Pendulum definitions and example sentences on Wordnik

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Definitions (39)

American Heritage Dictionary (2)

noun A body suspended from a fixed support so that it swings freely back and forth under the influence of gravity, commonly used to regulate various devices, especially clocks. Also called simple pendulum.
noun Something that swings back and forth from one course, opinion, or condition to another: the pendulum of public opinion.

Century Dictionary (35)

Anything that hangs down from a point of attachment and is free to swing.
In mech., a body so suspended from a fixed point as to move to and fro by the alternate action of gravity and its acquired energy of motion. The time occupied by a single oscillation or swing is counted from the time of the descent of the pendulum from the highest point on one side till it attains the highest point on the opposite side. This time is called the period of oscillation of the pendulum. A simple pendulum in the mechanical sense is a material particle suspended by a weightless rod and moving without friction. A single weight attached by a string, etc., approximates to an ideal simple pendulum. The period of oscillation of a simple pendulum in vacuo is where π=3.14159 + , g is the acceleration of gravity, l is the length of the pendulum, and A is the total arc of oscillation. The quantity in parentheses is not affected by the radical sign. It will be seen that, unless the arc is very large, the period is almost independent of its magnitude. A compound pendulum is any pendulum not simple. The same formula for the period applies, l being the square of the radius of gyration divided by the distance of the center of gravity from the axis of rotation. The common clock-pendulum usually consists of a rod of metal or wood, suspended so as to move freely about the point of suspension, and having a flat circular piece of brass or other heavy material, called a bob, attached to its lower end. The metal rod, however, is subject to variations in length in consequence of changes of temperature, and, as the accuracy of the pendulum considered as a regulating power depends upon its always maintaining the same length, various combinations of two different metals, as brass and steel, under the name of compensation pendulums, have been adopted in order to counteract the effects of changes of temperature. These take particular names, according to their forms and materials, as the gridiron pendulum, the mercurial pendulum, the lever pendulum, etc. The gridiron pendulum is composed of parallel rods of brass and steel, arranged in one plane, and so connected together that the different degrees of expansion of the different metals compensate each other and maintain the compound rod of fixed length. The mercurial pendulum, devised by Graham, consists of one rod with a vessel containing mercury at the lower end, so adjusted in quantity that, whatever alterations take place in the length of the pendulum, the center of oscillation remains the same, the mercury ascending when the rod descends, and vice versa. Another form of compensation or compensating pendulum employs a curved bar composed of iron and brass brazed together, which is attached to the rod in a horizontal position, the brass downward. The unequal expansion of the metals under a rise of temperature tends to lift the center of gravity of the bob, and thus to compensate for the simultaneous increase in length of the rod. The pendulum is of great importance as the regulating power of clocks. Our clocks are nothing more than pendulums with wheel-work attached to register the number of vibrations, and with a weight or spring having force enough to counteract retarding effects of friction and the resistance of the air. A reversible pendulum is a pendulum so arranged that it may be suspended from either of two axes on its length at unequal distances from its center of gravity, and so placed that in the two positions each becomes axis of suspension and axis of oscillation, so that the time of vibration shall be the same in both positions. Bessel's reversible pendulum is symmetrical in external figure with respect to the plane equidistant from the two axes. Such a pendulum eliminates the effect of the atmosphere. A pendulum which makes exactly one oscillation per second is called a seconds pendulum (also written seconds' pendulum and second's pendulum). The length of a pendulum is the length of the simple pendulum having the same period—that is, the distance between the point of suspension and the center of oscillation (see center). In the latitude of New York, and at the level of the sea, the length of the seconds pendulum is 39.1 inches nearly. As the force of gravity diminishes toward the equator and increases toward the poles, the seconds pendulum is shorter in lower latitudes and longer in higher. Besides its use as a regulator in clocks, the pendulum is applied to determine the relative and absolute acceleration of gravity at different places, and in this way the figure of the earth.
A chandelier or lamp pendent from a ceiling.

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When a pendulum is at the highest point of its swing, its velocity or kinetic energy is zero, but at that point its potential energy is greatest. — Aether and Gravitation
When the pendulum is at the lowest point its energy is wholly kinetic, the potential energy being zero at that point, while it has sufficient kinetic energy to raise it to the highest level again. — Aether and Gravitation
"They start the poor feller swinging like a pendulum, and every time he swings through the flames he's burned a little more--and a little more I turned sick with the horror of it. — Swept Out to Sea Clint Webb Among the Whalers
But, alas, when the pendulum is at its highest it begins to swing downwards. — About Peggy Saville
Wherever such a pendulum has been carefully observed in any district, it has been found that it indicates the occurrence of slight tremors. — Outlines of the Earth's History A Popular Study in Physiography

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pendulum

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