Standard gravity is the conventional reference accelerationexactly. It supplies a fixed reference for unit conversions and for expressing an acceleration as a multiple of . It is distinct from the locally measured gravitational acceleration, which depends on location and height.[ref]
NIST Guide to the SI. Appendix B.9, Acceleration: standard acceleration of free fall; bold conversion factors are exact
For example, . If a vertical force on a mass of is calculated using this reference, . The same calculation using a measured local value gives instead. The reference value's exactness does not remove measurement uncertainty from a real force or from the actual local gravitational field.
One can measure local gravitational acceleration by tracking a body in free fall with an optical interferometer, taking positive downward and fitting its vertical position to after instrumental corrections. Such an experiment estimates at the apparatus; it does not determine the already stipulated number .[ref]
Gravity laboratory by Istituto Nazionale di Ricerca Metrologica. Laboratory description, interferometric vertical-trajectory measurement and environmental corrections
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Standard gravity, often denoted by the symbol \( g_0 \), is a physical constant that represents the acceleration due to Earth's gravity at the surface. It is defined as approximately \( 9.80665 \, \text{m/s}^2 \) (meters per second squared). This value is based on the standard conditions and represents the mean gravitational acceleration experienced by objects at sea level at 45 degrees latitude.