimetric survey—**A survey made to determine the force of gravity at various places on the Earth\’s surface.

**gravity-**^{1} The gravitational force (as modified by centrifugal force due to rotation) exerted by the Earth on bodies at or near its surface, which results in their having weight. ^{2} The effect, on any body, of the gravitational attraction by all other bodies and of any centrifugal force which may act upon it. ^{3} The force exerted, at a point, by the gravitational attraction of all bodies acting at that point and by the revolution of that point about a given axis. ^{4} A unit of acceleration equal to the acceleration resulting from the average force of gravity at the Earth’s surface. By international agreement this unit is equal to 980.665 centimeters per second.

**gravity correction-**^{1}A quantity added to a theoretical value of the gravity to obtain a better approximation to the measured value. ^{2} A quantity added to a measured value to obtain a theoretical value of the gravity. The quantities in definitions (1) and (2) are of equal absolute value and opposite signs.

**gravity potential-**^{1}The potential created, at a point rotating with the Earth, by the combined action of gravitational and centrifugal forces. ^{2} The gravity potential per unit mass of the body creating the potential. ^{3} The quantity whose directional derivative is the negative of the acceleration of gravity. ^{4} The work done in moving a body of unit mass from one point on a rotating, massive body to another point on or rotating with the same body.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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