An approximation of the true gravity on Earth's surface by means of a mathematical model representing Earth is known as what?

• A. absolute gravity
• B. relative gravity
• C. normal gravity
• D. observed gravity

Answer: (C)

Normal gravity is the gravity value derived from a smooth, mathematical model of Earth—the reference ellipsoid—which provides a consistent baseline across the globe. Because the true gravity at a point on the real Earth varies with latitude, topography, and mass distribution, geodesy uses this model to assign a standard gravity that depends mainly on latitude. This approximated gravity is computed from the ellipsoid’s parameters (and the latitude) and serves as a convenient, uniform reference for calculations in surveying and mapping. Absolute gravity, by contrast, is the actual measured gravity at a point; relative gravity and observed gravity refer to measurements and comparisons rather than a model-based standard.