\Pen"du*lum\, n.; pl. {Pendulums}. [NL., fr. L.
pendulus hanging, swinging. See {Pendulous}.]
A body so suspended from a fixed point as to swing freely to
and fro by the alternate action of gravity and momentum. It
is used to regulate the movements of clockwork and other
machinery.
Note: The time of oscillation of a pendulum is independent of
      the arc of vibration, provided this arc be small.
{Ballistic pendulum}. See under {Ballistic}.
{Compensation pendulum}, a clock pendulum in which the effect
   of changes of temperature of the length of the rod is so
   counteracted, usually by the opposite expansion of
   differene metals, that the distance of the center of
   oscillation from the center of suspension remains
   invariable; as, the mercurial compensation pendulum, in
   which the expansion of the rod is compensated by the
   opposite expansion of mercury in a jar constituting the
   bob; the gridiron pendulum, in which compensation is
   effected by the opposite expansion of sets of rodsof
   different metals.
{Compound pendulum}, an ordinary pendulum; -- so called, as
   being made up of different parts, and contrasted with
   simple pendulum.
{Conical} or {Revolving}, {pendulum}, a weight connected by a
   rod with a fixed point; and revolving in a horizontal
   cyrcle about the vertical from that point.
{Pendulum bob}, the weight at the lower end of a pendulum.
{Pendulum level}, a plumb level. See under {Level}.
{Pendulum wheel}, the balance of a watch.
{Simple} or {Theoretical}, {pendulum}, an imaginary pendulum
   having no dimensions except length, and no weight except
   at the center of oscillation; in other words, a material
   point suspended by an ideal line.