Glossary of Gravity Terminology
ABSOLUTE GRAVITY: the value of the acceleration of gravity, also expressed by the length of the seconds pendulum.
RELATIVE GRAVITY: the value of the acceleration of gravity relative to the value at some standard point.
SIMPLE PENDULUM: see theoretical pendulum.
THEORETICAL PENDULUM: a heavy bob (point-mass) at the end of a weightless rod.
SECONDS PENDULUM: a theoretical or simple pendulum of such length that its time of swing (half-period) is one second. (This length is about one meter.)
GRAVITY PENDULUM: a precisely made pendulum used for the measurement of gravity.
COMPOUND PENDULUM: a pendulum in which the supporting rod is not weightless; in other words, any actual pendulum.
CONVERTIBLE PENDULUM: a compound pendulum having knife edges at different distances from the center of gravity. Huygens demonstrated (1673) that if such a pendulum were to swing with equal periods from either knife edge, the distance between those knife edges would be equal to the length of a theoretical or simple pendulum of the same period.
REVERSIBLE PENDULUM: a convertible pendulum which is also symmetrical in form.