Two distinctly different types of gravity measurements are: ______ and ______.

• A. absolute; relative
• B. observed; normal
• C. Bouguer; free-air
• D. gravity; acceleration

Answer: (A)

The key idea is that gravity measurements fall into two broad categories: absolute and relative. An absolute gravity measurement aims to determine the true value of local gravitational acceleration g at a point, providing an actual, standalone value in units like m/s². This uses instruments that track the free-fall motion or interfere with a test mass in a way that ties the reading to an inertial reference frame, giving g directly.

A relative gravity measurement, on the other hand, compares gravity between locations or over time, yielding differences (delta g) rather than an absolute value. Relative gravimeters are very sensitive to small changes and are ideal for mapping spatial variations or monitoring gravity over time, but they require an independent absolute measurement to anchor the scale.

Corrections like the Bouguer or free-air adjustments are applied to gravity data after measurement to account for topography and atmospheric effects; they are not the types of gravity measurements themselves. Also, gravity is the measurement of the gravitational acceleration, not a separate type; the distinction being tested is between obtaining an actual g value versus detecting differences in g.