MOMENT

(Lat. movere, to move.) A small but indefinite period of time. Sometimes the word instant is used synonymously with moment. Moment, Momentum. These terms have been used by writers on mechanics in various senses. Galileo, in his Dialogues, uses the phrase momentum of a power, or of a weight, applied to a machine, to denote the action, energy, or impetus of the power to move the machine; so that tit equilibrium subsists between two powers when their moments to move the machine in opposite directions are equal: and he shows that the momentum is proportional to the power multiplied into the virtual velocity. This notion of momentum was also adopted by Wv His, in his Mechanics, published in 1609; and when the term is used with respect to a weight, it is synonymous with the phrase quantity of motion, that is, the product of the ma by the velocity. The product of the ma by the square of the velocity, or the living force (sec Force), is sometimes called the moment of the moving force, or the moment of activity; and the produe i of the ma by the velocity and by a line (or, which is [s. 778]