Pen·du·lum n.; pl. Pendulums   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 rods of different metals.
 Compound pendulum, an ordinary pendulum; -- so called, as being made up of different parts, and contrasted with simple pendulum.
 Conical pendulum or Revolving pendulum, a weight connected by a rod with a fixed point; and revolving in a horizontal circle 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 pendulum 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.

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 Bal·lis·tic a.
 1. Of or pertaining to the ballista, or to the art of hurling stones or missile weapons by means of an engine.
 2. Pertaining to ballistics2, or to a projectile in a gravitational field.
 Ballistic pendulum, an instrument consisting of a mass of wood or other material suspended as a pendulum, for measuring the force and velocity of projectiles by means of the arc through which their impact impels it.

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 ballistic pendulum
      n : a physical pendulum consisting of a large mass suspended
          from a rod; its displacement is used to measure the
          velocity of a projectile